Syntheses and some applications of chemically defined multivalent glycoconjugates

Validation of Selective Capture of Fimbriated Uropathogenic Escherichia coli by a Label-free Engineering Detection System Using Mannosylated Surfaces

Label-free detection of pathogens is of major concern to the microbiologist community. Most procedures require several steps and amplification techniques. Carbohydrates are well-established receptors for host-pathogen interactions, which can be amplified using glycodendritic architectures on the basis of multivalent binding interactions. Given that uropathogenic Escherichia coli bacterial FimH is based on such mannopyranoside-binding interactions, we demonstrate herein that synthetic monomeric and trimeric thiolated α-d-mannosides can be effectively bound to gold substrate-functionalized self-assembled monolayers (SAMs) preactivated with maleimide functionalities. Mannosides grafted onto SAMs were followed using Quartz Crystal Microbalance with Dissipation (QCM-D). Binding recognition efficiency was first evaluated using the plant lectin from Canavalia ensiformis (ConA) also using QCM-D. We showed a direct correlation between the amount of mannoside bound and the lectin attachment. Even though there was less trimer bound (nM/cm²) to the surface, we observed a 7-fold higher amount of lectin anchoring, thus further demonstrating the value of the multivalent interactions. We next examined the relative fimbriated E. coli selective adhesion/capture to either the monomeric or the trimeric mannoside bound to the surface. Our results established the successful engineering of the surfaces to show E. coli adhesion via specific mannopyranoside binding but unexpectedly, the monomeric derivative was more efficient than the trimeric analog, which could be explained by steric hindrance. This approach strongly suggests that it could be broadly applicable to other Gram-negative bacteria sharing analogous carbohydrate-dependent binding interactions.

Progress in Antiviral Fullerene Research

Unlike traditional small molecule drugs, fullerene is an all-carbon nanomolecule with a spherical cage structure. Fullerene exhibits high levels of antiviral activity, inhibiting virus replication in vitro and in vivo. In this review, we systematically summarize the latest research regarding the different types of fullerenes investigated in antiviral studies. We discuss the unique structural advantage of fullerenes, present diverse modification strategies based on the addition of various functional groups, assess the effect of structural differences on antiviral activity, and describe the possible antiviral mechanism. Finally, we discuss the prospective development of fullerenes as antiviral drugs.

General Strategies for Glycan Microarray Data Processing and Analysis

Glycan microarrays provide a high-throughput technology for rapidly profiling interactions between carbohydrates and glycan-binding proteins (GBPs). Use of glycan microarrays involves several general steps, including construction of the microarray, carrying out the assay, detection of binding events, and analysis of the results. While multiple platforms have been developed to construct microarrays, most utilize fluorescence for detection of binding events. This chapter describes methods to acquire and process microarray images, including generating GAL files, imaging of the slide, aligning the grid, detecting problematic spots, and evaluating the quality of the data. The chapter focuses on processing our neoglycoprotein microarrays, but many of the lessons we have learned are applicable to other array formats.

Design, Synthetic Strategies, and Therapeutic Applications of Heterofunctional Glycodendrimers

Glycodendrimers have attracted considerable interest in the field of dendrimer sciences owing to their plethora of implications in biomedical applications. This is primarily due to the fact that cell surfaces expose a wide range of highly diversified glycan architectures varying by the nature of the sugars, their number, and their natural multiantennary structures. This particular situation has led to cancer cell metastasis, pathogen recognition and adhesion, and immune cell communications that are implicated in vaccine development. The diverse nature and complexity of multivalent carbohydrate-protein interactions have been the impetus toward the syntheses of glycodendrimers. Since their inception in 1993, chemical strategies toward glycodendrimers have constantly evolved into highly sophisticated methodologies. This review constitutes the first part of a series of papers dedicated to the design, synthesis, and biological applications of heterofunctional glycodendrimers. Herein, we highlight the most common synthetic approaches toward these complex molecular architectures and present modern applications in nanomolecular therapeutics and synthetic vaccines.

