All-trans retinoic acid (ATRA) inhibits insufficient radiofrequency ablation (IRFA)-induced enrichment of tumor-initiating cells in hepatocellular carcinoma

Objective: Local recurrence of hepatocellular carcinoma (HCC) after radiofrequency ablation (RFA) treatment remains a serious problem. Tumor-initiating cells (TICs) are thought to be responsible for tumor relapse. Here, we investigated the effect of the TIC differentiation inducer, all-trans retinoic acid (ATRA), on RFA and explored the potential molecular mechanisms. Methods: The proportions of CD133+ and epithelial cell adhesion molecule (EpCAM)+ TICs in recurrent HCC after RFA and primary HCC were first determined in clinic. Then, the effect of heat intervention or insufficient RFA (IRFA) on the malignant potential of HCC cells, including cell migration, sphere formation ability, tumor growth, the proportion of CD133+ and EpCAM+ TICs and expression of stem cell-related genes, was evaluated in vitro and in vivo. Finally, the effect of ATRA on the tumor growth and the proportion of TICs was evaluated. Results: In clinical data, a higher proportion of CD133+ and EpCAM+ TICs was found in recurrent tumors than in primary tumors. In vitro heat intervention promoted the cell migration and sphere formation ability. Additionally, it increased the proportion of CD133+ and EpCAM+ TICs and the expression of stem cell-related genes. In addition, after IRFA the residual tumors in xenografts grew faster and had more TICs than untreated tumors. ATRA remarkably inhibited residual tumor growth after IRFA by elimination of TICs though the PI3K/AKT pathway. Combination treatment with ATRA resulted in longer survival outcomes in mouse xenografts than RFA alone. Conclusions: ATRA, as a TIC differentiation inducer, could help to improve the effect of RFA treatment, which was partially attributed to its effect against TICs. The data indicated its potential as an alternative drug in the development of better therapeutic strategies for use in combination with RFA.