Fig. 2

U251, U87, H4 and LN229 (a) were treated with COP (0, 0.625, 1.25, 2.5, 5 and 10 mg/ml) for 24, 48 and 72 h, respectively; BV2 (b) cells as a control cell were treated with COP (0, 1.25, 2.5, 5 and 10 mg/ml) for 24 h; cell viability was analyzed by the MTT assay. All values represent the mean ± SD from 3 independent experiments. *, P < 0.05; **, P < 0.01; ***, P < 0.001 compared with the control group