Recent development in the design of small 'drug-like' and nanoscale glycomimetics against Escherichia coli infections

Glycoconjugates are involved in several pathological processes. Glycomimetics that can favorably emulate complex carbohydrate structures, while competing with natural ligands as inhibitors, are gaining considerable attention owing to their improved hydrolytic stability, binding affinity, and pharmacokinetic (PK) properties. Of particular interest are the families of α-d-mannopyranoside analogs, which can be used as inhibitors against adherent invasive Escherichia coli infections. Bacterial resistance to modern antibiotics triggers the search for new alternative antibacterial strategies that are less susceptible to acquiring resistance. In this review, we highlight recent progress in the chemical syntheses of this family of compounds, one of which having reached clinical trials against Crohn's disease (CD).

Polymer Stiffness Regulates Multivalent Binding and Liquid-Liquid Phase Separation

Multivalent binding is essential to many biological processes because it builds high-affinity bonds by using several weak binding interactions simultaneously. Multivalent polymers have shown promise as inhibitors of toxins and other pathogens, and they are important components in the formation of biocondensates. Explaining how structural features of these polymers change their binding and subsequent control of phase separation is critical to designing better pathogen inhibitors and also to understanding diseases associated with membraneless organelles. In this work, we will examine the binding of a multivalent polymer to a small target. This scenario could represent a polymeric inhibitor binding to a toxic protein or RNA binding to an RNA-binding protein in the case of liquid-liquid phase separation. We use simulation and theory to show that flexible random-coil polymers bind more strongly than stiff rod-like polymers and that flexible polymers nucleate condensed phases at lower binding energies than their rigid analogs. We hope these results will provide insight into the rational design of polymeric inhibitors and improve our understanding of phase separation in cells and membraneless organelles.

Aberrant glycosylation patterns on cancer cells: Therapeutic opportunities for glycodendrimers/metallodendrimers oncology

Despite exciting discoveries and progresses in drug design against cancer, its cure is still rather elusive and remains one of the humanities major challenges in health care. The safety profiles of common small molecule anti-cancer therapeutics are less than at acceptable levels and limiting deleterious side-effects have to be urgently addressed. This is mainly caused by their incapacity to differentiate healthy cells from cancer cells; hence, the use of high dosage becomes necessary. One possible solution to improve the therapeutic windows of anti-cancer agents undoubtedly resides in modern nanotechnology. This review presents a discussion concerning multivalent carbohydrate-protein interactions as this topic pertains to the fundamental aspects that lead glycoscientists to tackle glyconanoparticles. The second section describes the detailed properties of cancer cells and how their aberrant glycan surfaces differ from those of healthy cells. The third section briefly describes the immune systems, both innate and adaptative, because the numerous displays of cell surface protein receptors necessitate to be addressed from the multivalent angles, a strength full characteristic of nanoparticles. The next chapter presents recent advances in glyconanotechnologies, including glycodendrimers in particular, as they apply to glycobiology and carbohydrate-based cancer vaccines. This was followed by an overview of metallodendrimers and how this rapidly evolving field may contribute to our arsenal of therapeutic tools to fight cancer. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Influence of Binding Site Affinity Patterns on Binding of Multivalent Polymers

Using inspiration from biology, we can leverage multivalent binding interactions to enhance weak, monovalent binding between molecules. While most previous studies have focused on multivalent binders with uniform binding sites, new synthetic polymers might find it desirable to have multiple binding moieties along the chain. Here, we probe how patterning of heterogeneous binding sites along a polymer chain controls the binding affinity of a polymer using a reactive Brownian dynamics scheme. Unlike monovalent binders that are pattern-agnostic, we find that divalent binding is dependent on both the polymer pattern and binding target concentration. For dilute targets, blocky polymers provide high local concentrations of high-affinity sites, but at high target concentrations, competition for binding sites makes alternating polymers the strongest binders. Subsequently, we show that random copolymers are robust to target concentration fluctuations. These results will assist in the rational design of multivalent polymer therapeutics and materials.

