Abstract 3844: Targeting EZH2 in neuroendocrine prostate cancer

Abstract

Abstract Background and aim of the study EZH2 is the catalytic subunit of the Polycomb repressive complex 2 (PRC2) and it is involved in controlling gene expression through trimethylation of histone H3 lysine 27 (H3K27me3), a key mechanism that regulates chromatin structure and gene silencing. EZH2 is overexpressed in a wide range of cancers including prostate. Recent findings show that EZH2 can form a complex with the androgen receptor (AR), enhancing its transcriptional activity. However the role of EZH2 in AR low/negative prostate cancer has not been previously investigated. Long-term exposure to AR targeted therapies can cause an adaptive response mechanism in a subset of advanced prostate cancers. Often this adaptation is associated with loss of AR expression, clinical aggressiveness, and pathologic features of small cell or neuroendocrine carcinoma. This AR independent resistant phenotype is broadly termed neuroendocrine prostate cancer (NEPC). Initial studies from our lab have highlighted a landscape of genomic alterations that characterize NEPC. In this study we explore the hypothesis that the epigenetic modifier, EZH2, can lead the adaptive response towards an androgen-independent phenotype and towards NEPC. Results Using Next Generation RNA-sequencing, we profiled tumors from a cohort of patients including 20 NEPC, 68 Prostate Adenocarcinoma (PCa), and 19 castration resistant prostate cancer (CRPC) and we discovered that EZH2 is highly expressed in NEPC (characterized by low or absent AR and morphologic changes). These findings were also confirmed at protein level by immunohistochemistry. Based on the driving role of EZH2 in other tumor types and significant overexpression in NEPC tumors, we evaluated the effects of the EZH2 inhibitor, GSK343, in NEPC cells (NCI-H660) and PCa cells (LNCaP and DU145) in 3D Matrigel cultures. GSK343 effectively inhibited H3K27me3 and resulted in a significant reduction of NCI-H660 viability, measured with an ATP-based assay, whereas LNCaP and DU145 cells were minimally affected after 7 or 14 days of treatment. Using a custom designed Nanostring assay, we also demonstrated a significant increase in the expression of AR signaling genes (e.g. PSA, PSMA) and decrease in NEPC-associated genes (e.g. chromogranin A, AURKA, ENO2) when NEPC cells were treated with GSK343. These data suggest a modulation of the neuroendocrine phenotype via EZH2. We therefore extended these drug studies to patient-derived organoid models including both CRPC and NEPC organoids and we observed similar results with preferential sensitivity of the AR-negative NEPC organoids compared to AR-positive CRPC organoids and similar reversion of downstream AR/NEPC gene expression. Conclusions Altogether, these data suggest that EZH2-mediated epigenetic changes contribute to the AR-independent NEPC resistant phenotype, and this effect can be reverted or delayed by targeting EZH2 activity. EZH2 represents a promising drug target and a potential modulator of the NEPC phenotype. Citation Format: Loredana Puca, Dong Gao, Myriam Kossai, Clarisse Marotz, Juan Miguel Mosquera, Theresa Y. MacDonald, Kyung Park, Rema Rao, Andrea Sboner, Yu Chen, Mark A. Rubin, Himisha Beltran. Targeting EZH2 in neuroendocrine prostate cancer. [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 3844. doi:10.1158/1538-7445.AM2015-3844