Affinity and kinetics of sialyl Lewis-X and core-2 based oligosaccharides binding to L- and P-selectin

Pilot study of a heptavalent vaccine-keyhole limpet hemocyanin conjugate plus QS21 in patients with epithelial ovarian, fallopian tube, or peritoneal cancer

PURPOSE

To characterize the safety and immunogenicity of a heptavalent antigen-keyhole limpet hemocyanin (KLH) plus QS21 vaccine construct in patients with epithelial ovarian, fallopian tube, or peritoneal cancer in second or greater complete clinical remission.

EXPERIMENTAL DESIGN

Eleven patients in this pilot trial received a heptavalent vaccine s.c. containing GM2 (10 microg), Globo-H (10 microg), Lewis Y (10 microg), Tn(c) (3 microg), STn(c) (3 microg), TF(c) (3 microg), and Tn-MUC1 (3 microg) individually conjugated to KLH and mixed with adjuvant QS21(100 microg). Vaccinations were administered at weeks 1, 2, 3, 7, and 15. Periodic blood and urine samples were obtained to monitor safety (complete blood count, comprehensive panel, amylase, thyroid-stimulating hormone, and urinalysis) and antibody production (ELISA, fluorescence-activated cell sorting, and complement-dependent cytotoxicity).

RESULTS

Eleven patients were included in the safety analysis; 9 of 11 patients remained on study for at least 2 weeks past fourth vaccination and were included in the immunologic analysis (two withdrew, disease progression). The vaccine was well tolerated. Self-limited and mild fatigue (maximum grade 2 in two patients), fever, myalgia, and localized injection site reactions were most frequent. No clinically relevant hematologic abnormalities were noted. No clinical or laboratory evidence of autoimmunity was seen. Serologic responses by ELISA were largely IgM against each antigen with the exception of Tn-MUC1 where both IgM and IgG responses were induced. Antibody responses were generally undetectable before immunization. After immunization, median IgM titers were as follows: Tn-MUC1, 1:640 (IgG 1:80); Tn, 1:160; TF, 1:640; Globo-H, 1:40; and STn, 1:80. Only one response was seen against Lewis Y; two were against GM2. Eight of nine patients developed responses against at least three antigens. Antibody titers peaked at weeks 4 to 8 in all patients. Fluorescence-activated cell sorting and complement-dependent cytotoxicity analysis showed substantially increased reactivity against MCF7 cells in seven of nine patients, with some increase seen in all patients.

CONCLUSIONS

This heptavalent-KLH conjugate plus QS21 vaccine safely induced antibody responses against five of seven antigens. Investigation in an adequately powered efficacy trial is warranted.

Microparticle adhesive dynamics and rolling mediated by selectin-specific antibodies under flow

In vitro studies were performed to characterize the relative performance of candidate receptors to target microparticles to inflammatory markers on vascular endothelium. To model the interactions of drug-bearing microparticles or imaging contrast agents with the vasculature, 6 micron polystyrene particles bearing antibodies, peptides, or carbohydrates were perfused over immobilized E- or P-selectin in a flow chamber. Microparticles conjugated with HuEP5C7.g2 (HuEP), a monoclonal antibody (mAb) specific to E- and P-selectin, supported leukocyte-like rolling and transient adhesion at venular shear rates. In contrast, microparticles conjugated with a higher affinity mAb specific for P-selectin (G1) were unable to form bonds at venular flow rates. When both HuEP and G1 were conjugated to the microparticle, HuEP supported binding to P-selectin in flow which allowed G1 to form bonds leading to stable adhesion. While the microparticle attachment and rolling performance was not as stable as that mediated by the natural ligands P-selectin Glycoprotein Ligand-1 or sialyl Lewis(x), HuEP performed significantly better than any previously characterized mAb in terms of mediating microparticle binding under flow conditions. HuEP may be a viable alternative to natural ligands to selectins for targeting particles to inflamed endothelium.

