Abstract: PD37-09
Sources of Funding: Andersen-Hebbeln Prostate Cancer Research Fund

Introduction

Metastasis, the major driver of mortality in advanced prostate cancer, starts in the prostate when cancer cells start to invade the surrounding stromal tissue. This first step may involve EMT characterized by the loss of epithelial characteristics and the gain of mesenchymal features. Thus, developing therapeutic compounds specifically targeting this process may provide a therapeutic opportunity.

Methods

In this study, we have developed a cell-based high-throughput screening protocol using the high content Operetta imaging platform to identify EMT cytotoxic compounds. A library of 2,640 compounds (Microsource) was screened on a co-culture of epithelial-like prostate cancer cells (PC3E GFP cells) and EMT-like prostate cancer cells (TEM 4-18 mCherry cells), both derived from the PC-3 cell line. After 72h exposure to compounds, relative numbers of GFP- and mCherry-positive cells were quantitated using the Operetta system. Dose-response curves were established for each compound exhibiting a greater toxicity against EMT-like cells. _x000D_

Results

Among the compounds tested, monensin and salinomycin, both monovalent cation ionophores, exhibited a relatively greater toxicity against EMT-like cells. The highest potency and selectivity for the EMT-like cells was obtained with nigericin, another monovalent cation ionophore, followed by monensin and salinomycin. In addition to inducing apoptosis and a cell cycle arrest, monensin rapidly induced a swelling of golgi apparatus most likely resulting in a blockage of intracellular protein trafficking leading to cell death. In addition, we evaluated the toxicity of monensin in 24 cancer cell lines from different origins and classified them as resistant or sensitive. We analyzed publically available gene expression data and performed a Gene Set Enrichment Analysis to identify the gene sets differentially represented in the two groups. Supporting our hypothesis, the gene set involving EMT was enriched in the sensitive group.

Conclusions

In this study we identified monensin, salinomycin and nigericin as potent EMT-selective cytotoxic compounds. Understanding the mechanism-of-action of these compounds may lead to insight about the metastatic process and point to new therapeutic directions.

Funding

Andersen-Hebbeln Prostate Cancer Research Fund