Glycopolymers against pathogen infection.

Pathogens including viruses, bacteria, fungi, and parasites continue to shape our lives in profound ways every day. As we have learned to live in parallel with pathogens, we have gained a better understanding of the rules of engagement for how they bind, adhere, and invade host cells. One such mechanism involves the exploitation of host cell surface glycans for attachment/adhesion, one of the first steps of infection. This knowledge has led to the development of glycan-based diagnostics and therapeutics for the treatment and prevention of infection. One class of compounds that has become increasingly important are the glycopolymers. Glycopolymers are macromolecules composed of a synthetic scaffold presenting carbohydrates as side chain motifs. Glycopolymers are particularly attractive because their properties can be tuned by careful choice of the scaffold, carbohydrate/glycan, and overall presentation. In this review, we highlight studies over the past ten years that have examined the role of glycopolymers in pathogen adhesion and host cell infection, biofilm formation and removal, and drug delivery with the aim of examining the direct effects of these macromolecules on pathogen engagement. In addition, we also examine the role of glycopolymers as diagnostics for the detection and monitoring of pathogens.

Glycosaminoglycan Mimetic Precision Glycomacromolecules with Sequence-Defined Sulfation and Rigidity Patterns.

Sulfated glycosaminoglycans (sGAGs) such as heparan sulfate (HS) are structurally diverse linear polysaccharides that are involved in many biological processes and have gained interest as antiviral compounds. Their recognition is driven by a complex orchestra of structural parameters that are still under intense investigation. One distinct characteristic is the incorporation of sulfation patterns including highly sulfated and non-sulfated sequences that provide variations in flexibility and conformation, which in turn impact the biological function of sGAGs. However, these distinct features have not yet been fully realized in the synthetic preparation of sGAG mimetics. Here, we present the synthesis of three groups of sulfated glycomacromolecules as sGAG mimetics: (i) globally sulfated glycooligomers, (ii) glycooligomers with sequence-defined sulfation patterns, and (iii) a globally sulfated glycooligomer-oligo-L-proline hybrid structure. The complete synthesis, including chemical sulfation, was conducted on solid support, enabled by the introduction of a commercially available photocleavable linker allowing for the preservation of sensitive sulfates during cleavage of the products. Structures were obtained in good purity and with high degrees of sulfation demonstrating the wide applicability of this methodology to prepare tailor-made sulfated glycomacromolecules and similar sGAG mimetics. Structures were tested for their anticoagulant properties showing activity similar to their natural HS counterpart and significantly lower than HP.

Molecular Recognition of Glycan-Bearing Glycomacromolecules Presented at Membrane Surfaces by Lectins: An NMR View.

Lectin-glycan interactions are at the heart of a multitude of biological events. Glycans are usually presented in a multivalent manner on the cell surface as part of the so-called glycocalyx, where they interact with other entities. This multivalent presentation allows us to overcome the typical low affinities found for individual glycan-lectin interactions. Indeed, the presentation of glycans may drastically impact their binding by lectins, highly affecting the corresponding binding affinity and even selectivity. In this context, we herein present the study of the interaction of a variety of homo- and heteromultivalent lactose-functionalized glycomacromolecules and their lipid conjugates with two human galectins. We have employed as ligands the glycomacromolecules, as well as liposomes decorated with those structures, to evaluate their interactions in a cell-mimicking environment. Key details of the interaction have been unravelled by NMR experiments, both from the ligand and receptor perspectives, complemented by cryo-electron microscopy methods and molecular dynamics simulations.

Bactericidal activity of the organo-tellurium compound AS101 against Enterobacter cloacae.

