High Incidence of MGMT and RARβ Promoter Methylation in Primary Glioblastomas: Association with Histopathological Characteristics, Inflammatory Mediators and Clinical Outcome

Abstract

Glioblastomas, the most frequent primary brain tumors in adults, are characterized by a highly aggressive, inflammatory and angiogenic phenotype. Methylation of CpG islands in cancer-related genes may serve as an epigenetic biomarker for glioblastoma diagnosis and prognosis. The aim of this study was to analyze the methylation status of four critical tumor-associated genes (MGMT, RARbeta, RASSF1A, CDH13), and investigate possible links with inflammatory (interleukin [IL]-6, IL-8) and angiogenic mediators (vascular endothelial growth factor [VEGF], cyclooxygenase [COX]-2) and clinical outcome in 23 glioma samples (6 grade II astrocytomas, 17 grade IV glioblastomas). RARbeta and MGMT genes were more frequently methylated in 70.58% and 58.8% of glioblastomas, respectively. RASSF1A and CDH13 displayed a similar methylation frequency (23.52%) in glioblastomas. No gene methylation was observed in grade II astrocytomas. Tumor grade correlated positively with MGMT and RARbeta methylation (P = 0.005 and P = 0.019, respectively) and the extent of necrosis (P = 0.001 and P = 0.003). Interestingly, the marker of chronic inflammation, IL-6, was positively associated with methylation of MGMT (P = 0.004), RARbeta (P = 0.002), and RASSF1A (P = 0.0081) as well as the total number of methylated genes (P < 0.0001), indicating the important role of IL-6 in maintaining promoter methylation of these genes. VEGF expression correlated positively with MGMT and RARbeta methylation although these relationships were of marginal significance (P = 0.0679 and P = 0.0757). Kaplan-Meier univariate survival analysis indicated an unfavorable survival period in patients with MGMT methylation compared with those without methylation (P = 0.0474). Our study highlights the implication of MGMT and RARbeta methylation in the aggressive phenotype of primary glioblastomas. The association of MGMT methylation with clinical outcome indicates its potential prognostic value.