AP23464 inhibits proliferation, blocks cell cycle progression, and induces apoptosis of Bcr-Abl–positive K562 but not Bcr-Abl–negative HL60 leukemic cells. (A) Proliferation of K562 (Bcr-Abl–positive) or HL60 (Bcr-Abl–negative) cells in the presence of escalating concentrations of AP23464 or imatinib mesylate (0-10 000 nM). Cell growth was assessed by MTS-based viability assay. (B) Cell cycle analysis of K562 cells in the presence of AP23464. Cells (5 × 10⁵) were incubated in duplicate for 24 hours in 4 mL medium containing AP23464 (0, 0.01, 0.1, 1 μM). Fixed cells were stained with propidium iodide and analyzed on a FACSort flow cytometer to determine DNA content. The relative percentages of cells in G₁, S, or G₂/M phase were calculated from FL-2 histograms by using ModFit LT software. (C) Effect of AP23464 (0, 0.1, 1, or 10 μM) on induction of apoptosis in K562 (Bcr-Abl–positive) cells or HL60 (Bcr-Abl–negative) cells. Alexa Fluor 488 annexin V–stained cells were analyzed on a FACSort flow cytometer and histograms were generated by using CellQuest software.