Glycosulfopeptides modeled on P-selectin glycoprotein ligand 1 inhibit P-selectin-dependent leukocyte rolling in vivo

A PSGL-1 glycomimetic reduces thrombus burden without affecting hemostasis

Events mediated by the P-selectin/PSGL-1 pathway play a critical role in the initiation and propagation of venous thrombosis by facilitating the accumulation of leukocytes and platelets within the growing thrombus. Activated platelets and endothelium express P-selectin, which binds P-selectin glycoprotein ligand-1 (PSGL-1) that is expressed on the surface of all leukocytes. We developed a pegylated glycomimetic of the N terminus of PSGL-1, PEG40-GSnP-6 (P-G6), which proved to be a highly potent P-selectin inhibitor with a favorable pharmacokinetic profile for clinical translation. P-G6 inhibits human and mouse platelet-monocyte and platelet-neutrophil aggregation in vitro and blocks microcirculatory platelet-leukocyte interactions in vivo. Administration of P-G6 reduces thrombus formation in a nonocclusive model of deep vein thrombosis with a commensurate reduction in leukocyte accumulation, but without disruption of hemostasis. P-G6 potently inhibits the P-selectin/PSGL-1 pathway and represents a promising drug candidate for the prevention of venous thrombosis without increased bleeding risk.

Cell adhesion molecule-mediated therapeutic strategies in atherosclerosis: From a biological basis and molecular mechanism to drug delivery nanosystems

Atherosclerosis (AS), characterized by pathological constriction of blood vessels due to chronic low-grade inflammation and lipid deposition, is a leading cause of human morbidity and mortality worldwide. Cell adhesion molecules (CAMs) have the ability to regulate the inflammatory response and endothelial function, as well as potentially driving plaque rupture, which all contribute to the progression of AS. Moreover, recent advances in the development of clinical agents in the cardiovascular field are based on CAMs, which show promising results in the fight against AS. Here, we review the current literature on mechanisms by which CAMs regulate atherosclerotic progression from the earliest induction of inflammation to plaques formation. In particular, we focused on therapeutic strategies based on CAMs inhibitors that prevent leukocyte from migrating to endothelium, including high-affinity antibodies and antagonists, nonspecific traditional medicinal formulas and lipid lowering drugs. The CAMs-based drug delivery nanosystem and the available data on the more reasonable and effective clinical application of CAMs inhibitors have been emphasized, raising hope for further progress in the field of AS therapy.

Tools for generating and analyzing glycan microarray data

Glycans are one of the major biological polymers found in the mammalian body. They play a vital role in a number of physiologic and pathologic conditions. Glycan microarrays allow a plethora of information to be obtained on protein–glycan binding interactions. In this review, we describe the intricacies of the generation of glycan microarray data and the experimental methods for studying binding. We highlight the importance of this knowledge before moving on to the data analysis. We then highlight a number of tools for the analysis of glycan microarray data such as data repositories, data visualization and manual analysis tools, automated analysis tools and structural informatics tools.

Discovery of 2-[1-(4-chlorophenyl)cyclopropyl]-3-hydroxy-8-(trifluoromethyl)quinoline-4-carboxylic acid (PSI-421), a P-selectin inhibitor with improved pharmacokinetic properties and oral efficacy in models of vascular injury

Previously, we reported the discovery of PSI-697 (1a), a C-2 benzyl substituted quinoline salicylic acid-based P-selectin inhibitor. It is active in a variety of animal models of cardiovascular disease. Compound 1a has also been shown to be well tolerated and safe in healthy volunteers at doses of up to 1200 mg in a phase 1 single ascending dose study. However, its oral bioavailability was low. Our goal was to identify a back up compound with equal potency, increased solubility, and increased exposure. We expanded our structure-activity studies in this series by branching at the alpha position of the C-2 benzyl side chain and through modification of substituents on the carboxylic A-ring of the quinoline. This resulted in discovery of PSI-421 with marked improvement in aqueous solubility and pharmacokinetic properties. This compound has shown oral efficacy in animal models of arterial and venous injury and was selected as a preclinical development compound for potential treatment of such diseases as atherosclerosis and deep vein thrombosis.

