Potent divalent inhibitors with rigid glucose click spacers for Pseudomonas aeruginosa lectin LecA

Dual inhibitors of Pseudomonas aeruginosa virulence factors LecA and LasB

Dual inhibitors of two key virulence factors of Pseudomonas aeruginosa, the lectin LecA and the protease LasB, open up an opportunity in the current antimicrobial-resistance crisis. A molecular hybridization approach enabled the discovery of potent, selective, and non-toxic thiol-based inhibitors, which simultaneously inhibit these two major extracellular virulence factors and therefore synergistically interfere with virulence. We further demonstrated that the dimerization of these monovalent dual inhibitors under physiological conditions affords divalent inhibitors of LecA with a 200-fold increase in binding affinity. The bifunctional LecA/LasB-blocker 12 showed superiority for the inhibition of virulence mediated by both targets over the individual inhibitors or combinations thereof in vitro. Our study sets the stage for a systematic exploration of dual inhibitors as pathoblockers for a more effective treatment of P. aeruginosa infections and the concept can certainly be extended to other targets and pathogens.

Glycolipids mimicking biosurfactants of the synthetic origin as new immunomodulating and anticandidal derivatives

The immunobiological effectivity of glycolipids mimicking biosurfactants of the synthetic origin was followed up using macrophages cell line RAW264.7. These derivatives with different number of mannose units connected glycosidically or through triazole linker, and all having octyl aglycone, were evaluated with respect to their structure - immunomodulation activity relationship. This comparative study showed that the structural variations of the selected derivatives influenced the immunobiological cell behaviour as concerned pro-inflammatory TNF-α, IL-6, IL-1α, IL-17, IL-12 and anti-inflammatory IL-10 cytokines production and enhancement of RAW264.7 cell proliferation. The derivatives with mannose units linked through triazole linkers exerted in some cases stronger immunomodulative potency than (di)mannosides. On the other hand, a presence of triazole linker is a less favourable for an effective candidacidal activity as determined by in vitro using Candida albicans biofilm. The design of new defined immunomodulating formulas of the synthetic origin as possible antifungal agents and prospective participants in drug delivery systems may be of interest.

Glycomimetics for the inhibition and modulation of lectins

Carbohydrates are essential mediators of many processes in health and disease. They regulate self-/non-self- discrimination, are key elements of cellular communication, cancer, infection and inflammation, and determine protein folding, function and life-times. Moreover, they are integral to the cellular envelope for microorganisms and participate in biofilm formation. These diverse functions of carbohydrates are mediated by carbohydrate-binding proteins, lectins, and the more the knowledge about the biology of these proteins is advancing, the more interfering with carbohydrate recognition becomes a viable option for the development of novel therapeutics. In this respect, small molecules mimicking this recognition process become more and more available either as tools for fostering our basic understanding of glycobiology or as therapeutics. In this review, we outline the general design principles of glycomimetic inhibitors (Section 2). This section is then followed by highlighting three approaches to interfere with lectin function, i.e. with carbohydrate-derived glycomimetics (Section 3.1), novel glycomimetic scaffolds (Section 3.2) and allosteric modulators (Section 3.3). We summarize recent advances in design and application of glycomimetics for various classes of lectins of mammalian, viral and bacterial origin. Besides highlighting design principles in general, we showcase defined cases in which glycomimetics have been advanced to clinical trials or marketed. Additionally, emerging applications of glycomimetics for targeted protein degradation and targeted delivery purposes are reviewed in Section 4.

Neutralizing the Impact of the Virulence Factor LecA from Pseudomonas aeruginosa on Human Cells with New Glycomimetic Inhibitors

Bacterial adhesion, biofilm formation and host cell invasion of the ESKAPE pathogen Pseudomonas aeruginosa require the tetravalent lectins LecA and LecB, which are therefore drug targets to fight these infections. Recently, we have reported highly potent divalent galactosides as specific LecA inhibitors. However, they suffered from very low solubility and an intrinsic chemical instability due to two acylhydrazone motifs, which precluded further biological evaluation. Here, we isosterically substituted the acylhydrazones and systematically varied linker identity and length between the two galactosides necessary for LecA binding. The optimized divalent LecA ligands showed improved stability and were up to 1000-fold more soluble. Importantly, these properties now enabled their biological characterization. The lead compound L2 potently inhibited LecA binding to lung epithelial cells, restored wound closure in a scratch assay and reduced the invasiveness of P. aeruginosa into host cells.

