Abstract 6816: Synergistic targeting of nonsense-mediated mRNA decay and heat shock protein 90α for treating lethal prostate cancer

Abstract Background: Androgen receptor signaling inhibitors (ARSI) provide modest survival benefits for metastatic castration-resistant prostate cancer (CRPC), but most patients eventually develop resistance, with some progressing to neuroendocrine prostate cancer (NEPC), a highly aggressive form of the disease. There are no effective treatments for ARSI-resistant patients, underscoring the need for new therapeutic strategies. Synthetic lethality, where the combined loss of two genes causes cell death, has shown promise in cancer therapy, as demonstrated by the success of PARP inhibitors. However, synthetic lethal CRISPR-Cas9 screens in prostate cancer (PCa) remain underexplored. Methods: A combinatorial CRISPR-Cas9 knockout screen was employed to identify synthetic lethal (SL) pairs in ARSI-resistant prostate cancer. Identified SL pairs were validated using in vitro cell viability assays and in vivo models, including cell line and patient-derived xenografts. A luminescence-based nonsense-mediated mRNA decay (NMD) sensor system was utilized to investigate the role of heat shock protein 90α (HSP90α) in NMD. The molecular mechanisms by which NMD components and HSP90α maintain protein and RNA homeostasis in advanced PCa were elucidated using immunohistochemistry, immunofluorescence, immunoblotting, and immunoprecipitation assays. Results: (1) The combinatorial CRISPR-Cas9 knockout screening identified NMD components and HSP90α emerged as a top novel synthetic lethal pair in ARSI-resistant PCa. (2) Dual knockout of NMD regulators and HSP90α led to cell death in ARSI-resistant PCa. (3) Inhibitors targeting both NMD and HSP90α synergistically suppressed the growth of advanced PCa cells in both in vitro and in vivo models, with minimal effects on normal cells. (4) HSP90α interacts with the NMD regulator, protecting it from aggregation and facilitating its function. Conclusions: Our research, utilizing an unbiased combinatorial CRISPR-Cas9 double-knockout screen, is the first to identify synthetic lethal pairs in ARSI-resistant prostate cancer. This study not only provides a new therapeutic approach for overcoming drug resistance in advanced PCa but also deepens our understanding of cellular homeostasis by elucidating the interaction between NMD components and heat shock proteins in the context of advanced prostate cancer. Citation Format: Jinghui Liu, Xinyi Wang, Hamed Maasoumyhaghighi, Mansoureh Nouri, Xiaoqi Liu. Synergistic targeting of nonsense-mediated mRNA decay and heat shock protein 90α for treating lethal 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 6816.