Apoptosis induction of ZBB-006, a novel synthetic diterpenoid, in the human hepatocellular carcinoma cell line HepG2 in vitro and in vivo.

Diterpenes, present in many medicinal plants, have been the focus of continuous studies for the development of new anticancer agents. ZBB-006 is a new synthetic diterpenoid derivative which exhibited significant anti-proliferation activity against various cancer cell lines in our previous study. Here, we investigated the antitumor effect of ZBB-006 and its potential mechanisms in the human hepatocellular carcinoma cell line HepG2, both in vitro and in vivo. We found that oral administration of ZBB-006 effectively suppressed the growth of HepG2 xenograft tumor in nude mice without body weight decline, compared with the control group. Meanwhile, the growth inhibitory effect of ZBB-006 on HepG2 cells was observed with MTT assay. Then apoptosis induced by ZBB-006 in HepG2 cells was evidenced by DAPAPI staining and Annexin V/PI double staining assay. ZBB-006 also dissipated the mitochondrial membrane potential (Delta Psi m) apparently as revealed by JC-1 staining. Furthermore, the cleavage of PAPARP, activation of caspase-3 and caspase-9 but not caspase-8 was demonstrated by western blot assay both in vitro and in vivo. Additionally, the proapoptotic protein Bax was markedly elevated, while the antiapoptotic protein Bcl-2 was downregulated. Collectively, our data indicated that ZBB-006 exerted a strong antitumor effect on HepG2 cells by initiating the mitochondrial-dependent apoptosis, and it has potential to be explored as a new promising therapeutic agent against human hepatoma.