Abstract 5716: XPO1 inhibition synergizes with PARP inhibitor in metastatic castration resistant prostate cancer via the regulation of DNA damage response

Abstract Background: Dysregulated nuclear protein transport, commonly observed in cancer, results in the mislocalization-mediated inactivation of many proteins. We showed that overexpression of exportin 1 (XPO1) is linked to higher grade and Gleason score in metastatic castration-resistant prostate cancer (mCRPC). Using network topology computational approaches, XPO1 and PARP1 were identified as synthetic lethal partners and we have demonstrated synergy between XPO1 and PARP inhibitors in mCRPC cell lines. This study evaluates the combination’s efficacy in cell line-derived (CDX) and patient-derived xenograft (PDX) models, investigating the mechanisms of synergy. Methods: For the CDx and PDx models, 22rv1 cells and CTG-3581 tissue (Champions Oncology) were grown subcutaneously in ICR-SCID and CEIA/NOG male mice, respectively. XPO1 inhibitor was dosed orally at 10-15 mg/kg twice a week and PARP inhibitor was dosed orally at 50 mg/kg daily. For in vitro mechanistic study, 22rv1 cells were subjected to RNAseq, proteomic analysis, and Digital Spatial Profiling (DSP; 10x Genomics Visium platform) after treatment. Data analysis was performed using iPathwayGuide (advaitabio.com) and cLoupe browser. Results: The XPO1-PARP inhibitors combination showed enhanced anti-cancer efficacy in both CDx and PDx models, with no significant weight loss or organ toxicity such as liver, spleen, and kidney. Survival benefits were evident in the combination group. Immunohistochemistry revealed apoptotic cell death, shown by cleaved caspase 3 and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. Mechanistic studies with 22rv1 cells showed downregulation of DNA replication genes (e.g., MCM6 and CDC6) and reduced enrichment scores for DNA replication pathways in gene set enrichment analysis. The proteomic analysis highlighted decreased levels of DNA replication modulators HMGB2 and DNAJC9. Besides the suppression of various DNA damage response genes (e.g. BRCA2 and RAD51), XPO1 inhibition also reduced the PARylation of mCRPC cells. DSP analysis of 22rv1 CDx tissue revealed a reduction of unbiased cellular clusters and increased differentially expressed genes in the combination treatment. The DNA replication pathway was among the top 5 pathways modulated by XPO1i treatment in DSP analysis. Conclusions: Taken together, this study revealed the therapeutic potential of XPO1-PARP inhibitors combination via targeting of the DNA damage response pathway in mCRPC. Citation Format: Md. Hafiz Uddin, Aaban A. Azmi, Laiba M. Monir, Amro Aboukameel, Husain Y. Khan, Sahar F. Bannoura, Frank Cackowski, Yusra Shao, Vinod Shidham, Sunil Jaiman, Rafic Beydoun, Gregory Dyson, Seongho Kim, Yang Shi, Vy Ong, Julie Boerner, Ramzi M. Mohammad, Elisabeth I. Heath. XPO1 inhibition synergizes with PARP inhibitor in metastatic castration resistant prostate cancer via the regulation of DNA damage response [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 5716.