Abstract 3083: Targeting androgen receptor coregulators to enhance enzalutamide sensitivity in prostate cancer

Abstract Steroid hormone signaling axes drive proliferation and survival in prostate cancer (PCa), breast and other cancers. In late stage PCa, the androgen receptor (AR) is therapeutically antagonized with success, for example with Enzalutamide (Enza). Although initially successful, resistance emerges associated with tissue plasticity and patient mortality. Enza-resistance mechanisms include altered AR coregulator interactions. Identifying which coregulators change Enza sensitivity is attractive as they may represent new drug targets but challenging given the multitude of coregulators expressed in PCa and the diverse roles they play in transcription and translation.To meet this challenge, we designed a bioinformatic workflow to identify under-investigated yet clinically-impactful coregulators. We tested coactivators (CoA, n~750), corepressors (CoR, n ~600), and mixed function coregulators (Mixed, n~600) associations with patient outcome in TCGA PCa cohorts; applied partial correlation analyses to reveal coregulators that impacted AR target genes; utilized DepMap essentiality scores to rank importance; and examined interactions in publicly available AR RIME data. The impact of the top ranked coregulators (n=18) on Enza sensitivity was examined using shRNA or siRNA approaches, and with inhibitor drugs in Enza-resistant PCa cell lines (LNCaP C42B, 22Rv1). Finally, coregulator expression was examined in single cell RNA-Seq from PCa 3D organoids derived from the PBCre4:Ptenf/f:Rb1f/f (DKO) and the PBCre4:Ptenf/f:Rb1f/f:Trp53f/f (TKO) PCa mouse model, which recapitulate the loss of Enza sensitivity and lineage plasticity. ShRNA targeting coregulators was undertaken in organoids. The bioinformatics workflow identified 18 coregulators, including CoA (e.g., WDR5, KAT7, BLM, SMARCC1), CoR (e.g., SETDB1, PSPC1), and Mixed (e.g., KDM5A, BPTF, TCEGR1) to screen for impact on Enza. KAT7 shRNA modulated Enza sensitivity, regulated expression of AR target genes, and synergized with a KAT7 inhibitor (WM3835) to enhance Enza sensitivity. Similarly, a BLM inhibitor (ML216) synergized with Enza. Interestingly, although WDR5 siRNA alone did not alter Enza responses, the combination of KAT7 shRNA and WDR5 siRNA significantly potentiated Enza responses. Similarly, SMARCC1 shRNA cooperated with siRNA to several targets (TBX3, BPTF, or SETDB1) to enhance Enza responses. Smarcc1 and Tbx3 were upregulated in Enza-resistant neuroendocrine PCa, and the recently identified Pou2f3 Enza-resistant phenotypes, and Bptf was upregulated in the Tff3 Enza-resistant phenotype. We have shRNA targeted Blm, Smarcc1, Tbx3, and Bptf in the DKO and TKO organoids and are measuring the impact of Enza responses. Overall, we have identified potentially novel AR coregulators that associate with the development of therapy resistance and shown that targeting these coregulators may augment Enza sensitivity in PCa. Citation Format: Rayzel C. Fernandes, Debasis Nayak, Damien A. Leach, Meenalakshmi Chinnam, Wilbert Zwart, David W. Goodrich, Moray J. Campbell, Charlotte L. Bevan. Targeting androgen receptor coregulators to enhance enzalutamide sensitivity in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3083.