Objective: To investigate the therapeutic value of inhibiting the expression of insulin-like growth factor-I receptor (IGF-IR) using picropodophyllin (PPP) by studying the effects on proliferative and metastatic potentials of human hepatocellular carcinoma (HCC) using an in vitro cultured cell system.
Methods: IGF-IR expression in human HCC cell lines (Bel-7404, Bel-7402, HepG2, and Huh-7) and human hepatocytes (L02) was assessed at baseline (pre-treatment) and after PPP treatment by western blotting. Changes in cell cycle were analyzed by flow cytometry and in cell viability by sulforhodamine B staining. Early apoptosis was detected by annexin-V/FITC and propidium iodide double-staining assay. Caspase-3/7 activity was suppressed by z-VAD-FMK and analyzed by homogeneous luminescence assay. Effects on cell motility were tested by wound-scratch test. Between-group differences were assessed by t-test or one-way analysis of variance.
Results: IGF-IR was markedly up-regulated in all HCC cell lines (vs. non-hepatoma hepatocytes). HCC cells with PPP-inhibited IGF-IR showed time-dependent decreases in cell motility and viability. After treatment with PPP for 24 hours, the proportion of HCC cells in G1 phase was 2.1% +/- 0.4%, in S phase was 11.0% +/- 0.7%, and in G2/M phase was 87.1% +/- 0.6%, and no healing was observed in the wound-scratch assay. The PPP treatment induced cell apoptosis, as evidenced by enhanced caspase-3/7 activity; the proportion of annexin-V+/PI- cells was significantly higher in the HepG2 cells than in the non-hepatoma hepatocytes (16.4% +/- 0.4% vs. 5.8% +/- 0.2%, t = 14.05, P less than 0.01). After z-VAD-FMK treatment, the apoptosis rate was significantly higher in the HepG2 cells than in the non-hepatoma hepatocytes (11.3% +/- 0.7% vs. 5.8% +/- 0.2%, t = 11.83, P less than 0.01).
Conclusion: IGF-IR is associated with proliferation, cell motility, and apoptosis of HCC cells, and may be a promising molecular target for HCC.