Blockade of late-phase airway responses and airway hyperresponsiveness in allergic sheep with a small-molecule peptide inhibitor of VLA-4

Relapsing-remitting multiple sclerosis: what is the potential for combination therapy?

Multiple sclerosis is now a treatable disease and several immunomodulating therapies exist, but their clinical efficacy is moderate and treatment failure during the course of the disease is an increasing problem. As agents with different targets are available, the question was raised whether combination of these therapies would: be safe;result in reduction of adverse effects; andprovide synergistic benefit by additive or complementary modes of action. The areas under clinical investigation are general immunosuppression as well as more targeted approaches that interfere with antigen presentation, immune cell transmigration, release of myelinotoxic factors or even axonal damage. Combination of these immunomodulatory drugs seems to be rational and promising. Nevertheless, combination therapies need to be studied in carefully designed clinical trials in selected patient populations in order to demonstrate additive or synergistic effects. This article will summarise current drug combination strategies in relapsing-remitting multiple sclerosis and provide an overview of the initial clinical trials.

Heterocycle-substituted proline dipeptides as potent VLA-4 antagonists

A variety of N-linked tertiary amines and heteroarylamines were examined at the 4-position of sulfonylated proline dipeptides in order to improve VLA-4 receptor off-rates and overcome the issue of CYP3A4 time-dependent inhibition of ester prodrugs. A tight-binding inhibitor 5j with a long off-rate provided sustained receptor occupancy despite poor oral pharmacokinetics.

Modeling of asthma, COPD and cystic fibrosis in sheep

Sheep naturally allergic to Ascaris suum antigen have been used to study the pathophysiology of asthma and more recently allergic rhinitis, chronic obstructive pulmonary disease (COPD) and cystic fibrosis. The utility of the model as it relates to the study of these diseases is discussed.

Roles of integrin activation in eosinophil function and the eosinophilic inflammation of asthma

Eosinophilic inflammation is a characteristic feature of asthma. Integrins are highly versatile cellular receptors that regulate extravasation of eosinophils from the postcapillary segment of the bronchial circulation to the airway wall and airspace. Such movement into the asthmatic lung is described as a sequential, multistep paradigm, whereby integrins on circulating eosinophils become activated, eosinophils tether in flow and roll on bronchial endothelial cells, integrins on rolling eosinophils become further activated as a result of exposure to cytokines, eosinophils arrest firmly to adhesive ligands on activated endothelium, and eosinophils transmigrate to the airway in response to chemoattractants. Eosinophils express seven integrin heterodimeric adhesion molecules: alpha 4 beta 1 (CD49d/29), alpha 6 beta 1 (CD49f/29), alpha M beta 2 (CD11b/18), alpha L beta 2 (CD11a/18), alpha X beta 2 (CD11c/18), alpha D beta2 (CD11d/18), and alpha 4 beta 7 (CD49d/beta 7). The role of these integrins in eosinophil recruitment has been elucidated by major advances in the understanding of integrin structure, integrin function, and modulators of integrins. Such findings have been facilitated by cellular experiments of eosinophils in vitro, studies of allergic asthma in humans and animal models in vivo, and crystal structures of integrins. Here, we elaborate on how integrins cooperate to mediate eosinophil movement to the asthmatic airway. Antagonists that target integrins represent potentially promising therapies in the treatment of asthma.

A small molecule, orally active, alpha4beta1/alpha4beta7 dual antagonist reduces leukocyte infiltration and airway hyper-responsiveness in an experimental model of allergic asthma in Brown Norway rats

alpha(4)beta(1) and alpha(4)beta(7) integrins are preferentially expressed on eosinophils and mononuclear leukocytes and play critical roles in their recruitment to inflammatory sites. We investigated the effects of TR14035, a small molecule, alpha(4)beta(1)/alpha(4)beta(7) dual antagonist, in a rat model of allergic asthma. Actively sensitized rats were challenged with aerosol antigen or saline on day 21, and the responses evaluated 24 and 48-h later. TR14035 (3 mg kg(-1), p.o.) was given 1-h before and 4-h after antigen or saline challenge. Airway hyper-responsiveness to intravenous 5-hydroxytryptamine was suppressed in TR14035-treated rats. Eosinophil, mononuclear cell and neutrophil counts, and eosinophil peroxidase and protein content in the bronchoalveolar lavage fluid (BALF) were decreased in TR14035-treated rats. Histological study showed a marked reduction of lung inflammatory lesions by TR14035. At 24-h postchallenge, antigen-induced lung interleukin (IL)-5 mRNA upregulation was suppressed in TR14035-treated rats. By contrast, IL-4 levels in BALF were not significantly affected by TR14035 treatment. IL-4 selectively upregulates vascular cell adhesion molecule-1 (VCAM-1), which is the main endothelial ligand of alpha(4) integrins. Intravital microscopy within the rat mesenteric microcirculation showed that 24-h exposure to 1 microg per rat of IL-4 induced a significant increase in leukocyte rolling flux, adhesion and emigration. These responses were decreased by 48, 100 and 99%, respectively in animals treated with TR14035. In conclusion, TR14035, by acting on alpha(4)beta(1) and alpha(4)beta(7) integrins, is an orally active inhibitor of airway leukocyte recruitment and hyper-responsiveness in animal models with potential interest for the treatment of asthma.

Effect of a very late antigen-4 receptor antagonist on allergen-induced airway responses and inflammation in asthma

BACKGROUND

Very late antigen-4 (VLA(4)) plays a key role in the recruitment of eosinophils in allergic responses in animal studies.

OBJECTIVE

We investigated whether pretreatment with multiple doses of a VLA(4) receptor antagonist, HMR 1031, protects against allergen-induced airway responses and airway inflammation in humans.

METHODS

Fourteen asthmatics (7F/7M), 18-49 years, PC(20) forced expiratory volume in 1 s (FEV(1)) methacholine (M) (<8 mg/mL; FEV(1) 82.3-116.1% predicted) with dual responses to inhaled allergen participated in a double-blind, placebo-controlled, cross-over study. Each treatment period consisted of 9 days, separated by >or=2 weeks. Exhaled nitric oxide (eNO), PC(20)FEV(1)(M) and hypertonic saline-induced sputum was obtained on Days 1, 7 and 9. Subjects inhaled HMR 1031 (20 mg b.i.d.) or placebo (P) on Days 1--8. On Day 8, an allergen bronchoprovocation test was performed, the airway response was measured by FEV(1), and expressed as %fall from baseline. Data from 12 evaluable subjects are presented here.