Small Carbohydrate Derivatives as Potent Antibiofilm Agents

Biofilm formation by most pathogenic bacteria is considered as one of the key mechanisms associated with virulence and antibiotic resistance. Biofilm-forming bacteria adhere to the surfaces of biological or implant medical devices and create communities within their self-produced extracellular matrix that are difficult to treat by existing antibiotics. There is an urgent need to synthesize and screen structurally diverse molecules for their antibiofilm activity that can remove or minimize the bacterial biofilm. The development of carbohydrate-based small molecules as antibiofilm agents holds a great promise in addressing the problem of the eradication of biofilm-related infections. Owing to their structural diversity and specificity, the sugar scaffolds are valuable entities for developing antibiofilm agents. In this perspective, we discuss the literature pertaining to carbohydrate-based natural antibiofilm agents and provide an overview of the design, activity, and mode of action of potent synthetic carbohydrate-based molecules.

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.

Chimeric Ligands of Pili and Lectin A Inhibit Tolerance, Persistence, and Virulence Factors of Pseudomonas aeruginosa over a Wide Range of Phenotypes

Bacteria readily form resilient phenotypes to counter environmental and antibiotic stresses. Here, we demonstrate a class of small molecules that inhibit a wide range of Pseudomonas aeruginosa phenotypes and enable antibiotics to kill previously tolerant bacteria, preventing the transition of tolerant bacteria into a persistent population. We identified two proteins, type IV pili and lectin LecA, as receptors for our molecules by methods including a new label-free assay based on bacterial motility sensing the chemicals in the environment, the chemical inhibition of bacteriophage adsorption on pili appendages of bacteria, and fluorescence polarization. Structure–activity relationship studies reveal a molecule that inhibits only pili appendage and a class of chimeric ligands that inhibit both LecA and pili. Important structural elements of the ligand are identified for each protein. This selective ligand binding identifies the phenotypes each protein receptor controls. Inhibiting LecA results in reducing biofilm formation, eliminating small colony variants, and is correlated with killing previously tolerant bacteria. Inhibiting pili appendages impedes swarming and twitching motilities and pyocyanin and elastase production. Because these phenotypes are controlled by a broad range of signaling pathways, this approach simultaneously controls the multiple signaling mechanisms preventing bacteria to elude antibiotic treatments.

Multivalent Presentations of Glycomimetic Inhibitor of the Adhesion of Fungal Pathogen Candida albicans to Human Buccal Epithelial Cells

Candida albicans causes some of the most prevalent hospital-acquired fungal infections, particularly threatening for immunocompromised patients. C. albicans strongly adheres to the surface of epithelial cells so that subsequent colonization and biofilm formation can take place. Divalent galactoside glycomimetic 1 was found to be a potent inhibitor of the adhesion of C. albicans to buccal epithelial cells. In this work, we explore the effect of multivalent presentations of glycomimetic 1 on its ability to inhibit yeast adhesion and biofilm formation. Tetra-, hexa-, and hexadecavalent displays of compound 1 were built on RAFT cyclopeptide- and polylysine-based scaffolds with a highly efficient and modular synthesis. Biological evaluation revealed that the scaffold choice significantly influences the activity of the lower valency conjugates, with compound 16, constructed on a tetravalent polylysine scaffold, found to inhibit the adhesion of C. albicans to human buccal epithelial cells more effectively than the glycomimetic 1; however, the latter performed better in the biofilm reduction assays. Interestingly, the higher valency glycoconjugates did not outperform the anti-adhesion activity of the original compound 1, and no significant effect of the core scaffold could be appreciated. SEM images of C. albicans cells treated with compounds 1, 14, and 16 revealed significant differences in the aggregation patterns of the yeast cells.

