EZH2 inhibition sensitizes IDH1R132H mutant gliomas to Panobinostat

Isocitrate Dehydrogenase-1 (IDH1) is commonly mutated in lower grade diffuse gliomas. The IDH1R132H mutation is an important diagnostic tool for tumor diagnosis and prognosis, however its role in glioma development, and its impact on response to therapy, is not fully understood. We developed a murine model of proneural IDH1R132H mutated glioma that shows elevated production of 2-Hydroxyglutarate (2-HG) and increased tri-methylation of lysine residue K27 on histone H3 (H3K27me3) compared to IDH1 wild-type tumors. We found that using Tazemetostat to inhibit the methyltransferase for H3K27, Enhancer of Zeste 2 (EZH2), reduced H3K27me3 levels and increased acetylation on H3K27. We also found that, although the histone deacetylase inhibitor (HDACi) Panobinostat was less cytotoxic in IDH1R132H mutated cells (either isolated from murine glioma or oligodendrocyte progenitor cells infected in vitro with a retrovirus expressing IDH1R132H) compared to IDH1-wildtype cells, co-treatment with Tazemetostat is synergistic in both mutant and wildtype models. These findings indicate a novel therapeutic strategy for IDH1-mutated gliomas that targets the specific epigenetic alteration in these tumors. To determine the effect of IDH1 R132H mutation on gliomagenesis, we established an in vivo and in vitro model for both mutant and wildtype IDH1 murine gliomas initated by targeting glial progenitors of the subcortical white matter. We performed transcriptional profiling by RNA-seq on the IDH1R132H mutant and wildtype tumors to determine if these tumors would recapitulate the molecular profile of human proneural gliomas from the Verhaak et al. subtype classifers gene signatures. We compared the expression profile of the wildtype (N=5) and IDH1R132H (n=6) endstage murine tumors to the TCGA database using Gene Set Enrichment Analysis (GSEA),

异柠檬酸脱氢酶1（Isocitrate Dehydrogenase-1, IDH1）在低级别弥漫性胶质瘤中常发生突变。IDH1R132H突变是肿瘤诊断与预后评估的重要标志物，但其在胶质瘤发生发展中的作用，以及对治疗应答的影响尚未完全阐明。我们构建了原神经型IDH1R132H突变胶质瘤的小鼠模型，与IDH1野生型肿瘤相比，该模型的2-羟基戊二酸（2-Hydroxyglutarate, 2-HG）生成水平升高，且组蛋白H3第27位赖氨酸三甲基化修饰（H3K27me3）水平显著上调。我们发现，使用他泽司他（Tazemetostat）抑制H3K27甲基转移酶Zeste同源物2增强子（Enhancer of Zeste 2, EZH2），可降低H3K27me3水平，并上调H3K27位点的乙酰化修饰。我们同时发现，相较于IDH1野生型细胞，组蛋白去乙酰化酶抑制剂（HDACi）帕比司他（Panobinostat）对IDH1R132H突变细胞（包括从小鼠胶质瘤中分离的细胞，或体外用携带IDH1R132H的逆转录病毒感染的少突胶质前体细胞）的细胞毒性更弱，但在突变型与野生型模型中，他泽司他与帕比司他联合给药均具有协同效应。上述研究结果为靶向IDH1突变胶质瘤特异性表观遗传改变的新型治疗策略提供了实验依据。为明确IDH1 R132H突变对胶质瘤发生的影响，我们通过靶向皮层下白质的胶质前体细胞，构建了突变型与野生型IDH1小鼠胶质瘤的体内及体外模型。我们对IDH1R132H突变型及野生型肿瘤进行RNA测序（RNA-seq）转录组分析，以验证这些小鼠肿瘤是否能够复现Verhaak等基于亚型分类基因特征定义的人类原神经型胶质瘤的分子谱特征。我们使用基因集富集分析（Gene Set Enrichment Analysis, GSEA），将5例野生型及6例IDH1R132H突变型终末期小鼠肿瘤的表达谱与癌症基因组图谱（The Cancer Genome Atlas, TCGA）数据库进行比对。