Activity of PP2 on normal HPCs and AML cell proliferation and survival. (A) Fresh AML cells (patient nos. 6, 51, 54) and normal HPC (right panel) were grown in clonogenic assays in the presence of increasing doses of PP2 (black bars, control; gray bars, 2 μM; hatched bars, 5 μM; white bars, 10 μM). Results are presented as percentage of control and are mean plus or minus SEM of duplicates. Results shown for normal CD34⁺ HPCs are mean plus or minus SEM of 2 independent experiments performed in duplicate. IC₅₀ values were 4.8, 3.5, and 7.7 μM for patient nos. 6, 51, and 54, respectively. Five other patients (nos. 42, 47, 48, 50, 55) were also analyzed with IC₅₀ values of 28.2, 9.5, 10.2, 14.5, and 0.5 μM, respectively. (B) AML samples (patient nos. 13, 42, 43, 44–46) were incubated with or without 10 μM PP2 for 24 hours, then processed for apoptosis studies using annexinV/PI staining and Western blot analysis using anti-PARP and anti-caspase 3 antibodies. Results are presented as mean percentages (± SEM) of annexin V-positive cells in treated vs untreated cells (***P < .001). (C) Fresh AML samples (patient nos. 40 and 48) were electroporated with Lyn siRNA or control siRNA, and their clonogenic properties were analyzed. CFU-Ls numbers were scored at day 7. Results are expressed as absolute number of leukemic colonies and are mean plus or minus SEM of duplicates.