The Correlation between Promoter Methylation Status and the Expression Level of O6-Methylguanine-DNA Methyltransferase 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 -methylguanineDNA 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 ¼ 0.016). O 6 methylguanine-DNA methyltransferase mRNA level was correlated with the methylation status (P ¼ 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.