Abstract 382: Inhibition of BET bromodomain proteins as a therapeutic approach in prostate cancer

BET (bromodomain and extra-terminal) family proteins are epigenetic regulators known to control expression of genes involved in cell growth and oncogenesis. Selective small molecule BET inhibitors prevent binding of BET proteins to acetylated histones and inhibit transcriptional activation of BET target genes. BET inhibitors attenuate cell growth and survival in a number of hematologic cancer models, partially through down-regulation of the critical oncogene, MYC. We hypothesized that BET inhibitors will similarly regulate expression of MYC family genes (MYC, MYCN, MYCL1) in solid tumor models characterized by MYC family amplification or over-expression. We and others have recently shown activity for BET inhibitors in MYCN-amplified neuroblastoma models, with concomitant down-regulation of MYCN expression. Here we describe the effects of the highly specific BET inhibitor, I-BET762, on MYC expression and cell growth in prostate cancer models. I-BET762 treatment inhibited MYC expression accompanied by growth inhibition and decreased survival in prostate cancer cell lines that over-express MYC. In addition to MYC signatures, gene expression profiling in cell lines identified numerous cell cycle-associated genes as being significantly down-regulated by I-BET762. Importantly, our data suggests that I-BET762 effects are partially driven by MYC down-regulation and underlines the critical importance of additional mechanisms of I-BET762 induced phenotypes. Consistent with our in vitro observations, BET inhibition reduces MYC expression and tumor burden in a primary model of castration resistant prostate cancer that expresses high levels of MYC. Taken together, our data highlight the potential of BET inhibitors as a novel therapeutic approach to treat prostate tumors driven by MYC over-expression. Citation Format: Anastasia Wyce, Yan Degenhardt, Yuchen Bai, BaoChau Le, Susan Korenchuk, Ming-Chih Crouthamel, Charles F. McHugh, Robert Vessella, Caretha L. Creasy, Peter J. Tummino, Olena Barbash. Inhibition of BET bromodomain proteins as a therapeutic approach in prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 382. doi:10.1158/1538-7445.AM2014-382