Objective:To explore the effects of cinobufagin (CBF),an active component of toad venom (Bufo bufo gargarizans CANTOR),on the proliferation and apoptosis of PC3 human prostate cancer cells in vitro and preliminarily investigate the mechanism of CBF in suppressing tumor cell growth in vivo.Methods:The effect of CBF on PC3 cells proliferation was detected using MTT assay.The morphological changes of PC3 cells were observed under an optical microscope.Colony formation assays were used to observe the CBF effect on colony formation by PC3 cells.PC3 cell apoptosis after treatment with CBF for 48 hours was monitored using flow cytometry.Furthermore,the effect of CBF on the expression of myeloid cell leukemia-1 (MCL-1) and related apoptotic proteins was examined using western blotting.A xenograft model was established in BALB/c nude mice to evaluate the effect of CBF on prostate cancer in vivo.Results:The MT-T assay results illustrated that PC3 cell proliferation was inhibited in vitro by CBF in a concentration-and time-dependent manner.Compared with the control group findings,CBF significantly inhibited the formation of PC3 cells (P =.005).Flow cytometry revealed that after treatment with 50 nM CBF for 48 hours,the apoptotic rate of PC3 cells was 41.97 (5.16)%,indicating that CBF could significantly induce its apoptosis (P =.003).In addition,optical and fluorescence microscopy uncovered remarkable inhibition of cell proliferation accompanied by morphologic changes.The western blotting result indicated that CBF obviously downregulated the expression of the anti-apoptotic protein MCL-1.Most importantly,ClBF reduced the carcinogenicity of PC3 xenografts in nude mice.Conclusion:CBF can inhibit the growth of PC3 cells both in vitro and in vivo and induce apoptosis of tumor cells.The corresponding mechanism may be correlated with the activation of caspase family proteins via MCL-1.
