Abstract A113: Extracellular vesicles derived from enriched ovarian cancer stem cell fractions promote stem like properties in the more vulnerable tumor cell populations

Abstract Ovarian cancer stem cells (CSCs) are thought to serve as seed cells for recurrent drug resistant disease. Extracellular vesicles (EVs) derived from CSCs are known to promote a more favorable tumor microenvironment. However, there is limited research focused on the impact of EV exchange between tumor cells. We hypothesized that CSC enriched tumor cell fractions could confer their stem like properties to chemo-sensitive non-CSCs via EVs. To test our hypothesis, we utilized established ovarian cancer (OvCa) cell lines (SKOV3, A2780, and UWB1.289 olaparib sensitive (U-OlaSen) and resistant (U-OlaRes)) and high grade serous ovarian cancer (HGSOC) patient derived organoid (PDO) lines. Small EVs were isolated via ultra-filtration and centrifugation, validated, and quantified. EVs from CSC enriched cultures, PARP inhibitor resistant lines, or drug treated (olaparib or carboplatin) lines were cultured with treatment naïve or treatment sensitive lines for defined time points. The endpoints included assessment of changes in ALDH activity (ALDEFLUOR™ Kit) and cell viability (Annexin V staining) using flow cytometry. In addition, relative levels of Enhancer of Zeste Homologue 2 (EZH2), Histone 3 lysine 27 trimethylation (H3k27me3), Disrupted Meiotic cDNA recombinase 1 (DMC1), phosphorylated and non-phosphorylated CHK1 were determined by western blotting. Drug resistance was determined post exposure of the more sensitive cells to EVs derived from the more resistant cells by treatment by either carboplatin or olaparib. At least 3 independent experiments were completed for each endpoint. Statistical analysis was performed by GraphPad Prism and p < 0.05 was considered as statistically significant. Exposure of small EVs (2.5 ug/ml) derived from CSC enriched cultures or drug resistant cell fractions to the more sensitive tumor cell populations resulted in a marked increase in ALDH activity, indicating an increase in CSC markers. This increase was concurrent with an EV induced increase in the relative levels of EZH2, DMC1, total and phosphorylated CHK1 compared to controls. EVs derived from tumor cells treated with carboplatin or olaparib promoted resistance in the more sensitive tumor cell cultures further implicating the ability to exchange resistance properties. Similar results were observed in response to EVs from known drug resistant human HGSOC organoids on U-OlaSen cells. In summary, these findings provide evidence that EVs from CSC enriched fractions can confer CSC like properties via canonical and non-canonical signaling to the more sensitive tumor cells. We conclude that in addition to the concept that tumor cells can promote drug resistance by diluting cytotoxics among neighboring tumor cells, the more resistant CSCs can promote stem like activity in neighboring drug sensitive tumor cells allowing them to overcome anticancer drug treatment and ensuring their survival and adaptation. Citation Format: Venkatesh Pooladanda, Shaan Kumar, Yusuke Matoba, Maryam Azimi Mohammadabadi, Dominique T. Zarrella, Ursula A. Winter, Sarah J. Hill, Hyungsoon Im, Bo R. Rueda. Extracellular vesicles derived from enriched ovarian cancer stem cell fractions promote stem like properties in the more vulnerable tumor cell populations [abstract]. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_2):Abstract nr A113.