The Correlation between Promoter Methylation Status and the Expression Level of O6-Methylguanine-DNA Methyltransferase in Recurrent Glioma

BACKGROUND: The DNA repair protein O(6)-methylguanine-DNA methyltransferase is a drug-resistant protein, which protects the tumors from chemotherapeutic alkylating agents, such as temozolomide. The methylation status of O(6)-methylguanine-DNA methyltransferase promoter has been shown to be a major predictive factor for clinical outcome in glioma patients when treated by alkylating agents. Thereby, there were many reports on O(6)-methylguanine-DNA methyltransferase promoter methylation and mRNA expression in primary glioma, in contrast, there were only a few studies in recurrent glioma. METHODS: We evaluated the O(6)-methylguanine-DNA methyltransferase mRNA expression and promoter methylation status in glioma patients before and after recurrence by quantitative real-time PCR and methylation-specific PCR assay. Thirteen paired primary and recurrent glioma patients were analyzed, including four patients in whom malignant transformation occurred from Grade II to Grade III. RESULTS: Methylation-specific PCR assay demonstrated that the status of O(6)-methylguanine-DNA methyltransferase promoter changed from methylated to unmethylated in 10 of 13 samples when the tumor relapsed. Moreover, intra-individual O(6)-methylguanine-DNA methyltransferase mRNA level increased in recurrent gliomas than in primary ones (P = 0.016). O(6)-methylguanine-DNA methyltransferase mRNA level was correlated with the methylation status (P = 0.012). CONCLUSIONS: Our results give the evidence that the increase of O(6)-methylguanine-DNA methyltransferase mRNA expression caused by methylation changes in recurrence may be associated with chemoresistance in the recurrent glioma.