Fig. 4. Compound 2 induced apoptosis in HL- 60 cells. A, Morphology of HL-60 cells treated with 2. HL-60 cells were stained with DAPI after treatment with either 0.5 μM of 2 or 15 μM of etoposide for 20 h and then observed under a fluorescence microscope. B, Cell cycle progression of the HL-60 cells treated with 2. HL-60 cells were treated with either 0.5 μM of 2 or 15 μM of etoposide for 10 h, and the cell cycle distribution was analyzed by a flow cytometer. C, Electrophoretic profile of the DNA of HL- 60 cells treated with 2. HL-60 cells were incubated with either 0.5 μM of 2 or 15 μM of etoposide for 14 h. DNA was then extracted and analyzed by agarose gel electrophoresis. D, Caspase-3 activity in the lysates of HL-60 cells treated with 2. HL-60 cells were incubated with either 0.5 μM of 2 or 15 μM of etoposide for 12 h, and the caspase-3 activity in the lysates was measured using a caspase-3 colorimetric kit. The data are presented as the mean ± S.E.M. of three experiments. Results significantly different from that of the control group are indicated by * (p <0.001).