RESULTS

Both treatments were well tolerated. There was no significant difference between HMR 1031 and P in the early asthamatic response: mean AUC (0-3 h)+/-SEM (%fall h): 26.01+/-4.26 and 17.41+/-4.26, respectively (P=0.18), nor in the late response: mean AUC (3-9 h)+/-SEM (%fall h): 97.09+/-8.63 and 97.61+/-8.63, respectively, P=0.97. This corresponded to the absence of significant allergen-induced changes in PC(20)FEV(1)(M), eNO, sputum eosinophils and soluble inflammation markers between both treatment periods.

CONCLUSIONS

Treatment with multiple inhaled doses of the VLA(4) antagonist, HMR 1031, did not result in detectable protection against allergen-induced airway responses or airway inflammation in asthma.

Therapeutic anti-integrin (alpha4 and alphaL) monoclonal antibodies: two-edged swords?

Anti-alpha4 and anti-alphaL integrin chain monoclonal antibodies have shown a clear-cut beneficial effect in different animal models of autoimmune and inflammatory disorders as well as in human diseases, including multiple sclerosis, inflammatory bowel disease, and psoriasis. It has been widely assumed that this therapeutic effect is mainly consequence of the blockade of leucocyte adhesion to endothelium, inhibiting thus their extravasation and the inflammatory phenomenon. However, it is evident that both alpha4beta1 (very late antigen-4) and alphaLbeta2 (leucocyte function-associated antigen-1) integrins have additional important roles in other immune phenomena, including the formation of the immune synapse and the differentiation of T helper 1 lymphocytes. Therefore, it is very feasible that the long-term administration of blocking agents directed against these integrins to patients with inflammatory/autoimmune conditions may have undesirable or unexpected effects.

Effect of IVL745, a VLA-4 antagonist, on allergen-induced bronchoconstriction in patients with asthma

BACKGROUND

Very late antigen (VLA-4) antagonists have been proposed as potential therapies for diseases in which cell recruitment and accumulation are causative. Asthma, which is characterized by airway inflammation involving the accumulation of eosinophils and mononuclear cells, is one such disease.

OBJECTIVE

We sought to assess the effect of IVL745, a VLA-4 antagonist, on the early and late asthmatic response (LAR) and on markers of airway inflammation after allergen inhalation.

METHODS

The study was of a placebo-controlled, double-blind, randomized, 2-way crossover design. Sixteen subjects with mild-to-moderate asthma controlled with short-acting beta2-agonists only and with a LAR to inhaled allergen participated in the study. At one treatment period they took 20 mg of IVL745 and one treatment period placebo. Both treatments were taken twice daily for 7 days, with a single dose on day 8. Treatments were separated by a washout period of at least 2 weeks. On day 7 of each treatment period, sputum was induced and collected, and exhaled nitric oxide (NO) was measured. On day 8, an inhaled bolus allergen challenge was performed, and blood was taken for pharmacokinetics. On day 9, exhaled NO was measured, and a methacholine challenge was done. On day 10, sputum was induced and collected. Adverse events, peak expiratory flow (PEF), use of short-acting beta2-agonists, and asthma symptoms were recorded daily throughout the study.

RESULTS

There was no statistically significant difference between IVL745 and placebo in the effect on the LAR after allergen challenge, as measured by the area under the curve of the percentage change in FEV1 from the prechallenge baseline (mean [SEM], -81.99 [18.80] after IVL745 and -72.58 [21.29] after placebo; 95% CI of difference, -36 to 16.8; P = .46) or by the maximum percentage change from the prechallenge baseline (mean [SEM], -23.44 [4.73] after IVL745 and -21.30 [5.17] after placebo; 95% CI of difference, -11 to 6.29; P = .60). There was a statistically significant decrease in the percentage of eosinophils in sputum on day 7 of treatment with IVL745 (mean [SEM], 7.32 [1.46]) compared with placebo (mean [SEM], 15.00 [1.92]; 95% CI of difference, -13 to -1.2; P = .02). There was no statistically significant difference between IVL745 and placebo with respect to the early asthmatic response, methacholine hyperresponsiveness, exhaled NO, postallergen sputum, symptoms, inhaled beta2-agonist use, or PEF.

CONCLUSION

In patients with mild-to-moderate atopic asthma, IVL745 did not affect the early and late response to inhaled allergen or markers of airway inflammation, except for a modest reduction in sputum eosinophils.

Small molecule antagonists of alpha4 integrins: novel drugs for asthma

The alpha4 integrins, alpha4beta1 (VLA-4) and alpha4beta7, are heterodimeric cell-surface proteins expressed on leukocytes involved in both cell-cell and cell-matrix interactions. These two integrins are key regulators of physiologic and pathologic responses in inflammation and autoimmune disease. In particular, their central role in animal models of allergic lung disease has been well documented, and suggests a key role in human asthma. In addition, integrins are proven valid targets for small molecule drugs, following the development of both parenteral and orally active antagonists of platelet integrin alphaIIbbeta3, and more recently, integrin alphaVbeta3. Therefore, there is a significant drive to develop small molecule inhibitors of alpha4 integrins for autoimmune diseases in general, and asthma in particular. The biology of alpha4 integrins in asthma has been recently reviewed, as has early work on the chemistry of alpha4 integrin antagonists. Here we summarise the recent rapid advances in this arena, particularly in the chemistry of alpha4 integrin small molecule antagonists, with emphasis on asthma as a clinical target.

Design, synthesis, and analysis of a polyethelene glycol-modified (PEGylated) small molecule inhibitor of integrin {alpha}4{beta}1 with improved pharmaceutical properties

Integrin alpha4beta1 plays an important role in inflammatory processes by regulating the migration of leukocytes into inflamed tissues. Previously, we identified BIO5192 [2(S)-{[1-(3,5-dichloro-benzenesulfonyl)-pyrrolidine-2(S)-carbonyl]-amino}-4-[4-methyl-2(S)-(methyl-{2-[4-(3-o-tolyl-ureido)-phenyl]-acetyl}-amino)-pentanoylamino]-butyric acid], a highly selective and potent (K(D) of 9 pM) small molecule inhibitor of alpha4beta1. Although BIO5192 is efficacious in various animal models of inflammatory disease, high doses and daily treatment of the compound are needed to achieve a therapeutic effect because of its relatively short serum half-life. To address this issue, polyethylene glycol modification (PEGylation) was used as an approach to improve systemic exposure. BIO5192 was PEGylated by a targeted approach in which derivatizable amino groups were incorporated into the molecule. Two sites were identified that could be modified, and from these, five PEGylated compounds were synthesized and characterized. One compound, 2a-PEG (K(D) of 19 pM), was selected for in vivo studies. The pharmacokinetic and pharmacodynamic properties of 2a-PEG were dramatically improved relative to the unmodified compound. The PEGylated compound was efficacious in a rat model of experimental autoimmune encephalomyelitis at a 30-fold lower molar dose than the parent compound and required only a once-a-week dosing regimen compared with a daily treatment for BIO5192. Compound 2a-PEG was highly selective for alpha4beta1. These studies demonstrate the feasibility of PEGylation of alpha4beta1-targeted small molecules with retention of activity in vitro and in vivo. 2a-PEG, and related compounds, will be valuable reagents for assessing alpha4beta1 biology and may provide a new therapeutic approach to treatment of human inflammatory diseases.

