Site-Directed Conjugation of “Clicked” Glycopolymers To Form Glycoprotein Mimics: Binding to Mammalian Lectin and Induction of Immunological Function

DNA-polymer conjugates for immune stimulation through Toll-like receptor 9 mediated pathways

Oligodeoxynucleotides (ODNs) containing unmethylated CpG dinucleotide motifs are agonists of Toll-like receptor 9 and are currently being investigated for use as vaccine adjuvants through the promotion of type I immunity. Several classes of ODN have been developed which differ in their propensity to aggregate, which in turn alters cytokine profiles and cellular subsets activated. Although aggregation state is correlated with the change in cytokine response, it is unknown if this results from a change in the number of ODNs available for binding and/or the possible engagement of multiple TLR9 molecules. Here, we examined the role of ligand valency on the activation of TLR9 through the synthesis of ODN-poly(acrylic acid) (PAA) conjugates. The compositions and size of the conjugates were characterized by UV-vis spectroscopy, proton nuclear magnetic resonance, gel permeation chromatography and dynamic light scattering. Enzyme-linked immunosorbent assays of cytokine secretion by murine-like macrophages indicate that these ODN-PAA polymer conjugates show enhanced immunostimulation at 100-fold lower concentrations than those required for ODN alone, for both TNF-α and IL-6 release, and are more potent than any other previously reported multivalent ODN constructs. Increasing valency was shown to significantly enhance cytokine expression, particularly for IL-6. Knockdown by siRNA demonstrates that these polymer conjugates are specific to TLR9. Our results define valency as a critical design parameter and polymer conjugation as an advantageous strategy for producing ODN immunomodulatory agents.

Multiblock sequence-controlled glycopolymers via Cu(0)-LRP following efficient thiol–halogen, thiol–epoxy and CuAAC reactions

The combination of copper(0) mediated living radical polymerization (Cu(0)-LRP) with thiol–halogen, thiol–epoxy and copper catalysed alkyne azide coupling (CuAAC) click chemistry has been employed to give a new route to multiblock sequence-controlled glycopolymers.

Glycopolymer-coated iron oxide nanoparticles: shape-controlled synthesis and cellular uptake

Serum-stable glyco-nanoparticles with controlled shape were easily obtained and exhibit shape-dependent cell uptake behaviors as well as enhanced activity toward specific lectins.

Synthesis of a Novel Polyaniline Glycopolymer and its Lectin Binding Studies

We report the multistep synthesis and polymerisation of a novel aniline derivative with a pendant α-d-mannose substituent. The α-D-mannose functionality was successfully introduced before polymerisation via copper-catalysed azide alkyne click chemistry and the resulting monomer was polymerised using general oxidative polymerisation conditions, producing a water soluble mannosylated polyaniline. The polymer was characterised by several techniques and compared with standard polyaniline. The selective binding of the polymer to Concanavalin A (ConA) was successfully demonstrated by the precipitation of polymer–ConA aggregates. Potential applications of these novel polyaniline glycopolymers could include the development of electroactive biomaterials with the ability to bind mannose receptors, or as sensors for proteins or microbes.

Antifouling glycocalyx-mimetic peptoids

The glycocalyx of the cell is composed of highly hydrated saccharidic groups conjugated to protein and lipid cores. Although components of the glycocalyx are important in cell-cell interactions and other specific biological recognition events, a fundamental role of the glycocalyx is the inhibition of nonspecific interactions at the cell surface. Inspired by glycoproteins present in the glycocalyx, we describe a new class of synthetic antifouling polymer composed of saccharide containing N-substituted polypeptide (glycopeptoid). Grafting of glycopeptoids to a solid surface resulted in a biomimetic shielding layer that dramatically reduced nonspecific protein, fibroblast, and bacterial cell attachment. All-atom molecular dynamics simulation of grafted glycopeptoids revealed an aqueous interface enriched in highly hydrated saccharide residues. In comparison to saccharide-free peptoids, the interfacial saccharide residues of glycopeptoids formed a higher number of hydrogen bonds with water molecules. Moreover, these hydrogen bonds displayed a longer persistence time, which we believe contributed to fouling resistance by impeding interactions with biomolecules. Our findings suggest that the fouling resistance of glycopeptoids can be explained by the presence of both a 'water barrier' effect associated with the hydrated saccharide residues as well as steric hindrance from the polymer backbone.

