Multivalent binding of galactosylated cyclodextrin vesicles to lectin

Multivalent Scaffolds to Promote B cell Tolerance

Autoimmune diseases are characterized by aberrant immune responses toward self-antigens. Current treatments lack specificity, promoting adverse effects by broadly suppressing the immune system. Therapies that specifically target the immune cells responsible for disease are a compelling strategy to mitigate adverse effects. Multivalent formats that display numerous binding epitopes off a single scaffold may enable selective immunomodulation by eliciting signals through pathways unique to the targeted immune cells. However, the architecture of multivalent immunotherapies can vary widely, and there is limited clinical data with which to evaluate their efficacy. Here, we set forth to review the architectural properties and functional mechanisms afforded by multivalent ligands and evaluate four multivalent scaffolds that address autoimmunity by altering B cell signaling pathways. First, we address both synthetic and natural polymer backbones functionalized with a variety of small molecule, peptide, and protein ligands for probing the effects of valency and costimulation. Then, we review nanoparticles composed entirely from immune signals which have been shown to be efficacious. Lastly, we outline multivalent liposomal nanoparticles capable of displaying high numbers of protein antigens. Taken together, these examples highlight the versatility and desirability of multivalent ligands for immunomodulation and illuminate strengths and weaknesses of multivalent scaffolds for treating autoimmunity.

Structural Considerations for Building Synthetic Glycoconjugates as Inhibitors for Pseudomonas aeruginosa Lectins

Pseudomonas aeruginosa is a pathogenic bacterium, responsible for a large portion of nosocomial infections globally and designated as critical priority by the World Health Organisation. Its characteristic carbohydrate-binding proteins LecA and LecB, which play a role in biofilm-formation and lung-infection, can be targeted by glycoconjugates. Here we review the wide range of inhibitors for these proteins (136 references), highlighting structural features and which impact binding affinity and/or therapeutic effects, including carbohydrate selection; linker length and rigidity; and scaffold topology, particularly for multivalent candidates. We also discuss emerging therapeutic strategies, which build on targeting of LecA and LecB, such as anti-biofilm activity, anti-adhesion and drug-delivery, with promising prospects for medicinal chemistry.

Recent Development in the Design of Neoglycoliposomes Bearing Arborescent Architectures

This brief review highlights systematic progress in the design of synthetic glycolipid (neoglycolipids) analogs evolving from the conventional architectures of natural glycosphingolipids and gangliosides. Given that naturally occurring glycolipids are composed of only one hydrophilic sugar head-group and two hydrophobic lipid tails embedded in the lipid bilayers of the cell membranes, they usually require extraneous lipids (phosphatidylcholine, cholesterol) to confer their stability. In order to obviate the necessity for these additional stabilizing ingredients, recent investigations have merged dendrimer chemistry with that of neoglycolipid syntheses. This singular approach has provided novel glycoarchitectures allowing reconsidering the necessity for the traditional one to two hydrophilic/hydrophobic ratio. An emphasis has been provided in the recent design of modular arborescent neoglycolipid syntheses coined glycodendrimersomes.

Cyclodextrin-Based Functional Glyconanomaterials

Cyclodextrins (CDs) have long occupied a prominent position in most pharmaceutical laboratories as "off-the-shelve" tools to manipulate the pharmacokinetics of a broad range of active principles, due to their unique combination of biocompatibility and inclusion abilities. The development of precision chemical methods for their selective functionalization, in combination with "click" multiconjugation procedures, have further leveraged the nanoscaffold nature of these oligosaccharides, creating a direct link between the glyco and the nano worlds. CDs have greatly contributed to understand and exploit the interactions between multivalent glycodisplays and carbohydrate-binding proteins (lectins) and to improve the drug-loading and functional properties of nanomaterials through host-guest strategies. The whole range of capabilities can be enabled through self-assembly, template-assisted assembly or covalent connection of CD/glycan building blocks. This review discusses the advancements made in this field during the last decade and the amazing variety of functional glyconanomaterials empowered by the versatility of the CD component.

Clustering of PK-trisaccharides on amphiphilic cyclodextrin reveals unprecedented affinity for the Shiga-like toxin Stx2

Amphiphilic cyclodextrin-based P^K-glycoarrays show remarkable binding avidity and selectivity for Stx2 in solid phase assay formats.

