Identification of side population cells in human hepatocellular carcinoma cell lines with stepwise metastatic potentials

Purpose  To identify the side population (SP) cells from four hepatocellular carcinoma (HCC) cell lines with stepwise metastatic potentials. Methods  SP cells were sorted from HCCLM3, MHCC97-H, MHCC97-L and Hep3B by flow cytometry, and then analyzed by differentiation study, clonogenic assay, chemoresistance study and tumorigenicity assay in vivo. The expression of ABCG₂ in SP cells was detected by immunocytochemistry, western blotting and real-time quantitative PCR, respectively. Results  There was significant difference in SP proportion among HCCLM3, MHCC97-H, MHCC97-L and Hep3B (28.7 ± 1.6%, 14.5 ± 0.6%, 4.2 ± 0.4%, 0.9 ± 0.1%, respectively, P < 0.01). All the SP cells showed similar characteristics of self-renewal, high clonogenicity, remarkable chemo-resistance and high expression of ABCG₂. As low as 2,000 SP cells could initiate tumors in non-obese diabetic/severe combined immunodeficiency mice successfully. Conclusions  SP cells purified from HCC cell lines harbors cancer stem cell-like properties, and may be related to the metastatic potentials and therapeutic-resistance of HCC. Guo-Ming Shi and Yang Xu contributed equally to this work. This is an original work by all the authors and no previous presentations, reports, or publications contain any material that appears in the article.