Action at a distance: lengthening adhesion bonds with poly(ethylene glycol) spacers enhances mechanically stressed affinity for improved vascular targeting of microparticles

Poly(ethylene glycol) (PEG) chains were used to decorate microparticles with long adhesion ligands to emulate the efficacy of selectin-mediated leukocyte homing mechanisms. Ligands for P-selectin, an endothelial cell inflammatory marker, were coupled to PEG spacers of two sizes (MW 3400 and 10,000 Da) to investigate the effects on adhesion kinetics to P-selectin substrates. Under shear flow 80 nm PEG spacers improved P-selectin-antibody adhesion frequency by up to 4.5-fold and bond lifetimes by 7-fold compared to microparticles bearing chemisorbed antibody. Presentation of the glycosulfopeptide P-selectin ligands (2-GSP-6) and its nonsulfated low affinity form (2-GP-6) by long PEG spacers led to improved lifetimes of stressed bonds formed with P-selectin in shear flow and the rolling fluxes. Thus, structural features far removed from the binding pocket of a receptor that increase molecular contour length may enhance affinity in mechanically stressed environments such as those existing within the confines of the blood vessel. Such features may be useful for improving the performance of vascular-targeted micro- and nanoparticles used for drug, gene, and image contrast delivery. Ligand presentation on molecularly extended stalks may also serve to enhance any particle-surface interaction that takes place in laminar shear flow.

Elevated shear stress protects Escherichia coli cells adhering to surfaces via catch bonds from detachment by soluble inhibitors

Soluble inhibitors find widespread applications as therapeutic drugs to reduce the ability of eukaryotic cells, bacteria, or viruses to adhere to surfaces and host tissues. Mechanical forces resulting from fluid flow are often present under in vivo conditions, and it is commonly presumed that fluid flow will further add to the inhibitive effect seen under static conditions. In striking contrast, we discover that when surface adhesion is mediated by catch bonds, whose bond life increases with increased applied force, shear stress may dramatically increase the ability of bacteria to withstand detachment by soluble competitive inhibitors. This shear stress-induced protection against inhibitor-mediated detachment is shown here for the fimbrial FimH-mannose-mediated surface adhesion of Escherichia coli. Shear stress-enhanced reduction of bacterial detachment has major physiological and therapeutic implications and needs to be considered when developing and screening drugs.

C-type natriuretic peptide inhibits leukocyte recruitment and platelet-leukocyte interactions via suppression of P-selectin expression

The multifaceted process of immune cell recruitment to sites of tissue injury is key to the development of an inflammatory response and involved in the pathogenesis of numerous cardiovascular disorders. We recently identified C-type natriuretic peptide (CNP) as an important endothelium-derived mediator that regulates vascular tone and protects against myocardial ischemia/reperfusion injury. Herein, we investigated whether CNP inhibits leukocyte recruitment and platelet aggregation and thereby exerts a potential antiinflammatory influence on the blood vessel wall. We assessed the effects of CNP on leukocyte-endothelial cell interactions in mouse mesenteric postcapillary venules in vivo in animals with high basal leukocyte activation (endothelial nitric oxide synthase knockout mice, eNOS(-/-)) or under acute inflammatory conditions (induced by interleukin-1beta or histamine). CNP suppressed basal leukocyte rolling in eNOS(-/-) mice in a rapid, reversible, and concentration-dependent manner. These effects of CNP were mimicked by the selective natriuretic peptide receptor-C agonist cANF(4-23). CNP also suppressed leukocyte rolling induced by IL-1beta or histamine, inhibited platelet-leukocyte interactions, and prevented thrombin-induced platelet aggregation of human blood. Furthermore, analysis of human umbilical vein endothelial cells, leukocytes, and platelets revealed that CNP selectively attenuates expression of P-selectin. Thus, CNP is a modulator of acute inflammation in the blood vessel wall characterized by leukocyte and platelet activation. These antiinflammatory effects appear to be mediated, at least in part, via suppression of P-selectin expression. These observations suggest that endothelial CNP might maintain an anti-atherogenic influence on the blood vessel wall and represent a target for therapeutic intervention in inflammatory cardiovascular disorders.

L- and P-selectins collaborate to support leukocyte rolling in vivo when high-affinity P-selectin-P-selectin glycoprotein ligand-1 interaction is inhibited

