Diagnosis of diseases associated with dna replication

(54) DIAGNOSIS OF DISEASES ASSOCIATED WITH DNA REPLICATION

(76) Inventors: Alexander Olek, Berlin (DE); Kurt
Berlin, Stahnsdorf (DE)

Correspondence Address:
DAVIDSON, DAVIDSON & KAPPEL, LLC
485 SEVENTH AVENUE, 14TH FLOOR
NEW YORK, NY 10018 (US)

(21) Appl. No.: 10/240,708

(22) PCT Filed: Apr. 6, 2001
(86) PCT No.: PCT/EP01/03971

(30) Foreign Application Priority Data

Apr. 6, 2000 (DE) 100190588

Apr. 7, 2000 (DE) 100191738

Jun. 30, 2000 (DE) 100325297

Sep. 1, 2000 (DE) 100438261

Publication Classification

(51) Int. CI.7 C12Q 1/68; C07H 21/04;

C12P 19/34; C12M 1/34

(52) U.S. CI 435/6; 435/91.2; 435/287.2;

536/23.1

(57) ABSTRACT

Chemically modified genomic sequences of genes associated with DNA replication, to oligonucleotides and/or PNAoligomers for detecting the cytosine methylation state of genes associated with DNA replication which are directed against the sequence are disclosed. In addition, a method for ascertaining genetic and/or epigenetic parameters of genes associated with DNA replication is disclosed.

DIAGNOSIS OF DISEASES ASSOCIATED WITH DNA REPLICATION

FIELD OF THE INVENTION

[0001] The levels of observation that have been well studied by the methodological developments of recent years in molecular biology, are the genes themselves, the translation of these genes into RNA, and the resulting proteins. The question of which gene is switched on at which point in the course of the development of an individual, and how the activation and inhibition of specific genes in specific cells and tissues are controlled is correlatable to the degree and character of the methylation of the genes or of the genome. In this respect, pathogenic conditions may manifest themselves in a changed methylation pattern of individual genes or of the genome.

[0002] The present invention relates to nucleic acids, oligonucleotides, PNA-oligomers and to a method for the diagnosis and/or therapy of diseases which have a connection with the genetic and/or epigenetic parameters of genes associated with DNA replication and, in particular, with the methylation status thereof.

PRIOR ART

[0003] The replication of double stranded genomic DNA is a complex activity. It is carried out in three key stages, initiation, elongation and termination. Each stage involves specific protein and enzyme complexes. During initiation, the double helix is temporarily separated and stabilized into two single strands, each of which acts as a template for the replication of the DNA from the replication fork. Separation of the two strands is carried out by a helicase, and stabilisation of the strands is achieved using a single stranded binding protein. Replication of the DNA is then carried out by a polymerase after synthesis of a short 'primer' sequence. Replication is carried out in a semi-discontinuous fashion. The leading strand is continuously synthesised in the 5' to 3' direction. Whereas replication of the lagging strand, in the 3' to 5' direction is made by the synthesis of short fragments in the 5' to 3' direction. In the final stage, replication is terminated, and the lagging strand complementary DNA fragments are ligated into a continuous strand.

[0004] A further overview of the components of the DNA replication system is available from references such as Alberts et. al. 'Molecular Biology of the cell' Garland Publishing.

[0005] Disruptions to the ordered replication of DNA may impact on a wide variety of disease phenotypes. These range from chromosomal disorders to disorders at a molecular level. Malfunctions in the specific genes involved in DNA replication have been implicated in several disease phenotypes, including, but not limited to cancer:

[0006] Ataxia-telangiectasia; Meyn MS. 'Ataxia-telangiectasia, cancer and the pathobiology of the ATM gene'. Clin Genet. 1999 May; 55(5):289-304.

[0007] ATR-X; Wada T. 'Molecular genetic study of japanese patients with X-linked alpha-thalassemia/ mental retardation syndrome'. Am J Med Genet. 2000 Sep. 18; 94(3):242-8.

[0008] Bloom's syndrome; German J. 'Bloom's syndrome'. Dermatol Clin. 1995 January; 13(1):7-18.

[0009] Cancer; Sturgis et. al. 'XPD/ERCC2 polymorphisms and risk of head and neck cancer: a casecontrol analysis.' Carcinogenesis. 2000 December; 21(12):2219-23.

