Department of Neurological Surgery, Northwestern University, Chicago, IL, USA.
Department of Pathology, Microbiology, and Immunology, UC Davis School of Veterinary Medicine, Davis, CA, USA.
J Cancer Res Clin Oncol. 2022 Sep;148(9):2275-2285. doi: 10.1007/s00432-022-04018-w. Epub 2022 Apr 25.
Mutations in isocitrate dehydrogenase 1/2 (IDH) identify a subset of gliomas that exhibit epigenetic dysregulation via aberrant DNA methylation. These tumors are ultimately fatal and lack effective therapeutic strategies. Considering the epigenetic dysregulation of IDH gliomas, we hypothesized that epigenetic-targeting drugs may yield therapeutic benefits in gliomas bearing IDH. One set of targets includes the bromodomain and extraterminal (BET) family of transcriptional coactivators.
We used TCGA data from glioma patients to determine whether BET proteins affect patient survival differently based on IDH status. Follow-up experiments using a set of IDH wildtype/mutant glioma cultures, as well as an IDH wildtype glioblastoma cell line expressing exogenous R132H IDH1, focused on cell health assays to investigate whether IDH was associated with increased sensitivity to the BET inhibitor JQ1. Immunoblots were used to evaluate the molecular response to JQ1 in these cultures.
We identified that high BRD4 expression associated with decreased survival only in IDH glioma patients. Cell viability analysis showed that IDH sensitized glioma cells to delayed cytotoxicity (10 days) in response to JQ1. Early effects of JQ1 (3 days) were primarily antiproliferative, with IDH glioma exhibiting a modest increase in sensitivity. Finally, exogenous R132H IDH1 expression in a resistant IDH wildtype cell line recapitulated the JQ1-mediated delayed cytotoxicity seen in our endogenous IDH glioma cells.
Overall, these data suggest that BRD4 enhances malignancy primarily in gliomas bearing IDH and is associated with greater sensitivity to BET inhibition. The finding that BET inhibition primarily exhibits delayed cytotoxicity may be overlooked in conventional short endpoint dose-response assays. Follow-up mechanistic and animal studies will help address the translational potential of these findings.
异柠檬酸脱氢酶 1/2（IDH）突变鉴定出一组表现为异常 DNA 甲基化的表观遗传失调的神经胶质瘤，这些肿瘤最终是致命的，并且缺乏有效的治疗策略。鉴于 IDH 神经胶质瘤的表观遗传失调，我们假设表观遗传靶向药物可能对携带 IDH 的神经胶质瘤产生治疗益处。一组靶标包括溴结构域和末端（BET）家族转录共激活剂。
我们使用来自神经胶质瘤患者的 TCGA 数据来确定 BET 蛋白是否根据 IDH 状态不同影响患者的生存。使用一组 IDH 野生型/突变型神经胶质瘤培养物以及表达外源性 R132H IDH1 的 IDH 野生型神经母细胞瘤细胞系的后续实验，重点关注细胞健康测定，以研究 IDH 是否与对 BET 抑制剂 JQ1 的敏感性增加相关。免疫印迹用于评估这些培养物对 JQ1 的分子反应。
我们发现 BRD4 高表达仅与 IDH 神经胶质瘤患者的生存率降低相关。细胞活力分析表明，IDH 使神经胶质瘤细胞对 JQ1 产生延迟的细胞毒性（10 天）敏感。JQ1 的早期作用（3 天）主要是抗增殖作用，IDH 神经胶质瘤的敏感性略有增加。最后，在耐药性 IDH 野生型细胞系中外源表达 R132H IDH1 再现了我们内源性 IDH 神经胶质瘤细胞中观察到的 JQ1 介导的延迟细胞毒性。
总的来说，这些数据表明 BRD4 主要增强 IDH 携带的神经胶质瘤的恶性程度，并与 BET 抑制的敏感性增加相关。BET 抑制主要表现出延迟的细胞毒性的发现可能在传统的短终点剂量反应测定中被忽视。后续的机制和动物研究将有助于解决这些发现的转化潜力。
