An investigation of novel interacting drug combinations in the treatment of high-grade serous ovarian cancer

The mechanism of action of the drugs was investigated by western blot (WB) analysis. </div><div><br></div><div>DSS-based profiling provided more robust clustering of HGSOC cell lines and PADCs by chemosensitivity than IC50 or chemoresistance-associated gene expression, supporting its applicability as a summary metric for high-throughput screening. Drug screening results showed that the chemoresistant cell lines showed limited responses to most single agents but remained selectively vulnerable to specific combination regimens identified in the multiplex screen.

Combinations containing conventional DNA-damaging or mitotic agents produced the strongest synergy in chemosensitive models, whereas all cell lines, and particularly chemoresistant lines and PADCs, displayed pronounced sensitivity to copanlisib (PI3K inhibitor) and cerivastatin (HMG-CoA reductase inhibitor) at sub-maximal, clinically relevant concentrations. Co-inhibition of PI3K and HMG-CoA reductase markedly reduced viability and long-term growth of HGSOC spheroids, while PADCs demonstrated intrinsic sensitivity to HMG-CoA reductase inhibition, with PI3K blockade enabling further dose reduction.

Mechanistic studies showed that HMG-CoA reductase inhibition increased phospho-Akt levels in chemoresistant models, thereby creating a dependency that was efficiently suppressed by PI3K inhibition, leading to enhanced apoptosis. However, cerivastatin has been associated with clinically significant rhabdomyolysis, highlighting the need to prioritise safer, high-potency statins in future translational studies.</div><div><br></div><div>The chick chorioallantoic membrane (CAM) xenograft model was optimised for HGSOC tumour formation as an in vivo-like platform.

OVCAR3 CAM tumours retained key histopathological features of HGSOC including similar morphology and relative expression of biomarkers. The pharmacodynamic responses of OVCAR3 CAM tumour to cisplatin and copanlisib were determined by PARP cleavage using WB, demonstrating measurable treatment effects. Engraftment of PADCs on the CAM resulted in the formation of regions suspicious for tumour.

Cells derived from OVCAR3 CAM tumours exhibited enhanced stem-like and mesenchymal features with reduced sensitivity to carboplatin compared to parental cells. The model supported tumour formation of HGSOC cells and enabled pharmacological testing which could serve as a rapid, cost-effective in vivo-like platform in the future.</div><div><br></div><div>Our study established an optimised phenotypic drug screening pipeline based on multiplex drug combination screening that can identify clinically actionable therapies for HGSOC and, using this platform, identified PI3K and HMG‑CoA reductase co‑inhibition as a promising repurposed strategy for chemoresistant HGSOC.<br><i><br>Thesis is embargoed until 31 July 2029.</i></div>