Differential expression of superoxide dismutases in lung cancer

Oxidant-antioxidant balance is known to regulate growth factors and invasion of tumor cells. Manganese superoxide dismutase (MnSOD), copper zinc SOD (CuZnSOD), and extracellular SOD (ECSOD), the first-line antioxidant defenses, were studied in lung carcinomas by immunohistochemical analysis (n = 139, 56, and 37, respectively) and in 8 lung tumor specimens by Western blot analysis and SOD activity measurement. Altogether, 49% of squamous cell carcinomas and 43% of the adenocarcinomas were positive for MnSOD by immunohistochemical analysis; corresponding values for CuZnSOD were 79% and 93%, respectively. MnSOD and CuZnSOD by Western blot analysis were 27% and 22% higher, and CuZnSOD activity was 93% higher (P = .06) in carcinomas than in nonmalignant lung tissue samples. ECSOD, a mainly extracellular enzyme, showed weak positivity only in 4 of 37 carcinomas, and by Western blot analysis showed 70% lower immunoreactivity (P < .0001) than in nonmalignant lung tissue samples. It is highly likely that low expression of ECSOD might have fundamental effects on the extracellular redox state of lung tumors with potential consequences on tumor behavior.