A novel, conformation-specific allosteric inhibitor of the tachykinin NK2 receptor (NK2R) with functionally selective properties

The orthosteric agonist neurokinin A (NKA) interacts with the tachykinin NK2 receptors (NK2Rs) via an apparent sequential binding process, which stabilizes the receptor in at least two different active conformations (A1L and A2L). The A1L conformation exhibits fast NKA dissociation kinetics and triggers intracellular calcium elevation; the A2L conformation exhibits slow NKA dissociation kinetics and triggers cAMP production. The new compound LPI805 is a partial and noncompetitive inhibitor of NKA binding to NK2Rs. Analysis of NKA dissociation in the presence of LPI805 suggests that LPI805 decreases the number of NKA-NK2R complexes in A2L conformation while increasing those in the A1L conformation. Analysis of signaling pathways of NK2Rs shows that LPI805 dramatically inhibits the NKA-induced cAMP response while slightly enhancing the NKA-induced calcium response. Analysis of NKA association kinetics reveals that LPI805 promotes strong and specific destabilization of the NKA-NK2R complexes in the A2L conformation whereas access of NKA to the A1L conformations is unchanged. Thus, to our knowledge, LPI805 is the first example of a conformation-specific allosteric antagonist of a G-protein-coupled receptor. This work establishes the use of allosteric modulators in order to promote functional selectivity on certain agonist-receptor interactions.