Synthesis of Glycodendrimers with Antiviral and Antibacterial Activity

Glycodendrimers are an important class of synthetic macromolecules that can be used to mimic many structural and functional features of cell-surface glycoconjugates. Their carbohydrate moieties perform key important functions in bacterial and viral infections, often regulated by carbohydrate-protein interactions. Several studies have shown that the molecular structure, valency and spatial organisation of carbohydrate epitopes in glycoconjugates are key factors in the specificity and avidity of carbohydrate-protein interactions. Choosing the right glycodendrimers almost always helps to interfere with such interactions and blocks bacterial or viral adhesion and entry into host cells as an effective strategy to inhibit bacterial or viral infections. Herein, the state of the art in the design and synthesis of glycodendrimers employed for the development of anti-adhesion therapy against bacterial and viral infections is described.

Ruthenium-centred btp glycoclusters as inhibitors for Pseudomonas aeruginosa biofilm formation

Carbohydrate-decorated clusters (glycoclusters) centred on a Ru(ii) ion were synthesised and tested for their activity against Pseudomonas aeruginosa biofilm formation. These clusters were designed by conjugating a range of carbohydrate motifs (galactose, glucose, mannose and lactose, as well as galactose with a triethylene glycol spacer) to a btp (2,6-bis(1,2,3-triazol-4-yl)pyridine) scaffold. This scaffold, which possesses a C₂ symmetry, is an excellent ligand for d-metal ions, and thus the formation of the Ru(ii)-centred glycoclusters 7 and 8Gal was achieved from 5 and 6Gal; each possessing four deprotected carbohydrates. Glycocluster 8Gal, which has a flexible spacer between the btp and galactose moieties, showed significant inhibition of P. aeruginosa bacterial biofilm formation. By contrast, glycocluster 7, which lacked the flexible linker, didn't show significant antimicrobial effects and neither does the ligand 6Gal alone. These results are proposed to arise from carbohydrate–lectin interactions with LecA, which are possible for the flexible metal-centred multivalent glycocluster. Metal-centred glycoclusters present a structurally versatile class of antimicrobial agent for P. aeruginosa, of which this is, to the best of our knowledge, the first example.

Ruthenium-centred glycoclusters based on carbohydrate-functionalised bis(triazolyl)pyridine ligands show Pseudomonas aeruginosa biofilm inhibition, with activity that is dependent on ligand structure.

Synthesis and evaluation of porphyrin glycoconjugates varying in linker length: preliminary effects on the photodynamic inactivation of Mycobacterium smegmatis

Porphyrins have served as common photosensitizing agents in photomedicine due to their unique properties and broad therapeutic potential. While photodynamic therapy (PDT) offers a promising avenue for novel drug development, limitations in application due to selectivity, and the inherent hydrophobicity and poor solubility of porphyrins and other organic photosensitizers has been noted. Porphyrin glycoconjugates have recently gained attention for their potential to overcome these limitations. However, little has been done to explore the effects of the linker between the carbohydrate and porphyrin analog. Here we report the synthesis of over 30 new carbohydrate-porphyrin conjugates which vary in the nature of the sugar (Gal, Glc, GalNAc, GlcNAc, Lac and Tre) and the distance between the porphyrin macrocycle and the carbohydrate. Porphyrin glycoconjugates were synthesized in three steps from a readily available meso-brominated diphenylporphyrin analog by (i) C-O coupling of an appropriate TMS-protected alkynol consisting of two to six carbon spacers (ii) removal of the TMS protecting group, and (iii) CuAAC conjugation with an appropriate glycosyl azide. First studies with trehalose-based glycoporphyrins and M. smeg were used to determine the effects of the linker in photodynamic inactivation (PDI) studies. Preliminary results demonstrated an increase in photodynamic inactivation with a decrease in linker length. Investigations are underway to determine the mechanism for these results.

