Assessment of apoptosis in total CML cells and the quiescent fraction by measurement of caspase-3 activity (n = 4). Percentage of (A) total and (B) quiescent (CD34⁺ CFSE^max) caspase-3⁺ CML cells in the different treatment arms after 72 hours of culture. In the quiescent fraction, P = .045 for BMS-214662-containing versus noncontaining arms. Data are represented as mean plus or minus SEM. Illustrative FACS histograms demonstrate (C) increased TUNEL activity (FL-1 channel) in CD34⁺ CML cells, cultured in SFM only, treated with BMS-214662 compared with no drug control or treatment with BMS-225975, and (D) BMS-214662-induced decrease in the membrane potential, as indicated by a decrease in TMRE signal (FL-2 channel). (E) Percentage of caspase-3⁺ cells in both CML CD34⁺38⁻ and CD34⁺38⁺ cells after 24 and 48 hours of treatment with BMS-214662 in SFM alone. (F) Percentage of caspase-3⁺ cells in normal CD34⁺38⁻ cells after 24 and 48 hours of treatment with BMS-214662. (C-F) Representative results for 3 independent experiments. FSC indicates forward scatter.