Abstract 5604: Preclinical antitumor activity of novel small molecule glutaminase inhibitors in triple-negative breast cancer.

Abstract

Abstract Many tumor cells are dependent on glutamine (Gln) and Gln-derived metabolites to meet bioenergetic and biosynthetic demands. A key cellular reaction in the utilization of Gln is its deamidation by the enzyme glutaminase to yield glutamate (Glu). We have developed a series of potent and selective small molecule glutaminase inhibitors for evaluation as novel cancer therapeutics. These inhibitors exhibit 5-20 nM potency against the broadly-expressed form of glutaminase (GLS) with minimal activity against the liver form of the enzyme (GLS2). Expression analysis (see below) has identified triple-negative breast cancer (TNBC) as a potential clinical target population for GLS inhibitors. TNBC is a poor prognosis breast cancer subtype lacking estrogen receptor (ER), progesterone receptor (PR) and the growth factor receptor Her2. TNBC is insensitive to approved targeted therapies (ER antagonists and anti-Her2 agents) and is currently treated with conventional cytotoxic drugs. Therefore, TNBC represents a critical unmet medical need for which new targeted therapeutics are urgently needed. Analysis of a primary breast tumor mRNA expression dataset (The Cancer Genome Atlas; n=756) revealed that low ER, PR, and Her2 expression is associated with high GLS expression and low expression of both GLS2 and glutamine synthetase, an enzyme that opposes the action of glutaminase by synthesizing Gln from Glu. This expression pattern, together with published work on the Gln dependence of breast tumor cell lines [Kung et al. (2011) PLOS Genet 7:e1002229] suggests that TNBC may be particularly dependent on GLS. To test this hypothesis, we evaluated the anti-tumor activity of our GLS inhibitors on a panel of breast tumor-derived cell lines (n>25) that included a mixture of TNBC and ER-positive subtypes. The TNBC subtype displayed the greatest sensitivity to GLS inhibitor treatment (IC50s ranging from 5-100 nM) and this sensitivity correlated with a dependence on extracellular Gln for cell growth. In the TNBC cell line MDA-MB-231 the antiproliferative effect of the GLS inhibitor was associated with a dose-dependent accumulation of Gln and depletion of Glu. Additionally, GLS inhibition showed additive in vitro activity in combination with paclitaxel, a standard-of-care treatment in TNBC. In a mouse orthotopic tumor xenograft model with MDA-MB-231 cells implanted in the mammary fat pad, oral delivery of a GLS inhibitor caused an accumulation of tumor Gln, a reduction in tumor Glu, and enhanced the anti-tumor efficacy of the paclitaxel. Experiments aimed at expanding this observation with other TNBC xenograft models are in progress. Overall, these results demonstrate that a selective inhibitor of GLS, either as a single agent or in combination with standard-of-care chemotherapeutics, may be effective as a targeted therapeutic in TNBC. Citation Format: Susan Demo, Tania Chernov-Rogan, Matthew Gross, Julie Janes, Raja Kawas, Evan Lewis, Francesco Parlati, Hector Rodriguez, Mirna Rodriguez, Jinfu Yang, Frances Zhao, Adam Richardson, Mark K. Bennett. Preclinical antitumor activity of novel small molecule glutaminase inhibitors in triple-negative breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5604. doi:10.1158/1538-7445.AM2013-5604