Fig. 1

Effect of shikonin on TRAIL-induced cell cytotoxicity. The viability of (a) A549 and (b) HEK-293 cells after treatment were determined by a CCK8 assay. Cells were pretreated with different concentrations of shikonin for 12 h and then further incubated in the presence or absence of TRAIL (50 ng/ml) for another 12 h. c In the long-term cytotoxicity experiment, HEK-293 cell viability was not influenced by shikonin and TRAIL over the 96 h incubation period; however, the viability of A549 cells was significantly inhibited by shikonin, especially with TRAIL cotreatment. d These data show the efficacy of shikonin (4 μM) and TRAIL (50 ng/ml) on A549 cells pretreated with Z-VAD-FMK (50 μM). The data are presented as the means ± SDs of at least three independent experiments, *p < 0.05 and **p < 0.01. S + T: Shikonin + TRAIL