The blockade of IL-6 signaling in rational drug design

After three decades from the development of the hybridoma technology, a monoclonal antibody-based therapy targeting the inflammatory cytokine has been established as an ultimate treatment for chronic inflammatory diseases. Interleukine-6 (IL-6) is one of the inflammatory cytokines playing a pivotal role in these conditions, and strategies targeting IL-6 signal show promise in the treatment of chronic inflammatory diseases such as rheumatoid arthritis, juvenile idiopathic arthritis, and Crohn's disease. Although many groups have been exploring the approach to block the IL-6 signal, tocilizumab, a humanized monoclonal antibody of the IL- 6 receptor, has been the most intensively studied agent for clinical use. Clinical trials regarding chronic inflammatory diseases described above have demonstrated efficacy of tocilizumab, however, this treatment has limitations in terms of economic costs and ease of administration, and further advances are necessary to expand the concept of IL-6-specific therapeutics. In this review, we discuss targeting IL- 6 in a rational drug design and present the various strategies to achieve this.