Inhibition of cell growth and induction of apoptosis by bilobalide in FaDu human

Abstract

Bilobalide isolated from leaves of Ginkgo biloba has several pharmacological activities such as neuroprotective, anti-inflammatory and anticonvulsant effects. However, the effect of bilobalide on cancers has not been clearly established. The main purpose of this study was to investigate the effect of bilobalide on cell growth and apoptosis induction in FaDu human pharyngeal squamous cell carcinoma. This was examined by MTT assay, nuclear DAPI staining, DNA fragmentation analysis and immunoblotting in FaDu cells. The bilobalide inhibited the growth of FaDu cells in the dose- and time-dependent manners. Treatment with bilobalide resulted in nuclear condensation and DNA fragmentation in the FaDu cells. The bilobalide promoted the proteolytic cleavages of procaspase-3/-7/-8/-9 with increases in the amount of cleaved caspase-3/-7/-8/-9. The bilobalide-induced apoptosis in the FaDu cells was mediated by the expression of Fas and activation of caspase-8, caspase-3 and poly(ADP-ribose) polymerase. Immunoblotting revealed the anti-apoptotic mitochondrial protein Bcl-2 to be downregulated, but the pro-apoptotic protein Bax to be upregulated by bilobalide in FaDu cells. The bilobalide significantly increased the Bax/Bcl-2 ratio. These results suggest that the bilobalide inhibits the cell proliferation and induces the apoptotic cell death in FaDu human pharyngeal squamous cell carcinoma via both the death receptor-mediated extrinsic apoptotic pathway and the mitochondria-mediated intrinsic apoptotic pathway.