Effect of axitinib on the intracellular accumulation of Dox and Rho123 in S1 and S1-M1-80 cells. The accumulation of Dox (A) and Rho 123 (B) was measured by flow cytometric analysis after cells were preincubated with or without axitinib and FTC for 3 h at 37°C and then incubated with 10 μmol/L Dox or 5 μmol/L Rho123 for another 3 h or 0.5 h at 37°C, respectively, as described in Materials and Methods. (A) Intracellular accumulation of Dox and Rho123 was not significant affected by axitinib in S1 cells. (B) The accumulation of Dox and Rho123 was increased in a dose-dependent manner in S1-M1-80 cells. (C, D) Dox and Rho123 levels were expressed as fold change in fluorescence intensity relative to control MDR cells. They are calculated by dividing the fluorescence intensity of each sample with that of MDR cells treated with Dox and Rho123. Columns, means of triplicate determinations; bars, standard deviation. **P < 0.01 versus the MDR control group. Independent experiments were performed at least three times, and a representative experiment is shown.