Figure 5. Cytotoxicity and combination experiments in MDCKII-ABCB1 and parental cell lines.

Cytotoxic effect of (A, E) purvalanol A (▪), (B, F) olomoucine II (▾), (C, G) roscovitine (▴) or daunorubicin (•) and their combination (⧫) on MDCKII-ABCB1 or MDCKII parent cells. For combinations, concentrations corresponding to particular points in the graph are sums of concentrations of the individual drugs administered in fixed concentration ratios (Table 2), based on the ratio of their respective EC₅₀ values. Presented data are means ± SD obtained from at least three independent experiments performed in triplicate. (D, H) The cytotoxic effect (combination index, CI, plot) of CDKi and daunorubicin combinations on MDCKII-ABCB1 or MDCKII parent cells, obtained using CompuSyn software. Fractional effects (Fa) were calculated from the cell viability values of individual compounds; Fa  =  0 means no antiproliferative effect, Fa  =  1 means 100% antiproliferative effect. CI  =  0.9–1.1 indicates additive effect, CI <0.9 synergism and CI > 1.1 antagonism.