Figure 1. Commitment of BCR-ABL-positive cells to apoptosis following acute exposure to ABL TKIs varies by inhibitor, concentration, and extent of washout.

(A) Schematic outlining general experimental washout protocol. Briefly, BCR-ABL-positive cells were incubated in complete media alone or in the presence of each of five clinically relevant ABL TKIs either continuously (72 h) or for a short exposure (2 h for cell lines, 4 h for primary cells). For acute exposure conditions, cells were subjected to our previously published 3-wash-step protocol (standard washout) followed by an additional 5 wash steps (expanded washout) and cultured in fresh complete media for the remainder of the 72 h experiment. (B) Levels of apoptosis in K562 cells following continuous or acute exposure to ABL kinase inhibitors. Cells were incubated in the presence of the indicated inhibitor concentrations for 2 h, and samples were collected just prior to washout and immediately following standard and expanded washout. Annexin V-positivity was measured at 72 h after the start of the experiment, and bars represent the mean of at least three independent experiments performed in triplicate ± S.E.M.