Drugs Targeting Tumor-Initiating Cells Prolong Survival in a Post-Surgery, Post-Chemotherapy Ovarian Cancer Relapse Model

Abstract

Disease recurrence is the major cause of morbidity and mortality of ovarian cancer (OC). In terms of maintenance therapies after platinum-based chemotherapy, PARP inhibitors significantly improve the overall survival of patients with BRCA mutations but is of little benefit to patients without homologous recombination deficiency (HRD). The stem-like tumor-initiating cell (TIC) population within OC tumors are thought to contribute to disease recurrence and chemoresistance. Therefore, there is a need to identify drugs that target TICs to prevent relapse in OC without HRD. RNA sequencing analysis of OC cells grown in TIC conditions revealed a strong enrichment of genes involved in drug metabolism, oxidative phosphorylation and reactive oxygen species (ROS) pathways. Concurrently, a high-throughput drug screen identified drugs that showed efficacy against OC cells grown as TICs compared to adherent cells. Four drugs were chosen that affected drug metabolism and ROS response: disulfiram, bardoxolone methyl, elesclomol and salinomycin. The drugs were tested in vitro for effects on viability, sphere formation and markers of stemness CD133 and ALDH in TICs compared to adherent cells. The compounds promoted ROS accumulation and oxidative stress and disulfiram, elesclomol and salinomycin increased cell death following carboplatin treatment compared to carboplatin alone. Disulfiram and salinomycin were effective in a post-surgery, post-chemotherapy OC relapse model in vivo, demonstrating that enhancing oxidative stress in TICs can prevent OC recurrence.

Characterization of SOX2, OCT4 and NANOG in Ovarian Cancer Tumor-Initiating Cells

“…A Metascape GO tree showed that cell cycle regulation terms cluster together, while metabolism regulation terms also cluster ( Figure 1 C). These data suggest that in addition to altered metabolism and oxidative stress, which we have previously shown support ovarian cancer spheroids [ 27 ], cell cycle regulation plays a critical role in growth in 3-D and may correlate with specific markers of TICs.…”

“…We next measured spheroid formation efficiency in 3-D conditions. Spheroids are multicellular tumor cell aggregates that resemble those found in patient ascites, and are often used as an in vitro surrogate to measure tumor-initiation capacity [ 9 , 27 , 31 , 32 ]. All cell lines had relatively equal ability to form spheroids with 3-D media ( Figure 2 C,D).…”

Characterization of SOX2, OCT4 and NANOG in ovarian cancer tumor-initiating cells

“…1C). These data suggest that in addition to altered metabolism and oxidative stress, which we have previously shown to support ovarian cancer spheroids [38], cell cycle regulation pathways play a critical role in supporting growth of ovarian cancer cells in 3-D and may correlate with specific markers of TICs.…”

“…We previously showed that ovarian cancer cells cultured in 3-D conditions enhances growth of tumor cells as multicellular spheroids and enriches for TICs with elevated expression of stem cell markers, increased tumorinitiating capacity, and greater resistance to chemotherapies [15,25]. Subsequent RNA-sequencing and Gene Set Enrichment Analysis (GSEA) showed an increase in genes involved in drug metabolism and oxidative stress in OV90 cells cultured in 3-D relative to 2-D conditions [38]. A further query of this sequencing data identifies 10,222 significantly differentially expressed genes (DEGs) in the 3-D cultured cells relative to 2-D cultured cells (Fig.…”

“…We next measured spheroid formation efficiency in TIC enriching 3-D conditions. Spheroids are multicellular tumor cell aggregates that mimic those found in patient ascites and exhibit enhanced drug resistance and high tumorigenicity [15,38,42,43]. Spheroid formation is an in vitro surrogate used to identify cell lines with potentially high tumor-initiation capacity [44][45][46].…”