Controlled polymerization for the development of bioconjugate polymers and materials

Conjugates of various biopolymers with synthetic polymers were preparedvialiving radical polymerization. The conjugates have precise structures and potential for novel biofunctional materials.

Computational Insights into Avidity of Polymeric Multivalent Binders

Multivalent binding interactions are commonly found throughout biology to enhance weak monovalent binding such as between glycoligands and protein receptors. Designing multivalent polymers to bind to viruses and toxic proteins is a promising avenue for inhibiting their attachment and subsequent infection of cells. Several studies have focused on oligomeric multivalent inhibitors and how changing parameters such as ligand shape, size, linker length, and flexibility affect binding. However, experimental studies of how larger structural parameters of multivalent polymers, such as degree of polymerization, affect binding avidity to targets have mixed results, with some finding an improvement with longer polymers and some finding no effect. Here, we use Brownian dynamics simulations to provide a theoretical understanding of how the degree of polymerization affects the binding avidity of multivalent polymers. We show that longer polymers increase binding avidity to multivalent targets but reach a limit in binding avidity at high degrees of polymerization. We also show that when interacting with multiple targets simultaneously, longer polymers are able to use intertarget interactions to promote clustering and improve binding efficiency. We expect our results to narrow the design space for optimizing the structure and effectiveness of multivalent inhibitors as well as be useful to understand biological design strategies for multivalent binding.

Effect of Dendrimer Generation and Aglyconic Linkers on the Binding Properties of Mannosylated Dendrimers Prepared by a Combined Convergent and Onion Peel Approach

An efficient study of carbohydrate-protein interactions was achieved using multivalent glycodendrimer library. Different dendrimers with varied peripheral sugar densities and linkers provided an arsenal of potential novel therapeutic agents that could be useful for better specific action and greater binding affinities against their cognate protein receptors. Highly effective click chemistry represents the basic method used for the synthesis of mannosylated dendrimers. To this end, we used propargylated scaffolds of varying sugar densities ranging from 2 to 18 for the attachment of azido mannopyranoside derivatives using copper catalyzed click cycloaddition. Mannopyranosides with short and pegylated aglycones were used to evaluate their effects on the kinetics of binding. The mannosylated dendrons were built using varied scaffolds toward the accelerated and combined "onion peel" strategy These carbohydrates have been designed to fight E. coli urinary infections, by inhibiting the formation of bacterial biofilms, thus neutralizing the adhesion of FimH type 1 lectin present at the tip of their fimbriae against the natural multiantennary oligomannosides of uroplakin 1a receptors expressed on uroepithelial tissues. Preliminary DLS studies of the mannosylated dendrimers to cross- link the leguminous lectin Con A used as a model showed their high potency as candidates to fight the E. coli adhesion and biofilm formation.

Designing the new generation of intelligent biocompatible carriers for protein and peptide delivery

Therapeutic proteins and peptides have revolutionized treatment for a number of diseases, and the expected increase in macromolecule-based therapies brings a new set of challenges for the pharmaceutics field. Due to their poor stability, large molecular weight, and poor transport properties, therapeutic proteins and peptides are predominantly limited to parenteral administration. The short serum half-lives typically require frequent injections to maintain an effective dose, and patient compliance is a growing issue as therapeutic protein treatments become more widely available. A number of studies have underscored the relationship of subcutaneous injections with patient non-adherence, estimating that over half of insulin-dependent adults intentionally skip injections. The development of oral formulations has the potential to address some issues associated with non-adherence including the interference with daily activities, embarrassment, and injection pain. Oral delivery can also help to eliminate the adverse effects and scar tissue buildup associated with repeated injections. However, there are several major challenges associated with oral delivery of proteins and peptides, such as the instability in the gastrointestinal (GI) tract, low permeability, and a narrow absorption window in the intestine. This review provides a detailed overview of the oral delivery route and associated challenges. Recent advances in formulation and drug delivery technologies to enhance bioavailability are discussed, including the co-administration of compounds to alter conditions in the GI tract, the modification of the macromolecule physicochemical properties, and the use of improved targeted and controlled release carriers.