2,3-Diphenylpropionic acids as potent VLA-4 antagonists

The discovery and SAR of 2,3-diphenylpropionic acid derivatives as highly potent VLA-4 antagonists are described. One representative compound, 9cc has inhibited intercellular adhesion by a VCAM-1/VLA-4 interaction with an IC(50) of 1.7 nM, and has good pharmacokinetics and oral bioavailability.

Targeting the issues in chronic obstructive lung disease

Chronic obstructive pulmonary disease (COPD) is a disease of unclear aetiology and variable pathology among patients. Little is known about the cellular mechanisms which cause this condition and, although the incidence of COPD has been rising worldwide for some time, research efforts have only very recently increased. Medication thus far has focused on symptom treatment rather than targeting identifiable disease mechanisms. Such treatment has consisted primarily of bronchodilators, both beta-agonists and anticholinergic in action. Treatment with steroids has been disappointing, except in the case of acute exacerbation, and this has shifted the research focus to characterising the inflammatory process in COPD as distinct from that in asthma. New targets for pharmacotherapy are coming to light as information is gained about specific inflammatory mediators active in COPD and the role of oxidative stress in this disease. In addition, new approaches include describing the role of exogenous antiproteases in restoring the balance between protease-antiprotease mechanisms that may be defective in this disease. Ultimately, exploration of the molecular genetics of COPD will provide new targets for future pharmacological agents.

An assessment of the mechanistic differences between two integrin alpha 4 beta 1 inhibitors, the monoclonal antibody TA-2 and the small molecule BIO5192, in rat experimental autoimmune encephalomyelitis

Integrin alpha 4 beta 1 plays an important role in inflammatory processes by regulating the migration of lymphocytes into inflamed tissues. Here we evaluated the biochemical, pharmacological, and pharmacodynamic properties and efficacy in experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis, of two types of alpha 4 beta 1 inhibitors, the anti-rat alpha 4 monoclonal antibody TA-2 and the small molecule inhibitor BIO5192 [2(S)-[[1-(3,5-dichloro-benzenesulfonyl)-pyrrolidine-2(S)-carbonyl]-amino]-4-[4-methyl-2(S)-(methyl-[2-[4-(3-o-tolyl-ureido)-phenyl]-acetyl]-amino)-pentanoylamino]-butyric acid]. TA-2 has been extensively studied in rats and provides a benchmark for assessing function. BIO5192 is a highly selective and potent (KD of <10 pM) inhibitor of alpha 4 beta 1. Dosing regimens were identified for both inhibitors, which provided full receptor occupancy during the duration of the study. Both inhibitors induced leukocytosis, an effect that was used as a pharmacodynamic marker of activity, and both were efficacious in the EAE model. Treatment with TA-2 caused a decrease in alpha 4 integrin expression on the cell surface, which resulted from internalization of alpha 4 integrin/TA-2 complexes. In contrast, BIO5192 did not modulate cell surface alpha 4 beta 1. Our results with BIO5192 indicate that alpha 4 beta 7 does not play a role in this model and that blockade of alpha 4 beta 1/ligand interactions without down-modulation is sufficient for efficacy in rat EAE. BIO5192 is highly selective and binds with high affinity to alpha 4 beta 1 from four of four species tested. These studies demonstrate that BIO5192, a novel, potent, and selective inhibitor of alpha 4 beta 1 integrin, will be a valuable reagent for assessing alpha 4 beta 1 biology and may provide a new therapeutic for treatment of human inflammatory diseases.

VLA-4 antagonists: potent inhibitors of lymphocyte migration

Circulating lymphocytes normally migrate through extravascular spaces in relatively low numbers as important members of the immunosurveillance process. That is until signals are received by endothelial cells that there is an underlying infection or inflammatory condition. These vascular surface cells in turn overexpress and present ligands to circulating lymphocyte adhesion molecules. Upon encountering this higher density of ligands, lymphocytes, which had been leisurely rolling along the vascular surface, now become more firmly attached, change shape, and migrate through tight junctions to the sites of infection or inflammation. If the initiating events are not resolved and the condition becomes chronic, there can be a sustained extravasation of lymphocytes that can exacerbate the inflammatory condition, which in turn will continue to recruit more inflammatory cells resulting in unwanted tissue destruction. It is for the attenuation of this cycle of sustained inflammatory cell recruitment that very late activating antigen-4 (VLA-4) antagonists are being developed. Most lymphocytes, except neutrophils, express VLA-4 on their surface and they interact with endothelial vascular cell adhesion molecule-1 (VCAM-1). It is this interaction that VLA-4 antagonists are intended to disrupt, thus, putting an end to the cycle of chronic inflammation, which is the hallmark of many diseases. This review will provide an update of VLA-4 antagonists that have appeared since early 2001 and will discuss some of the issues, both positive and negative, that may be encountered in their development.

Prolonged reversal of chronic experimental allergic encephalomyelitis using a small molecule inhibitor of alpha4 integrin

CNS leukocytic invasion in experimental allergic encephalomyelitis (EAE) depends on alpha4beta1 integrin/vascular cell adhesion molecule-1 (VCAM-1) interactions. A small molecule inhibitor of alpha4beta1 integrin (CT301) was administered to guinea pigs in the chronic phase (>d40) of EAE for 10, 20, 30 or 40 days. CT301 elicited a rapid, significant improvement in the clinical and pathological scores that was maintained throughout the treatment period. A progressive loss of cells in the spinal cord of treated animals confirmed the resolution of inflammation associated with clinical recovery. Therefore, prolonged inhibition of alpha4beta1 integrin caused a sustained reversal of disease pathology in chronic EAE and may be similarly useful in MS.

Alpha4 integrins and the immune response

The alpha4 integrins (alpha4beta1 and alpha4beta7) play multiple roles in the immune system. Alpha4 integrins impact hematopoiesis, leukocyte trafficking in immune surveillance and inflammation, and leukocyte activation and survival. To perform these functions, alpha4 integrins act as both adhesive and signaling receptors. Paxillin, a signaling adapter molecule, binds directly to the alpha4 subunit cytoplasmic domain, and its binding is regulated by serine phosphorylation of the alpha4 subunit. This regulated interaction of paxillin with the alpha4 subunit is likely to regulate the diverse functions of alpha4 integrins in the immune system. Furthermore, this protein-protein interaction may provide novel targets for the modulation of the immune response.