OBJECTIVES: The antibacterial effect of the organo-tellurium compound AS101 on the Gram-negative bacterium Enterobacter cloacae is shown in this study for the first time. METHODS: The antimicrobial effect of the drug was shown by inhibition of growth, by inhibition of biofilm formation and by its ability to penetrate the bacterial cell and to cause damage and ultrastructural changes. RESULTS: AS101 was found to be a bactericidal drug with MICs and MBCs of 9.4 mg/L. It inhibits bacterial growth and causes a six orders of magnitude decrease in viability in a protein-rich medium, but not in a protein-poorer medium, unless 2-mercaptoethanol is added. Subinhibitory concentrations inhibit motility and biofilm formation. AS101 enters the bacterium through its porins and causes bacterial damage to Na(+)/K(+) pumps and leakage of potassium, phosphorous and sulphur. Ultrastructural changes within the bacterial cell and on its surface demonstrate an incomplete surface with a concavity in the centre that looks like a hole from which aggregates are liberated as well as cell lysis. CONCLUSIONS: AS101 has antibacterial activity, which may be useful against E. cloacae and other species of Enterobacteriaceae as a substitute for current antibiotics that have become ineffective due to increasing bacterial resistance.

Polymers Inspired by Heparin and Heparan Sulfate for Viral Targeting.

Heparin (HP) and heparan sulfate (HS) are linear, anionically charged polysaccharides well-known for their diverse biological activities. While HP is generally localized in mast cells and in connective tissues, HS is part of the glycocalyx and involved in the attachment of viruses to host cells, constituting the first step of an infection. HP and HS also exhibit antiviral activity by blocking viral receptors, thereby inhibiting viruses from engaging with host cells. Inspired by their structural features, such as their high molecular weight and polyanionic character, various synthetic polymers mimicking HP/HS have been developed and used as model systems to study bioactivity, as well as for therapeutic applications. This Perspective provides an overview of the roles of HP/HS in viral engagement, and examines historical and recent approaches toward oligo-/polysaccharide, glycopolymer, and anionic polymer HP/HS mimetics. An overview of current applications and future prospects of these molecules is provided, demonstrating their potential in addressing current and future epidemics and pandemics.

A potential antimicrobial treatment against ESBL-producing Klebsiella pneumoniae using the tellurium compound AS101.

Due to the extensive spread of antibiotic-resistant Klebsiella pneumoniae, the non-toxic immunomodulator, ammonium trichloro (dioxoethylene-o, o') tellurate (AS101), was introduced for the first time in this study. Eleven strains of K. pneumoniae were tested: five were extended spectrum beta lactamase (ESBL)-producing strains and six were non-ESBL-producing strains. The MIC and MBC of ten strains were 9 microg/ml AS101 and 18 microg/ml for one strain. AS101 treatment inhibited bacterial growth in a dose-dependent manner on protein-rich media. No inhibition by AS101 was observed on poorer media. In combination with beta-mercaptoethanol (2-ME) or cysteamine, AS101 inhibited bacterial growth in both types of media. Growth inhibition was also shown following AS101 treatment at both lag and log phases. Our data indicate that AS101 enters the bacterium through its porins, causing bacterial destruction. The mechanism of cell death was characterized using several techniques: (a) scanning electron microscopy showed that bacteria treated with AS101 or in combination with cysteamine exhibited evidence of cell-wall damage; (b) X-ray microanalysis demonstrated damage to Na/K pumps; and (c) transmission electron microscopy demonstrated cell lysis. These phenomena suggest that AS101 has antibacterial potential against K. pneumoniae infections.

Effects of linker and liposome anchoring on lactose-functionalized glycomacromolecules as multivalent ligands for binding galectin-3.

In this work, we present a bottom-up approach for the synthesis of lactose-functionalized glycomacromolecules and glycofunctionalized liposomes and apply these compounds to investigate their effects of multivalent presentation on binding to galectin-3. Step-wise assembly of tailor-made building blocks on solid supports was used to synthesize a series of oligo(amidoamine) scaffolds that were further conjugated to lactose via copper catalyzed 1,3-dipolar cycloaddition. Binding studies with galectin-3 revealed affinities in the micromolar range that increased with increasing carbohydrate valency, and decreased with increasing size and linker flexibility. To further explore their multivalency, selected glycomacromolecules were conjugated to lipids and used in liposomal formulations. Binding studies show a further increase in binding in nanomolar ranges in dependence of both ligand structure and liposomal presentation, demonstrating the power of combining the two approaches.