[0010] Neurological disorders; Hermon et. al. 'Expression of DNA excision-repair-cross-complementing proteins p80 and p89 in brain of patients with Down Syndrome and Alzheimer's disease.' Neurosci Lett. 1998 Jul. 17; 251(l):45-8.

[0011] The diversity of components involved in DNA replication provides an alternative target for therapies and diagnosis for diseases. In particular this may be relevant to diseases where current therapies may have unwanted side effects or fail to provide effective treatment. For cancer patients such methods constitute a considerable advantage over conventional methods such as chemotherapy, which with their massive side effects, sometimes result in unacceptable morbidity or lead up to the death of the patient. In practice, the unwanted side effects associated with cancer therapies frequently limit the treatment which could help a patient.

[0012] A global analysis of the status of DNA replication mechanisms would provide a basis for the development of appropriate and specific therapies for diseases associated with DNA replication. The current state of the art is such that the analysis may be carried out in a gene specific manner based on the results of gene expression, e.g. DNA micro array analysis of mRNA expression or proteomic analysis. The next step would then be to look at the causal factors involved at earlier stages in the regulatory mechanisms controlling DNA replication. DNA methylation provides such a novel level of information at which to analyse the genome.

[0013] 5-mefhylcytosine is the most frequent covalent base modification in the DNA of eukaryotic cells. It plays a role, for example, in the regulation of the transcription, in genetic imprinting, and in tumorigenesis. Therefore, the identification of 5-mefhylcytosine as a component of genetic information is of considerable interest. However, 5-mefhylcytosine positions cannot be identified by sequencing since 5-mefhylcytosine has the same base pairing behaviour as cytosine. Moreover, the epigenetic information carried by 5-mefhylcytosine is completely lost during PCR amplification. A relatively new and currently the most frequently used method for analyzing DNA for 5-methylcytosine is based upon the specific reaction of bisulfite with cytosine which, upon subsequent alkaline hydrolysis, is converted to uracil which corresponds to thymidine in its base pairing behavior. However, 5-methylcytosine remains unmodified under these conditions. Consequently, the original DNA is converted in such a manner that methylcytosine, which originally could not be distinguished from cytosine by its hybridization behavior, can now be detected as the only remaining cytosine using "normal" molecular biological techniques, for example, by amplification and hybridization or sequencing. All of these techniques are based on base pairing which can now be fully exploited. In terms of sensitivity, the prior art is defined by a method which encloses the DNA to be analyzed in an agarose matrix, thus preventing the diffusion and renaturation of the DNA (bisulfite only reacts with single-stranded DNA), and which replaces all precipitation and purification steps with fast dialysis (Olek A, Oswald J, Walter J. A modified and improved method for bisulphite based cytosine methylation analysis. Nucleic Acids Res. 1996 Dec. 15; 24(24):5064-6). Using this method, it is possible to analyze individual cells, which illustrates the potential of the method. However, currently only individual regions of a length of up to approximately 3000 base pairs are analyzed, a global analysis of cells for thousands of possible methylation events is not possible. However, this method cannot reliably analyze very small fragments from small sample quantities either. These are lost through the matrix in spite of the diffusion protection.

[0014] An overview of the further known methods of detecting 5-methylcytosine may be gathered from the following review article: Rein, T., DePamphilis, M. L., Zorbas, H., Nucleic Acids Res. 1998, 26, 2255.

[0015] To date, barring few exceptions (e.g., Zeschnigk M, Lich C, Buiting K, Doerfler W, Horsthemke B. A single-tube PCR test for the diagnosis of Angelman and Prader-Willi syndrome based on allelic methylation differences at the SNRPN locus. Eur J Hum Genet. 1997 MarchApril; 5(2):94-8) the bisulfite technique is only used in research. Always, however, short, specific fragments of a known gene are amplified subsequent to a bisulfite treatment and either completely sequenced (Olek A, Walter J. The pre-implantation ontogeny of the H19 methylation imprint. Nat Genet. 1997 November; 17(3):275-6) or individual cytosine positions are detected by a primer extension reaction (Gonzalgo M L, Jones P A. Rapid quantitation of methylation differences at specific sites using mefhylationsensitive single nucleotide primer extension (Ms-SNuPE). Nucleic Acids Res. 1997 Jun. 15; 25(12):2529-31, WO 95/00669) or by enzymatic digestion (Xiong Z, Laird P W. COBRA: a sensitive and quantitative DNA methylation assay. Nucleic Acids Res. 1997 Jun. 15; 25(12):2532-4). In addition, detection by hybridization has also been described (Olek et al, WO 99/28498).

