SKI-606 does not specifically induce apoptosis in CML primitive and committed progenitors. CML and normal CD34⁺CD38⁻ primitive and CD34⁺CD38⁺ committed progenitors were exposed to SKI-606 or imatinib at indicated concentrations for 96 hours. Apoptosis was analyzed by FACS as the percentage of cells positively labeled by Annexin V-PE. (A) Representative data for apoptosis of CML CD34⁺CD38⁻ primitive and CML CD34⁺CD38⁺ committed progenitors. (B,C) Compiled data (mean ± SEM) for apoptosis of CML (n = 4) and normal (n = 3) primitive progenitors, respectively. (D,E) Apoptosis of CML (n = 5) and normal (n = 3) committed progenitors, respectively. Significant increase in the percentage of apoptotic cells seen in CML committed progenitors in response to imatinib is indicated (†P < .05). (F) Apoptosis in CD34⁺CD38⁺ cells after exposure to SKI-606 (0.5 μM) and imatinib (5 μM) in combination. Results represent the mean plus or minus SEM of replicate experiments (n = 7); ns, not significant.