A hypermethylated phenotype is a better predictor of survival than MGMT methylation in anaplastic oligodendroglial brain tumors: a report from EORTC study 26951.

PURPOSE: The MGMT promoter methylation status has been suggested to be predictive for outcome to temozolomide chemotherapy in patients with glioblastoma (GBM). Subsequent studies indicated that MGMT promoter methylation is a prognostic marker even in patients treated with radiotherapy alone, both in GBMs and in grade III gliomas. EXPERIMENTAL DESIGN: To help determine the molecular mechanism behind this prognostic effect, we have conducted genome-wide methylation profiling and determined the MGMT promoter methylation status, 1p19q LOH, IDH1 mutation status, and expression profile on a series of oligodendroglial tumors [anaplastic oligodendrogliomas (AOD) and anaplastic oligoastrocytomas (AOA)] within EORTC study 26951. The series was expanded with tumors of the same histology and treatment from our own archive. RESULTS: Methylation profiling identified two main subgroups of oligodendroglial brain tumors of which survival in the CpG island hypermethylation phenotype (CIMP(+)) subgroup was markedly better than the survival of the unmethylated (CIMP(-)) subgroup (5.62 vs. 1.24 years; P < 0.0001). CIMP status correlated with survival, MGMT promoter methylation, 1p19q LOH, and IDH1 mutation status. CIMP status strongly increases the predictive accuracy of survival in a model including known clinical prognostic factors such as age and performance score. We validated our results on an independent data set from the Cancer Genome Atlas (TCGA). CONCLUSION: The strong association between CIMP status and MGMT promoter methylation suggests that the MGMT promoter methylation status is part of a more general, prognostically favorable genome-wide methylation profile. Methylation profiling therefore may help identify AODs and AOAs with improved prognosis.

IDH1 R132H decreases proliferation of glioma cell lines in vitro and in vivo.

OBJECTIVE: A high percentage of grade II and III gliomas have mutations in the gene encoding isocitrate dehydrogenase (IDH1). This mutation is always a heterozygous point mutation that affects the amino acid arginine at position 132 and results in loss of its native enzymatic activity and gain of alternative enzymatic activity (producing D-2-hydroxyglutarate). The objective of this study was to investigate the cellular effects of R132H mutations in IDH1. METHODS: Functional consequences of IDH1(R132H) mutations were examined among others using fluorescence-activated cell sorting, kinome and expression arrays, biochemical assays, and intracranial injections on 3 different (glioma) cell lines with stable overexpression of IDH1(R132H) . RESULTS: IDH1(R132H) overexpression in established glioma cell lines in vitro resulted in a marked decrease in proliferation, decreased Akt phosphorylation, altered morphology, and a more contact-dependent cell migration. The reduced proliferation is related to accumulation of D-2-hydroxyglutarate that is produced by IDH1(R132H) . Mice injected with IDH1(R132H) U87 cells have prolonged survival compared to mice injected with IDH1(wt) or green fluorescent protein-expressing U87 cells. INTERPRETATION: Our results demonstrate that IDH1(R132H) dominantly reduces aggressiveness of established glioma cell lines in vitro and in vivo. In addition, the IDH1(R132H) -IDH1(wt) heterodimer has higher enzymatic activity than the IDH1(R132H) -IDH1(R132H) homodimer. Our observations in model systems of glioma might lead to a better understanding of the biology of IDH1 mutant gliomas, which are typically low grade and often slow growing.