WO2011149962A1

WO2011149962A1 - Mutant ngal proteins and uses thereof

Info

Publication number: WO2011149962A1
Application number: PCT/US2011/037774
Authority: WO
Inventors: Jonathan Barasch; Andong Qiu
Original assignee: The Trustees Of Columbia University In The City Of New York
Priority date: 2010-05-24
Filing date: 2011-05-24
Publication date: 2011-12-01
Also published as: ES2667066T3; US9534027B2; US20210038686A1; JP2013529907A; US11730790B2; EP2576587A4; US20230414709A1; EP2576587A1; US20170189482A1; US10588937B2; US20130217637A1; EP2576587B1

Abstract

In one aspect the present invention is directed to mutant NGAL proteins that have the ability to bind to siderophores, such as enterochelin, and to chelate and transport iron, and that are excreted in the urine. Such NGAL mutants, and complexes thereof with siderophores, can be used to clear excess iron from the body, for example in the treatment of iron overload. The NGAL mutants of the invention also have antibacterial activity and can be used in the treatment of bacterial infections, such as those of the urinary tract.

Description

MUTANT NGAL PROTEINS AND USES THEREOF

[0001] The present applications claims priority to U.S. Serial No. 61/347,587 filed May 24, 2010, and U.S. Serial No. 61/354973 filed June 15, 2010, the contents of which are hereby incorporated by reference in their entirety.

[0002] All patents, patent applications and publications cited herein are hereby incorporated by reference in their entirety.

[0003] A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

[0004] The instant application contains a Sequence Listing which has been submitted in ASCII format via EFS-Web and is hereby incorporated by reference in its entirety. Said ASCII copy, created on May 24, 2011, is named 19248951.txt and is 524,416 bytes in size.

BACKGROUND

[0005] NGAL (Lipocalin 2) is a small protein with a molecular weight of about 22kD. NGAL binds to iron-binding siderophores, such as enterochelin, with high affinity and thus chelates and traffics iron. Once produced in cells, NGAL is secreted into the extracellular space and transported to the kidney where it passes the filtration barrier of the glomerulus and enters the primary urine. However NGAL is then efficiently reabsorbed by megalin receptors localized on the apical side of the epithelia of the proximal tubules. Once NGAL is reabsorbed and endocytosed, it is trafficked to lysosomes and degraded. Once degraded, any iron which NGAL transported to the kidney is reabsorbed.

SUMMARY OF THE INVENTION

[0006] The present invention is based, in part, on the development of mutant versions of the NGAL protein that are not reabsorbed in the kidney and thus, unlike wild-type NGAL, are excreted in significant amounts in the urine. Like wild-type NGAL, these mutant forms of NGAL have the ability to bind to iron-binding siderophores, such as enterochelin. Thus, these NGAL mutants can be used to traffic iron out of the body by facilitating its excretion in the urine. As such, the mutant NGAL proteins of the invention can be used in the treatment of iron overload and diseases and disorders associated with iron overload. In addition, the mutant NGAL proteins of the invention have bacteriostatic activity and can be used to treat bacterial infections of the urinary tract. These and other aspects of the present invention are described in more detail below, and in other sections of this application.

[0007] In one embodiment the present invention provides a mutant NGAL protein comprising an amino acid sequence that is at least 70% identical to the sequence of wild-type human NGAL (SEQ ID NO.1), or a fragment thereof, wherein one or more residues from among Lys 15, Lys 46, Lys 50, Lys 59, Lys 62, Lys 73, Lys 74, Lys 75, Lys 98, His 118, Arg 130, Lys 149, and His 165 is mutated by deletion or by substitution with a non-positively charged amino acid residue, and wherein one or more of, or preferably all of, residues Asn 39, Ala 40, Tyr 52, Ser 68, Trp 79, Arg 81, Tyr 100, Tyr 106, Phe 123, Lys 125, Tyr 132, Phe 133, and Lysine 134 are either not mutated or are conservatively substituted, and wherein the mutant NGAL protein is able to bind to a siderophore and/or to a siderophore- iron complex, and/or is excreted in the urine, and/or has bacteriostatic activity.

[0008] In preferred embodiments five, six, seven, eight, nine, ten, or more residues from among Lys 15, Lys 46, Lys 50, Lys 59, Lys 62, Lys 73, Lys 74, Lys 75, Lys 98, His 118, Arg 130, Lys 149, and His 165 are substituted with a non-positively charged amino acid.

[0009] In some embodiments the % of the mutant NGAL protein that accumulates in the urine following systemic administration of the mutant NGAL protein to a subject is greater than the % of WT NGAL protein that accumulates in the urine following systemic administration of WT NGAL protein to a subject. In some embodiments the % of the mutant NGAL protein that accumulates in the urine following systemic administration of the mutant NGAL protein to a subject is greater than 10-fold or greater than 100-fold more than the % of WT NGAL protein that accumulates in the urine following systemic administration of WT NGAL protein to a subject. In one embodiment the % of the mutant NGAL protein that accumulates in the urine three hours after systemic administration of the mutant NGAL protein to a subject is 1% or more, or 2% or more, or 5% or more, or 10%> or more, or 20%> or more. This is significantly higher than the % of WT NGAL protein that accumulates in the urine - typically only about 0.1% of WT NGAL that is administered to a subject systemically accumulates in the urine over the same time period.

[0010] In some embodiments the present invention provides a nucleic acid sequence that encodes a mutant NGAL protein. In some embodiments the present invention provides an expression vector comprising such a nucleic acid sequence operatively linked to a promoter. The present invention also provides bacterial cells and mammalian cells that stably express such nucleic acids and that may be useful for the production of recombinant mutant NGAL proteins.

[0011] The present invention also provides pharmaceutical compositions comprising the mutant NGAL proteins of the invention and pharmaceutical compositions comprising complexes of such mutant NGAL proteins together with a siderophore, such as enterochelin, pyrogallol, carboxymycobactin, catechol, or variants thereof.

[0012] The present invention also provides methods for treating iron overload in a subject in need thereof, comprising administering to the subject an effect amount of a pharmaceutical composition comprising a mutant NGAL protein and a siderophore.

[0013] The present invention also provides methods for treating bacterial urinary tract infections in a subject in need thereof, comprising administering to the subject an effect amount of a pharmaceutical composition comprising a mutant NGAL protein.

[0014] These and other embodiments of the invention are further described in the following sections of the application, including the Detailed Description, Examples, Claims, and Drawings.

BRIEF DESCRIPTION OF THE FIGURES

[0015] Figure 1. Alignment of Ngal protein from human (iftNgal; NP 005555 - WT Human NGAL - SEQ ID NO: 1), mouse ( /wNgal; NP_032517, SEQ ID NO: 17), rat (R/iNgal; NP 570097, SEQ ID NO: 18), Chimpanzee ( tNgal, XP 001 153985, SEQ ID NO: 14), bovine (BtNgal; XP_605012; SEQ ID NO: 16), dog (C/Ngal; SEQ ID NO: 12), wild boar (&Ngal; SEQ ID NO: 13), Rhesus Monkey ( amNgal, SEQ ID NO: 15), and horse (Equus caballus (Ec) NGAL, SEQ ID NO: 1 1). Human NGAL protein sequence is Bold, and the amino acid residues on the surface of NGAL proteins are underlined. Δ and 0 indicate the conserved and the non-conserved positively charged residues (Arginine [R], Lysine [K] and Histidine [H]) on the surface of functional Ngal protein, respectively. Magenta: positive charged residues; Blue: negative charged residues; red: nonpolar and hydrophobic residues; Green: polar and hydrophilic residues.

[0016] Figure 2. Comparison of human (SEQ ID NO: 19) and mouse (SEQ ID NO: 20) megalin proteins. The sequences of the human and mouse megalin proteins were aligned by using ClustalW2 (htt ://www. ebi .ac.uk/Tools/clustalw2/), and were shown to share 76% identity and 87% similarity, respectively. \

[0017] Figure 3. Screening for NGAL mutants exhibiting specific accumulation in urine. (A). NGAL mutants bind to enterochelin (Ent) and ⁵⁵Fe³⁺ to form a complex. Apo NGAL mutant protein (4nmol) was mixed with equal molar Ent and ⁵⁵Fe³⁺, and incubated at room temperature (RT) for 30 minutes. The mixture was then washed for 4 x 5 minutes in a filter column with a 10K cutoff, and the NGAL-bound Ent-⁵⁵Fe³⁺ was calculated as percentage of the starting total 55 Fe 3^~l^~ . B-D. The prepared NGAL-Ent- 55 Fe 3^~l^~ complex was intraperitoneally injected into mice (female, 4 weeks), and the urine (B) was collected for 3 hours in a metabolic cage. Liver (C) and kidneys (D) were dissected and solubilized in IMNaOH and 2%SDS for examination of ⁵⁵Fe³⁺ accumulation, expressed as a percentage of total NGAL- Ent-⁵⁵Fe³⁺ complex.

[0018] Figure 4. Comparison of structures of wild-type NGAL and the K3 mutant NGAL protein. (A). Crystal structure of wild-type NGAL protein (Accession number: InglA.pdb) was used to predict the 3D structure of the K3 mutant protein by using Swissmodel

(http://swissmodel.expasy.org). The organization of the Ent-iron binding pocket in the K3 protein is predicted to be very similar to that in wild-type NGAL. (B). The K3 mutant protein has less positively charged residues (arginine, lysine or histidine) on its surface in comparison to wild-type NGAL according to the modeled 3D structure. Positive charged residues are shown as ball-and-stick molecules, and the yellow color indicates the solvent accessible surface of the NGAL protein.

[0019] Figure 5. Percentage recovery of ⁵⁵Fe³⁺ following injection of NGAL mutant

55 3^~l^~ 55 3^~l^~ proteins complexed with enterochelin and Fe . The amount of NGAL-bound Ent- Fe was calculated as percentage of the starting total ⁵⁵Fe³⁺. Recovery in the urine, kidney, lung, spleen, liver, and heart is shown. Dl is SEQ ID NO: 32; Bl is SEQ ID NO: 24; Kl is SEQ ID NO: 7; K2 is SEQ ID NO: 3; K3 is SEQ ID NO: 2; K5 is SEQ ID NO: 6; 15 is SEQ ID NO: 45.

[0020] Figure 6. (A), Left Enterochelin:Fe. The essential siderophore of gram negative organisms. It is composed of three catechol groups bound together by a backbone. Iron (red) is bound with affinity 10-49M. (B), Right Enterochelin:Fe bound within the calyx of the Ngal protein with an affinity of 0.4nM. Mutants Kl - K8 represent the mutants Dl-4, Dl-4- 1, Dl-4-2-1, dl-4-2-1-1, dl-4-2-1-3, dl-4-2-1-4, WT-3 and Dl-4-2 for which the sequences are provided herein.

[0021] Figure 7. Clearance of Ngal by the proximal tubule. Fl-Ngal was introduced into the peritoneum, and after 1 hour the kidney harvested. Ngal was localized to proximal tubule lysosomes. Mutants Kl - K8 represent the mutants Dl-4, Dl-4-1, Dl-4-2-1, dl-4-2-1-1, dl- 4-2-1-3, dl-4-2-1-4, WT-3 and Dl-4-2 for which the sequences are provided herein.

[0022] Figure 8. While ligand-metal charge-transfers between Ent and Fe3+ (lmax = 498 nm) were not modified by the addition of Ngal protein (note red coloration in 2 left tubes), catechol:Fe3+ converted from a FeL complex (blue, lmax = 575 nm) to a FeL3 complex (red, lmax= 498 nm) when bound to Ngal (right tubes) and produced an identical spectrum as En Fe.

[0023] Figure 9. Trafficking of 55Fe bound to Ngal through the serum to the kidney was visualized by radioautography. Note the black silver grains in proximal tubules but not in distal nephrons after introduction of Ngal:Ent:55Fe or Ngal:catechol:55Fe. Mutants Kl - K8 represent the mutants Dl-4, Dl-4-1, Dl-4-2-1, dl-4-2-1-1, dl-4-2-1-3, dl-4-2-1-4, WT-3 and Dl-4-2 for which the sequences are provided herein.

[0024] Figure 10. Urine was collected from both wild type and megalin deleted mice. Ngal was detected by immunoblot using polyclonal anti-mouse Ngal antibodies. Mutants Kl - K8 represent the mutants Dl-4, Dl-4-1, Dl-4-2-1, dl-4-2-1-1, dl-4-2-1-3, dl-4-2-1-4, WT- 3 and Dl-4-2 for which the sequences are provided herein.

[0025] Figure 11. Human kidney biopsy for AKI stained with anti-Ngal antibodies. Note the association of NGAL with Bowman's Capsule and with the proximal tubule (red-brown staining) apical endosomes. Mutants Kl - K8 represent the mutants Dl-4, Dl-4-1, Dl-4-2-1, dl-4-2-1-1, dl-4-2-1-3, dl-4-2-1-4, WT-3 and Dl-4-2 for which the sequences are provided herein.

[0026] Figure 12. Release of ligands from Ngal as a result of acidification. Low pH released 55Fe from Ngal:catechol:FeIII complexes but not from Ngal:Ent:FeIII. Felll loading at pH 7.0 was defined as 100% of the assay. Catechol differed significantly from Ent (P=0.00012). Mutants Kl - K8 represent the mutants Dl-4, Dl-4-1, Dl-4-2-1, dl-4-2-1-1, dl-4-2-1-3, dl-4-2-1-4, WT-3 and Dl-4-2 for which the sequences are provided herein. [0027] Figure 13. Top Urine Immunodetection by Western Blot.of wt and mutant Ngal in the urine 3 hrs after i.p. injection (80mg). Middle Starting Material shows immunoblot of purified WT and Mutant Ngal proteins (lOOng) and Bottom SDS-Page and Coomassie stain. Mutants Kl - K8 represent the mutants Dl-4, Dl-4-1, Dl-4-2-1, dl-4-2-1-1, dl-4-2-1-3, dl- 4-2-1-4, WT-3 and Dl-4-2.

[0028] Figure 14. 55Fe3+ retaining activity of wild-type and mutant NgahEnt. Mutants Kl - K8 represent the mutants Dl-4, Dl-4-1, Dl-4-2-1, dl-4-2-1-1, dl-4-2-1-3, dl-4-2-1-4, WT-3 and Dl-4-2.

[0029] Figure 15. Determination of the affinity of siderophore:iron in complex with wild type Ngal. (A) Fluorescence quenching analysis of Ngal with siderophores ("L") (B) or Ngal with Felll-siderophores ("FeL3"). Note that Felll dramatically enhanced the affinity of Ngal for different catechols. 2,3DHBA= Ent. Mutants Kl - K8 represent the mutants Dl-4, Dl-4- 1, Dl-4-2-1, dl-4-2-1-1, dl-4-2-1-3, dl-4-2-1-4, WT-3 and Dl-4-2 for which the sequences are provided herein.

[0030] Figure 16. Analysis of 55Fe3+ which was delivered by wild-type or mutant NgakEnt into mouse urine. In this figure Kl - K8 represent the mutants Dl-4, Dl-4-1, Dl-4- 2-1, dl-4-2-1-1, dl-4-2-1-3, dl-4-2-1-4, WT-3 and Dl-4-2.

[0031] Figure 17. Ngal effectively chelates Felll. Conversion of HPF to fluorescein (Ex 490 nm, Em 515 nm) was detected in the presence of catechol, ironlll and H202 (black line), but the addition of Ngal blocked this reaction (grey line); P<10-5. Mutants Kl - K8 represent the mutants Dl-4, Dl-4-1, Dl-4-2-1, dl-4-2-1-1, dl-4-2-1-3, dl-4-2-1-4, WT-3 and Dl-4-2 for which the sequences are provided herein.