Novel approaches to glycomimetic design: development of small molecular weight lectin antagonists

Introduction: The direct binding of carbohydrates or those presented on glycoproteins or glycolipids to proteins is the primary effector of many biological responses. One class of carbohydrate-binding proteins, lectins are important in all forms of life. Their functions in animals include regulating cell adhesion, glycoprotein synthesis, metabolism, and mediating immune system response while in bacteria and viruses a lectin-mediated carbohydrate-protein interaction between host cells and the pathogen initiates pathogenesis of the infection.Areas covered: In this review, the authors outline the structural and functional pathogenesis of lectins from bacteria, amoeba, and humans. Mimics of a carbohydrate are referred to as glycomimetics, which are much smaller in molecular weight and are devised to mimic the key binding interactions of the carbohydrate while also allowing additional contacts with the lectin. This article emphasizes the various approaches used over the past 10-15 years in the rational design of glycomimetic ligands.Expert opinion: Medicinal chemistry efforts enabled by X-ray structural biology have identified small-molecule glycomimetic lectin antagonists that have entered or are nearing clinical trials. A common theme in these strategies is the use of biaryl ring systems to emulate the carbohydrate interactions with the lectin.

A rapid synthesis of low-nanomolar divalent LecA inhibitors in four linear steps from d-galactose pentaacetate

Design and four step synthesis of simple, readily accessible low-nanomolar divalent LecA ligands with selectivity over human galectin-1.

Deciphering multivalent glycocluster-lectin interactions through AFM characterization of the self-assembled nanostructures

Pseudomonas aeruginosa is a human opportunistic pathogen responsible for lung infections in cystic fibrosis patients. The emergence of resistant strains and its ability to form a biofilm seem to give a selective advantage to the bacterium and thus new therapeutic approaches are needed. To infect the lung, the bacterium uses several virulence factors, like LecA lectins. These proteins are involved in bacterial adhesion due to their specific interaction with carbohydrates of the host epithelial cells. The tetrameric LecA lectin specifically binds galactose residues. A new therapeutic approach is based on the development of highly affine synthetic glycoclusters able to selectively link with LecA to interfere with the natural carbohydrate-LecA interaction. In this study, we combined atomic force microscopy imaging and molecular dynamics simulations to visualize and understand the arrangements formed by LecA and five different glycoclusters. Our glycoclusters are small scaffolds characterized by a core and four branches, which terminate in a galactose residue. Depending on the nature of the core and the branches, the glycocluster-lectin interaction can be modulated and the affinity increased. We show that glycocluster-LecA arrangements highly depend on the glycocluster architecture: the core influences the rigidity of the geometry and the directionality of the branches, whereas the nature of the branch determines the compactness of the structure and the ease of binding.

Assembly of Divalent Ligands and Their Effect on Divalent Binding to Pseudomonas aeruginosa Lectin LecA

Divalent ligands were prepared as inhibitors for the adhesion protein of the problematic Pseudomonas aeruginosa pathogen. Bridging two binding sites enables simultaneous binding of two galactose moieties, which strongly enhances binding. An alternating motif of glucose and triazole and aryl groups was shown to have the right mix of rigidity, solubility, and ease of synthesis. Spacers were varied with respect to the core unit as well as the aglycon portions in an attempt to optimize dynamics and enhance interactions with the protein. Affinities of the divalent ligands were measured by ITC, and K_d’s as low as 12 nM were determined, notably for a compounds with either a rigid (phenyl) or flexible (butyl) unit at the core. Introducing a phenyl aglycon moiety next to the galactoside ligands on both termini did indeed lead to a higher enthalpy of binding, which was more than compensated by entropic costs. The results are discussed in terms of thermodynamics and theoretical calculations of the expected and observed multivalency effects.

