Abstract B016: Repurposing nelfinavir for re-sensitizing platinum-resistant high grade serous ovarian cancer cells
Authors: Forgie Benjamin N. , Goyeneche Alicia A. , Telleria Carlos M. 
Published: March 2024

Abstract
High grade serous ovarian cancer (HGSOC) is the deadliest gynecological malignancy, with a 50% 5-year survival rate. The high mortality rate of HGSOC can be partly attributed to high rates of acquired chemotherapy resistance. HGSOC is treated with surgery and platinum (Pt)-based chemotherapy, represented by cisplatin (CDDP) or CDDP derivatives. Initial treatment is often successful, however, over 80% of patients will acquire Pt resistance. Therefore, Pt resistance remains one of the greatest challenges in HGSOC therapy, and novel therapeutics that increase Pt sensitivity in resistant patients are essential. In this study, we demonstrate that the HIV protease inhibitor nelfinavir (NFV), shown in past work to have anti-cancer properties against HGSOC as a monotherapy, can re-sensitize CDDP-resistant cells to CDDP in vitro. In addition, we show that NFV and CDDP together may be sufficient to induce immunogenic cell death (ICD), an immunostimulatory form of apoptosis characterized by the release of damage associated molecular patterns (DAMPS). HGSOC cell lines that were clinically sensitive (PEO1) or resistant (PEO4) to CDDP were used in cytometric cell counting and colony formation assays to assess the toxicity of the CDDP/NFV combination. Co-treatment of CDDP at increasing concentrations together with a constant concentration of NFV reduced the IC50 of CDDP in PEO4 cells by 6-fold, back down to the IC50 of CDDP observed in PEO1 cells. Using Annexin V/7-AAD staining, we showed that CDDP and NFV together significantly increased the proportion of apoptotic PEO4 cells compared to CDDP alone. DNA damage, assessed through western blotting for gH2AX, was also significantly increased by CDDP/NFV co-treatment compared to CDDP alone. Furthermore, using flow cytometry to detect reactive oxygen species (ROS), we showed that PEO4 cells treated with NFV and CDDP showed increased ROS levels compared to either drug alone. Pre-treatment with a-tocopherol, a ROS scavenger, resulted in partial rescue of PEO4 cell viability, indicating that the toxicity is, at least in part, ROS-dependent. Through western blotting, we showed that CDDP and NFV co-treatment induces high levels of endoplasmic reticulum (ER) stress, resulting in activation of the unfolded protein response (UPR). Of note, we observed increased C/EBP homologous protein (CHOP), a pro-apoptotic factor upregulated upon acute ER stress. Furthermore, co-treatment resulted in phosphorylation of eukaryotic initiation factor 2a (eIF2a), an event required for triggering ICD. Finally, through luminescence-based assays, we showed that CDDP/NFV co-treatment in PEO4 cells resulted in the extracellular release of ATP and the protein high mobility group box 1 (HMGB1), DAMPS required for the induction of ICD. Overall, our results indicate that NFV, when combined with CDDP, is capable of re-sensitizing PEO4 cells to CDDP, through increasing ROS and DNA damage ultimately resulting in apoptosis. Furthermore, NFV and CDDP trigger the ER stress response and DAMP release, suggesting the induction of ICD.
Citation Format: Benjamin N. Forgie, Alicia A. Goyeneche, Carlos M. Telleria. Repurposing nelfinavir for re-sensitizing platinum-resistant high grade serous ovarian cancer cells [abstract]. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_2):Abstract nr B016.