Developing Inhibitors of the p47phox-p22phox Protein-Protein Interaction by Fragment-Based Drug Discovery

Nicotinamide adenine dinucleotide phosphate oxidase isoform 2 is an enzyme complex, which generates reactive oxygen species and contributes to oxidative stress. The p47phox-p22phox interaction is critical for the activation of the catalytical NOX2 domain, and p47phox is a potential target for therapeutic intervention. By screening 2500 fragments using fluorescence polarization and a thermal shift assay and validation by surface plasmon resonance, we found eight hits toward the tandem SH3 domain of p47phox (p47phox^SH3A-B) with K_D values of 400-600 μM. Structural studies revealed that fragments 1 and 2 bound two separate binding sites in the elongated conformation of p47phox^SH3A-B and these competed with p22phox for binding to p47phox^SH3A-B. Chemical optimization led to a dimeric compound with the ability to potently inhibit the p47phox^SH3A-B-p22phox interaction (K_i of 20 μM). Thereby, we reveal a new way of targeting p47phox and present the first report of drug-like molecules with the ability to bind p47phox and inhibit its interaction with p22phox.