OV6+ tumor-initiating cells contribute to tumor progression and invasion in human hepatocellular carcinoma

Background & Aims

Accumulating evidence suggests the involvement of tumor-initiating cells (T-ICs) in cancer genesis, but whether liver T-ICs contribute to HCC invasion and metastasis remains unclear.

Methods

OV6⁺ T-ICs were isolated from SMMC7721 and HuH7 cell lines by magnetic sorting. Characteristics of T-ICs were assessed by in vitro and mouse xenograft assays. Expression of OV6 was determined by immunostaining in specimens from 218 HCC patients, and Kaplan–Meier survival analysis was used to determine the correlation of OV6 expression with prognosis.

Results

OV6⁺ T-ICs isolated from HCC cell lines not only possess a higher capacity to form tumor spheroids in vitro, but also had a greater potential to form tumors when implanted in non-obese diabetic/severe combined immunodeficient mice, suggesting their elevated self-renewal capacity and tumorigenicity. Moreover, OV6⁺ T-ICs exhibited more invasive and metastatic potentials both in vitro and in vivo. Patients with more OV6⁺ tumor cells were associated with aggressive clinicopathologic features and poor prognosis. CXCR4 is expressed at higher levels in OV6⁺ cells. Recombinant stromal cell-derived factor-1 (SDF-1) treatment expanded the OV6⁺ HCC T-ICs population, by sustaining the stem cell property of OV6⁺ cells. The SDF-1 effect was blocked by a specific CXCR4 inhibitor, AMD3100, or transfection of siRNA targeting CXCR4.

Conclusions

OV6⁺ HCC cells may represent a subpopulation of T-ICs with augmented invasion and metastasis potential, which contribute to progression and metastasis of HCC. The SDF-1/CXCR4 axis also provides therapeutic targets for elimination of liver T-ICs.