Elucidating Potential Therapeutic Targets In A Model Of Pten/Tp53 Null Prostate Cancer Using High-Throughput Screening Technology

Prostate cancer (PCa) demonstrates significant intra and inter tumor heterogeneity, similar to many other solid tumors. The “gold standard” of therapy for metastatic prostate cancer is androgen deprivation therapy (ADT). Although ADT is initially effective, acquired resistance, termed castration resistant prostate cancer (CRPC), almost always occurs. It is believed that development of CRPC is governed by both intrinsically resistant progenitor cells and by acquired genomic mutations. Clinically advanced CRPC tumors often display loss of PTEN (40%) and aberrations in TP53 (50%), the presence of which in primary prostate cancer are associated with poor clinical prognosis. Our goal is to identify novel targeted therapies against progenitor cells harboring Pten/Tp53 mutations. To enable high throughput screening, we derived multiple cell lines from a PB-Cre4 Ptenfl/fl;Tp53fl/fl mouse model before (intact) and after (castrate) castration. The RNA-seq analyses of the 8 resultant cell lines revealed distinct clustering of intact and castrate lines as well as patterns of expression characteristic of progenitor cells. Cell lineage marker analysis showed strong KRT8 and minimal KRT5 expression. Using these 8 distinct luminal cell lines, we performed the mechanism interrogation plate (MIPe) screen, a high throughput 1,912 compound screening assay at the National Center for Advancing Translational Science (NCATS). Post-screen informatics data processing and subsequent analysis sorted out compounds that displayed strong activity (1.1 and 1.2 curve class). Multiple compounds were unique to each cell line, however, no difference in sensitivity between the two groups of intact and castrate cell types was observed. Grouping of intact and castrate cell lines together as one population identified a diverse array of 235 compounds (12% of MIPe library) with robust activity against most of the cell lines. Some of these compounds are redundant for specific targets that are key regulators of a multitude of signaling pathways, such as the heat shock protein HSP90AB1, which was targeted by 11 different compounds. In contrast, other targets, like BIRC5, were potently targeted by only one compound. A majority of the 235 compounds targeted components of signaling pathways important in PCa, including: 28 compounds targeting PI3K/AKT/mTOR signaling (AKT1, PIK3CA, mTORc 1/2), 13 compounds targeting cell cycle regulators (CDK1, CDK4), 13 compounds targeting DNA repair and replication (CHEK1, TOP2A), 6 compounds targeting NFKB signaling (IKBKB,ITK) and 5 compounds targeting MAPK signaling (MAPK8, MAP2K1). Using high throughput screening technology to sort for compounds based on potency and activity identified clinically and biologically relevant therapeutic applications for existing compounds in a novel context, Pten/Tp53 null PCa progenitor cells. Citation Format: Keith H. Jansson, John K. Simmons, Caitlyn Fuller, Supreet Agarwal, Paul G. Hynes, Lei Fang, Ross Lake, Jacob Cawley, Lauren Stahl, Xiaohu Zhang, Rajarshi Guha, Craig Thomas, Kathleen Kelly. Elucidating potential therapeutic targets in a model of Pten/Tp53 null prostate cancer using high-throughput screening technology. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-281.