Comparative assessment of the ligand and metal ion binding properties of integrins alpha9beta1 and alpha4beta1

Integrins alpha9beta1 and alpha4beta1 form a distinct structural class, but while alpha4beta1 has been subjected to extensive study, alpha9beta1 remains poorly characterized. We have used the small molecule N-(benzenesulfonyl)-(L)-prolyl-(L)-O-(1-pyrrolidinylcarbonyl)tyrosine (3) to investigate the biochemical properties of alpha9beta1 and directly compare these properties with those of alpha4beta1. Compound 3 has a high affinity for both integrins with K(D) values of < or =3 and 180 pM for alpha9beta1 in 1 mM Mn2+ (activating) and 1 mM Ca2+ and 1 mM Mg2+ (nonactivating) conditions and < or =5 and 730 pM for alpha4beta1 under the corresponding conditions. Ca2+ treatment promoted the binding of 3 to both integrins (EC50 = 30 microM Ca2+ in both cases). Compound 3 binding to both integrins was also stimulated by the addition of the activating monoclonal antibody TS2/16. These findings indicate that the mechanisms by which metal ions and TS2/16 regulate ligand binding to alpha9beta1 and alpha4beta1 are similar. The binding of 3 to both integrins induced the mAb 9EG7 LIBS epitope, a property consistent with occupancy of the receptor's ligand binding site by 3. But whereas EGTA treatment inhibited the binding of 9EG7 to alpha4beta1, it stimulated the binding of 9EG7 to alpha9beta1. The 9EG7 and TS2/16 effects point to contributions of the beta1-chains on binding. Cross-linking data revealed that the integrin alpha-chains are also involved in binding the small molecule, as stable linkages were observed on both the alpha9 chain of alpha9beta1 and the alpha4 chain of alpha4beta1. Extensive structure-activity analyses with natural and synthetic ligands indicate distinct features of the ligand binding pockets. Most notable was the estimated >1000-fold difference in the affinity of the integrins for VCAM-1, which binds alpha4beta1with an apparent K(D) of 10 nM and alpha9beta1 with an apparent K(D) of >10 microM. Differences were also seen in the binding of alpha9beta1 and alpha4beta1 to osteopontin. Compound 3 competed effectively for the binding of VCAM-1 and osteopontin to both integrins. While these studies show many similarities in the biochemical properties of alpha9beta1 and alpha4beta1, they identify important differences in their structure and function that can be exploited in the design of selective alpha9beta1 and alpha4beta1 inhibitors.

Pulmonary eosinophilia in a murine model of allergic inflammation is attenuated by small molecule alpha4beta1 antagonists

Inhibition of alpha4beta1/vascular cell adhesion molecule-1 (VCAM-1) interactions have therapeutic potential in treating allergic airway disease because of the importance of these adhesion molecules in the trafficking of eosinophils, lymphocytes, and monocytes. We examined several small molecule inhibitors of alpha4beta1/VCAM-1 interactions with in vitro potencies (IC(50) values) ranging from 0.52 nM (CP-664511; 3-[3-(1-[2-[3-methoxy-4-(3-O-tolyl-ureido)phenyl]-acetylamino]-3-methyl-butyl)isoxazol-5-yl]-propionic acid) to 38.5 nM (CP-609643; 3-[3-methyl-1-[2-[4-(3-O-tolyl-ureido)-phenyl]-acetylamino]-butyl)-isoxazol-5-yl]-propionic acid). The same compounds were evaluated in vivo using a murine model of ovalbumin-induced pulmonary eosinophilia. In this model, systemic administration of antibodies against alpha4 reduced bronchoalveolar lavage (BAL) eosinophilia approximately 60%. Small molecule alpha4beta1 antagonists were administered by intratracheal instillation and demonstrated dose-dependent inhibition of BAL eosinophil numbers and achieved a maximum inhibition of approximately 60%. In general, the rank order of potency for these compounds in vitro was consistent with that observed in vivo, which confirms that their efficacy is likely via blockade of alpha4beta1/VCAM-1 interactions. The most potent compound, CP-664511, also inhibited BAL eosinophilia following s.c. administration (1-10 mg/kg, s.c.). These data support the utility of small molecule alpha4beta1 antagonists in the treatment of relevant diseases, such as asthma.

Human mast cell progenitors use alpha4-integrin, VCAM-1, and PSGL-1 E-selectin for adhesive interactions with human vascular endothelium under flow conditions

Mast cells (MCs) are central to asthma and other allergic diseases, and for responses to infection and tissue injuries. MCs arise from committed progenitors (PrMCs) that migrate from the circulation to tissues by incompletely characterized mechanisms, and differentiate in situ in perivascular connective tissues of multiple organs. PrMCs derived in vitro from human cord blood were examined for adhesion molecule expression and their ability to adhere to human umbilical vein endothelial cells (HUVECs) under conditions that mimic physiologic shear flow. The PrMCs expressed alpha(4)beta(1), low levels of beta7, and the beta2-integrins alphaLbeta2 and alphaMbeta2. The PrMCs also expressed PSGL-1, but not L-selectin. At low (0.5 dynes/cm(2)-1.0 dynes/cm(2)) shear stress, PrMCs attached and rolled on recombinant E-selectin and P-selectin and VCAM-1. An anti-PSGL-1 monoclonal antibody (mAb) blocked essentially all adhesion to P-selectin but reduced adhesion to E-selectin by only 40%, suggesting PrMCs express other ligands for E-selectin. PrMCs adhered strongly to tumor necrosis factor-alpha (TNF-alpha)-activated HUVECs, whereas adhesion to interleukin 4 (IL-4)-activated HUVECs was lower. PrMC adhesion to IL-4-activated HUVECs was totally alpha4-integrin- and VCAM-1-dependent. Adhesion to TNF-alpha-activated HUVECs was blocked by 50% by mAbs against alpha4-integrin, vascular cell adhesion molecule-1 (VCAM-1), E-selectin, or PSGL-1, whereas combinations of mAbs to alpha4-integrin plus PSGL-1, or VCAM-1 plus E-selectin, blocked adhesion by greater than 70%. Thus, PrMCs derived in vitro predominantly use alpha4-integrin, VCAM-1, PSGL-1, and other ligands that bind E-selectin for adhesion to cytokine-activated HUVEC monolayers. These observations may explain the abundance of MCs at sites of mucosal inflammation, where VCAM-1 and E-selectin are important inducible receptors.

