Tumour vasculature: On the verge of collapse

BACKGROUND Sporadic colorectal cancers often arise from a region of cells characterized by a "field defect" that has not been well defined molecularly. DNA methylation has been proposed as a candidate mediator of this field defect. The DNA repair gene O6-methylguanine-DNA methyltransferase (MGMT) is frequently methylated in colorectal cancer. We hypothesized that MGMT methylation could be one of the mediators of field cancerization in the colon mucosa. METHODS We studied MGMT promoter methylation by three different bisulfite-based techniques in tumor, adjacent mucosa, and non-adjacent mucosa from 95 colorectal cancer patients and in colon mucosa from 33 subjects with no evidence of cancer. Statistical tests were two-sided. RESULTS MGMT promoter methylation was present in 46% of the tumors. Patients whose cancer had MGMT promoter methylation also had substantial MGMT promoter methylation in apparently normal adjacent mucosa. This methylation was seen with a quantitative assay in 50% (22/44; 95% confidence interval [CI] = 34% to 65%) of normal samples with MGMT promoter methylation in the adjacent tumors, 6% (3/51; 95% CI = 1% to 16%) of samples without MGMT methylation in adjacent tumors, and 12% (4/33; 95% CI = 3% to 28%) of control samples (P < .001 for comparison between each of the latter two groups and the first group). MGMT methylation was detected with a more sensitive assay in 94%, 34%, and 27% of these samples, respectively (P < .001). In grossly normal colonic mucosa of colon cancer patients, methylation was detected 10 cm away from the tumor in 10 of 13 cases. Tumors with MGMT promoter methylation had a higher rate of G-to-A mutation in the KRAS oncogene than tumors without MGMT promoter methylation (10/42 versus 3/46, P = .03). Using a sensitive mutant allele-specific amplification assay for KRAS mutations, we also found KRAS mutations in 12% (3/25; 95% CI = 2.5% to 31%) of colorectal mucosas with detectable MGMT methylation and 3% (2/64; 95% CI = 0.4% to 11%) of colorectal mucosas without MGMT methylation (P = .13). CONCLUSION Some colorectal cancers arise from a field defect defined by epigenetic inactivation of MGMT. Detection of this abnormality may ultimately be useful in risk assessment for colorectal cancer.

[1]  F. V. von Eyben,et al.  Colorectal cancer screening: clinical guidelines and rationale. , 1997, Gastroenterology.

[2]  Issa Jp.  CpG-island methylation in aging and cancer. , 2000 .

[3]  M. Christmann,et al.  BER, MGMT, and MMR in defense against alkylation-induced genotoxicity and apoptosis. , 2001, Progress in nucleic acid research and molecular biology.

[4]  N. Ahuja,et al.  Distinct genetic profiles in colorectal tumors with or without the CpG island methylator phenotype. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[5]  J. Issa.  Epigenetic variation and human disease. , 2002, The Journal of nutrition.

[6]  S. Baylin,et al.  Aging and DNA methylation in colorectal mucosa and cancer. , 1998, Cancer research.

[7]  Peter A. Jones,et al.  Cancer-epigenetics comes of age , 1999, Nature Genetics.

[8]  A. Pegg.  Repair of O(6)-alkylguanine by alkyltransferases. , 2000, Mutation research.

[9]  C. R. Leemans,et al.  A genetic explanation of Slaughter's concept of field cancerization: evidence and clinical implications. , 2003, Cancer research.

[10]  B. Leggett,et al.  Methylation of O-6-methylguanine DNA methyltransferase characterizes a subset of colorectal cancer with low-level DNA microsatellite instability. , 2001, Cancer research.

[11]  J. Jass.  Serrated route to colorectal cancer: back street or super highway? , 2001, The Journal of pathology.

[12]  J. Herman,et al.  Inactivation of the DNA repair gene O6-methylguanine-DNA methyltransferase by promoter hypermethylation is associated with G to A mutations in K-ras in colorectal tumorigenesis. , 2000, Cancer research.

[13]  David Sidransky,et al.  Emerging molecular markers of cancer , 2002, Nature Reviews Cancer.

[14]  J. Costello,et al.  Graded methylation in the promoter and body of the O6-methylguanine DNA methyltransferase (MGMT) gene correlates with MGMT expression in human glioma cells. , 1994, The Journal of biological chemistry.

[15]  S. Baylin,et al.  Methylation of the oestrogen receptor CpG island links ageing and neoplasia in human colon , 1994, Nature Genetics.

[16]  G. Margison,et al.  Variability and regulation of O6-alkylguanine-DNA alkyltransferase. , 2003, Carcinogenesis.

[17]  D. Cooper,et al.  DNA alkylation and repair in the large bowel: animal and human studies. , 2002, The Journal of nutrition.

[18]  J. Herman,et al.  CpG island methylator phenotype in colorectal cancer. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[19]  Jeffrey S. Morris,et al.  Concordant CpG island methylation in hyperplastic polyposis. , 2002, The American journal of pathology.

[20]  M. Emi,et al.  Detailed analysis of genetic alterations in colorectal tumors from patients with and without familial adenomatous polyposis (FAP). , 1993, Oncogene.

[21]  J. Herman,et al.  Alterations in DNA methylation: a fundamental aspect of neoplasia. , 1998, Advances in cancer research.

[22]  A. Pegg.  Repair of O6-alkylguanine by alkyltransferases , 2000 .

[23]  T. Brent,et al.  Immunoaffinity purification of human O6-alkylguanine-DNA alkyltransferase using newly developed monoclonal antibodies. , 1990, Cancer research.

[24]  J. Issa,et al.  CpG-island methylation in aging and cancer. , 2000, Current topics in microbiology and immunology.

[25]  Edward S. Kim,et al.  Chemoprevention of aerodigestive tract cancers. , 2002, Annual review of medicine.

[26]  J. Issa.  The Epigenetics of Colorectal Cancer , 2000, Current opinion in gastroenterology.

[27]  P. Laird,et al.  Sensitive Detection of DNA Methylation , 2003, Annals of the New York Academy of Sciences.

[28]  S. Clark,et al.  High sensitivity mapping of methylated cytosines. , 1994, Nucleic acids research.

[29]  N. Ahuja,et al.  Accelerated age-related CpG island methylation in ulcerative colitis. , 2001, Cancer research.

[30]  F. Gilliland,et al.  Aberrant promoter methylation in bronchial epithelium and sputum from current and former smokers. , 2002, Cancer research.

[31]  T. Brent,et al.  Localization of methylation sites in the human O6-methylguanine-DNA methyltransferase promoter: correlation with gene suppression. , 1995, Carcinogenesis.