Effect of genetic deletion or pharmacological antagonism of tumor necrosis factor alpha on colitis-associated carcinogenesis in mice

Background: Intestinal inflammation in inflammatory bowel diseases is driven by abnormal levels of proinflammatory cytokines, where tumor necrosis factor (TNF)-α seems to be particularly important. Chronic inflammatory signaling in the colon increases the risk of colorectal cancer, so we sought to evaluate the role of TNF-α in a mouse model of this condition. Methods: TNF^-/- mice were treated with azoxymethane/dextran sulfate sodium to induce inflammation and tumorigenesis. Etanercept was used to produce pharmacological ablation of TNF-α in wild-type mice. Subsequent activation of procarcinogenic transcription factor NF-B and relevant proinflammatory cytokines of the TNF superfamily were measured through immunohistochemistry and quantitative polymerase chain reaction methods. Results: Results showed that the severity of colitis, as assessed by mortality, histological scoring, and cytokine expression levels, was similar or slightly higher in mice lacking TNF-α than in control mice. Activation levels of NF-B were not influenced by the presence of TNF-α. We also observed upregulated expression of TNF family member TNF-β, TNF receptors 1 and 2 and a variety of other proinflammatory factors in colitis-associated tumors of TNF^-/- mice, compared with levels in tumors of control mice. Neither genetic ablation of TNF-α nor pharmacological inhibition of the TNF family using etanercept reduced tumor number. Conclusions: Our results reveal a redundant role for TNF-α in a mouse model of colitis-associated tumorigenesis, indicating a high degree of redundancy in proinflammatory cytokine networks in this model.