P-selectin glycoprotein ligand-1 (PSGL-1) binding to P-selectin controls early leukocyte rolling during inflammation. Interestingly, antibodies and pharmacological inhibitors (eg, rPSGL-Ig) that target the N-terminus of PSGL-1 reduce but do not abolish P-selectin-dependent leukocyte rolling in vivo whereas PSGL-1-deficient mice have almost no P-selectin-dependent rolling. We have investigated mechanisms of P-selectin-dependent, PSGL-1-independent rolling using intravital microscopy. Initially we used fluorescent microspheres to study the potential of L-selectin and the minimal selectin ligand sialyl Lewis(x) (sLe(x)) to interact with postcapillary venules in the absence of PSGL-1. Microspheres coated with combinations of L-selectin and sLe(x) interacted with surgically stimulated cremaster venules in a P-selectin-dependent manner. Microspheres coated with either L-selectin or sLe(x) alone showed less evidence of interaction. We also investigated leukocyte rolling in the presence of PSGL-1 antibody or inhibitor (rPSGL-Ig), both of which partially inhibited P-selectin-dependent leukocyte rolling. Residual rolling was substantially inhibited by L-selectin-blocking antibody or a previously described sLe(x) mimetic (CGP69669A). Together these data suggest that leukocytes can continue to roll in the absence of optimal P-selectin/PSGL-1 interaction using an alternative mechanism that involves P-selectin-, L-selectin-, and sLe(x)-bearing ligands.

Identification of equine P-selectin glycoprotein ligand-1 (CD162)

P-selectin glycoprotein ligand-1 (PSGL-1, CD162) is a dimeric, mucin-like, transmembrane glycoprotein constitutively expressed on leukocytes. A high baseline level of P-selectin expression in circulating equine platelets suggests a primed state toward inflammation and thrombosis via P-selectin/PSGL-1 adhesion. To investigate the potential role of equine P-selectin in these events, we first identified the cDNA sequence of equine PSGL-1 (ePSGL-1) using degenerate PCR and RACE-PCR and then compared the predicted sequence with that of human PSGL-1 (hPSGL-1). ePSGL-1 protein subunit is predicted to be 43 kDa and composed of 420 amino acids with a predicted 18-amino-acid signal sequence showing 78% homology to hPSGL-1. Previously published work has shown that binding of P-selectin requires sulfation of at least one of three tyrosines and O-glycosylation of one threonine in the N-terminus of human PSGL-1. However, the corresponding domain in ePSGL-1, spanning residues 19-43, contains only one tyrosine in the vicinity of two threonines at positions 25 and 41. ePSGL-1 contains 14 threonine/serine-rich decameric repeats as compared to hPSGL-1 which contains 14-16 threonine-rich decameric repeats. The transmembrane and cytoplasmic domains display 91% and 74% homology to corresponding human PSGL-1 domains, respectively. In summary, there is 71% homology in comparing the open reading frame (ORF) of ePSGL-1 with that of hPSGL-1. The greatest homologies between species exist in the transmembrane domain and cytoplasmic tail while substantial differences exist in the extracellular domain.

The anti-inflammatory effects of a selectin ligand mimetic, TBC-1269, are not a result of competitive inhibition of leukocyte rolling in vivo

Selectins and their ligands support leukocyte rolling, facilitating the subsequent firm adhesion and migration that occur during inflammation. TBC-1269 (Bimosiamose), a structural mimetic of natural selectin ligands, inhibits P-, E-, and L-selectin in vitro, has anti-inflammatory effects in vivo, and recently underwent phase II clinical trials for childhood asthma and psoriasis. We studied whether the anti-inflammatory effects of TBC-1269 could be related to leukocyte rolling in vivo. Although TBC-1269 inhibited rolling of a murine leukocyte cell line on murine P-selectin in vitro and thioglycollate-induced peritonitis in vivo, it did not alter leukocyte rolling in mouse cremaster venules. TBC-1269 reduced neutrophil recruitment in thioglycollate-induced peritonitis in wild-type and P-selectin-/- mice but not in E-selectin-/- mice. We suggest that the in vivo effects of TBC-1269 may be mediated through E-selectin but do not appear to involve leukocyte rolling.

The discovery, biology, and drug development of sialyl Lea and sialyl Lex

The discoveries of sialylated, fucosylated lacto-, and neolacto-type carbohydrate structures were accomplished with the aid of analytical methods and monoclonal antibodies such as the immunostaining of thin layer chromatograms. Based on the use of such antibodies, these structures, notably sialyl Le(a) and sialyl Le(x), were demonstrated to be highly expressed in many malignant cancers. A diagnostic assay using one of these antibodies (CA19-9) is now established as one of the more commonly used assays for pancreatic and gastrointestinal cancers worldwide. Upon further study, several laboratories have demonstrated that the level of expression of these carbohydrate tumor markers is also positively correlated with patient survival and is a prognostic indicator of metastatic disease. Concurrent with this finding, both sialyl Le(a) and sialyl Le(x) were shown to bind to a family of carbohydrate-binding proteins involved in the extravasation of cells from the bloodstream, called the selectins. Thus, sialyl Le(a) and sialyl Le(x) expressed on cell surfaces play functional roles in medical conditions that require extravasation of cells from the bloodstream which include a wide range of inflammatory diseases and cancer metastasis. Many studies have confirmed the function of sialyl Le(a) and sialyl Le(x) in animal models of these diseases and the inhibition of binding of sialyl Le(a) and sialyl Le(x) to the selectins is a validated drug target in the pharmaceutical industry. Thus, a new class of drugs, arising from the field of glycobiology, is based on the rational design of small molecule drugs that mimic the structures sialyl Le(a) and sialyl Le(x) and can potently inhibit their functional binding to the selectins.

