Circulating Hepatocellular Carcinoma Cells are Characterized by CXCR4 and MMP26

Primary hepatocellular carcinoma (HCC) is highly invasive, and often results in an early distal metastasis resulting in poor prognosis and therapeutic outcome. Cancer cells disseminating from the tumor and entering circulation are termed circulating tumor cells (CTCs). Although substantial progress has been made to identify those CTCs in HCC, no good marker (cocktail) has so far been identified.

Since only tumorigenic CTCs form metastatic tumor in distal organs, we thus compared the HCC cells that form tumor spheres in culture to those that do not. We transduced HCC cells with a RFP reporter under MMP26 promoter and purified MMP26+CXCR4+ HCC cells. We examined tumor sphere formation in culture, presence of tumor cells in the circulation as well as capability of developing metastatic tumor after transplantation of MMP26+CXCR4+ HCC cells into nude mice, compared to other populations in HCC.

Sphere-forming HCC cells expressed high levels of MMP26 and CXCR4. MMP26+CXCR4+ HCC cells formed significantly more tumor spheres in culture, compared to MMP26-CXCR4-, MMP26-CXCR4+ or MMP26+CXCR4- HCC cells. Moreover, tumor cells were more frequently detected in the circulation when MMP26+CXCR4+ HCC cells were subcutaneously transplanted. Further, subcutaneous transplantation of MMP26+CXCR4+ HCC cells, but not transplantation of MMP26-CXCR4-, MMP26-CXCR4+ or MMP26+CXCR4-HCC cells significantly developed distal metastatic tumors.

MMP26+CXCR4+ cells may be CTCs in HCC. Selective elimination of MMP26+CXCR4+ cells may substantially reduce HCC metastasis after primary tumor resection.