[0032] Figure 18. K3 Ngal mutant inhibits the Redox Activity of Iron. Oxidative radicals produced by Fe(III), catechol and H202 was detected by a fluorescent probe, 3 '-(p- hydroxyphenyl) fluorescein (HPF), and the production of the Oxidative radicals was completely inhibited by wild-type (WT) and K3 Ngal proteins.

[0033] Figure 19. Shows sequences and amino acid alignment of WT NGAL (SEQ ID NO: 1) and K3 NGAL mutant (SEQ ID NO: 2).

[0034] Figure 20. Left tube shows that NGAL binds CatechokFe found in the urine, generating a bright red color. The tube contains the K3 mutant form of NGAL which can bypass the proximal tubule and deliver Iron or Apo-NGAL to the urine. Right tube: Apo- Ngal. These data show that the K3 mutant NGAL is capable of binding to siderophores such as En Fe and therefore are predicted to transport iron from the blood into the urine.

DETAILED DESCRIPTION

[0035] The present invention is based, in part, on the development of mutant versions of the NGAL protein that are not reabsorbed in the kidney and thus, unlike wild-type NGAL, are excreted in the urine. These mutant forms of NGAL have the ability to bind to iron- binding siderophores, such as enterochelin, and can be used to traffic iron out of the body by excretion in the urine. As such, the mutant NGAL proteins of the invention can be used in the treatment of iron overload and diseases and disorders associated with iron overload. In addition, the mutant NGAL proteins of the invention have bacteriostatic activity and can be used to treat infections of the urinary tract. Thus, the present invention provides mutant NGAL proteins, pharmaceutical compositions comprising such mutant NGAL proteins, either alone or complexed with siderophores, and the use of such mutant NGAL proteins and compositions in the treatment of various disorders and diseases, such as in the treatment of disorders associated with iron overload and in the treatment of bacterial infections of the urinary tract. These and other aspects of the present invention are described more fully below, and also in other sections of this application.

Abbreviations and Definitions

[0036] The abbreviation "NGAL" refers to Neutrophil Gelatinase Associated Lipocalin. NGAL is also referred to in the art as human neutrophil lipocalin, siderocalin, a- micropglobulin related protein, Scn-NGAL, lipocalin 2, 24p3, superinducible protein 24 (SIP24), uterocalin, and neu-related lipocalin. These alternative names for NGAL may be used interchangeably herein. Unless stated otherwise, the term "NGAL", as used herein, includes any NGAL protein, fragment, or mutant. In some embodiments the NGAL protein is wild-type human NGAL. In other embodiments the NGAL protein is a mutant NGAL protein.

[0037] The abbreviation hNGAL refers to human NGAL.

[0038] The abbreviation "WT" refers to wild-type, such as a wild-type nucleotide or amino acid sequence.

[0039] As used herein the term "about" is used herein to mean approximately, roughly, around, or in the region of. When the term "about" is used in conjunction with a numerical range, it modifies that range by extending the boundaries above and below the numerical values set forth. In general, the term "about" is used herein to modify a numerical value above and below the stated value by a variance of 20 percent up or down (higher or lower).

NGAL

[0040] NGAL is a small protein with a molecular weight of about 22kD and is a siderophore binding protein. A siderophore is an organic molecule that binds to and chelates iron. Bacteria produce the siderophore enterochelin, and mammals endogenously express a similar type, but simpler molecule called catechol. Enterochelin has an extremely high affinity for iron, and wild type NGAL has a high affinity for the enterochelin-iron complex. The enterochelin-iron-NGAL complex is pH insensitive and the bound iron is redox inactive. Thus the iron bound by such NGAL complexes is not available to catalyze oxygen radical formation, making NGAL an ideal iron chelator for in vivo use.

[0041] NGAL, and once produced in cells, is secreted into extracellular space and quickly cleared by kidney with a half-life of 10 minutes. Serum and urine levels of the protein can become very high in a number of disease models. The NGAL protein is transported into the kidney of healthy humans and can pass the filtration barrier of the glomerulus (the cut-off size of filtration is about 70kD) to enter the primary urine, but then NGAL is efficiently reabsorbed by megalin or megalin-cubilin-cubilin receptors localized on the apical side of the epithelia of the proximal tubules. Megalin is a universal receptor with broad substrate specificity and is expressed at the apical surface of the proximal tubules of the kidney where it is involved in protein reabsorption. The binding of megalin to its substrates is mediated by ionic interactions, and its negative charged substrate binding domains can efficiently bind to the positively charged surfaces of proteins in the urinary filtrate. Once absorbed and endocytosed, NGAL is trafficked to lysosomes, where it is degraded. Once degraded, the iron which NGAL transported to the kidney is reabsorbed.

NGAL Mutants

[0042] The present invention provides mutant NGAL proteins, including, but not limited to those which have been mutated to remove positively charged residues that may be involved in the megalin interaction. Like WT NGAL, the NGAL mutants of the invention have high affinity for enterochelin-iron complexes but appear to have significantly reduced affinity for megalin (Table 1). Thus, rather than being reabsorbed by a megalin receptor mediated mechanism in the kidney, the NGAL mutants of the invention, and complexes of these mutants with enterochelin and iron, are not efficiently reabsorbed in the kidney and are instead excreted in the urine. The mutant NGAL proteins of the invention can thus be used to efficiently remove excessive iron from the body and traffic it into the urine in a safe redox inactive form. Furthermore, previous reports have shown that NGAL-enterochelin-iron has little or no chemical or cellular toxicity, suggesting that it could be safely used

therapeutically, for example in the therapeutic treatment of diseases and disorders associated with iron overload, such as hemochromatosis.

[0043] The terms "mutant NGAL protein" and "NGAL mutant" as used herein, refer to a protein or an amino acid sequence that differs by one or more amino acids from the amino acid sequence of WT human NGAL (SEQ ID NO.l, see sequence of HsNGAL in Figure 1).

[0044] The mutant NGAL proteins of the invention may have one or more "non conservative" changes, wherein a given amino acid is substituted with another amino acid that has different structural or chemical properties. In several embodiments of the invention basic/positively charged lysine, arginine, and/or histidine residues on the surface of the NGAL protein, such as those that interact with megalin, are mutated by substituting these residues with non-basic / non-positively charged residues. These are non-conservative changes. For example, in several embodiments of the invention basic/positively charged lysine (Lys - K), arginine (Arg - R), and/or histidine (His - H), residues, such as those on the surface of the NGAL protein that may be involved in the megalin interaction, are substituted with non-basic / non-positively charged residues such as alanine (Ala - A), asparagine (Asn - N), aspartic acid (Asp - D), cysteine (Cys - C), glutamine (Gin - Q), glutamic acid (glu - E), glycine (Gly - G), isoleucine (He - I), leucine (Leu - L), methionine (Met - M),

phenylalanine (Phe - F), proline (Pro - P), serine (Ser - S), threonine (thr - T), tryptophan (Trp - W), tyrosine (Tyr - Y), and valine (Val - V). In some embodiments, basic/positively charged lysine, arginine, and/or histidine residues are substituted with negatively charged residues such as aspartic acid (Asp - D) and glutamic acid (Glu - E).

[0045] In some embodiments the mutant NGAL proteins of the invention may have one or more "conservative" changes, wherein a given amino acid is substituted for another amino acid that has similar structural or chemical properties. For example, in some embodiments it is desirable to either leave the residues of NGAL that are involved in the siderophore interaction intact or to only make conservative changes at those residues. Various other conservative amino acid substitutions may be made throughout the NGAL protein, such as conservative amino acid substitutions that do not destroy the ability of the NGAL mutants of the invention to transport iron out of the body. One type of conservative amino acid substitution refers to the interchangeability of residues having similar side chains. For example, a group of amino acids having aliphatic side chains is glycine, alanine, valine, leucine, and isoleucine; a group of amino acids having aliphatic hydroxyl side chains is serine and threonine; a group of amino acids having amide containing side chains is asparagine and glutamine; a group of amino acids having aromatic side chains is phenylalanine, tyrosine, and tryptophan; a group of amino acids having basic side chains is lysine, arginine, and histidine; and a group of amino acids having sulfur containing side chains is cysteine and methionine. Useful conservative amino acids substitution groups are: valine leucine isoleucine, phenylalanine tyrosine, lysine arginine, alanine valine, and asparagine glutamine.

[0046] The mutant NGAL proteins of the invention may contain various mutations (including additions, deletions, and substitutions) in addition to the mutations of specific residues set forth herein (below), including, for example, additions to or deletions from the N- and/or C-termini of the NGAL mutants. Any such mutations can be made to the extent that they do not adversely affect the ability of the NGAL mutants to bind to a siderophore, to transport iron, and/or to be excreted in the urine.

[0047] In further embodiments, the NGAL mutants of the invention may comprise one or more non-naturally occurring amino acids. Non-natural amino acids, such as those that contain unique side chain functional groups including halogens, unsaturated hydrocarbons, heterocycles, silicon, and organometallic units, can offer advantages in improving the stability of proteins. Many such non-naturally occurring amino acids are known. Such non- naturally occurring amino acids can be used in the NGAL mutants of the invention.

[0048] In certain embodiments, the present invention provides NGAL mutants having a certain % identity to WT human NGAL or to some other NGAL mutant. The following terms are used to describe the sequence relationships between two or more polynucleotides or amino acid sequences: "sequence identity," "percentage sequence identity" and "identity." These terms are used in accordance with their usual meaning in the art. Percentage sequence identity is measured with reference to a reference sequence. The term "sequence identity" means that two polynucleotide or amino acid sequences are identical (i.e., on a

nucleotide-by-nucleotide basis). The term "percentage of sequence identity" is calculated by comparing two optimally aligned sequences, determining the number of positions at which the identical nucleic acid base or amino acid occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions, and multiplying the result by 100 to yield the percentage of sequence identity.

Thirteen Non-Conserved Positive Surface Residues in NGAL

[0049] The NGAL protein contains thirteen basic/positive surface amino acid residues that are not conserved among species, namely residues Lys 15, Lys 46, Lys 50, Lys 59, Lys 62, Lys 73, Lys 74, Lys 75, Lys 98, His 118, Arg 130, Lys 149, and His 165. Data presented in the present application demonstrate that mutations of various combinations of these thirteen amino acid residues results in the generation of NGAL mutants that, like WT NGAL, have the ability to bind to enterochelin-iron but, unlike WT NGAL, are not effectively reabsorbed in the kidney. Such NGAL mutants, when complexed with a siderophore such as enterochelin, can be used to transport excess iron out of the body by facilitating its excretion in the urine. Such NGAL mutants may also have bacteriostatic activity and can be used to treat bacterial infections of the urinary tract.

[0050] In one embodiment, the mutant NGAL proteins of the invention comprise, consist of, or consist essentially of amino acid sequences that are based on the amino acid sequence of WT human NGAL, or a fragment thereof, but that contain one or more mutations. In one embodiment, the present invention provides an NGAL mutant having one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, or all thirteen of the following amino acid positions mutated as compared to WT human NGAL: Lys 15, Lys 46, Lys 50, Lys 59, Lys 62, Lys 73, Lys 74, Lys 75, Lys 98, His 118, Arg 130, Lys 149, and His 165. In some embodiments five or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments six or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments seven or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments eight or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments nine or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments ten or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL.

[0051] In one embodiment the mutated amino acid residues are deleted. In another embodiment the mutated amino acid residues are substituted with a non-positively charged amino acid (i.e. a non-conservative substitution). In another embodiment the mutated amino acid residues are substituted with a negatively charged amino acid (i.e. a non-conservative substitution). In another embodiment the NGAL mutant may comprise any combination of such mutations, i.e. any combination of deletions, substitutions for non-positively charged amino acids, or substitutions for negatively charged amino acids may be present at any one, two, three, four, five, six, seven, eight nine, ten, eleven, twelve, or all thirteen of the above listed amino acid residues. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL- enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine

132, Phenylalanine 133, and Lysine 134, or if mutated at these residues only conservative substitutions are made.

[0052] In one preferred embodiment the present invention provides an NGAL mutant in which Lys (K) 15 is substituted with an uncharged amino acid, including, but not limited to, Ser (S). In one preferred embodiment the present invention provides an NGAL mutant in which Lys (K) 46 is substituted with a negatively charged amino acid, including, but not limited to, Glu (E). In one preferred embodiment the present invention provides an NGAL mutant in which Lys (K) 50 is substituted with an uncharged amino acid, including, but not limited to, Thr (T). In one preferred embodiment the present invention provides an NGAL mutant in which Lys (K) 59 is substituted with an uncharged amino acid, including, but not limited to, Gin (Q). In one preferred embodiment the present invention provides an NGAL mutant in which Lys (K) 62 is substituted with an uncharged amino acid, including, but not limited to, Gly (G). In one preferred embodiment the present invention provides an NGAL mutant in which Lys (K) 73 is substituted with a negatively charged amino acid, including, but not limited to, Asp (D). In one preferred embodiment the present invention provides an NGAL mutant in which Lys (K) 74 is substituted with a negatively charged amino acid, including, but not limited to, Asp (D). In one preferred embodiment the present invention provides an NGAL mutant in which Lys (K) 75 is substituted with an aliphatic amino acid, including, but not limited to, Gly (G). In one preferred embodiment the present invention provides an NGAL mutant in which Lys (K) 98 is substituted with an uncharged amino acid, including, but not limited to, Gin (Q). In one preferred embodiment the present invention provides an NGAL mutant in which His (H) 118 is substituted with a non-polar amino acid, including, but not limited to, Phe (F). In one preferred embodiment the present invention provides an NGAL mutant in which Arg (R) 130 is substituted with an uncharged amino acid, including, but not limited to, Gin (Q). In one preferred embodiment the present invention provides an NGAL mutant in which Lys (K) 149 is substituted with an uncharged amino acid, including, but not limited to, Gin (Q). In one preferred embodiment the present invention provides an NGAL mutant in which His (H) 165 is substituted with an uncharged amino acid, including, but not limited to, Asn (N).

[0053] In one embodiment, the present invention provides an NGAL mutant that comprises, consists essentially of, or consists of an amino acid sequence that is at least 70%, or at least 75%, or at least 80%>, or at least 85%, or at least 90%, or at least 95%, or at least 98% identical to the sequence of WT human NGAL (SEQ ID NO.l), or a fragment thereof, wherein one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, or all thirteen residues from among Lys 15, Lys 46, Lys 50, Lys 59, Lys 62, Lys 73, Lys 74, Lys 75, Lys 98, His 118, Arg 130, Lys 149, and His 165 is deleted or substituted with a non-positively charged amino acid, such as a negatively charged amino acid, and wherein the NGAL mutant: (a) is excreted in the urine or exhibits a greater level of excretion in the urine than WT human NGAL, and/or (b) is not reabsorbed in the proximal tubule of the kidney or exhibits a lower level of reabsorption in the proximal tubule of the kidney as compared to WT human NGAL, and/or (c) is not a substrate for reabsorption in the kidney by a megalin- cubilin-cubilin-receptor mediated mechanism, and/or (d) has reduced affinity for the megalin- cubilin-receptor as compared to WT NGAL, and/or (e) has fewer positively charged residues on its solvent accessible surface as compared to WT human NGAL, and wherein the NGAL mutant also (i) is able to bind to a siderophore, and/or (ii) is able to bind to a siderophore complexed with iron, and/or (iii) has a preserved three-dimensional structure of the enterochelin binding pocket and/or (iv) has bacteriostatic activity. In some embodiments five or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments six or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments seven or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments eight or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments nine or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments ten or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL-enterochelin interaction:

Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine 132, Phenylalanine 133, and Lysine 134, or if mutated at these residues only conservative substitutions are made.

