Molecular characterization of neuroendocrine prostate cancer (NEPC) and identification of new drug targets.

4536 Background: NEPC is an aggressive variant of prostate cancer that can arise de novo or from existing prostate adenocarcinoma (PCA), and is promoted by the use of hormonal therapy. We sought to better understand the molecular transformation of NEPC and identify new drug targets. METHODS Using Next Generation RNA sequencing and oligonucleotide arrays, we profiled 7 NEPC, 30 PCA, and 5 benign prostate (BEN), and validated findings on tumors from a large cohort of patients (30 NEPC, 118 PCA, 30 BEN) using IHC and FISH. Functional studies were performed using NCI-H660 (NEPC), VCaP and LNCaP (PCA), RWPE (BEN). RESULTS ERG rearrangement was present in 47% of NEPC, but ERG protein expression was absent and corresponded with lack of AR. There were significant molecular differences between NEPC and PCA, with 936/25932 genes differentially expressed (P<0.001). Aurora kinase A (AURKA) and N-myc (MYCN) were overexpressed in NEPC vs PCA (P<0.001), and both genes were amplified in 35% of NEPC, 5% of PCA, and none of BEN. Transfection of MYCN induced AURKA expression and kinase activity in vitro, and AURKA induced MYCN. Either MYCN or AURKA induced expression of neuroendocrine markers (SYP, NSE) in RWPE and LNCaP, and N-myc directly binds promoters of NSE, SYP, and AR to regulate their expression (and downstream androgen regulated genes). After validating NCI-H660 as model of NEPC, we observed enhanced in vitro and in vivo sensitivity to the Aurora kinase inhibitor PHA-739358 compared to LNCaP and VCaP, with > 50% tumor shrinkage in NEPC and minimal to no effect in PCA. Phospho-H3, a downstream marker of Aurora kinase activity, was inhibited in the treated NCI-H660 and not in PCA. Notably, NE marker expression was suppressed in the treated NCI-H660 xenografts, again supporting a role of Aurora kinase in modulating the NE phenotype. CONCLUSIONS There is likely clonal origin of NEPC from PCA (with ERG fusion in both), but ERG expression limited to PCA and driven by AR signaling. We discovered significant overexpression and amplification of AURKA and MYCN in NEPC and a small subset of PCA, and evidence that that they cooperate and induce a NE phenotype in prostate cells. In vitro and in vivo data confirms that these are novel drug targets for NEPC.