After being washed three times with TBST(20 mM Tris-Cl, pH 7.5, 150 mM NaCl, 1 g/L Tween20), membranes were incubated with secondary antibodies. After incubation, the membranes were washed three times with TBST, and visualization was made using an ECL kit. Statistical SC75741 mouse analysis The data are expressed as mean ± SD. Statistical correlation of data was checked for significance by ANOVA and Student’s t test. Differences with P < 0.05 were considered significant. These analyses were performed using SPSS 11.0 software. Results Osthole inhibited A549 cell proliferation To investigate the growth inhibition effects of Osthole, the cells were treated with

different concentrations of Osthole for 24, 48 and 72 h, and the rate of inhibition was determined by MTT assay. We observed that growth of A549 cells was suppressed in a dose- and time-dependent manner(Figure 2). Figure 2 The proliferative inhibition effects

of Osthole on human lung cancer A549 cells. *p < 0.001 versus control group. Osthole induces G 2/M arrest To determine whether Osthole inhibits the cell cycle progression of A549 cells, the cells were treated with different concentrations of Osthole (0, 50, 100, and 150 μM) for 48 h and the cell cycle distribution was analyzed by flow cytometry. As shown in Figure 3, the percentage of cells in G2/M phase with Osthole treatment were 4.9%, 8.8%, 14.1% and 19.5% after 48 h, respectively. Figure 3 click here Cell cycle distribution analysis by DNA flow cytometry. (A) A549 cells were treated with (0, 50, 100 and 150 μM) Osthole for 48 h. Then the cells were harvested and treated with RNase, stained with PI. The cell cycle distribution was analyzed by flow cytometry. (B) The percentage of cells in G2/M

phase in histograms. *p < 0.01, **p < 0.001 versus Florfenicol control group. Osthole induces the apoptosis of A549 cells A549 cells were treated with different concentrations of Osthole (0, 50, 100, and 150 μM) for 48 h and were analyzed by flow cytometry. As showed in Figure 4A, B, the numbers of early and late apoptotic cells were significantly increased compared to control group. The proportion of early and late apoptotic cells in the 150 μM treatment group was about six times higher than in the drug-free group. The proportion of apoptotic cells in treated cells were increased in a dose-dependent manner. Figure 4 Apoptosis analysis by flow cytometry and fluorescent microscopy. (A) Apoptotic rates analysis by Annexin V/PI staining. A549 cells were treated with (0, 50, 100 and 150 μM) Osthole for 48 h. Then the cells were harvested and were stained with Annexin V/PI and flow cytometric analysis was performed to analyze apoptosis rates. (B) Summaries of the apoptosis rates in histograms. *p < 0.05, **p < 0.01, ***p < 0.001 versus control group. (C) Cell apoptosis observed by Hoechst 33342 staining. A549 cells treated with (0, 50, 100 and 150 μM) Osthole for 48 h.