Abstract LB-072: The N-Myc transcriptional program driving the neuroendocrine prostate cancer phenotype

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA Although neuroendocrine prostate cancer (NEPC) rarely arises de novo, up to 30% of patients with prostate adenocarcinoma (PCa) develop NEPC features in later stages of their disease as a mechanism of treatment resistance to hormonal therapies including abiraterone and enzalutamide. NEPC is clinically more aggressive than PCa, commonly metastases to visceral organs such as liver and brain, and can be suspected in patients with progressive disease and a disproportionately low serum PSA. There is currently no effective therapy for NEPC, and most patients with NEPC survive less than one year. The development of novel treatment strategies for patients with NEPC represents a significant clinical unmet need. We have previously discovered significant over-expression and gene amplification of AURKA (encoding Aurora-A) and MYCN (encoding N-Myc) in NEPC as compared to prostate adenocarcinoma. As in neuroblastoma, N-Myc interacts with Aurora-A in NEPC which leads to a co-stabilization of both proteins that is targetable with allosteric inhibitors of Aurora A. We have also shown that ectopic expression of N-Myc induces neuroendocrine transformation of prostate adenocarcinoma cells. However, the molecular mechanisms that underlie N-Myc driven NEPC phenotype have yet to be characterized. To address this, we performed RNA-sequencing (RNAseq) and ChIP-sequencing from multiple stable prostate adenocarcinoma cells with and without N-Myc over-expression. We have identified a signature of N-Myc deregulated genes that are both biologically and clinically relevant. Based on RNAseq data from 128 clinical samples (17 NEPC, 10 castrate resistant prostate cancer 68 prostate adenocarcinoma patient tumors and 33 matched benign prostate samples) we found that majority (70%) of the N-Myc deregulated genes identified in our in vitro models distinguish the NEPC from PCa tumor samples. Based on GSEA and pathway analysis we found that N-Myc induces a profile enriched in pro-metastatic, dedifferentiation and Polycomb Repressive Complex deregulated genes and dramatically reduces AR signaling. Furthermore we show that N-Myc is recruited to AR-bound enhancers of AR target genes. To further determine the role of N-Myc in driving the NEPC phenotype we have generated transgenic mice that carry an integrated MYCN gene behind a lox-stop-lox (LSL) cassette at the ROSA26 locus, a floxed Pten locus and a tamoxifen-activated Cre recombinase driven by Tmprss2. N-Myc over-expression in the context of Ptenfl/+ leads to focal high levels of activated AKT pathway that accompany mouse high grade prostatic intraepithelial neoplasia (mHGPIN) at 3 months post-induction and other clinically relevant molecular changes. Littermates that harbor Ptenfl/+ alone do not display mHGPIN or AKT activation. In the context of Pten homozygous loss (Ptenfl/fl), N-Myc is associated with diffuse mHGPIN in the ventral and dorsolateral prostate lobes and irregular gland borders, nuclear atypia and high levels of AKT activity at 3 months (MYCN homozygous) or 6 months (MYCN heterozygous) post-induction. In conclusion, our findings support the role of N-Myc as one of the drivers of the NEPC phenotype and have the potential to ultimately lead to the identification of a new class of disease specific biomarkers and therapeutic alternatives for this aggressive subgroup of prostate cancer. Citation Format: Etienne Dardenne, Kaitlyn Gayvert, Adeline Berger, Andrea Sboner, Brian Robinson, Kenneth Hennrick, Juan Miguel Mosquera, Cynthia Cheung, Martin Eilers, Himisha Beltran, Mark A. Rubin, Olivier Elemento, David S. Rickman. The N-Myc transcriptional program driving the neuroendocrine prostate cancer phenotype. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-072. doi:10.1158/1538-7445.AM2015-LB-072