Background: Forkhead box M1 (FOXM1) is a master transcriptional regulator and multifunctional oncoprotein that is widely overexpressed in ovarian cancer and associated with poor prognosis. Due to its promotion of numerous oncogenic phenotypes in ovarian cancer, FOXM1 has emerged as an attractive therapeutic target for ovarian cancer treatment. Recently, we reported that 1,1-diarylethylene compounds, NB-55, NB-73, and NB-115 (NB compounds), potently inhibit FOXM1 in breast cancer cells and mediate anti-cancer effects. Given the high molecular similarity between triple-negative breast cancer (TNBC) and high-grade serous ovarian cancer (HGSC), we characterized this new class of FOXM1 inhibitors in HGSC cells in the present study and compared their effects to other reported FOXM1 inhibitors. Methods: We conducted dose-response curves of NB compounds and other FOXM1 inhibitors in HGSC cells (CAOV3 and OVCAR4) and normal control (FT282 C11) cells. Western blot analyses probed for FOXM1, p-FOXM1, CCNB1, FOXA1, and FOXO3A in HGSC cells treated with NB compounds. We used the proteosome inhibitor MG132 to investigate the mechanism of FOXM1 inhibition by NB-73 and NB-115. We investigated FOXM1 transcriptional activity, colony formation, cell cycle, and apoptosis in HGSC cells treated with NB-73 and NB-115. Results: Dose-response curves in HGSC cells revealed IC50 values in the low nM for monensin; mid-nM for NB-73 and NB-115; high nM for thiostrepton; and low µM for NB-55, FDI-6, and n-phenylphenanthren-9-amine. RCM-1 did not affect HGSC cell proliferation. Dose-response curves in normal control fallopian tube epithelial (FTE) cells revealed IC50 values of high nM for thiostrepton and low µM for NB compounds and FDI-6. HGSC cells treated with NB compounds demonstrated decreased levels of FOXM1 and p-FOXM1 but not FOXA1 and FOXO3A. NB-73 and NB-115 decreased FOXM1 promoter activity and gene target expression but were no longer able to decrease FOXM1 levels when combined with MG132 in HGSC cells. Clonogenic assays of HGSC cells treated with NB-73 and NB-115 revealed decreased colony formation at low nM concentrations. HGSC cells treated with NB-73 and NB-115 have higher cell populations in G2/M and undergo higher rates of apoptosis compared to non-treated HGSC cells. Conclusions: NB-73 and NB-115 promote proteasomal degradation of FOXM1 and are more potent FOXM1 inhibitors of cell proliferation than previously characterized FOXM1 inhibitors in HGSC cells. NB-73 and NB-115 potently reduce HGSC survival and selectively inhibit HGSC cells as compared to normal control FTE cells. Our data encourage further assessment of NB compounds as a novel therapeutic strategy in the vast majority of HGSC that overexpress FOXM1. Support: NIH T32CA009476(CL), research grants 083(BSK) and 084(JAK) from the Breast Cancer Research Foundation, the Landfield Cancer Research Fund(BSK), NIH R03CA224339(ARK), The Marsha Rivkin Center(ARK), The Betty J. and Charles D. McKinsey Ovarian Cancer Research Fund(ARK), and The Fred & Pamela Buffett Cancer Center (NCI P30CA036727)(ARK).

Citation Format: Cassie Liu, Catalina Muñoz-Trujillo, John A. Katzenellenbogen, Benita S. Katzenellenbogen, Adam R. Karpf. Novel 1,1-diarylethylene compounds degrade FOXM1 and selectively and potently reduce survival of high-grade serous ovarian cancer cells [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P205.