A, The response curve of HL-60 cells to YM155 was generated by MTS assays. B & C, HL-60 cells were cultured in 1640 medium with 5% FBS containing 0, 2 or 4 nmol/L of YM155 for 24 hr, or cultured in 1640 medium with 5% FBS containing 2.5 nmol/L of YM155 for 0, 24, or 48 hr. Cells were collected and subjected to Western blot analyses of survivin, caspase-8, caspase-3, PARP, γH2A.X (Ser139), H2A.X, P-CHK2 (Thr68), CHK2, or β-actin (B) or a specific apoptosis ELISA (C). Bars, SD.