Role of Exosomes in Liver Cancer Metastasis

Abstract

Role of Exosomes in Liver Cancer Metastasis Background: Hepatocellular carcinoma (HCC) is a primary malignancy of liver. HCC is often diagnosed at an advanced stage accompanied by extrahepatic metastasis. Despite the studies on extrahepatic metastasis in HCC carried out over the years, the precise mechanistic basis of HCC metastasis has not been fully explained. Emerging evidences have demonstrated cancer cells derived exosomes play an important role in influencing the local tumor microenvironment and forming pre-metastatic niche in distant organ sites. Thus, exosome research may bring new hope to solve the mystery of metastatic organotropism in HCC. Methods: Exosomes were isolated from the conditioned medium of different cell lines by ultracentrifugation and validated by transmission electron microscopy, nanoparticle tracking analysis and immunoblotting of exosome markers. The biological effects of exosomes were studied using transwell and matrigel invasion assays. The in vivo effect of exosomes in promoting liver tumor growth and distant metastasis were analysed in mice “educated” with repeated intravenous injection of exosomes. In lung metastatic site, the pulmonary vasculature and vascular leakiness were revealed by FITC-lectin stain and presence of Texas Red-dextran, respectively. Results: Exosomes were isolated and a higher amount of exosome protein was obtained from metastatic MHCC97L and MHCCLM3 cells when compared to normal liver cell MIHA and non-metastatic BEL7402 cells. Functionally, exosomes of metastatic cells significantly augmented both the migratory and invasive properties of naïve normal liver cells LO2 and non-metastatic SMMC7721 and BEL7402 cells. Exosome “education” of mice by MHCC97L-exosomes enhanced the growth of primary tumor in liver and distant metastasis to lungs. Analysis of exosome organotropism showed that fluorescently labelled MHCC97L-exosomes were frequently observed in the lung as compared to other organ sites. Further study of vascular permeability in the lung revealed MHCC97L-exosomes destabilized the pulmonary vasculature and enhanced the endothelial permeability of lung. Proteomic profiling of MIHA- and MHCC97L-exosomes revealed distinct expression profiles. Conclusion: Exosomes plays a crucial role in the interplay between HCC cells and microenvironment of the distant organ that enhances liver cancer metastasis.