Mechanistic evaluation and transcriptional signature of a Glutathione S-transferase Omega 1 inhibitor

Glutathione S-transferase omega 1 (GSTO1) is an atypical GST isoform that is overexpressed in several cancers and has been implicated in drug resistance. Currently, no small-molecule drug targeting GSTO1 is under clinical development. In this study we show that silencing of GSTO1 with siRNA significantly impairs cancer cell viability, validating GSTO1 as a potential new target in oncology. We report on the development and characterization of a series of chloroacetamide-containing potent GSTO1 inhibitors. Co-crystal structures of GSTO1 with our inhibitors demonstrate covalent binding to the active site cysteine. These potent GSTO1 inhibitors suppress cancer cell growth, enhance the cytotoxic effects of cisplatin, and inhibit tumor growth in colon cancer models as single agent. Bru-seq-based transcription profiling unraveled novel roles for GSTO1 in cholesterol metabolism, oxidative and endoplasmic stress responses, cytoskeleton, and cell migration. Our findings demonstrate the therapeutic utility of GSTO1 inhibitors as anticancer agents and identify novel cellular pathways under GSTO1 regulation in colorectal cancer. HCT116 (human colorectal carcinoma) cells were exposed to DMSO, C1-27 or C1-14 for 4 h and GSTO1 siRNA or C1-27 for 24 h, followed by labeling of nascent RNA using bromouridine.