Recent Advances in the Chemistry of Glycoconjugate Amphiphiles

Glyconanoparticles essentially result from the (covalent or noncovalent) association of nanometer-scale objects with carbohydrates. Such glyconanoparticles can take many different forms and this mini review will focus only on soft materials (colloids, liposomes, gels etc.) with a special emphasis on glycolipid-derived nanomaterials and the chemistry involved for their synthesis. Also this contribution presents Low Molecular Weight Gels (LMWGs) stabilized by glycoconjugate amphiphiles. Such soft materials are likely to be of interest for different biomedical applications.

A glycoporphyrin story: from chemistry to PDT treatment of cancer mouse models

Glycoporphyrin: from bench to preclinical studies on PDX xenografted on mice.

Towards carborane-functionalised structures for the treatment of brain cancer

Boron neutron capture therapy (BNCT) is a promising targeted chemoradiotherapeutic technique for the management of invasive brain tumors, such as glioblastoma multiforme (GBM). A prerequisite for effective BNCT is the selective targeting of tumour cells with ¹⁰B-rich therapeutic moieties. To this end, polyhedral boranes, especially carboranes, have received considerable attention because they combine a high boron content with relative low toxicity and metabolic inertness. Here, we review progress in the molecular design of recently investigated carborane derivatives in light of the widely accepted performance requirements for effective BNCT.

“Onion peel” glycodendrimer syntheses using mixed triazine and cyclotriphosphazene scaffolds

An expeditious synthetic protocol for the construction of glycodendrimers is illustrated using the newly discovered “onion peel” strategy. The onion peel approach and orthogonal coupling strategies were accomplished with rationally design sequential modifications of cyanuric acid. Carefully chosen building blocks and their effective attachment by chemoselective atom economical click reactions, namely Cu (I) azide–alkyne cycloaddition reaction (CuAAC) and photocatalyzed thiol-ene reaction (TEC), allowed rapid build-up of glycodendrimers in contrast to traditional dendrimers syntheses that are based on the repetitive use of identical building blocks to form each layer. The newly formed glycodendrimers were evaluated for their capacity to cross-link carbohydrate-lectin interactions using dynamic light scattering (DLS). Rapid increase in particle size was observed as a function of time when compared to their monomer counterparts resulting from the multivalent lectin cross-linking ability of the new glycodendrimers.

Development and validation of a Luminex assay for detection of a predictive biomarker for PROSTVAC-VF therapy

Cancer therapies can provide substantially improved survival in some patients while other seemingly similar patients receive little or no benefit. Strategies to identify patients likely to respond well to a given therapy could significantly improve health care outcomes by maximizing clinical benefits while reducing toxicities and adverse effects. Using a glycan microarray assay, we recently reported that pretreatment serum levels of IgM specific to blood group A trisaccharide (BG-A_tri) correlate positively with overall survival of cancer patients on PROSTVAC-VF therapy. The results suggested anti-BG-A_tri IgM measured prior to treatment could serve as a biomarker for identifying patients likely to benefit from PROSTVAC-VF. For continued development and clinical application of serum IgM specific to BG-A_tri as a predictive biomarker, a clinical assay was needed. In this study, we developed and validated a Luminex-based clinical assay for measuring serum IgM specific to BG-A_tri. IgM levels were measured with the Luminex assay and compared to levels measured using the microarray for 126 healthy individuals and 77 prostate cancer patients. This assay provided reproducible and consistent results with low %CVs, and tolerance ranges were established for the assay. IgM levels measured using the Luminex assay were found to be highly correlated to the microarray results with R values of 0.93–0.95. This assay is a Laboratory Developed Test (LDT) and is suitable for evaluating thousands of serum samples in CLIA certified laboratories that have validated the assay. In addition, the study demonstrates that discoveries made using neoglycoprotein-based microarrays can be readily migrated to a clinical assay.

