Alpha 4 integrin antagonists

4-(Pyrrolidinyl)methoxybenzoic acid derivatives as a potent, orally active VLA-4 antagonist

A novel series of benzoic acid derivatives as VLA-4 antagonists were synthesized. Optimization, focusing on activity and lipophilicity needed for cell permeability, resulted in the identification of 15b and 15e with good activity (IC50 = 1.6 nM each) and moderate lipophilicity (Log D = 2.0, 1.8). Furthermore, 15e demonstrated efficacy in murine asthma model by an oral dose of 30 mg/kg.

Synthesis and biological evaluation of benzoic acid derivatives as potent, orally active VLA-4 antagonists

A series of benzoic acid derivatives was synthesized as VLA-4 antagonists. Introduction of chlorine or bromine into the 3-position on the central benzene of the diphenylurea portion as in lead compound 2 led to improvement in the pharmacokinetic properties. In particular, 12l demonstrated an acceptable plasma clearance and bioavailability in mice and rats as well as dogs (mice, CL=18.5 ml/min/kg,F=28%; rats, CL=5.2 ml/min/kg,F=36%; dogs, CL=3.6 ml/min/kg,F=55%). Additionally, 12l exhibited potent activity with an IC50 value of 0.51 nM and efficacy by oral administration at a dosage of 10 mg/kg in a rat pleurisy model.

Leukemia-targeting ligands isolated from phage-display peptide libraries

Ligands specifically binding to leukemia cells may be used for drug targeting, resulting in more effective treatment with less side effects. Little is known about receptors specifically expressed on acute myeloid leukemia (AML) cells or ligands thereof. We selected random phage display peptide libraries on Kasumi-1 AML cells. A peptide with the sequence CPLDIDFYC was enriched. Phage displaying this peptide strongly bound to Kasumi-1 and SKNO-1 cells and binding could be inhibited by the cognate peptide. Both, Kasumi-1 and SKNO-1 cells carry the chromosomal translocation t(8;21), leading to aberrant expression of the fusion protein AML1/ETO. CPLDIDFYC also strongly and specifically bound primary AML1/ETO-positive AML blasts as well as U-937 cells with forced AML1/ETO expression, suggesting that the CPLDIDFYC receptor may be upregulated upon AML1/ETO expression. Gene expression profiling comparing a panel of CPLDIDFYC-binding and CPLDIDFYC-nonbinding cell lines identified a set of potential receptors for the CPLDIDFYC peptide. Further analysis suggested that alpha4beta1 integrin (VLA-4) is the CPLDIDFYC receptor. Finally, we showed that the CPLDIDFYC-phage is internalized upon receptor binding, suggesting that the CPLDIDFYC-receptor-ligand interaction may be exploitable for targeting drugs or gene therapy vectors to leukemia cells carrying the suitable receptor.

Evolving Therapies For Multiple Sclerosis

The introduction of immunomodulatory and immunosuppressive agents for treatment of multiple sclerosis (MS) has forever altered the natural course of this incurable and disabling neurodegenerative disorder. Despite early diagnosis of relapsing-remitting MS and early initiation of therapy, patients still experience breakthrough relapses and progression of their underlying MS pathology. The imperfect effectiveness, side effects, and toxicity of these agents, emphasize the necessity for development of more effective medications with less adverse events. This chapter presents readers with the most current information on the nature, mechanism(s) of action, and side effects of the most promising experimental agents currently under clinical trials. Some of the agents now at different stages of clinical trial have emerged as both safe and promising. The understanding of MS etiology will lead to the development of increasingly specific, safer, and effective treatments for MS by neuroscientists and neurologists.

Conformational analysis of an alpha3beta1 integrin-binding peptide from thrombospondin-1: implications for antiangiogenic drug design

The integrin alpha3beta1 plays important roles in development, angiogenesis, and the pathogenesis of cancer, suggesting potential therapeutic uses for antagonists of this receptor. Recently, an alpha3beta1 integrin-binding site was mapped to residues 190-201 (FQGVLQNVRFVF) of the N-terminal domain of the secreted protein thrombospondin-1 (TSP1). This sequence displays diverse biological activities in vitro and inhibits angiogenesis in vivo. Herein we describe the NMR solution conformation of this segment in both water and dodecylphosphocholine micelles. While essentially unstructured in water, a more well-defined conformation is populated in micelles, particularly in the C-terminal half of the peptide and correlated with increased biological activity of the micellar peptide. The data suggested that the residues that are critical for biological activity are contained in a structurally well-defined segment of the peptide. These data support the role of the NVR motif as a required element of full-length TSP1 for specific molecular recognition by the alpha3beta1 integrin.

