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, RARβ, 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). RARβ 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 RARβ 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), RARβ (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 RARβ 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 RARβ methylation in the aggressive phenotype of primary glioblastomas. The association of MGMT methylation with clinical outcome indicates its potential prognostic value.

MGMT promoter methylation and immunoexpression in aggressive pituitary adenomas and carcinomas

“…Our results are also in keeping with most studies showing MGMT epigenetic silencing in higher grade and more aggressive tumors arising outside the pituitary gland [22,23]. Piperi et al reported MGMT promoter methylation in 59% of the 17 GBMs studied, and that a correlation existed between methylation status and patient survival, thus suggesting methylation is a prognostic indicator [22].…”

“…Epigenetic silencing of MGMT via methylation of its promoter is associated with higher tumor grade and with prognosis in several human neoplasms [3,[22][23][24][25][26][27][28][29]. Accordingly, we report MGMT promoter methylation in 33% of pituitary carcinomas and in 42% of SS3 adenomas.…”

“…Piperi et al reported MGMT promoter methylation in 59% of the 17 GBMs studied, and that a correlation existed between methylation status and patient survival, thus suggesting methylation is a prognostic indicator [22]. Similarly, Kim et al observed MGMT promoter hypermethylation in 34% of the 63 soft tissue sarcomas, there being a strong correlation with tumor stage, grade, and aggressive behavior [23].…”

“…Interestingly, MGMT promoter methylation status is also associated with higher tumor grade and invasiveness as well as poor prognosis in most human neoplasms studied. These include GBM, various sarcomas, nonsmall cell lung carcinoma, carcinomas of bladder, cervix, prostate and salivary gland, as well as other tumors including pituitary neoplasms [3,[22][23][24][25][26][27][28][29]. In cell culture, Nakasu et al recently found loss of MGMT expression to be correlated to anaplastic transformation of astrocytomas [30].…”

Pathophysiological mechanisms regulated by cytokines in gliomas

“…This regulatory system of gene expression is under the control of cytokines network. In 2010, Piperi et al demonstrated the correlation between IL-6 and the promoter methylation profile of 3 genes RARb, MGMT (mainly in astrocytoma, anaplastic astrocytoma, and secondary glioblastoma) and RASSF1A [94]. O6-methylguanine-DNA methyltransferase (MGMT) is a DNA repair enzyme and its down regulation in normal cells is crucial for carcinogenesis [95].…”