[0054] Exemplary NGAL mutants of the invention include those that comprise the sequence of mutants Kl, K2, K3, K5, II, 13, F4, F5, and B2 (see Table 2), or that comprise fragments or variants of such sequences. In some embodiments such variants have the amino acids specified in Table 2 at residues 15, 46, 59, 62, 73, 74, 75, 98, 118, 130, 149, and 165, but other amino acid residues can differ from the specified sequences provided that the NGAL mutant is at least 70%, or at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 98% identical to the sequence of WT human NGAL (SEQ ID NO.1), or a fragment thereof, and provided that the NGAL mutant: (a) is excreted in the urine or exhibits a greater level of excretion in the urine than WT human NGAL, and/or (b) is not reabsorbed in the proximal tubule of the kidney or exhibits a lower level of reabsorption in the proximal tubule of the kidney as compared to WT human NGAL, and/or (c) is not a substrate for reabsorption in the kidney by a megalin-cubilin-receptor mediated mechanism, and/or (d) has reduced affinity for the megalin-cubilin-receptor as compared to WT NGAL, and/or (e) has fewer positively charged residues on its solvent accessible surface as compared to WT human NGAL, and also provided that he NGAL mutant (i) is able to bind to a siderophore, and/or (ii) is able to bind to a siderophore complexed with iron, and/or (iii) has a preserved three-dimensional structure of the enterochelin binding pocket and/or (iv) has bacteriostatic activity. In some embodiments five or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments six or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments seven or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments eight or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments nine or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments ten or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL-enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine 132, Phenylalanine 133, and Lysine 134, or if mutated at these residues only conservative substitutions are made.

[0055] In one embodiment, the present invention provides an NGAL mutant that comprises, consists essentially of, or consists of an amino acid sequence that is at least 70%, or at least 75%>, or at least 80%>, or at least 85%>, or at least 90%>, or at least 95%>, or at least 98%o identical to the sequence of the K3 NGAL mutant (SEQ ID NO.2), wherein residues 15, 46, 73, 74, 75, 98, 118, 130, 149, and 165 each differ from the sequence of WT human NGAL and are each non-positively charged amino acids, and wherein the NGAL mutant: (a) is excreted in the urine or exhibits a greater level of excretion in the urine than WT human NGAL, and/or (b) is not reabsorbed in the proximal tubule of the kidney or exhibits a lower level of reabsorption in the proximal tubule of the kidney as compared to WT human NGAL, and/or (c) is not a substrate for reabsorption in the kidney by a megalin-cubilin-receptor mediated mechanism, and/or (d) has reduced affinity for the megalin-cubilin-receptor as compared to WT NGAL, and/or (e) has fewer positively charged residues on its solvent accessible surface as compared to WT human NGAL, and wherein the NGAL mutant also (i) is able to bind to a siderophore, and/or (ii) is able to bind to a siderophore complexed with iron, and/or (iii) has a preserved three-dimensional structure of the enterochelin binding pocket and/or (iv) has bacteriostatic activity. In some embodiments five or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments six or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments seven or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments eight or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments nine or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments ten or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL-enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine 132, Phenylalanine 133, and Lysine 134, or if mutated at these residues only conservative substitutions are made.

[0056] In another embodiment, the present invention provides an NGAL mutant that comprises, consists essentially of, or consists of an amino acid sequence that is at least 70%, or at least 75%, or at least 80%>, or at least 85%, or at least 90%, or at least 95%, or at least 98%) identical to the sequence of the K2 NGAL mutant (SEQ ID NO.3), wherein residues 15, 73, 74, 75, 98, 118, 130, 149, and 165 each differ from the sequence of WT human NGAL and are each non-positively charged amino acids, and wherein the NGAL mutant: (a) is excreted in the urine or exhibits a greater level of excretion in the urine than WT human NGAL, and/or (b) is not reabsorbed in the proximal tubule of the kidney or exhibits a lower level of reabsorption in the proximal tubule of the kidney as compared to WT human NGAL, and/or (c) is not a substrate for reabsorption in the kidney by a megalin-cubilin-cubilin- receptor mediated mechanism, and/or (d) has reduced affinity for the megalin-cubilin-cubilin- receptor as compared to WT NGAL, and/or (e) has fewer positively charged residues on its solvent accessible surface as compared to WT human NGAL, and wherein the NGAL mutant also (i) is able to bind to a siderophore, and/or (ii) is able to bind to a siderophore complexed with iron, and/or (iii) has a preserved three-dimensional structure of the enterochelin binding pocket and/or (iv) has bacteriostatic activity. In some embodiments five or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments six or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments seven or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments eight or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments nine or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments ten or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL-enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine 132, Phenylalanine 133, and Lysine 134, or if mutated at these residues only conservative substitutions are made. [0057] In another embodiment, the present invention provides an NGAL mutant that comprises, consists essentially of, or consists of an amino acid sequence that is at least 70%, or at least 75%, or at least 80%>, or at least 85%, or at least 90%, or at least 95%, or at least 98%) identical to the sequence of the 13 NGAL mutant (SEQ ID NO.4), wherein residues 62, 73, 74, 75, and 98 each differ from the sequence of WT human NGAL and are each non- positively charged amino acids, and wherein the NGAL mutant: (a) is excreted in the urine or exhibits a greater level of excretion in the urine than WT human NGAL, and/or (b) is not reabsorbed in the proximal tubule of the kidney or exhibits a lower level of reabsorption in the proximal tubule of the kidney as compared to WT human NGAL, and/or (c) is not a substrate for reabsorption in the kidney by a megalin-cubilin-cubilin-receptor mediated mechanism, and/or (d) has reduced affinity for the megalin-cubilin-cubilin-receptor as compared to WT NGAL, and/or (e) has fewer positively charged residues on its solvent accessible surface as compared to WT human NGAL, and wherein the NGAL mutant also (i) is able to bind to a siderophore, and/or (ii) is able to bind to a siderophore complexed with iron, and/or (iii) has a preserved three-dimensional structure of the enterochelin binding pocket and/or (iv) has bacteriostatic activity. In some embodiments five or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments six or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments seven or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments eight or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments nine or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments ten or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL-enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine 132, Phenylalanine 133, and Lysine 134, or if mutated at these residues only conservative substitutions are made.

[0058] In another embodiment, the present invention provides an NGAL mutant that comprises, consists essentially of, or consists of an amino acid sequence that is at least 70%>, or at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 98% identical to the sequence of the II NGAL mutant (SEQ ID NO.5), wherein residues 15, 73, 74, 75, and 130 each differ from the sequence of WT human NGAL and are each non- positively charged amino acids, and wherein the NGAL mutant: (a) is excreted in the urine or exhibits a greater level of excretion in the urine than WT human NGAL, and/or (b) is not reabsorbed in the proximal tubule of the kidney or exhibits a lower level of reabsorption in the proximal tubule of the kidney as compared to WT human NGAL, and/or (c) is not a substrate for reabsorption in the kidney by a megalin-cubilin-receptor mediated mechanism, and/or (d) has reduced affinity for the megalin-cubilin-receptor as compared to WT NGAL, and/or (e) has fewer positively charged residues on its solvent accessible surface as compared to WT human NGAL, and wherein the NGAL mutant also ((i) is able to bind to a

siderophore, and/or (ii) is able to bind to a siderophore complexed with iron, and/or (iii) has a preserved three-dimensional structure of the enterochelin binding pocket and/or (iv) has bacteriostatic activity. In some embodiments five or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments six or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments seven or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments eight or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments nine or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments ten or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL-enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine 132, Phenylalanine 133, and Lysine 134, or if mutated at these residues only conservative substitutions are made.

[0059] In another embodiment, the present invention provides an NGAL mutant that comprises, consists essentially of, or consists of an amino acid sequence that is at least 70%>, or at least 75%>, or at least 80%>, or at least 85%>, or at least 90%>, or at least 95%>, or at least 98%o identical to the sequence of the K5 NGAL mutant (SEQ ID NO.6), wherein residues 15, 46, 98, 118, 130, 149, and 165 each differ from the sequence of WT human NGAL and are each non-positively charged amino acids, and wherein the NGAL mutant: (a) is excreted in the urine or exhibits a greater level of excretion in the urine than WT human NGAL, and/or

(b) is not reabsorbed in the proximal tubule of the kidney or exhibits a lower level of reabsorption in the proximal tubule of the kidney as compared to WT human NGAL, and/or

(c) is not a substrate for reabsorption in the kidney by a megalin-cubilin-receptor mediated mechanism, and/or (d) has reduced affinity for the megalin-cubilin-receptor as compared to WT NGAL, and/or (e) has fewer positively charged residues on its solvent accessible surface as compared to WT human NGAL, and wherein the NGAL mutant also (i) is able to bind to a siderophore, and/or (ii) is able to bind to a siderophore complexed with iron, and/or (iii) has a preserved three-dimensional structure of the enterochelin binding pocket and/or (iv) has bacteriostatic activity. In some embodiments five or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments six or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments seven or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments eight or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments nine or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments ten or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL-enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine 132, Phenylalanine 133, and Lysine 134, or if mutated at these residues only conservative substitutions are made.

[0060] In another embodiment, the present invention provides an NGAL mutant that comprises, consists essentially of, or consists of an amino acid sequence that is at least 70%, or at least 75%, or at least 80%>, or at least 85%>, or at least 90%>, or at least 95%>, or at least 98%o identical to the sequence of the F4 NGAL mutant (SEQ ID NO.8), wherein residues 15 and 46 each differ from the sequence of WT human NGAL and are each non-positively charged amino acids, and wherein the NGAL mutant: (a) is excreted in the urine or exhibits a greater level of excretion in the urine than WT human NGAL, and/or (b) is not reabsorbed in the proximal tubule of the kidney or exhibits a lower level of reabsorption in the proximal tubule of the kidney as compared to WT human NGAL, and/or (c) is not a substrate for reabsorption in the kidney by a megalin-cubilin-receptor mediated mechanism, and/or (d) has reduced affinity for the megalin-cubilin-receptor as compared to WT NGAL, and/or (e) has fewer positively charged residues on its solvent accessible surface as compared to WT human NGAL, and wherein the NGAL mutant also (i) is able to bind to a siderophore, and/or (ii) is able to bind to a siderophore complexed with iron, and/or (iii) has a preserved three- dimensional structure of the enterochelin binding pocket and/or (iv) has bacteriostatic activity. In some embodiments five or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments six or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments seven or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments eight or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments nine or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments ten or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL-enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine 132, Phenylalanine 133, and Lysine 134, or if mutated at these residues only conservative substitutions are made.

[0061] In another embodiment, the present invention provides an NGAL mutant that comprises, consists essentially of, or consists of an amino acid sequence that is at least 70%, or at least 75%, or at least 80%>, or at least 85%>, or at least 90%>, or at least 95%>, or at least 98%o identical to the sequence of the F5 NGAL mutant (SEQ ID NO.9), wherein residues 15, 46, and 165 each differ from the sequence of WT human NGAL and are each non-positive ly charged amino acids, and wherein the NGAL mutant: (a) is excreted in the urine or exhibits a greater level of excretion in the urine than WT human NGAL, and/or (b) is not reabsorbed in the proximal tubule of the kidney or exhibits a lower level of reabsorption in the proximal tubule of the kidney as compared to WT human NGAL, and/or (c) is not a substrate for reabsorption in the kidney by a megalin-cubilin-receptor mediated mechanism, and/or (d) has reduced affinity for the megalin-cubilin-receptor as compared to WT NGAL, and/or (e) has fewer positively charged residues on its solvent accessible surface as compared to WT human NGAL, and wherein the NGAL mutant also (i) is able to bind to a siderophore, and/or (ii) is able to bind to a siderophore complexed with iron, and/or (iii) has a preserved three- dimensional structure of the enterochelin binding pocket and/or (iv) has bacteriostatic activity. In some embodiments five or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments six or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments seven or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments eight or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments nine or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments ten or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL-enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine 132, Phenylalanine 133, and Lysine 134, or if mutated at these residues only conservative substitutions are made.

[0062] In another embodiment, the present invention provides an NGAL mutant that comprises, consists essentially of, or consists of an amino acid sequence that is at least 70%, or at least 75%, or at least 80%>, or at least 85%>, or at least 90%>, or at least 95%>, or at least 98%o identical to the sequence of the B2 NGAL mutant (SEQ ID NO.10), wherein residues 15, 46, 118, and 165 each differ from the sequence of WT human NGAL and are each non- positively charged amino acids, and wherein the NGAL mutant: (a) is excreted in the urine or exhibits a greater level of excretion in the urine than WT human NGAL, and/or (b) is not reabsorbed in the proximal tubule of the kidney or exhibits a lower level of reabsorption in the proximal tubule of the kidney as compared to WT human NGAL, and/or (c) is not a substrate for reabsorption in the kidney by a megalin-cubilin-receptor mediated mechanism, and/or (d) has reduced affinity for the megalin-cubilin-receptor as compared to WT NGAL, and/or (e) has fewer positively charged residues on its solvent accessible surface as compared to WT human NGAL, and wherein the NGAL mutant also (i) is able to bind to a siderophore, and/or (ii) is able to bind to a siderophore complexed with iron, and/or (iii) has a preserved three-dimensional structure of the enterochelin binding pocket and/or (iv) has bacteriostatic activity. In some embodiments five or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments six or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments seven or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments eight or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments nine or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments ten or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL-enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine 132, Phenylalanine 133, and Lysine 134, or if mutated at these residues only conservative substitutions are made.

[0063] In another embodiment, the present invention provides an NGAL mutant that comprises, consists essentially of, or consists of an amino acid sequence that is at least 70%, or at least 75%>, or at least 80%>, or at least 85%>, or at least 90%>, or at least 95%>, or at least 98%o identical to the sequence of the Kl NGAL mutant (SEQ ID NO.7), wherein residues 15, 46, 59, 98, 118, 130, 149, and 165 each differ from the sequence of WT human NGAL and are each non-positively charged amino acids, and wherein the NGAL mutant: (a) is excreted in the urine or exhibits a greater level of excretion in the urine than WT human NGAL, and/or (b) is not reabsorbed in the proximal tubule of the kidney or exhibits a lower level of reabsorption in the proximal tubule of the kidney as compared to WT human NGAL, and/or (c) is not a substrate for reabsorption in the kidney by a megalin-cubilin-receptor mediated mechanism, and/or (d) has reduced affinity for the megalin-cubilin-receptor as compared to WT NGAL, and/or (e) has fewer positively charged residues on its solvent accessible surface as compared to WT human NGAL, and wherein the NGAL mutant also (i) is able to bind to a siderophore, and/or (ii) is able to bind to a siderophore complexed with iron, and/or (iii) has a preserved three-dimensional structure of the enterochelin binding pocket and/or (iv) has bacteriostatic activity. In some embodiments five or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments six or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments seven or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments eight or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments nine or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In some embodiments ten or more of the thirteen listed amino acid positions are mutated as compared to WT human NGAL. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL-enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine 132, Phenylalanine 133, and Lysine 134, or if mutated at these residues only conservative substitutions are made.

[0064] In further embodiments the NGAL mutants described above that have mutations in one or more of the thirteen non-conserved positive/basic surface residues, can also have mutations in one or more of the five conserved positive/based surface residues below, or one or more of the other mutations described in other following sections of this Detailed

Description.

