Abstract
Ovarian cancer stem cells (CSCs) can seed recurrent drug-resistant disease. Likewise, non-CSCs can acquire CSC phenotypic properties. How this process is orchestrated is of interest to inform how it might be prevented. We tested the hypothesis that ovarian CSC and/or drug-resistant tumor cells confer stem-like properties via extracellular vesicles (EVs). We focused our investigation on how EVs might mediate EZH2 signaling to promote a phenotypic change in drug-sensitive, non-CSCs. To accomplish this, we utilized paired PARP inhibitor-sensitive and - resistant ovarian cancer (OvCa) cell lines, EZH2 knockdown lines, and patient-derived organoids (PDOs) originating from recurrent high-grade serous OvCa. Small EVs isolated from drug-sensitive, CSC and/or drug-resistant enriched cultures, PARP inhibitor (olaparib) resistant lines, or drug-treated (olaparib or carboplatin) lines were cultured with treatment naïve or sensitive lines for defined time points. The impact of small EV exposure was determined by assessing cell number, metabolic activity, viability, sphere and colony-forming capacity, ALDH activity, DNA damage, and changes in associated signaling pathways. We found that EVs from CSC or drug-resistant enriched cell fractions communicate CSC-like phenotypes to the more sensitive tumor cells via EZH2 canonical and non-canonical signaling pathways, promoting stemness. We conclude that EV-mediated activation of EZH2 signaling represents a targetable mechanism contributing to stemness-associated drug resistance in OvCa.