Abstract B026: Identification of small RNAs that function as multi-target therapeutics and as tools for novel target discovery in prostate cancer
Authors: Corbin Joshua M , Young Hamilton , Wilhelm Stefan , Asch Adam S , Xu Chao , Ruiz Echevarria Maria J 
Published: November 2024

Abstract
Introduction: A major contributor to prostate cancer (PCa) mortality is the development of resistance to single agents targeting androgen receptor (AR) signaling. We have developed an unbiased shRNA-based negative selection screen to identify small RNAs (shRNAs and siRNAs) that inhibit PCa cell growth and survival (toxic sRNAs). Computational analyses of the most toxic sRNAs identified revealed that each can simultaneously target multiple known AR-coregulatory mRNAs. AR-coregulators modulate AR transcriptional response and are essential to AR signaling. We have proposed that the identified toxic sRNAs inhibit androgen signaling through seed-mediated targeting of androgen regulatory gene networks, resulting in inhibition of cell growth and viability. The goal of the current studies was to begin to analyze the broad therapeutic potential of these toxic sRNAs for PCa. We focused on analyzing i) their potential to thwart cell growth and/or viability when delivered to preclinical models of PCa, and ii) the targetome of the toxic sRNAs as a mean to uncover novel AR-coregulators that represent a targetable axis within androgen signaling. Methods: i) cationic lipid nanoparticles (LNPs), that efficiently deliver the toxic siRNAs to PCa cell lines, were used to deliver toxic siRNAs to organoids grown from PCa patient derived xenografts (PDX) models. 3D image analysis using the Ominer® software package was used to determine organoid count and size, the numbers of nuclei per organoid, and the fraction of dead cells to discriminate between cytotoxic and cytostatic effects. ii) to identify novel AR-coregulators, toxic siRNA direct targets were identified by sequencing of transcripts captured by biotinylated toxic siRNAs. Directly bound targets, were subjected to pathway enrichment and network analysis followed by identification of hub genes (Cytoscape). The effect of individually silencing potential AR-coregulators on the expression of androgen responsive genes was analyzed using Nanostring. Results and Conclusions: i) The effect of the toxic siRNAs on growth and viability of the PCa PDX-derived organoids will be presented and discussed as compelling preliminary data for therapeutic testing in more complex pre-clinical models (PCa PDXs). ii) Based on bioinformatic and downstream analysis of the direct targets of two toxic siRNAs, we selected 12 potentially novel AR- coregulators, with varied known functions including chromatin modifiers, transcriptional regulators, etc. Silencing of several of these potential AR-coregulators significantly affect expression of numerous AR responsive genes. Future experiments will focus on analyzing their interaction and functional association with the AR (i.e. effect of AR binding to chromatin). In conclusion, we have developed an assay that allowed the identification of toxic sRNAs for PCa cells and demonstrated their potential as therapeutics and as a tool for discovery of potential novel targets for PCa.
Citation Format: Joshua M Corbin, Hamilton Young, Stefan Wilhelm, Adam S Asch, Chao Xu, Maria J Ruiz Echevarria. Identification of small RNAs that function as multi-target therapeutics and as tools for novel target discovery in prostate cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: RNAs as Drivers, Targets, and Therapeutics in Cancer; 2024 Nov 14-17; Bellevue, Washington. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(11_Suppl):Abstract nr B026.