Five Conserved Positive/Basic Surface Residues in NGAL

[0065] The NGAL protein contains five basic/positive surface amino acid residues that are conserved among human, rat, mouse, chimpanzee, cow, dog, wild boar and rhesus monkey species, namely residues Arg(R) 43, Arg(R) 72, Arg(R) 140, Lys(K) 142, and Lys(K) 157. In one embodiment, the present invention provides an NGAL mutant having one, two, three, four, or all five of these amino acid positions mutated as compared to WT human NGAL. In one embodiment the mutated amino acid residue or residues are deleted. In another embodiment the mutated amino acid residue or residues are substituted with a non- positively charged amino acid (i.e. a non-conservative change). In another embodiment the mutated amino acid residue or residues are substituted with a negatively charged amino acid (i.e. a non-conservative change). In another embodiment the NGAL mutant may comprise any combination of such mutations, i.e. any combination of deletions, substitutions for non- positively charged amino acids, or substitutions for negatively charged amino acids may be provided at one, two, three, four, or five of the above listed amino acid residues. [0066] In one embodiment, the present invention provides an NGAL mutant that comprises, consists essentially of, or consists of an amino acid sequence that is at least 70%, or at least 75%, or at least 80%>, or at least 85%, or at least 90%, or at least 95%, or at least 98% identical to the sequence of WT human NGAL (SEQ ID NO.l), or a fragment thereof, wherein one, two, three, four, or all five residues from among (R) 43, Arg(R) 72, Arg(R) 140, Lys(K) 142, and Lys(K) 157 is deleted or substituted with a non-positively charged amino acid, such as a negatively charged amino acid, and wherein the NGAL mutant: (a) is excreted in the urine or exhibits a greater level of excretion in the urine than WT human NGAL, and/or (b) is not reabsorbed in the proximal tubule of the kidney or exhibits a lower level of reabsorption in the proximal tubule of the kidney as compared to WT human NGAL, and/or (c) is not a substrate for reabsorption in the kidney by a megalin-cubilin-receptor mediated mechanism, and/or (d) has reduced affinity for the megalin-cubilin-receptor as compared to WT NGAL, and/or (e) has fewer positively charged residues on its solvent accessible surface as compared to WT human NGAL, and wherein the NGAL mutant also (i) is able to bind to a siderophore, and/or (ii) is able to bind to a siderophore complexed with iron, and/or (iii) has a preserved three-dimensional structure of the enterochelin binding pocket and/or (iv) has bacteriostatic activity. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL- enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine

[0067] In further embodiments the NGAL mutants described in this section that have mutations in one or more of the five conserved positive/basic surface residues, can also have mutations in one or more of the thirteen non-conserved positive/based surface residues described in the previous section of the Detailed Description, or one or more of the other mutations described in the following sections of this Detailed Description.

Additional Surface Residues in NGAL

[0068] The following amino acid residues are located on the surface of the NGAL protein and can play a role in the interaction of the NGAL protein with the megalin protein and/or in the reabsorption of NGAL in the kidney: amino acid residues 1-15, 17-26, 40-50, 57-62, 71- 82, 84-89, 96-105, 114-118, 128-131, 134, 140-151, 157-165, and 170-174.

[0069] In one embodiment, the mutant NGAL proteins of the invention comprise, consist of, or consist essentially of amino acid sequences that are based on the amino acid sequence of human NGAL, or a fragment thereof, but that contain mutations as at one or more of the individual amino acid residues located at residues 1-15, 17-26, 40-50, 57-62, 71-82, 84-89, 96-105, 114-118, 128-131, 134, 140-151, 157-165, and/or 170-174 of WT human NGAL. In one embodiment one or more of the mutated amino acid residues can be deleted. In another embodiment one or more of the mutated amino acid residues can be substituted with a non- positively charged amino acid, including, but not limited to a negatively charged amino acid. In another embodiment the NGAL mutant may comprise any combination of such mutations, i.e. any combination of deletions, substitutions for non-positively charged amino acids, and/or substitutions for negatively charged amino acids at any one or more of the above listed amino acid residues. Table 2 provides details of all possible mutations of the surface residues of NGAL that are contemplated by the present invention. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL-enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine 132, Phenylalanine 133, and Lysine 134, or if mutated at these residues only conservative substitutions are made.

[0070] In one embodiment, the present invention provides an NGAL mutant that comprises, consists essentially of, or consists of an amino acid sequence that is at least 70%, or at least 75%, or at least 80%>, or at least 85%>, or at least 90%>, or at least 95%>, or at least 98% identical to the sequence of WT human NGAL (SEQ ID NO.l), or a fragment thereof, wherein one or more of the individual amino acid residues located at residues 1-15, 17-26, 40-50, 57-62, 71-82, 84-89, 96-105, 114-118, 128-131, 134, 140-151, 157-165, and/or 170- 174 of WT human NGAL is deleted or substituted with a non-positively charged amino acid, such as a negatively charged amino acid, and wherein the NGAL mutant: (a) is excreted in the urine or exhibits a greater level of excretion in the urine than WT human NGAL, and/or

(c) is not a substrate for reabsorption in the kidney by a megalin-cubilin-receptor mediated mechanism, and/or (d) has reduced affinity for the megalin-cubilin-receptor as compared to WT NGAL, and/or (e) has fewer positively charged residues on its solvent accessible surface as compared to WT human NGAL, and wherein the NGAL mutant (i) is able to bind to a siderophore, and/or (ii) is able to bind to a siderophore complexed with iron, and/or (iii) has a preserved three-dimensional structure of the enterochelin binding pocket and/or (iv) has bacteriostatic activity. In preferred embodiments such NGAL mutants are not mutated (i.e. have the same amino acid sequence as WT human NGAL), at one or more, or more preferably all, of the following amino acid residues that are involved in the NGAL- enterochelin interaction: Asparagine 39, Alanine 40, Tyrosine 52, Serine 68, Trptophan 79, Arginine 81, Tyrosine 100, Tyrosine 106, Phenylalanine 123, Lysine 125, Tyrosine

Functional Properties of NGAL Mutants

[0071] In certain embodiments the mutant NGAL proteins of the invention have certain specified functions. For example, in some embodiments the mutant NGAL proteins of the invention have one or more of the following properties: (a) they are excreted in the urine or exhibit a greater level of excretion in the urine than WT human NGAL, and/or (b) they are not reabsorbed in the proximal tubule of the kidney or exhibit a lower level of reabsorption in the proximal tubule of the kidney than WT human NGAL, and/or (c) they are not a substrate for reabsorption in the kidney by a megalin-cubilin-receptor mediated mechanism. Similarly, in some embodiments the mutant NGAL proteins of the invention have one or more of the following properties: (i) they are able to bind to enterochelin-type siderophores, and/or (ii) they are able to bind to enterochelin-type siderophores complexed with iron, and/or (iii) they have a preserved three-dimensional structure of the enterochelin binding pocket and/or (iv) they have bacteriostatic activity.

[0072] Each of the above properties of the mutant NGAL proteins of the invention can be tested for and/or quantified, and in some embodiments the mutant NGAL proteins of the invention have functional properties that fall within a certain numeric range.

[0073] For example, in some embodiments the mutant NGAL proteins of the invention are excreted in the urine or exhibit a greater level of excretion in the urine than WT human NGAL. Excretion of the mutant NGAL proteins of the invention can be detected and quantified, for example using the methods described in the Examples section of this application. For example the amount of the mutant NGAL protein present in the urine a given time after its is administered to a subject, such as a mouse or a human subject, can be measured and can be expressed as a percentage of the total amount administered (see Examples and Table 1) to give a % accumulation in the urine. The % accumulation in the urine of a given NGAL mutant can be compared to that of other mutants or of WT NGAL. NGAL or an NGAL mutant or siderophore complex thereof can be radiolabeled (e.g. with radioactive iron) or labeled with some other detectable moiety in order to facilitate its detection and quantification. In some embodiments the present invention provides that the mutant NGAL proteins of the invention exhibit a greater level of excretion in the urine than does WT human NGAL. For example, the NGAL mutants can have a 6-fold, 7-fold, 8-fold, 9-fold, 10-fold, 15-fold, 20-fold, 25-fold, 30-fold, 40-fold, 50-fold, 100-fold or higher level of excretion in the urine than WT human NGAL. As seen in Figure 5, WT NGAL can have a % accumulation in the urine (measured as a % of the amount administered intraperitoneally) of less than 0.2%. In contrast, as can be seen from Figure 3, Figure 5, and Table 1, the NGAL mutants of the invention can have a % accumulation in the urine (measured as a % of the amount administered intraperitoneally 3 hours after administration) of greater than 1%, or greater than 2%, or greater than 3%, or greater than 4%, or greater than 5%, or greater than 6%, or greater than 7%, or greater than 8%, or greater than 9%, or greater than 10%, or greater than 15%, or greater than 20%, or more.

[0074] In some embodiments the mutant NGAL proteins of the invention are able to bind to siderophores, such as enterochelin, and/or they are able to bind to siderophores complexed with iron. The ability of the NGAL mutants of the invention to bind to siderophores and siderophore-iron complexes can be tested and/or quantified, for example using the methods described in the Examples section of this application. For example NGAL (including the NGAL mutants of the invention) and siderophore molecules such as enterochelin and iron associate with each other in a 1 : 1 : 1 molar ratio and NGAL (including the NGAL mutants of the invention) and siderophore molecules such as catechol and iron associate with each other in a 1 :3: 1 molar ratio. Accordingly using a radiolabeled form of iron the binding of NGAL to siderophore molecules and iron can be measured or estimated by examining the % of radiolabeled iron that is retained by a given NGAL protein. The % of iron (iron- siderophore) that is retained can be compared between NGAL mutants or between an NGAL mutant and WT NGAL. In some embodiments the present invention provides that the mutant NGAL proteins of the invention exhibit a similar % of iron (iron-siderophore) retention as compared to WT NGAL. In some embodiments the present invention provides that the mutant NGAL proteins of the invention exhibit a higher % of iron (iron-siderophore) retention as compared to WT NGAL, such as a 1.5-fold, 2-fold, 2.5-fold or greater-fold higher % of iron (iron-siderophore) retention. In some embodiments, the mutant NGAL proteins of the invention exhibit a % iron (iron-siderophore) retention of about 20% or more, or about 30% or more, or about 40% or more.

[0075] In some embodiments the mutant NGAL proteins of the invention have antibacterial activity. Antibacterial activity of the NGAL mutants of the invention can be tested and/or quantified, for example using standard methodologies known in the art, for example by culturing bacteria in the presence of the NGAL mutants and assessing the effect of the NGAL mutants on bacterial growth, survival, numbers, etc. in comparison to control conditions in which no NGAL mutant is present.

Non-NGAL Lipocalins

[0076] In addition to mutants of NGAL, the present invention also contemplates that mutants of other lipocalins can be made that, like the NGAL mutants described herein, have the ability to bind to siderophore-iron complexes but that are not reabsorbed in the kidney. It is expected that such lipocalin mutants could be used similarly to the NGAL mutants described herein to traffic iron out of the body and could thus be used in the treatment of iron overload disorders. It is also expected that such lipocalin mutants could also be used to treat bacterial infections of the urinary tract.

[0077] There are about 20 known proteins in the lipocalin family. Any lipocalin protein, or homolog, variant, derivative, fragment, or mutant thereof, that binds to a siderophore-iron complex can be mutated in order to provide a lipocalin mutant of the invention. Examples of lipocalins that can be used in accordance with the present invention include, but are not limited to, retinol binding protein, lipocalin allergen, aphrodisin, alpha-2-microglobulin, prostaglandin D synthase, beta-lactoglobulin, bilin-binding protein, the nitrophorins, lipocalin 1, lipcalin 12, and lipocalin 13.

Siderophores

[0078] Siderophores are high affinity iron (e.g. Fe³⁺) binding compounds. The vast majority of siderophores known are produced by bacteria. Bacteria release siderophores into the surrounding environment for the purpose of scavenging or chelating iron and transporting the iron to the bacteria - a process necessary for survival of bacteria. Siderophores that are known in the art include, but are not limited to enterochelin, TRENCAM, MECAM,

TRENCAM-3,2-HOPO, parabactin, carboxymycobactin, fusigen, triacetylfusarinine, feriichrome, coprogen, rhodotorulic acid, ornibactin, exochelin, ferrioxamine,

desferoxamine B, aerobactin, ferrichrome, rhizoferrin, pyochelin, pyoverdin. The structures of these compounds are disclosed in Holmes et al, Structure, 2005, 13:29-41 and Flo et al, Nature, 2004, 432: 917-921, the contents of which are hereby incorporated by reference.

[0079] Several of the above siderophores are known to bind to lipocalins, including NGAL, and complexes of these siderophores and lipocalins are known to be able to sequester iron (see for example, Holmes et al, Structure, 2005, 13:29-41 and Flo et al, Nature, 2004, 432: 917-921; Goetz et al, Molecular Cell, 2002, 10: 1033-1043 and Mori, et al, "Endocytic delivery of lipocalin-siderophore-iron complex rescues the kidney from ischemia-reperfusion injury." J. Clin Invest., 2005, 115, 610-621). The mutant NGAL proteins of the invention can also form complexes with siderophores and can thereby chelate and transport iron.

[0080] In some aspects the present invention provides complexes of a mutant NGAL protein of the invention and a siderophore, including, but not limited to, the siderophores listed herein. In preferred aspects the siderophore is selected from the group consisting of enterochelin, pyrogallol, carboxymycobactin, catechol, and variants or derivatives thereof. Any variant or derivative of such siderophores that retains the ability to bind to iron (ideally in a pH insensitive manner) and that retains the ability to bind to NGAL and/or one or more of the NGAL mutants of the invention may be used.

Manufacture of Mutant NGAL Proteins and Complexes with Siderophores

[0081] The mutant NGAL proteins of the invention can be manufactured by any suitable method known in the art for manufacture of protein drugs. For example the mutant NGAL proteins can be made using standard techniques known for the production of recombinant proteins, for example by delivering to a cell, such as a bacterial cell or a mammalian cell, an expression vector containing a nucleotide sequence that encodes an NGAL mutant under the control of a suitable promoter, and culturing the cell under conditions in which the protein will be expressed. Methods for the large scale culture, isolation, and purification of recombinant proteins are well known in the art and can be used in the manufacture of the NGAL mutants of the present invention. Similarly, methods of producing peptides and proteins synthetically are known in the art and can be used in the manufacture of the NGAL mutants of the present invention.

[0082] In certain embodiments, the present invention provides fusion proteins comprising the NGAL mutants of the invention and one or more additional "tags". Such additional tags can be fused to the N- or C-terminus of the NGAL mutants, or can in some instances be added at an internal location to the extent that the inclusion of the tag does not adversely affect the function of the NGAL mutant. Suitable tags include, but are not limited to glutathione-S-transferase (GST), poly-histidine (His), alkaline phosphatase (AP), horseradish peroxidase (HRP), and green fluorescent protein (GFP). Other suitable tags will also be apparent to those skilled in the art. The tags may be useful for several applications, including to assist in the isolation and/or purification of the NGAL mutants and/or to facilitate their detection.

[0083] Many chemical modifications of proteins are known in the art to be useful for improving the properties of protein-based drugs and such modifications can be used in accordance with the present invention to improve the stability and reduce the immunogenicity of the mutant NGAL proteins of the invention for therapeutic applications. For example, it is well known in the art that the process of covalent attachment of polyethylene glycol polymer chains to another molecule (i.e. PEGylation) can "mask" a proteinaceous agent from the host's immune system, and also increase the hydrodynamic size (size in solution), prolongs the circulatory half-life, and improve water solubility of protein-based drugs. Various other chemical modifications are also known and used in the art and can be used in conjunction with the mutant NGAL proteins of the invention.