Cyclodextrin nanoassemblies: a promising tool for drug delivery

Among the biodegradable and nontoxic compounds that can form nanoparticles for drug delivery, amphiphilic cyclodextrins are very promising. Apart from ionic cyclodextrins, which have been extensively studied and reviewed because of their application in gene delivery, our purpose is to provide a clear description of the supramolecular assemblies of nonionic amphiphilic cyclodextrins, which can form nanoassemblies for controlled drug release. Moreover, we focus on the relationship between their structure and physicochemical characteristics, which is crucial for self assembly and drug delivery. We also highlight the importance of the nanoparticle technology preparation for the stability and application of this nanodevice.

Inclusion complexation of isoprenaline and methyl dopa with α- and β-cyclodextrin nanocavities: spectral and theoretical study

Inclusion complex formation of isoprenaline (ISOP) and methyldopa (MDOP) with α-CD and β-CD were investigated. Solid inclusion complex nanomaterials were characterized by SEM, TEM, FTIR, DSC, (1)H NMR and XRD methods. Spectral results showed that single emission (monomer) noticed in aqueous solution where as dual emission (excimer) in CD. Both drugs formed 1:2 (CD-drug2) inclusion complexes with CDs. Time-resolved fluorescence studies show that single exponential decay observed in water whereas biexponential decay observed in CD. Nano-sized particles were found in ISOP/CD while vesicles were obtained in MDOP/CD complexes. DSC results revealed that the thermal stability of drugs was improved when it was included in the CD nanocavity. Based on PM3 calculations, the inclusion structure of ISOP/CD and MDOP/CD complexes were proposed. Thermodynamic parameters and binding affinity of complexation of CD were determined by PM3 method.

Cyclodextrin-based supramolecular systems for drug delivery: recent progress and future perspective

The excellent biocompatibility and unique inclusion capability as well as powerful functionalization capacity of cyclodextrins and their derivatives make them especially attractive for engineering novel functional materials for biomedical applications. There has been increasing interest recently to fabricate supramolecular systems for drug and gene delivery based on cyclodextrin materials. This review focuses on state of the art and recent advances in the construction of cyclodextrin-based assemblies and their applications for controlled drug delivery. First, we introduce cyclodextrin materials utilized for self-assembly. The fabrication technologies of supramolecular systems including nanoplatforms and hydrogels as well as their applications in nanomedicine and pharmaceutical sciences are then highlighted. At the end, the future directions of this field are discussed.

Multivalent glycoliposomes and micelles to study carbohydrate-protein and carbohydrate-carbohydrate interactions

This tutorial review describes multivalent carbohydrate-protein and carbohydrate-carbohydrate interaction studies that utilize self-assembled aggregates of thermodynamically stable liposomes and micelles. Strategies to prepare multivalent glycoliposomes and micelles include: (i) insertion of synthetic glycolipids into matrix lipids; (ii) preparation of glycolipids that aggregate to liposomes and micelles and (iii) modification of the hydrophilic surfaces with desired sugars. Several design strategies have been developed in order to obtain constituent glycolipids, having multivalent sugar moieties and their subsequent interactions with proteins were assessed in relation to the type of linkers that connect the hydrophilic and lipophilic segments. Lipophilic segments other than alkyl chains have also been developed. Polymer based glycoliposomes and micelles form an emphasis. Further, glycoliposomes facilitate studies of carbohydrate-carbohydrate interactions. An overview of the various types of glycoliposomes and micelles used to study carbohydrate-protein and carbohydrate-carbohydrate recognition phenomena is presented.

