Characteristics of Extracellular Vesicles from a High-Grade Serous Ovarian Cancer Cell Line Derived from a Platinum-Resistant Patient as a Potential Tool for Aiding the Prediction of Responses to Chemotherapy

Abstract

Platinum-resistant high-grade serous ovarian cancer (HGSOC) is invariably a fatal disease. A central goal of ovarian cancer research is therefore to develop new strategies to overcome platinum resistance. Treatment is thus moving towards personalized therapy. However, validated molecular biomarkers that predict patients’ risk of developing platinum resistance are still lacking. Extracellular vesicles (EVs) are promising candidate biomarkers. EpCAM-specific EVs are largely unexplored biomarkers for predicting chemoresistance. Using transmission electron microscopy, nanoparticle tracking analysis and flow cytometry, we compared the characteristics of EVs released from a cell line derived from a clinically confirmed cisplatin-resistant patient (OAW28) and EVs released from two cell lines from tumors sensitive to platinum-based chemotherapy (PEO1 and OAW42). We demonstrated that EVs released from the HGSOC cell line of chemoresistant patients exhibited greater size heterogeneity, a larger proportion of medium/large (>200 nm) Evs and a higher number of released EpCAM-positive EVs of different sizes, although the expression of EpCAM was predominant in EVs larger than 400 nm. We also found a strong positive correlation between the concentration of EpCAM-positive EVs and the expression of cellular EpCAM. These results may contribute to the prediction of platinum resistance in the future, although they should first be validated in clinical samples.

Higher EpCAM-Positive Extracellular Vesicle Concentration in Ascites Is Associated with Shorter Progression-Free Survival of Patients with Advanced High-Grade Serous Carcinoma

“…The chemoresistant cell line released more EpCAM-positive EVs. Also, a strong positive correlation between cellular EpCAM expression and the concentration of released EpCAM-positive EVs was observed [ 36 ]. On the other hand, the chemoresistant cell line did not release more total EVs.…”

“…Preparation of blood and ascites samples for flow cytometric measurement was based on the “International Society on Thrombosis and Haemostasis Protocol” developed by Lacroix et al, which was adopted by the American Heart Association as methodological guidelines for EVs studies [ 39 , 40 ]. Later, this protocol was further validated, and all steps are described in detail in the publication “Protocol for measuring Concentration of extracellular vesicles in Human Blood Plasma with Flow Cytometry” [ 36 ]. This protocol or slightly different centrifugation protocols were used in several published EV biomarker studies [ 41 , 42 , 43 , 44 ].…”

“…In the present study, a flow cytometer (CytoFLEX, Beckman Coulter, Brea, CA, USA) was used to determine the concentration of calcein-positive and EpCAM-positive EVs in plasma and ascites samples of HGSC patients [ 36 ]. We performed assay control/proof of single EV detection in accordance with the recommendations included in a positional paper (MIFlowCytEV) developed and published by the EV Flow Cytometry Working Group [ 47 ], which is also referred to in the “MISEV 23 guidelines” prepared by the International Society for Extracellular Vesicles (ISEV) [ 48 ].…”