New approaches to blockade of alpha4-integrins, proven therapeutic targets in chronic inflammation

The recruitment of leukocytes into tissue is a pivotal step in inflammation. alpha4-Integrins are adhesion receptors on circulating leukocytes that mediate attachment to the endothelium and facilitate their migration into the inflamed tissue. This multistep process is mediated by the interaction of alpha4-integrins with their counter receptors VCAM-1 and MadCAM-1 that are expressed on endothelial cells. alpha4-Integrins act as both adhesive and signaling receptors. Paxillin, a signaling adaptor molecule, binds directly to the alpha4 cytoplasmic tail and its binding is important for cell migration. Blocking the adhesive functions of alpha4-integrins has been shown to be an effective therapeutic approach in the treatment of autoimmune diseases, but also carries the risk of defects in development, hematopoiesis and immune surveillance. Interfering with alpha4 signaling by inhibiting the alpha4-paxillin interaction decreases alpha4-mediated cell migration and adhesion to VCAM-1 and MadCAM under shear flow. These in vitro effects are accompanied by a selective impairment of leukocyte migration into inflammatory sites when the alpha4-paxillin interaction is blocked in vivo. Thus, blockade of alpha4-integrin signaling may offer a novel strategy for interfering with the functions of these receptors in pathological events while sparing important physiological functions.

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.

Synthesis, biological evaluation, and pharmacokinetic study of prolyl-1-piperazinylacetic acid and prolyl-4-piperidinylacetic acid derivatives as VLA-4 antagonists

A series of prolyl-1-piperazinylacetic acid and prolyl-4-piperidinylacetic acid derivatives were synthesized and evaluated for their activity as VLA-4 antagonists. Of 22 compounds synthesized, 19 compounds showed potent activity with low nanomolar IC50 values. In addition, the representative compounds 11o and 11p with a hydroxy group in the pyrrolidine ring showed moderate plasma clearance in rats (11o, 30 ml/min/kg and 11p, 21 ml/min/kg) and in dogs (11o, 12 ml/min/kg and 11p, 9 ml/min/kg).

Aza-bicyclic amino acid carboxamides as α4β1/α4β7 integrin receptor antagonists

A series of N-carboxy, N-alkyl, and N-carboxamido azabicyclo[2.2.2]octane carboxamides were prepared and assayed for inhibition of alpha4beta1-VCAM-1 and alpha4beta7-MAdCAM-1 interactions. Potency and alpha4beta1/alpha4beta7 selectivity were sensitive to the substituent R1-R3 in the structures 6, 7, and 8. Several compounds demonstrated low nanomolar balanced alpha4beta1/alpha4beta7 in vitro activity. Two compounds were selected for in vivo leukocytosis studies and demonstrated increases in circulating lymphocytes up to 250% over control.

Involvement of alpha4 integrins in maintenance of cardiac sympathetic axons

Sympathetic neurons extend and maintain axons that innervate the myocardium, and proper innervation is important for cardiac function. However, the molecular basis for axon outgrowth and maintenance is not well understood. We have shown previously that the integrin alpha4beta1 is expressed on developing axons, and the alpha4 function is important for the development of innervation in vivo [Wingerd, K.L., Goodman, N.L., Tresser, J.W., Smail, M.M., Leu, S.T., Rohan, S.J., Pring, J.L., Jackson, D.Y., and Clegg, D.O., 2002. Alpha 4 integrins and vascular cell adhesion molecule-1 play a role in sympathetic innervation of the heart. J. Neurosci. 22,10772-10780]. Here we examine the function of alpha4beta1 integrins in the maintenance of cardiac sympathetic innervation in vitro and in vivo, and investigate integrin expression and function after myocardial infarction and in hypertensive rats. On substrates of vascular cell adhesion molecule-1 (VCAM-1), alpha4beta1 was required for both initial outgrowth and maintenance of neurites in vitro. On fibronectin substrates, initial outgrowth requires only alpha4 integrins, but maintenance requires both alpha4 integrins and RGD-dependent integrins. In vivo, in adult Long Evans rats, inhibition of alpha4 integrins resulted in decreased maintenance of sympathetic fibers innervating the apex of the heart. However, alpha4 integrins were not detected on most sympathetic axons that sprout after myocardial infarction, and alpha4 function was not required for sprouting. Spontaneously hypertensive rats (SHR) have increased numbers of cardiac sympathetic fibers compared to the parental Wistar strain, but many of these lack alpha4 expression, and alpha4 function is not required for maintenance of these fibers in the heart. These results suggest that developing sympathetic axons and sprouting sympathetic axons use different mechanisms of outgrowth, and that maintenance of cardiac sympathetic innervation involves alpha4 integrins in some rat strains.

