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Clin Cancer Res. 2011 Jan 15;17(2):255-66. doi: 10.1158/1078-0432.CCR-10-1931. Epub 2010 Nov 19.

Extent and patterns of MGMT promoter methylation in glioblastoma- and respective glioblastoma-derived spheres.

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1
Laboratory of Brain Tumor Biology, Department of Clinical Neurosciences, Centre Hospitalier Universitaire Vaudois and University of Lausanne, Lausanne, Switzerland.

Abstract

PURPOSE:

Quantitative methylation-specific tests suggest that not all cells in a glioblastoma with detectable promoter methylation of the O6-methylguanine DNA methyltransferase (MGMT) gene carry a methylated MGMT allele. This observation may indicate cell subpopulations with distinct MGMT status, raising the question of the clinically relevant cutoff of MGMT methylation therapy. Epigenetic silencing of the MGMT gene by promoter methylation blunts repair of O6-methyl guanine and has been shown to be a predictive factor for benefit from alkylating agent therapy in glioblastoma.

EXPERIMENTAL DESIGN:

Ten paired samples of glioblastoma and respective glioblastoma-derived spheres (GS), cultured under stem cell conditions, were analyzed for the degree and pattern of MGMT promoter methylation by methylation-specific clone sequencing, MGMT gene dosage, chromatin status, and respective effects on MGMT expression and MGMT activity.

RESULTS:

In glioblastoma, MGMT-methylated alleles ranged from 10% to 90%. In contrast, methylated alleles were highly enriched (100% of clones) in respective GS, even when 2 MGMT alleles were present, with 1 exception (<50%). The CpG methylation patterns were characteristic for each glioblastoma exhibiting 25% to 90% methylated CpGs of 28 sites interrogated. Furthermore, MGMT promoter methylation was associated with a nonpermissive chromatin status in accordance with very low MGMT transcript levels and undetectable MGMT activity.

CONCLUSIONS:

In MGMT-methylated glioblastoma, MGMT promoter methylation is highly enriched in GS that supposedly comprise glioma-initiating cells. Thus, even a low percentage of MGMT methylation measured in a glioblastoma sample may be relevant and predict benefit from an alkylating agent therapy.

PMID:
21097691
DOI:
10.1158/1078-0432.CCR-10-1931
[Indexed for MEDLINE]
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