Cyclic thioether peptide mimetics as VCAM-VLA-4 antagonists

Selective substitution of a sulfur atom by carbon in a highly potent 13-membered cyclic disulfide was accomplished by intramolecular displacement of a bromide. The potency of the resulting thioethers in the VCAM/VLA-4 assay was dependent on ring size and the position of the sulfur atom.

The chemokine SDF-1 activates the integrins LFA-1, VLA-4, and VLA-5 on immature human CD34(+) cells: role in transendothelial/stromal migration and engraftment of NOD/SCID mice

Hematopoietic stem cell homing and engraftment require several adhesion interactions, which are not fully understood. Engraftment of nonobese/severe combined immunodeficiency (NOD/SCID) mice by human stem cells is dependent on the major integrins very late activation antigen-4 (VLA-4); VLA-5; and to a lesser degree, lymphocyte function associated antigen-1 (LFA-1). Treatment of human CD34(+) cells with antibodies to either VLA-4 or VLA-5 prevented engraftment, and treatment with anti-LFA-1 antibodies significantly reduced the levels of engraftment. Activation of CD34(+) cells, which bear the chemokine receptor CXCR4, with stromal derived factor 1 (SDF-1) led to firm adhesion and transendothelial migration, which was dependent on LFA-1/ICAM-1 (intracellular adhesion molecule-1) and VLA-4/VCAM-1 (vascular adhesion molecule-1). Furthermore, SDF-1-induced polarization and extravasation of CD34(+)/CXCR4(+) cells through the extracellular matrix underlining the endothelium was dependent on both VLA-4 and VLA-5. Our results demonstrate that repopulating human stem cells functionally express LFA-1, VLA-4, and VLA-5. Furthermore, this study implies a novel approach to further advance clinical transplantation.

Discovery and evaluation of potent, tyrosine-based alpha4beta1 integrin antagonists

Using disulphide cysteine-based inhibitors as lead structures, this communication describes our strategy for identifying more stable, potent antagonists of the alpha4beta1 integrin. These studies ultimately discovered potent, low molecular weight inhibitors based on D-thioproline-L-tyrosine.

Discovery and evaluation of potent, cysteine-based alpha4beta1 integrin antagonists

Acyclic, disulphide derivatives of cysteine have been identified as moderately potent antagonists of alpha4beta1-mediated leukocyte cell adhesion to VCAM. This communication describes how they were discovered from a simple L-cystine derivative and using the structure-activity data of C*DThioPC* related cyclic peptides.

N-benzylpyroglutamyl-L-phenylalanine derivatives as VCAM/VLA-4 antagonists

A series of N-(N-benzylpyroglutamyl)-4-substituted-L-phenylalanine derivatives was prepared as VLA-4/VCAM antagonists. Analogues substituted by electron deficient benzoylamino groups bearing bulky ortho substituents had low-nM potency in an ELISA assay and low-microM activity in a cell based assay.

N-acyl phenylalanine analogues as potent small molecule VLA-4 antagonists

We have identified a series of low molecular weight (Mr < 500) N-acylphenylalanines that are effective inhibitors of the VCAM-VLA-4 interaction. Investigation of the SAR of the N-acyl moiety led to the identification of N-benzylpyroglutamyl derivatives as being particularly potent.

Regulation of megakaryocytopoiesis in an in vitro stroma model: preferential adhesion of megakaryocytic progenitors and subsequent inhibition of maturation

OBJECTIVE

Studies of megakaryocytic progenitor cell interactions have focused on single receptor-ligand interactions using isolated components of the extracellular matrix. To approach a physiologic condition, we studied megakaryocytic development of human progenitor cells cultured on two stromal cell lines and on human bone marrow stroma.

MATERIALS AND METHODS

Human CD34(+) cells were cocultured with stromal layers in the presence of thrombopoietin. Megakaryocytes were quantified by monoclonal antibodies against glycoprotein (GP) IIb/IIIa (CD41) and GPIX (CD42a). Megakaryocytic clonogenic capacity (burst-forming unit-megakaryocyte and colony-forming unit-megakaryocyte) was determined using fibrin clot assays.

