Compared with HL-60, HL-60/LR cells are highly resistant to apoptosis induced by LAQ824, SAHA, and LBH589. HL-60 (A) or HL-60/LR cells (B) were treated with the indicated concentrations of LAQ824 (top panel), SAHA (middle panel), and LBH589 (bottom panel) for 48 hours. After this, the percentage of annexin V–stained apoptotic cells was determined by flow cytometry. Values on the curves represent the mean of 2 experiments performed in duplicate. IC₅₀ values were determined and indicated in the top left of each graph. Error bars indicate SE. (C) After treatment of cells with 500 nM LAQ824 for 24 hours, cells were Wright stained and the morphology of the untreated and LAQ824-treated cells was determined by light microscopy with a Nikon Eclipse 50i microscope (Nikon, Melville, NY) using a PLAN 40×/0.65 NA objective and a Nikon CCD camera. (D) HL-60 and HL-60/LR cells were treated with 500 nM LAQ824 for 24 hours. After treatment, CD11b expression on the surface of the cells was measured by flow cytometry.