alpha(4) integrin-dependent eosinophil recruitment in allergic but not non-allergic inflammation

Potent in vivo suppression of inflammation by selectively targeting the high affinity conformation of integrin α4β1

The development of antagonists to the α4 integrin family of cell adhesion molecules has been an active area of pharmaceutical research to treat inflammatory and autoimmune diseases. Presently being tested in human clinical trials are compounds selective for α4β1 (VLA-4) as well as several dual antagonists that inhibit both α4β1 and α4β7. The value of a dual versus a selective small molecule antagonist as well as the consequences of inhibiting different affinity states of the α4 integrins have been debated in the literature. Here, we characterize TBC3486, a N,N-disubstituted amide, which represents a unique structural class of non-peptidic, small molecule VLA-4 antagonists. Using a variety of adhesion assay formats as well as flow cytometry experiments using mAbs specific for certain activation-dependent integrin epitopes we demonstrate that TBC3486 preferentially targets the high affinity conformation of α4β1 and behaves as a ligand mimetic. The antagonist is capable of blocking integrin-dependent T-cell co-activation in vitro as well as proves to be efficacious in vivo at low doses in two animal models of allergic inflammation. These data suggest that a small molecule α4 integrin antagonist selective for α4β1 over α4β7 and, specifically, selective for the high affinity conformation of α4β1 may prove to be an effective therapy for multiple inflammatory diseases in humans.

Contribution of alpha4beta1 integrin to the antiallergic effect of levocabastine

Levocabastine is an antiallergic drug acting as a histamine H1-receptor antagonist. In allergic conjunctivitis (AC), it may also antagonize up-regulation of the intercellular adhesion molecule-1 (ICAM-1) expressed on epithelial conjunctival cells. However, little is known about its effects on eosinophils, important effector cells in AC. The adhesion molecule integrin alpha(4)beta(1) is expressed in eosinophils; it interacts with the vascular cell adhesion molecule-1 (VCAM-1) and fibronectin (FN) in vascular endothelial cells and contributes to eosinophil activation and infiltration in AC. This study provides evidence that in a scintillation proximity assay levocabastine (IC(50) 406 microM), but not the first-generation antihistamine chlorpheniramine, displaced (125)I-FN binding to human integrin alpha(4)beta(1) and, in flow cytometry analysis, levocabastine antagonized the binding of a primary antibody to integrin alpha(4) expressed on the Jurkat cell surface. Levocabastine, but not chlorpheniramine, binds the alpha(4)beta(1) integrin and prevents eosinophil adhesion to VCAM-1, FN or human umbilical vascular endothelial cells (HUVEC) in vitro. Similarly, levocabastine affects alpha(L)beta(2)/ICAM-1-mediated adhesion of Jurkat cells. In a model of AC levocabastine eye drops reduced the clinical aspects of the late-phase reaction and the conjunctival expression of alpha(4)beta(1) integrin by reducing infiltrated eosinophils. We propose that blockade of integrin-mediated cell adhesion might be a target of the antiallergic action of levocabastine and may play a role in preventing eosinophil adhesion and infiltration in AC.

Pharmacological characterization of guinea pig chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2)

Chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2), a G protein-coupled receptor activated by prostaglandin D(2) (PGD(2)), has been identified as a receptor expressed on cell types critical to the pathogenesis of asthma. The cDNA encoding guinea pig CRTH2 was cloned and mRNA expression examined in selected tissues. Transcript profiling of guinea pig CRTH2 indicated relatively high levels of expression in bone marrow, intermediate levels in brain and relatively low levels in lung, spleen, thymus, lymph node, etc. Characterization of the molecular pharmacology of guinea pig CRTH2 revealed that guinea pig CRTH2 exhibited a greater affinity for Delta(12)-PGJ(2), a stable PGD(2) metabolite relative to human CRTH2. The CRTH2 selective agonists 13,14-dihydro-15-keto PGD(2) and Delta(12)-PGJ(2) induced the recruitment of eosinophils following intradermal administration of these ligands in guinea pigs. Chemotaxis of guinea pig eosinophils was elicited by either PGD(2) or Delta(12)-PGJ(2), and was abolished by a CRTH2-specific antagonist. These results indicate that PGD(2) and the stable metabolite, Delta(12)-PGJ(2), play important roles in CRTH2 activation in the guinea pig.