RESULTS

After 6 days, a higher percentage of megakaryocytes and more megakaryocytic colonies were recovered from the adherent cell fraction compared to the nonadherent cell fraction. In contrast, significantly more granulocytic and erythroid colonies were recovered from the nonadherent cell fraction. Repeated replating of nonadherent cells onto fresh stroma showed a decline in megakaryocytic recovery of the remaining adherent cells, pointing toward selective adhesion of megakaryocytic progenitors. This was supported further by the finding that burst-forming unit and colony-forming unit megakaryocytes were preferentially recovered from the adherent cell fraction at 24 hours. No effect of blocking the beta(1) integrins VLA-4 and VLA-5 on human progenitor cells was observed. A higher expression of CD42a antigen and a higher percentage of morphologically recognizable polyploid megakaryocytes were found when cells were grown in noncontact cultures compared to when grown adhered to stroma.

CONCLUSION

In contrast to granulocytic and erythroid progenitors, both very early and more mature megakaryocytic progenitors are preferentially located in the adherent fraction in an in vitro stromal model, leading to inhibition of maturation of megakaryocytes. This suggests that the presence of stroma components in ex vivo expansion cultures, aimed at preservation and expansion of megakaryocytic progenitors, might be a prerequisite.

Urokinase-type plasminogen activator inhibits alpha 4 beta 1 integrin-mediated T lymphocyte adhesion to fibronectin independently of its catalytic activity

The urokinase-type plasminogen activator (u-PA)/plasmin system plays an important role in promoting cell migration and invasion, an effect which is largely ascribed to the proteolytic activity of these enzymes. We investigated whether u-PA modulates integrin-dependent T lymphocyte migration and adhesion on fibronectin independently of its plasminogen activator function. Here we report that u-PA reduced the spontaneous and phorbol 12-myristate 13-acetate-induced migration of peripheral blood T lymphocytes on fibronectin by 20-50%, decreased the T lymphocyte and alpha4beta1(+)/alpha5beta1(+) K562 cell adhesion on fibronectin by 30-40%, and completely suppressed integrin alpha4beta1-dependent T lymphocyte and alpha4beta1(+)/alpha5beta1(+) K562 cell adhesion to the LDV-containing 40-kDa fibronectin fragment. The u-PA receptor was not essential for this effect. In contrast, adhesion of alpha4beta1(-)/alpha5beta1(+) K562 cells to an RGD-containing fibronectin fragment was unaffected. A recombinant protein comprising the N-terminal fragment of u-PA, but lacking its proteolytic domain, had the same inhibitory effect. Decreased adhesion was neither associated with a diminished cell surface expression of alpha4beta1 nor with a suppression of alpha4beta1 ligand-binding function. Our results demonstrate that u-PA inhibits alpha4beta1- but not alpha5beta1-mediated lymphocyte/leukocyte adhesion to fibronectin independently of its proteolytic activity. This finding provides additional evidence that matrix proteinases may participate in cell adhesion and migration control independently of their matrix-degrading activity.

Adhesion of hematopoietic progenitor cells to human bone marrow or umbilical vein derived endothelial cell lines: a comparison

