Abstract 4186: Monensin is selectively cytotoxic to cancer cells in an EMT-like state

Abstract

Abstract Metastatic, drug-resistant cancer is lethal. Epithelial-to-mesenchymal transition (EMT) is a type of phenotypic plasticity that has been implicated in cancer metastasis and drug resistance. One potential therapeutic approach is to specifically target cancer cells in an EMT-like state. In this study, we have developed a cell-based high-throughput screening (HTS) protocol using the high content Operetta imaging platform to identify EMT cytotoxic compounds. This screen was performed on epithelial (PC-3E) and mesenchymal-like (TEM 4-18) cell lines, both isolated from the parental PC-3 prostate cancer cell line based on their differential ability to invade an endothelial monolayer. A library of 2,640 compounds was screened on co-cultured PC-3E GFP cells and TEM 4-18 mCherry cells. After 72h exposure to compounds, relative numbers of GFP- and mCherry-positive cells were quantitated. Dose-response curves were established for each compound exhibiting a greater toxicity against EMT-like cells. The mechanisms of action of one of the most potent and selective compound against EMT-like cells, monensin, were further evaluated. Among the 2,640 compounds tested, salinomycin and monensin, both monovalent cation ionophores, displayed a potent and selective cytotoxic effect against EMT-like cells. A closely related compound absent from the compound library, nigericin, was also evaluated and appeared to be the most potent of the three compounds tested. Monensin (10nM) induced apoptosis, cell cycle arrest, and an increase in ROS production in TEM 4-18 cells. In addition, monensin rapidly induced swelling of Golgi apparatus, a previously known effect of monensin, in multiple cell lines most likely resulting in a blockage of intracellular protein trafficking and cell death. We then evaluated the toxicity of monensin in 24 human cancer cell lines and classified them as resistant or sensitive based on IC50 cutoff of 100nM. Supporting these findings, Gene Set Enrichment Analysis identified EMT as the top of the gene sets enriched in the sensitive group. Increased monensin sensitivity in EMT-like cells is associated with elevated uptake of H3-monensin compared to resistant cells. In conclusion, using a high-throughput screening approach, we identified monensin as a potent and specific inhibitor of cancer cells in an EMT-like state where it rapidly disrupts Golgi function. At least part of selectivity of monensin for EMT-like cells is due to increased uptake of this compound. Citation Format: Marion Vanneste, Huang Qin, Devon Moose, Mengshi Li, Michael Schultz, Meng Wu, Michael Henry. Monensin is selectively cytotoxic to cancer cells in an EMT-like state [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 4186.