Objective: To investigate the effect of three kind of steroid saponins

extract obtained from Cestrum nocturnum on the human hepatocellular carcinoma BEL-7404 cell proliferation and its mechanism in vitro. Method: Three kind of steroid saponins of the leaves of C. nocturnum(SSCN) were separated and identified their structures by solvent. The BEL-7404 cells were cultured in vitro and cell colony measurement technique assay was used to determine the inhibition of cell proliferation. Alteration of cell cycle and apoptosis rate was defected by flow cytometry(FCM). The single cell microgel electrophoresis technique was used to analyse effect of DNA damage of BEL-7404.The effects of SSCN on Topo II mediated-pBR322 DNA unwinding were measured by using agarose gel electrophoresis. Result: SSCN significantly inhibited the proliferation of BEL-7404 cells in a time and dose-dependent manner. The results from FCM assay indicated that the percentage of cells in S phase decreased

while the percentage of cells in G0/G1 and G2/M phases increased

the phenomenon of blockage appeared and cell death was induced. The bioactive components of SSCN have effect on DNA damaged and inhibited the Topo II mediated relaxation of supercoiled pBR322 DNA effectively. Conclusion: SSCN could effectively inhibit cell proliferation and induce BEL-7404 apoptosis. With a direct relation to the dose and time

which may be correlated with factors as follows:①SSCN can arrest the cell cycle at G0/G1 and G2/M phase; ②DNA damage and cleavage of SSCN on DNA double strands may be a potential mechanism. ③CNSN can inhibit the catalytic activity of Topo II.