Cell adhesion molecules, leukocyte trafficking, and strategies to reduce leukocyte infiltration

Leukocyte-endothelial cell interactions are mediated by various cell adhesion molecules. These interactions are important for leukocyte extravasation and trafficking in all domestic animal species. An initial slowing of leukocytes on the vascular endothelium is mediated by selectins. This event is followed by (1) activation of beta2 integrins after leukocyte exposure to cytokines and pro-inflammatory mediators, (2) adherence of leukocyte beta2 integrins to vascular endothelial ligands (eg, intercellular adhesion molecule-1 [ICAM-1]), (3) extravasation of leukocytes into tissues through tight junctions of endothelial cells mediated by platelet and endothelial cell adhesion molecule-1 (PECAM-1), and (4) perivascular migration through the extracellular matrix via beta1 integrins. Inhibiting excessive leukocyte egress and subsequent free radical-mediated damage caused by leukocyte components may attenuate or eliminate tissue damage. Several methods have been used to modify leukocyte infiltration in various animal models. These methods include nonspecific inhibition of pro-inflammatory mediators and adhesion molecules by nonsteroidal anti-inflammatory drugs (NSAIDs) and glucocorticoids, inhibition of cytokines and cytokine receptors, and inhibition of specific types of cell adhesion molecules, with inhibitors such as peptides and antibodies to beta2 integrins, and inhibitors of selectins, ICAMs, and vascular cell adhesion molecule-1 (VCAM-1). By understanding the cellular and molecular events in leukocyte-endothelial cell interactions, therapeutic strategies are being developed in several animal models and diseases in domestic animal species. Such therapies may have clinical benefit in the future to overcome tissue damage induced by excessive leukocyte infiltration.

Inhibition of LFA-1/ICAM-1 and VLA-4/VCAM-1 as a therapeutic approach to inflammation and autoimmune diseases

This review focuses on providing insights into the structural basis and clinical relevance of LFA-1 and VLA-4 inhibition by peptides and small molecules as adhesion-based therapeutic strategies for inflammation and autoimmune diseases. Interactions of cell adhesion molecules (CAM) play central roles in mediating immune and inflammatory responses. Leukocyte function-associated antigen (LFA-1, alpha(L)beta(2), and CD11a/CD18) and very late antigen (VLA-4, alpha(4)beta(1), and CD49d/CD29) are members of integrin-type CAM that are predominantly involved in leukocyte trafficking and extravasation. LFA-1 is exclusively expressed on leukocytes and interacts with its ligands ICAM-1, -2, and -3 to promote a variety of homotypic and heterotypic cell adhesion events required for normal and pathologic functions of the immune systems. VLA-4 is expressed mainly on lymphocyte, monocytes, and eosinophils, but is not found on neutrophils. VLA-4 interacts with its ligands VCAM-1 and fibronectin (FN) CS1 during chronic inflammatory diseases, such as rheumatoid arthritis, asthma, psoriasis, transplant-rejection, and allergy. Blockade of LFA-1 and VLA-4 interactions with their ligands is a potential target for immunosuppression. LFA-1 and VLA-4 antagonists (antibodies, peptides, and small molecules) are being developed for controlling inflammation and autoimmune diseases. The therapeutic intervention of mostly mAb-based has been extensively studied. However, due to the challenging relative efficacy/safety ratio of mAb-based therapy application, especially in terms of systemic administration and immunogenic potential, strategic alternatives in the forms of peptide, peptide mimetic inhibitors, and small molecule non-peptide antagonists are being sought. Linear and cyclic peptides derived from the sequences of LFA-1, ICAM-1, ICAM-2, VCAM-1, and FN C1 have been shown to have inhibitory effects in vitro and in vivo. Finally, understanding the mechanism of LFA-1 and VLA-4 binding to their ligands has become a fundamental basis in developing therapeutic agents for inflammation and autoimmune diseases.

Beneficial effect of modified peptide inhibitor of alpha4 integrins on experimental allergic encephalomyelitis in Lewis rats

An important event in the pathogenesis of the autoimmune disease multiple sclerosis (MS) is the recruitment of lymphocytes and inflammatory macrophages to the central nervous system (CNS). Recruitment requires adhesive interactions between the leukocytes and the microvascular endothelium, perivascular cells, and astrocytes in the CNS parenchyma. Previous studies using an animal model of MS, experimental allergic encephalomyelitis (EAE), have shown the involvement of the alpha4 integrin VLA-4 (beta4beta1). In the present study, the effect of a modified peptide inhibitor of alpha4 integrins on the clinical course and leukocyte infiltration during EAE is investigated. EAE was either induced actively, by immunizing Lewis rats with whole guinea pig MBP, or passively, by transfer of an MBP-specific T cell line. Treatment with the inhibitor (CS1 ligand mimic) completely prevented both clinical signs and cellular infiltration in passively induced EAE. Peptide treatment of actively induced EAE, which has a more severe disease course than the transfer model, significantly reduced clinical signs although the recruitment of inflammatory cells and induction of MHC class II expression was not prevented. The alpha4 inhibitor did inhibit the adhesion of lymphocytes to primary astrocytes in vitro suggesting a role for astrocyte-leukocyte interactions in the pathogenesis of induced EAE. Astrocytes were found to express an extracellular matrix protein distinct from fibronectin, which shows immune cross-reactivity with the CS1 domain of fibronectin. Our results show that small-molecule inhibitors of alpha4 integrins act therapeutically in EAE possibly by interfering with cell adhesion events involved in this autoimmune disease.

Hypoxia mediates increased neutrophil and macrophage adhesiveness to alveolar epithelial cells

Leukocyte infiltration is known to play an important role in hypoxia-induced tissue damage. There is a paucity of information on the role of hypoxia in the expression of adhesion molecules on respiratory epithelial cells. The current studies focus on the adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), their expression pattern on alveolar epithelial cells, and their biologic function under hypoxic conditions. Rat alveolar epithelial cells (AEC) were exposed to hypoxia for several time periods. With 5% oxygen, mRNA for ICAM-1 and VCAM-1 rose by 100%, peaking between 0.5 and 1 h. ICAM-1 and VCAM-1 protein showed an increase between 2 and 4 h. Neutrophil adherence to hypoxia-exposed AEC was enhanced by 115%. This increase was reduced by 83% with anti-ICAM-1 antibody. Adherence of alveolar macrophages to AEC increased by 118% and could be blocked by 95% with anti-VCAM-1 antibody. The present study shows for the first time an early increase of ICAM-1 and VCAM-1 expression on rat AEC under hypoxic conditions. These adhesion molecules are involved in increased adhesiveness of neutrophils and macrophages. Such responses might play an important role in the adhesion of leukocytes and macrophages to lung epithelial cells during hypoxic conditions.

