Abstract LB-290: Oncometabolites induce a BRCAness state that can be exploited by PARP inhibitors

2-Hydroxyglutarate (2HG) exists as two enantiomers, R-2HG and S-2HG, and both are implicated in tumor progression via their inhibitory effects on α-ketoglutarate (αKG)-dependent dioxygenases. The former is an oncometabolite that is induced by the neomorphic activity conferred by isocitrate dehydrogenase-1 and -2 (IDH1/2) mutations, while the latter is produced under pathologic process such as hypoxia. Recurring IDH1/2 mutations were first identified gliomas and acute myeloid leukemia (AML), and subsequently they were found in multiple other tumor types. Many IDH1/2-mutant tumors are known to be chemo- and radiosensitive, although the mechanisms underlying this enhanced sensitivity have been elusive. Here, we report that IDH1/2 mutations induce a homologous recombination (HR) defect which renders tumor cells exquisitely sensitive to Poly (ADP-Ribose) polymerase (PARP) inhibitors. Remarkably, this “BRCAness” phenotype can be completely reversed by small molecule mutant IDH1/2 inhibitors, and it can be entirely recapitulated by treatment with either 2HG enantiomer in cells with intact IDH1/2. We performed a comprehensive series of studies directly implicate two αKG-dependent dioxygenases, KDM4A and KDM4B, as key mediators of the observed phenotype. In addition, we demonstrate that 2HG-induced HR suppression cannot be explained by mutant IDH1/2-associated alterations in NAD+ levels. We have demonstrated IDH1/2-dependent PARP inhibitor sensitivity in a range of clinically relevant models, including primary patient-derived glioma cells and AML bone marrow cultures in vitro, as well as genetically-matched tumor xenografts in vivo. Finally, we have extended these findings to several structurally related and clinically relevant oncometabolites. We demonstrate profound synthetic lethality with PARP inhibitors in tumors which produce these other oncometabolites, and our data suggest a similar mechanism of action via which HR is suppressed. Small molecule inhibition of oncogenic kinases is a pillar of precision medicine in modern oncology, and this approach has been extrapolated to treat IDH1/2-mutant and other oncometabolite-producing cancers with small molecule inhibitors which block the neomorphic activity of the mutant proteins. The findings present here directly challenge this therapeutic strategy, and they instead provide a novel approach to treat these tumors oncometabolite-producing tumors with DNA repair inhibitors. Furthermore, our results uncover an unexpected link between oncometabolites, altered DNA repair and genetic instability. We previously reported that hypoxia suppresses HR, driving genetic instability and conferring a BRCAness phenotype in hypoxic tumor cells. It is tempting to speculate that the findings reported here provide a novel commonality between hypoxia and IDH1/2 mutations as mediating a “hit-and-run” mechanism for genetic instability and tumor progression through 2HG, but at the same time bestowing a vulnerability to PARP inhibition that can be therapeutically exploited. Based on these findings, we are planning a multi-center Phase II trial testing the efficacy of olaparib for the treatment of recurrent IDH1/2-mutant tumors, and we anticipate this trial will be open for enrollment later this year. Citation Format: Parker Sulkowski, Christopher Corso, Nathaniel Robinson, Susan Scanlon, Karin Purshouse, Hanwen Bai, Yanfeng Liu, Ranjini Sundaram, Denise Hegan, Nathan Fons, Gregory Breuer, Yuanbin Song, Ketu Mishra, Henk De Feyter, Robin de Graaf, Yulia Surovtseva, Maureen Kachman, Stephanie Halene, Murat Gunel, Peter Glazer, Ranjit S. Bindra. Oncometabolites induce a BRCAness state that can be exploited by PARP inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-290. doi:10.1158/1538-7445.AM2017-LB-290