Homing of hematopoietic progenitor cells (HPC) to the bone marrow may be mediated by adhesion molecules specifically expressed on human bone marrow endothelial cells (HBMEC). This hypothesis suggests that HPC would preferentially bind to HBMEC compared to endothelial cells from other origins. In this study, HPC were allowed to adhere either to HBMEC cell lines or to human umbilical vein endothelial cells (HUVEC) in two different experimental set-ups. First, adherence was measured using a flow cytometric assay with three different colors identifying each cell population (HPC, HBMEC, HUVEC). HPC could adhere (in a competitive way) to the two endothelial cell lines under stirring conditions, which simulated adhesion under shear stress, as present in blood vessels. Because this assay requires relatively firm adhesion and the endothelial cells don't form a monolayer, we studied the same interactions under less stringent conditions. HPC were allowed to adhere to endothelial monolayers under gently rocking conditions. Differential adhesion of HPC to a set of endothelial cell lines did not correlate with the origin of the endothelial cells. Adhesion of HPC to both types of endothelial cells was inhibited in the presence of various combinations of monoclonal antibodies against the adhesion molecules VLA-4, CD18, and/or E-selectin. No indications were obtained for qualitative differences in the role of these molecules in adhesion of HPC to either HBMEC or HUVEC cell lines. In conclusion, no preferential adhesion of HPC to HBMEC compared to HUVEC cells was observed. This may be due to a lack of origin-specific differences between endothelial cells, implying that the specificity of homing is not regulated at the entrance of the bone marrow. Otherwise, the origin-specific differences between endothelial cells of different origins may be microenvironment-induced, rather then intrinsic, implying that care should be exercised with the use of endothelial cell lines in studies investigating the specificity of homing of HPC.

Multiple activation states of integrin alpha4beta1 detected through their different affinities for a small molecule ligand

We have used the highly specific alpha4beta1 inhibitor 4-((N'-2-methylphenyl)ureido)-phenylacetyl-leucine-aspartic acid-valine-proline (BIO1211) as a model LDV-containing ligand to study alpha4beta1 integrin-ligand interactions on Jurkat cells under diverse conditions that affect the activation state of alpha4beta1. Observed KD values for BIO1211 binding ranged from a value of 20-40 nM in the non-activated state of the integrin that exists in 1 mM Mg2+, 1 mM Ca2+ to 100 pM in the activated state seen in 2 mM Mn2+ to 18 pM when binding was measured after co-activation by 2 mM Mn2+ plus 10 microgram/ml of the integrin-activating monoclonal antibody TS2/16. The large range in KD values was governed almost exclusively by differences in the dissociation rates of the integrin-BIO1211 complex, which ranged from 0.17 x 10(-4) s-1 to >140 x 10(-4) s-1. Association rate constants varied only slightly under the same conditions, all falling in the narrow range from 0.9 to 2.7 x 10(6) M-1 s-1. The further increase in affinity observed upon co-activation by divalent cations and TS2/16 compared with that observed at saturating concentrations of metal ions or TS2/16 alone indicates that the mechanism by which these factors bring about activation are distinct and identified a previously unrecognized high affinity state on alpha4beta1 that had not been detected by conventional assay methods. Similar changes in affinity were observed when the binding properties of vascular cell adhesion molecule-1 and CS1 to alpha4beta1 were studied, indicating that the different affinity states detected with BIO1211 are an inherent property of the integrin.

Antigen-induced hyperreactivity to histamine: role of the vagus nerves and eosinophils

M2 muscarinic receptors limit acetylcholine release from the pulmonary parasympathetic nerves. M2 receptors are dysfunctional in antigen-challenged guinea pigs, causing increased vagally mediated bronchoconstriction. Dysfunction of these M2 receptors is due to eosinophil major basic protein, which is an antagonist for M2 receptors. Histamine-induced bronchoconstriction is composed of a vagal reflex in addition to its direct effect on airway smooth muscle. Because hyperreactivity to histamine is seen in antigen-challenged animals, we hypothesized that hyperreactivity to histamine may be due to increased vagally mediated bronchoconstriction caused by dysfunction of M2 receptors. In anesthetized, antigen-challenged guinea pigs, histamine-induced bronchoconstriction was greater than that in control guinea pigs. After vagotomy or atropine treatment, the response to histamine in antigen-challenged animals was the same as that in control animals. In antigen-challenged animals, blockade of eosinophil influx into the airways or neutralization of eosinophil major basic protein prevented the development of hyperreactivity to histamine. Thus hyperreactivity to histamine in antigen-challenged guinea pigs is vagally mediated and dependent on eosinophil major basic protein.