Influence of acid surrogates toward potency of VLA-4 antagonist

A series of VLA-4 antagonist were synthesized wherein carboxylic acid was replaced by various acid surrogates. The effect of these acid surrogates toward potency was evaluated in a binding assay. A number of acid surrogates were potent antagonist of VLA-4, albeit significantly less potent than the corresponding carboxylic acid. Heterocyclic acid surrogate, oxadiazolidinone 3, demonstrated an improved pharmacokinetic property when dosed intravenously.

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.

A novel model of allograft rejection: immune reconstitution of Rag-1 recipients with 2C transgenic T-cell receptor lymphocytes

The complexity of allorejection (cell activation, homing, and effector function) makes detailed studies difficult. We have developed a model of allograft rejection using purified monoclonal alloreactive effector cells. Immunodeficient C57Bl/6-Rag-1 (H-2(b)) recipients of Balb/c (H-2(d)) islet or skin grafts were reconstituted via adoptive transfer of splenocytes from 2C transgenic mice containing CD8+ cytotoxic effector cells directed against L(d). Recipients were assessed for engraftment, activation and homing of effector cells, and ability to reject grafts. Both unpurified 2C splenocytes and purified 2C/CD8+ cells durably reconstitute immunodeficient mice. Naive 2C effector cells reject skin grafts, but not islet allografts. However, when effector cells are primed prior to reconstitution, islet allografts are rejected. Using this model, blockade of adhesion molecules LFA-1 and alpha4-integrin delayed infiltration of islet allografts and prolonged allograft survival. This model of allorejection may be useful to study the activation and homing of allospecific cells in vivo.

Identified a morpholinyl-4-piperidinylacetic acid derivative as a potent oral active VLA-4 antagonist

An investigation into the structure-activity relationship of a lead compound, prolyl-5-aminopentanoic acid 4, led to the identification of a novel series of 4-piperidinylacetic acid, 1-piperazinylacetic acid, and 4-aminobenzoic acid derivatives as potent VLA-4 antagonists with low nanomolar IC(50) values. A representative compound morpholinyl-4-piperidinylacetic acid derivative (13d: IC(50)=4.4 nM) showed efficacy in the Ascaris-antigen sensitized murine airway inflammation model by oral administration.

Integrin α4β1 function is required for cell survival in developing retina

In the retina, integrins in the beta1 family have been shown to be important in many phases of neuronal development, particularly neuroblast migration and axon outgrowth. However, the functions of specific integrin heterodimers are not well defined. In this study, we investigated the functions of beta1 integrins in developing chicken retina by expression of a dominant-negative beta1A construct using a replication-competent retrovirus. Inhibition of integrins using this approach resulted in alteration of cell morphology and increased apoptosis, but did not preclude migration and axon elongation. In an attempt to identify which specific beta1 heterodimer was important, expression and function of the alpha4beta1 heterodimer were also investigated. At early developmental stages, alpha4 protein and mRNA were detected in undifferentiated neuroblasts throughout the retina. At later stages, expression was confined to retinal ganglion cells (RGCs) and amacrine cells. A small molecule antagonist of alpha4 integrins was shown to inhibit neurite outgrowth on recombinant soluble vascular cell adhesion molecule-1 (VCAM-1), a known ligand of alpha4beta1. Introduction of alpha4 antagonist in vivo gave rise to increased apoptosis and led to a thinning of the retina and reduced numbers of retinal ganglion cells (RGCs). We conclude that the integrin alpha4beta1 is important for survival of developing retinal neurons, including RGCs.

