ObjectiveTo investigate the effects of cinobufagin on the apoptosis in U-2OS osteosarcomas cells (U-2OS cells) and explore its potential mechanism. MethodsThe cytostatic effects of cinobufagin (10, 20, 50, 100, 200, and 400 nmol/L) on U-2OS cells were evaluated by MTT assay at 24, 48, and 72 hours after culture; simple U-2OS cells served as control group. The impact of cinobufagin (100 nmol/L) on the apoptosis in U-2OS cells was determined by flow cytometry at 48 hours after culture, which were treated with cinobufagin (experimental group) or with cinobufagin plus Z-VAD-FMK (control group), and simple U-2OS cells served as blank control group. The Caspase-3 activity was measured by Caspase-3 activity assay kit at 48 hours after culture, which were treated with cinobufagin (20, 50, and 100 nmol/L), and simple U-2OS cells served as control group.The expression of apoptosis signal pathway related proteins in U-2OS cells treated with cinobufagin were detected by Western blot at 48 hours after culture, which were treated with cinobufagin (20, 50, and 100 nmol/L), and simple U-2OS cells served as control group. ResultsThe results of MTT assay showed that cinobufagin inhibited the proliferation of U-2OS cells in a dose- and time-dependent manners. At each time point, the growth rate of U-2OS cells was significantly reduced with the increasing cinobufagin concentration, and as time prolonged, the growth rate of U-2OS cells behaved the same way in the same group. There were significant differences among different time points and groups (P<0.05). The apoptotic rate of experimental group (46.87%±11.23%) was significantly higher than that of the control group (2.34%±0.98%) and blank control group (1.04%±0.25%) (P<0.05). The Caspase-3 activity in 20, 50, and 100 nmol/L groups were 1.14±0.32, 1.31±0.41, and 1.92±0.54, respectively, which were significantly higher than that in control group (P<0.05). Compared with 20 and 50 nmol/L groups, 100 nmol/L group significantly increased the Caspase-3 activity in U-2OS cells (P<0.05). Compared with the control group, the expressions of cleaved Caspase-3, cleaved Caspase-9, and Bax were obviously up-regulated; the Bcl-2 expression was down-regulated; and the ratio of Bax/Bcl-2 was increased in different cinobufagin-treated groups (P<0.05). The same tendency was seen in different cinobufagin-treated goups, showing significant differences among groups (P<0.05). ConclusionCinobufagin can inhibite the proliferation of U-2OS cells, and induce cell apoptosis. The potential mechanism of cinobufagin-induced apoptosis may be related to the mitochondria-mediated pathway.