Cytokines in colitis associated cancer: potential drug targets?

In inflammatory bowel disease (IBD), such as UC and CD, the development of colorectal carcinoma can be initiated through chronic inflammation, depending on the duration and severity of the disease. Growing evidence supports a role for various cytokines, released by epithelial and immune cells, in the pathogenesis of colitis associated cancer (CAC). For instance, TNF-alpha has been recently shown to promote tumor development in experimental colitis. Due to its role in the pathogenesis of IBD, TNF-alpha blockade has become one of the cornerstones of IBD therapy. Thus, anti-TNF-alpha strategies could also provide effective anti-tumor therapies. TGF-beta has been shown to attenuate an anti-tumor immune-response through the induction of regulatory T cells in spontaneous and inflammation associated cancer. However, IL-6 signaling promotes tumor growth in experimental CAC, and this signaling is inhibited by TGF-beta. Members of the IL-12 family, such as IL-12, IL-23, and IL-27, have been implicated in pathogenesis of colitis and IL-23 seems to be involved in inflammation associated carcinogenesis. However, a role for those cytokines in CAC remains to be shown. Whereas the above-mentioned cytokines promote tumor growth, others provide an anti tumor effect. IL-10 deficient mice develop colitis and CAC a few weeks after birth. Besides its immunosuppressive properties, IL-10 also has anti angiogenic and both tumor promoting and -inhibiting properties, which could be responsible for these observations. Since most of the above mentioned cytokines are involved in both, inflammation and carcinogenesis, it is difficult to account their contribution to the individual steps during pathogenesis of CAC. However, as already shown in IBD, cytokines may also provide promising therapeutic targets in CAC.