SR9009-induced apoptosis was caspase-dependent in SCLC cells. (A-H) SCLC cells were incubated with indicated concentration of SR9009 in the presence or absence of 20 µM z-VAD-fmk for 48 h (A and E, 10µM; B and F, 5µM; C and G, 20µM; D and H, 10µM). Densitometric values were quantified using the ImageJ software and normalized to control. The values of control were set to 1. The data are presented as means ± SD of three independent experiments. *P < 0.05; **P < 0.01. (I-L) SR9009-induced cytotoxicity could be partially rescued by 20 µM z-VAD-fmk for 72 h (concentration of SR9009: I, 10µM; J, 5µM; K, 20µM; L, 10µM). Results were expressed as mean ± S.D. (n = 3) and analyzed by Student's t-test (two-tailed), *P< 0.05; **P< 0.01.