O6-Methyguanine-DNA Methyl Transferase (MGMT) Promoter Methylation in Serum DNA of Iranian Patients with Colorectal Cancer

Introduction: Colorectal cancer (CRC) is a leading cause of cancer deaths worldwide but current molecular targetedtherapy is not providing major success in CRC treatment, so early detection by non-invasive methods continues tobe vital. Aberrant methylation of CpG islands in promoter regions is associated with inactivation of various tumorsuppressor genes. O6-methyguanine-DNA methyltransferase (MGMT) is a DNA repair enzyme that removes mutagenicand cytotoxic adducts from O6-guanine in DNA. Aberrant hypermethylation of the MGMT promoter has beenassociated with lack of mRNA expression, with concomitant loss of protein content and enzyme activity. AIM: Ouraim was to determine whether MGMT promoter methylation might be detectable in circulating free DNA in the serumof CRC patients and normal individuals using a methylation specific (MSP) polymerase chain reaction (PCR) method.Methods: A total of 70 subjects were enrolled in the study. Of these, 30 patients who were diagnosed previously asuntreated colon adenocarcinoma by a gastroenterologist and the other 40 were nearly age-matched individuals who hada normal colonoscopic evaluation (except for hemorrhoids or fissures) and normal pathologic reports. After bisulphitemodification of DNA, serum samples were examined for MGMT promoter methylation using MSP. Results: Ninetypercent of CRC patients had MGMT promoter hypermethylation as compared to no methylation in normal subjects’serum. Most of the cancers were stage П and moderately differentiated adenocarcinomas; nearly 60% were found inthe left colon. No statistically significant correlation was found between the promoter methylation status and genderand age. Discussion and Conclusions: MGMT hypermethylation can be detected in free circulating DNA in serum ofCRC patients and can be used “as a clinical biomarker” for early diagnosis and prognostic assessment of the disease.Our data confirm previous studies indicating utility for free circulating DNA as a serum biomarker for early detection,diagnosis and monitoring of CRC patients.