Using chemogenomic techniques, researchers in Seattle describe the design of a novel molecule, PNRI-299, that reduces the inflammation associated with asthma, a disease reaching epidemic proportions worldwide.

Asthmatics experience a complex inflammatory response characterized by airway infiltration of immune cells that undergo respiratory burst activation that releases reactive oxygen species (ROS). Redox-sensitive transcription factors, activator protein (AP)-1 and nuclear factor-κB, are activated and lead to the expression of certain cytokines, interleukin (IL) 4, IL-5 and IL-13, the molecular hallmarks of asthma. Although the side effects are severe, corticosteroids are able to control the inflammation for many asthmatics. However, a subset of patients respond poorly to these drugs, and their immune cells have increased activity of AP-1.

Michael Kahn and colleagues set out to develop and test a series of designer molecules that might inhibit transcription by redox-sensitive protein AP-1 and validate it as a therapeutic target for asthma. Taking advantage of the fact that protein–protein interactions can be mimicked by small molecules bearing similar local structural features, they used a bicyclic template designed to act as a β-strand, a motif common in redox-sensitive proteins. The template incorporated a functional group, an enedione, which can trap the crucial cysteine residue in the active site of redox proteins. Variation was introduced at two points on the template, by adding different amino acid side-chains, using a highly automated combinatorial approach to generate a library of designer molecules that could be screened for the ability to inhibit AP-1 in human airway epithelial cells.

Once PNRI-299 was identified as an AP-1 inhibitor, the authors tested it in a mouse model of asthma and found that it reduced airway swelling and mucus secretion in the mouse. Furthermore, they discovered that PNRI-299 inhibits the action of an AP-1 activator, Ref-1. They predicted that because regulation of IL-5 and IL-13 is independent of AP-1 activation, the expression of these molecules would be unchanged in the presence of PNRI-299. As expected, IL-4 expression, but not that of IL-5 and IL-13, was decreased.

Chemogenomics is a powerful approach for the generation of drug leads. In the case of inflammatory disorders, it can be used to validate a range of redox superfamily members as important targets for drug design.