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.