Pseudoenantiomeric glycoclusters: synthesis and testing of heterobivalency in carbohydrate–protein interactions

Multivalent carbohydrate–protein interactions are key events in cell recognition processes and have been extensively studied by means of synthetic glycomimetics.

CuAAC click chemistry for the enhanced detection of novel alkyne-based natural product toxins

In the context of discovering and quantifying terminal alkyne-based natural products, here we report the combination of CuAAC click chemistry with LC-MS for the detection of polyether toxins (prymnesins) associated with harmful algal blooms. The added-value of the CuAAC-based approach is evident from our ability to detect novel prymnesin-like compounds in algal species with previously uncharacterised toxins.

The anti-adhesive effect of glycoclusters on Pseudomonas aeruginosa bacteria adhesion to epithelial cells studied by AFM single cell force spectroscopy

The human opportunistic pathogen Pseudomonas aeruginosa (PA) is responsible for chronic infections of the respiratory epithelium in cystic fibrosis patients. PA takes advantage of an arsenal of virulence factors to infect and colonize human lungs. Among them, the lectin LecA favours epithelium invasion by interacting with host cell globotriaosylceramide (Gb3). A new therapeutic approach is based on the development of synthetic multivalent molecules (glycoclusters) targeting LecA with a higher affinity than its natural ligand. Atomic force microscopy-single cell force spectroscopy has been used to study the effect of glycoclusters on the bacteria-cell interaction. Glycoclusters have been shown to affect the detachment work and detachment force of the bacteria-cell interaction. The specificity and the efficiency of the glycocluster in targeting the lectin and destabilizing the PA-epithelial cell adhesion are demonstrated and discussed.

Stereodivergent synthesis of right- and left-handed iminoxylitol heterodimers and monomers. Study of their impact on β-glucocerebrosidase activity

A library of dimers and heterodimers of both enantiomers of 2-O-alkylated iminoxylitol derivatives has been synthesised and evaluated on β-glucocerebrosidase (GCase), the enzyme responsible for Gaucher disease (GD). Although the objective was to target simultaneously the active site and a secondary binding site of the glucosidase, the (-)-2-iminoxylitol moiety seemed detrimental for imiglucerase inhibition and no significant enhancement was obtained in G202R, N370S and L444P fibroblasts. However, all compounds having at least one (+)-2-O-alkyl iminoxylitol are GCase inhibitors in the nano molar range and are significant GCase activity enhancers in G202R fibroblats, as confirmed by a decrease of glucosylceramide levels and by co-localization studies.

Development and optimization of a competitive binding assay for the galactophilic low affinity lectin LecA from Pseudomonas aeruginosa

Infections with the Gram-negative bacterium Pseudomonas aeruginosa result in a high mortality among immunocompromised patients and those with cystic fibrosis. The pathogen can switch from planktonic life to biofilms, and thereby shields itself against antibiotic treatment and host immune defense to establish chronic infections. The bacterial protein LecA, a C-type lectin, is a virulence factor and an integral component for biofilm formation. Inhibition of LecA with its carbohydrate ligands results in reduced biofilm mass, a potential Achilles heel for treatment. Here, we report the development and optimization of a fluorescence polarization-based competitive binding assay with LecA for application in screening of potential inhibitors. As a consequence of the low affinity of d-galactose for LecA, the fluorescent ligand was optimized to reduce protein consumption in the assay. The assay was validated using a set of known inhibitors of LecA and IC50 values in good agreement with the known Kd values were obtained. Finally, we employed the optimized assay to screen sets of synthetic thio-galactosides and natural blood group antigens and report their structure-activity relationship. In addition, we evaluated a multivalent fluorescent assay probe for LecA and report its applicability in an inhibition assay.