[0084] Complexes containing a mutant NGAL protein of the invention and a siderophore, such as enterochelin or a derivative or variant thereof, can readily be prepared used standard methodologies known in the art, such as those provided in the Examples section of this application. For example, an NGAL-siderophore complex can be prepared by mixing NGAL (including mutant NGAL) and a siderophore together in a molar ratio of 1 : 1 (e.g. Ent) or 1 :3 (e.g. catechol). The mixture can be incubated at room temperature for a suitable time, e.g. 30 minutes, to allow for complex formation. Unbound siderophore can then be removed / separated from the bound siderophore-NGAL complexes using standard separation techniques, such as centrifugation based techniques, filter-based techniques, or other size- based separation techniques. Methods of Treatment - Iron Overload

[0085] In one embodiment, the mutant NGAL proteins of the invention, and complexes and compositions comprising such mutant NGAL proteins, can be used to treat conditions, diseases, or disorders associated with excessive iron levels or iron overload. In particular, complexes of the mutant NGAL proteins of the invention with a siderophore, such as enterochelin, and compositions comprising such complexes, can be used to chelate iron in the body and facilitate its excretion in the urine.

[0086] Large amounts of free iron in the bloodstream can lead to cell damage, especially in the liver, heart and endocrine glands. The causes of excess iron may be genetic, for example the iron excess may be caused by a genetic condition such as hemochromatosis type 1 (classical hemochromatosis), hemochromatosis type 2A or 2B (juvenile hemochromatosis), hemochromatosis type 3, hemochromatosis type 4 (African iron overload), neonatal hemochromatosis, aceruloplasminemia, or congenital atransferrinemia. Examples of non- genetic causes of iron excess include dietary iron overload, transfusional iron overload (due to a blood transfusion given to patients with thalassaemia or other congenital hematological disorders), hemodialysis, chronic liver disease (such as hepatitis C, cirrhosis, non-alcoholic steatohepatitis), porphyria cutanea tarda, post-portacaval shunting, dysmetabolic overload syndrome, iron tablet overdose (such as that caused by consumption by children of iron tablets intended for adults), or any other cause of acute or chronic iron overload.

[0087] The two common iron-chelating agents available for the treatment of iron overload are deferoxamine (DFO) and deferiprone (oral DFO). Due to its high cost and need for parenteral administration, the standard iron chelator deferoxamine is not used in many individuals with acute and/or chronic iron poisoning. Deferoxamine must be administered parenterally, usually as a continuous subcutaneous infusion over a 12-hour period, from three to seven times a week. Treatment is time consuming and can be painful. As a result compliance is often poor. Side-effects include local skin reactions, hearing loss,

nephrotoxicity, pulmonary toxicity, growth retardation and infection. Deferiprone is the only orally active iron-chelating drug to be used therapeutically in conditions of transfusional iron overload. It is indicated as a second-line treatment in patients with thalassaemia major, for whom deferoxamine therapy is contraindicated, or in patients with serious toxicity to deferoxamine therapy. Deferiprone is an oral iron-chelating agent which removes iron from the heart, the target organ of iron toxicity and mortality in iron-loaded thalassaemia patients. However, although deferiprone offers the advantage of oral administration, it is associated with significant toxicity and there are questions about its long-term safety and efficacy. It is recommended to be used in patients who are unable to use desferoxamine because of adverse effects, allergy, or lack of effectiveness. Deferiprone is associated with serious safety issues include genotoxicity, neutropenia and agranulocytos s. Weekly monitoring of neutrophils is recommended . Gastrointestinal and joint problems can occur and liver toxicity has been reported. Therefore, there is clearly a need for alternative convenient, safe, and effective iron chelation therapies, such as those provided by the present invention.

[0088] The mutant NGAL proteins of the invention, and in particular complexes thereof with siderophores, can be used to chelate free iron and clear the excess iron from the body via the kidneys, for example to reduce toxic circulating levels of iron to below toxic levels.

Methods of Treatment - Bacterial Infections of the Urinary Tract

[0089] WT NGAL is known to have bacteriostatic activity, in part due to its ability to tightly bind to bacterial siderophores, leading to depletion of bacterial iron and inhibition of bacterial growth (Goetz et al, Mol. Cell. (2002), 10(5) 1033-1043). The mutant NGAL proteins of the invention, like WT NGAL, have the ability to bind to bacterial siderophores, and thus can have anti-bacterial activity. Furthermore, because the mutant NGAL proteins of the invention are not reabsorbed by the kidney and accumulate in the urine, they are particularly well-suited to use in the treatment of bacterial infections of the urinary tract.

Pharmaceutical Compositions & Administration

[0090] The present invention also provides pharmaceuctical compositions, formulations, kits, and medical devices that comprise the mutant NGAL proteins described herein, and complexes thereof with siderophores, and which may be useful to treat various diseases, disorders, and conditions, including iron overload and bacterial infections. Pharmaceutical formulations include those suitable for oral or parenteral (including intramuscular, subcutaneous and intravenous) administration. Examples of medical devices provided by the invention include, but are not limited to, beads, filters, shunts, stents, and extracorporeal loops which are coated with or otherwise contain a mutant NGAL or complexes thereof, as described herein, such that the device is implanted in or otherwise administered to a subject in a manner which permits the mutant NGAL or complexes thereof to chelate or absorb excess iron in the subject. [0091] Administration of a therapeutically effective amount of the mutant NGAL proteins, and complexes thereof can be accomplished via any mode of administration suitable for therapeutic agents. One of skill in the art can readily select mode of administration without undue experimentation. Suitable modes may include systemic or local administration such as oral, nasal, parenteral, transdermal, subcutaneous, vaginal, buccal, rectal, topical, intravenous (both bolus and infusion), intraperitoneal, or intramuscular administration modes. In preferred embodiments, oral or intravenous administration is used. In other preferred embodiments, the compositions of the invention are administered directly to the desired site of action, such as for example, the kidney, for example by local injection or local infusion or by use of (e.g. conjugation to) agents useful for targeting proteins or pharmaceuticals to specific tissues, such as antibodies etc.

[0092] Depending on the intended mode of administration, the mutant NGAL proteins and complexes of the invention, in a therapeutically effective amount, may be in solid, semi-solid or liquid dosage form, such as, for example, injectables, tablets, suppositories, pills, time- release capsules, elixirs, tinctures, emulsions, syrups, powders, liquids, suspensions, or the like. In one embodiment the mutant NGAL proteins and complexes of the invention may be formulated in unit dosage forms, consistent with conventional pharmaceutical practices. Liquid, particularly injectable, compositions can, for example, be prepared by dissolution or dispersion. For example, mutant NGAL proteins and complexes of the invention can be admixed with a pharmaceutically acceptable solvent such as, for example, water, saline, aqueous dextrose, glycerol, ethanol, and the like, to thereby form an injectable isotonic solution or suspension.

[0093] Parental injectable administration can be used for subcutaneous, intramuscular or intravenous injections and infusions. Injectables can be prepared in conventional forms, either as liquid solutions or suspensions or solid forms suitable for dissolving in liquid prior to injection. One embodiment, for parenteral administration, employs the implantation of a slow-release or sustained-released system, according to U.S. Pat. No. 3,710,795, incorporated herein by reference.

[0094] The mutant NGAL proteins and complexes of the invention can be sterilized and may contain any suitable adjuvants, preservatives, stabilizers, wetting agents, emulsifying agents, solution promoters, salts (e.g. for regulating the osmotic pressure), pH buffering agents, and/or other pharmaceutically acceptable substances, including, but not limited to, sodium acetate or triethanolamine oleate. In addition, the compositions of the invention may also contain other therapeutically useful substances, such as, for example, other iron chelators or other agents useful in the treatment of iron overload, or other agents useful in the treatment of any of the conditions described herein.

[0095] The compositions of the invention can be prepared according to conventional mixing, granulating or coating methods, respectively, and the present pharmaceutical compositions can contain from about 0.1% to about 99%, preferably from about 1% to about 70% of the compound or composition of the invention by weight or volume.

[0096] The dose and dosage regimen to be used can be determined in accordance with a variety of factors including the species, age, weight, sex and medical condition of the subject; the severity of the condition; the route of administration; the renal or hepatic function of the subject; and the particular mutant or complex employed. A person skilled in the art can readily determine and/or prescribe an effective amount of a mutant or complex of the invention useful for treating or preventing a condition, for example, taking into account the factors described above. Dosage strategies are also provided in L.S. Goodman, et al, The Pharmacological Basis of Therapeutics, 201-26 (5th ed.1975), which is herein incorporated by reference in its entirety. In one embodiment, compositions of the invention are administered such that the NGAL component is administered at a dose range of about 1 to about 100 mg/kg body weight, and typically at a dosage of about 1 to about 10 mg/kg body weight is administered at a dose that results in a concentration in the range of about 0.1 ng/ml to about 100 ng/ml, e.g., in the range of about 1.0 ng/ml to about 20 ng/ml, in the blood. The amount of a siderophore component of a composition of the invention will be chosen accordingly, such that the desired stoichiometry, e.g. 1 : 1 or 1 :3 binding with the mutant NGAL protein, is achieved.

[0097] In addition to the above methods of treatment, the mutant NGAL protein - siderophore complexes of the invention may be useful to chelate and/or remove iron from samples, wherein the samples are not in a subject's body. Thus, in one embodiment, the present invention provides a method for removing iron from a fluid, the method comprising admixing the fluid with a mutant NGAL protein - siderophore complex for a period of time sufficient for iron in the sample to bind to the mutant NGAL protein - siderophore complexes, wherein the mutant NGAL protein - siderophore complex can chelate iron from the sample. In one embodiment, the mutant NGAL protein - siderophore complexes having iron bound thereto may then be removed from the sample. In preferred embodiments, the sample is a biological fluid, such as blood, serum, plasma, or urine. In certain embodiments the mutant NGAL protein - siderophore complexes are admixed with the sample outside the body, e.g. in an extracorporeal device, and the sample is then delivered to or returned to the body. For example, such methods can be used to chelate and/or remove excess iron in blood samples for transfusion, or in a dialysis procedure. For example, blood or another bodily fluid from a subject may be removed from the body, treated with a compound or composition of the invention to chelate or remove excess iron, and then returned to the subject.

EXAMPLES

EXAMPLE 1

Mutant NGAL Proteins and Their Use as Therapeutic Iron Chelators

and as Antimicrobial Agents

[0098] Lipocalin 2 (Lcn2), also called Neutrophil Gelatinase-Associated Lipocalin (NGAL) is a protein that binds to iron with high affinity. To bind iron, NGAL binds a cofactor called a siderophore produced by bacteria (Binding constant K_m=0.41x lO^~9M for the NGAL:enterochelin-iron interaction; K_m=10^~49M for the enterochelin (enterobactin):iron interaction) or catechol containing compounds (K_m=0.4+10^~9M for catechol-iron; K_m=10^~ ^45'9M for the catechohiron interaction) produced by a combination of bacterial and mammalian enzymes. NGAL is also a secretory protein that is markedly upregulated by bacterial infection and acute kidney injury and is secreted into the blood and urine. During bacterial infection, NGAL sequesters iron from bacteria by binding enterochelin-iron, resulting in the inhibition of bacterial growth.

[0099] Serum NGAL with bound enterochelin:Fe is filtered by the glomerulus in the kidney, but then the majority of it is retained (reabsorbed) by kidney where it is degraded. Very little NGAL escapes to the urine and is excreted. For example, as demonstrated by recent research, when NGAL is injected intraperitoneally, more than 70% of the WT NGAL accumulates in kidney while less than 0.1% is found in the urine after 3 hours.

[00100] The capture and retention of serum NGAL in the kidney is achieved by the absorption of NGAL by megalin, a multi-ligand receptor also called low-density lipoprotein receptor-related protein 2 (LRP2). Megalin is located at the apical plasma membrane of proximal tubular epithelial cells where it contacts the glomerular filtrate. Megalin associates with cubilin. NGAL can transport iron by using cofactors such as enterochelin or catechol and deliver the iron specifically to the kidney.

[00101] Mutant NGAL as a Therapeutic Iron Chelator and Antimicrobial Agent

[00102] The molecular cutoff for glomerular filtration is about 70 kD. Recombinant or native NGAL protein with molecular weights of about 20.5 kD and 23-25 kD respectively can be filtered in the glomerulus, but is then efficiently reabsorbed into the proximal epithelia by megalin and/or by a megalin associated complex which includes cubilin. Megalin has a binding affinity for apo- and iron-loaded NGAL of about 60nM (Hvidberg, et al., FEBS Letters, 2005, 579: 773-777)). Megalin is a multi-ligand, endocytic receptor, responsible for reabsorption of many proteins including NGAL, apoE, lipoprotein lipase, lactoferrin, approtinin, etc., after glomerular filtration (Christensen and Birn, Nature Reviews-Molecular Cell Biology, 2002, 3: 258-2682002). Electrostatic interactions between megalin' s acidic regions of "type A repeats" in megalin protein and basic regions of ligands are involved in ligand-receptor recognition i.e. megalin recognizes positively charged surfaces of ligand proteins (Moestrup and Verrost, Annual Reviews of Nutrition, 2001, 21 : 407-428. 2001). Some basic amino acid residues on the surface of human NGAL protein can therefore be involved in its high binding affinity to megalin, and mutation of these basic residues can disrupt the electrostatic interactions between NGAL and megalin while preserving the binding affinity for enterochelin-iron in its interior clayx. The disabled interaction between mutant NGAL and megalin can allow mutant NGAL:enterocalin:iron or apo-mutant NGAL to be filtered into the urine without being reabsorbed from the filtrate after glomerular filtration. In the former case, where enterochelin is present in the mutant NGAL complex, it can absorb iron from the blood and traffic it into the urine. This can allow removal of iron from the subject (e.g. animal or human) associated with the siderophore-iron. Alternatively, in the case of the mutant apo-NGAL, it can lead to an accumulation of NGAL in the urine which can inhibit bacterial growth in the urinary tract.

[00103] The mutant NGAL proteins of the invention have at least two potential applications in clinical therapeutics.

[00104] Firstly, the mutant NGAL proteins can be used as efficient iron chelators to remove excess iron from subjects, such as human subjects, with iron overload disorders. Iron overload patients (e.g. due to hemachromatosis, sickle cell disease, thalassemia, multiple transfusion of red blood cells or other biological products) are administered mutant NGAL bound to iron-free siderophore, such as enterochelin, by intravenous infusion. Enterochelin chelates serum iron to form an NGAL-enterochelin-iron complex. This complex is mostly transported to the kidney and subsequently filtered by glomerulus. It remains in the glomerular filtrate without being reabsorbed due to its inability to bind megalin in the proximal tubular epithelial cells. It then appears in the urine and is ultimately excreted together with the iron that it binds. Mutant NGAL can be an efficient tool to remove excessive iron from iron overloaded human subjects. The molar ratio for NGAL binding to enterochelin and iron is 1 : 1 : 1. If lOg of mutant apo-NGAL, which equals about 500 μιηοΐεβ, is given to an iron overloaded patient, about 500 μιηοΐεβ or about 27.9 mg of iron can theoretically bind mutant NGAL and enterochelin and be delivered into the urine for excretion (assuming accumulation of mutant NGAL protein in urine is 100%). This is a very efficient way to remove excessive iron from a human patient with iron overload given that the human only loses 1-2 mg iron per day mainly via the shedding of intestinal cells and dead skin cells, and only gains 1-2 mg per day from food.

[00105] Secondly, the mutant NGAL protein can be used as an anti-microbial to treat patients with a urinary tract infection (UTI). Mutant apo-NGAL is given to human subjects with a UTI by infusion. The mutant NGAL is transported to the kidney and filtered into the urine without reabsorption due to its loss of binding affinity for megalin. Once inside the urine, the mutant apo-NGAL protein binds siderophores of UTI bacteria (e.g. enterochelin) and results in the inhibition of their growth.

