Abstract 5899: Genome-wide CRISPR-Cas9 screening identifies genetic vulnerabilities and potential therapeutic targets in castration resistant prostate cancer

Abstract

Abstract Background: Treatment options for castration-resistant prostate cancer (CRPC) are limited and only a few agents (e.g. enzalutamide, docetaxel) are routinely used in the clinic. Unfortunately, CRPC tumors will invariable develop resistance to these agents and only a subset of patients will respond. Thus, novel predictive biomarkers are urgently needed to ensure that an expensive and potentially harmful agent is given only to patients who will benefit from it. Furthermore, to enable new treatment strategies, a better understanding of drug resistance mechanisms is required. Methods: To identify novel drug resistance genes and mechanisms of therapy resistance, we performed genome-wide CRISPR-Cas9 knockout screens in LNCaP (hormone naïve) and in the isogenic C4 (castration resistant) PC cell line, respectively. Using 77,441 unique sgRNAs (Brunello library), a total of 19,114 protein-coding genes were tested for their potential functional role in enzalutamide or docetaxel resistance. Both IC50 and IC90 values were used for selection. MAGeCK was used to identify enriched and depleted sgRNAs (treatment vs. DMSO). Results: Among the highest ranked hits for the C4 dropout screens, several potential genetic vulnerabilities and mechanisms of resistance were identified, as knockout of specific genes sensitized C4 cells to enzalutamide. None of these hits were observed in LNCaP, which suggest CRPC-specific resistance mechanisms. For the positive screens, increased enzalutamide resistance was observed after knockout of genes encoding e.g. phosphokinases and specific solute carriers (SLCs) for C4 and LNCaP, respectively. Lastly, our results suggest that knockout of specific zinc finger nucleases (ZFNs), posttranslational modification enzymes or microtubule components may modulate docetaxel resistance in C4 cells. Conclusion: Drug resistance is a major clinical problem. Here, we identified genetic vulnerabilities that may be translated into predictive biomarkers, combination therapies and/or novel drug development strategies for CRPC. Citation Format: Jakob Haldrup, Linnéa Schmidt, Jakob S. Pedersen, Karina D. Sørensen. Genome-wide CRISPR-Cas9 screening identifies genetic vulnerabilities and potential therapeutic targets in castration resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5899.