Effects of the very late adhesion molecule 4 antagonist WAY103 on human peripheral blood eosinophil vascular cell adhesion molecule 1-dependent functions

BACKGROUND

Eosinophil infiltration to the lung in allergic inflammation can be initiated by the tethering of circulating cells through very late adhesion molecule 4 (VLA-4; alpha4beta1, CD49d/CD29) to vascular cell adhesion molecule 1 (VCAM-1) expressed on pulmonary vascular endothelium. Small-molecule VLA-4 antagonists have been proposed as a therapeutic mechanism to prevent eosinophil infiltration in asthma; however, they might affect other eosinophil functions.

OBJECTIVE

The small-molecule VLA-4 antagonist (2S)-3-(4-Dimethylcarbamoyloxyphenyl)-2-{[(4R)-5,5-dimethyl-3-(1-methyl-1H-pyrazole-4 sulfonyl)thiazolidine-4-carbonyl]amino}propionic acid (WAY103) was assessed for its effects on eosinophil VLA-4-dependent functions, including adhesion, migration, respiratory burst, and degranulation.

METHODS

Human peripheral blood eosinophils were preincubated with WAY103, anti-alpha4, and/or anti-beta2 integrin mAbs and then assessed for adhesion to recombinant VCAM-1, intercellular adhesion molecule 1, and endothelial cell monolayers. Transmigration was measured by using human pulmonary microvascular endothelial cell monolayers and Transwell filters. Superoxide anion generation was determined by means of cytochrome C reduction and degranulation by means of eosinophil-derived neurotoxin release.

RESULTS

WAY103 inhibition of eosinophil adhesion to recombinant VCAM-1 was dose dependent (63% inhibition with 100 nM WAY103, P < .04) and comparable with inhibition caused by anti-alpha4 mAb (60.1% inhibition). Although pretreatment with WAY103 also decreased eosinophil adhesion to TNF-alpha plus IL-4-activated human pulmonary microvascular endothelial cell monolayers, it did not prevent eosinophil transendothelial migration in response to RANTES. Finally, WAY103 inhibited VCAM-1-stimulated superoxide generation but enhanced cytokine-activated eosinophil-derived neurotoxin degranulation.

CONCLUSION

Although small-molecule VLA-4 antagonists, such as WAY103, might reduce eosinophil adhesion, this approach might not be sufficient to eliminate this cell from in vivo allergic airway inflammatory participation and could even promote specific cell activation.

The effect of anti-integrin monoclonal antibodies on antigen-induced pulmonary inflammation in allergic rabbits

The integrin adhesion molecules are involved in the recruitment and activation of inflammatory cells at sites of inflammation in a variety of diseases. In the present study, we have investigated the effects of blocking monoclonal antibodies (mAbs) directed against CD49d (alpha(4) integrin), CD18 (beta(2) integrin) and the alpha sub-units of beta(2) integrin CD11a (LFA-1 integrin) and CD11b (Mac-1 integrin), on antigen (Ag)-induced acute bronchoconstriction and cellular recruitment in allergic rabbits in vivo. Inhaled Ag (Alternaria tenuis) challenge of neonatally sensitised rabbits caused an acute bronchoconstriction demonstrated by an increase in lung resistance (R(L)) and decrease in dynamic compliance (C(dyn)) and pulmonary inflammation characterised by an increase in bronchoalveolar lavage (BAL) inflammatory cells, particularly eosinophils, 24 h after challenge. Pre-treatment with the anti-CD49d mAb (Max-68P), significantly inhibited the Ag-induced acute bronchoconstriction in terms of R(L) and (C(dyn)). Treatment with the other anti-integrin mAbs had no effect on the acute bronchoconstriction after inhaled Ag challenge.Pre-treatment with the anti-integrin mAbs had differential effects in blocking the recruitment of inflammatory cells 24 h after inhaled Ag in the allergic rabbits. The data show that in the allergic rabbit model of asthma, VLA-4 (CD49d/CD29) only, is involved in the acute bronchoconstriction, suggesting an involvement of mast cell degranulation. Furthermore, eosinophil recruitment and activation appears to be mediated by a combination of VLA-4 (CD49d/CD29) and LFA-1 (CD18/CD11a). However in contrast, lymphocyte recruitment appears to be mediated by a combination of LFA-1 (CD18/CD11a) and Mac-1 (CD18/CD11b).