Abstract 301: PARP inhibitor-induced senescent fibroblasts enhance prostate cancer cell proliferation and suppress NK cell-mediated cytotoxicity

Abstract Introduction: Prostate cancer (PCa) is a leading cause of cancer-related morbidity and mortality in men. Despite initial tumor response to androgen deprivation therapy (ADT), most patients with PCa progress to a castrate-resistant disease state. Therapy-induced cellular senescence modulates the tumor microenvironment (TME) through the senescence-associated secretory phenotype (SASP), contributing to tumor growth, progression, and treatment resistance. We have demonstrated increased patient serum levels of SASP-related cytokines following treatment with ADT (Schwermann, AACR 2024). We investigated the ability of PARP inhibitors (PARPi) to induce senescence of fibroblasts and its impact on the proliferation of PCa cell lines and NK cell-mediated cytotoxicity. Methods: Senescence of fibroblasts (IMR-90) was induced by treatment with etoposide (40uM), olaparib (15uM), and talazoparib (20uM) for 3 weeks. The senescent population was stained with the SPiDER-Gal live cell marker and sorted (BD FACS Aria). Cytokines (SASP) from senescent fibroblasts were characterized using bead-based multiplex assay (Luminex® xMAP®). Senescent fibroblasts were co-cultured with PCa cell lines (LNCaP, DU145, 22Rv1, PC3) in a 10:1 ratio over 12 days. The growth rate of PCa cells was assessed by colony assay formation. Senescent fibroblasts were co-cultured with NK cells (1:30 ratio) over 5 days. The NK proliferation status and cytotoxic markers were analyzed by flow cytometry. NK cells exposed to senescent fibroblasts were incubated with fluorescently labeled PCa cells. Results: PCa cell lines displayed increased proliferation when co-cultured with senescent fibroblasts (PC3+IMR-90 [C] = 59.6±4.72, PC3+etoposide treated IMR-90 [T1]=111.7±10.6, PC3+olaparib treated IMR-90 [T2]=97±11.3, p<0.005, LNCaP+[C]=16.67±5.6, LNCaP+[T1]=86.33±5.1, LNCaP +[T2]=65.3±8.3, p<0.001). Senescent fibroblasts induced by etoposide, olaparib, and talazoparib displayed an increased secretion of the SASP IL-6, IL-8, IL-1, IL-15, CCL2, CCL3, and CCL20. NK cells exhibited a lower proliferation rate when co-cultured with senescent fibroblasts (Ki67% [C]:71.6±3.5, [T1]: 26.3±5.1, [T2]: 41.5±3.5, p<0.002) and reduced IFN-y secretion ([C]:32±4, [T1]: 26±3.1, [T2]: 29±6.5, p=0.32). NK cells co-cultured with senescent fibroblasts also exhibited reduced killing of PCa cells (tumor-NK cell ratio 10:1 and 20:1). Conclusions: Etoposide and PARPi-induced senescent fibroblasts displayed increased SASP production and promoted the proliferation of PCa cells in vitro. These senescent fibroblasts also limited NK cell proliferation and reduced their cytotoxicity. Future experiments will investigate the impact of therapy-induced senescent fibroblasts in vivo growth of PCa tumors. Citation Format: Maximillian Pinho-Schwermann, Claire Lin, Shaolei Lu, Shengliang Zhang, Praveen Srinivasan, William MacDonald, Connor Purcell, Matthew J. Hadfield, Galina Lagos, Vida Tajiknia, Nolan Stubbs, Kimberly Meza, Dragan Golijanin, Elias Hyams, Anthony Mega, Wafik S. El-Deiry, Benedito A. Carneiro. PARP inhibitor-induced senescent fibroblasts enhance prostate cancer cell proliferation and suppress NK cell-mediated cytotoxicity [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 301.