A Detailed Study on Understanding Glycopolymer Library and Con A Interactions

Synthetic glycopolymers are important natural oligosaccharides mimics for many biological applications. To develop glycopolymeric drugs and therapeutic agents, factors that control the receptor-ligand interaction need to be investigated. A library of well-defined glycopolymers has been prepared by the combination of copper mediated living radical polymerization and CuAAC click reaction via post-functionalization of alkyne-containing precursor polymers with different sugar azides. Employing Concanavalin A as the model receptor, we explored the influence of the nature and densities of different sugars residues (mannose, galactose, and glucose) on the stoichiometry of the cluster, the rate of the cluster formation, the inhibitory potency of the glycopolymers, and the stability of the turbidity through quantitative precipitation assays, turbidimetry assays, inhibitory potency assays, and reversal aggregation assays. The diversities of binding properties contributed by different clustering parameters will make it possible to define the structures of the multivalent ligands and densities of binding epitopes tailor-made for specific functions in the lectin-ligand interaction. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2588-2597.

Glycopolymer probes of signal transduction

Glycans are key participants in biological processes ranging from reproduction to cellular communication to infection. Revealing glycan roles and the underlying molecular mechanisms by which glycans manifest their function requires access to glycan derivatives that vary systematically. To this end, glycopolymers (polymers bearing pendant carbohydrates) have emerged as valuable glycan analogs. Because glycopolymers can readily be synthesized, their overall shape can be varied, and they can be altered systematically to dissect the structural features that underpin their activities. This review provides examples in which glycopolymers have been used to effect carbohydrate-mediated signal transduction. Our objective is to illustrate how these powerful tools can reveal the molecular mechanisms that underlie carbohydrate-mediated signal transduction.

Optimization of brush-like cationic copolymers for nonviral gene delivery

Polyethylenimine (PEI) is one of the most broadly used polycations for gene delivery due to its high transfection efficiency and commercial availability but materials are cytotoxic and often polydisperse. The goal of current work is to develop an alternative family of polycations based on controlled living radical polymerization (CLRP) and to optimize the polymer structure for efficient gene delivery. In this study, well-defined poly(glycidyl methacrylate)(P(GMA)) homopolymers were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization followed by decoration using three different types of oligoamines, i.e., tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), and tris(2-aminoethyl)amine (TREN), respectively, to generate various P(GMA-oligoamine) homopolycations. The effect of P(GMA) backbone length and structure of oligoamine on gene transfer efficiency was then determined. The optimal polymer, P(GMA-TEPA)(50), provided comparable transfection efficiency but lower cytotoxicity than PEI. P(GMA-TEPA)(50) was then used as the cationic block in diblock copolymers containing hydrophilic N-(2-hydroxypropyl) methacrylamide (HPMA) and oligo(ethylene glycol) monomethyl ether methacrylate (OEGMA). Polyplexes of block copolymers were stable against aggregation in physiological salt condition and in Opti-MEM due to the shielding effect of P(HPMA) and P(OEGMA). However, the presence of the HPMA/OEGMA block significantly decreased the transfection efficacy of P(GMA-TEPA)(50) homopolycation. To compensate for reduced cell uptake caused by the hydrophilic shell of polyplex, the integrin-binding peptide, RGD, was conjugated to the hydrophilic chain end of P(OEGMA)(15)-b-P(GMA-TEPA)(50) copolymer by Michael-type addition reaction. At low polymer to DNA ratios, the RGD-functionalized polymer showed increased gene delivery efficiency to HeLa cells compared to analogous polymers lacking RGD.

