To test the involvement of P‐gp in resistance to DNR and VCR in t(17;19)‐ALL cell lines, we evaluated the functional drug‐efflux activity using calcein‐AM (CAM), an ABC transporter‐dependent dye.26 We performed flow cytometric analyses of CAM staining in the presence or absence of ABC transporter inhibitors such as verapamil,27 CyA,28, 29 and nilotinib.30, 31 In HALO1 cells, CAM staining level was remarkably intensified in the presence of verapamil, CyA, or nilotinib in a dose‐dependent manner (Figure 5A). Here, PGP is linked to acute lymphoblastic leukemia.