Trypsinlike serine protease is required for the execution of necrosis. (A) BV173 cells were treated with zVAD + imatinib and TLCK + zVAD + imatinib for 12 hours, followed by morphologic evaluation of cytospin specimens. Original magnification, × 1000. (B-C) BV173 cells and K562 cells were treated with the indicated agents for 72 hours, followed by incubation with DiOC6(3) and PI, and analysis by dual-parameter flow cytometry. The concentrations of TLCK and TPCK were as follows: 100 μM and 25 μM for BV173 cells, 200 μM and 50 μM for K562 cells. (B) Values indicate the percentage of the DiOC6(3)^low and PI⁺ populations. (C) Cell death is the percentage of the PI⁺ populations. Data represent means ± SEM of 4 individual experiments. Striped bars indicate imatinib; gray bars, TLCK + imatinib; black bars, zVAD + imatinib; and white bars, TLCK + zVAD + imatinib.