Analysis of O6-methylguanine-DNA methyltransferase methylation status in sporadic colon polyps

O6-methylguanine-DNA Methyltransferase Promoter Methylation in Patients with Rectal Adenocarcinoma After Chemoradiotherapy Treatment: Clinical Implications

Aims:

To analyze the clinical relevance of O6-methylguanine-DNA methyltransferase in rectal adenocarcinoma treated with chemoradiotherapy followed by surgery.

Methods:

Tissue samples from 29 rectal adenocarcinoma patients were obtained after chemoradiotherapy. O6-methylguanine-DNA methyltransferase promoter methylation status was established by methylation-specific polymerase chain reaction. O6-methylguanine-DNA methyltransferase protein levels were determined by immunohistochemistry. Clinicopathologic variables, including treatment regression grade, recurrence, lymph node invasion, and stage and differentiation grade of the tumor, were determined.

Results:

The O6-methylguanine-DNA methyltransferase gene promoter was methylated in 81.5% of samples. Most patients (88.9%) showed low O6-methylguanine-DNA methyltransferase protein expression. O6-methylguanine-DNA methyltransferase methylation status was not correlated with any of the clinicopathological variables determined in rectal adenocarcinomas selected for chemoradiotherapy.

Conclusion:

O6-methylguanine-DNA methyltransferase methylation status is not correlated with clinicopathologic variables examined in rectal adenocarcinoma selected for chemoradiotherapy, although its role as a biomarker awaits further investigation.

Sensitive and Noninvasive Detection of Aberrant SFRP2 and MGMT-B Methylation in Iranian Patients with Colon Polyps

BACKGROUND

The pathogenesis of sporadic colorectal cancer (CRC) is influenced by the patient genetic background and environmental factors. Based on prior understanding, these are classified in two major pathways of genetic instability. Microsatellite instability (MSI) and CPG island methylator phenotype (CIMP) are categorized as features of the hypermethylated prototype, and chromosomal instability (CIN) is known to be indicative of the non-hypermethylated category. Secreted frizzled related protein 2 (SFRP2), APC1A in WNT signaling pathway and the DNA repair gene, O6-methylguanine-DNA methyltransferase (MGMT), are frequently hypermethylated in colorectal cancer. Detection of methylated DNA as a biomarker by easy and inexpensive methods might improve the quality of life of patients with CRC via early detection of cancer or a precancerous condition.

AIM

To evaluate the rate of SFRP2 and MGMT hypermethylation in both polyp tissue and serum of patients in south Iran as compared with matched control normal population corresponding samples.

MATERIALS AND METHODS

Methylation-specific PCR was used to detect hypermethylation in DNA extracted from 48 polypoid tissue samples and 25 healthy individuals.

RESULTS

Of total polyp samples, 89.5% had at least one promoter gene hypermethylation. The most frequent methylated locus was SFRP2 followed by MGMT-B (81.2 and 66.6 percent respectively). Serologic detection of hypermethylation was 95% sensitive as compared with polyp tissue. No hypermethylation was detected in normal tissue and serum and its detection in patients with polyps, especially of serrated type, was specific.

CONCLUSIONS

Serologic investigation for detection of MGMT-B, SFRP2 hypermethylation could facilitate prioritization of high risk patients for colonoscopic polyp detection and excision.

Homeostatic responses of colonic LGR5+ stem cells following acute in vivo exposure to a genotoxic carcinogen

Perturbations in DNA damage, DNA repair, apoptosis and cell proliferation in the base of the crypt where stem cells reside are associated with colorectal cancer (CRC) initiation and progression. Although the transformation of leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5)(+) cells is an extremely efficient route towards initiating small intestinal adenomas, the role of Lgr5(+) cells in CRC pathogenesis has not been well investigated. Therefore, we further characterized the properties of colonic Lgr5(+) cells compared to differentiated cells in Lgr5-EGFP-IRES-creER(T2) knock-in mice at the initiation stage of carcinogen azoxymethane (AOM)-induced tumorigenesis using a quantitative immunofluorescence microscopy approach. At 12 and 24h post-AOM treatment, colonic Lgr5(+) stem cells (GFP(high)) were preferentially damaged by carcinogen, exhibiting a 4.7-fold induction of apoptosis compared to differentiated (GFP(neg)) cells. Furthermore, with respect to DNA repair, O(6)-methylguanine DNA methyltransferase (MGMT) expression was preferentially induced (by 18.5-fold) in GFP(high) cells at 24h post-AOM treatment compared to GFP(neg) differentiated cells. This corresponded with a 4.3-fold increase in cell proliferation in GFP(high) cells. These data suggest that Lgr5(+) stem cells uniquely respond to alkylation-induced DNA damage by upregulating DNA damage repair, apoptosis and cell proliferation compared to differentiated cells in order to maintain genomic integrity. These findings highlight the mechanisms by which colonic Lgr5(+) stem cells respond to cancer-causing environmental factors.

The anti-cancer actions of O6-methylguanine-DNA-methyltransferase in relation to colon polyps

BACKGROUND

Genetic variability in DNA repair genes may contribute to differences in DNA repair capacity and susceptibility to colon polyps and cancer. In this study, we examined the role of MGMT polymorphisms in colon polyps formation.

METHODS

PCR-SSCP analysis was performed included 254 patients with colon polyps and 330 controls.

RESULTS

The homozygous F84F genotype was significantly more prevalent in study group than in controls. The polymorphic allele 84F was more frequent appeared in group of older patients and in group of smoking patients. On the other hand, there were no association between 84F and gender, size of polyps, cancer family history.

CONCLUSIONS

We concluded that high frequency of 84F allele in the group of patients may suggest the role of the MGMT variant in colon polyps etiology.