Molecular Characterization of PARP Inhibitor Response Reveals Co-Targeting Strategies in Advanced Prostate Cancer

Background/Objectives: Though PARP inhibition has improved the management of advanced prostate cancer, patient outcomes may be modest and disease progression on treatment is common. We sought to improve understanding of tumor cell response to PARP inhibition to support development of novel strategies to enhance and/or prolong PARP inhibitor (PARPi) efficacy. Methods: Cell viability assays and microscopy were used for initial characterization of PARPi response in models of advanced prostate cancer. RNA sequencing was performed to investigate time-dependent transcriptomic changes induced by PARP inhibition. Western blots, flow cytometry, and both additional viability assays and microscopy were used to validate RNA sequencing results and test potential therapeutic strategies. Results: Characterization of responses to PARP inhibition reveals time-dependent changes which may be targeted to improve treatment efficacy. In line with the expected PARPi mechanism of action, short-term treatment is largely associated with activation of ATM and the DNA damage response and cell cycle checkpoint signaling. Targeting ATM with clinical stage inhibitors significantly enhances reduction of tumor cell viability by PARP inhibition. Tumor cells exposed to longer-term treatment exhibit SLUG-dependent epithelial-mesenchymal transition (EMT) and evidence for altered fatty acid metabolism, both of which may be targeted to enhance PARPi anti-tumor cell effects. Conclusions: This study provides insight into both short and longer-term cellular response to PARPi treatment and provides a foundation for additional efforts to explore effective strategies to maximize the utility of PARP inhibition for managing prostate cancer.