Abstract PR02: Identification of Mechanisms of Resistance to Enzalutamide Treatment Using in Vitro Castration-Resistant Prostate Cancer Models

Abstract Prostate cancer (PCa) disproportionately affect African American (AA) men. Compared to their European American (EA) counterparts, AA men are at higher risk of developing PCa and more likely to develop metastatic castration-resistant PCa (mCRPC). Enzalutamide (ENZ), a second-generation antiandrogen for treatment of mCPRC, prolongs survival of patients; however, its overall benefit is modest (4.8 months) and most patients relapse in less than two years. To date, the molecular mechanism underlying ENZ resistance has not been well illustrated. Identifying molecular pathways underlying hormone therapy resistance is critical for developing novel combinatorial therapies to inhibit resistance, prevent tumor recurrence, and extend patient survival. Presently, in vitro models commonly used for research on PCa are of EA origin. A primary versus mCRPC model specific to AAs was developed by subjecting primary prostate tumor cell lines (non CRPC/AA)—RC77T, RC43T, RC165T to invasion chamber and ENZ selection pressure. The resulting castration Resistant prostate tumor isogenic cell lines—RC77T-CR, RC43T-CR, RC165T-CR (CRPC/AA) were maintained in K-SFM containing 10μM MDV3100. The primary prostate tumor non-CRPC/AA cell lines were epithelial in appearance, while the CRPC/AA lines appeared mesenchymal. To identify transcriptomic signatures associated with acquisition of ENZ resistance, we profiled gene expression in ENZ-sensitive and -resistant mCRPC cells using RNA sequencing. Analysis revealed a panel of 352 genes differentially expressed between non CRPC/AA and CRPC/AA cells. Comparison of CRPC/AA and CRPC/EA cell lines (C4-2B, PC3 and DU-145) revealed 1,005 DEGs, suggesting a substantial difference between EA and AA cell line models. Comparison between CRPC/AA and CRPC/EA identified 2,802 DEGs, while up to 6,104 DEGs were identified between EA and AA cells lines. Overlapping DEGs in the ENZ-sensitive and -resistant cells were ranked by gene set enrichment analysis (GSEA), which identified regulation of organelle organization, central nervous system development, regulation of hydrolase activity, cell proliferation, and regulation of cytokine production as the top five biologic pathways upregulated by the DEGs. LEF1, IGF2BP1, and TBC1D3 were the three most common genes associated with upregulated biologic processes. On the other hand, KRT4, EDAR, GJA5, and EDNA2 were the most common genes involved in downregulated biologic processes. The present results showed that different genes are expressed between EA and AA cell lines in general and between CRPC/EA and CRPC/AA. These transcriptional changes have potential for further study as predictive biomarkers and as targets of mCRPC treatment. Our findings suggest that RNA alteration profiling can identify potential mechanisms of ENZ resistance that may not only contribute to the recurrence of CRPC, but also serve as new targets for CRPC therapy. This abstract is also being presented as Poster B072. Citation Format: Joakin O. Mori, Hui-Xian Lin, Jason White, Alahni Becks, Raven Williams, Clayton Yates, Honghe Wang. Identification of mechanisms of resistance to enzalutamide treatment using in vitro castration-resistant prostate cancer models [abstract]. In: Proceedings of the Twelfth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2019 Sep 20-23; San Francisco, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl_2):Abstract nr PR02.