[00106] Experimental design and experimental procedures

[00107] Cloning of human NGAL

[00108] Human NGAL cDNA (Ganbank accession number: NM 005564) is obtained from Open Biosystems, and the open reading frame encoding the secreted NGAL protein is PCR-amplified by using a PfuUltra DNA polymerase (Stratagene), and cloned into a pGEX- 4T-3 plasmid vector (GE Healthcare) for site-directed mutagenesis.

[00109] Structure of human NGAL protein

[00110] Based on the structure of the human NGAL protein, amino acid residues, especially basic residues (arginine, lysine and histidine), on the surface of the protein can mediate the electrostatic interaction with megalin for high affinity binding (Figure 1 and Figure 4A). [00111] Designation of NGAL mutants

[00112] There are five basic amino acid residues on the surface of NGAL protein which are conserved (R43, 72, 140, and K142, 157) among different mammalian species including human, mouse, rat, Chimpanzee, bovine, dog, wild boar, and Rhesus Monkey, while there are 13 non-conserved basic residues (R130; K15, 46, 50, 59, 62, 73, 74, 75, 97, 149; HI 18, 165). These basic residues can be mutated to other non-basic residues.

[00113] Generation of NGAL mutants

[00114] A variety of different amino acid residues on the surface of NGAL protein were mutated by using a Quickchange Site-Directed Lightning Multi Mutagenesis Kit (Stratagene), and this resulted in the generation of many mutants with mutations at different sites of the NGAL protein. 57 NGAL mutants were made as shown in Table 2, SEQ ID NOS:2-10, 21- 68, 247-251.

Production of NGAL protein

[00115] Wild-type and mutant plasmid constructs are electroporated into BL21 E. coli (GE Healthcare), and expression of wild-type and mutant apo-NGAL proteins are induced by the addition of IPTG to a final concentration of 0.2mM for 5 hours, and subsequently purified by a combination of GST-based pull-down and gel filtration in a FPLC system with a Sepharose column.

Binding affinity of mutant NGAL for enterochelin and iron

[00116] The NGAL mutant proteins are examined for their ability to bind enterochelin and iron by using a radioactive form of iron, ⁵⁵Fe³⁺. The binding affinity of NGAL for

55 3^~l^~ 55 3^~l^~ enterochelin and Fe was estimated by examining the percentage of Fe which was retained by mutant and wild type NGAL proteins, and the wild-type NGAL protein can be used as a positive control.

Preparation of NGAL-enterochelin-iron complex

[00117] The NGAL-enterochelin-iron complex is prepared by mixing NGAL protein, enterochelin and ⁵⁵Fe³⁺ together in a molar ratio of 1 : 1 : 1 (4 nmole each). The mixture is incubated at RT for 30 minutes, and washed in a 10 K microcon by centrifugation 4 times at 7000 rpm for 5 minutes to remove the unbound enterochelin and ⁵⁵Fe³⁺, and the NGAL- enterochelin-⁵⁵Fe³⁺ complex is retained in the microcon. Screening of NGAL mutants in mice

[00118] There is 76% amino acid identity and 87% amino acid similarity between human mouse megalin proteins, indicating that they likely have very similar binding properties. In the present experiments the binding of human NGAL protein to mouse megalin was tested. Due to the high degree of amino acid identity and similarity between human and mouse megalin protein, the mouse system provides a useful model to screen mutant NGAL proteins for their ability to escape megalin-cubilin-dependent renal reabsorption and ultimately to be delivered into urine.

[00119] The radiolabeled NGAL-enterocalin-⁵⁵Fe³⁺ complex is intraperitoneally injected into female C57BL/6 mice (4 weeks), and urine is collected in metabolic cages. After urine collection for 3 hours, the mice are sacrificed and kidneys and liver are collected, weighed and solubilized in a solution of 0.5M NaOH and 1% SDS at 70°C overnight. The

radioactivity in urine, kidney and liver is examined in a scintillation counter, and the accumulation of the NGAL-enterochelin-iron complex will be calculated as the percentage of total injected complex.

[00120] Experimental Results

[00121] 57 NGAL mutants were generated (Table 2; SEQ ID NOS:2-10, 21-68, 247-251). Twenty nine mutant apo-proteins were produced in BL21 E. coli, and were examined for their binding affinity to enterochelin and trafficking in C57B6L/6 mice after intraperitoneal (i.p.) injection. As shown in Figure 3 A, all mutant human NGAL proteins retained 16.7 % to 45.7% of total iron after incubation with enterochelin-iron in a molar ratio of 1 : 1 : 1 (4 nmole each) for 30 minutes at room temperature, indicating their preserved binding affinity for enterochelin-iron (high amounts of enterochelin will increase loading of NGAL).

[00122] When administered by i.p. injection, six mutant NGAL-enterochelin-⁵⁵Fe³⁺ complexes showed a markedly increased accumulation in urine compared with wild-type NGAL complex (mutants K3, K2, 13, II, K5, and Kl). Decreased accumulation in liver and kidney after 3 hours (Figure 3B, C, D; Table 1) was also seen. There were 6%, 6.9%>, 1.9%, 9.3%, 19.6% and 2.9% of II, 13, Kl, K2, K3 and K5 mutant NGAL complexes which were delivered to urine after 3 hours, respectively, while there were only 0.18%, 0.13%, 0.26%>, 0.1%, 0.11%, 0.17%, 0.27% and 0.05% of A2, B4, C3, Dl, F2, G3, H2 and 15 mutant NGAL complexes in urine. [00123] Using the crystal structure of wild-type NGAL (PDB accession number: lnglA) as substrate, the structure of K3 mutant protein was predicted by using Swissmodel

(http://swissmodel.expasy.org). As shown in Figure 4A, the predicted 3D structure of K3 mutant protein contains a similar pocket as the wild type protein, supporting our finding that affinity for enterochelin-iron is preserved. However, K3 mutant protein exhibited fewer positive amino acids on the solvent accessible surface than wild-type NGAL protein (Figure 4B), consistent with its decreased ability for electrostatic interaction with megalin, and increased accumulation in urine once introduced into mice.

[00124] Table 1. Binding of mutant Ngal proteins to enterochelin-⁵⁵Fe³⁺ and accumulation of mutant Ngal-enterochelin-⁵⁵Fe³⁺ in urine, kidney and liver 3 hours after i.p. injection into C57BL/6 mice.

EXAMPLE 2

[00125] The superscripted numbers in this Example refer to the numbered references in the list of references that follows this Example. Mutants Kl - K8 throughout Example 2, and Figures 6-17, represent the mutants Dl-4, Dl-4-1, Dl-4-2-1, dl-4-2-1-1, dl-4-2-1-3, dl-4-2- 1-4, WT-3 and D 1-4-2 for which the sequences are provided herein in Table 2.

[00126] The transport of iron poses a significant problem because free ferric iron is insoluble (< 10-18 M) in aerobic solutions at physiologic pH, while upon solubilization by some chelators, a reactive form of iron is created that can produce toxic oxygen species. Specialized mechanisms are consequently required to traffic iron and these specialized mechanisms are found in proteins which utilize conserved motifs to directly bind iron (transferrin and ferritin) or utilize embedded cofactors. While extracellular iron transport is largely mediated by transferrin, mice carrying deletions of these genes displayed surprisingly limited phenotypes (Barasch, Developmental Cell, 2009). It was found that a member of the lipocalin superfamily called Ngal acted as a high affinity iron carrier (Barasch, Molecular Cell, 2002) when binding a family of novel cofactors called the catechols or related bacterial siderophores constructed from catechol. In the presence of iron, formation of the

Ngal:siderophore:FeIII complex occurred at subnanomolar affinity (Barasch, Nature

Chemical Biology, 2010) forming a bright red protein, which was stable for many days in solution and stable in vivo for transport of its tightly bound iron. Ngal is expressed in vivo, but a number of "damage" stimuli raise its concentration by orders of magnitude. Thereafter, Ngal traffics in the serum and is thought to be captured by the kidney receptor megalin, where Ngal clears the siderophore:Fe complex. While a great deal is known about the metabolism of the urinary form of Ngal (it is expressed from the distal nephron and is excreted in the urine as a full length protein), much less is known about this clearance system and the role of the megalin receptor, which is the only confirmed receptor for Ngal. To study this process in depth a conditional mutant of megalin can be examined. Also, for studies in wild type mice a series of Ngal mutants can be tested. Some such mutants bypass the proximal tubule where megalin is located, resulting in their presence in the urine. These mutants can still bind to siderophore:FeIII at high affinity (and produce red colored proteins), and can definitely excrete iron, likely in a redox inactive manner. Indeed, rather than donate iron to micro-organisms, which is a major concern for small molecule chelators, the

Ngal:siderophore:Fe complexes sequester iron from bacteria. The hypothesis that megalin is the key recycling receptor for Ngal can be tested. It is expected that when the megalin-Ngal complex is inhibited, Ngal can carry tightly bound iron in the urine, hence serving as a safe therapeutic for the common syndromes of iron overload diseases.

[00127] Iron overload diseases are common occurrences in clinical medicine, and their therapies have proved toxic to many cell lineages as well as inductive of bacterial growth. Iron overload is a common sequela of blood transfusions, but it is well known in hepatitis, chronic kidney disease as well as in common hereditary diseases such as hemachromatosis. The present invention involves the discovery of an iron trafficking pathway based on the protein Ngal, which is massively expressed in the human in different types of tissue damage. Our studies in Ngal metabolism provide proof of concept that Ngal can be used as a safe therapeutic iron chelator.

[00128] Iron is specifically bound by transferrin in circulation, which preserves its bioavailability and prevents its redox toxicity. However, non-transferrin-bound iron (NTBI) appears in patients with a variety of diseases^1"3 including both genetic causes and the non-

4 7 8 12 13 18 19 21 genetic causes. NTBI damages liver ^" , heart ^" , endocrine glands ^" and kidney ^" and severe overload can be fatal²²'²³ by catalyzing reactive oxygen species (ROS) via the Haber- Weiss and Fenton reactions^24"25.

[00129] To date, two small molecules, deferoxamine (DFO) and deferiprone are available for the chelation of NTBI and the treatment of iron overload^26"28. However, these molecules demonstrate significant toxicity. DFO causes skin reactions, hearing loss, renal and pulmonary toxicity, and most interestingly fungal infection^29"32, which results because DFO (which is a derivative of a fungal "siderophore") can deliver iron to pathogens³². Deferiprone is also associated with genotoxicity, neutropenia and agranulocytosis and kidney disease³³'³⁴. Hence, new agents are required for non-toxic NTBI excretion, that do not deliver iron to microorganisms .

[00130] The present invention utilizes an endogenous mechanism of iron transport (Molecular Cell, 2002; Nature N&V, 2005; Nature Chemical Biology, 2010)^35"38, which is manipulated to safely export iron from the body. The carrier is called Neutrophil Gelatinase- Associated Lipocalin (Ngal). The present invention involves Ngal mutants which allow Ngal to be safely excreted in urine, still tightly binding its iron.

[00131] Ngal is a small iron carrier protein (22KDa) which is markedly expressed in the serum and in the urine when a human or an animal is exposed to a stimulus which typically causes acute kidney injury (AKI: JASN, 2003; JCI, 2005; Lancet, 2005; Ann Int Med, 2008) ^" . As a result, the protein is now well known as a "biomarker" of AKI, with well over 100 papers confirming its robust expression, yet only a few labs study its biology. We have found that once Ngal is expressed, it is rapidly secreted into circulation, where it can capture iron by binding cofactors such as endogenous catechols or related catecholate-type siderophores (Enterochelin, Ent)³⁶ which are synthesized by bacteria to capture iron (See Fig. 6). Hence, Ngal interrupts the nutrient supply of iron for bacteria, providing bacteriostasis.

[00132] Ngal complexes are stable for transport, and they are filtered by the glomerulus and captured by the proximal tubule (Fig. 7), where Ngal is degraded and iron is released for recycling³⁸. Ngal is thought to be endocytosed by megalin in proximal tubule cells and a direct interaction between Ngal-megalin has been characterized using surface plasmon resonance (SPR/Biacore)⁴³. The present invention involves Ngal mutants that may bypass megalin, yet still bind En iron, hence providing a therapeutic that can safely excrete NTBI in the urine.

[00133] Evaluation of the Ngal-Megalin Interaction using Ngal Mutants

[00134] Since megalin may be the major receptor mediating the reabsorption of filtered Ngal⁴³, 40 mutant Ngal proteins were produced, some of which are believed to target the Ngal-megalin interaction. The megalin hypothesis can be tested using one of these mutants (K6) and its optimized derivatives, which partially bypass the proximal tubule and appear in the urine. This mutant can be used to study protein interactions, and cellular, and organ capture in wild type mice and in conditional megalin knockouts, to confirm that the interruption of megalin permits the excretion of iron. Additional mutants can also be tested using this system.

[00135] Evaluation of the Ngal:Ent:Fe^m Interaction in Ngal Mutants

[00136] Ngal contains a central calyx where, when Ent:Feⁱⁿ is bound, a bright red protein³⁵ is produced (Fig. 8). Ngal mutants, engineered to reduce their interactions with megalin, were also brightly red colored when mixed with Ent:Feⁱⁿ, indicating retention of ligand affinity. The Ngal complexes can be quantitatively analyzed using Flourescence Quenching techniques and X-Ray Crystallography.

[00137] Safe Excretion of Iron by the Delivery of Mutant NGAL:Ent:Fe^m

[00138] K6 and optimized mutants can be administered to mice to test NTBI chelation and urinary excretion of Feⁱⁿ in murine models of hereditary (HFE ) ⁴⁴'⁴⁵ and acquired hemochromatosis . Efficacy can be evaluated by measuring the depletion of NTBI from serum and liver, and toxicity can be ruled out by measuring oxidative stress and the expression of endogenous Ngal, which we previously discovered, indicates the onset of kidney damage.

[00139] Significance Iron overloaded patients demonstrate elevated serum transferrin saturation (>50%) and elevated serum ferritin levels (>100(^g/L)^1-3. They also demonstrate non-transferrin-bound iron in circulation (NTBI, e.g. 0.9-12.8μιηο1/Ε in thalassemic sera; 4- 16.3μΜ in hereditary hemachromatosis (HH) sera²), as well as a labile iron pool (LIP) within cells⁴⁶. These abnormal pools of iron participate in Haber- Weiss and Fenton reactions which oxidize lipids and proteins and mutate nucleotides by forming hydroxyl, ferryl, or perferryl

24 25 47

species ^" ' . Ultimately, cell death is found in a variety of sensitive organs, including liver (fibrosis/cirrhosis and hepatocellular carcinoma) ^4"7, heart (congestive cardiomyopathy)^8"12, kidney (necrosis and apoptosis of proximal tubular cells) ^{19 21} and endocrine glands (diabetes, hypothyroidism, and hypogonadism)^13"18.