Targeting leukocyte integrins in human diseases

As our understanding of integrins as multifunctional adhesion and signaling molecules has grown, so has their recognition as potential therapeutic targets in human diseases. Leukocyte integrins are of particular interest in this regard, as they are key molecules in immune-mediated and inflammatory processes and are thus critically involved in diverse clinical disorders, ranging from asthma to atherosclerosis. Antagonists that interfere with integrin-dependent leukocyte trafficking and/or post-trafficking events have shown efficacy in multiple preclinical models, but these have not always predicted success in subsequent clinical trials (e.g., ischemia-reperfusion disorders and transplantation). However, recent successes of integrin antagonists in psoriasis, inflammatory bowel disease, and multiple sclerosis demonstrate the tremendous potential of antiadhesion therapy directed at leukocyte integrins. This article will review the role of the leukocyte integrins in the inflammatory process, approaches to targeting leukocyte integrins and their ligands, and the results of completed clinical trials.

alpha4beta1-integrin blockade and cyclosporine decreases the prevalence and severity of transplant vasculopathy in a rat transplant model

BACKGROUND

Transplant vasculopathy leads to neointimal proliferation of allograft arteries, and alpha4beta1-integrin (very late antigen-4 [VLA-4]) seems to play an important role in the pathogenesis. This study evaluates the effect of a new, synthetic, VLA-4 blocker (S3429) on transplant vasculopathy in a rat cardiac transplant model.

METHODS

After transplantation (Lewis to Fisher), rats were divided randomly into 6 therapy groups: Group 1, n = 14, saline solution (vehicle); Group 2, n = 14, 3 mg/kg/day cyclosporine; Group 3, n = 21, 10 mg/kg/day S3429 + 3 mg/kg/day cyclosporine; Group 4, n = 21, 5 mg/kg/day S3429 + 3 mg/kg/day cyclosporine; Group 5: n = 21, 10 mg/kg/day S3429; Group 6, n = 21, 5 mg/kg/day S3429. Cyclosporine was given continuously until rats were killed. S3429 was either given for the entire study time or was discontinued after 20 days and animals were killed at Day 80. Twenty-eighty days after grafting, we assessed vasculopathy prevalence and mean vessel occlusion in coronary arteries.

RESULTS

Cyclosporine decreased the prevalence of vasculopathy and mean vessel occlusion compared with controls. We observed a further decrease in prevalence and mean vessel occlusion with 80 days of therapy with S3429 and cyclosporine. After discontinuing S3429 therapy at Day 20, prevalence and mean vessel occlusion increased to values seen in cyclosporine-treated animals at Day 80. S3429 alone decreased mean vessel occlusion only within the first 20 days compared with controls but had no effect on the prevalence of vasculopathy.

CONCLUSION

Because of the further decrease with S3429 therapy and the dramatic increase after discontinuation of S3429 therapy, we conclude that blocking VLA-4 receptors may prevent the development of transplant vasculopathy.

Blocking endothelial adhesion molecules: a potential therapeutic strategy to combat atherogenesis

PURPOSE OF REVIEW

This review provides a concise update of the involvement of endothelial adhesion molecules in atherogenesis, an overview of current advances in the development of adhesion molecule blocking agents, as well as an insight into the potential of these molecules in cardiovascular therapy.

RECENT FINDINGS

As endothelial adhesion molecules are deemed to play an important role in the development and progression of atherosclerotic lesions, they are interesting targets for therapeutic intervention in this process. In particular, P-selectin and vascular cell adhesion molecule 1 are widely considered to hold promise in this regard. Current research efforts centre on the design of agents that directly block the interaction of the receptor with its ligand (e.g. soluble P-selectin glycoprotein ligand 1, blocking antibodies, EWVD-based peptides) or that interfere with their synthesis (e.g. antisense oligonucleotides) or their regulatory control by nuclear factor kappa B or peroxisome proliferator-activated receptor gamma. Furthermore, adhesion molecules have been exploited as a target for the specific delivery of drug carriers (e.g. biodegradable particles with entrapped dexamethasone) or therapeutic compounds (e.g. dexamethasone) to the plaque. All approaches have been shown to be effective in blocking adhesion molecule function in in-vitro studies and in-vivo models for inflammation or atherosclerosis.

