Copy number analysis to identify tumor suppressor genes associated with enzalutamide (Enza) resistance and poor prognosis in metastatic castration-resistant prostate cancer (mCRPC) patients

5011 Background: Although enza prolongs life in mCRPC pts, the development of drug resistance and subsequent disease progression is nearly universal. Seeking to clarify molecular mechanisms that underlie enza resistance, we analyzed whole genome sequencing (WGS) and RNA sequencing (seq) of tumors obtained from patients with enza-naive or -resistant mCRPC. Methods: One hundred and one men with mCRPC who underwent image-guided biopsy and subsequent WGS were included (n = 64 with enza-naive and n = 37 with enza-resistant mCRPC). The differential copy number alteration (CNA) events enriched in enza-resistant vs. naïve samples were determined, and the prognostic significance of differential CNAs was assessed. RNA-seq data were evaluated to confirm that CNAs correlated with changes in gene expression of relevant loci and to identify potentially druggable targets selectively activated in tumors with specific CNAs. Results: Copy number loss was more common than gain in enza-resistant tumors. Specifically, we identified 123 protein-coding genes that were more commonly lost in enza-resistant samples—eight of which were previously described tumor suppressor genes. There was a strong concordance of copy number loss and reduced mRNA expression of these genes. We identified one gene from this list of eight genes whose copy number loss was associated with poor overall survival (median overall survival from date of CRPC was 19.1 months in tumors with gene loss vs. 42.0 months in intact tumors, hazard ratio 3.8 [1.46–9.8], log-rank p = 0.003). Finally, Master Regulator analysis determined that tumors with copy number loss of this poor prognosis gene had activation of several potentially targetable factors, including the kinases Akt and PLK1. Conclusions: Copy number loss of specific tumor suppressor genes is associated with enza resistance in mCRPC patients. Previously unappreciated molecular subsets of enza-resistant CRPC were identified, including one subset associated with poor clinical outcome.