PWWP module of human hepatoma-derived growth factor forms a domain-swapped dimer with much higher affinity for heparin

Hepatoma-derived growth factor (hHDGF)-related proteins (HRPs) comprise a new growth factor family sharing a highly conserved and ordered N-terminal PWWP module (residues 1-100, previously referred to as a HATH domain) and a variable disordered C-terminal domain. We have shown that the PWWP module is responsible for heparin binding and have solved its structure in solution. Here, we show that under physiological conditions, both the PWWP module and hHDGF can form dimers. Surface plasmon resonance (SPR) studies revealed that the PWWP dimer binds to heparin with affinity that is two orders of magnitude higher (K(d)=13 nM) than that of the monomeric PWWP module (K(d)=1.2 microM). The monomer-dimer equilibrium properties and NMR structural data together suggest that the PWWP dimer is formed through a domain-swapping mechanism. The domain-swapped PWWP dimer structures were calculated on the basis of the NMR data. The results show that the two PWWP protomers exchange their N-terminal hairpin to form a domain-swapped dimer. The two monomers in a dimer are linked by the long flexible L2 loops, a feature supported by NMR relaxation data for the monomer and dimer. The enhanced heparin-binding affinity of the dimer can be rationalized in the framework of the dimer structure.

Protective role of selectin ligand inhibition in a large animal model of kidney ischemia-reperfusion injury

Experiments in rodents have demonstrated an important role for selectins in kidney ischemia-reperfusion injury (IRI). However, the relevance of this in larger mammals, as well as the impact on long-term structure and function is unknown. We tested the hypothesis that small molecule selectin ligand inhibition attenuates IRI, cellular inflammation, and long-term effects on renal interstitial fibrosis. We used a porcine model of kidney IRI and used Texas Biotechnology Corporation (TBC)-1269, a selectin ligand inhibitor. Renal function, tissue inflammation, and tubulointerstitial fibrosis development were evaluated up to 16 weeks. Both warm and cold ischemia models were studied for relevance to native and transplant kidney injury. Pigs treated with TBC-1269 during 45 min of warm ischemia (WI) showed significantly increased glomerular filtration rate compared to control animals. In pigs with severe IRI (WI for 60 min), TBC-1269 treatment during IRI significantly increased renal recovery. Cellular inflammation was strongly reduced, particularly influx of CD4 cells. Quantitative measurement of fibrosis by picrosirius red staining showed strong reduction in TBC-1269-treated groups. TBC-1269 also reduced cold IRI, inflammation, and fibrosis in kidneys preserved for 24 h at 4 degrees C and autotransplanted. The selectin ligand inhibitor TBC-1269 provides a novel and effective approach to attenuate IRI in both warm and cold ischemia in large mammals, in both short and long terms. Selectin ligand inhibition is an attractive strategy for evaluation in human kidney IRI.

The influence of various structural parameters of semisynthetic sulfated polysaccharides on the P-selectin inhibitory capacity

Selectin-mediated leukocyte rolling along the endothelium is of key importance for maintaining the cellular immune response. The anti-inflammatory activities of heparin have partly been related to inhibition of P-selectin binding. Heparin, however, suffers from its heterogeneous variable structure, the animal origin and multiple in vivo effects. As P-selectin is a promising target for anti-inflammatory approaches, we focused on P-selectin inhibition by other sulfated polysaccharides and compared them with six heparins. We examined 15 structurally defined semisynthetic sulfated glucans, non-animal-derived from the linear glucans phycarin, curdlan or pullulan. The derivatives gradually differ in their degree of sulfation, molecular weight, and glycosidic linkage. The inhibitory capacity was analysed in a parallel plate flow chamber, detecting the rolling of U937 cells on P-selectin layers. Unfractionated heparins displayed variabilities between different preparations. Considering fractionated heparins, exceeding of a minimal mass is essential for activity. Comparing the glucan sulfates, charge density is the most important parameter for P-selectin binding. Highly sulfated derivatives are excellent inhibitors, the reduced cell binding up to 16.2+/-6.4% strongly exceeded the heparin activities. Molecular weight is of minor effects, while glycosidic backbone linkage holds certain importance. To check the P-selectin inhibition in vivo, heparin and one phycarin sulfate were tested using intravital microscopy of microvasculature in mice. Both compounds significantly reduced the rolling fractions of activated platelets on endothelium as effective as a blocking P-selectin antibody. Our study indicates that semisynthetic glucan sulfates with optimal structures block P-selectin excellently and might become promising candidates for anti-inflammatory drugs to replace heparin for certain applications.

