Abstract 3223: Prospective study for the assessment of exosomes in ascitic fluid as prognostic markers in patients with advanced ovarian cancer
Authors: Quiralte Miguel , Barquin Arantzazu , Sevillano Elena , Navarro Paloma , Yagüe Monica , Barba Maria , Rodriguez-Moreno Juan F. , Balarezo Alejandra , Peinado Héctor , Izquierdo Elena , García-Donas Jesús , Ruiz-Llorente Sergio 
Published: June 2022

Abstract
Background: Exosomes have been involved in tumor progression and the development of therapeutic resistances in several malignancies. These extracellular vesicles (EVs) promote angiogenesis, premetastatic niches formation and the communication between the tumor and its environment. Ovarian cancer (OC) is a highly lethal tumor that typically spreads within the abdominal cavity rather than through the blood vessels. Based on this behavior, we aimed to study the presence of exosomes in ascitic fluid of OC patients and explore their potential as predictors of tumor volume and chemoresistance.
Methods: We designed an observational prospective study in advanced OC patients who underwent a diagnostic laparoscopy or cytoreductive surgery at our institution. Abdominal washings of a cohort of non-cancer patients were collected as controls. All cases provided written consent. Clinical data and tumor genomic alterations (NGS, FoundationOne CDx) were recorded. EVs pellets were collected by ultracentrifugation and profiled by NTA and western blot (WB) (EVs markers: CD9, TSG101 and ALIX; non EVs related markers: ALB and APOB). PAX8, a protein characteristically expressed in OC cells, was used as a marker of tumor EVs. EVs proteins were quantified by BCA assay; mass spectrometry profiling is ongoing.
Results: 45 peritoneal fluids from 40 OC patients (median age [range] 62 [44-79] years) and 29 peritoneal washings from controls have been collected. Our cohort comprise various histological subtypes (high-grade serous, n=32 [80%]; low-grade serous, n=2 [5%]; endometrioid, n=3 [8%)]; clear cells, n=2 [5%] and mucinous, n=1 [2%]) and tumor stages (TI-II, n=5 [12%]; TIII; n=24 [60%]; TIV, n=11 [28%]). Samples were collected either from primary, n=18 (40%); interval, n=15 (33%); or relapse surgery, n=12 (27%). Pathogenic BRCA events were detected in 25% of patients. Mean concentration of exosomes (MCE) was 6.5x106 vs. 3.2x106 particles/ml (p/ml) in cases vs. controls (p&lt;0.0005). No differences in MCE were observed regarding stages I-II vs. stages III-IV (7.1x106 vs. 6.5x106 p/ml; p=0.84), BRCA status (mutant=6.9x106 vs. wild type=6.8x106 p/ml, p=0.46) or platinum response (resistant=7.7x106 vs. sensitive=9.5x106 p/ml, p=0.14). WB analysis showed an enrichment in EVs markers from cancer patients vs. controls (&gt;3-fold). Protein mean concentration in EVs of cancer patients vs. controls was 0.85µg/µl and 0.51µg/µl respectively (p=0.04). Proteomic characterization through mass spectrometry is ongoing and will be presented at the time of the meeting.
Conclusions: Our data, although preliminary, show a higher concentration of EVs and EVs proteins in OC cases vs controls with no difference between stages or genomic backgrounds. These results lead to the notion that exosomes could be involved in OC evolution and spread regardless of tumor volume or the molecular subtype.
Citation Format: Miguel Quiralte, Arantzazu Barquin, Elena Sevillano, Paloma Navarro, Monica Yagüe, Maria Barba, Juan F. Rodriguez-Moreno, Alejandra Balarezo, Héctor Peinado, Elena Izquierdo, Jesús García-Donas, Sergio Ruiz-Llorente. Prospective study for the assessment of exosomes in ascitic fluid as prognostic markers in patients with advanced ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3223.