IDH mutation and MGMT promoter methylation in glioblastoma: results of a prospective registry

Abstract

Background: The relative contribution of isocitrate dehydrogenase mutations (mIDH) and O6-methylguanine-DNA methyltransferase promoter methylation (methMGMT) as biomarkers in glioblastoma remain poorly understood.

Methods: We investigated the association between methMGMT and mIDH with progression free survival and overall survival in a prospectively collected molecular registry of 274 glioblastoma patients.

Results: For glioblastoma patients who underwent Temozolomide and Radiation Therapy, OS and PFS was most favorable for those with tumors harboring both mIDH and methMGMT (median OS: 35.8 mo, median PFS: 27.5 mo); patients afflicted glioblastomas with either mIDH or methMGMT exhibited intermediate OS and PFS (mOS: 36 and 17.1 mo; mPFS: 12.2 mo and 9.9 mo, respectively); poorest OS and PFS was observed in wild type IDH1 (wtIDH1) glioblastomas that were MGMT promoter unmethylated (mOS: 15 mo, mPFS: 9.7 mo). For patients with wtIDH glioblastomas, TMZ+RT was associated with improved OS and PFS relative to patients treated with RT (OS: 15.4 mo v 9.6 mo, p < 0.001; PFS: 9.9 mo v 6.5 mo, p < 0.001). While TMZ+RT and RT treated mIDH patients exhibited improved overall survival relative to those with wtIDH, there were no differences between the TMZ+RT or RT group. These results suggest that mIDH1 conferred resistance to TMZ. Supporting this hypothesis, exogenous expression of mIDH1 in independent astrocytoma/glioblastoma lines resulted in a 3-10 fold increase in TMZ resistance after long-term passage.

Conclusions: Our study demonstrates IDH mutation and MGMT promoter methylation status independently associate with favorable outcome in TMZ+RT treated glioblastoma patients. However, these biomarkers differentially impact clinical TMZ response.

Keywords: IDH; MGMT; glioblastomas; radiation; temozolomide.

Figure 1

The Kaplan–Meier estimates for overall survival A. and progression-free survival B. indicated that patients underwent RT plus TMZ treatment exhibited much longer survivals than did who received RT only.

Figure 2. Kaplan–Meier curves showing that, among GBMs, patients with both IDH mutation and MGMT promoter methylation exhibited the best prognosis; patients harboring either mutated IDH or methylated MGMT promoter exhibited intermediate prognosis; patients with wild-type IDH and unmethylated MGMT promoter exhibited the worst

Figure 3

A. The Kaplan–Meier estimates for overall survival indicated that the group of GBM patients with wt IDH who were randomly assigned to the RT plus TMZ treatment groups exhibited significantly longer survival than did the group who were randomly assigned to RT only. B. Among GBM patients with IDH mutation, a more favorable survival benefit was not observed in the RT plus TMZ treatment group compared to the RT alone group.

Figure 4. A. Prolonged passage after IDH1-R132H expression increased chromatin deposition of H3K27me3 in human U87MG glioblastoma and murine Ink4a/Arf−/− astrocytic cells

Cell lysates from short (5 passages) and long-term passaged (28 passages) cells were prepared, fractionated by gel-electrophoresis, and probed with an anti-H3K27me3 (Abcam#6002), anti-Flag (Sigma#8592), or anti-Ku86 (Santa Cruz#sc-1485) antibody. Right: Densitometry quantitation of the immuno-blot. The H3K27me3 signal was normalized to the Ku86 signal. B. Prolonged passage after IDH1-R132H expression in human U87 glioblastoma cells induced altered DNA methylation patterns from a G-CIMP- pattern to a G-CIMP+ pattern. Red indicates that the genomic region of interest is methylated. Green indicates the lack of DNA methylation. C. Prolonged passage after IDH1-R132H expression increased TMZ resistance of human U87MG glioblastoma and murine Ink4a/Arf−/− astrocytic cells. Clonogenic survival was assessed 14 days after TMZ treatment. Please note that the Y-axis is plotted on a log-scale.