Abstract 3582: Drugs targeting ovarian cancer tumor-initiating cells enhance oxidative stress and prevent disease recurrence
Authors: Harrington Brittney S. , Annunziata Christina M. 
Published: September 2020

Abstract
Ovarian cancer (OC) is a global health burden with the poorest 5-year survival rate of the gynecological malignancies. Disease recurrence is the major cause of morbidity and mortality of OC, likely driven by the survival of chemoresistant, self-renewing tumor-initiating cells (TICs). The TIC population in OC acquires features to survive cellular stress and avoid apoptosis but these can also be targeted as vulnerabilities specific to the TIC population of OC to prevent recurrence. To reveal these vulnerabilities, a high-throughput drug screen was performed to identify drugs that showed increased efficacy against OC cells grown in TIC-enriching spheroid (TES) conditions compared to adherently grown cells. Four drugs were selected for further investigation. Disulfiram, Bardoxolone Methyl, Elesclomol and Salinomycin were tested in vitro to confirm the effects on viability of OC cells in adherent or TES conditions. The drugs' efficacy against sphere formation and expression of markers of stemness as high ALDH activity and CD133 expression (ALDH+CD133+) as single agents or in combination with carboplatin was also investigated in vitro. Disulfiram showed the greatest efficacy against spheroid viability and decreased the ALDH+CD133+ population of several OC cell lines. This effect was enhanced when combined with carboplatin. Bardoxolone Methyl, Elesclomol and Salinomycin showed similar efficacy against cell viability in OC cells grown adherently or in TES conditions; Elesclomol significantly inhibited the ALDH+CD133+ population of the OC cells which was again enhanced in combination with carboplatin. RNAseq analysis revealed a strong enrichment of genes involved in oxidative phosphorylation and reactive oxygen species (ROS) pathways in TES conditions compared to adherent conditions. The drugs were investigated for their ability to promote oxidative stress and OC cells were measured for accumulation of intracellular ROS and mitochondrial superoxide after exposure to the drugs. OC cells grown in TES conditions had higher basal intracellular ROS levels than adherently grown cells and the level of ROS was significantly enhanced in TES cells treated with Elesclomol or Disulfiram but no differences were seen in adherently grown cells. Salinomycin and Bardoxolone Methyl increased mitochondrial superoxide accumulation in some OC cell lines under TES conditions. In a model of OC relapse in vitro, Disulfiram and Elesclomol following carboplatin treatment significantly increased cell death compared to carboplatin alone. Disulfiram and Salinomycin were incorporated into a mouse model to test their ability to prevent OC relapse after chemotherapy in vivo. These results demonstrate that targeting key pathways mediating increased oxidative stress in TICs can eliminate this population and provide a means to prevent OC recurrence.
Citation Format: Brittney S. Harrington, Christina M. Annunziata. Drugs targeting ovarian cancer tumor-initiating cells enhance oxidative stress and prevent disease recurrence [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3582.