NSAIDs and butyrate sensitize a human colorectal cancer cell line to TNF-alpha and Fas ligation: the role of reactive oxygen species.

The nonsteroidal antiinflammatory drugs (NSAIDs) indomethacin and salicylic acid and the short chain fatty acid butyrate are effective colon cancer chemopreventive agents that increase reactive oxygen species (ROS) generation in colon cancer cells. Here we demonstrate that these agents sensitize the normally resistant human HT-29 colon cancer cell line to apoptosis induced by TNF-alpha or a Fas ligating antibody. The role of ROS in this sensitization is supported by the finding that direct exposure of the cells to H2O2 is sufficient for sensitization. Neither TNF-alpha nor Fas ligation alter basal or chemopreventive agent-activated ROS generation, suggesting that the death ligands and chemopreventive agents act in a complementary fashion. The dual chemopreventive agent/death ligand treatments do not increase Fas, TNF receptor 1, Bak or c-myc expression (although salicylic acid moderately induces of Fas expression). Cell death does correlate with alterations in NF-kappa B activity: the NSAIDs, butyrate and H2O2 enhance c-Rel complex formation by TNF-alpha and provide an overall enhancement of NF-kappa B activation by Fas. The antioxidant N-acetylcysteine (NAC) blocks cell death and NF-kappa B activation induced by Fas ligation, suggesting a potential role for NF-kappa B in Fas-induced apoptosis in these cells. The effects of NAC on TNF-alpha-induced cell death are more complex, with NAC being marginally protective and itself enhancing the formation of c-Rel containing complexes at higher concentrations (25 mM). The influence of NSAIDs and butyrate on ROS generation and death ligand sensitivity may be relevant to their ability to suppress colon carcinogenesis.