CS-6 induced apoptosis by modulating cytochrome c/caspase signaling. Human A549 cells were treated with CS-6 at the indicated doses. Treatment with CS-6 in a time-course manner, the apoptosis was determined by a FACS analysis (A), and the levels of the cleaved caspase-3/9, cleaved PARP proteins in A549 and H1299 cells was analyzed by Western blot (B). The release of Cytc in A549 and H1299 cells was determined by immunofluorescence imaging analysis to monitor Cytc release from the mitochondrial intermembrane space into the cytosol (C). The apoptosis is represented by relative percentages of apoptotic cells versus that in DMSO-treated cells. (*P < 0.05,**P < 0.01, significant differences between CS-6 treatment groups and DMSO vehicle control groups; #P < 0.05, ##P < 0.01, significant differences between 48 h treatment group and 12 h treatment group).