Morphologic and functional changes induced by gefitinib in AML cell lines. May-Grünwald Giemsa staining of HL-60 cells treated with (A) 0.02% DMSO and (B) 10 μM gefitinib for 4 days, Kasumi-1 cells treated with (C) 0.01% DMSO and (D) 5 μM gefitinib for 3 days, and U937 cells treated with (E) 0.02% DMSO and (F) 8 μM gefitinib for 3 days. Doses were chosen at which optimal differentiation occurs. Images were acquired with an Olympus BH-2 microscope (Melville, NY), × 100/1.25 magnification under oil, an Olympus Q-Color 5 digital camera, and Adobe Photoshop CS version 8.0 software (San Jose, CA). (G) HL-60 cells were treated in triplicate for 5 days with gefitinib in a 2-fold dose response series from 10 μM to 1.25 μM and the percentage of NBT-positive cells compared with DMSO-treated controls (Ctl) with a one-tailed t test analysis.