SUMMARY

Although the field has achieved considerable progress in recent years, leading to the development of a number of interesting leads, final proof of their efficacy in cardiovascular therapy is eagerly awaited.

Aza-bicyclic amino acid sulfonamides as alpha(4)beta(1)/alpha(4)beta(7) integrin antagonists

The design, synthesis, and biological activity of novel alpha(4)beta(1) and alpha(4)beta(7) integrin antagonists, containing a bridged azabicyclic nucleus, are reported. Conformational analysis of targets containing an azabicyclo[2.2.2]octane carboxylic acid and known integrin antagonists indicated that this azabicycle would be a suitable molecular scaffold. Variation of substituents on the pendant arylsulfonamide and phenylalanine groups resulted in potent alpha(4)beta(1)-selective and dual alpha(4)beta(1)/alpha(4)beta(7) antagonists. Potent compounds 11i, 11h, and 14 were effective in the antigen-sensitized sheep model of asthma.

Blood transcriptional signatures of multiple sclerosis: unique gene expression of disease activity

Multiple sclerosis (MS) is a central nervous system disease with an unpredictable course and outcome. Peripheral blood mononuclear cells (PBMCs) are involved in the disease pathogenesis and induce active demyelination. Using oligonucleotide microarrays, we identified a statistically significant transcriptional signature of 1,109 genes in PBMCs from 26 MS patients, irrespective of disease activation state or immunomodulatory treatment. This signature contains genes that implicate underlying processes involved in MS pathogenesis including T-cell activation and expansion, inflammation, and apoptosis. Another transcriptional signature of 721 genes involved in cellular recruitment, epitope spreading, and escape from regulatory immune surveillance identified MS patients in acute relapse compared with remission. Our results offer new opportunity for understanding the mechanisms involved in MS and indicate that gene expression patterns in PBMCs contain information about a remote-target disease process that may be useful for diagnosis and future tailoring of therapeutic strategies for MS.

Leukocyte and endothelial cell adhesion molecules as targets for therapeutic interventions in inflammatory disease

Inflammation is a fundamental response to tissue injury and invasion of pathogens, but it is detrimental in clinically important inflammatory disorders. Leukocytes are key players in the inflammatory response because of their antimicrobial, secretory and phagocytic activities. They are recruited to the inflamed tissue by sequential adhesive interactions between leukocytes and the endothelium that are mediated by cell-adhesion molecules (CAMs) on the surface of the interacting cells. The effects of many anti-inflammatory drugs can be ascribed, in part, to inhibition of the expression of CAMs. However, in the search for more selective and potent drugs for clinically important diseases such as multiple sclerosis, asthma, rheumatoid arthritis, inflammatory bowel disease, allergies and atherosclerosis, direct inhibition of the function of CAMs has attracted increasing interest. In recent years, the development of synthetic antagonists has provided better opportunities for drug targeting. Future advances in this field hold new prospects for therapeutic intervention in human inflammatory disorders.

Conformationally tailored N-[(2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl)carbonyl]proline templates as molecular tools for the design of peptidomimetics. Design and synthesis of fibrinogen receptor antagonists

The proline peptide bond was shown by 2D proton NMR studies to exist exclusively in the trans conformation in benzyl (2S)-1-[[(2S)-2-methyl-6-nitro-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl]carbonyl]-2-pyrrolidinecarboxylate [(S,S)-11], benzyl (2S)-1-[[(2S)-2-methyl-7-nitro-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl]carbonyl]-2-pyrrolidinecarboxylate [(S,S)-9], and in the corresponding 6-amino and 7-amino carboxylic acids (S,S)-3 and (S,S)-4. On the other hand, the diastereomers (R,S)-11 and (R,S)-9 containing an (R)[2-methyl-6/7-nitro-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl]carbonyl moiety, and the diastereoisomers (R,S)-3 and (R,S)-4 incorporating an (R)[6/7-amino-2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl]carbonyl moiety were found to exist as equilibria of trans(63-83%) and cis(17-37%) isomers. These conformationally defined templates were applied in the construction of RGD mimetics possessing antagonistic activity at the platelet fibrinogen receptor.

