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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 13C 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., National Institutes of Health (U.S.) (Grants R01CA168653 and 5-P30-CA14051-39), David H. Koch Institute for Integrative Cancer Research at MIT. DFHCC Bridge Project, Burroughs Wellcome Fund, Smith Family Foundation, Virginia and D.K. Ludwig Fund for Cancer Research, Damon Runyon Cancer Research Foundation

Mutations in the genes encoding isocitrate dehydrogenase 1 and 2 (IDH1/2) occur in a variety of tumor types, resulting in production of the proposed oncometabolite, 2-hydroxyglutarate (2-HG). How mutant IDH alters central carbon metabolism, though, remains unclear. To address this question, we performed 13C metabolic flux analysis (MFA) on an isogenic cell panel containing heterozygous IDH1/2 mutations. We observe a dramatic and consistent decrease in the ability of IDH1, but not IDH2, mutant cell lines to utilize reductive glutamine metabolism via the carboxylation of α-ketoglutarate to isocitrate. Additionally we find that cells with IDH1 mutations exhibit increased oxidative tricarboxylic acid (TCA) metabolism. Similar metabolic trends were observed in vivo as well, and also in endogenous, non-engineered IDH1/2 mutant cell lines. Interestingly, IDH1-mutant specific inhibitors were unable to reverse the decrease in reductive metabolism, suggesting that this metabolic phenotype is independent of 2-HG. Furthermore, this metabolic reprogramming increases the sensitivity of IDH1 mutant cells to hypoxia or electron transport chain (ETC) inhibition in vitro. IDH1 mutant cells also grow poorly as subcutaneous xenografts within hypoxic in vivo microenvironments. These results suggest that exploiting metabolic defects specific to IDH1 mutant cells could be an interesting avenue to explore therapeutically. Citation Format: Alexandra R. Grassian, Seth Parker, Shawn Davidson, Ajit Divakaruni, Courtney Green, Xiamei Zhang, Kelly Slocum, Minying Pu, Fallon Lin, Chad Vickers, Carol Joud-Caldwell, Franklin Chung, Hong Yin, Erika Handly, Christopher Straub, Joseph D. Growney, Matt Vander Heiden, Anne Murphy, Raymond Pagliarini, Christian Metallo. IDH1 mutations alter citric acid cycle metabolism and increase dependence on oxidative mitochondrial metabolism. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-139. doi:10.1158/1538-7445.AM2014-LB-139

Mutations in isocitrate dehydrogenase 1 and 2 (IDH1/2) occur in a variety of tumor types. Although these mutations are loss-of-function for conversion of isocitrate to α-ketoglutarate, the mutant enzymes greatly increase the production of the proposed oncometabolite, 2-hydroxyglutarate (2-HG). However the full metabolic consequences of IDH1/2 mutation in their heterozygous cellular context have yet to be fully explored. To address this question, we utilized a panel of isogenic cell lines with wild-type IDH1/2 or clinically relevant IDH1/2 mutations and examined the metabolic consequences of IDH mutation using (13)C metabolic flux analysis (MFA). We observe a dramatic and consistent decrease in the ability of IDH1 mutant cell lines to utilize reductive glutamine metabolism via the carboxylation of α-ketoglutarate back to isocitrate. This was not seen either in IDH2 mutant cell lines or in wild-type cell lines treated with exogenous 2-HG. Consistent with these changes, the IDH1 mutant cell lines, but not IDH2 mutant or 2-HG treated cells, were deficient in the utilization of glutamine for de novo lipogenesis. Similar trends were observed in endogenous, non-engineered IDH1/2 mutant cell lines. The decrease in reductive carboxylation in the IDH1 mutant cell lines raises the hypothesis that these cells may be more reliant on mitochondrial metabolism. Indeed, IDH1 mutant cells were more sensitive to either treatment with an electron transport chain inhibitor or growth in hypoxia (which also inhibits mitochondrial metabolism). These results show heterozygous IDH1 mutation robustly impacts wild-type cellular metabolism in a different manner than IDH2 mutation. Furthermore, these results suggest that IDH1 and IDH2 mutant tumors may be differentially sensitive to inhibitors of specific metabolic pathways. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B159. Citation Format: Alexandra R. Grassian, Seth Parker, Shawn Davidson, Courtney Green, Fallon Lin, Carol Joud-Caldwell, Hong Yin, Franklin Chung, Christopher Straub, Matthew Vander Heiden, Raymond Pagliarini, Christian Metallo. Heterozygous IDH1 mutations modify the citric acid (TCA) cycle metabolism and sensitize cells to inhibition of mitochondrial respiration/oxidative phosphorylation. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B159.