ABCG2 is overexpressed on CML CD34⁺cells, is functional, and interacts with IM. (A) Cell lines were tested for their capacity to efflux B-P. Unstained cells (filled curve), ABCG2-positive AML6.2 cells with B-P (light gray shaded curve; labeled B-P alone), and AML6.2 with B-P + 10 μM FTC (dark gray shaded curve; labeled FTC) and with increasing concentrations of IM added (open curve; labeled 0.1 IM, 0.5 IM, 2.5 IM, 5 IM). (B) Normal CD34⁺ cells were tested in the same manner. Normal CD34⁺ cells with no B-P (unstained control [filled curve]) and incubated with B-P alone (light gray shaded curve; labeled B-P alone), B-P + 10 μM FTC (dark gray shaded curve; labeled FTC), and B-P + 5 μM IM (open curve; labeled 5 IM). Representative data shown. (C) CML CD34⁺ cells assayed similarly. CML CD34⁺ cells with no B-P (unstained control [filled curve]) and incubated with B-P alone (light gray shaded curve; labeled B-P alone), B-P + 10 μM FTC (dark gray shaded curve; labeled FTC), and B-P + 5 μM IM (open curve; labeled IM). Plots are one representative plot from n = 6 samples assayed in duplicate. (D) Mean data from CML cells. Mean data (n = 6) normalized to the maximum B-P retention as determined by incubation of CML CD34⁺ cells in B-P + 10 μM FTC (dark gray bar), cells with B-P alone and capable of efflux (light gray bar), and cells with B-P and 5 μM IM (open bar). Statistical analysis was by paired Student t test. All data are mean ± SEM.