We found that 5 μM of sitravatinib was able to block the drug transport function of ABCB1 and significantly increased the intracellular accumulation of calcein, a fluorescent product of an ABCB1 substrate calcein-AM [45], in ABCB1-transfected MDR19-HEK293 cells (Figure 4a) and ABCB1-overexpressing KB-V-1 cancer cells (Figure 4b). Here, ABCB1 is linked to cancer.