Photoswitchable Janus glycodendrimer micelles as multivalent inhibitors of LecA and LecB from Pseudomonas aeruginosa

The first example of the self-assembly and lectin binding properties of photoswitchable glycodendrimer micelles is reported. Light-addressable micelles were assembled from a library of 12 amphiphilic Janus glycodendrimers composed of variable carbohydrate head groups and hydrophobic tail groups linked to an azobenzene core. Spontaneous association in water gave cylindrical micelles with uniform size distribution as determined by dynamic light scattering (DLS) and small angle neutron scattering (SANS). Trans-cis photoisomerization of the azobenzene dendrimer core was used to probe the self-assembly behaviour and lectin binding properties of cylindrical micelles, revealing moderate-to-potent inhibition of lectins LecA and LecB from Pseudomonas aeruginosa.

Innovative Solutions to Sticky Situations: Antiadhesive Strategies for Treating Bacterial Infections

Bacterial adherence to host tissue is an essential process in pathogenesis, necessary for invasion and colonization and often required for the efficient delivery of toxins and other bacterial effectors. As existing treatment options for common bacterial infections dwindle, we find ourselves rapidly approaching a tipping point in our confrontation with antibiotic-resistant strains and in desperate need of new treatment options. Bacterial strains defective in adherence are typically avirulent and unable to cause infection in animal models. The importance of this initial binding event in the pathogenic cascade highlights its potential as a novel therapeutic target. This article seeks to highlight a variety of strategies being employed to treat and prevent infection by targeting the mechanisms of bacterial adhesion. Advancements in this area include the development of novel antivirulence therapies using small molecules, vaccines, and peptides to target a variety of bacterial infections. These therapies target bacterial adhesion through a number of mechanisms, including inhibition of pathogen receptor biogenesis, competition-based strategies with receptor and adhesin analogs, and the inhibition of binding through neutralizing antibodies. While this article is not an exhaustive description of every advancement in the field, we hope it will highlight several promising examples of the therapeutic potential of antiadhesive strategies.

C-Glycopyranosyl Arenes and Hetarenes: Synthetic Methods and Bioactivity Focused on Antidiabetic Potential

This Review summarizes close to 500 primary publications and surveys published since 2000 about the syntheses and diverse bioactivities of C-glycopyranosyl (het)arenes. A classification of the preparative routes to these synthetic targets according to methodologies and compound categories is provided. Several of these compounds, regardless of their natural or synthetic origin, display antidiabetic properties due to enzyme inhibition (glycogen phosphorylase, protein tyrosine phosphatase 1B) or by inhibiting renal sodium-dependent glucose cotransporter 2 (SGLT2). The latter class of synthetic inhibitors, very recently approved as antihyperglycemic drugs, opens new perspectives in the pharmacological treatment of type 2 diabetes. Various compounds with the C-glycopyranosyl (het)arene motif were subjected to biological studies displaying among others antioxidant, antiviral, antibiotic, antiadhesive, cytotoxic, and glycoenzyme inhibitory effects.

Polymeric mannosides prevent DC-SIGN-mediated cell-infection by cytomegalovirus

Dextrans coated with triazolylheptylmannoside ligands block human cytomegalovirus trans-infection at picomolar polymer concentrations.

Designing sugar mimetics: non-natural pyranosides as innovative chemical tools

The importance of oligosaccharides in myriad biological processes is becoming increasingly clear. However, these carbohydrate-mediated processes are often challenging to dissect due to the often poor affinity, stability and selectivity of the oligosaccharides involved. To circumvent these issues, non-natural carbohydrates-carbohydrate mimics-are being designed as innovative tools to modify biomolecules of interest or to understand biological pathways using fluorescence microscopy, X-ray or nuclear magnetic resonance spectroscopy (NMR). This review focuses on key examples of recently developed non-natural sugars to answer specific biological needs.

