Sodium nitroprusside (SNP) sensitizes human gastric cancer cells to TRAIL-induced apoptosis

Aim: To investigate the effects of the nitrous oxide (NO)-donor sodium nitroprusside (SNP) on tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated Apoptosis in human gastric Cancer cells.

Methods: The MTT assay and flow cytometry were used to detect cellular proliferation and markers of Apoptosis, respectively. Expression levels of caspases-8, and 9 were determined by Western blot. Changes in Nitric Oxide Synthase (NOS) activity, NO production, and Caspase activation were also evaluated.

Results: We found that TRAIL induced Apoptosis and cell cycle arrest in human gastric Cancer cell lines, and that this effect was mediated by NO production, and activation of both the extrinsic and intrinsic signaling pathways of Apoptosis. In addition, we found that the NO-donor SNP sensitizes gastric Cancer cells to TRAIL-mediated Apoptosis. Treatment of cells with both TRAIL and SNP resulted in increased activation of Caspase-8 and caspase-9 and NO release. Inhibition of Caspase-8 blocked cell TRAIL-induced Apoptosis, while a selective caspase-9 inhibitor was unable to prevent Apoptosis induced by either TRAIL or TRAIL plus SNP. Inhibition of NOS could block the activation of caspase-9, but had no obvious effect on cell Apoptosis.

Conclusions: SNP-sensitized gastric Cancer cells to TRAIL-induced cytotoxicity by stimulating the release of NO, in turn facilitating the mitochondria-mediated signal transduction pathway. The engagement of the mitochondria signaling pathways along with the TRAIL death receptor signaling pathway synergistically increase levels of Apoptosis in these cells.