Sensitization to TRAIL-induced apoptosis in human neuroblastoma SK-N-AS cells by NF-κB inhibitors is dependent on reactive oxygen species (ROS).

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to induce apoptosis in a variety of cancer cell lines with almost no toxicity toward normal cells. However, many neuroblastoma cells acquire resistance to TRAIL by mechanisms that are poorly understood. The objective of this study was to investigate involvement of the transcription factor NF-κB in the resistance of human neuroblastoma SK-N-AS cells to TRAIL-induced apoptosis. We used five compounds previously reported to inhibit NF-κB activity. SN50, curcumin, oridonin, and pyrrolidine dithiocarbamate (PDTC) all sensitized cells to TRAIL-induced apoptosis. In contrast, N-alpha-tosyl-L: -phenylalanyl chloromethyl ketone (TPCK) did not affect sensitivity to TRAIL, although reporter gene assay clearly showed inhibition of NF-κB activity. In addition, neither curcumin nor oridonin had any inhibitory effect on NF-κB activity at concentrations at which sensitization to TRAIL was observed. Instead, the free radical scavenger N-acetyl-L: -cysteine (NAC) completely blocked the effect on TRAIL-induced apoptosis caused by curcumin, oridonin, and PDTC. Furthermore, exposure of SK-N-AS cells to H(2)O(2) could mimic the TRAIL-sensitizing effect of other agents. In conclusion, our results suggest that sensitization of neuroblastoma SK-N-AS cells to TRAIL-induced apoptosis is correlated with induction of reactive oxygen species (ROS) rather than inhibition of NF-κB.