Purpose: In glioblastoma multiforme (GBM), the cytotoxic effect of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and temozolamide is dependent on O(6) alkylation, which correlates inversely with expression of the DNA repair enzyme O(6)-methyl-guanine-DNA methyltransferase (MGMT). Thus, MGMT assessment can be useful in predicting response in GBM, but the scarcity of neoplastic cells limits the practicality of MGMT assessment in these tumors. Although GBM grows within the skull, we investigated the concordance of methylation in glioma tissue, and paired serum DNA and the potential correlation with response and time to progression.
Experimental design: Using MSP assay, we assessed the methylation of MGMT, p16, DAPK, and RASSF1A in tumor and serum DNA from 28 GBM patients treated with BCNU or with temozolamide plus cisplatin.
Results: The concordance between methylation in tumor and serum was highly significant. Overall, response plus stable disease was noted in 10 of 11 (90.9%) patients with MGMT methylation and in 5 of 14 (35.7%) patients without (P = 0.01). In the 16 patients treated with temozolamide plus cisplatin, no significant correlation between MGMT methylation status and response was observed, whereas in BCNU-treated patients, a significant difference was observed in favor of those with methylated MGMT. Time to progression was 29.9 weeks in 12 patients with MGMT methylation and 15.7 weeks in 10 patients without (P = 0.006). No correlation was observed between response or time to progression and p16, DAPK, or RASSF1A methylation.
Conclusions: Methylated MGMT, p16, DAPK, and RASSF1A were found in serum DNA of GBM patients, with a good correlation between serum and primary tumor tissue. Serum MGMT methylation predicted response and time to progression in BCNU-treated GBM patients. The methylation-specific PCR assay in serum DNA could be a good predictive tool for selecting GBM patients to be treated with BCNU or alternatively with the combination of temozolamide plus cisplatin.