The virulence factor LecB varies in clinical isolates: consequences for ligand binding and drug discovery

P. aeruginosa causes a substantial number of nosocomial infections and is the leading cause of death of cystic fibrosis patients. This Gram-negative bacterium is highly resistant against antibiotics and further protects itself by forming a biofilm. Moreover, a high genomic variability among clinical isolates complicates therapy. Its lectin LecB is a virulence factor and necessary for adhesion and biofilm formation. We analyzed the sequence of LecB variants in a library of clinical isolates and demonstrate that it can serve as a marker for strain family classification. LecB from the highly virulent model strain PA14 presents 13% sequence divergence with LecB from the well characterized PAO1 strain. These differences might result in differing ligand binding specificities and ultimately in reduced efficacy of drugs directed towards LecB. Despite several amino acid variations at the carbohydrate binding site, glycan array analysis showed a comparable binding pattern for both variants. A common high affinity ligand could be identified and after its chemoenzymatic synthesis verified in a competitive binding assay: an N-glycan presenting two blood group O epitopes (H-type 2 antigen). Molecular modeling of the complex suggests a bivalent interaction of the ligand with the LecB tetramer by bridging two separate binding sites. This binding rationalizes the strong avidity (35 nM) of LecB_PA14 to this human fucosylated N-glycan. Biochemical evaluation of a panel of glycan ligands revealed that LecB_PA14 demonstrated higher glycan affinity compared to LecB_PAO1 including the extraordinarily potent affinity of 70 nM towards the monovalent human antigen Lewis^a. The structural basis of this unusual high affinity ligand binding for lectins was rationalized by solving the protein crystal structures of LecB_PA14 with several glycans.

Mannose-centered aromatic galactoclusters inhibit the biofilm formation of Pseudomonas aeruginosa

Pseudomonas aeruginosa (PA) is a major public health care issue due to its ability to develop antibiotic resistance mainly through adhesion and biofilm formation. Therefore, targeting the bacterial molecular arsenal involved in its adhesion and the formation of its biofilm appears as a promising tool against this pathogen. The galactose-binding LecA (or PA-IL) has been described as one of the PA virulence factors involved in these processes. Herein, the affinity of three tetravalent mannose-centered galactoclusters toward LecA was evaluated with five different bioanalytical methods: HIA, ELLA, SPR, ITC and DNA-based glycoarray. Inhibitory potential towards biofilms was then assessed for the two glycoclusters with highest affinity towards LecA (Kd values of 157 and 194 nM from ITC measurements). An inhibition of biofilm formation of 40% was found for these galactoclusters at 10 μM concentration. Applications of these macromolecules in anti-bacterial therapy are therefore possible through an anti-adhesive strategy.

Vinyl sulfone modified-azidofuranoside building-blocks: 1,4-/1,5-disubstituted-1,2,3-triazole linked trisaccharides via an aqueous/ionic-liquid route and “Click” chemistry

1,5-Disubstituted 1,2,3-triazole (1,5-DT) linked disaccharides have been synthesized from stable building blocks having both vinyl sulfone and azido groups using aqueous ionic-liquid media.

Structural Insight into Multivalent Galactoside Binding to Pseudomonas aeruginosa Lectin LecA

Multivalent galactosides inhibiting Pseudomonas aeruginosa biofilms may help control this problematic pathogen. To understand the binding mode of tetravalent glycopeptide dendrimer GalAG2 [(Gal-β-OC6H4CO-Lys-Pro-Leu)4(Lys-Phe-Lys-Ile)2Lys-His-Ile-NH2] to its target lectin LecA, crystal structures of LecA complexes with divalent analog GalAG1 [(Gal-β-OC6H4CO-Lys-Pro-Leu)2Lys-Phe-Lys-Ile-NH2] and related glucose-triazole linked bis-galactosides 3u3 [Gal-β-O(CH2)n-(C2HN3)-4-Glc-β-(C2HN3)-[β-Glc-4-(N3HC2)]2-(CH2)n-O-β-Gal (n = 1)] and 5u3 (n = 3) were obtained, revealing a chelate bound 3u3, cross-linked 5u3, and monovalently bound GalAG1. Nevertheless, a chelate bound model better explaining their strong LecA binding and the absence of lectin aggregation was obtained by modeling for all three ligands. A model of the chelate bound GalAG2·LecA complex was also obtained rationalizing its unusually tight LecA binding (KD = 2.5 nM) and aggregation by lectin cross-linking. The very weak biofilm inhibition with divalent LecA inhibitors suggests that lectin aggregation is necessary for biofilm inhibition by GalAG2, pointing to multivalent glycoclusters as a unique opportunity to control P. aeruginosa biofilms.