Mimicking Complex Biological Membranes and Their Programmable Glycan Ligands with Dendrimersomes and Glycodendrimersomes

Synthetic vesicles have been assembled and coassembled from phospholipids, their modified versions, and other single amphiphiles into liposomes, and from block copolymers into polymersomes. Their time-consuming synthesis and preparation as stable, monodisperse, and biocompatible liposomes and polymersomes called for the elaboration of new synthetic methodologies. Amphiphilic Janus dendrimers (JDs) and glycodendrimers (JGDs) represent the most recent self-assembling amphiphiles capable of forming monodisperse, stable, and multifunctional unilamellar and multilamellar onion-like vesicles denoted dendrimersomes (DSs) and glycodendrimersomes (GDSs), dendrimercubosomes (DCs), glycodendrimercubosomes (GDCs), and other complex architectures. Amphiphilic JDs consist of hydrophobic dendrons connected to hydrophilic dendrons and can be thought of as monodisperse oligomers of a single amphiphile. They can be functionalized with a variety of molecules such as dyes, and, in the case of JGDs, with carbohydrates. Their iterative modular synthesis provides efficient access to sequence control at the molecular level, resulting in topologies with specific epitope sequence and density. DSs, GDSs, and other architectures from JDs and JGDs serve as powerful tools for mimicking biological membranes and for biomedical applications such as targeted drug and gene delivery and theranostics. This Review covers all aspects of the synthesis of JDs and JGDs and their biological activity and applications after assembly in aqueous media.

Dual-Targeted Multifunctional Nanoparticles for Magnetic Resonance Imaging Guided Cancer Diagnosis and Therapy

Hybrid nanostructures with combined functionalities can be rationally designed to achieve synergistic effects for efficient cancer treatment. Herein, a multifunctional nanoplatform is constructed, containing an inner core of an anticancer drug MTX surrounding by a nanometer-thin layer of gold as the shell with Fe₃O₄ magnetic nanoparticles (NPs) evenly distributed in the gold layer, and the outermost hybrid LA-PEG-MTX molecules as surface coating agent (denoted as MFG-LPM NPs). This nanocomposite possesses very high drug loading capacity as the entire core is MTX and integrates magnetic- and active- targeting drug delivery, light-controlled drug release, magnetic resonance imaging (MRI), as well as photothermal and chemotherapy. With a strong near-infrared (NIR) absorbance at 808 nm, the nanocomposite enables temperature elevation and light-triggered MTX release. In vitro cytotoxicity studies indicate that the strategy of combining therapy leads to a synergistic effect with high cancer cell killing efficacy. In consistency with this, due to the high accumulation of MFG-LPM NPs at tumor site and their combinatorial chemo-photothermal effects, 100% in vivo tumor elimination can be achieved. Additionally, in vivo MRI of tumor-bearing mice demonstrates an impressive performance of MFG-LPM NPs as a T₂ contrast agent. Therefore, such multifunctional nanocomposite has the potential to serve as an excellent theranostic agent that collectively integrates multiple functions for efficient MRI guided cancer diagnosis and treatment.

Application of nanotechnology for the development of microbicides

The vaginal route is increasingly being considered for both local and systemic delivery of drugs, especially those unsuitable for oral administration. One of the opportunities offered by this route but yet to be fully utilised is the administration of microbicides. Microbicides have an unprecedented potential for mitigating the global burden from HIV infection as heterosexual contact accounts for most of the new infections occurring in sub-Saharan Africa, the region with the highest prevalent rates. Decades of efforts and massive investment of resources into developing an ideal microbicide have resulted in disappointing outcomes, as attested by several clinical trials assessing the suitability of those formulated so far. The highly complex and multi-level biochemical interactions that must occur among the virus, host cells and the drug for transmission to be halted means that a less sophisticated approach to formulating a microbicide e.g. conventional gels, etc may have to give way for a different formulation approach. Nanotechnology has been identified to offer prospects for fabricating structures with high capability of disrupting HIV transmission. In this review, predominant challenges seen in microbicide development have been highlighted and possible ways of surmounting them suggested. Furthermore, formulations utilising some of these highly promising nanostructures such as liposomes, nanofibres and nanoparticles have been discussed. A perspective on how a tripartite collaboration among governments and their agencies, the pharmaceutical industry and academic scientists to facilitate the development of an ideal microbicide in a timely manner has also been briefly deliberated.