Design and synthesis of potent and selective inhibitors of integrin VLA-4

The synthesis and identification of a novel series of inhibitors of integrin VLA-4 are described. Their in vitro activity and selectivity against closely related integrins are also presented.

Evidence that ligand and metal ion binding to integrin alpha 4beta 1 are regulated through a coupled equilibrium

We have used the highly selective alpha(4)beta(1) inhibitor 2S-[(1-benzenesulfonyl-pyrrolidine-2S-carbonyl)-amino]-4-[4-methyl-2S-(methyl-[2-[4-(3-o-tolyl-ureido)-phenyl]-acetyl]-amino)-pentanoylamino]-butyric acid (BIO7662) as a model ligand to study alpha(4)beta(1) integrin-ligand interactions on Jurkat cells. Binding of [(35)S]BIO7662 to Jurkat cells was dependent on the presence of divalent cations and could be blocked by treatment with an excess of unlabeled inhibitor or with EDTA. K(D) values for the binding of BIO7662 to Mn(2+)-activated alpha(4)beta(1) and to the nonactivated state of the integrin that exists in 1 mm Mg(2+), 1 mm Ca(2+) were <10 pm, indicating that it has a high affinity for both activated and nonactivated integrin. No binding was observed on alpha(4)beta(1) negative cells. Through an analysis of the metal ion dependences of ligand binding, several unexpected findings about alpha(4)beta(1) function were made. First, we observed that Ca(2+) binding to alpha(4)beta(1) was stimulated by the addition of BIO7662. From solution binding studies on purified alpha(4)beta(1), two types of Ca(2+)-binding sites were identified, one dependent upon and the other independent of BIO7662 binding. Second, we observed that the metal ion dependence of ligand binding was affected by the affinity of the ligand for alpha(4)beta(1). ED(50) values for the metal ion dependence of the binding of BIO7762 and the binding of a lower affinity ligand, BIO1211, differed by 2-fold for Mn(2+), 30-fold for Mg(2+), and >1000-fold for Ca(2+). Low Ca(2+) (ED(50) = 5-10 microm) stimulated the binding of BIO7662 to alpha(4)beta(1). The effects of microm Ca(2+) closely resembled the effects of Mn(2+) on alpha(4)beta(1) function. Third, we observed that the rate of BIO7662 binding was dependent on the metal ion concentration and that the ED(50) for the metal ion dependence of BIO7662 binding was affected by the concentration of the BIO7662. These studies point to an even more complex interplay between metal ion and ligand binding than previously appreciated and provide evidence for a three-component coupled equilibrium model for metal ion-dependent binding of ligands to alpha(4)beta(1).

Diamine containing VLA-4 antagonists

Design and synthesis of a library as potential VLA-4 antagonists has been accomplished, based around a proposed pharmacophoric model. Compounds possessing submicromolar potency were identified and structure-activity relationships were seen across the library. Further derivatisation produced compounds with IC(50)'s <10 nmol for inhibiting the VLA-4 mediated binding of fibronectin to RAMOS cells, providing an ideal starting point for a lead optimisation Programme.

Blockade of CD49d inhibits allergic airway pathologies independent of effects on leukocyte recruitment

Lymphocyte and/or eosinophil recruitment is dependent on the sequential interactions between adhesion molecules expressed on activated endothelial cells and both leukocyte subtypes. Endothelial P- and E-selectins mediate tethering and rolling of leukocytes through interactions with P-selectin glycoprotein ligand-1 (PSGL-1), and diapedesis subsequently occurs by engagement of endothelial vascular cell adhesion molecule-1 and CD49d (alpha(4)-integrins). The anti-inflammatory potential of interfering with these adhesive interactions was assessed with an ovalbumin challenge mouse model of asthma. Administration of a soluble form of PSGL-1 reduced eosinophils (80%) and lymphocytes (50%) in bronchoalveolar lavage fluid without affecting epithelial changes or airway hyperreactivity (AHR). In contrast, although administration of anti-CD49d monoclonal antibodies (PS/2) resulted in similar reductions in eosinophils (75%) and lymphocytes (50%), PS/2 reduced and abolished mucous cell metaplasia and AHR, respectively. Administration of both PSGL-1 and PS/2 had the additive effect of eliminating eosinophils from the airways (96% decrease), with few or no additional reductions (relative to PS/2 administration alone) in lymphocyte recruitment, mucous cell metaplasia, or AHR. These data show that eosinophils and lymphocytes differentially utilize adhesive interactions during recruitment and that the inhibition of AHR is independent of this recruitment.

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

1. Although anti-alpha(4) integrin mAbs reduce eosinophil accumulation in several models of allergic inflammation, it is not clear whether this occurs via a direct action to block eosinophil alpha(4) integrins or indirectly on another cell type. The role of alpha(4) integrins on the accumulation of (111)In-labelled eosinophils in allergic and non-allergic inflammation in guinea-pig skin was therefore investigated. 2. Intradermal injection of antigen in sensitized skin sites induced accumulation of (111)In-eosinophils that was reduced up to 70% by two anti-alpha(4) integrin mAbs. In contrast, accumulation of (111)In-eosinophils to intradermal chemoattractants was unaffected by the same mAbs. 3. Accumulation of (111)In-eosinophils in allergic and non-allergic conditions was partly inhibited by a low dose of an anti-beta(2) integrin mAb. In combination with anti-alpha(4) integrin mAb, responses were not further reduced suggesting that these adhesion pathways are not additive or synergic. 4. Pretreating skin sites with antiserum or contaminating LPS did not reveal an alpha(4) integrin dependent pathway for chemoattractant-induced (111)In-eosinophil accumulation. These data suggest that alpha(4) integrins are involved in the response to antigen in sensitized skin sites. 5. Pretreating (111)In-eosinophil with alpha(4) integrin mAb blocked their adhesion to fibronectin in vitro but did not inhibit their accumulation in allergic inflammation suggesting that the blocking effect in vivo was eosinophil independent. 6. These data support the concept that targeting alpha(4) integrins on cells other than eosinophils could control eosinophil accumulation and have therapeutic potential in allergic diseases such as asthma and atopic dermatitis.

