Alpelisib enhances cisplatin mediated cytotoxicity in non-mutated, PIK3CA-dependent high-grade serous ovarian cancer.

High-Grade Serous Ovarian Cancer (HGSOC) has a dismal five-year survival rate (< 30%) owing to late detection and recurrence caused by platinum resistance. Targeted therapy exhibits efficacy only within a limited patient population, warranting the need to identify new therapeutic regimes. Herein, we investigated the efficacy of a PIK3CA inhibitor, alpelisib, combined with cisplatin using malignant ascites-derived tumour cells from HGSOC patients, cell lines, patient derived xenografts. Malignant ascites-derived tumour cells were collected from treatment-naïve and relapsed HGSOC patients. The efficacy of the cisplatin-alpelisib combination in primary cells and p53 mutant cell lines was assessed through cell viability assays. Targeted next-generation sequencing was performed to identify somatic and germline mutations. Real-time PCR, clonogenic assay, chromatin immunoprecipitation, immunoblotting, immunofluorescence, pre-clinical tumour models, and patient-derived xenograft were used to identify and validate molecular determinants of treatment response. The cisplatin-alpelisib combination induced significant apoptosis in 33% of patient samples and 80% of the responders had harbored amplification in PIK3CA gene. Intriguingly, primary tumor cells expressing p53 mutations-R196Q or R175H, in a PIK3CA non-mutated background conferred sensitivity to cisplatin-alpelisib. Expression of certain p53 mutants (R196Q, R175H, and R282W) in p53-null SKOV3 cells or EOC cells indigenously harboring p53-R175H (TOV112D) showed enhanced PIK3CA expression following cisplatin treatment. This effect was found to be associated with reduced occupancy of mutant p53, coupled with increased NFκB binding on the PIK3CA promoter, leading to enhanced PIK3CA transcription and susceptibility to the cisplatin-alpelisib combination. The combinatorial treatment effectively arrested TOV112D tumour growth (p53-R175H) but not A2780 (Wtp53) compared to cisplatin alone, and significantly reduced the ascites burden in a PDX mouse model. High somatic BRCA2 mutations were also observed without any association with the cisplatin-alpelisib efficacy in our cohort. Our findings highlight the potential of cisplatin-alpelisib treatment in a subset of HGSOC patients with PIK3CA overexpression, mediated either through gene amplification or transcriptional modulation, reflecting the wider application of alpelisib in PIK3CA-non-mutated ovarian cancer.