Figure 2
Time effect and dose effect of phenolic acids on the proliferation of T47D breast cancer cells. (a) Cells (2 × 104) were seeded in 24-well culture plates, and incubated for the indicated number of days with 10-8 M of different phenolic acids. In another series of experiments, cells were cultured in the absence of phenolic acids. The figure presents the ratio of the cell number in the presence/absence of the different phenolic acids. A typical experiment is presented, which was performed three more times with similar results. Inset: Data presented in the figure were analyzed by the application of the exponential decay equation 
, in which y is the observed ratio of the cell number in the presence/absence of the phenolic acid, y0 is the maximal observed decrease of cell proliferation (plateau), A1 is 1 - y0, x0 is the initial time of observation (= 0), and x is the time (in days) of the y observation (abscissa of the y observation). The equation after transformation is rearranged as ln [(y - y0) / (1 - y0)] = -xt, the left side of which is the logit of the earlier quantity. From this equation one can obtain the calculation of t, which is an estimate of the half-life (t1/2) of the effect of the applied agent. In the case of the monotonous curves (sinapic acid, syringic acid, protocatechuic acid, and 3,4-dihydroxy-phenylacetic acid), this t1/2 was varying between 0.9 and 1.3 days. In the case of ferulic acid, in which the observed curve follows that of sinapic acid and ferulic acid for short incubation times and jumps to that of protocatechuic acid and 3,4-dihydroxy-phenylacetic acid for longer incubation times, the calculated t1/2 was 5.7 days. Finally, for caffeic acid, in which a sigmoidal curve was observed, data were not well fitted to the curve and the calculated t1/2 was 4.1 days. (b) Dose effect of phenolic acids on T47D cell proliferation. Cells (2 × 104) were incubated for 5 days in the absence or the presence of the indicated concentrations of phenolic acids, ranging from 10-12 to 10-6 M. The figure presents the ratio of the number of cells in the presence/absence of the indicated phenolic acids. A typical experiment is presented, repeated three more times with similar results.