The role of cytokines and adhesion molecules for mobilization of peripheral blood stem cells

CD34(+) hematopoietic stem cells from peripheral blood are commonly used for autologous or allogeneic transplantation following high-dose therapy in malignant diseases. The introduction of hematopoietic growth factors such as G-CSF has greatly facilitated the mobilization of CD34(+) cells. The mechanism of stem cell mobilization is not yet clear. It seems to be a multistep process with a crosstalk between cytokines and adhesion molecules. In this review, the role of hematopoietic growth factors, chemokines, and adhesion molecules for mobilization and homing of CD34(+) cells is summarized. In addition, factors influencing the cytokine-induced mobilization in patients and healthy donors are described. The review closes with an overview of new classes of mobilizing drugs such as monoclonal antibodies, specific peptides, or antisense oligonucleotides targeting adhesion molecules.

Asthma: where beyond steroids?

The prevalence of asthma is increasing dramatically despite major changes in monitoring and treatment of this disease. Currently available bronchodilators and anti-inflammatory drugs are effective in most patients, although these can have side effects and are mainly symptomatic. Many drugs are now in development for the treatment of asthma. Most of these new therapies are aimed at inhibition of the inflammatory components, with better safety profiles than steroids.

A small-molecule, tight-binding inhibitor of the integrin alpha(4)beta(1) blocks antigen-induced airway responses and inflammation in experimental asthma in sheep

The leukocyte integrin very late antigen-4 (alpha(4)beta(1), CD49d/CD29) is an adhesion receptor that plays an important role in allergic inflammation and contributes to antigen-induced late responses (LAR) and airway hyperresponsiveness (AHR). In this study, we show that single doses of a new small-molecule, tight-binding inhibitor of alpha(4), BIO-1211, whether given by aerosol or intravenously, either before or 1.5 h after antigen challenge blocks allergen- induced LAR and post-antigen-induced AHR in allergic sheep. Multiple treatments with doses of BIO-1211 that were ineffective when given singly, were protective. BIO-1211 also provided dose-dependent inhibition of the early airway response (EAR) to antigen. In conjunction with the functional protection against the antigen-induced LAR and AHR, sheep treated with BIO-1211 before challenge showed significantly reduced: (1) numbers of eosinophils in bronchoalveolar lavage (BAL), (2) BAL levels of the inflammatory marker tissue kallikrein, and (3) numbers of inflammatory cells (lymphocytes, eosinophils, metachromatic staining cells, and neutrophils) in bronchial biopsies obtained after challenge when compared with corresponding biopsies after vehicle treatment. More importantly, we show for the first time that an inhibitor of alpha(4) was able to reverse post-antigen-induced AHR, thereby decreasing the time of recovery from the normal period of > 9 d to 3 d. Our results show that effective inhibition of antigen-induced airway responses can be achieved with single doses of a potent small-molecule inhibitor of alpha(4) and that such agents may be used therapeutically, as well as prophylactically, to alleviate allergen- induced inflammatory events. These data provide further support and extend the evidence for the role of alpha(4) integrins in the pathophysiologic events that follow airway antigen challenge.

The increased number of very late activation antigen-4-positive cells correlates with eosinophils and severity of disease in the induced sputum of asthmatic patients

BACKGROUND

Lymphocyte function associate-1 (LFA-1), macrophage antigen-1 (Mac-1), and very late activation antigen-4 (VLA-4) are involved in the infiltration of leukocytes into the tissues. Experimental models of allergic inflammation suggest that VLA-4 could determine the selective recruitment of eosinophils into the inflamed airways.

OBJECTIVE

Our purpose was to evaluate the involvement of integrins in eosinophil recruitment in asthma.

METHODS

We evaluated by immunocytochemistry the expression of VLA-4, LFA-1, and Mac-1 and their relationship with inflammatory cells and severity of disease in the induced sputum of 20 mild to moderate atopic asthmatic subjects and in 8 healthy subjects.

RESULTS

The number of VLA-4+ cells is increased in asthmatic patients and VLA-4 is mainly localized on eosinophils. Furthermore, VLA-4+ cells are significantly related to eosinophils. In contrast, LFA-1 and Mac-1 cellular expressions do not differ between asthmatic and control subjects and are not related to any specific cell type. Eosinophils and VLA-4+ cells are significantly higher in moderately compared with mildly asthmatic patients (P <.01, P <.05) and with healthy control subjects (P <.0005, P <.001). Eosinophils and VLA-4+ cells are also higher in mildly asthmatic patients compared with control subjects (P <.001, P <.005).

CONCLUSION

This is the first report demonstrating, by a noninvasive method in humans, that VLA-4+ cells are increased and correlate with the eosinophils in the induced sputum of atopic patients with mild to moderate asthma and that VLA-4 expression is related to the severity of disease.

Advances in the immunobiology of eosinophils and their role in disease

Eosinophils play a protective role in host immunity to infections by parasitic worms and, detrimentally, are involved in the pathophysiology of asthma and other allergic diseases. Airway inflammation is central to the pathology of asthma and is characterized by infiltration of the bronchial mucosa by large numbers of proinflammatory cells, amongst which the eosinophil is prominent despite being a minority constituent of circulating leukocytes. Crucial steps in eosinophilic inflammation include augmented production of eosinophils in the bone marrow, their increased release into the circulation, and their selective accumulation in the conducting airways. The eosinophil has a potent armory of proinflammatory mediators, including cytotoxic granule proteins, cytokines and lipid mediators with considerable potential to initiate and sustain an inflammatory response. Thus there is much interest in the elucidation of the mechanisms responsible for eosinophil accumulation, persistence, activation and ultimate fate. This article reviews our current understanding of the role of the eosinophil in human disease and the immunobiology of this important proinflammatory cell.

Selectin blockade prevents antigen-induced late bronchial responses and airway hyperresponsiveness in allergic sheep

Antigen challenge can elicit an allergic inflammatory response in the airways that involves eosinophils, basophils, and neutrophils and that is expressed physiologically as a late airway response (LAR) and airway hyperresponsiveness (AHR). Although previous studies have suggested that E-selectin participates in these allergic airway responses, there is little information concerning the role of L-selectin. To address this question, we examined the effects of administering an L-selectin-specific monoclonal antibody, DU1-29, as well as three small molecule selectin binding inhibitors, on the development of early airway responses (EAR), LAR and AHR in allergic sheep undergoing airway challenge with Ascaris suum antigen. Sheep treated with aerosol DU1-29 before antigen challenge had a significantly reduced LAR and did not develop postchallenge AHR. No protective effect was seen when sheep were treated with a nonspecific control monoclonal antibody. Treatment with DU1-29 also reduced the severity of the EAR to antigen. Similar results were obtained with each of the three small molecule selectin inhibitors at doses that depended on their L-, but not necessarily E-selectin inhibitory capacity. The inhibition of the EAR with one of the inhibitors, TBC-1269, was associated with a reduction in histamine release. Likewise, treatment with TBC-1269 reduced the number of neutrophils recovered in bronchoalveolar lavage (BAL) during the time of LAR and AHR. TBC-1269, given 90 min after antigen challenge also blocked the LAR and the AHR, but this protection was lost if the treatment was withheld until 4 h after challenge, a result consistent with the proposed time course of L-selectin involvement in leukocyte trafficking. These are the first data indicating that L-selectin may have a unique cellular function that modulates allergen-induced pulmonary responses.