Anti-inflammatory activity of c(ILDV-NH(CH2)5CO), a novel, selective, cyclic peptide inhibitor of VLA-4-mediated cell adhesion

1. Small, N- to C-terminal cyclized peptides containing the leucyl-aspartyl-valine (LDV) motif from fibronectin connecting segment-1 (CS-1) have been investigated for their effects on the adhesion of human T-lymphoblastic leukaemia cells (MOLT-4) to human plasma fibronectin in vitro mediated by the integrin Very Late Antigen (VLA)-4 (alpha4beta1, CD49d/CD29). 2. Cyclo(-isoleucyl-leucyl-aspartyl-valyl-aminohexanoyl-) (c(ILDV-NH(CH2)5CO)) was approximately 5 fold more potent (IC50 3.6+/-0.44 microM) than the 25-amino acid linear CS-1 peptide. Cyclic peptides containing two more or one less methylene groups had similar potency to c(ILDV-NH(CH2)5CO) while a compound containing three less methylene groups, c(ILDV-NH(CH2)2CO), was inactive at 100 microM. 3. c(ILDV-NH(CH2)5CO) had little effect on cell adhesion mediated by two other integrins, VLA-5 (alpha5,beta1, CD49e/CD29) (K562 cell adhesion to fibronectin) or Leukocyte Function Associated molecule-1 (LFA-1, alphabeta2, CD11a/CD18) (U937 cell adhesion to Chinese hamster ovary cells transfected with intercellular adhesion molecule-1) at concentrations up to 300 microM. 4. c(ILDV-NH(CH2)5CO) inhibited ovalbumin delayed-type hypersensitivity or oxazolone contact hypersensitivity in Balb/c mice when dosed continuously from subcutaneous osmotic mini-pumps (0.1-10 mg kg(-1) day(-1)). Maximum inhibition (approximately 40%) was similar to that caused by the monoclonal antibody PS/2 (7.5 mg kg(-1) i.v.) directed against the alpha4 integrin subunit. 5. c(ILDV-NH(CH2)5CO) also inhibited oxazolone contact hypersensitivity when dosed intravenously 20 h after oxazolone challenge (1-10 mg kg(-1)). Ear swelling was reduced at 3 h and 4 h but not at 1 h and 2 h post-dose (10 mg kg(-1)). 6. Small molecule VLA-4 inhibitors derived from c(ILDV-NH(CH2)5CO) may be useful as anti-inflammatory agents.

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.

1,25-Dihydroxyvitamin D3 suppresses the expression of the VCAM-1 receptor, VLA-4 in human leukemic HL-60 cells

Very late antigen-4 (VLA-4) is the complex with alpha4 and beta1 integrins, which is the receptors to fibronectin and VCAM-1. We evaluate the effect of 1,25(OH)2D3 on the expression of VLA-4 in human leukemic HL-60, U937 cells and human melanoma A375 cells. Flow cytometric analysis demonstrate that the expression of alpha4 integrin is negatively regulated in the cell lines we studied. The expression of beta1 integrin is also decreased in HL-60 and U937 cells. The mRNA expression of alpha4 integrin is significantly decreased by the treatment with 1,25(OH)2D3, whereas 1,25(OH)2D3 does not alter the expression of beta1 mRNA. The adhesion assay demonstrate that the number of adherent cells treated with 1, 25(OH)2D3 is significantly lower than that untreated on VCAM-1-coated wells. Because VCAM-1 is highly expressed in the endothelial cells, it is possible that 1,25(OH)2D3 prevents the attachment of the cells from the endothelial cells in vivo.

Selective requirements for leukocyte adhesion molecules in models of acute and chronic cutaneous inflammation: participation of E- and P- but not L-selectin