Cyclodextrin-based multivalent glycodisplays: covalent and supramolecular conjugates to assess carbohydrate-protein interactions

Covalent attachment of biorecognizable sugar ligands in several copies at precise positions of cyclomaltooligosaccharide (cyclodextrin, CD) macrocycles has proven to be an extremely flexible strategy to build multivalent conjugates. The commercial availability of the native CDs in three different sizes, their axial symmetry and the possibility of position- and face-selective functionalization allow a strict control of the valency and spatial orientation of the recognition motifs (glycotopes) in low, medium, high and hyperbranched glycoclusters, including glycodendrimer-CD hybrids. "Click-type" ligation chemistries, including copper(i)-catalyzed azide-alkyne cycloaddition (CuAAC), thiol-ene coupling or thiourea-forming reactions, have been implemented to warrant full homogeneity of the adducts. The incorporation of different glycotopes to investigate multivalent interactions in heterogeneous environments has also been accomplished. Not surprisingly, multivalent CD conjugates have been, and continue to be, major actors in studies directed at deciphering the structural features ruling carbohydrate recognition events. Nanometric glycoassemblies endowed with the capability of adapting the inter-saccharide distances and orientations in the presence of a receptor partner or capable of mimicking the fluidity of biological membranes have been conceived by multitopic inclusion complex formation, rotaxanation or self-assembling. Applications in the fields of sensors, site-specific drug and gene delivery or protein stabilization attest for the maturity of the field.

Multivalent ligand: design principle for targeted therapeutic delivery approach

Multivalent interactions of biological molecules play an important role in many biochemical events. A multivalent ligand comprises of multiple copies of ligands conjugated to scaffolds, allowing the simultaneous binding of multivalent ligands to multiple binding sites or receptors. Many research groups have successfully designed and synthesized multivalent ligands to increase the binding affinity, avidity and specificity of the ligand to the receptor. A multimeric ligand is a promising option for the specific treatment of diseases. In this review, the factors affecting multivalent interactions, including the size and shape of the ligand, geometry and an arrangement of ligands on the scaffold, linker length, thermodynamic, and kinetics of the interactions are discussed. Examples of the multivalent ligand applications for therapeutic delivery are also summarized.

Mannose-decorated cyclodextrin vesicles: The interplay of multivalency and surface density in lectin-carbohydrate recognition

Cyclodextrin vesicles are versatile models for biological cell membranes since they provide a bilayer membrane that can easily be modified by host–guest interactions with functional guest molecules. In this article, we investigate the multivalent interaction of the lectin concanavalin A (ConA) with cyclodextrin vesicles decorated with mannose–adamantane conjugates with one, two or three adamantane units as well as one or two mannose units. The carbohydrate–lectin interaction in this artificial, self-assembled glycocalyx was monitored in an agglutination assay by the increase of optical density at 400 nm. It was found that there is a close relation between the carbohydrate density at the cyclodextrin vesicle surface and the multivalent interaction with ConA, and the most efficient interaction (i.e., fastest agglutination at lowest concentration) was observed for mannose–adamantane conjugates, in which both the cyclodextrin–adamantane and the lectin–mannose interaction is inherently multivalent.

Targeted gene delivery to hepatocytes with galactosylated amphiphilic cyclodextrins

Objectives

Achieving targeted delivery of gene medicines is desirable to maximise activity. Here, galactosylated amphiphilic cyclodextrins (CDs) are examined in terms of their ability to transfect asialoglycoprotein receptor-bearing HepG2 cells.

Methods

Cationic amphiphilic CDs were synthesised as well as amphiphilic CDs bearing galactose-targeting ligands with different linker lengths. Binding of galactosylated CDs to a galactose-specific lectin was examined by surface plasmon resonance. CDs were formulated with and without the helper lipid DOPE and complexed with plasmid DNA. Transfection was evaluated by luciferase assay. Intracellular trafficking was assessed by confocal microscopy.

Key findings

Binding of targeted CDs to a galactose-specific lectin was achieved. Binding decreased with linker length between the galactosyl group and the CD core. Contrary to the lectin binding results, transfection levels increased with an increase in linker length from 7 atoms to 15. Compared to non-targeted formulations, a significant increase in transfection was observed only in the presence of the helper lipid DOPE. Confocal microscopy revealed that DOPE caused a pronounced effect on cellular distribution.

Conclusions

The galactose-targeting ligand induced substantial increases in transfection over non-targeted formulations when DOPE was included, indicating the potential for targeted gene delivery using CD-based delivery systems.

Site-selective modification of proteins for the synthesis of structurally defined multivalent scaffolds

A combination of classical site-directed mutagenesis, genetic code engineering and bioorthogonal reactions delivered a chemically modified barstar protein with one or four carbohydrates installed at specific residues. These protein conjugates were employed in multivalent binding studies, which support the use of proteins as structurally defined scaffolds for the presentation of multivalent ligands.

