Nelfinavir Synergizes with Cisplatin and Promotes GSDME-Associated Lytic Cell Death in Platinum-Resistant Ovarian Cancer Cells

Background/Objectives: Platinum resistance limits the efficacy of ovarian cancer treatment and arises through multiple mechanisms, including enhanced DNA repair, activation of stress responses, and increased survival signaling. Nelfinavir (NFV), an HIV protease inhibitor with reported anti-tumor activity, is a candidate for drug repurposing, but its interaction with cisplatin (CDDP) in ovarian cancer has not been established. Here, we investigated whether NFV enhances CDDP cytotoxicity in platinum (Pt)-resistant ovarian cancer cells and characterized the associated cell death response. Methods: Drug interaction was assessed using cell vitality and viability assays and Loewe additivity modeling together with Bliss and ZIP analyses. Cell death was characterized by Annexin V/7-AAD staining, mitochondrial membrane potential analysis, lactate dehydrogenase (LDH) release, immunoblotting, pharmacological caspase inhibition, and bulk mRNA sequencing with differential expression and gene set enrichment analyses. Results: NFV synergistically enhanced CDDP cytotoxicity across three Pt-resistant ovarian cancer cell lines, reducing CDDP IC50 values by 4.2–5.8-fold and producing mean Loewe synergy scores of approximately 25–30. Combination treatment increased LDH release and was accompanied by caspase-8, caspase-3, PARP, and the pore-forming death effector gasdermin E (GSDME) cleavage. Caspase inhibition attenuated viability loss and GSDME processing. Transcriptomic analysis identified enrichment of stress- and death-associated programs, including the unfolded protein response (UPR), apoptosis, reactive oxygen species (ROS)-associated signaling, and TNF/NF-κB signaling. Conclusions: Together, these findings demonstrate a reproducible synergistic interaction between CDDP and NFV in Pt-resistant ovarian cancer cells and characterize an associated lytic cell death phenotype involving apoptotic signaling and accompanied by GSDME processing. These findings support further investigation of NFV as a repurposed combination partner to enhance CDDP cytotoxicity in Pt-resistant ovarian cancer.