Adhesion molecules borne by both endothelial cells and circulating leukocytes are in large measure responsible for guiding the process of extravasation. The selectin family has been primarily associated with the early stages of adhesion involving initial contact and rolling. A significant body of evidence has accumulated indicating a fundamental role for the endothelial members of this family, E- and P-selectin, in a variety of inflammatory states and models. Although originally identified as the lymph node-specific lymphocyte homing receptor, L-selectin has also been suggested to play an important role in leukocyte recruitment to sites of inflammation. We have recently demonstrated, using L-selectin-deficient mice, that defects in contact hypersensitivity (CHS) responses are in essence due to the inability of T cells to home to and be sensitized within peripheral lymph nodes, whereas nonspecific effector cells are fully capable of entry into sites of cutaneous inflammation (Catalina et al, J Exp Med 184:2341, 1996). In the present study, we perform an analysis of adhesion molecule usage in two models of skin inflammation and show in both L-selectin-deficient as well as wild-type mice that a combination of P- and E-selectin is crucial for the development of both acute (croton oil) and chronic (contact hypersensitivity) inflammation at sites of the skin, whereas L-selectin does not appear to play a significant role. Moreover, alpha4 integrins are shown to be integral to a CHS but not an acute irritant response, whereas CD44 does not significantly contribute to either. These results provide a systematic examination in one study of major adhesion molecules that are critical in acute and chronic skin inflammation. They reinforce the essential role of the collaboration of E- and P-selectin in both specific and nonspecific skin inflammatory responses and the importance of alpha4 in the specific response only. In addition, they substantiate only a limited role, if any, for L-selectin in these cutaneous effector mechanisms and demonstrate the essential equivalence in this analysis of L-selectin-deficient mice compared with normal mice treated with blocking antibodies.

Blood monocyte migration to acute lung inflammation involves both CD11/CD18 and very late activation antigen-4-dependent and independent pathways

In acute lung inflammation, blood neutrophils and monocytes migrate into the lung parenchyma and bronchoalveolar space. The infiltration of the inflamed lung by monocytes is poorly understood because of difficulties in quantifying these cells in the presence of resident macrophages. Radiolabeled monocytes were used to study monocyte migration into the inflamed rat lung. Monocytes and neutrophils were purified from blood, labeled with 51Cr and (111)In, respectively, and injected i.v. into rats given an intratracheal injection of LPS. The accumulation of 51Cr-labeled monocytes increased > 10-fold in the lung parenchyma and 170-fold in the bronchoalveolar lavage (BAL) 18 h after LPS. (111)In-labeled neutrophils increased > 30-fold in the lung tissue and 500-fold in the BAL. Treatment of rats with a blocking anti-CD18 mAb inhibited monocyte accumulation in the lung and BAL by about 30%, whereas blocking very late activation Ag-4 (VLA-4) had no effect. Combined blockade of VLA-4 and CD18 inhibited approximately 30% of the migration to the lung parenchyma, but decreased the BAL by 80%. Monocyte migration to cutaneous inflammation was completely abolished by the combined mAb treatment. Neutrophil accumulation in the lung and BAL was not decreased by blocking either CD18 or VLA-4 and was only partially reduced by blocking CD18 plus VLA-4. Thus, monocyte migration to the LPS inflamed lung is substantially CD11/CD18 and VLA-4 independent, but accumulation in BAL is mediated by CD18 and VLA-4. Monocytes as well as neutrophils may use a previously unrecognized endothelial adhesion and migration pathway in the lung.

Alpha4beta1 and alpha5beta1 control cell migration on fibronectin by differentially regulating cell speed and motile cell phenotype

Computer-aided time lapse fluorescence videomicroscopy was used to study single cell migration behavior of human aortic endothelial cells on fibronectin coated substrates of varying protein surface density. The role of receptors alpha5beta1, alpha(v)beta3, and alpha4beta1 in mediating cell adhesion and migration on fibronectin was characterized using integrin specific monoclonal antibodies. Matrix density had a direct effect on controlling the proportion of migrating cells and the directional persistence of cell movement (p<0.01). While there was relatively little influence of fibronectin surface density on absolute migration speed, the ability of endothelial cells to disperse over a surface, as measured by the dispersion coefficient, was biphasic with respect to the surface density of this matrix protein (p<0.005). Both cell speed and the proportion of migrating cells was controlled by alpha4beta1 (p<0.01). However, alpha5beta1 selectively regulated the transformation of stationary cells to those exhibiting motile behavior (p<0.05). Migratory responses on fibronectin were not influenced by blockade of the alpha(v)beta3 receptor. It is noteworthy that cell surface adhesive receptors which control commitment to a motile phenotype are not necessarily the same as those that control migration speed.

