Figure 4. MDR1 expression was associated with volasertib-resistance.

(A) The expressions of MDR1 in both the parental and the volasertib-resistant K562 and HEL cells were assessed by FCM. (B) Drug efflux assay was performed in the volasertib-resistant K562 cell using a fluorescent dye which was a substrate of MDR1. (C) The GI₅₀ values of volasertib in both parental and volasertib-resistant K562 and HEL cells with or without MDR1 inhibitor, zosuquidar. (D) The expressions of MDR1 in HAL01, KG1a, and SU-DHL4 cells were analyzed by FCM. (E) The GI₅₀ values of volasertib in HAL01, KG1a, and SU-DHL4 cells with or without zosuquidar. Error bars represent the mean values ± S.D. of at least three independent experiments.