Growth inhibition and apoptosis-inducing effect on human cancer cells by RCE-4, a spirostanol saponin derivative from natural medicines

Reineckia carnea has been used to treat several diseases in folk remedies. RCE-4 has been isolated from several plants of the family Liliaceae, but its biological activity has not yet been reported. In the present study, we found that RCE-4 exhibited potent cytotoxicity to the tested human cancer cell lines, and the CaSki cell line was the most sensitive with an IC50 of 3.37 mu M. Thus, we presented the apoptosis-inducing effect of RCE-4 on CaSki cervical cancer cells and investigated the relevant mechanisms. Based on observations using transmission electron microscopy, RCE-4-treated cells manifested nuclear shrinkage, condensation and fragmentation. Annexin V/PI dual staining flow cytometry assay further confirmed that RCE-4 caused a dose-dependent early apoptotic effect. Prior to these events, RCE-4 triggered a rapid decrease of the mitochondrial membrane potential and caused the release of cytochrome c from the mitochondria into the cytoplasm. RCE-4 increased the expression of Bax and decreased the expression of Bcl-2, thus augmenting the Bax/Bcl-2 ratio. These findings suggest that RCE-4 induces mitochondrial-mediated apoptosis in CaSki cells and has the potential to be developed as an anticancer agent.