Abstract 1951: Identification of novel molecular targets for treatment of castration-resistant prostate cancer

Abstract

Abstract One of the major limitations of current therapies for treatment of prostate cancer is the acquisition of castration-resistance by tumor cells. Castration-resistant prostate cancer (CRPC) proceeds through multiple signaling pathways that utilize the PI3K/AKT axis to direct anti-apoptotic and pro-survival responses in CRPC cells. We performed in-depth genomic and phenotypic analysis which revealed that two transcription factors, Cyclic AMP Response Element Binding protein (CREB) and Forkhead Box O3 (FOXO3a), were inversely expressed in CRPC cells. Specifically, an upregulation of CREB in stage-specific manner in CRPC tumor cells was suggestive of its proliferative role in tumor growth. Conversely, downregulation of FOXO3a expression suggested inhibition of this transcription factor's pro-apoptotic function, which may also facilitate tumor growth. In pre-clinical models of CRPC, both CREB and FOXO3a transcriptionally regulated the function of prostate tumor suppressor, Par-4 (prostate apoptotic response gene-4). Promoter bashing studies identified consensus regulatory target binding sites of CREB and FOXO3a on Par-4 promoter. The sequential deletion of three CREB binding sites in the Par-4 promoter relieved CREB-mediated suppression of Par-4, whereas sequential deletion of FOXO3a binding sites in Par-4 promoter abrogated Par-4 promoter activity. We further dissected upstream events of CREB and FOXO3a, which are regulated by protein kinase-B AKT using a small-molecule AKT inhibitor (SMAI) drug. Overexpression of AKT in CRPC (DU-145/AKT, C4-2B/AKT and PC-3/AKT) cells induced pro-survival machinery by activating CREB and inhibiting pro-apoptotic function of FOXO3a and resulting in resistance of cells to drug. The in vivo efficacy of our SMAI drug was evaluated in DU-145/AKT and C4-2B/AKT tumor xenografts in nude mouse model. AKT overexpressing tumors exhibited aggressive growth rates and exhibited high vascularisation and angiogenesis as compared to vector-transfected tumors. Daily oral administration of SMAI drug significantly inhibited tumor growth in both DU-145 and C4-2B AKT-overexpressing tumors. IHC analysis of these tumor tissues revealed reduced FOXO3a expression and increased pCREB expression following treatment with SMAI drug in AKT versus control tumors. The cooperative effects of CREB and FOXO3a in AKT-mediated signaling suggests that the development of small molecule inhibitors targeting AKT/CREB function while simultaneously inducing FOXO3a/Par-4 activation in CRPC tumors, represents an attractive target for drug development. Citation Format: Jim Moselhy, Ram V. Roy, Suman Suman, Trinath P. Das, Murali Ankem, Chendil Damodaran. Identification of novel molecular targets for treatment of castration-resistant prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1951. doi:10.1158/1538-7445.AM2015-1951