C3a levels and occurrence of subdermal vascular thrombosis are age-related in deep second-degree burn wounds

BACKGROUND

After second-degree burns, thrombosis of the subdermal vascular plexus may occur, necessitating epifascial necrectomy instead of tangential excision to ensure split skin graft healing. Until now, no parameter has been obtained to explain this phenomenon.

METHODS

Thirty-four patients with deep second-degree burn wounds were divided into 2 groups. In group 1, patients' age was < 60 years, in group 2, > 60 years. In each patient, 2 microdialysis catheters were introduced into subdermal tissue of deep second-degree thermal wounds immediately after admission. Another 2 catheters were introduced in control tissue. We measured biochemical parameters (lactate, glycerol and glucose) and complement 3a (C3a) until surgery was performed. The surgically removed tissue was examined histologically.

RESULTS

In thermal wounds of both groups, glucose levels fell, but lactate and glycerol levels rose compared to healthy tissue. Within the first 24 hours after trauma, C3a levels were significant higher in both groups, compared with controls (P < .01). After 24 hours the levels in group 1 had fallen to nonsignificant values, while in group 2 these levels remained high until surgery was performed (P < .001). We found significantly more thrombotic blood vessels in deep dermal tissue of group 2 (P < .005). Abbreviated burn severity index score was comparable in both groups.

CONCLUSIONS

C3a is continuously elevated in deep second-degree burned wounds in patients > 60 years. This finding may be related to the occurrence of significantly more thrombotic blood vessels in deep dermal tissue of elderly patients. Microdialysis therapy is a useful tool to measure metabolic and immunologic parameters in thermally damaged tissue.

Human milk oligosaccharides affect P-selectin binding capacities: In vitro investigation

OBJECTIVE

In the initial phase of cellular immune response, selectins mediate the emigration of leukocytes from the blood stream into inflammatory regions. Human milk oligosaccharides (HMOs) possess binding epitopes of selectin ligands such as sialyl Lewis(x) and sialyl Lewis(a) and therefore might impair the interaction of selectins with cellular ligands. Neutral, acidic, sialylated, or fucosylated HMO fractions with polymerization degrees of 3 to 50 were investigated regarding this interaction in a dynamic flow chamber model that considers physiologic shear stress conditions.

METHODS

Human milk oligosaccharides were compared with kappa-carrageenans and pectin oligosaccharides to deduce structure-activity relations. Fucoidan and sialyl Lewis(x) served as positive controls.

RESULTS

All HMO fractions affected P-selectin ligand binding capacity but were not comparable to fucoidan. The activity of the acidic HMO fraction resembled sialyl Lewis(x) in decreasing the binding of the ligand to P-selectin.

CONCLUSION

Human milk oligosaccharides modulate rather than block the function of P-selectin.

Targeted ultrasound contrast agent for molecular imaging of inflammation in high-shear flow