Heterolayered hybrid dendrimers with optimized sugar head groups for enhancing carbohydrate–protein interactions

Novel heterolayered (“onion peel”) hybrid glycodendrimers containing optimised sugar head groups with galactoside and mannoside units with affinities for two different lectins.

Light-controlled active release of photocaged ciprofloxacin for lipopolysaccharide-targeted drug delivery using dendrimer conjugates

We report an active delivery mechanism targeted specifically to Gram(-) bacteria based on the photochemical release of photocaged ciprofloxacin carried by a cell wall-targeted dendrimer nanoconjugate.

ATP dephosphorylation can be either enhanced or inhibited by pH-controlled interaction with a dendrimer molecule

Synthetic polyammonium/polyamine receptors are known to enhance ATP dephosphorylation in solution. ATP interaction with a G-3 poly(ethylene imine) dendrimer shows an unprecedented behaviour, the dendrimer catalyst being able to enhance or inhibit dephosphorylation of the nucleotide depending on the solution pH.

Force spectroscopy of multivalent binding of riboflavin-conjugated dendrimers to riboflavin binding protein

Putative riboflavin receptors are considered as biomarkers due to their overexpression in breast and prostate cancers. Hence, these receptors can be potentially exploited for use in targeted drug delivery systems where dendrimer nanoparticles with multivalent ligand attachments can lead to greater specificity in cellular interactions. In this study, the single molecule force spectroscopy technique was used to assess the physical strength of multivalent interactions by employing a riboflavin (RF)-conjugated generation 5 PAMAM dendrimer G5(RF)n nanoparticle. By varying the average RF ligand valency (n = 0, 3, 5), the rupture force was measured between G5(RF)n and the riboflavin binding protein (RFBP). The rupture force increased when the valency of RF increased. We observed at the higher valency (n = 5) three binding events that increased in rupture force with increasing loading rate. Assuming a single energy barrier, the Bell-Evans model was used to determine the kinetic off-rate and barrier width for all binding interactions. The analysis of our results appears to indicate that multivalent interactions are resulting in changes to rupture force and kinetic off-rates.

A fast track strategy toward highly functionalized dendrimers with different structural layers: an “onion peel approach”

A novel strategy is described for the rapid syntheses of polyhydroxylated dendrimers in which the layer by layer building blocks are different from one another. The resulting dendrimers showed no cytotoxicity.

Multifaceted glycodendrimers with programmable bioactivity through convergent, divergent, and accelerated approaches using polyfunctional cyclotriphosphazenes

The cyclotriphosphazene-based platform facilitates versatile synthesis of glycodendrimers active as inhibitors of two biomedically relevant lectins.

Glyconanosynthons as powerful scaffolds and building blocks for the rapid construction of multifaceted, dense and chiral dendrimers

The arsenal of available carbohydrates can be manipulated to provide versatile building blocks toward the syntheses of complex and chiral dendrimers.

Acyclic tethers mimicking subunits of polysaccharide ligands: selectin antagonists

We report on the design and synthesis of molecules having E- and P-selectins blocking activity both in vitro and in vivo. The GlcNAc component of the selectin ligand sialyl Lewis(X) was replaced by an acyclic tether that links two saccharide units. The minimization of intramolecular dipole-dipole interactions and the gauche effect would be at the origin of the conformational bias imposed by this acyclic tether. The stereoselective synthesis of these molecules, their biochemical and biological evaluations using surface plasmon resonance spectroscopy (SPR), and in vivo assays are described. Because the structure of our analogues differs from the most potent E-selectin antagonists reported, our acyclic analogues offer new opportunities for chemical diversity.