[0016] Further publications dealing with the use of the bisulfite technique for methylation detection in individual genes are: Grigg G, Clark S. Sequencing 5-methylcytosine residues in genomic DNA. Bioessays. 1994 June; 16(6):4316, 431; Zeschnigk M, Schmitz B, Dittrich B, Buiting K, Horsthemke B, Doerfler W. Imprinted segments in the human genome: different DNA methylation patterns in the Prader-Willi/Angelman syndrome region as determined by the genomic sequencing method. Hum Mol Genet. 1997 March; 6(3):387-95; Feil R, Charlton J, Bird A P, Walter J, Reik W. Methylation analysis on individual chromosomes: improved protocol for bisulphite genomic sequencing. Nucleic Acids Res. 1994 Feb. 25; 22(4):695-6; Martin V, Ribieras S, Song-Wang X, Rio M C, Dante R. Genomic sequencing indicates a correlation between DNA hypomethylation in the 5' region of the pS2 gene and its expression in human breast cancer cell lines. Gene. 1995 May 19; 157(1-2):2614; WO 97/46705, WO 95/15373 and WO 97/45560.

[0017] An overview of the Prior Art in oligomer array manufacturing can be gathered from a special edition of Nature Genetics (Nature Genetics Supplement, Volume 21, January 1999), published in January 1999, and from the literature cited therein.

[0018] Fluorescently labelled probes are often used for the scanning of immobilised DNA arrays. The simple attach

ment of Cy3 and Cy5 dyes to the 5'-OH of the specific probe are particularly suitable for fluorescence labels. The detection of the fluorescence of the hybridized probes may be carried out, for example via a confocal microscope. Cy3 and Cy5 dyes, besides many others, are commercially available.

[0019] Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-TOF) is a very efficient development for the analysis of biomolecules (Karas M, Hillenkamp F. Laser desorption ionization of proteins with molecular masses exceeding 10,000 daltons. Anal Chem. 1988 Oct. 15; 60(20):2299-301). An analyte is embedded in a light-absorbing matrix. The matrix is evaporated by a short laser pulse thus transporting the analyte molecule into the vapor phase in an unfragmented manner. The analyte is ionized by collisions with matrix molecules. An applied voltage accelerates the ions into a field-free flight tube. Due to their different masses, the ions are accelerated at different rates. Smaller ions reach the detector sooner than bigger ones.

[0020] MALDI-TOF spectrometry is excellently suited to the analysis of peptides and proteins. The analysis of nucleic acids is somewhat more difficult (Gut I G, Beck S. DNA and Matrix Assisted Laser Desorption Ionization Mass Spectrometry. Current Innovations and Future Trends. 1995, 1; 147-57). The sensitivity to nucleic acids is approximately 100 times worse than to peptides and decreases disproportionally with increasing fragment size. For nucleic acids having a multiply negatively charged backbone, the ionization process via the matrix is considerably less efficient. In MALDI-TOF spectrometry, the selection of the matrix plays an eminently important role. For the desorption of peptides, several very efficient matrixes have been found which produce a very fine crystallization. There are now several responsive matrixes for DNA, however, the difference in sensitivity has not been reduced. The difference in sensitivity can be reduced by chemically modifying the DNA in such a manner that it becomes more similar to a peptide. Phosphorothioate nucleic acids in which the usual phosphates of the backbone are substituted with thiophosphates can be converted into a charge-neutral DNA using simple alkylation chemistry (Gut I G, Beck S. A procedure for selective DNA alkylation and detection by mass spectrometry. Nucleic Acids Res. 1995 Apr. 25; 23(8): 1367-73). The coupling of a charge tag to this modified DNA results in an increase in sensitivity to the same level as that found for peptides. A further advantage of charge tagging is the increased stability of the analysis against impurities which make the detection of unmodified substrates considerably more difficult.

[0021] Genomic DNA is obtained from DNA of cell, tissue or other test samples using standard methods. This standard methodology is found in references such as Fritsch and Maniatis eds., Molecular Cloning: A Laboratory Manual, 1989.

Description

[0022] The object of the present invention is to provide the chemically modified DNA of genes associated with DNA replication, as well as oligonucleotides and/or PNA-oligomers for detecting cytosine methylations, as well as a method which is particularly suitable for the diagnosis and/or therapy of genetic and epigenetic parameters of genes associated with DNA replication. The present invention is