Small molecule integrin antagonists that bind to the beta2 subunit I-like domain and activate signals in one direction and block them in the other

Leukocyte integrins contain an inserted (I) domain in their alpha subunits and an I-like domain in their beta(2) subunit, which directly bind ligand and regulate ligand binding, respectively. We describe a novel mechanistic class of integrin inhibitors that bind to the metal ion-dependent adhesion site of the beta(2) I-like domain and prevent its interaction with and activation of the alpha(L) I domain. The inhibitors do not bind to the alpha(L) I domain but stabilize alpha/beta subunit association and can show selectivity for alpha(L)beta(2) compared to alpha(M)beta(2). The inhibitors reveal a crucial intersection for relaying conformational signals within integrin extracellular domains. While blocking signals in one direction to the I domain, the antagonists induce the active conformation of the I-like domain and stalk domains, and thus transmit conformational signals in the other direction toward the transmembrane domains.

Therapeutic antagonists and conformational regulation of integrin function

Integrins are a structurally elaborate family of adhesion molecules that transmit signals bi-directionally across the plasma membrane by undergoing large-scale structural rearrangements. By regulating cell-cell and cell-matrix contacts, integrins participate in a wide range of biological processes, including development, tissue repair, angiogenesis, inflammation and haemostasis. From a therapeutic standpoint, integrins are probably the most important class of cell-adhesion receptors. Recent progress in the development of integrin antagonists has resulted in their clinical application and has shed new light on integrin biology. On the basis of their mechanism of action, small-molecule integrin antagonists fall into three different classes. Each of these classes affect the equilibria that relate integrin conformational states, but in different ways.

A small molecule alpha4beta1/alpha4beta7 antagonist differentiates between the low-affinity states of alpha4beta1 and alpha4beta7: characterization of divalent cation dependence

An alpha4beta1/alpha4beta7 dual antagonist, 35S-compound 1, was used as a model ligand to study the effect of divalent cations on the activation state and ligand binding properties of alpha4 integrins. In the presence of 1 mM each Ca2+/Mg2+, 35S-compound 1 bound to several cell lines expressing both alpha4beta1 and alpha4beta7, but 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), a specific alpha4beta1 antagonist, completely inhibited 35S-compound 1 binding, suggesting that alpha4beta1 was responsible for the observed binding. 35S-Compound 1 bound RPMI-8866 cells expressing predominantly alpha4beta7 with a KD of 1.9 nM in the presence of 1 mM Mn2+, and binding was inhibited only 29% by BIO7662, suggesting that the probe is a potent antagonist of activated alpha4beta7. With Ca2+/Mg2+, 35S-compound 1 bound Jurkat cells expressing primarily alpha4beta1 with a KD of 18 nM. In contrast, the binding of 35S-compound 1 to Mn2+-activated Jurkat cells occurred slowly, reaching equilibrium by 60 min, and failed to dissociate within another 60 min. The ability of four alpha4beta1/alpha4beta7 antagonists to block binding of activated alpha4beta1 or alpha4beta7 to vascular cell adhesion molecule-1 or mucosal addressin cell adhesion molecule-1, respectively, or to 35S-compound 1 was measured, and a similar rank order of potency was observed for native ligand and probe. Inhibition of 35S-compound 1 binding to alpha4beta1 in Ca2+/Mg2+ was used to identify nonselective antagonists among these four. These studies demonstrate that alpha4beta1 and alpha4beta7 have distinct binding properties for the same ligand, and binding parameters are dependent on the state of integrin activation in response to different divalent cations.

Essential role of VLA-4/VCAM-1 pathway in the establishment of CD8+ T-cell-mediated Trypanosoma cruzi-elicited meningoencephalitis

Central nervous system (CNS) damage can occur during Trypanosoma cruzi infection, especially in immunosuppressed patients. The enhanced susceptibility of C3H/He mice to CD8-mediated acute meningoencephalitis is associated with higher up-regulation of vascular cell adhesion molecule-1 (VCAM-1) on CNS vascular endothelia than in the less susceptible C57BL/6. Further, in vitro adhesion of activated peripheral blood cells to CNS blood vessels was abrogated by anti-VLA-4 antibodies that also inhibited cell migration into the CNS of T. cruzi-infected mice. Lastly, the reactivation of meningoencephalitis in immunosuppressed chronically infected mice was associated with VCAM-1 up-regulation. Therefore, we hypothesize that VLA-4/VCAM-1 pathway plays a pivotal role in the establishment of T. cruzi-elicited encephalitis.