Expeditive synthesis of trithiotriazine-cored glycoclusters and inhibition of Pseudomonas aeruginosa biofilm formation

Readily accessible, low-valency glycoclusters based on a triazine core bearing D-galactose and L-fucose epitopes are able to inhibit biofilm formation by Pseudomonas aeruginosa. These multivalent ligands are simple to synthesize, are highly soluble, and can be either homofunctional or heterofunctional. The galactose-decorated cluster shows good affinity for Pseudomonas aeruginosa lectin lecA. They are convenient biological probes for investigating the roles of lecA and lecB in biofilm formation.

Synthesis and solvodynamic diameter measurements of closely related mannodendrimers for the study of multivalent carbohydrate-protein interactions

This paper describes the synthesis of three closely related families of mannopyranoside-containing dendrimers for the purpose of studying subtle structural parameters involved in the measurements of multivalent carbohydrate-protein binding interactions. Toward this goal, two trimers 5 and 9, three 9-mers 12, 17, 21, and one 27-mer 23, varying by the number of atoms separating the anomeric and the core carbons, were synthesized using azide-alkyne cycloaddition (CuAAc). Compound 23 was prepared by an efficient convergent strategy. The sugar precursors consisted of either a 2-azidoethyl (3) or a prop-2-ynyl α-D-mannopyranoside (7) derivative. The solvodynamic diameters of 9-mer 12, 17, and 21 were determined by pulsed-field-gradient-stimulated echo (PFG-STE) NMR experiments and were found to be 3.0, 2.5, and 3.4 nm, respectively.

Aromatic thioglycoside inhibitors against the virulence factor LecA from Pseudomonas aeruginosa

Three small families of hydrolytically stable thioaryl glycosides were prepared as inhibitors of the LecA (PA-IL) virulence factor corresponding to the carbohydrate binding lectin from the bacterial pathogen Pseudomonas aeruginosa. The monosaccharidic arylthio β-d-galactopyranosides served as a common template for the major series that was also substituted at the O-3 position. Arylthio disaccharides from lactose and from melibiose constituted the other two series members. In spite of the fact that the natural ligand for LecA is a glycolipid of the globotriaosylceramide having an α-d-galactopyranoside epitope, this study illustrated that the β-d-galactopyranoside configuration having a hydrophobic aglycon could override the requirement toward the anomeric configuration of the natural sugar. The enzyme linked lectin assay together with isothermal titration microcalorimetry established that naphthyl 1-thio-β-d-galactopyranoside () gave the best inhibition with an IC50 twenty-three times better than that of the reference methyl α-d-galactopyranoside. In addition it showed a KD of 6.3 μM which was ten times better than that of the reference compound. The X-ray crystal structure of LecA with was also obtained.

A highly versatile convergent/divergent “onion peel” synthetic strategy toward potent multivalent glycodendrimers

Both convergent and divergent strategies for the synthesis of “onion peel” glycodendrimers are reported which resulted in one of the best multivalent ligands known against the virulent factor from a bacterial lectin isolated from Pseudomonas aeruginosa.

“Onion peel” dendrimers: a straightforward synthetic approach towards highly diversified architectures

We report herein a novel “onion peel strategy” for the divergent construction of glycodendrimers using different building blocks at each layer of the dendritic growth.

Modulation of glycan recognition by clustered saccharide patches

All cells in nature are covered with a dense and complex array of glycan chains. Specific recognition and binding of glycans is a critical aspect of cellular interactions, both within and between species. Glycan-protein interactions tend to be of low affinity but high specificity, typically utilizing multivalency to generate the affinity required for biologically relevant binding. This review focuses on a higher level of glycan organization, the formation of clustered saccharide patches (CSPs), which can constitute unique ligands for highly specific interactions. Due to technical challenges, this aspect of glycan recognition remains poorly understood. We present a wealth of evidence for CSPs-mediated interactions, and discuss recent advances in experimental tools that are beginning to provide new insights into the composition and organization of CSPs. The examples presented here are likely the tip of the iceberg, and much further work is needed to elucidate fully this higher level of glycan organization.