Targeted ultrasound contrast materials (gas-filled microbubbles carrying ligands to endothelial selectins or integrins) have been investigated as potential molecular imaging agents. Such microbubbles normally exhibit good targeting capability at the slower flow conditions. However, in the conditions of vigorous flow, binding may be limited. Here, we describe a microbubble capable of efficient binding to targets both in slow and fast flow (exceeding 4 dyne/cm(2) wall shear stress) using a clustered polymeric form of the fast-binding selectin ligand sialyl Lewis(X). Microbubbles were prepared from decafluorobutane gas and stabilized with a monolayer of phosphatidylcholine, PEG stearate and biotin-PEG-lipid. Biotinylated PSLe(x) (sialyl Lewis(X) polyacrylamide) or biotinylated anti-P-selectin antibody (RB40.34) was attached to microbubbles via a streptavidin bridge. In a parallel plate flow chamber targeted adhesion model, PSLe(x) bubbles demonstrated specific adhesion, retention and slow rolling on P-selectin-coated plates. Efficiency of firm targeted adhesion to a P-selectin surface (140 molecules/microm(2)) was comparable for antibody-carrying bubbles and PSLe(x)-targeted bubbles at 0.68 dyne/cm(2) shear stress. At fast flow (4.45 dyne/cm(2)), PSLe(x)-targeted bubbles maintained their ability to bind, while antibody-mediated targeting dropped more than 20-fold. At lower surface density of P-selectin (7 molecules/microm(2)), targeting via PSLe(x) was more efficient than via antibody under all the flow conditions tested. Negative control casein-coated plates did not retain bubbles in the range of flow conditions studied. To confirm echogenicity, targeted PSLe(x)-bubbles were visualized on P-selectin-coated polystyrene plates by ultrasound imaging with a clinical scanner operated in pulse inversion mode; control plates lacking targeted bubbles did not show significant acoustic backscatter. In vivo, in a murine model of inflammation in the femoral vein setting, targeting efficacy of intravenously administered PSLe(x)-microbubbles was comparable with targeting mediated by anti-P-selectin antibody, and significantly exceeded the accumulation of non-targeted control bubbles. In the inflamed femoral artery setting, PSLe(x)-mediated microbubble targeting was superior to antibody-mediated targeting.

Survey of the year 2005 commercial optical biosensor literature

We identified 1113 articles (103 reviews, 1010 primary research articles) published in 2005 that describe experiments performed using commercially available optical biosensors. While this number of publications is impressive, we find that the quality of the biosensor work in these articles is often pretty poor. It is a little disappointing that there appears to be only a small set of researchers who know how to properly perform, analyze, and present biosensor data. To help focus the field, we spotlight work published by 10 research groups that exemplify the quality of data one should expect to see from a biosensor experiment. Also, in an effort to raise awareness of the common problems in the biosensor field, we provide side-by-side examples of good and bad data sets from the 2005 literature.

Biomechanics of P-selectin PSGL-1 bonds: shear threshold and integrin-independent cell adhesion

Platelet-leukocyte adhesion may contribute to thrombosis and inflammation. We examined the heterotypic interaction between unactivated neutrophils and either thrombin receptor activating peptide (TRAP)-stimulated platelets or P-selectin-bearing beads (Ps-beads) in suspension. Cone-plate viscometers were used to apply controlled shear rates from 14 to 3000/s. Platelet-neutrophil and bead-neutrophil adhesion analysis was performed using both flow cytometry and high-speed videomicroscopy. We observed that although blocking antibodies against either P-selectin or P-selectin glycoprotein ligand-1 (PSGL-1) alone inhibited platelet-neutrophil adhesion by approximately 60% at 140/s, these reagents completely blocked adhesion at 3000/s. Anti-Mac-1 alone did not alter platelet-neutrophil adhesion rates at any shear rate, though in synergy with selectin antagonists it abrogated cell binding. Unstimulated neutrophils avidly bound Ps-beads and activated platelets in an integrin-independent manner, suggesting that purely selectin-dependent cell adhesion is possible. In support of this, antagonists against P-selectin or PSGL-1 caused dissociation of previously formed platelet-neutrophil and Ps-bead neutrophil aggregates under shear in a variety of experimental systems, including in assays performed with whole blood. In studies where medium viscosity and shear rate were varied, a shear threshold for P-selectin PSGL-1 binding was also noted at shear rates <100/s when Ps-beads collided with isolated neutrophils. Results are discussed in light of biophysical computations that characterize the collision between unequal-size particles in linear shear flow. Overall, our studies reveal an integrin-independent regime for cell adhesion and weak shear threshold for P-selectin PSGL-1 interactions that may be physiologically relevant.