Exosome in ascites can be a potential therapeutic target for gastric cancer with malignant ascites.

Abstract

e15008 Background: Recently, exosomes widely distributed in body fluids, including blood, urine, saliva, and ascites, serve as an essential biomarker in cancers. Exosomes are considered as a cargo of potential oncogenic protein such as MET during cancer progression. Methods: Exosomes from the malignant ascites (exoAscites) of four patients with stage IV gastric cancers (GCs) were isolated by different serial centrifugation steps (300 g, 2000 g, 10,000 g, and 110,000 g at 4). After ultracentrifugation, nanoparticle tracking analysis, western blotting, and immunocytochemistry were performed for characterization of the exoAscites. Results: In this study, we enrolled 4 patients with malignant ascites which needed to be drained for symptom control. In all 4 patients, we successfully isolated highly concentrated exosomes in 50 ml of ascites (range, 55108 – 260 108exosomes/ml). (pt#1, 140108 particles/ml; pt#2, 138 108, pt#3, 55.6 108; pt#4, 260 108 exosomes/ml). In twopatients with MET amplification (METamp) in tumor specimens, exoAscites retrieved from the ascites harbored cMET protein in exosomes. In addition, the in-vitro cancer microenvironment model showed that tropism of exoAscitesharboring cMET oncogenic protein had the potential to induce cancer progression (EpCAM immunofluorescent intensity value; a 2.4-fold increase compared to control). In this model, the cancer invasiveness and angiogenesis were significantly enhanced by treatment with exoAscites with over time. (2.4-(EpCAM immunofluorescent intensity) and 3.6-(CD31 immunofluorescent intensity) fold increase, respectively). Furthermore, the cancer invasiveness was substantially increased as the exosome concentration increased from 0, 101, 103, 105, 107 exosome particles/ml. Cancer invasiveness measured by EpCAM immunofluorescent intensity was significantly decreased upon exosiMET treatment in MET amplified GC cells when compared to the control. Conclusions: For the first time, we demonstrated that exosomes from malignant ascites carry MET protein in their exosomes. Exosomes may be early mediators of cancer spread in GC.