Abstract 1023: Functional Genomics Reveals Dependency on 6-Phosphogluconate Dehydrogenase in OXPHOS-deficient Tumors

Abstract Cancer cells display metabolic properties distinct from normal cells and are therefore believed to be dependent on key metabolic enzymes. The effectiveness of targeting metabolism for cancer therapy has been largely restricted due to metabolic adaptability. We postulate that tumors with metabolic vulnerabilities will be limited in such adaptation, thus providing a unique opportunity for therapeutic intervention. Hereditary leiomyomatosis renal cell carcinoma (HLRCC) is a metabolically vulnerable cancer, due to mutations in a key TCA cycle enzyme - fumarate hydratase (FH), thus rendering them deficient in oxidative phosphorylation (OXPHOS). We performed a loss-of-function genetic screen in a FH-null HLRCC model (UOK262 cells) and identified 6-phosphogluconate dehydrogenase (6PGD) - a rate-limiting enzyme in the non-oxidative arm of pentose phosphate pathway - as a critical regulator of cell growth. Inhibition of 6PGD using either dox-inducible shRNA or a small molecule inhibitor dramatically blocks the growth of UOK262 cells, and in contrast, has no effect on 6PGD-deficient NB1 cells. The growth inhibition from knockdown is fully rescued by expressing shRNA-resistant 6PGD. Conversely, ectopic expression of 6PGD in NB1 cells results in a gain of function phenotype. Importantly, in vivo, 6PGD knockdown causes robust regression of established UOK262 xenografts. Mechanistically, 6PGD inhibition causes the accumulation of 6-phosphogluconate, blocks glycolysis, and induces ROS production. Furthermore, in tumors with intact TCA cycle, 6PGD inhibition shows synergism with OXPHOS Complex I inhibitor IACS-10759. Together, our data suggest that 6PGD is a bona fide oncology target and provide a strong rationale for developing small molecule inhibitors that could be used to treat OXPHOS-deficient tumors as single agent, or combined with inhibitors of OXPHOS. Citation Format: Yuting Sun, Madhavi Bandi, Timothy Lofton, Melinda Smith, Christopher Bristow, Norma Rogers, Chang Edward, Mary Geck Do, Yongying Jiang, Pietro Morlacchi, Florian Muller, Faika Mseeh, Barbara Czako, Wylie Palmer, Carlo Toniatti, Philip Jones, Giulio Draetta, Timothy Heffernan, Joseph Marszalek. Functional genomics reveals dependency on 6-phosphogluconate dehydrogenase in OXPHOS-deficient tumors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1023.