Regulation of macrophage phagocytosis of apoptotic neutrophils by adhesion to fibronectin

The potential for leukocyte-mediated host tissue damage during resolution of inflammatory responses is influenced by the rate at which extravasated apoptotic leukocytes are cleared from inflammatory sites. Regulation of macrophage capacity for clearance of apoptotic granulocytes is likely to be an important factor determining whether inflammation ultimately resolves or progresses to a chronic state. In this study we have investigated the molecular basis for rapid augmentation of macrophage phagocytosis of apoptotic neutrophils, which was observed following macrophage adhesion to fibronectin. We used a combination of monoclonal antibodies, blocking peptides, and recombinant fibronectin fragments to investigate the role of beta1 integrins in mediating the fibronectin effects. Blockade of alpha5beta1 or alpha4beta1 alone did not attenuate fibronectin-augmentation of phagocytosis. In addition, adhesion of macrophages to recombinant fibronectins lacking alpha4beta1 recognition motifs failed to promote phagocytosis of apoptotic neutrophils. Our results would be consistent with a model in which multiple fibronectin receptors, including beta1 integrins, act co-operatively to augment macrophage phagocytic responses. Together, these data suggest that the extracellular matrix environment of macrophages may provide regulatory signals that act indirectly to rapidly alter the potential for removal of apoptotic cells and influence the process of resolution of inflammation.

Novel inhibitors of alpha 4 beta 1 integrin receptor interactions through library synthesis and screening

A library of 2302 small molecule beta-turn mimetics was screened for inhibition of the alpha 4 beta 1 integrin-CS1 splice variant binding interaction. Preliminary data revealed several active ligands, and validation with purified material culminated in the identification of some of the first small molecule ligands (1, IC50 = 5 microM, and 2, IC50 = 8 microM) to be reported for this class of integrins.

Interference of nonsteroidal antiinflammatory drugs with very late activation antigen 4/vascular cells adhesion molecule 1-mediated lymphocyte-endothelial cell adhesion

OBJECTIVE

To study the effect of nonsteroidal antiinflammatory drugs (NSAIDs) on the adhesion of peripheral blood lymphocytes (PBL) to activated human umbilical vein endothelial cells (HUVEC) under conditions that resemble blood flow.

METHODS

Assays of adhesion of PBL to HUVEC or recombinant vascular cell adhesion molecule 1 (rVCAM-1), intercellular adhesion molecule 1 (ICAM-1), and E-selectin were performed under continuous rotation at 37 degrees C. The phenotype of PBL subpopulations attached was characterized by flow cytometry. Lymphocytes were pretreated with different doses (5-100 microg/ml) of aceclofenac, diclofenac, indomethacin, or piroxicam or with inhibitory monoclonal antibodies (MAb) prior to the adhesion assays. The effect of NSAIDs on lymphocyte adhesion molecules was assessed by flow cytometry. To determine whether NSAIDs interfere with the affinity state of very late activation antigen 4 (VLA-4) integrin, we studied the effect of these drugs on the appearance of a beta1 activation-dependent epitope recognized by the HUTS21 MAb both on human T lymphoblasts and on synovial fluid lymphocytes (SFL).

RESULTS

In the flow-resembling model, PBL-HUVEC adhesion was mainly mediated by the VLA-4/ VCAM-1 adhesion pathway. The major PBL subset attached was the CD3+, CD45RO+ memory T cell, with CD49d(high) expression. Aceclofenac, diclofenac, and indomethacin, but not piroxicam, were able to inhibit PBL adhesion to HUVEC or rVCAM-1. However, the quantitative expression of VLA-4 was not affected by treatment of PBL with any of the NSAIDs studied. On T lymphoblasts and SFL, mostly CD45RO+ cells, the expression of the beta1 activation-dependent epitope detected by HUTS21 MAb was significantly decreased by aceclofenac, diclofenac, and indomethacin.

