Abstract 3441: A multivalent peptoid conjugate that inhibits therapy-resistant prostate cancer cell proliferation by modulating androgen receptor transcriptional activity

Abstract

Abstract Prostate cancers adapt to androgen receptor (AR) pathway inhibitors and progress to castration resistance despite the continued expression and function of the AR. We developed a new approach to antagonize the proliferative activity of AR and inhibit castration-resistant prostate cancer (CRPC) growth using multivalent peptoid conjugates (MPCs). Our strategy is to display multiple copies of the AR antagonist, ethisterone, on a peptoid scaffold. Such a multivalent display increases the ligand’s effective local concentration, thus targeting AR with high affinity and affecting AR interactions with coregulators. Here, we report a new potent MPC called MPC309, which displays three ethisterone groups and binds to AR with nanomolar affinity. MPC309 reduces the proliferation of enzalutamide-resistant prostate cancer cells, including those harboring AR splice variants, AR ligand binding mutations, and non-canonical AR gene expression programs. We provide evidence that MPC309 enters cells via macropinocytosis, which facilitates the fluid-phase uptake of extracellular macromolecules. Macropinocytotic uptake of MPC309 enhances cancer cell-specific delivery, thus limiting systemic toxicities. MPC309 displays favorable pharmacological properties and produced significantly greater tumor suppression in xenograft studies than enzalutamide, the standard of care anti-androgen in clinical use. Mechanistically, MPC309 inhibits prostate cancer growth by eliciting a unique gene expression program through alterations in AR chromatin occupancy compared to dihydrotestosterone (DHT) or enzalutamide. Thus, MPC309 represents a novel AR antagonist that activates an AR anti-proliferative program to repress the growth of CRPC and supports further investigation of the MPC compound class for treating CRPC. Citation Format: Justine Habault, Jeffrey A. Schneider, Susan Ha, Rachel Ruoff, Joseph Puccini, Dafna Bar-Sagi, Kwok-Kin Wong, Amina Zoubeidi, Frank Claessens, David R. Wise, Susan K. Logan, Kent Kirshenbaum, Michael J. Garabedian. A multivalent peptoid conjugate that inhibits therapy-resistant prostate cancer cell proliferation by modulating androgen receptor transcriptional activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3441.