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#500 Protein composition of extracellular vesicles from malignant ascites defines the key components of tumor microenvironment and predicts prognosis of ovarian cancer patients
  1. Anna Vyhlídalová Kotrbová1,
  2. Kristína Gömöryová1,
  3. Antónia Mikulová1,
  4. Hana Plešingerová1,
  5. Marek Kravec1,
  6. David Potešil2,
  7. Camille Blériot3,4,
  8. Mathilde Bied3,
  9. Garett Dunsmore3,
  10. Jan Kotoucek5,
  11. Markéta Bednaríková6,
  12. Jitka Hausnerová6,
  13. Luboš Minár6,
  14. Igor Crha6,
  15. Michal Felsinger6,
  16. Zbynek Zdráhal2,
  17. Florent Ginhoux3,
  18. Vít Weinberger6,
  19. Vítezslav Bryja1 and
  20. Vendula Hlavácková Pospíchalová1
  1. 1Faculty of Science, Masaryk University, Brno, Czech Republic
  2. 2Central European Institute of Technology, Masaryk University, Brno, Czech Republic
  3. 3Institut Gustave Roussy, Villejuif, France
  4. 4Institut Necker Enfants Malades, Paris, France
  5. 5Veterinary Research Institute, Brno, Czech Republic
  6. 6University Hospital Brno and Medical Faculty, Masaryk University, Brno, Czech Republic


Introduction/Background High-grade serous carcinoma of the ovary, fallopian tube and peritoneum (HGSC), the most common type of ovarian cancer, ranks among the deadliest malignancies in women. Many HGSC patients present with ascites at the time of diagnosis. Malignant ascites is a complex tumor microenvironment (TME) containing various cells, proteins and extracellular vesicles (EVs). EVs are small membrane-bound particles that convey proteins, lipids and nucleic acids between cells and their cargo reflects the cell of origin. EVs play important role in cancerogenesis and hold great promise as biomarkers. Small size and polydispersity of EVs bring various challenges to their isolation and characterization, including method-dependent enrichment of different EV subtypes as well as contaminants.

Methodology We isolated EVs from malignant ascites of eleven patients by two orthogonal methods and analyzed them by tandem mass spectrometry (MS/MS). We also included MS/MS analysis of EVs from related non-malignant control patient fluids and analysis of ascitic cells by spectral flow cytometry (FC).

Results We identified a set of ‘core ascitic EV proteins’ and also described proteins present only on EVs from HGSC patients. We believe this list contains important players of HGSC progression as well as potential biomarkers. Using single cell RNA sequencing data, we mapped the origin of EVs to different types of cells present in ascites. EVs in ascites did not come predominantly from tumor cells, but rather from a variety of non-malignant cell types. FC of ascitic cells in combination with the analysis of EV cells of origin incriminate critical contribution of macrophages to the ascitic TME, including the association of macrophage-derived EVs with patient prognosis.

Conclusion This is the first study attempting to link EV composition to the cell types producing it. As such it opens numerous avenues both for a better understanding of EV role in tumor promotion/prevention and for improved HGSC diagnostics.

Disclosures The authors disclose no potential conflict of interest.

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