Sorafenib suppresses extrahepatic metastasis de novo in hepatocellular carcinoma through inhibition of mesenchymal cancer stem cells characterized by the expression of CD90

Cancer stem cells (CSCs) are a pivotal target for eradicating hepatocellular carcinoma (HCC). We previously reported that distinctive CSCs regulating tumorigenicity (EpCAM+ CSCs) and metastasis (CD90+ CSCs) have different epithelial/mesenchymal gene expression signatures. Here, we examined the influence of sorafenib, a multiple-receptor tyrosine kinase inhibitor used as a first-line treatment for advanced HCC, on EpCAM+ and CD90+ CSCs. CD90+ cells showed higher c-Kit gene/protein expression than EpCAM+ cells. Sorafenib treatment reduced the number of CD90+ cells with attenuated c-Kit phosphorylation, whereas it enriched the EpCAM+ cell population. We evaluated the role of CD90+ and EpCAM+ CSCs in vivo by subcutaneously injecting these CSCs together in immune-deficient mice. We observed that sorafenib subtly affected the suppression of primary tumor growth maintained by EpCAM+ CSCs, but completely inhibited the lung metastasis mediated by CD90+ CSCs. We further evaluated the effect of sorafenib on extracellular vesicle (EV) production and found that sorafenib suppressed the production of EVs containing TGF-β mRNA in CD90+ cells and inhibited the cell-cell communication and motility of EpCAM+ cells. Our data suggest the following novel effects of sorafenib: suppressing CD90+ CSCs and inhibiting the production of EVs regulating distant metastasis.