Background: Buddlejasaponin IV (BS-IV), a triterpene saponin isolated from Pleurospermum kamtschaticum HOFFMANN (Umbelliferae), is known to have potent anti-inflammatory activity and cytotoxicity against diverse cancer cell lines. In the present study, we attempted to verify whether BS-IV could inhibit cell growth, and induce cell cycle arrest and apoptosis in highly invasive YD-10B human oral squamous cell carcinoma (OSCC) cells.
Methods: YD-10B cells were treated with various concentrations of BS-IV, and the cell viability was evaluated by MTT assay. Flow cytometry was conducted to examine cell phase distribution and DAPI staining was performed to observe apoptotic morphological changes in BS-IV-treated YD-10B cells. Western blot analysis was used to investigate the expression of proteins associated with cell cycle arrest and apoptosis.
Results: BS-IV treatment significantly reduced the viability of YD-10B cells and partially arrested cell cycle progression at the G2/M phase. Treatment with BS-IV substantially decreased the levels of cyclin B1 and stimulated the phosphorylation of checkpoint kinase 2 (Chk2). The expression of p21 was increased but the phosphorylation of Akt was inhibited in BS-IV-treated YD-10B cells. Furthermore, BS-IV induced release of cytochrome c from mitochondria by reducing anti-apoptotic Bcl-2 level and increasing pro-apoptotic Bax level. Active caspase-3 level and the cleavage of poly (ADP-ribose) polymerase (PARP) were enhanced by BS-IV treatment. In addition, BS-IV increased the expression of Fas death receptor and its ligand (FasL) in YD-10B cells.
Conclusions: The treatment with BS-IV inhibits the growth of YD-10B cells by inducing p21-dependent cell cycle arrest at G2/M phase and apoptosis through both mitochondrial-dependent and death receptor-mediated pathways. Thus, BS-IV is an excellent candidate for a chemopreventive agent to block the progression of human OSCC.
Keywords: Apoptosis; Buddlejasaponin IV; Cell cycle arrest; Oral squamous cell carcinoma.