[00140] In general there are two types of iron overload disorders, hereditary

hemachromatosis (HH) and acquired hemochromatosis (AH). HH is caused by loss of function of genes associated with the regulation of iron metabolism, such as HFE (type 1 HH), HJF(type 2A HH), HAMP (type 2B HH), TfR2 (type 3 HH), SLC40A1 (type 4 HH), CP (aceruloplasminaemia), TF (hypotransferrinaemia)³'⁴⁸. In the most common entity, Type I HFE C282Y allele, 28% of males were iron overloaded⁴⁹. AH in contrast is caused by blood transfusions, thalassaemia major, sideroblastic and hemolytic anemias, dietary iron overload, chronic kidney and liver diseases due to hepatitis C or alcohol or porphyria³'⁴⁴'⁴⁸. The 5 million blood transfusions, >15 million units/yr in the US are the most common cause of AH⁵⁰. Blood transfusions cause iron overload because while the human loses l-2mg iron per day, each unit of blood contains 250mg of iron and clear evidence of toxicity appears after 20 transfusions^51"53. Chronic kidney diseases can also produce a syndrome of excess iron deposition in the proximal tubule and in the urinary space. Iron is deposited in the kidney cortex in HIV associated nephropathy⁵⁴ as well as in other forms of nephrotic syndrome⁵⁵. Urinary iron is also a common finding in AKI of various etiologies including hemoglobinuria and myoglobinuria⁵⁶, chemotherapy (cis-platin⁵⁷; doxorubicin⁵⁸), ischemia-reperfusion⁵⁹'⁶⁰ and transplant ischemia⁶¹. It is believed that the release of iron into the urine is a critical step in cell damage ^" . In sum, both HH and AH patients suffer organ damage without iron chelation therapy²²'²³.

[00141] Two iron-chelating chemicals are currently in clinical use^26"28, but both are limited by toxicity and long-term safety concerns (e.g. "Deferasirox: Uncertain future following renal failure fatalities, agranulocytosis and other toxicities. Expert Opin Drug Saf. 2007 6:235-9)^29~ ³⁴. The present invention provides a novel strategy which takes advantage of the endogenous mechanisms of iron trafficking which is manipulated to develop a highly efficient, non-toxic iron chelator for the treatment of iron overload. Ngal is well suited to this approach because of the following characteristics. Ngal was first identified as an iron carrier and growth factor in kidney cells³⁵. Second, Ngal binds iron (Fig. 6) by using bacterial siderophores (such as enterochelin [Ent] from Gram-negative bacteria, bacillibactin from Gram-positive bacteria and carboxymycobactins from mycobacteria³⁶'⁷⁰) or alternatively endogenous catechols found in mammals³⁸. Ent and catechols have extremely high affinity for iron (Kd=10^"49M and 10^" ^{45 9}M, respectively)⁷¹'⁷², and Ngal strongly binds En Fe and catechokFe (Kd=0.4nM)³⁶'³⁸, which allows these complexes to sequester iron. In fact, the chelation of bacterial

siderophores by Ngal is a critical aspect of the innate immune response, given that the Ngal^"7" mice do not clear bacterial inocula³⁷. These data stand in contrast to the high affinity iron chelator DFO (Kd=10^"30M)⁷³ which can deliver its iron to Rhizopus and induce fatal

MucorMycosis³². Third, binding of iron to Ngal limited its reactivity as demonstrated by the suppression of phenanthroline and 3'-(p-hydroxyphenyl) fluorescein (HPF) tests of reactive Fe²⁺; in other words, binding to Ngal blocked the Fenton reaction³⁸. Fourth, Ngal can load with iron in vivo when it was presented with Ent:⁵⁵Fe or Catechol :⁵⁵Fe; the Ngal complex can then be recovered from the serum five minutes later. Fourth, Ngal loaded with iron traveled through the circulation and targeted the mouse kidney, as demonstrated by radioautography³⁸'⁴⁰(Fig. 9). This process most likely involved glomerular filtration of the Ngal complex, followed by megalin-mediated endocytosis at the apical membrane of the proximal tubule⁴³ since we found Ngal in the urine of megalin knock-out mice⁷⁴ (Fig. 10), and since Surface Plasmon Resonance Analysis (Biacore) showed that Ngal and megalin interacted directly (K_d=60nM⁴³). Fifth, the same process was ongoing in humans, since Ngal was visualized in lysosomes of the proximal tubule of patients with AKI (Fig. 6). Sixth, Ent had a very high affinity for Ngal even in the absence of iron (K_d=3.57nM)⁷⁵, while catechol itself bound to Ngal with poor affinity (K_d=200±6 nM)³⁸ meaning that Ent was even a better candidate for iron capture and transport than catechol. Finally, the Ngal:Ent:Feⁱⁿ complex was H insensitive, failing to dissociate even at pH 4.0, while Ngal:catechol:Fe complexes were stable until pH6.5, but acidification progressively reversed catechol-dependent fluorescence quenching and resulted in the dissociation of iron by pH 6.0 (Fig. 12)³⁸. Hence, because of its stability at acidic pH, Ngal:Ent:Feⁱⁿ is not expected to dissociate in acidified urine.

[00142] In summary, Ngal:catechol/Ent can chelate NTBI in the circulation with high affinity and clear iron in the kidney. This pathway is active in humans in vivo and potentially traffics large amounts of Ngal and iron: if the GFR is 140 L/Day and the concentration of serum Ngal is 20ng/ml, 2.8mg/day of NGAL (0. Μμιηοΐε) and 8μg iron are recycled in the proximal tubule, but in the setting of ischemia, renal failure, sepsis, the level of Ngal rises 100-1000 fold, meaning a very substantial mechanism of clearance may be ongoing

(depending on the residual GFR). Therefore, to understand the capture of iron in the kidney and to create a new therapy, we have decided to disrupt the reabsorption of Ngal.

[00143] Innovation: A. The first area of innovation has to do with the treatment of iron overload diseases which for too long has relied on toxic chelators^29"34. The present invention provides a strategy to develop high-efficacy, non-toxic NTBI chelators. This strategy has many advantages over current iron chelators in that (1) Ngal provides an endogenous pathway for delivering iron to the kidney 35 ' 36 ' 38 ' 39 ; (2) NgakEnt has higher affinity for iron

71 72 III 38 III than any other known substance ' ; (3) Ngal:Ent:Fe is redox inactive ; (4) Ngal:Ent:Fe is stable in acidified urine³⁸ and hence (5) may chelate urinary iron, perhaps alleviating damage in certain renal diseases. B. A second area of innovation is a description of the metabolism of Ngal-iron. A bio luminescent mouse can be used to compare the timing and intensity of Ngal gene expression in the kidney and in the urine, which has provided a clear understanding of the biosynthesis and excretion of this pool (Paragas et al, In Review). Ngal mutants can directly test the role of megalin in wild type mice and provide complimentary data for the analysis of megalin defective mice. This approach can also test the notion that a second NGAL receptor (24p3R)⁷⁶ may be present in the nephron.

[00144] Evaluation of the Ngal-Megalin Interaction by the Generation of Ngal Mutants

[00145] Megalin is thought to bind its ligands using a series of electrostatic interactions between megalin' s negatively-charged ligand-binding domains and the positively-charged surface-domains of the ligand⁷⁷. Consequently, by mutating Ngal's positively charged surface residues the megalin-Ngal interaction can be disrupted. Surface domains of human Ngal were identified based on its crystal structure (R. Strong; PDB no. 1L6M) using the software Pymol⁷⁸. The surface domains contained 18 positively charged amino acids (Lys 15, Lys 46, Lys 50, Lys 59, Lys 62, Lys 73, Lys 74, Lys 75, Lys 98, His 118, Arg 130, Lys 149, and His 165, R43, 72, 140, and K142, 157), 5 of which were conserved in mammalians³⁶, and these residues were chosen for site-directed mutagenesis. The human Ngal ORF (without signal peptide sequence) was cloned into pGEX-4T-3 bacterial expression plasmid (Amersham) to generate a GST-Ngal fusion to create a template for mutagenesis. The conserved positively charged surface residues were then mutated to alanine. Non-conserved amino acids were mutated to non-positively charged residues which occupied the same position in non-human Ngal proteins. For mutagenesis a single or a combined strategy with the Quick-Change Site- Directed Mutagenesis kit (Stratagene) was used, producing 40 Ngal mutant clones. Wild- type and mutant Ngal proteins were then produced in BL21 E. coli by induction with 0.2mM IPTG, and purification by GST-based affinity isolation and gel filtration chromatography using our established protocols³⁵'³⁸. We then functionally screened these Ngal proteins by introducing them (80μg/400μl) into C57BL/6 mice (4 weeks) to identify which mutants could bypass renal absorption and appear in urine within 3 hrs. Ngal mutants Kl, K2, K3, K5, K6, and K8 were detected in the urine by SDS-PAGE as well as by immunoblot using a human Ngal-specific antibody developed in rat (R&D System) (recombinant Ngal=21KDa;

endogenous Ngal=25KDa), suggesting that the mutations resulted in loss of affinity for the recycling receptors on the apical plasma membrane of proximal tubular epithelia. In contrast, wild-type, K4 and K7 mutants could not be detected in the urine and consequently were most likely reabsorbed (Fig 13). These data provide valuable information about the Ngal-megalin interaction because they test whether variations in Ngal reabsorption may be ascribed to variations in the megalin-Ngal interaction, providing insight into the mechanisms of clearance of serum Ngal, and allowing the optimization of mutants to excrete iron.

[00146] Structural basis for NGAL-megalin interaction

[00147] Interactions with Me alin

[00148] The interaction between wild-type human Ngal (ligand-free) and chip-coupled megalin (Kd=~60nM)⁴³ purified from human kidney cortex was previously analyzed by a₂- macroglobulin-affinity chromatography⁷⁹. Biacore T100 technology can be used to compare wild type and K6 (or other mutant) interactions with megalin. Whether ligand-binding influences Ngal-Megalin interaction can also be tested by using bacterial siderophores and catechol ligands. Data can be calculated with BIAevaluation 4.1 software (Biacore), globally fitting data to derive kinetic and equilibrium parameters. A range of coupling and

regeneration conditions can also be used, though antibody-capture often provides the cleanest data.

[00149] Megalin Mediated Endocytosis

[00150] Classical megalin-expressing cell models can be used to investigate megalin- binding and endocytosis. Such cells include HK-2⁹⁰ and Brown Norway rat yolk sac epithelia⁴³. Rat yolk sac cells are important because megalin is the only receptor which mediates endocytosis of human Ngal in these cells, since uptake was completely abolished with anti-megalin antibodies⁴³ (the neutralizing antibodies proved more effective than megalin shRNA). Wild-type and K6 mutant proteins (and other mutants) can be labeled with fluorescent probes (Alexa 488, Molecular Probes) cleaned-up by gel filtration (GE Biotech, PD10) and dialysis (Pierce 10K cassette)³⁵'⁴³ in order to study their rate of uptake (50 μg/ml in serum- free DMEM for 0.5-6 hours) in the presence or absence of anti-human or anti-rat megalin antibodies (Santa Cruz; 200μg/ml)⁴³ which were previously shown to block uptake of wild type human Ngal in BN cells⁴³ . Endocytosis of Ngal can be measured both by using a Zeiss LSM510-META inverted confocal laser scanning microscope and immunoblots of cell extracts to detect the presence of human Ngal. These experiments can determine whether the failure to capture K6 (or other mutants) can be ascribed to defective Ngal-megalin interactions and if the affinity defect or the endocytosis defect is truly partial. If so, then additional mutations can be provided to disrupt the remaining interactions with megalin. The remaining positively charged surface residues in K6 (or other mutants) can be mutated using a single or combinational approach as above, and then reiteratively tested using the Biacore assays and the cellular uptake assays. As a result of these mutations, the role in megalin in Ngal capture and Ngal's megalin binding domain can be defined. Additionally optimized mutants can be generated.

[00151] Alternative Receptors

[00152] Our data (Fig. 9 and 13) and a previously published report⁴³ suggests that megalin is an essential receptor for Ngal. However, there may be non-megalin receptor(s) in the proximal tubule. The main candidate is 24p3R (SLC22A17), which is found throughout the kidney and shown to mediate Ngal endocytosis⁷⁶, but its function is not yet confirmed. Stably transfected HEK293 cells over-expressing human 24p3R can be generated, and the uptake of Alexa-488 labeled wild-type and K6 mutant Ngal and Ngal:Ent:Fe can be determined, for example by using confocal microscopy and immunoblots. If 24p3R stimulates the uptake of wild-type Ngal, it can be a receptor for Ngal, and the K6 mutant (and other mutants) may show defective interactions with this receptor.

[00153] Distribution of Ngal mutants in vivo

[00154] A further test of the Ngal-megalin interaction can be performed using a megalin conditional knockout murine model⁹¹, in which megalin is deleted in the proximal tubular epithelia using floxed-megalin mice and gGT-Cre which specifically deletes genes in 80% of cells in the S3 segment of the proximal tubule⁹². According to TE Willnow⁹¹, these conditionally deleted mice are viable and fertile. The efficiency of the megalin deletion can be confirmed by immunohistochemical staining with anti-megalin antibodies. If the deletion f/f f/ "

is complete, megalin mice can be bred with megalin gGT-Cre mice to generate

f/f f/f f/ " megalin :gGT-Cre mice (25%) and littermate controls megalin (25%), megalin :gGT-Cre (25%) and megalin^f/+ (25%). The megalin deleted mice (n=12) can be identified by PCR- genotyping the floxed allele and the gGT-cre recombinase. Alexa-488- or rhodamine labeled wild-type or K6 mutants (two different labels to avoid the contribution of negative (Alexa- 488) or positive (Rhodamine) charges) can be tested by i.p. injection into 4 week old mice and their trafficking analyzed by using a Zeiss LSM510-META inverted confocal laser scanning microscope and immunoblots with anti-human antibodies. Since megalin expression is limited to proximal kidney epithelia, parathyroid cells, epididymal epithelial cells, type II pneumocytes, mammary epithelial and thyroid follicular cells, the distribution of both wt and mutant Ngal in wt and knockout mice can be investigarted to explore the Ngal-megalin interaction in vivo. If the capture of wt Ngal by the proximal tubule is abolished in the conditional megalin-ko kidney, and Ngal is excreted (similar to Fig. 10), megalin is likely the only Ngal receptor in the kidney and the proposed receptor 24p3R is non-essential. If this is the case, then the distribution of wt Ngal should also correlate with the distribution of megalin in different tissues. Moreover, if Ngal mutants such as K6 have poor affinity for megalin, their escape in the urine can be directly explained. On the other hand, if wt Ngal is captured in the megalin knockout proximal tubule and by cells of the body where megalin is not expressed, then alternative receptor(s) are expected. In this case, the excretion of mutant Ngal may be the result of loss-of-affinity not only for megalin, but for non-megalin receptors.

[00155] Evaluation of the Ngal:Ent:Fe^m Interaction in Ngal Mutants [00156] Ngal specifically binds Ent:Fe^m and Ent with high affinities ( 0.4nM and 3.57nM, respectively)³⁶'⁷⁵, and it fails to release bound iron even at low pH³⁸. Ngal sequestered iron no longer participates in chemical reactions and the complex is stable for transport in circulation. Whether loss-of- "reabsorption" mutants still have the capacity to bind ferric siderophores at high affinity can be tested. Initial data shows that the mutants retain iron in the presence of Ent (Fig. 14) and demonstrates a distinct red coloration. The K6 NgakEnt interaction can be quantified and the structural effects of the introduced mutations can be determined.

[00157] Quantitative measurement of Ent:Fe^m binding by Ngal

[00158] A fluorescence quenching (FQ) strategy {Nature Chemical Biology, 2010³⁸, Fig 10) can be utilized to quantify the spectrum of Ngal and Ngal mutant: ferric siderophore interactions^93"98 to derive affinity measurements for Ent binding. Excitation _exc = 281 nm and emission λ_βπι = 340 nm data can be collected from 100 nM K6 Ngal mutant protein solutions (with 32μg/mL ubiquitin and 5% DMSO), exposed to En Fe. The pH sensitivity of the complex can be determined by incrementally adjusting the solution's pH until the

fluorescence signal stabilizes. The data can be examined using nonlinear regression analysis using a one-site binding model (DYNAFIT)⁹⁹. Control experiments can be performed to ensure protein stability. Alternative techniques include SPR and isothermal titration calorimetry (e. g. from the Strong group⁸⁶).

