Triptolide inhibits viability and induces apoptosis in liver cancer cells through activation of the tumor suppressor gene p53

The present study investigated the effect of triptolide on viability and apoptosis along with underlying mechanism in liver cancer cells. CCK-8 assay showed that triptolide treatment for 48 h significantly reduced the viability of HepG2 and QSG7701 cells at 50 µM concentration. Annexin V-FITC and propidium iodide staining showed that triptolide treatment of HepG2 cells at 50 µM concentrations induced apoptosis in 56.45% cells compared to only 2.36% cells in the control cultures. Western blot assay showed that treatment of HepG2 cells with 50 µM concentration of triptolide significantly induced phosphorylation of p53 in a 2 h-treatment. Phosphorylation of histone H2A.X indicator of DNA damage was induced by triptolide treatment after 12 h in HepG2 cells. The level of nuclear p53 in a 6 h-treatment with 0, 10, 20, 30, 40 and 50 µM concentration of triptolide was found to be 15.3, 19.6, 28.5, 43.7, 63.8 and 91.5%, respectively. Treatment of HepG2 cells with triptolide at 50 µM concentration caused a significant increase in the binding potential of p53 to DNA. Triptolide treatment of HepG2 cells caused a significant increase in the expression of p21, Bax and DR5 genes in HepG2 cells. It also increased the expression of miR-34b and miR-34c in HepG2 cells markedly. Treatment of HepG2 cells with p53 inhibitor, pifithrin-α prior to incubation with triptolide significantly prevented induction of cell apoptosis. Suppression of p53 expression by siRNA inhibited the expression of p53 as well as its target genes along with the prevention of apoptosis induction. In conclusion, triptolide inhibits viability and induces apoptosis in liver cancer cells through activation of the tumor suppressor gene p53. Thus, triptolide can be used for the treatment of liver cancer.