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

<p>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 (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0083467#pone-0083467-t002" target="_blank">Table 2</a>), 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.