Selective, tight-binding inhibitors of integrin alpha4beta1 that inhibit allergic airway responses

Integrin alpha4beta1 mediates leukocyte recruitment, activation, mediator release, and apoptosis inhibition, and it plays a central role in inflammatory pathophysiology. High-affinity, selective inhibitors of alpha4beta1, 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 approximately 10(6)-fold more potent than the starting peptide and exhibited tight-binding properties (koff = 1.4 x 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 alpha4beta1, and it stimulated expression of ligand-induced epitopes on the integrin beta1 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 alpha4beta1 as a therapeutic target for asthma.

Hyperresponsiveness in the human nasal airway: new targets for the treatment of allergic airway disease

Allergic rhinitis is a condition which affects over 15% of the population in the United Kingdom. The pathological process involves two stages: nasal inflammation, and the development of nasal airway hyperresponsiveness (AHR) to allergen and a number of other stimuli. This results in the amplification of any subsequent allergic reaction, contributing to the chronic allergic state. A number of different hypotheses have been proposed to explain the underlying mechanism of AHR, including a role for eosinophil-derived proteins, free radicals and neuropeptides. While there may be a number of independent pathways which can result in AHR, evidence obtained from both animal models and in vivo experiments in humans indicate that some mediators may interact with one another, resulting in AHR. Further research into these interactions may open new avenues for the pharmacological treatment of chronic allergic rhinitis, and possibly other allergic airway diseases.

Involvement of alpha-4 integrins in allergic airway responses and mast cell degranulation in vivo

Antibodies against integrins have been shown to inhibit allergic airway responses. The purpose of this study was to test the hypothesis that the beta1 integrin, very late antigen-4 (VLA-4), is involved in mast cell activation triggered by allergen exposure in sensitized animals. To do this we studied Brown Norway rats that were sensitized to ovalbumin (OA; 1 mg subcutaneously) using Bordetella pertussis as an adjuvant. Two weeks later rats were challenged with OA, pulmonary resistance (RL) was determined, and the concentrations of histamine and tryptase in bronchoalveolar lavage fluid and N-acetyl-leukotriene (LT)E4 in bile were measured. Pretreatment with a monoclonal antibody against VLA-4 (TA-2) attenuated the early response after OA challenge (342.9 +/- 24.4% baseline RL versus 153.3 +/- 19.4%; p < 0.01). There were significantly lower concentrations of histamine (67.11 +/- 11.90 microgram/ml versus 26.69 +/- 1.84; p < 0.01) and tryptase (0.143 +/- 0. 035 microgram/ml versus 0.053 +/- 0.022 microgram/ml; p < 0.01) in TA-2-treated animals. The increases in the concentrations of biliary N-acetyl-LTE4 after OA challenge were also significantly lower in TA-2-treated animals. These data suggest that a selective anti-VLA-4 monoclonal antibody prevents early responses through inhibition of mast cell activation.

Budesonide affects allergic mucociliary dysfunction

Airway inflammation characterized by neutrophils and free elastase contributes to allergic mucociliary dysfunction. Glucocorticosteroids are the most important anti-inflammatory agents used in the treatment of asthma, but their effect on allergic mucociliary dysfunction is not known. Therefore, we assessed both the prophylactic and therapeutic effects of the glucocorticosteroid budesonide on antigen-induced mucociliary dysfunction in sheep. Tracheal mucus velocity (TMV), a marker of mucociliary clearance, was measured by using a roentgenographic technique. When budesonide was administered either 30 min before or 1 h after airway challenge with Ascaris suum, the antigen-induced fall in TMV at 6 h was prevented. The effects on TMV at 8 and 24 h after challenge were also determined when budesonide and, for comparative purposes, alpha1-protease inhibitor were given 6 h after antigen challenge. Budesonide treatment improved TMV at 8 h, but TMV was not significantly different from antigen alone at 24 h. Treatment with alpha1-protease inhibitor, however, caused only a significant reversal of the antigen-induced fall in TMV at 24 h after challenge; this indicates a more prolonged effect than budesonide. Our results suggest that antiproteases may have a potential role as a therapeutic approach to mucociliary dysfunction in asthma and provide evidence for another means by which glucocorticosteroids contribute to the control of the disease.

Very late antigen 4 (VLA4) antagonists as anti-inflammatory agents

In recent years antagonists of very late antigen-4 (VLA4, also known as integrin alpha(4) beta(1)) have shown great promise in treating inflammatory disorders in a number of animal models. The most advanced in this endeavor is a humanized anti-alpha(4) antibody, Antegren, which is in phase II clinical trials for multiple sclerosis. The first reported small-molecule VLA4 antagonist to advance into clinical trials is currently in phase I as an aerosol for treating asthma. A number of peptides, cyclic peptides and peptidomimetics have been disclosed and are in preliminary stages of development.

Identification of ligand binding sites on integrin alpha4beta1 through chemical cross-linking

We have used chemical cross-linking to identify sequences in integrin alpha4beta1 that are involved in its interactions with ligands. A recently described leucine-aspartic acid-valine (LDV)-based small molecule inhibitor of alpha4beta1 (BIO-1494), that contained a single reactive amino group for targeting the cross-linking, was used for these studies. The specificity of the interaction was defined by (i) the ability to block the interaction with a competitive inhibitor lacking the reactive group, (ii) the absolute requirement of divalent cations for cross-linking, and (iii) the lack of cross-linking to the functionally related integrin alpha4beta7. With ANB-NOS as the cross-linker, only the beta1 chain was labeled with BIO-1494, while with the more flexible cross-linker DSS both the alpha4 and beta1 chains were modified. Similar results were obtained when cross-linking was performed on K562 cells expressing alpha4beta1 but not on K562 cells expressing alpha2beta1. The site of cross-linking on the beta1 chain was localized by CNBr peptide mapping within residues 130-146, a region that contains the putative metal binding site DXSXS and for which analogous data had been generated with RGD binding to integrin alphaIIbbeta3. The striking similarity between the data we generated for an LDV ligand and published data for the RGD family supports the notion of a common ligand binding pocket formed by both integrin chains. The cross-linking strategy developed here should serve as a useful tool for studying alpha4beta1 function.