Humoral and cell-mediated immunity following vaccination with synthetic Candida cell wall mannan derived heptamannoside-protein conjugate: immunomodulatory properties of heptamannoside-BSA conjugate

Chemically defined glycoprotein conjugate composed of synthetically prepared mannan-derived heptamannoside with terminal β-1,2-linked mannose residue attached to the α-1,3-linked mannose residues and BSA as carrier protein (M7-BSA conjugate) was analysed for the capacity to induce protective humoral immunity and appropriate alteration cellular immunity. To identify protective antigenic structure of Candida cell wall mannan M7-BSA conjugate was used for BALB/c mice immunization. The obtained results were compared with placebo group and with heat-inactivated C. albicans whole cells immunization. The administration route of M7-BSA conjugate secondary booster injection significantly affected the intensity of humoral immune response and the specificity of produced antibodies. All prepared sera were able to elevate candidacidal activity of polymorphonuclear leukocytes (PMN) in cooperation with complement. Moreover, polyclonal sera obtained after secondary subcutaneous (s.c.) booster injection of M7-BSA conjugate were able to induce candidacidal activity of PMN also in complement independent manner. M7-BSA conjugate immunization induced increases of phagocytic activity and respiratory burst of granulocytes, caused a raise of the proportion of CD3(+) T lymphocytes and increased the CD4(+)/CD8(+) T lymphocyte ratio. We observed also an increasing proportion of CD4(+)CD25(+) T cells compared to immunization with heat inactivated whole C. albicans cells, which in turn promoted an increase of the CD8(+)CD25(+) cell proportion. Immunization with M7-BSA conjugate induced Th1, Th2 and Th17 immune responses as indicated by the elevation of relevant cytokines levels. These data provide some insights on the immunomodulatory properties of oligomannosides and contribute to the development of synthetic oligosaccharide vaccines against fungal diseases.

Immobilized sialyloligo-macroligand and its protein binding specificity

We report a chemoenzymatic synthesis of chain-end functionalized sialyllactose-containing glycopolymers with different linkages and their oriented immobilization for glycoarray and SPR-based glyco-biosensor applications. Specifically, O-cyanate chain-end functionalized sialyllactose-containing glycopolymers were synthesized by enzymatic α2,3- and α2,6-sialylation of a lactose-containing glycopolymer that was synthesized by cyanoxyl-mediated free radical polymerization. (1)H NMR showed almost quantitative α2,3- and α2,6-sialylation. The O-cyanate chain-end functionalized sialyllactose-containing glycopolymers were printed onto amine-functionalized glass slides via isourea bond formation for glycoarray formation. Specific protein binding activity of the arrays was confirmed with α2,3- and α2,6-sialyl specific binding lectins together with inhibition assays. Further, immobilizing O-cyanate chain-end functionalized sialyllactose-containing glycopolymers onto amine-modified SPR chip via isourea bond formation afforded SPR-based glyco-biosensor, which showed specific binding activity for lectins and influenza viral hemagglutinins (HA). These sialyloligo-macroligand derived glycoarray and SPR-based glyco-biosensor are closely to mimic 3D nature presentation of sialyloligosaccharides and will provide important high-throughput tools for virus diagnosis and potential antiviral drug candidates screening applications.

Evanescent wave cavity ring-down spectroscopy (EW-CRDS) as a probe of macromolecule adsorption kinetics at functionalized interfaces

