Effect of multiple TKI washouts on early apoptosis in K562 cells. Cells were treated in vitro with imatinib (A) or dasatinib (B) at a low-dose (i; 2.5 μM or 1 nM, respectively) or high-dose (ii; 32.5 μM or 100 nM, respectively). Cells were cultured under four conditions, as indicated: 1) continuous TKI; 2) TKI washout after 0.3 hours (1× washout); 3) TKI washout after 0.3 hours + second washout after 1 hour (2× washout) and 4) TKI washout after 0.3 hours + second washout after 1 hour + third washout after 2 hours (3× washout). Each TKI washout was performed three times with 10 ml of PBS. Cell aliquots were harvested after 0.3, 24, 48, and 72 hours, and Annexin-V was used to measure apoptosis by flow cytometry (n=3).