Direct In Vivo Monitoring of Acute Allergic Reactions in Human Conjunctiva

Immediate allergic reactions are initiated by allergen-induced, specific IgE-mediated mast cell degranulation and involve leukocyte recruitment into the inflamed site. We compared conjunctival signs, symptoms, and in vivo leukocyte rolling and extravasation into sites of inflammation in five patients allergic to birch pollen and in 10 nonallergic controls who received a challenge to birch allergen or histamine. Both the specific allergen in allergic patients and histamine, both in patients and in healthy controls, induced symptoms and signs of an immediate allergic reaction together with leukocyte rolling within the conjunctival blood vessels. However, only allergen, not histamine, caused leukocyte extravasation into the site of inflammation in the allergic patients. Allergen also increased expression of endothelial P-selectin in conjunctival vessels and slowed the rolling of leukocytes which is required for their extravasation from blood circulation into the target tissue. Finally, i.v. heparin strongly reduced the number of slowly rolling cells during allergen- or histamine-induced reactions and this can probably hinder the leukocyte extravasation after allergen exposure. These findings suggest that slow rolling is required for leukocyte extravasation in acute allergic reactions, and it can be inhibited by heparin in vivo in therapeutically relevant conditions.

Phagocytes: mechanisms of inflammation and tissue destruction

Macrophages and neutrophils are the professional phagocytes of the innate immune system. Once in the inflammatory joint or the vasculitic lesion, macrophages and neutrophils contribute to the pathology observed. This article examines the mechanisms by which phagocytes contribute to the pathogenesis of these diseases.

Discovery of a potent nanoparticle P-selectin antagonist with anti-inflammatory effects in allergic airway disease

The severity of allergic asthma is dependent, in part, on the intensity of peribronchial inflammation. P-selectin is known to play a role in the development of allergen-induced peribronchial inflammation and airway hyperreactivity. Selective inhibitors of P-selectin-mediated leukocyte endothelial-cell interactions may therefore attenuate the inflammatory processes associated with allergic airway disease. Novel P-selectin inhibitors were created using a polyvalent polymer nanoparticle capable of displaying multiple synthetic, low molecular weight ligands. By assembling a particle that presents an array of groups, which as monomers interact with only low affinity, we created a construct that binds extremely efficiently to P-selectin. The ligands acted as mimetics of the key binding elements responsible for the high-avidity adhesion of P-selectin to the physiologic ligand, PSGL-1. The inhibitors were initially evaluated using an in vitro shear assay system in which interactions between circulating cells and P-selectin-coated capillary tubes were measured. The nanoparticles were shown to preferentially bind to selectins expressed on activated endothelial cells. We subsequently demonstrated that nanoparticles displaying P-selectin blocking arrays were functionally active in vivo, significantly reducing allergen-induced airway hyperreactivity and peribronchial eosinophilic inflammation in a murine model of asthma.

Polymers carrying sLe x ‐mimetics are superior inhibitors of E‐selectin‐dependent leukocyte rolling in vivo

Selectins mediate leukocyte rolling and may represent good anti-inflammatory drug targets. Detailed knowledge regarding the structure of selectin ligands has permitted development of selectin antagonists with varying specificities and activity. Efficacy of monovalent selectin antagonists may be increased by presenting them on a polymer backbone. We have synthesized a range of multivalent selectin antagonists and characterized their activity by using intravital microscopy of the mouse cremaster muscle. The monovalent inhibitor CGP77175A inhibited E-selectin-dependent leukocyte rolling at a dose of 3 mg/kg. Multivalent presentation of CGP77175A on a modified polylysine backbone (degree of polymerization = 1200; 50% of the polylysines carry the inhibitor) greatly enhanced in vivo activity giving an inhibitor that produced an equivalent effect at 0.1 mg/kg. The polylysine conjugate was also longer acting than the monovalent antagonist. In spite of greatly enhanced activity against E-selectin compared with monovalent inhibitor, the multivalent inhibitor had no measurable effect on P- or L-selectin-dependent leukocyte rolling.