Evanescent wave cavity ring-down spectroscopy (EW-CRDS) has been employed to study the interfacial adsorption kinetics of coumarin-tagged macromolecules onto a range of functionalized planar surfaces. Such studies are valuable in designing polymers for complex systems where the degree of interaction between the polymer and surface needs to be tailored. Three tagged synthetic polymers with different functionalities are examined: poly(acrylic acid) (PAA), poly(3-sulfopropyl methacrylate, potassium salt) (PSPMA), and a mannose-modified glycopolymer. Adsorption transients at the silica/water interface are found to be characteristic for each polymer, and kinetics are deduced from the initial rates. The chemistry of the adsorption interfaces has been varied by, first, manipulation of silica surface chemistry via the bulk pH, followed by surfaces modified by poly(L-glutamic acid) (PGA) and cellulose, giving five chemically different surfaces. Complementary atomic force microscopy (AFM) imaging has been used for additional surface characterization of adsorbed layers and functionalized interfaces to allow adsorption rates to be interpreted more fully. Adsorption rates for PSPMA and the glycopolymer are seen to be highly surface sensitive, with significantly higher rates on cellulose-modified surfaces, whereas PAA shows a much smaller rate dependence on the nature of the adsorption surface.

Synthesis of heteroglycoclusters by using orthogonal chemoselective ligations

Synthetic heteroglycoclusters are being subjected to increasing interest due to their potential to serve as selective ligands for carbohydrate-binding proteins. In this paper, we describe an expedient strategy to prepare cyclopeptides displaying well-defined distributions and combinations of carbohydrates. By using both oxime ligation and copper(I)-catalyzed alkyne–azide cycloaddition, two series of compounds bearing binary combinations of αMan, αFuc or βLac in an overall tetravalent presentation, and either 2:2 or 3:1 relative proportions, have been prepared.

Development of star polymers as unimolecular containers for nanomaterials

Star polymers containing one central core surrounded by multiple radiating arms represent an intriguing type of globular platform to be used as unimolecular containers and reactors. The core domain can encapsulate guest "cargos", whereas protective shell and chain ends can be functionalized with reactive groups and ligands. This Feature Article highlights the recent development on using core-shell structured amphiphilic star polymers as unimolecular containers for applications in drug delivery, catalysis, and template of hybrid nanomaterials. As compared with dendrimers, star polymers enjoy advantages of facile synthesis, flexible compositions, and tunable sizes, which allow them being able to carry more and multiple "cargos" within one molecule.

Synthesis and assessment of globotriose-chitosan conjugate, a novel inhibitor of shiga toxins produced by Escherichia coli

Shiga toxin (Stx)-producing Escherichia coli (STEC) causes diarrhea and colitis in humans that can develop into a life-threatening hemolytic uremic syndrome (HUS). Developing efficient means of controlling STEC diseases, for which no drugs or vaccines are currently available, remains a high priority. We report here the construction and development of chitosan conjugates bearing the Stx ligand trisaccharide globotriose to demonstrate their potential as STEC disease treatment agents. The synthesis was accomplished by grafting a globotriose derivative containing an aldehyde-functionalized aglycone to chitosan amino groups. The obtained globotriose-chitosan conjugate bound with high affinity to Stx and efficiently neutralized its toxicity on Vero cells. Moreover, Stx levels in the gut of infected mice receiving oral doses of the conjugate were greatly diminished, enabling the mice to resist a fatal STEC challenge. The conjugate appears to function as a Stx adsorbent in the gut, preventing toxin entry into the bloodstream and consequent development of HUS. As such, the conjugate could act as a novel agent against STEC disease.

Dibromomaleimide End Functional Polymers by RAFT Polymerization Without the Need of Protecting Groups

Polymers bearing the dibromomaleimide (DBM) group as a functional chain end have been synthesized by RAFT polymerization. A DBM functional chain transfer agent (CTA) was utilized to afford well-defined P^tBA, PMA, and PTEGA, without the requirement of protecting group chemistry. It was found that RAFT polymerization of NIPAM and styrene with this CTA was severely retarded/inhibited which is ascribed to their relatively low propagation rate constants compared to acrylates. This observation is accounted for by a reversible trapping of propagating radicals by the DBM group in RAFT polymerizations using a monomer with low k_p. However, further attempts to synthesize DBM-terminated P^tBA and PMA by ATRP using an analogous initiator were unsuccessful, and broad PDI were observed. Furthermore, highly efficient postpolymerization functionalization of DBM-terminated PMA produced by RAFT, with the model compound thiophenol was also demonstrated.