Promoter Hypermethylation of the DNA-Repair Gene O 6 -Methylguanine-DNA Methyltransferase and p53 Mutation in Diffuse Large B-Cell Lymphoma

Abstract

The gene for the DNA-repair enzyme O6-methylguanine-DNA methyltransferase (MGMT), which is closely related with cellular sensitivity to alkylating agents, is inactivated by promoter hypermethylation in several human cancers, including malignant lymphoma. Promoter hypermethylation of the MGMT gene is a favorable prognostic factor in diffuse large B-cell lymphoma (DLBCL). Although inactivation of the MGMT gene is closely related to p53 gene mutations in several cancers, the relationship between p53 gene mutation and MGMT inactivation in malignant lymphoma has not been thoroughly examined. We studied the correlation between MGMT hypermethylation and p53 mutation in DLBCL and their impacts on patient prognosis. In a retrospective cohort study, we used a methylation-specific polymerase chain reaction technique to analyze the methylation status of the promoter region of the MGMT gene in 116 DLBCL patients who received cyclophosphamide as part of multidrug combination chemotherapies. Denaturing high-performance liquid chromatography and direct sequencing were used to search for p53 gene mutations in exons 5 through 9 in 96 of the 116 samples. Disease-free survival and overall survival were estimated by the Kaplan-Meier method. Multivariate survival analyses were performed with the Cox proportional hazards model. Forty-five (38.8%) of 116 DLBCL patients showed MGMT promoter hypermethylation. The presence of MGMT hypermethylation was associated with better overall survival (P = .036). MGMT promoter hypermethylation was a prognostic factor that was independent of established prognostic factors, such as age, disease stage, serum lactic dehydrogenase level, and the number of extranodal disease sites (hazard ratio, 2.43; 95% confidence interval, 1.28-4.61; P = .007). p53 mutations were detected in 19 (19.8%) of 96 patients and were identified as a risk factor in the complete remission rate and overall survival (P = .0040, and P = .027, respectively). A correlation between MGMT hypermethylation and p53 mutation or p53 G:C-to-A:T mutation was not observed (P = .88, and P = .31, respectively). MGMT promoter hypermethylation and p53 mutation are useful prognostic markers in DLBCL. The impact of MGMT inactivation on p53 mutation in DLBCL is unclear.

Determination of apoptosis, proliferation status and O6-methylguanine DNA methyltransferase methylation profiles in different immunophenotypic profiles of diffuse large B-cell lymphoma

“…MGMT methylation was reported at a frequency from 36% to 52% in Western populations in previous studies [1,3,30,46,47]. Higher rates (75.9%) were found in Middle Eastern populations [38].…”

“…Diffuse large B-cell lymphoma (DLBCL) constitutes the largest group of aggressive lymphomas in adults and 30-40% of adult non-Hodgkin lymphomas (NHL) in western countries [1,2]. DLBCLs show diversity in clinical presentation, morphology and genetic and molecular properties, which suggests that these tumors represent a heterogeneous group of neoplasms rather than a single clinicopathologic entity [2,3].…”

“…DLBCLs show diversity in clinical presentation, morphology and genetic and molecular properties, which suggests that these tumors represent a heterogeneous group of neoplasms rather than a single clinicopathologic entity [2,3]. Therefore, patients who are diagnosed as DLBCL could show remarkably different history, clinical behavior and outcome [1].…”

“…In human cancers, the gene encoding the DNA-repair enzyme O 6 -methylguanine-DNA methyltransferase (MGMT) is not commonly mutated or deleted. Loss of MGMT expression is mainly due to epigenetic changes, specifically methylation of the promoter region [1,30]. MGMT protects cells from the toxicity of environmental and therapeutic alkylating agents, which frequently target the O 6 position of guanine.…”

“…MGMT protects cells from the toxicity of environmental and therapeutic alkylating agents, which frequently target the O 6 position of guanine. Inactivation of the MGMT gene via hypermethylation of its promoter region increases sensitivity of cells to the genotoxic effect of alkylating agents both in vitro and in vivo [1,3]. Recent research has focused on the relationship between MGMTmethylation status and immunophenotypic differentiation in DLBCLs [30,31].…”