As₄S₄ and/or imatinib induce the apoptosis of the K562 cell line and primary CML cells. (A) The morphology of K562 cells untreated or treated with 2 μM As₄S₄ and/or 0.2 μM imatinib for 48 hours. The K562 cells were stained with Wright staining and observed on an Olympus BX 50 light microscope (Olympus, Tokyo, Japan) provided with MCDS-20/0 Super Bone Marrow Cell Analysis System (Chongqing, China). Original magnification, ×1000 (objective × 100). Images were captured using a Polaroid Dmc (Polaroid, Miami, FL). (B) Annexin V–PI assessment of the K562 cells and CD34⁺ cells from patients with CML. Cells were treated with As₄S₄ and/or imatinib for 24 to 72 hours and measured for annexin V positivity (n = 3, mean ± SD). (C) The reduction of mitochondrial transmembrane potential in K562 cells and CML CD34⁺ cells after treatment with As₄S₄ and/or imatinib for 24 to 72 hours (n = 3, mean ± SD). (D) Caspase-3 activity of K562 cells and CML CD34⁺ cells after 48 hours of incubation with As₄S₄ and/or imatinib (n = 4, mean ± SD). (E) Western blot analysis of some proteins related to apoptosis after K562 cells, after 48 hours of exposure to As₄S₄ and/or imatinib. Statistical analysis using a one-side paired t test (☆, P < .05 versus imatinib, As₄S₄ group, and control; ⋆, P < .01 versus imatinib group, As₄S₄ group, and control). CON indicates control; I 0.2, 0.2 μM imatinib; I 0.25, 0.25 μM imatinib; I 0.3, 0.3 μM imatinib; A2, 2 μM As₄S₄; A2.5, 2.5 μM As₄S₄; A3, 3 μM As₄S₄; I 0.2A2, 0.2 μM imatinib and 2 μM As₄S₄; I 0.25A2.5, 0.25 μM imatinib and 2.5 μM As₄S₄; and I 0.3A3, 0.3 μM imatinib and 3 μM As₄S₄.