Apoptotic cells were assayed by using the Annexin-V-FITC Apoptosis Detection Kit (BD Biosciences, USA) according to the manufacturer's instruction. In brief, K562 cells were treated with DMSO or chalcone derivatives (30m M) for 48 h. Cells were then harvested, washed twice with ice-cold PBS and resuspended in 1Binding buffer to reach afinal concentration of 1106 cells/ml. Cells were stained by adding 5mL of Annexin-V-FITC and 5m LofPI (50m g/mL), sit for 15 min at room temperature in the dark and analyzed byfl ow cytometry.