Cinobufagin-induced apoptosis in osteosarcoma cells in vitro

Objective To study the growth inhibition,apoptosis induction effects of cinobufagin(CB)on human osteosarcoma(OS) cell line U2OS,MG63 and SaO2 in vitro and the underlying mechanism of action of cinobufagin in OS cells.Methods Cell viability was assessed by MTT assay.Cell-cycle status,apoptosis-inducing effects were evaluated by flow cytometry,fluorescent staining and DNA fragmentation assays.Inhibitors of apoptosis proteins (IAPs) and Bcl-2 family proteins including Bax,cleaved-PARP,xIAP,cIAP-1,survivin and p65 were tested by Western blot.Results MTT assay showed that CB could inhibited the growth of U2OS,MG63 and SaO2 cells in a dose-and time-dependent manner.The 48 h IC50 of CB on U2OS,MG63 and SaO2 cells were (104.83± 16.96) nmol/L,(47.07±7.5) nmol/L,and (136.72±10.08) nmol/L respectively.The induction of G2/M cell-cycle arrest was seen in the cells treated with CB.After cells were cultured for 12 h in the presence of 100 nmol/L CB,the percentages of cells in the G0/G1 phase were decreased,while G2/M phase were increased in U2OS,MG63 and SaOS2 cells,respectively.The results showed CB inhibited the proliferation of osteosarcoma cells through blocking the cell cycle in G2/M phase.Induction of apoptosis was confirmed by Hoechst 33258 and Annexin V/PI staining.After treating with 100 nmol/L CB for 48 h,the extents of apoptosis were 33.6％±6.4％,36.4％±7.8％ and 29.3％±5.1％,respectively.These results indicate that the anti-tumor activity of cinobufagin in osteosarcoma cells was due to a G2/M cell cycle arrest and apoptosis inducing effect.Western blot showed that CB could induce the apoptosis related family proteins Bax,cleaved-PARP up-regulation,xIAP,cIAP-1,survivin and p65 downregulation in OS cells.Conclusion CB can inhibit the cell viability and induce G2/M cell cycle arrest and apoptosis in U2OS,MG63 and SaO2 cells.The apoptosis-inducing effect of CB is confirmed by the regulation of apoptosis related proteins IAPs and Bcl-2 in vitro. Key words: Cinobufagin;  Osteosarcoma;  Apoptosis