Multivalent interaction of cyclodextrin vesicles, carbohydrate guests, and lectins: a kinetic investigation

An artificial glycocalix self-assembles when unilamellar bilayer vesicles of amphiphilic β-cyclodextrins are decorated with maltose- and lactose-adamantane conjugates by host-guest interactions. The maltose-decorated vesicles aggregate in the presence of lectin concanavalin A whereas the lactose-decorated vesicles aggregate in the presence of lectin peanut agglutinin. The kinetics of the orthogonal multivalent interfacial interactions present in this ternary system of vesicles, carbohydrates, and lectins were studied by time-dependent measurements of the optical density at 400 nm. The average vesicle and vesicle aggregate sizes were monitored by dynamic light scattering. The aggregation process was evaluated as a function of lectin concentration, vesicle concentration, and surface coverage of the vesicles by the carbohydrate-adamantane conjugates. The initial rate of vesicle aggregation scales linearly with the lectin as well as the cyclodextrin vesicle concentration. Furthermore, each lectin requires a characteristic critical density of carbohydrates at the vesicle surface. These observations allow a prediction of the response of the ternary supramolecular system at different concentrations of its components. Also, the effective binding site separation in a multivalent receptor such as a multiple binding site protein can be accurately determined. This methodology can be extended to multivalent noncovalent interactions in other ligand-receptor systems at interfaces.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for the period 2005-2006

This review is the fourth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2006. The review covers fundamental studies, fragmentation of carbohydrate ions, method developments, and applications of the technique to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, glycated proteins, glycolipids from bacteria, glycosides, and various other natural products. There is a short section on the use of MALDI-TOF mass spectrometry for the study of enzymes involved in glycan processing, a section on industrial processes, particularly the development of biopharmaceuticals and a section on the use of MALDI-MS to monitor products of chemical synthesis of carbohydrates. Large carbohydrate-protein complexes and glycodendrimers are highlighted in this final section.

Poly-6-cationic amphiphilic cyclodextrins designed for gene delivery

A new series of amphiphilic cyclodextrins containing cationic groups at the 6-positions and alkyl or biolabile ester groups at the 2-positions has been synthesised. Selective 2-O-allylation followed by photochemical addition of lipophilic thiols made it possible to control lipophilicity in these mesomolecules and allow solubility and self-assembly in water. The cationic groups are cysteamine-derived, while the alkyl and ester groups are C(1)-C(16) and benzyl ester groups. This is a new general synthetic route to a potentially wide range of polycationic cyclodextrins capable of acting as gene delivery vectors by condensing DNA and forming liquid crystalline complexes with oligonucleotides.

Beyond molecular recognition: using a repulsive field to tune interfacial valency and binding specificity between adhesive surfaces

Surface-bound biomolecular fragments enable "smart" materials to recognize cells and other particles in applications ranging from tissue engineering and medical diagnostics to colloidal and nanoparticle assembly. Such smart surfaces are, however, limited in their design to biomolecular selectivity. This feature article demonstrates, using a completely nonbiological model system, how specificity can be achieved for particle (and cell) binding, employing surface designs where immobilized nanoscale adhesion elements are entirely nonselective. Fundamental principles are illustrated by a model experimental system where 11 nm cationic nanoparticles on a planar negative silica surface interact with flowing negative silica microspheres having 1.0 and 0.5 microm diameters. In these systems, the interfacial valency, defined as the number of cross-bonds needed to capture flowing particles, is tunable through ionic strength, which alters the range of the background repulsion and therefore the effective binding strength of the adhesive elements themselves. At high ionic strengths where long-range electrostatic repulsions are screened, single surface-bound nanoparticles capture microspheres, defining the univalent regime. At low ionic strengths, competing repulsions weaken the effective nanoparticle adhesion so that multiple nanoparticles are needed for microparticle capture. This article discusses important features of the univalent regime and then illustrates how multivalency produces interfacial-scale selectivity. The arguments are then generalized, providing a possible explanation for highly specific cell binding in nature, despite the degeneracy of adhesion molecules and cell types. The mechanism for the valency-related selectivity is further developed in the context of selective flocculation in the colloidal literature. Finally, results for multivalent binding are contrasted with the current thinking for interfacial design and the presentation of adhesion moieties on engineered surfaces.

