Elucidation of Etiology of Colorectal Cancer: A Study on Silencing of MGMT Gene by Promoter Hypermethylation

Prevalence of Promoterhypermethylation of MGMT Gene in Colorectal Cancer Patients of Kashmir Valley. Colorectal cancer, one of the most aggressive cancers, occurs with a high incidence in most countries. Colorectal cancer (CRC) is one of the leading malignancies worldwide. Cancer development and progression is dictated by series of alterations in genes such as tumor suppressor genes, DNA repair genes, oncogenes and others. In this study, efforts were made to identify promoter hypermethylation of CpG islands of MGMT gene in CRC patients among the Kashmiri population. Methylation status of CpG islands in the promoter region of MGMT gene in colorectal cancers and normal corresponding colonic mucosa was analysed. Fresh tissue samples were obtained from 50 patients (age of 21 to 81 years) undergoing resective surgery for CRC with primary colorectal adenocarcinonia and corresponding histopathologically normal tissues. Methylation-specific polymerase chain reaction (MSP) was used for analysis of the promoter methylation status of MGMT gene. The male to female ratio of the disease came out to be 1.38. The epigenetic analysis of the cases and controls revealed that unlike other high risk regions, Kashmiri population has a different hypermethylation profile of MGMT gene promoter hypermethylation. The frequency of cases with MGMT promoter hypermethylation was more as compared to controls (54% vs. 20%) and was statistically significant (O.R = 4.69, 95% C.I = 1.37 – 16.05, P = 0.015) using χ2 test with Odds Ratio. It was also found that the frequency of male cases with promoter hypermethylation of MGMT gene was more as seen against male controls (72.41% vs. 30%), which also showed statistically significant results (O.R = 6.13, 95% C.I = 1.26 – 29.71, P = 0.026) using Fisher’s Exact test, though the frequency of promoter hypermethylation of MGMT gene of female cases was more as compared to female controls (28.57% vs. 10%), the data was found not to be statistically significant (O.R = 3.6, 95% C.I = 0.37 – 34.93, P = 0.37) using Fisher’s Exact. While for the male verses female cases of promoter hypermethylation of MGMT gene the results were statistically significant (O.R = 6.563, 95% C.I = 1.882 - 22.82, P = 0.0037) using Fisher’s Exact Test. In this study it was concluded that male gender is generally associated with higher methylation levels for most CpG islands hypermethylation of MGMT gene in normal as well as cancerous colonic mucosa. The results indicate that MGMT aberrant methylation may play an important role in colorectal cancer. This study clearly demonstrates that promoter hypermethylation of MGMT gene can be designated as epigenetic biomarker for early diagnosis and better prognosis of the disease