Abstract 5472: Basal-like breast cancer subtype is characterized by deregulated glutamine metabolism and is sensitive to GLS inhibition
Authors: Henry Christophe , Lampa Michael , He Timothy , Ospina Beatriz , Zhang Bailin , Deng Gejing , Barberis Claude , Hoffmann Dietmar , Pollard Jack , Francisco Adrian , Arlt Heike , Reeves Jason , Murtie Joshua , Winter Christopher , Richon Victoria , Cheng Hong , Garcia-Echeverria Carlos , Wiederschain Dmitri , Srinivasan Lakshmi 
Published: August 2018

Abstract
Tumor cells display enhanced requirements for energy and building blocks such as amino acids, nucleic acids and lipids to sustain their proliferation. Metabolic demands of cancer cells are often met in the context of limited access to nutrients and the need to maintain redox balance. Glutamine catabolism is considered critical to cancer cell survival by not only delivering carbon and nitrogen atoms needed for nucleic acid and amino acid precursors but also by serving as the source of antioxidants such as NADPH and glutathione. A vital step in the catabolism of glutamine is its conversion to glutamate by the mitochondrial enzyme glutaminase (GLS).In this study, we confirmed the significance of GLS and enhanced glutamine utilization in the basal subtype of breast cancer as evidenced by higher GLS to GLUL (Glutamine synthetase) ratio in a panel of breast cancers in The Cancer Genome Atlas (TCGA) database. Using inducible shRNA mediated gene knockdown, we discovered that loss of GLS function in triple-negative breast cancer (TNBC) cell lines led to profound tumor growth inhibition in vitro and in vivo. This anti-tumor effect of GLS knockdown was rescued either using shRNA resistant cDNAs encoding both GLS isoforms or by addition of an a-ketoglutarate analog thus confirming the critical role of GLS in TNBC. Along with these observations, we have found that pharmacological inhibition of GLS with the small molecule inhibitor CB-839 reduced cell growth and led to a decrease in mammalian target of rapamycin (mTOR) coupled with an increase in the stress response pathway driven by activating transcription factor 4 (ATF4). In line with the observed impact on mTOR pathway we found that GLS inhibition synergizes with mTOR inhibition. In conclusion, our preliminary investigation revealed that glutaminolysis is deregulated in a majority of TNBC cancer patients. Our target credentialing studies confirmed that GLS is essential for the survival of TNBC cell lines and xenografts tumors. The synergistic activity of GLS and mTOR inhibitors in this specific breast cancer subtype suggests a new therapeutic modality that may bring benefit to TNBC patients with high unmet need.
Citation Format: Christophe Henry, Michael Lampa, Timothy He, Beatriz Ospina, Bailin Zhang, Gejing Deng, Claude Barberis, Dietmar Hoffmann, Jack Pollard, Adrian Francisco, Heike Arlt, Jason Reeves, Joshua Murtie, Christopher Winter, Victoria Richon, Hong Cheng, Carlos Garcia-Echeverria, Dmitri Wiederschain, Lakshmi Srinivasan. Basal-like breast cancer subtype is characterized by deregulated glutamine metabolism and is sensitive to GLS inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5472.