IDH1-R132H acts as a tumor suppressor in glioma via epigenetic up-regulation of the DNA damage response.

Mutant IDH1 coexpressed with inactivating TP53 and ATRX mutations in glioma enhances DNA repair, causing resistance to genotoxic therapies. Linking glioma metabolism and DNA repair: Mutations in isocitrate dehydrogenase 1 (IDH1) are frequently found in gliomas and are associated with better outcomes. Núñez et al. discovered that, in addition to its roles in metabolism and epigenetics, mutant IDH1 also helps maintain genomic stability in tumors by enhancing the DNA damage response. This finding helps explain why patients with IDH1-mutant tumors have better survival despite their tumors being less sensitive to radiation than other gliomas. The authors also examined the mechanism for this phenomenon in mouse models and demonstrated that pharmacological inhibition of the DNA damage response sensitizes IDH1-mutant tumors to radiation, suggesting a potential direction for further therapeutic advances. Patients with glioma whose tumors carry a mutation in isocitrate dehydrogenase 1 (IDH1^R132H) are younger at diagnosis and live longer. IDH1 mutations co-occur with other molecular lesions, such as 1p/19q codeletion, inactivating mutations in the tumor suppressor protein 53 (TP53) gene, and loss-of-function mutations in alpha thalassemia/mental retardation syndrome X-linked gene (ATRX). All adult low-grade gliomas (LGGs) harboring ATRX loss also express the IDH1^R132H mutation. The current molecular classification of LGGs is based, partly, on the distribution of these mutations. We developed a genetically engineered mouse model harboring IDH1^R132H, TP53 and ATRX inactivating mutations, and activated NRAS G12V. Previously, we established that ATRX deficiency, in the context of wild-type IDH1, induces genomic instability, impairs nonhomologous end-joining DNA repair, and increases sensitivity to DNA-damaging therapies. In this study, using our mouse model and primary patient-derived glioma cultures with IDH1 mutations, we investigated the function of IDH1^R132H in the context of TP53 and ATRX loss. We discovered that IDH1^R132H expression in the genetic context of ATRX and TP53 gene inactivation (i) increases median survival in the absence of treatment, (ii) enhances DNA damage response (DDR) via epigenetic up-regulation of the ataxia-telangiectasia–mutated (ATM) signaling pathway, and (iii) elicits tumor radioresistance. Accordingly, pharmacological inhibition of ATM or checkpoint kinases 1 and 2, essential kinases in the DDR, restored the tumors' radiosensitivity. Translation of these findings to patients with IDH1^132H glioma harboring TP53 and ATRX loss could improve the therapeutic efficacy of radiotherapy and, consequently, patient survival. [ABSTRACT FROM AUTHOR]