Screening for small-molecule fragments that can lead to potent inhibitors of protein-protein interactions (PPIs) is often a laborious step as the fragments cannot dissociate the targeted PPI due to their low μM-mM affinities. Here, we describe an NMR competition assay called w-AIDA-NMR (weak-antagonist induced dissociation assay-NMR), which is sensitive to weak μM-mM ligand-protein interactions and which can be used in initial fragment screening campaigns. By introducing point mutations in the complex's protein that is not targeted by the inhibitor, we lower the effective affinity of the complex, allowing for short fragments to dissociate the complex. We illustrate the method with the compounds that block the Mdm2/X-p53 and PD-1/PD-L1 oncogenic interactions. Targeting the PD-/PD-L1 PPI has profoundly advanced the treatment of different types of cancers.
Keywords: Mdm2/p53; NMR; PD-1/PD-L1; protein–protein interaction; small molecule.