Consequences of altered transporter expression on intracellular imatinib accumulation. (A) Under normal conditions (A), an adequate imatinib concentration is achieved inside the cell and the leukemia cell undergoes cell death. (B) With the underexpression of uptake transporters or the overexpression of efflux transporters, the intracellular imatinib concentration is too low to inhibit BCR-ABL to an extent that will cause cell death. Im indicates imatinib.