Cyclodextrin-based aggregates and characterization by microscopy

Cyclodextrin-based aggregates have been widely investigated with microscopies such as STM, AFM, SEM, TEM, and fluorescent microscopy to obtain the direct morphology and structure of samples. In the present review, we discuss various types of cyclodextrin aggregates, that is, native and modified cyclodextrins, inclusion complexes and their aggregates of cyclodextrins, cyclodextrin rotaxanes and polyrotaxanes, cyclodextrin nanotubes and their secondary assembly, and other high-order aggregates of cyclodextrins. Especially, we focus on the use of microscopy to characterize above aggregates. The application of modern microscopy tools promotes the investigation on cyclodextrins.

Amphiphilic N-Glycosyl-thiocarbamoyl Cyclodextrins: Synthesis, Self-Assembly, and Fluorimetry of Recognition by Lens culinaris Lectin

Amphiphilic beta-cyclodextrins have been synthesized bearing hexylthio, dodecylthio, and hexadecylthio chains at the 6-positions and glycosylthiocarbamoyl-oligo(ethylene glycol) units at the 2-positions. The glycosyl residues (alpha-D-mannosyl and beta-L-fucosyl) are intended for cell-targeting. Self-assembly of these new amphiphilic glycosylated cyclodextrins in water to form vesicles was investigated by dynamic light scattering and transmission electron microscopy. Selective binding of the hexylthio assemblies to a protein receptor (Lens culinaris lectin) was confirmed by fluorescence spectroscopy.

One-pot regioselective synthesis of 2I,3I-O-(o-xylylene)-capped cyclomaltooligosaccharides: tailoring the topology and supramolecular properties of cyclodextrins

The alpha,alpha'-dibromo-o-xylylene cap has been installed at the secondary hydroxyls of a single glucopyranosyl residue in cyclodextrins in one pot and with total regioselectivity; the resulting cyclic ether acts as a removable hinge, allowing selective elaboration of the secondary face and modulating both the self-association and the inclusion capabilities of the hosts.

Bilayer vesicles of amphiphilic cyclodextrins: host membranes that recognize guest molecules

A family of amphiphilic cyclodextrins (6, 7) has been prepared through 6-S-alkylation (alkyl=n-dodecyl and n-hexadecyl) of the primary side and 2-O-PEGylation of the secondary side of alpha-, beta-, and gamma-cyclodextrins (PEG=poly(ethylene glycol)). These cyclodextrins form nonionic bilayer vesicles in aqueous solution. The bilayer vesicles were characterized by transmission electron microscopy, dynamic light scattering, dye encapsulation, and capillary electrophoresis. The molecular packing of the amphiphilic cyclodextrins was investigated by using small-angle X-ray diffraction of bilayers deposited on glass and pressure-area isotherms obtained from Langmuir monolayers on the air-water interface. The bilayer thickness is dependent on the chain length, whereas the average molecular surface area scales with the cyclodextrin ring size. The alkyl chains of the cyclodextrins in the bilayer are deeply interdigitated. Molecular recognition of a hydrophobic anion (adamantane carboxylate) by the cyclodextrin vesicles was investigated by using capillary electrophoresis, thereby exploiting the increase in electrophoretic mobility that occurs when the hydrophobic anions bind to the nonionic cyclodextrin vesicles. It was found that in spite of the presence of oligo(ethylene glycol) substituents, the beta-cyclodextrin vesicles retain their characteristic affinity for adamantane carboxylate (association constant K(a)=7.1 x 10(3) M(-1)), whereas gamma-cyclodextrin vesicles have less affinity (K(a)=3.2 x 10(3) M(-1)), and alpha-cyclodextrin or non-cyclodextrin, nonionic vesicles have very little affinity (K(a) approximately 100 M(-1)). Specific binding of the adamantane carboxylate to beta-cyclodextrin vesicles was also evident in competition experiments with beta-cyclodextrin in solution. Hence, the cyclodextrin vesicles can function as host bilayer membranes that recognize small guest molecules by specific noncovalent interaction.