[00159] Structural basis for the formation of mutant Ngal:Ent:Fe^m

[00160] In order to confirm that mutations introduced to disable megalin binding do not interfere with ferric siderophore ligand recognition, the structure of K6 ± EntFe¹¹¹ can be determined by X-Ray Crystallography. Over 20 Ngal crystal structures, including human, murine and mutant forms, ± N-linked CHO, both empty and bound to a series of natural siderophores or synthetic analogs have been determined previously ⁽³⁶'³⁸'⁹³'⁹⁹'¹⁰⁰⁾ Since the K6 mutations affect crystal contacts in all the known Ngal crystal forms, this can be approached as a de novo structure determination. For crystallization, the protein can be highly purified by GST chromatography, followed by gel filtration and ion exchange chromatography, with purity and monodispersivity determined by reduced/non-reduced PAGE and mass- spectroscopy with concurrent static/dynamic light scattering (SLS/DLS). Monodispersed protein preparations can be screened for crystallizability using sub-microliter robotics and commercially-available factorial screens. Preliminary crystals can be optimized in conventional crystallization formats using established methodologies that catalyze crystallization. Alternatively, the protein can be more stringently purified or complexed with Fabs (the structure of a murine NgakFab complex [crystallized from 20% PEG 4000 and 10% isopropanol, pH = 7.0; space group: ¥2{∑{l_\, a = 37.9A, b = 69.4A, c = 117.6A; d_mi_n = 2.15A, Rmerge ⁼ 0.04] was determined - a panel of over 16 anti-human Ngal antibody Fabs can be used for co-crystallization). Diffraction data can be collected. Data can be reduced with any of a variety of available software packages and can be phased by direct difference Fourier (for isomorphous crystals), molecular replacement (MR), MAD (generally using

selenomethionine) or MIRAS (using any of a variety of derivatization strategies). These data can quantitatively characterize NgakEnt interactions, indicating whether K6 (or other mutants) have retained affinity for Ent:Feⁱⁿ. These studies can show that the introduced mutations impair ligand binding, and the structures can be used to engineer additional mutations.

[00161] Safe Excretion of Iron by the Delivery of Mutant NGAL:Ent:Fe^m

[00162] To test whether K6Ngal:Ent can efficiently chelate and deliver NTBI to the urine through the kidney, the K6:Ent:⁵⁵Feⁱⁿ complex (80μg) was introduced into mice (4 weeks), and collected the urine for 3hrs in metabolic cages. As shown in Fig. 16, 23% of the injected K6-⁵⁵Feⁱⁿ complex was delivered to the urine, paralleling the percentage of K6 protein found in the urine (Fig. 13), while less than 0.1% of the wild type injectate was excreted. Only trace amounts of ⁵⁵Feⁱⁿ accumulated in the liver (<1%), indicating that once iron was chelated by K6:Ent, it was mainly delivered to the kidney and the urine. Based on these results, it can be tested whether K6:Ent can capture, chelate, traffic and remove endogenous NTBI.

[00163] Chelation and Excretion of NTBI by 6:Ent in Murine Models of

Hemochromatosis

[00164] Establishment and evaluation of mouse models

[00165] A mouse model of Type 1 hereditary hemochromatosis lacking the Hfe gene is available from the Jackson Labs (Stock #: 003812). These mice develop organ iron overload 12 weeks after weaning⁴⁵. A mouse model of acquired hemochromatosis can be established as reported previously¹⁰¹. This mouse model of transfusion mediated iron overload was made by transfusing stored (14 days at 4°C) mouse RBC (200 or 400μΕ at 17.0-17.5 g/dL hemoglobin) into a recipient via the retro-orbital plexus of isoflurane-anesthetized mice, which is the equivalent of transfusing a human with 1-2 units of RBC. Briefly, the RBCs are obtained from 30-50 C57BL/6 mice in CPDA-1 solution (Baxter), leukoreduced using a Neonatal High-Efficiency Leukocyte Reduction Filter (Purecell Neo) and then concentrated by centrifugation to a final hemoglobin level of 17g/dL, as determined by Drabkin assays (Ricca)¹⁰² and the optical density (540nm) compared with the Count-a-Part

Cyanmethemoglob-in Standards (Diagnostic Technology)¹⁰¹. Residual leukocytes are counted by cytometry (LeucoCOUNT; BD)¹⁰¹. NTBI was previously observed in both HFE^1' (~3.7μΜ)¹⁰³ and RBC transfused (~2.5μΜ) mice . NTBI can be measured in these models using a standard nitrilotriacetic acid (NT A) ultrafiltration assay¹⁰¹. This can be done by incubating heparinized plasma (90μί) with NTA (800mM, pH 7.0) and then preparing a 30K ultrafiltrate (NanoSep, 30-kDa cutoff, polysulfone type) and measuring NTBI with ferrozine¹⁰⁴. Total organ iron can be determined using a procedure which involves desiccation at 65°C, followed by acidification and detection of NTBI with a chromogen (1.6mM bathophenanthroline)¹⁰⁵. Hemoglobinemia can be detected spectrophotometrically using a PowerWave XS spectrophotometer (BioTek)¹⁰¹. Intracellular iron accumulation in the liver and spleen can be detected in paraffin sections with Perl's reagent which reveals blue granules⁵⁴ and in sections with co-immunostaining to detect macrophages with anti-mouse F4/80 antibody (eBioscience) and ABC and DAB kits (Vector Laboratories)¹⁰¹.

[00166] As reported previously, a number of cytokines/chemokines, especially interleukin- 6 (IL-6), monocyte chemoattractant protein- 1 (MCP-1), macrophage inhibitory protein- 1 β (ΜΙΡ-1 β), and keratinocyte-derived chemokine/CXCLl (KC/CXCL1) are increased in the plasma 2 hrs after transfusion of old stored RBC¹⁰¹. Hence, these cytokines can be measured as markers of iron overload and as a measure of treatment efficacy of Ngal. The

cytokines/chemokines can be quantified using the Cytometric Bead Array Mouse Flex Kit (BD Biosciences) and plasma with a FACSCalibur cytometer (BD Biosciences) equipped with Flow Jo software¹⁰¹.

[00167] Treatment of Iron Overload with K6:Ent and Evaluation of Treatment Efficacy.

[00168] The K6:Ent complex can be introduced into HFE^1' or RBC transfused mice by intravenous infusion with a micro-osmotic pump (ALZET®). For HFE^1' mice, the dose of K6:Ent can be 17.9 mg K6:Ent for 12 hours, 3 times a week for 4 weeks. This dose is based on the following calculation: For HFE^1' mice, NTBI is ~3.7μΜ and blood volume is ~1.6ml; to maximize iron chelation and removal, equal moles of NgakEnt should be continually present in circulation for a 12 hour treatment with the consideration of Ngal's half life of 10 min, or approximately ~0.85μι οΐ68 (~17.9mg) of NgakEnt are theoretically required over 12-hours. Similarly, for the transfusion mice the dose is -0.58 μιηοΐεβ (~12mg) of NgakEnt over 12 hours in a single treatment period. Apo-K6 is as a negative control because it does not bind iron and associated endogenous catechols would dissociate. Wt Ngal is also a useful control because it is captured by megalin, and it does not traffic iron into the urine.

[00169] The efficacy of treatment can be evaluated by the measurement of serum and urinary iron, iron concentration in the liver, spleen and kidney, intracellular iron

accumulation in macrophages and hepatocytes, and cytokines/chemokines in the plasma of K6:Ent- vs K6- or Wt- treated mice as described above. K6 Ngal can be detected in urine by immunoblot with anti-human antibodies. Preliminary data suggests that K6 will appear in the urine, and that K6:Ent will markedly diminish serum NTBI, decrease the iron content of HFE^~f~ mice and transfusion overload, and additionally normalize the levels of

cytokines/chemokines in old-RBC transfusions.

[00170] Effect of 6:Ent treatment on iron-mediated cell damage

[00171] Measurement of Redox Activity in the Kidney Peroxidized lipids are a marker of iron catalyzed oxidant stress, which are measured by malondialdehyde. The renal cortex of mice subjected to K6 treatment is separated from the medulla, homogenized¹⁰⁶'¹⁰⁷ and treated with TCA and thiobarbituric acid and the supernatant read at 535 nm. Malondialdehyde, expressed in nmoles, is calculated using a molar extinction coefficient of 1.56 x 10⁵ M^_1cm^_1 at 535nm. An additional measurement of kidney damage during the treatment with K6 is the detection of endogenous mouse uNgal (25KDa) with mouse antibody (R&D system). Ngal is expressed within 3 hrs of damage by stimuli that cause AKI including radical attack, and here we will measure uNgal in the different treatment groups.

[00172] Measurement of Free Iron and Redox Activity in Mouse Urine

[00173] The data presented herein suggests that the iron will be tightly bound to K6 Ngal and redox inactive even in the acidic urine. This can be tested usin the classic

spectrophotometric bleomycin test of Gutteridge⁵⁷ to measure urinary "catalytic" iron in mice treated with K6, K6:Ent and wild type Ngal. Urine is collected in Chelex-treated, pyrogen- free water and an ultrafiltrate created using a microcon (10K, Millipore) measured with the bleomycin assays. A standard curve is prepared with urine spiked with FeCl₃ and bleomycin- detectable iron recorded per mg creatinine (Abeam). A second strategy to measure redox activity can also be used - the iron mediated generation of hydroxyl radicals can be detected by the conversion of 3'-(p-hydroxyphenyl) fluorescein (HPF; Invitrogen) to fluorescein in the presence of ascorbic acid (Ex 490 nm, Em 515 nm). As shown in Fig. 12 wild type Ngal quenched the activity of catechol:Feⁱⁿ - urine from mice treated with K6, K6:Ent and Wt NgakEnt is tested. A positive control is Ent/catechol:Feⁱⁿ followed by K6 which inhibits the production of superoxide radicals.

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Claims

claimed is:

A mutant NGAL protein comprising an amino acid sequence that is at least 70% identical to the sequence of wild-type human NGAL (SEQ ID NO.l), or a fragment thereof, wherein:

(a) five or more residues from among Lys 15, Lys 46, Lys 50, Lys 59, Lys 62, Lys 73, Lys 74, Lys 75, Lys 98, His 118, Arg 130, Lys 149, and His 165 is mutated by deletion or by substitution with a non-positively charged amino acid residue, and

(b) residues Asn 39, Ala 40, Tyr 52, Ser 68, Trp 79, Arg 81, Tyr 100, Tyr 106, Phe 123, Lys 125, Tyr 132, Phe 133, and Lysine 134 are either not mutated or are conservatively substituted, and wherein the mutant NGAL protein

(c) is able to bind to a siderophore, and

(d) is excreted in the urine.

The mutant NGAL protein of claim 1 , wherein six or more residues from among Lys 15, Lys 46, Lys 50, Lys 59, Lys 62, Lys 73, Lys 74, Lys 75, Lys 98, His 118, Arg 130, Lys 149, and His 165 are substituted with a non-positively charged amino acid.

The mutant NGAL protein of claim 1 , wherein seven or more residues from among Lys 15, Lys 46, Lys 50, Lys 59, Lys 62, Lys 73, Lys 74, Lys 75, Lys 98, His 118, Arg 130, Lys 149, and His 165 are substituted with a non-positively charged amino acid.

The mutant NGAL protein of claim 1 , wherein eight or more residues from among Lys 15, Lys 46, Lys 50, Lys 59, Lys 62, Lys 73, Lys 74, Lys 75, Lys 98, His 118, Arg 130, Lys 149, and His 165 are substituted with a non-positively charged amino acid.

The mutant NGAL protein of claim 1 , wherein nine or more residues from among Lys 15, Lys 46, Lys 50, Lys 59, Lys 62, Lys 73, Lys 74, Lys 75, Lys 98, His 118, Arg 130, Lys 149, and His 165 are substituted with a non-positively charged amino acid.

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6. The mutant NGAL protein of claim 1 , wherein ten or more residues from among Lys 15, Lys 46, Lys 50, Lys 59, Lys 62, Lys 73, Lys 74, Lys 75, Lys 98, His 118, Arg 130, Lys 149, and His 165 are substituted with a non-positively charged amino acid.

7. The mutant NGAL protein of claim 1 , wherein the mutant NGAL protein has

bacteriostatic activity.

8. The mutant NGAL protein of claim 1 , wherein the % of the mutant NGAL protein that accumulates in the urine at a certain time following systemic administration of the mutant NGAL protein to a subject is greater than the % of WT NGAL protein that accumulates in the urine following systemic administration of WT NGAL protein to a subject over the same time period.

9. The mutant NGAL protein of claim 1 , wherein the % of the mutant NGAL protein that accumulates in the urine at a certain time following systemic administration of the mutant NGAL protein to a subject is 10-fold or more greater than the % of WT NGAL protein that accumulates in the urine following systemic administration of WT NGAL protein to a subject over the same time period.

10. The mutant NGAL protein of claim 1 , wherein the % of the mutant NGAL protein that accumulates in the urine at a certain time following systemic administration of the mutant NGAL protein to a subject is 100-fold or more greater than the % of WT NGAL protein that accumulates in the urine following systemic administration of WT NGAL protein to a subject over the same time period.

11. The mutant NGAL protein of claim 1 , wherein the % of the mutant NGAL protein that accumulates in the urine at a certain time following systemic administration of the mutant NGAL protein to a subject is 100-fold or more greater than the % of WT NGAL protein that accumulates in the urine following systemic administration of WT NGAL protein to a subject over the same time period.

12. The mutant NGAL protein of claim 1 , wherein the % of the mutant NGAL protein that accumulates in the urine three hours after systemic administration of the mutant NGAL protein to a subject is 1% or more.

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13. The mutant NGAL protein of claim 1 , wherein the % of the mutant NGAL protein that accumulates in the urine three hours after systemic administration of the mutant NGAL protein to a subject is 2% or more.

14. The mutant NGAL protein of claim 1 , wherein the % of the mutant NGAL protein that accumulates in the urine three hours after systemic administration of the mutant NGAL protein to a subject is 5% or more.

15. A nucleic acid sequence that encodes a mutant NGAL protein according to claim 1.

16. An expression vector comprising a nucleic acid sequence according to claim 15 operatively linked to a promoter.

17. A bacterial cell that stably expresses a nucleic acid according to claim 15.

18. A mammalian cell that stably expresses a nucleic acid according to claim 15.

19. A pharmaceutical composition comprising a mutant NGAL protein according to claim 1.

20. A pharmaceutical composition comprising a complex of a mutant NGAL protein according to claim 1 and a siderophore.

21. The pharmaceutical composition of claim 20, wherein the siderophore is selected from the group consisting of enterochelin, pyrogallol, carboxymycobactin, catechol, and variants thereof.

22. The pharmaceutical composition of claim 20, wherein the siderophore is pH

insensitive.

23. The pharmaceutical composition of claim 20, wherein the siderophore binds to the mutant NGAL protein and iron at urinary pH.

24. The pharmaceutical composition of claim 20, wherein the siderophore binds to the mutant NGAL protein and iron in the urine.

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25. The pharmaceutical composition of claim 20, wherein the siderophore binds to the mutant NGAL protein and iron at blood pH.

26. The pharmaceutical composition of claim 20, wherein the siderophore binds to the mutant NGAL protein and iron in the blood.

27. The pharmaceutical composition of claim 20, wherein the mutant NGAL protein and the siderophore are present in a 1 : 1 molar ratio.

28. A method for treating iron overload in a subject in need thereof, the method

comprising administering to the subject an effect amount of the pharmaceutical composition of claim 20.

29. A method of treating a urinary tract infection in a subject in need thereof, the method comprising administering to the subject an effective amount of the pharmaceutical composition of claim 19.

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