Selective, tight-binding inhibitors of integrin alpha 4 beta 1 that inhibit allergic airway responses

Integrin alpha 4 beta 1 mediates leukocyte recruitment, activation, mediato r release, and apoptosis inhibition, and it plays a central role in inflamm atory pathophysiology. High-affinity, selective inhibitors of alpha 4 beta 1, based on the Leu-Asp-Val (LDV) sequence from the alternatively spliced c onnecting segment-1 (CS-1) peptide of cellular fibronectin, are described t hat employ a novel N-terminal peptide "cap" strategy. One inhibitor, BIO-12 11, was similar to 10(6)-fold more potent than the starting peptide and exh ibited tight-binding properties (k(off) = 1.4 x 10(-4) s(-1), K-D = 70 pM, a remarkable finding for a noncovalent, small-molecule inhibitor of a prote in receptor. BIO-1211 was also 200-fold selective for the activated form of alpha 4 beta 1, and it stimulated expression of ligand-induced epitopes on the integrin beta 1 subunit, a property consistent with occupancy of the r eceptor's ligand-binding site. Pretreatment of allergic sheep with a 3-mg n ebulized dose of BIO-1211 inhibited early and late airway responses followi ng antigen challenge and prevented development of nonspecific airway hyperr esponsiveness to carbachol. These results show that highly selective and po tent small-molecule antagonists can be identified to integrins with primary specificity for peptide domains other than Arg-Gly-Asp (RGD); they confirm the generality of integrins as small molecule targets; and they validate a lpha 4 beta 1 as a therapeutic target for asthma.