Therapeutic Discovery High-Throughput Screen Identifies Novel Inhibitors of Cancer Biomarker a-Methylacyl Coenzyme A Racemase (AMACR/P504S)

a-methylacyl coenzyme A racemase (AMACR) is a metabolic enzyme whose overexpression has been shown to be a diagnostic indicator of prostatic adenocarcinoma and other solid tumors. Here, we confirm that attenuation of AMACR expression diminishes the growth of prostate cancer cell lines by using stably expressed short-hairpin RNA constructs. This observation strongly suggests that the AMACR enzymemay be a target for therapeutic inhibition in prostate cancer. To this end, we report here a novel assay capable of screening libraries of diverse small molecules for inhibitors of AMACR activity. This assay facilitated the screening of approximately 5,000 unique compounds and the discovery of 7 distinct chemical entities capable of inhibiting AMACR at low micromolar concentrations. The most potent inhibitor discovered is the selenoorganic compound ebselen oxide [inhibitory concentration (IC50): 0.80 mmol/L]. The parent compound, ebselen (IC50: 2.79 mmol/L), is a covalent inactivator of AMACR (KI(inact): 24 mmol/L). Two of the AMACR inhibitors are selectively toxic to prostate cancer cell lines (LAPC4/LNCaP/PC3) that express AMACR compared to a normal prostate fibroblast cell line (WPMY1) that does not express the protein. This report shows the first high-throughput screen for the discovery of novel AMACR inhibitors, characterizes the first nonsubstrate-based inhibitors, and validates that AMACR is a viable chemotherapeutic target in vitro. Mol Cancer Ther; 10(5); 825–38. 2011 AACR.