Abstract B021: Targeting nucleotide excision repair in non-muscle invasive bladder cancer

Abstract Background: Previous studies demonstrated that nucleotide excision repair (NER) plays a critical role in cisplatin-based chemotherapy response in muscle-invasive bladder cancer (MIBC), and that spironolactone (SP) is a potent NER inhibitor. We sought to investigate the role of SP in enhancing the response to mitomycin chemotherapy in non-muscle invasive bladder cancer (NMIBC). Materials and Methods: KU1919 cells (NER proficient) were used for chemotherapy response to mitomycin. Cell viability was examined using CellTiter-Glo. IC50 concentrations were calculated using a four-parameter sigmoidal model and plots generated by GraphPad Prism 9. Drug combination indexes (CI) of chemotherapy and SP were calculated using Chou-Talalay method. Cell cycle and apoptosis analysis were measured by assay and Annexin V apoptosis detection kit. DNA damage response and apoptosis signaling were examined by Western blot of gamma-H2AX, cleaved Caspase-3, and cleaved PARP. Results: Combinations of mitomycin and SP (2 μM: 40 μM, CI = 0.09) resulted in strong synergies in KU1919 cells. Mitomycin combined with SP led to more cells with a sub-G1 phase DNA content (9.43% vs. 4.69%, P < 0.01) and apoptosis (55.85% vs. 13.11% P < 0.01) than treatment with mitomycin alone. Western blot analyses showed that the addition of SP to mitomycin treatment induced increased protein expression of DNA damage response genes (gamma-H2AX) and activation of apoptosis (cleaved Caspase-3 and cleaved PARP). Conclusion: Targeting the NER pathway with SP in NMIBC enhances mitomycin-induced DNA damage signaling and subsequent cell apoptosis. These findings offer proof of concept and rationale for combining NER inhibitors with intravesical chemotherapy in NMIBC. Citation Format: Dongbo Xu, Li Wang, Kyle Wieczorekl, Zhiyu Tian, Qiang Li. Targeting nucleotide excision repair in non-muscle invasive bladder cancer [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2024 May 17-20; Charlotte, NC. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(10_Suppl):Abstract nr B021.