Induction of apoptosis in human Hep3B hepatoma cells by norcantharidin through a p53 independent pathway via TRAIL/DR5 signal transduction

To investigate the inhibitory activities of norcantharidin (NCTD), a demethylated analogue of cantharidin, on Hep3B cells (a human hepatoma cell line) with deficiency of p53. The survival rate of the Hep3B cells after treating with NCTD was measured by MTT assay. Cell cycle of treated cells was analyzed by flow cytometry, and DNA fragmentation was observed by electrophoresis. The influence of inhibitors for various caspases and anti-death receptors antibodies on the NCTD-induced apoptosis in the cells was determined. NCTD treatment resulted in growth inhibition of Hep3B cells in a dose- and time-dependent manner. Cell cycle analysis of the cells after treatment with NCTD for 48 h shows that NCTD induced G(2)M phase arrest occurs at low concentration (a (c) 1/2 25 mu mol/L) but G(0)G(1) phase arrest at high concentration (50 mu mol/L). The addition of both caspase-3 and caspase-10 inhibitors completely inhibited DNA fragmentation. Addition of anti-TRAIL/DR5 antibody significantly inhibited DNA fragmentation. NCTD may inhibit the proliferation of Hep3B cells by arresting cell cycle at G(2)M or G(0)G(1) phase, and induce cells apoptosis via TRAIL/DR5 signal transduction through activation of caspase-3 and caspase-10 by a p53-independent pathway.