Abstract: BACKGROUND ＆ AIM: To investigate the effects of quercetin on proliferation, cell cycle and apoptosis of colon carcinoma cell line SW480 and to study its probable molecular mechanisms. MATERIALS AND METHODS: SW480 cells were treated with different concentrations of quercetin(10, 20, 40, 80, 160 μmol/L)for 24 h, 48 h and 72 h. Then the cell proliferation, cell cycle, apoptosis rate and cyclin B1 protein expression of SW480 cells were analyzed using MTT assay, flow cytometry and immunoblot methods, respectively. RESULTS: Proliferation of SW480 cells was promoted by quercetein at a concentration of 20 μmol/L(P<0.05), while it was significantly inhibited by quercetin at concentrations of 40, 80, 160 μmol/L(P<0.01), in a dose_and time_dependent manner. After treatment with 20, 40, 60, 80 μmol/L quercetin for 48 h, the percentages of SW480 cells at G0/G1 phase were decreased, and those at G2/M phase were increased markedly (P<0.01). when SW480 cells were incubated with 80 μmol/L quercetin for 48 h, the apoptosis rate increased from baseline of 2.68％±1.04％ to 13.32％±4.62％(P<0.01). The expression of cyclin B1 protein could be down_regulated by quercetin at concentrations of 40, 60, 80 μmol/L. CONCLUSION: Quercetin at lower concentrations could promote proliferation of colon carcinoma cell line SW480, while it could inhibit proliferation and induce apoptosis of these cells at higher concentrations. Quercetin might exert its anti_tumor effect by blocking the cell cycle, inducing apoptosis and down_regulation of cyclin B1 protein.

Key words: quercetin, SW480, cell cycle, cell apoptosis, cyclin B1