Combretastatin A4 phosphate (CA4P) induces caspase-independent apoptosis in leukemic cells. (A) CA4P induces apoptosis of leukemic cells. Leukemic cells were treated with or without CA4P for 48 hours, and the percentage of apoptotic leukemic cells was determined by annexin-V and PI staining using flow cytometry. Results are representative of 3 independent experiments. Numbers in the quadrants are log fluorescent intensity. (B) CA4P induces cell death without evidence of necrosis. Western blot shows release of pelleted (“P”) nuclear HMG1 protein into the supernatant (“S”) in necrotic (freeze-thaw), but not apoptotic (staurosporine-treated) or CA4P-treated KG1a leukemic cells. Identical results were obtained in 3 independent experiments. (C) CA4P-mediated apoptosis of leukemic cells is partially reversed by the caspase inhibitor Q-VD. Leukemic cells were treated with or without CA4P for 48 hours in presence of caspase inhibitor Q-VD, and the percentage of apoptotic leukemic cells was determined by annexin-V and PI staining using flow cytometry. Percentage of live annexin-V⁻/PI⁻ cells was plotted. Results are average of 3 independent experiments (*P = .008 as compared with CA4P-treated cells).