Avidity modulation of folate-targeted multivalent dendrimers for evaluating biophysical models of cancer targeting nanoparticles

We investigated two types of generation 5 polyamidoamine (PAMAM) dendrimers, each conjugated stochastically with a mean number of 5 or 10 methotrexate (MTX) ligands per dendrimer (G5-MTX5, G5-MTX10), for their binding to surface-immobilized folate binding protein (FBP) as a function of receptor density. The binding study was performed under flow by surface plasmon resonance spectroscopy. Two multivalent models were examined to simulate binding of the dendrimer to the receptor surface, showing that at relatively high receptor density, both dendrimer conjugates exhibit high avidity. However, upon reducing the receptor density by a factor of 3 and 13 relative to the high density level, the avidity of the lower-valent G5-MTX5 decreases by up to several orders of magnitude (KD = nM to μM), whereas the avidity of G5-MTX10 remains largely unaffected regardless of the density variation. Notably, on the 13-fold reduced FBP surface, G5-MTX5 displays binding kinetics similar to that of monovalent methotrexate, which is patently different from the still tight binding of the higher-valent G5-MTX10. Thus, the binding analysis demonstrates that avidity displayed by multivalent MTX conjugates varies in response to the receptor density and can be modulated for achieving tighter, more specific binding to the higher receptor density by modulation of ligand valency. We believe this study provides experimental evidence supportive of the mechanistic hypothesis of multivalent NP uptake to a cancer cell over a healthy cell where the diseased cell expresses the folate receptor at higher density.

Modular synthesis of amphiphilic Janus glycodendrimers and their self-assembly into glycodendrimersomes and other complex architectures with bioactivity to biomedically relevant lectins

The modular synthesis of 7 libraries containing 51 self-assembling amphiphilic Janus dendrimers with the monosaccharides D-mannose and D-galactose and the disaccharide D-lactose in their hydrophilic part is reported. These unprecedented sugar-containing dendrimers are named amphiphilic Janus glycodendrimers. Their self-assembly by simple injection of THF or ethanol solution into water or buffer and by hydration was analyzed by a combination of methods including dynamic light scattering, confocal microscopy, cryogenic transmission electron microscopy, Fourier transform analysis, and micropipet-aspiration experiments to assess mechanical properties. These libraries revealed a diversity of hard and soft assemblies, including unilamellar spherical, polygonal, and tubular vesicles denoted glycodendrimersomes, aggregates of Janus glycodendrimers and rodlike micelles named glycodendrimer aggregates and glycodendrimermicelles, cubosomes denoted glycodendrimercubosomes, and solid lamellae. These assemblies are stable over time in water and in buffer, exhibit narrow molecular-weight distribution, and display dimensions that are programmable by the concentration of the solution from which they are injected. This study elaborated the molecular principles leading to single-type soft glycodendrimersomes assembled from amphiphilic Janus glycodendrimers. The multivalency of glycodendrimersomes with different sizes and their ligand bioactivity were demonstrated by selective agglutination with a diversity of sugar-binding protein receptors such as the plant lectins concanavalin A and the highly toxic mistletoe Viscum album L. agglutinin, the bacterial lectin PA-IL from Pseudomonas aeruginosa, and, of special biomedical relevance, human adhesion/growth-regulatory galectin-3 and galectin-4. These results demonstrated the candidacy of glycodendrimersomes as new mimics of biological membranes with programmable glycan ligand presentations, as supramolecular lectin blockers, vaccines, and targeted delivery devices.

Carbohydrate microarrays

In the last decade, carbohydrate microarrays have been core technologies for analyzing carbohydrate-mediated recognition events in a high-throughput fashion. A number of methods have been exploited for immobilizing glycans on the solid surface in a microarray format. This microarray-based technology has been widely employed for rapid analysis of the glycan binding properties of lectins and antibodies, the quantitative measurements of glycan-protein interactions, detection of cells and pathogens, identification of disease-related anti-glycan antibodies for diagnosis, and fast assessment of substrate specificities of glycosyltransferases. This review covers the construction of carbohydrate microarrays, detection methods of carbohydrate microarrays and their applications in biological and biomedical research.