ABCB1 and cancer: In order to distinguish the potential growth retardation effect from the drug-induced cytotoxicity restored by sitravatinib, we examined the effect of sitravatinib on apoptosis induced by colchicine or topotecan, both known inducers of apoptosis [38,43], in ABCB1-overexpressing KB-V-1 cancer cells and ABCG2-overexpressing S1-M1-80 cancer cells, respectively.