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

Document Type: Research Articles

Authors

1 Gastroenterohepatology Research Center, Nemazi Hospital, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran.

2 Department of Internal Medicine, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran.

3 Department of Biotechnology, School of Advanced Medical Science and Technologies, Shiraz University of Medical Sciences, Shiraz, Iran.

4 Department of Internal Medicine Hamadan University of Medical Sciences, School of Medicine, Hamedan, Iran.

5 Department of Pathology, School of Medicine, Shiraz University of Medical sciences, Shiraz, Iran.

6 Colorectal Research Center, Nemazi hospital, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran.

7 Department of Biochemistry, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran.

Abstract

Introduction: Colorectal cancer (CRC) is a leading cause of cancer deaths worldwide but current molecular targeted
therapy is not providing major success in CRC treatment, so early detection by non-invasive methods continues to
be vital. Aberrant methylation of CpG islands in promoter regions is associated with inactivation of various tumor
suppressor genes. O6-methyguanine-DNA methyltransferase (MGMT) is a DNA repair enzyme that removes mutagenic
and cytotoxic adducts from O6-guanine in DNA. Aberrant hypermethylation of the MGMT promoter has been
associated with lack of mRNA expression, with concomitant loss of protein content and enzyme activity. AIM: Our
aim was to determine whether MGMT promoter methylation might be detectable in circulating free DNA in the serum
of 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 as
untreated colon adenocarcinoma by a gastroenterologist and the other 40 were nearly age-matched individuals who had
a normal colonoscopic evaluation (except for hemorrhoids or fissures) and normal pathologic reports. After bisulphite
modification of DNA, serum samples were examined for MGMT promoter methylation using MSP. Results: Ninety
percent 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 in
the left colon. No statistically significant correlation was found between the promoter methylation status and gender
and age. Discussion and Conclusions: MGMT hypermethylation can be detected in free circulating DNA in serum of
CRC 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.

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