Abstract 1731: Combination therapy with onvansertib and carboplatin demonstrate anti-tumorigenic effects in endometrioid endometrial cancer cell lines

Abstract Objectives: Polo-like kinase 1 (PLK1) is a serine/threonine kinase that plays a key role in cell cycle regulation, tumor cell proliferation, and DNA damage repair. PLK1 has arose as a potential cancer therapeutic target, since it is overexpressed in many tumor types including endometrial cancer (EC). Onvansertib is a highly specific PLK1 inhibitor and has shown promising results when combined with chemotherapy in pre-clinical models of several solid tumor types. Onvansertib is being tested in phase 1/2 trials for breast and colon cancer. PLK1 is also a downstream product of the mTOR pathway, a pathway often altered in EC, supporting that ovansertib may be a logical drug for EC treatment. We aimed to investigate the effects of onvansertib combined with carboplatin on cell proliferation, adhesion, apoptosis, and cellular stress in endometrioid EC cells. Methods: Human endometrioid EC cell lines, HEC1B and KLE, were treated with onvansertib and carboplatin, both alone and in combination. Cell proliferation was assessed by colony formation and MTT assays. Cellular stress was evaluated by quantifying levels of reactive oxygen species (ROS) via DCFH-DA assay and changes in mitochondrial membrane potential (MMP) via the JC-1 assay. Apoptosis was measured using cleaved caspace-3 assays. Cell adhesion was evaluated using laminin-1 assay, and cell migration by wound healing assay. Western immunoblotting was used to measure downstream protein expression related to cell cycle progression, cellular invasion, and apoptosis. Results: Onvansertib and carboplatin both inhibited cell colony formation in endometrioid EC cells, and when combined, showed a synergistic effect (Combination Index or CI<1). Combination therapy in both cell lines exhibited increased levels of ROS formation (p<0.05) and decreased MMP (p<0.05) compared to single-drug treatment. Combination therapy was found to significantly increase caspase-3 activity relative to either drug alone (p<0.05). Combination therapy also decreased cellular adhesion and inhibited migration (scratch closure) of the endometrioid EC cells (p<0.05). These results were confirmed by western immunoblotting demonstrating that combined therapy upregulated the cellular stress protein Bax, and downregulated the cell cycle regulatory proteins CKD2, CDK4, and cyclin D1. Proteins important for cellular adhesion and migration, SLUG and beta-catenin, were also downregulated with combination therapy. Conclusion: Combination therapy with onvansertib and carboplatin demonstrate compelling anti-tumorigenic effects in endometrioid EC cell lines. Ongoing investigation is merited for pursuit of possible translation into clinical treatment options of this novel drug combination in EC. Citation Format: Chelsey Vranes, Glenn Boyles, Haomeng Zhang, Michael Emanuele, Chunxiao Zhou, Victoria Bae-Jump. Combination therapy with onvansertib and carboplatin demonstrate anti-tumorigenic effects in endometrioid endometrial cancer cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1731.