CONCLUSION

Some NSAIDs are able to inhibit the adhesion of PBL to HUVEC under conditions that resemble blood flow by interfering with the conformational change in VLA-4 that increases its affinity for VCAM-1.

Cytokine and adhesion molecule requirements for lung injury induced by anti-glomerular basement membrane antibody

Acute hemorrhagic lung injury occurs in humans with anti-GBM antibody (Goodpasture's syndrome), however, the mechanism of this injury is still largely unknown. To date, treatment has been confined to steroids and plasmaphoresis. Infusion of anti-GBM antibody into rats caused lung injury with intra-alveolar hemorrhage and intrapulmonary accumulation of neutrophils. Lung injury was dependent on the presence of neutrophils and complement and required both TNF alpha and IL-1. Experiments employing blocking antibodies to adhesion molecules demonstrated requirements for the beta 1 integrin VLA-4, beta 2 integrins LFA-1 and Mac-1, and L-selection. The endothelial cell adhesion molecules, E-selectin and ICAM-1, were also required for the full development of lung injury. Inhibition of TNF alpha or IL-1 or adhesion molecules reduced both lung injury and tissue neutrophil accumulation. Thus, this study underscores cytokine and adhesion molecule requirements for neutrophil mediated injury in lung and kidney caused by anti-GBM, suggesting potential targets for the treatment of Goodpasture's syndrome in humans.

Role of adhesion molecules in the homing and mobilization of murine hematopoietic stem and progenitor cells

Bone marrow (BM) transplantation still must overcome multiple difficulties and should benefit from better understanding of stem-cell homing and mobilization. Here, we analyzed the involvement of several adhesion molecules in the two processes by treating mice with monoclonal antibodies against these molecules. Treatment of lethally irradiated mice grafted with isogeneic BM cells showed that at least two migration pathways are important for stem-cell homing to the BM, whereas only one of them is involved in lodging of colony-forming unit-spleen (CFU-S) in the spleen. We confirm that the VLA-4/VCAM-1 adhesion pathway is important for stem-cell homing to the BM only and show that CD44 is involved in CFU-S lodging in both BM and spleen. These results show that entry of CFU-S into the spleen is regulated. The observation that when one migration pathway is altered, CFU-S do not enter the BM via the other pathway may indicate that the two mechanisms involved in CFU-S homing into the BM are linked. The adhesion molecules VLA-4 and CD44 are also implied in the mobilization of stem cells into the blood stream of mice injected once with anti-VLA-4 or anti-CD44. Anti-VLA-4 administration led to a significant increase in circulating stem cells as early as 8 hours after treatment. Stem cells mobilized by anti-VLA-4 comprise cells with high self-renewal potential and thus may be used for long-term reconstitution of the hematopoietic tissue.

Different adhesive characteristics and VLA-4 expression of CD34(+) progenitors in G0/G1 versus S+G2/M phases of the cell cycle

We identified the cell cycle status of CD34(+) cells of steady-state bone marrow (BM) and peripheral blood (PB) obtained from healthy volunteers, and those of apherasis PB samples collected from healthy donors who had been administered granulocyte colony-stimulating factor (G-CSF). More than 10% of CD34(+) cells in BM were in S+G2/M phase. In contrast, regardless of whether G-CSF treatment was performed, less than 2% of CD34(+) cells in PB were cycling. BM CD34(+) cells showed greater VLA-4 expression and adherence to stromal cells than PB CD34(+) cells. In addition, when cycling and dormant BM CD34(+) cells were analyzed separately, the cells in S+G2/M phase expressed more VLA-4 and adhered to the stromal cell monolayer more efficiently than the cells in G0/G1 phase. Furthermore, this adhesion of CD34(+) cells to the stromal cell layer was almost completely inhibited by anti-VLA-4 antibody. Taken together, these results suggest that CD34(+) progenitors in G0/G1 phase of the cell cycle differ from those in S+G2/M phase in adhesiveness mediated by VLA-4 in the hematopoietic microenvironment.

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.