Selective, Tight-Binding Inhibitors of Integrin α4β1 That Inhibit Allergic Airway Responses

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Abstract
Integrin α4β1 mediates leukocyte recruitment, activation, mediator release, and apoptosis inhibition, and it plays a central role in inflammatory pathophysiology. High-affinity, selective inhibitors of α4β1, based on the Leu-Asp-Val (LDV) sequence from the alternatively spliced connecting segment-1 (CS-1) peptide of cellular fibronectin, are described that employ a novel N-terminal peptide “cap” strategy. One inhibitor, BIO-1211, was ∼106-fold more potent than the starting peptide and exhibited tight-binding properties (koff = 1.4 × 10-4 s-1, KD = 70 pM), a remarkable finding for a noncovalent, small-molecule inhibitor of a protein receptor. BIO-1211 was also 200-fold selective for the activated form of α4β1, and it stimulated expression of ligand-induced epitopes on the integrin β1 subunit, a property consistent with occupancy of the receptor's ligand-binding site. Pretreatment of allergic sheep with a 3-mg nebulized dose of BIO-1211 inhibited early and late airway responses following antigen challenge and prevented development of nonspecific airway hyperresponsiveness to carbachol. These results show that highly selective and potent 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 α4β1 as a therapeutic target for asthma.