Dose response curves of inhibitory activities of emodin, baicalin, icariin, kaempferol, celastrol and curcumin. The IC50 values were calculated by fitting with the four parameter logistic (4-PL) model: A. emodin IC50=81.05 μM, R2=0.97. B. baicalin IC50=83.52 μM, R2=0.99. C. icariin IC50=88.67 μM, R2=0.99. D. kaempferol IC50=106.74 μM, R2=0.99. E. celastrol IC50=114.02 μM, R2=0.98. F. curcumin IC50=114.27 μM, R2=0.99. R2, adjust R square values. Dose response curves of inhibitory activity were presented. Data are shown as mean ± SD of three independent experiments.