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 biologicalactivity has not yet been reported. In the present study, we found that RCE-4exhibited potent cytotoxicity to the tested human cancer cell lines, and the CaSkicell line was the most sensitive with an IC50 of 3.37 µM. Thus, we presented theapoptosis-inducing effect of RCE-4 on CaSki cervical cancer cells and investigatedthe 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 causeda dose-dependent early apoptotic effect. Prior to these events, RCE-4 triggereda rapid decrease of the mitochondrial membrane potential and caused the releaseof cytochrome c from the mitochondria into the cytoplasm. RCE-4 increased theexpression of Bax and decreased the expression of Bcl-2, thus augmenting the Bax/Bcl-2ratio. These findings suggest that RCE-4 induces mitochondrial-mediated apoptosisin CaSki cells and has the potential to be developed as an anticancer agent.