Lipka, D.Wagner, M.Dziadosz, M.Schnoder, T.Heidel, F.Schemionek, M.Vaz de Melo, J.Kindler, T.Muller-Tidow, C.Koschmieder, S.Fischer, T.Fields, A.P.2012-09-272012-09-272012PLoS One, 2012; 7(7):1-161932-62031932-6203http://hdl.handle.net/2440/73312Clinical development of imatinib in CML established continuous target inhibition as a paradigm for successful tyrosine kinase inhibitor (TKI) therapy. However, recent reports suggested that transient potent target inhibition of BCR-ABL by highdose TKI (HD-TKI) pulse-exposure is sufficient to irreversibly commit cells to apoptosis. Here, we report a novel mechanism of prolonged intracellular TKI activity upon HD-TKI pulse-exposure (imatinib, dasatinib) in BCR-ABL-positive cells. Comprehensive mechanistic exploration revealed dramatic intracellular accumulation of TKIs which closely correlated with induction of apoptosis. Cells were rescued from apoptosis upon HD-TKI pulse either by repetitive drug wash-out or by overexpression of ABC-family drug transporters. Inhibition of ABCB1 restored sensitivity to HD-TKI pulse-exposure. Thus, our data provide evidence that intracellular drug retention crucially determines biological activity of imatinib and dasatinib. These studies may refine our current thinking on critical requirements of TKI dose and duration of target inhibition for biological activity of TKIs.enCopyright: © 2012 Lipka et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Cell Line, TumorIntracellular SpaceHumansBenzamidesPiperazinesPyrimidinesProto-Oncogene Proteins c-ablAnnexin A5ATP-Binding Cassette TransportersProtein Kinase InhibitorsDrug Screening Assays, AntitumorSignal TransductionApoptosisDose-Response Relationship, DrugKineticsTime FactorsCaspase 3Leukemia, Myelogenous, Chronic, BCR-ABL PositiveImatinib MesylateJournal article002012106110.1371/journal.pone.00408530003064661000832-s2.0-8486399429623641Vaz de Melo, J. [0009-0009-5343-4893]