Background: Harmine has antitumor and antinociceptive effects, and inhibits human DNA topoisomerase. However, no detailed data are available on the mechanisms of action of harmine in hepatocellular carcinoma. This study aimed to investigate the effects of harmine on proliferation and apoptosis, and the underlying mechanisms in the human hepatocellular carcinoma cell line HepG2.
Methods: The proliferation of HepG2 cells was determined by the cell counting kit-8 (CCK-8) assay and the clone formation test. The morphology of HepG2 cells was examined using fluorescence microscopy after Hoechst 33258 staining. Annexin V/propidium iodide (PI) was used to analyze apoptosis and PI to analyze the cell cycle. Western blotting was used to assess expression of the apoptosis-regulated genes Bcl-2, Bax, Bcl-xl, Mcl-1, caspase-3, and caspase-9. Mitochondrial transmembrane potential (ψm) was determined using JC-1.
Results: Harmine inhibited the proliferation of HepG2 cells in a dose-dependent manner. Hoechst 33258 staining revealed nuclear fragmentation and chromosomal condensation, cell shrinkage, and attachment loss in HepG2 cells treated with harmine. The percentage of the sub/G1 fraction was increased in a concentration-dependent manner, indicating apoptotic cell death. PI staining showed that harmine changed the cell cycle distribution, by decreasing the proportion of cells in G0/G1 and increasing the proportion in S and G2/M. Harmine induced apoptosis in a concentration-dependent manner, with rates of 20.0%, 32.7% and 64.9%, respectively. JC-1 revealed a decrease in ψm. Apoptosis of HepG2 cells was associated with caspase-3 and caspase-9 activation, down-regulation of Bcl-2, Mcl-1, and Bcl-xl, and no change in Bax.
Conclusions: Harmine had an anti-proliferative effect in HepG2 cells by inducing apoptosis. Mitochondrial signal pathways were involved in the apoptosis. The cancer-specific selectivity shown in this study suggested that harmine is a promising novel drug for human hepatocellular carcinoma.