Correlation of MGMT promoter methylation status with gene and protein expression levels in glioblastoma

OBJECTIVES: 1) To correlate the methylation status of the O6-methylguanine-DNA-methyltransferase (MGMT) promoter to its gene and protein expression levels in glioblastoma and 2) to determine the most reliable method for using MGMT to predict the response to adjuvant therapy in patients with glioblastoma. BACKGROUND: The MGMT gene is epigenetically silenced by promoter hypermethylation in gliomas, and this modification has emerged as a relevant predictor of therapeutic response. METHODS: Fifty-one cases of glioblastoma were analyzed for MGMT promoter methylation by methylation-specific PCR and pyrosequencing, gene expression by real time polymerase chain reaction, and protein expression by immunohistochemistry. RESULTS: MGMT promoter methylation was found in 43.1 percent of glioblastoma by methylation-specific PCR and 38.8 percent by pyrosequencing. A low level of MGMT gene expression was correlated with positive MGMT promoter methylation (p = 0.001). However, no correlation was found between promoter methylation and MGMT protein expression (p = 0.297). The mean survival time of glioblastoma patients submitted to adjuvant therapy was significantly higher among patients with MGMT promoter methylation (log rank = 0.025 by methylation-specific PCR and 0.004 by pyrosequencing), and methylation was an independent predictive factor that was associated with improved prognosis by multivariate analysis. DISCUSSION AND CONCLUSION: MGMT promoter methylation status was a more reliable predictor of susceptibility to adjuvant therapy and prognosis of glioblastoma than were MGMT protein or gene expression levels. Methylation-specific polymerase chain reaction and pyrosequencing methods were both sensitive methods for determining MGMT promoter methylation status using DNA extracted from frozen tissue.

A Consideration of MGMT Gene Promotor Methylation Analysis for Glioblastoma Using Methylation-Specific Polymerase Chain Reaction and Pyrosequencing

BACKGROUND: O6-methylguanine-DNA methyltransferase (MGMT) gene promoter methylation is currently the most promising predictive marker for the outcome and benefit from temozolomide treatment in patients with glioblastoma, but there is no consensus on the analysis method for assessing the methylation status in the molecular diagnostic field. The objective of this study was to evaluate methylation-specific polymerase chain reaction (MSP) and pyrosequencing methods for assessing MGMT gene promotor methylation of glioblastoma as well as assessing the MGMT protein expression by immunohistochemistry. METHODS: Twenty-seven cases of glioblastoma from the archives at the Department of Pathology Konkuk University Hospital were selected. MGMT promoter methylation was evaluated by MSP and the pyrosequencing methods. The MGMT expression was also measured at the protein level by immunohistochemistry. RESULTS: Overall, MGMT hypermethylation was observed in 44.4% (12/27 cases) of the case of glioblastoma using either MSP or pyrosequencing. The concordant rate was 70.3% (19/27 cases) between MSP and pyrosequencing for MGMT methylation. There was no correlation between MGMT methylation and the protein expression. No significant differences in progression free survival and overall survival were seen between the methylated group and the unmethylated group by using either MSP or pyrosequencing. The status of the MGMT protein expression was correlated with progression free survival (p=0.026). CONCLUSIONS: In this study the concordance rate between MSP and the pyrosequencing methods for assessing MGMT gene promotor methylation was relatively low for the cases of glioblastoma. This suggests that more reliable techniques for routine MGMT methylation study of glioblastoma remain to be developed because of quality control and assurance issues.

Role of Loss of O(6)-Methylguanine DNA Methyltransferase (MGMT) Expression in Non-Small Cell Lung Carcinomas (NSCLCs): with Reference to the Relationship with p53 Overexpression / Journal of the Korean Cancer Association, 대한암학회지

PURPOSE: Functional inactivation of the O(6)-methylguanine-DNA methyltransferase (MGMT) gene has been demonstrated as loss of MGMT protein and suggested that it plays an important role in primary human neoplasia, including lung cancer. It has also been reported to be associated with the G : C-->A : T transition mutation in the p53 gene of lung cancer. The aims of this study were to investigate the role of MGMT expression loss and its prognostic significance in non-small cell lung carcinomas (NSCLCs), and its correlation with p53 overexpression as well as influence on patient survival. MATERIALS AND METHODS: 112 surgically resected NSCLC specimens were reviewed by medical records for their clinicopathologic variables. Their tissue microarray blocks were immunostained with anti-human MGMT and p53 primary antibodies. Correlation between MGMT loss and the clinicopathologic prognostic factors, including p53 overexpression and the single or combined actions of MGMT loss and p53 overexpression on patient survival were statistically analyzed by SPSS15.0. RESULTS: Reduced or absent MGMT expression was found in 48 of 112 NSCLCs (43%), and significantly associated with nodal metastasis and squamous or undifferentiated cell types. Loss of MGMT expression was correlated with p53 overexpression in adenocarcinomas, but not in overall NSCLCs. Its solitary or combined actions with p53 overexpression did not have influence on patient survival. CONCLUSION: Loss of MGMT expression is a relatively common event in NSCLCs and significantly associated with nodal metastasis and p53 overexpression, suggesting that it may play a major role in pulmonary carcinogenesis, and also in disease progression of NSCLCs.