Recent clinical trials on patients with glioblastoma revealed that O6-Methylguanine-DNA methyltransferase (MGMT) methylation status significantly predicts patient's response to alkylating agents. In this study, we sought to develop and validate a quantitative MGMT methylation assay using pyrosequencing on glioblastoma. We quantified promoter methylation of MGMT using pyrosequencing on paraffin-embedded fine needle aspiration biopsy tissues from 43 glioblastoma. Using a 10% cutoff, MGMT methylation was identified in 37% cases of glioblastoma and 0% of the non-neoplastic epileptic tissue. Methylation of any individual CpG island in MGMT promoter ranged between 33% and 95%, with a mean of 65%. By a serial dilution of genomic DNA of a homogenously methylated cancer cell line with an unmethylated cell line, the analytical sensitivity is at 5% for pyrosequencing to detect MGMT methylation. The minimal amount of genomic DNA required is 100 ng (approximately 3,000 cells) in small fine needle biopsy specimens. Compared with methylation-specific PCR, pyrosequencing is comparably sensitive, relatively specific, and also provides quantitative information for each CpG methylation.
Keywords: MGMT; epigenetics; glioblastoma; methylation; pyrosequencing.