New approaches to the treatment of inflammatory disorders small molecule inhibitors of p38 MAP kinase

The therapy of chronic inflammatory diseases like rheumatoid arthritis (RA) and inflammatory bowel disease (IBD) has recently been enriched by the successful launch of the anti-cytokine biologicals Etanercept (tumor necrosis factor (TNF) receptor-p75 Fc fusion protein), Infliximab (chimeric anti-human TNF-alpha monoclonal antibody), Adalimumab (recombinant human anti-human TNF-a monoclonal antibody) and Anakinra (recombinant form of human interleukin 1 beta (IL-1) receptor antagonist) [1-3]. The success of these novel treatments has impressively demonstrated the clinical benefit that can be gained from therapeutic intervention in cytokine signalling, highlighting the central role of proinflammatory cytokine systems like IL-1 beta and TNF alpha to be validated targets [4] However, all of the anti-cytokine biologicals available to date are proteins, and therefore suffering to a varying degree from the general disadvantages associated with protein drugs. Therefore, small molecular, orally active anti-cytokine agents, which target specific pathways of proinflammatory cytokines, would offer an attractive alternative to anti-cytokine biologicals. A number of molecular targets have been identified for the development of such small molecular agents but p38 mitogen-activated protein (MAP) kinase occupies a central role in the regulation of IL-1 beta and TNF-alpha signalling network at both the transcriptional and translational level [5, 6]. Since the mid-1990s, an immense number of inhibitors of p38 MAP kinase has been characterised in vitro, and to date several compounds have been advanced into clinical trials. This review will highlight the correlation between effective inhibition of p38 MAP kinase at the molecular target and cellular activity in functional assays of cytokine, particularly TNF-alpha and IL-1 beta production. SAR will be discussed regarding activity at the enzyme target, but also with regard to properties required for efficient in vitro and in vivo activity.