Discovery of small molecule leads in a biotechnology datastream

A case study of the discovery of small molecule antagonists to the integrins GPIIbIIIa (alphaII(B)beta3), alphavbeta3, LFA-1 (alphaLbeta2), alpha4beta1 and alpha4beta7 is presented from the perspective of a biotechnology research organization. A strategy incorporating protein mutagenesis and structural studies to develop a structure-activity relationship (SAR) that described the 'epitope' of the integrin ligand was crucial to the identification of peptide analogs of these proteins, and subsequently, through parallel trends in SAR, to the identification of small molecule mimetics of these peptides, which are active analogs of the protein ligands themselves.

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.

Dehydrophenylalanine derivatives as VLA-4 integrin antagonists

We describe a series of dehydrophenylalanine derivatives where the Z isomers are potent VLA-4 antagonists but are subject to rapid biliary clearance and the E isomers have poor activity but have a slower rate of clearance. These configurationally constrained molecules have led to the design of a novel class of benzodiazepine VLA-4 antagonists.

Immunomodulation in multiple sclerosis: from immunosuppression to neuroprotection

Multiple sclerosis (MS) is the most common disabling neurological disease of young adulthood. Following advances in the understanding of the immunological mechanisms that underlie the pathogenesis of MS, a growing arsenal of immunomodulatory agents is available. Two classes of immunomodulators are approved for long-term treatment of MS, the efficacy of several promising new concepts is being tested in clinical trials and classical immunosuppressive agents used in MS treatment have been shown to exert specific, immunomodulatory effects. Furthermore, two recent observations have changed our basic understanding of the pathogenesis of MS. First, immune cells in MS lesions have neuroprotective activity, which indicates a beneficial role of neuroinflammation. Second, there is evidence that axonal loss, rather than demyelination, underlies the progression of MS and, hence, constitutes a therapeutic target.

Alpha 4 integrins and vascular cell adhesion molecule-1 play a role in sympathetic innervation of the heart

Sympathetic neurons innervate the heart early in postnatal development, an event that is crucial for proper modulation of blood pressure and cardiac function. However, the axon guidance cues that direct sympathetic neurons to the heart, and the neuronal receptors that recognize those cues, are poorly understood. Here we present evidence that interactions between the alpha4beta1 integrin on sympathetic neurons and vascular cell adhesion molecule-1 (VCAM-1) in the heart plays a role in cardiac innervation. The alpha4 subunit was detected on postnatal rat superior cervical ganglion (SCG) neurons in culture and in cryosections of SCG and heart. VCAM-1 immunoreactivity was detected on cardiac myocytes that associate with invading sympathetic neurons. Purified recombinant soluble VCAM-1 (rsVCAM-1) stimulated SCG neurite outgrowth at levels comparable with laminin 2/4 and fibronectin (Fn), and outgrowth on rs-VCAM-1 and Fn was blocked by antibodies specific for the alpha4 and beta1 integrin subunits. Intrathoracic injection of function-blocking antibodies to alpha4 and VCAM-1, as well as a small molecule inhibitor of alpha4 integrins, significantly reduced sympathetic innervation of the heart. These results indicate that the interaction between alpha4 integrin and VCAM-1 is important for sympathetic innervation of the heart.

Integrins: bidirectional, allosteric signaling machines

In their roles as major adhesion receptors, integrins signal across the plasma membrane in both directions. Recent structural and cell biological data suggest models for how integrins transmit signals between their extracellular ligand binding adhesion sites and their cytoplasmic domains, which link to the cytoskeleton and to signal transduction pathways. Long-range conformational changes couple these functions via allosteric equilibria.

Solid-phase synthesis of dual α4β1/α4β7 integrin antagonists: two scaffolds with overlapping pharmacophores

Two structural classes of dual alpha4beta1/alpha4beta7 integrin antagonists were investigated via solid-phase parallel synthesis. Using an acylated amino acid backbone, lead compounds containing biphenylalanine or tyrosine carbamate scaffolds were optimized for inhibition of alpha4beta1/VCAM and alpha4beta7/MAdCAM. A comparison of the structure-activity relationships in the inhibition of the alpha4beta7/MAdCAM interaction for substituted amines employed in both scaffolds suggests a similar binding mode for the compounds.