The enzyme glutaminase (GLS1) is currently in clinical trials for oncology, yet there are no clear diagnostic criteria to identify responders. The evaluation of 25 basal breast lines expressing GLS1, predominantly through its splice isoform GAC, demonstrated that only GLS1-dependent basal B lines required it for maintaining de novo glutathione synthesis in addition to mitochondrial bioenergetics. Drug sensitivity profiling of 407 tumor lines with GLS1 and gamma-glutamylcysteine synthetase (GCS) inhibitors revealed a high degree of co-dependency on both enzymes across indications, suggesting that redox balance is a key function of GLS1 in tumors. To leverage these findings, we derived a pan-cancer metabolic signature predictive of GLS1/GCS co-dependency and validated it in vivo using four lung patient-derived xenograft models, revealing the additional requirement for expression of GAC above a threshold (logRPKM + 1 ≥ 4.5, where RPKM is reads per kilobase per million mapped reads). Analysis of the pan-TCGA dataset with our signature identified multiple indications, including mesenchymal tumors, as putative responders to GLS1 inhibitors.

Platinum-based drugs have been used to successfully treat diverse cancers for several decades. Cisplatin, the original compound of this class, cross-links DNA, resulting in cell cycle arrest and cell death via apoptosis. Cisplatin is effective against several tumor types, yet it exhibits toxic side effects and tumors often develop resistance. To mitigate these liabilities while maintaining potency, we generated a library of non-classical platinum-acridine hybrid agents and assessed their mechanisms of action using a validated genome-wide screening approach in Saccharomyces cerevisiae and in the distantly related yeast Schizosaccharomyces pombe. Chemogenomic profiles from both S. cerevisiae and S. pombe demonstrate that several of the platinum-acridines damage DNA differently than cisplatin based on their requirement for distinct modules of DNA repair.

Glutaminase is a key enzyme for the conversion of glutamine to glutamate with subsequent use as a fuel in the TCA cycle, glutathione production and protein synthesis. A subset of tumor cells shows preferential dependency on glutamine and glutaminase for cell proliferation and survival, consistent with “metabolic addiction” to this pathway. Between two glutaminase loci in the genome, the gene for kidney-type glutaminase (Gls1) has 2 alternatively spliced products (KGA and GAC), with distinct regulation and expression from liver-type glutaminase (Gls2). Furthermore, based on distinct C-termini and enzymatic properties, it has been proposed that the Gls1 alternatively spliced isoforms (KGA and GAC) may themselves have distinct functions. Our data further elucidates the role of glutaminase in cancer by addressing the following key questions: a) what is the major role of glutaminase in cells most sensitive to its inhibition? b) is GAC interchangeable with KGA in its expression pattern and role in tumor cells? c) how do tumors adapt to glutaminase inhibition? By generating and using a panel of GAC and KGA isoform-selective reagents we show that the two isoforms have distinct patterns of expression and distinct roles in cell proliferation, migration and tumor growth in vivo. In addition, based on metabolomics, functional and complementation assays, we propose a mechanistic basis for tumor cell dependency on glutaminase and the tumor adaptive response to glutaminase inhibition. Our data reveal the basis for the addiction of tumor subsets to glutaminase and elucidate the role of distinct isoforms of kidney-type glutaminase isoforms in cancer. Citation Format: Bonnie Liu, Kyung Song, Mandy Kwong, Min Gao, Rebecca Hong, Michelle Nannini, Deepak Sampath, Marcia Belvin, David Peterson, Marie Evangelista, Anneleen Daemen, Ron Firestein, Georgia Hatzivassiliou. Elucidating the role of distinct glutaminase isoforms in 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 4618. doi:10.1158/1538-7445.AM2013-4618