Potent anti-androgens such as Enzalutamide (Enza) have been approved for the treatment of mCRPC. Despite initial response, nearly all patients eventually develop resistance to Enza. Although a few mechanisms of Enza resistance have been identified, none have been translated into a clinical benefit for recurrent patients. Our goal is to identify new therapeutic targets to overcome Enza resistance. We performed a genome-wide CRISPR activation screen using deactivated Cas9 (dCas9) fused to VP64 transcriptional activator in the androgen-dependent prostate cancer cell line (LNCaP). We used the Calabrese sgRNA library which targets 18,885 genes using 3 different sgRNAs per gene (56,762 sgRNAs). Cells expressing the gRNA library were treated with Enza (20µM) for 7 weeks to allow for enrichment of potential resistance genes. We identified 10 genes which were targeted by at least 2 sgRNAs with a Fold Change (FC) > 4 in the Enza vs control group. Notably, AR was the most enriched gene. AR up-regulation is one of the main drivers of Enza resistance in patients. Pathway enrichment analysis using all the sgRNAs with FC> 5 revealed an over-representation of the RB1, TP53 and TGF-β pathways. Importantly, these pathways are also known to drive Enza resistance. Our screen also identified new candidate genes that have never been linked to Enza resistance. Interestingly, most of these genes are transcription factors. We validated the screen results in vitro. Further analysis of this target genes in vitro and in vivo will allow us to identify novel genes and potential therapeutic targets for Enza resistance.

Citation Format: Yara Rodriguez, Rajita Vatapalli, Huyin Han, Kenji Unno, Vinay Sagar, Zachary Chalmers, Barbara Lysy, Young A Yoo, Mihai Truica, Sarki Abdulkadir. Genome-wide CRISPRa screen reveals new drivers of Enzalutamide resistance in prostate cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4102.