Pseudoirreversible inhibition elicits persistent efficacy of a sphigosine-1-phosphate receptor-1 antagonist

ABSTRACT Sphingosine 1-phosphate receptor 1 (S1PR1), a G protein-coupled receptor, is required for lymphocyte trafficking, and is a promising therapeutic target in inflammatory diseases. We synthesized a competitive antagonist, KSI-6666, that persistently inhibits S1PR1 activity and effectively suppresses pathogenic inflammation. Metadynamics simulation proposed that the interaction of KSI-6666 with a methionine residue in the ligand-binding pocket of S1PR1 may inhibit the dissociation of KSI-6666 from S1PR1. Consistently, in vitro functional and mutational analyses revealed that KSI-6666 causes pseudoirreversible inhibition of S1PR1, dependent on the methionine residue of the protein and substituents on the distal benzene ring of KSI-6666. Moreover, in vivo study suggested that this pseudoirreversible inhibition is responsible for the persistent activity of KSI-6666. In this study, we discover that KSI-6666 is a potent S1PR1 antagonist, achieving pseudoirreversible inhibition of S1PR1 activity through interacting with a specific methionine residue.