Triazole linker-based trivalent sialic acid inhibitors of adenovirus type 37 infection of human corneal epithelial cells

Adenovirus type 37 (Ad37) is one of the principal agents responsible for epidemic keratoconjunctivitis (EKC), a severe ocular infection that remains without any available treatment. Recently, a trivalent sialic acid derivative (ME0322, Angew. Chem. Int. Ed., 2011, 50, 6519) was shown to function as a highly potent inhibitor of Ad37, efficiently preventing the attachment of the virion to the host cells and subsequent infection. Here, new trivalent sialic acid derivatives were designed, synthesized and their inhibitory properties against Ad37 infection of the human corneal epithelial cells were investigated. In comparison to ME0322, the best compound (17a) was found to be over three orders of magnitude more potent in a cell-attachment assay (IC50 = 1.4 nM) and about 140 times more potent in a cell-infection assay (IC50 = 2.9 nM). X-ray crystallographic analysis demonstrated a trivalent binding mode of all compounds to the Ad37 fiber knob. For the most potent compound ophthalmic toxicity in rabbits was investigated and it was concluded that repeated eye administration did not cause any adverse effects.

Functionalization of a Rigid Divalent Ligand for LecA, a Bacterial Adhesion Lectin

The bacterial adhesion lectin LecA is an attractive target for interference with the infectivity of its producer P. aeruginosa. Divalent ligands with two terminal galactoside moieties connected by an alternating glucose-triazole spacer were previously shown to be very potent inhibitors. In this study, we chose to prepare a series of derivatives with various new substituents in the spacer in hopes of further enhancing the LecA inhibitory potency of the molecules. Based on the binding mode, modifications were made to the spacer to enable additional spacer–protein interactions. The introduction of positively charged, negatively charged, and also lipophilic functional groups was successful. The compounds were good LecA ligands, but no improved binding was seen, even though altered thermodynamic parameters were observed by isothermal titration calorimetry (ITC).

Functionalized triazolopeptoids--a novel class for mitochondrial targeted delivery

Here we introduce linear 1,4-triazolopeptoids as a novel class of cell penetrating peptidomimetics suitable as organ targeting molecular transporters of bioactive cargo. Repetitive triazole moieties with up to three residues were assembled on solid supports using copper-catalyzed alkyne-azide cycloadditions (CuAAC) in a submonomer approach. Depending on the lipophilicity of their side chain appendages the 1,4-triazolopeptoids showed either endosomal localization or a strong colocalization with the mitochondria of HeLa cells with moderate toxicity. While the basic triazolopeptoids mainly target the neuromast cells in zebrafish embryos, the lipophilic ones colocalize with either cartilage in the jaws and the blood vessel system.

Thiourea-based spacers in potent divalent inhibitors of Pseudomonas aeruginosa virulence lectin LecA

A thiourea spacer adopts an extended conformation and forms the basis of a potent bivalent ligand for Pseudomonas aeruginosa lectin LecA.

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.

A LecA ligand identified from a galactoside-conjugate array inhibits host cell invasion by Pseudomonas aeruginosa

Lectin LecA is a virulence factor of Pseudomonas aeruginosa involved in lung injury, mortality, and cellular invasion. Ligands competing with human glycoconjugates for LecA binding are thus promising candidates to counteract P. aeruginosa infections. We have identified a novel divalent ligand from a focused galactoside(Gal)-conjugate array which binds to LecA with very high affinity (Kd = 82 nM). Crystal structures of LecA complexed with the ligand together with modeling studies confirmed its ability to chelate two binding sites of LecA. The ligand lowers cellular invasiveness of P. aeruginosa up to 90 % when applied in the range of 0.05-5 μM. Hence, this ligand might lead to the development of drugs against P. aeruginosa infection.