The role of oxygen-derived free radicals and nitric oxide in cytokine-induced antiproliferation of pancreatic cancer cells

Introduction: Pancreatic cancer cells are susceptible to antiproliferative effects of cytokines such as tumor necrosis factoralpha (TNF-α). However, little is known about the mechanisms involved. Aim: To determine the mechanisms of the antiproliferative effects of TNF-α on pancreatic cancer cells. Methodology and Results: In the current study, four of five pancreatic cancer cell lines tested were responsive to the antiproliferative effects of TNF-α. In two cell lines, the effects of TNF-α were completely abolished by superoxide dismutase, suggesting that superoxide anion mediates the effects. Further, inhibition of nitric oxide (NO) synthase by L-NAME potentiated the TNF-α response, suggesting a protective role for endogenously produced NO in these two cell lines. MiaPaCa-2 cells, which were unresponsive to the antiproliferative effects of TNF-α, produced five times more nitrite than the other cell lines. Treatment of MiaPaCa-2 cells with interferon-gamma (IFN-γ) increased inducible nitric oxide synthase mRNA as shown by reverse transcription-polymerase chain reaction. This induction was potentiated by TNF-α and further enhanced by a combination of three cytokines (INF-γ, TNF-α, and interleukin 1-beta (IL-1β). This combination of cytokines increased nitrite accumulation fourfold and inhibited the proliferation of this resistant cell line. These effects were prevented by L-NAME. Conclusions: These studies suggest that TNF-α inhibits proliferation of pancreatic cancer cells by increasing the production of superoxide anion and that endogenously produced NO protects against this effect. In addition, there is a direct correlation between the amount of NO produced and resistance to TNF-α in the only resistant cell line. In contrast, treatment with a combination of IFN-γ, TNF-α and IL-1β upregulates inducible nitric oxide synthase, and the resulting markedly enhanced NO production inhibits pancreatic cancer cell growth. This pathway may provide a valuable target for therapy of this devastating disease.