Abstract 3984: NB compound FOXM1 inhibitors have potent anti-cancer activity in high-grade serous ovarian carcinoma
Authors: Vorderbruggen Makenzie , Liu Cassie , Trujillo Catalina Muñoz , Kim Sung Hoon , Katzenellenbogen John A. , Katzenellenbogen Benita S. , Karpf Adam R. 
Published: April 2023

Introduction: High-grade serous ovarian carcinoma (HGSC) is characterized by frequent overexpression and activation of the Forkhead Box M1 (FOXM1) transcription factor, suggesting it as a therapeutic target. This study focused on characterizing the activity of 1,1-diarylethylene FOXM1 inhibitors (NB compounds) against HGSC models.

Methods: We assessed the effects of three NB compounds (NB-55, NB-73, and NB-115) on FOXM1, transcriptionally active p-FOXM1-T600, FOXM1 targets, and other FOX family members using western blotting. We used RT-qPCR to assess the effect of NB compounds on mRNA expression of FOXM1 and its canonical targets. We used CyQuant, colony formation, and apoptosis assays to determine the effects of NB compounds on cell viability. We compared the effects of NB compounds and other FOXM1 inhibitors on HGSC cells vs. non-transformed fallopian tube epithelial (FTE) cells. We determined the relationship between FOXM1 degradation and apoptosis and conducted drug washout to determine the length of FOXM1 reduction following NB compound treatment. We used Compusyn to determine whether NB compounds synergize with carboplatin.

Results: NB compounds caused a dose- and time-dependent decrease in FOXM1 and p-FOXM1 and reduced expression of FOXM1 targets with effects on FOXM1 maintained up to 72 hours post-washout in HGSC cells. In contrast, other FOX family members, including FOXA1 and FOXO3A, were minimally affected. RT-qPCR confirmed decreased mRNA levels of FOXM1 and its target genes, including CCNB1, SKP2, and CDC25B, in HGSC cells treated with NB compounds. As determined by CyQuant, NB compounds were potent in HGSC cells, with nanomolar IC50 values, and impaired both 2D and 3D HGSC cell colony formation. Compared to other FOXM1 inhibitors, e.g., thiostrepton and FDI-6, NB compounds were more potent in HGSC cells with reduced effects in non-transformed FTE cells (FT282). NB compounds promoted HGSC cell apoptosis, while FT282 cells were unaffected at similar concentrations. Additionally, ectopic FOXM1 expression sensitized FT282 cells to NB compound mediated reduced cell viability. Co-treatment with the pan-caspase inhibitor Q-VD-OPh abrogated apoptosis but not FOXM1 degradation in HGSC cells. NB compounds synergized with carboplatin following simultaneous treatment, and to a greater extent when HGSC cells were treated with NB compounds prior to carboplatin. In vivo toxicity studies using C57/BL6 mice indicate that NB compounds are tolerable when administered intraperitoneally. Ongoing studies are assessing the in vivo activity of NB compounds using the ID8, p53-/- syngeneic mouse HGSC model.

Conclusions: NB compounds target FOXM1 and the FOXM1 pathway, are potent inhibitors of HGSC cell viability, have a favorable therapeutic index in vitro, and are tolerable in mice in vivo. These data support NB compound FOXM1 inhibitors as a novel therapeutic approach for HGSC.

Citation Format: Makenzie Vorderbruggen, Cassie Liu, Catalina Muñoz Trujillo, Sung Hoon Kim, John A. Katzenellenbogen, Benita S. Katzenellenbogen, Adam R. Karpf. NB compound FOXM1 inhibitors have potent anti-cancer activity in high-grade serous ovarian carcinoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3984.