Identification of an Induced Orthosteric Pocket in IL-23: A New Avenue for Non-biological Therapeutic Targeting.

Interleukin 23 (IL23) is a key driver of autoimmune inflammatory pathology and has been successfully targeted by therapeutic antibodies for the treatment of psoriasis and ulcerative colitis. Identifying small-molecule inhibitors of IL23 signaling is of potential interest for drug development. We report the identification of an induced-fit orthosteric binding pocket on the IL23p19 subunit that may be suitable for small-molecule inhibition. X-ray crystallography was used to determine the structure of the IL23 heterodimer when bound to inhibitory peptide 23-446 and to confirm peptide binding to the IL23p19 subunit at the location of its interface with the IL23 receptor (IL23R). We then applied structure-based design to modify peptide 23-446. This process involved identifying key residues responsible for inhibitory activity and generating structure-activity relationship-optimized peptides with low nanomolar affinity for IL-23 and corresponding inhibitory potency against IL-23R binding. These optimized peptides show promise as potential therapeutic candidates in their own right and may also serve as valuable starting points for further discovery. The most potent of these peptides was used to develop a fluorescence polarization probe and to design a high-throughput screening assay, which was validated through a pilot screen using a small fragment-based compound library. This screening strategy has the potential to support the discovery of peptides or small molecules that bind to the orthosteric pocket, thereby blocking the IL-23R interaction and downstream signaling.