Epithelial ovarian cancer (EOC) is a global health burden and remains the fifth leading cause of cancer related death in women worldwide with the poorest five-year survival rate of the gynecological malignancies. EOC recurrence is considered to be driven by the survival of chemoresistant, stem-like tumor-initiating cells (TICs). We previously showed that disulfiram, an ALDH inhibitor, effectively targeted TICs compared to adherent EOC cells in terms of viability, spheroid formation, oxidative stress and also prevented relapse in an in vivo model of EOC. In this study we sought to determine whether specific targeting of ALDH isoenzyme ALDH1A1 would provide similar benefit to broader pathway inhibition by disulfiram. NCT-505 and NCT-506 are isoenzyme-specific ALDH1A1 inhibitors whose activity was compared to the effects of disulfiram. Following treatment with both the NCTs and disulfiram, the viability of TICs versus adherent cells, sphere formation, and cell death in our in vitro relapse model were measured and compared in EOC cell lines. We found that disulfiram decreased the viability of TICs significantly more effectively versus adherent cells, while no consistent trend was observed when the cells were treated with the NCTs. Disulfiram also affected the expression of proteins associated with NFκB signaling. Comparison of disulfiram to the direct targeting of ALDH1A1 with the NCTs suggests that the broader cellular effects of disulfiram are more suitable as a therapeutic to eradicate TICs from tumors and prevent EOC relapse. In addition to providing insight into a fitting treatment for TICs, the comparison of disulfiram to NCT-505 and -506 has increased our understanding of the mechanism of action of disulfiram. Further elucidation of the mechanism of disulfiram has the potential to reveal additional targets to treat EOC TICs and prevent disease recurrence.

Epithelial ovarian cancer (EOC) remains the fifth leading cause of cancer-related death in women worldwide, partly due to the survival of chemoresistant, stem-like tumor-initiating cells (TICs) that promote disease relapse. We previously described a role for the NF-κB pathway in promoting TIC chemoresistance and survival through NF-κB transcription factors (TFs) RelA and RelB, which regulate genes important for the inflammatory response and those associated with cancer, including microRNAs (miRNAs). We hypothesized that NF-κB signaling differentially regulates miRNA expression through RelA and RelB to support TIC persistence. Inducible shRNA was stably expressed in OV90 cells to knockdown RELA or RELB; miR-seq analyses identified differentially expressed miRNAs hsa-miR-452-5p and hsa-miR-335-5p in cells grown in TIC versus adherent conditions. We validated the miR-seq findings via qPCR in TIC or adherent conditions with RELA or RELB knocked-down. We confirmed decreased expression of hsa-miR-452-5p when either RELA or RELB were depleted and increased expression of hsa-miR-335-5p when RELA was depleted. Either inhibiting miR-452-5p or mimicking miR-335-5p functionally decreased the stem-like potential of the TICs. These results highlight a novel role of NF-κB TFs in modulating miRNA expression in EOC cells, thus opening a better understanding toward preventing recurrence of EOC.

Ovarian cancer is the gynecological cancer with the highest mortality rate. As resistance to treatment is acquired and many patients relapse, new treatment strategies are needed. A model that strongly reflects the features of recurrent ovarian cancer in the peritoneal cavity is the "cancer stem cells (CSCs)," which are enriched when cells are cultured in three dimensions (3D) on low-attachment plates. The unique metabolic system of the "3D CSCs" is the subject of a novel therapeutic approach. Here, we show that ovarian cancer 3D CSCs have strong NAD+ production capacity, which is particularly dependent on nicotinamide phosphoribosyl transferase (NAMPT), known as the rate-limiting enzyme in the salvage pathway of NAD+ production. We found that NAMPT inhibition blocks NADPH and ATP production as well as NAD+, and subsequently suppresses the synthesis capacity of proteins, fat droplets, and cholesterol in the 3D ovarian cancer cells. In addition, we found that the combination of NAMPT inhibitor and the ALDH inhibitor disulfiram had a pronounced synergistic effect. This synergy inhibits oxidative phosphorylation and ALDH activity and promotes reactive oxygen species and apoptosis via caspase 3/7 cleavage, which leads to death of the 3D cultured cells. Our results demonstrate that high NAMPT expression in ovarian cancer is likely to be a strong poor prognostic factor and that the combination of a NAMPT inhibitor and disulfiram could be a new treatment option to treat or prevent recurrent ovarian cancer. Our novel findings focus on NAMPT addiction as a property of ovarian cancer 3D CSCs, and strongly suggest the combined inhibition of NAMPT and ALDH as a potential therapeutic strategy. Citation Format: Kei Kudo, Brittney S. Harrington, Franklin Ning, Rahul Kamdar, Yusuke Shibuya, Soumya Korrapati, Maria Fergusson, Calen Kucera, Fantini Massimo, Christina M. Annunziata. New therapeutic strategies suppressing NAD+ and ATP production in cancer metabolism specific to 3D cultured ovarian cancer cells [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 488.