TUMOR-NECROSIS-FACTOR-ALPHA ALTERS RESPONSE OF LUNG-CANCER CELLS TO OXIDATIVE STRESS

Selected immunotherapies (tumor necrosis factor, interleukin-1, interleukin-2, and gamma interferon), chemotherapeutic agents (mitomycin, platinum, doxorubicin [Adriamycin], and bleomycin), and radiation therapy have been described to exert cytotoxicity through the generation of reactive oxygen species, including superoxide and hydrogen peroxide. Tumor necrosis factor, however, has been shown to impart increased resistance in vitro and in vivo against reactive oxygen species stress, including radiation therapy and oxygen toxicity, possibly because of the induction of increased cellular buffering capacities. It is unknown whether the sensitivity of a lung cancer cell to reactive oxygen species therapy is altered by tumor necrosis factor through the induction of free radical scavenging enzymes such as manganese superoxide dismutase. This question was investigated as follows: A549 lung adenocarcinoma cells, exposed for 24 hours to 0, 0.1, 1.0, or 10-mu-g/ml concentrations of tumor necrosis factor, were exposed to hypoxanthine plus xanthine oxidase, a superoxide generating system, for varying intervals. The number of cells surviving 5 days after the stress was determined, and cells exposed to tumor necrosis factor were examined by Northern Blot analysis for induction of the manganese superoxide dismutase gene. The hypoxanthine-xanthine oxidase stress alone caused a time-dependent decrease in survival; however, pretreatment with tumor necrosis factor increased cell survival significantly. Moreover, the cells exposed to tumor necrosis factor had a fivefold increase in the number of manganese superoxide dismutase transcripts. These findings suggest that tumor necrosis factor may confer resistance of lung cancer cells to subsequent reactive oxygen species-based therapies, and the resistance of these cells may be due to increased expression of manganese superoxide dismutase. Clinical treatment failures may result, especially if tumor necrosis factor is given concurrently with other therapies.