Abstract 3075: Targeting endoplasmic reticulum stress pathways to combat enzalutamide resistance in prostate cancer

Abstract Prostate cancer (PCa) is a significant public health issue, ranking as the second leading cause of cancer-related death in men in the United States, with projections for 2024 estimating 299,101 new cases and 35,250 deaths. A critical driver of PCa progression, the androgen receptor (AR) signaling pathway remains a major therapeutic target, particularly in castration-resistant prostate cancer (CRPC). Although AR-targeted therapies such as abiraterone and enzalutamide were developed to delay the need for chemotherapy, they provide only modest survival benefits of approximately five and two months, respectively, emphasizing the need for more effective strategies. This research investigates a resistance mechanism in CRPC mediated by a kinase-driven phosphorylation of GRP78, a key chaperone protein that aids in cellular survival independent of conventional AR signaling pathways. In this study, we examine how this phosphorylation of GRP78 triggers post-translational modifications that support CRPC cell survival under AR-targeted therapy. Using both in vitro and in vivo approaches, we characterize this adaptive resistance pathway. In vitro assays using CRPC cell lines include RNA sequencing (RNA-Seq) for transcriptomic profiling, cell viability assays, proteasome activity measurements, and Western blot analysis to evaluate protein expression changes. Confocal microscopy and flow cytometry are employed to assess cellular responses, while kinase assays and mass spectrometry elucidate specific GRP78 modifications. Chromatin immunoprecipitation sequencing (ChIP-Seq) further investigates the impact of GRP78 modification on AR’s genomic binding. In vivo, CRPC xenograft models are treated with enzalutamide, allowing us to assess tumor progression and validate cellular findings via immunohistochemistry (IHC) and RNA-Seq analysis. Preliminary data indicate that phosphorylation-induced modifications of GRP78 enhance CRPC cell resilience under AR inhibition, supporting a proteostasis mechanism that counters therapeutic pressure. Targeting this adaptive response pathway may offer a novel strategy to disrupt resistance and improve the effectiveness of AR-directed therapies in advanced CRPC. By advancing insights into the cellular reprogramming associated with AR resistance, this work contributes to identifying new therapeutic targets for enhanced PCa management. Citation Format: Amos Olalekan Akinyemi, Md Rakibul Alam, Mithu Howlader, Jianlin Wang, Lixiang Gu, Xiaoqi Liu, Zhiguo Li. Targeting endoplasmic reticulum stress pathways to combat enzalutamide resistance in prostate cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3075.