Objective: To study the effect of polyphyllin I(PPI) on the cell cycle of human colon cancer cell line HCT 116

and investigate the mechanism. Method: 3-(4

5-dimethyl-2 thiazolyl)-2

5-diphenyl-2-H-tetrazolium bromide (MTT) assay was used to detect the inhibitory activity of PPI on HCT116 cells in vitro

then effect of PPI on the number of HCT116 cellular nuclear was observed by Hoechst 33258 staining; flow cytometry was used to detect the cell cycle changes of HCT116 cells. Western blot assay was used to detect the expression and activity of cell division cyclin2 (CDC2)

cell division cyclin25 homolog C (cdc25c) protein in cells; and immunofluorescence and confocal laser scanning microscope were used to detect the effect of PPI on cell microtubules of HCT116 cells. Result: MTT assay showed that PPI inhibited the proliferation of HCT116 in a dose-time dependent manner. Hoechst 33258 nuclear staining showed that there the number of dual-core cells in PPI group was significantly increased(P<0.05

P<0.01); flow cytometry showed that the cell cycle was arrested in G2/M phase. Western blot assay indicated that PPI could not inhibit but could promote the expression and activity of the G2/M phase related proteins CDC2 and CDC25C. In addition

in confocal laser scanning microscope detection

we found that PPI could lead to cell microtubules disorder. Conclusion: PPI could make the HCT116 cells arrested in G2/M phase

and the action mechanism is related to interference with microtubule structure.