Department of Neurological Surgery, University of California, San Francisco, San Francisco, California.
Department of Neurological Surgery, University of California, San Francisco, San Francisco, California
Cancer Res. 2014 Sep 1;74(17):4836-44. doi: 10.1158/0008-5472.CAN-14-0924. Epub 2014 Jul 17.
Isocitrate dehydrogenase 1 (IDH1) mutations occur in most lower grade glioma and not only drive gliomagenesis but are also associated with longer patient survival and improved response to temozolomide. To investigate the possible causative relationship between these events, we introduced wild-type (WT) or mutant IDH1 into immortalized, untransformed human astrocytes, then monitored transformation status and temozolomide response. Temozolomide-sensitive parental cells exhibited DNA damage (γ-H2AX foci) and a prolonged G2 cell-cycle arrest beginning three days after temozolomide (100 μmol/L, 3 hours) exposure and persisting for more than four days. The same cells transformed by expression of mutant IDH1 exhibited a comparable degree of DNA damage and cell-cycle arrest, but both events resolved significantly faster in association with increased, rather than decreased, clonogenic survival. The increases in DNA damage processing, cell-cycle progression, and clonogenicity were unique to cells transformed by mutant IDH1, and were not noted in cells transformed by WT IDH1 or an oncogenic form (V12H) of Ras. Similarly, these effects were not noted following introduction of mutant IDH1 into Ras-transformed cells or established glioma cells. They were, however, associated with increased homologous recombination (HR) and could be reversed by the genetic or pharmacologic suppression of the HR DNA repair protein RAD51. These results show that mutant IDH1 drives a unique set of transformative events that indirectly enhance HR and facilitate repair of temozolomide-induced DNA damage and temozolomide resistance. The results also suggest that inhibitors of HR may be a viable means to enhance temozolomide response in IDH1-mutant glioma.
异柠檬酸脱氢酶 1（IDH1）突变发生在大多数低级别胶质瘤中，不仅驱动胶质瘤的发生，而且与患者生存时间延长和对替莫唑胺的反应改善相关。为了研究这些事件之间可能存在的因果关系，我们将野生型（WT）或突变型 IDH1 导入永生化、未转化的人星形胶质细胞中，然后监测转化状态和替莫唑胺的反应。替莫唑胺敏感的亲本细胞在暴露于替莫唑胺（100μmol/L，3 小时）3 天后出现 DNA 损伤（γ-H2AX 焦点）和持续超过 4 天的 G2 细胞周期阻滞。表达突变型 IDH1 转化的相同细胞表现出类似程度的 DNA 损伤和细胞周期阻滞，但与克隆形成存活增加而非减少相关的情况下，这两种事件的解决速度明显加快。DNA 损伤处理、细胞周期进程和克隆形成能力的增加是突变型 IDH1 转化细胞所特有的，而在 WT IDH1 或致癌形式（V12H）Ras 转化的细胞中未观察到。同样，在将突变型 IDH1 导入 Ras 转化的细胞或已建立的神经胶质瘤细胞中也未观察到这些效应。然而，它们与同源重组（HR）的增加有关，并且可以通过 HR DNA 修复蛋白 RAD51 的遗传或药理学抑制来逆转。这些结果表明，突变型 IDH1 驱动了一组独特的转化事件，这些事件间接增强了 HR，并促进了替莫唑胺诱导的 DNA 损伤和替莫唑胺耐药性的修复。这些结果还表明，HR 的抑制剂可能是增强 IDH1 突变型神经胶质瘤中替莫唑胺反应的可行手段。
