Abstract LB-240: LSD1 activates a lethal prostate cancer gene network independently of its demethylase function

Abstract

Abstract Background: Medical castration that interferes with androgen receptor (AR) function is the principal treatment for advanced prostate cancer. However, clinical progression is universal, and tumors with AR-independent resistance mechanisms appear to be increasing in frequency. Consequently, there is an urgent need to develop new treatments targeting molecular pathways enriched in lethal prostate cancer. Lysine specific demethylase 1 (LSD1) is a histone demethylase and important regulator of gene expression. Here we describe a distinct role of LSD1 as a driver of proliferation and survival of castration-resistant prostate cancer (CRPC) cells independently of its demethylase function and of the AR. Methods: We used loss of function studies to determine the importance of LSD1 for survival of prostate cancer cells. To identify transcriptional networks that contribute to cell survival, we suppressed LSD1 with RNAi and performed gene expression profiling. To determine the importance of LSD1's demethylase function in regulation of target genes, we measured LSD1's canonical histone substrates (H3K4me2 and H3K9me2) using genome-wide chromatin immunoprecipitation-sequencing and measured the effect of ectopically expressed wild type or catalytically deficient LSD1 on cell survival and target gene expression. We used mass spectrometry (MS) to identify important LSD1 protein complex members. Finally, we used multiple biochemical and cellular assays and an in vivo study to confirm the mechanism of action of a small molecule inhibitor that targets critical, non-canonical functions of LSD1 in CRPC cells. Results: Cell viability assays demonstrated that LSD1 is important for proliferation and survival of CRPC cells independently of the AR. Gene expression profiles demonstrated that LSD1 activates androgen-independent genes that are enriched in lethal human tumors. Importantly, our global epigenomic studies and biochemical experiments demonstrated that LSD1's demethylase function was dispensable for these effects, while our MS studies identified cooperating LSD1 binding proteins. Finally, we identified a reversible small molecule inhibitor of LSD1 that blocked critical, demethylase-independent functions in vitro and in vivo. Conclusions: Our results demonstrate that LSD1 promotes survival of prostate cancer cells, including those that are castration-resistant, independently of its demethylase function and of the AR. Importantly, this effect is explained in part by activation of a lethal prostate cancer gene network in collaboration with specific binding proteins. Finally, that a reversible small molecule LSD1 inhibitor blocks important demethylase-independent functions and suppresses CRPC cell viability demonstrates the potential of LSD1 inhibition in this disease. Citation Format: Archana Sehrawat, Dae-Hwan Kim, Lina Gao, Yuliang Wang, Armand Bankhead, Shannon McWeeney, Carly J. King, Jacob Schwartzman, Junior Tayou, Joshua Urrutia, William H. Bisson, Daniel J. Coleman, Sunil K. Joshi, David A. Sampson, Sheila Weinmann, Bhaskar VS Kallakury, Deborah L. Berry, Reina Haque, Stephen K. Van Den Eeden, Sunil Sharma, Jared Bearss, Tomasz M. Beer, George V. Thomas, Laura M. Heiser, Joshi J. Alumkal. LSD1 activates a lethal prostate cancer gene network independently of its demethylase function [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 LB-240.