Therapeutics , Targets , and Chemical Biology IDH 1 Mutations Alter Citric Acid Cycle Metabolism and Increase Dependence on Oxidative Mitochondrial Metabolism

Oncogenic mutations in isocitrate dehydrogenase 1 and 2 (IDH1/2) occur in several types of cancer, but the metabolic consequences of these genetic changes are not fully understood. In this study, we performed C metabolic flux analysis on a panel of isogenic cell lines containing heterozygous IDH1/2 mutations. We observed that under hypoxic conditions, IDH1-mutant cells exhibited increased oxidative tricarboxylic acid metabolism along with decreased reductive glutamine metabolism, but not IDH2-mutant cells. However, selective inhibition of mutant IDH1 enzyme function could not reverse the defect in reductive carboxylation activity. Furthermore, this metabolic reprogramming increased the sensitivity of IDH1-mutant cells to hypoxia or electron transport chain inhibition in vitro. Lastly, IDH1-mutant cells also grew poorly as subcutaneous xenografts within a hypoxic in vivo microenvironment. Together, our results suggest therapeutic opportunities to exploit the metabolic vulnerabilities specific to IDH1 mutation. Cancer Res; 74(12); 3317–31. 2014 AACR. Introduction Mutations in the metabolic enzymes isocitrate dehydrogenase 1 and 2 (IDH1/2) have been identified in a variety of tumor types, including acute myelogenous leukemia (AML), gliomas, cholangiocarcinomas, and chondrosarcomas (1–9). Thesemutations are almost exclusively heterozygous point mutations that occur in specific residues within the catalytic pocket, and are suggestive of activating, oncogenic mutations. Although IDH mutants are no longer capable of efficiently carrying out the normal oxidative reaction [converting isocitrate and NADPþ to a-ketoglutarate (aKG), CO2, and NADPH), IDHmutations result in a novel gain-of-function involving the reductive, NADPHdependent conversion of aKG to (D)2-hydroxyglutarate (2-HG; refs. 10, 11). 2-HG is not typically present at high levels in normal cells but accumulates considerably in cells with IDH1/2 mutations as well as in the tumors of patients with IDH1/2mutations, and has thus been termed an "oncometabolite" (10–12). Research into the oncogenic function of mutant IDH1/2 has focused in large part on the effects of 2-HG. Numerous reports have linked 2-HG accumulation to epigenetic changes, which are thought to contribute to alterations in cellular differentiation status (13–22). Additional mutant IDH phenotypes have also been reported, including changes in collagen maturation and hypoxia inducible factor-1a (HIF1a) stabilization (21, 23). These changes likely occur through inhibition of aKG-dependent dioxygenase activity by high levels of 2-HG. However, the diverse roles thataKG-dependent dioxygenases play in the cell and the numerous phenotypes associated with mutant IDH and 2-HG suggest that the phenotypes downstream of 2-HG induction could be cell typeor context-specific. We hypothesize that metabolic alterations induced by IDH mutations may also be present and might be a general phenotype that offers additional approaches to target these tumors. Previous work suggests that overexpression of mutant IDH alters the levels of several metabolites (24) and leads to increased sensitivity to glutaminase inhibitors (25). Studies by Leonardi and colleagues have indicated that the IDH1-mutant enzymes compromise the ability of this enzyme to catalyze the reductive carboxylation reaction (26). However, it is unclear how IDH mutations affect central carbon metabolism in the heterozygous cellular setting, and further exploration into how these metabolic differences could be therapeutically exploited is warranted. An important distinction between IDH1 and IDH2 is their localization in the cytosol/peroxisome and Authors' Affiliations: Novartis Institutes for Biomedical Research; Koch Institute for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts; Departments of Bioengineering and Pharmacology; and Moores Cancer Center, University of California, San Diego, La Jolla, California Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). A.R. Grassian and S.J. Parker contributed equally to this work. Current address of A.R. Grassian: Epizyme, Cambridge, MA. CorrespondingAuthors:ChristianM.Metallo, University ofCalifornia, San Diego, 9500 Gilman Drive, MC-0412, La Jolla, CA 92093. Phone: 858-5348209; Fax: 858-534-5722; E-mail: cmetallo@ucsd.edu; and Raymond Pagliarini, Novartis Institutes for Biomedical Research, 250Massachusetts Avenue, Cambridge, MA 02139. Phone: 617-871-4307; E-mail: raymond.pagliarini@novartis.com doi: 10.1158/0008-5472.CAN-14-0772-T 2014 American Association for Cancer Research. Cancer Research www.aacrjournals. org 3317 on April 28, 2017. © 2014 American Association for Cancer Research. cancerres.aacrjournals. org Downloaded from Published OnlineFirst April 22, 2014; DOI: 10.1158/0008-5472.CAN-14-0772-T