Cyanovirin-N binding to Manalpha1-2Man functionalized dendrimers

Manalpha1-2Man functionalized G(3) and G(4)-PAMAM dendrimers have been synthesized and characterized by MALDI-TOF MS and NMR spectroscopy. Precipitation assays to assess the binding of the dimannose-functionalized dendrimers to Cyanovirin-N, a HIV-inactivating protein that blocks virus-to-cell fusion through high mannose mediated interactions, are presented.

Amphiphilic Cyclodextrin Carriers Embedding Porphyrins: Charge and Size Modulation of Colloidal Stability in Heterotopic Aggregates

The interaction between the anionic 5,10,15,20-tetrakis(4-sulfonatophenyl)-21H,23H-porphyrin (TPPS) and cationic vesicles formed by heptakis(2-omega-amino-O-oligo(ethylene oxide)-6-hexylthio)-beta-cyclodextrin (SC6CDNH2) has been investigated in detail through a combination of elastic light scattering (ELS), quasi-elastic light scattering (QELS), zeta potential measurements, and time-resolved fluorescence anisotropy. ELS experiments provided the first structural characterization of these cationic vesicles both in the absence and in the presence of TPPS porphyrin, modeling the system as a spherical particle described by a single thin shell form factor. The structure of mixed hetero-aggregates is modulated by charge and size of the two components as function of different porphyrin/cyclodextrin (CD) molar ratios. At the limiting molar ratio studied, the absolute value of zeta potential (/zeta/ = 12.5 mV) seems to be a reference value for the formation of stable colloidal CD vesicular aggregates at thermodynamic equilibrium. New insights on the structure of these heterotopic colloids have been obtained by analysis of rotational correlation times at different molar ratios exploiting time-resolved fluorescence anisotropy experiments. At high porphyrin loads, the anisotropy decays behave as monoexponentials and the rotational correlation times (1-2 ns) together with the r(0) values close to zero suggest the presence of small amounts of TPPS embedded in a hydrophobic environment either in monomeric or in aggregated form. At the lower porphyrin/CD molar ratios, the anisotropy decays exhibit a double-exponential behavior showing a predominant component with a slow rotational correlation time (20-25 ns) and limiting anisotropy values of approximately 0.15. This component has been assigned to molecules that are more stabilized onto the CD vesicles, that is, porphyrins embedded into the oligo-ethylene "wall" of the CD vesicles. Scanning near-field optical microscopy of the samples evaporated on glass surfaces gave further insights on the morphology and optical properties of these systems, confirming the embedding of TPPS on the vesicles and evidencing the role of the solvent.

Survey of the year 2004 commercial optical biosensor literature

The year 2004 represents a milestone for the biosensor research community: in this year, over 1000 articles were published describing experiments performed using commercially available systems. The 1038 papers we found represent an approximately 10% increase over the past year and demonstrate that the implementation of biosensors continues to expand at a healthy pace. We evaluated the data presented in each paper and compiled a 'top 10' list. These 10 articles, which we recommend every biosensor user reads, describe well-performed kinetic, equilibrium and qualitative/screening studies, provide comparisons between binding parameters obtained from different biosensor users, as well as from biosensor- and solution-based interaction analyses, and summarize the cutting-edge applications of the technology. We also re-iterate some of the experimental pitfalls that lead to sub-optimal data and over-interpreted results. We are hopeful that the biosensor community, by applying the hints we outline, will obtain data on a par with that presented in the 10 spotlighted articles. This will ensure that the scientific community at large can be confident in the data we report from optical biosensors.

EPR and affinity studies of mannose-TEMPO functionalized PAMAM dendrimers

Mannose-TEMPO functionalized G4-PAMAM dendrimers with increasing mannose loadings have been synthesized and characterized by MALDI-TOF MS and EPR spectroscopy. Analysis of linebroadening effects in the EPR spectra of these dendrimers allowed us to determine the relative presentation of mannose and TEMPO on the dendrimer surface. Hemagglutination assays and affinity chromatography/EPR experiments to assess the activity of the mannose-TEMPO dendrimers with Concanavalin A are presented.