Exploring Rigid and Flexible Scaffolds to Develop Potent Glucuronic Acid Glycodendrimers for Dengue Virus Inhibition

Multivalent glycodendrimers are valuable tools for studying carbohydrate-protein interactions, and their scaffolds represent important components to increase specificity and affinity. Previous work by our group described the preparation of a tetravalent glucuronic acid rigid dendron that binds with good affinity to the dengue virus envelope protein (KD = 22 μM). Herein, the chemical synthesis and binding analysis of three new sets of rigid, semirigid, and flexible glucuronic acid-based dendrimers bearing different levels of multivalency and their interactions with the dengue virus envelope protein are described. The different oligoalkynyl scaffolds were coupled to glucuronic acid azides by a copper-catalyzed azide-alkyne cycloaddition reaction through optimized synthetic strategies to afford the desired glycodendrimers with good yields. Surface plasmon resonance studies have demonstrated that glycodendrimers 12b and 12c, with flexible scaffolds, give the best binding interactions with the dengue virus envelope protein (12b: KD = 0.487 μM and 12c: KD = 0.624 μM). Their binding constant values were 45 and 35 times higher than the one obtained in previous studies with a rigid tetravalent glucuronic acid dendron (KD = 22 μM), respectively. Molecular modeling studies were carried out in order to understand the difference in behavior observed for 12b and 12c. This work reports an efficient glycodendrimer chemical synthesis process that provides an appropriate scaffold that offers an easy and versatile strategy to find new active compounds against the dengue virus.

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.

CuAAC mediated synthesis of cyclen cored glycodendrimers of high sugar tethers at low generation

Glycodendrimers are receiving considerable attention to mimic a number of imperative features of cell surface glycoconjugate and acquired excellent relevance to a wide domain of investigations including medicine, pharmaceutics, catalysis, nanotechnology, carbohydrate-protein interaction, and moreover in drug delivery systems. Toward this end, an expeditious, modular, and regioselective triazole-forming CuAAC click approach along with double stage convergent synthetic method was chosen to develop a variety of novel chlorine-containing cyclen cored glycodendrimers of high sugar tethers at low generation of promising therapeutic potential. We developed a novel chlorine-containing hypercore unit with 12 alkynyl functionality originated from cyclen scaffold which was confirmed by its single crystal X-ray data analysis. Further, the modular CuAAC technique was utilized to produce a variety of novel 12-sugar coated (G₀) glycodendrimers 12-15 adorn with β-Glc-, β-Man-, β-Gal-, β-Lac, along with 36-galactose coated (G₁) glycodendrimer 18 in good-to-high yield. The structures of the developed glycodendrimer architectures have been well elucidated by extensive spectral analysis including NMR (¹H & ¹³CNMR), HRMS, MALDI-TOF MS, UV-Vis, IR, and SEC (Size Exclusion Chromatogram) data.

Glycomacromolecules: Addressing challenges in drug delivery and therapeutic development

Carbohydrate-based materials offer exciting opportunities for drug delivery. They present readily available, biocompatible components for the construction of macromolecular systems which can be loaded with cargo, and can enable targeting of a payload to particular cell types through carbohydrate recognition events established in biological systems. These systems can additionally be engineered to respond to environmental stimuli, enabling triggered release of payload, to encompass multiple modes of therapeutic action, or to simultaneously fulfil a secondary function such as enabling imaging of target tissue. Here, we will explore the use of glycomacromolecules to deliver therapeutic benefits to address key health challenges, and suggest future directions for development of next-generation systems.

Directing Drugs to Bugs: Antibiotic-Carbohydrate Conjugates Targeting Biofilm-Associated Lectins of Pseudomonas aeruginosa

Chronic infections by Pseudomonas aeruginosa are characterized by biofilm formation, which effectively enhances resistance toward antibiotics. Biofilm-specific antibiotic delivery could locally increase drug concentration to break antimicrobial resistance and reduce the drug's peripheral side effects. Two extracellular P. aeruginosa lectins, LecA and LecB, are essential structural components for biofilm formation and thus render a possible anchor for biofilm-targeted drug delivery. The standard-of-care drug ciprofloxacin suffers from severe systemic side effects and was therefore chosen for this approach. We synthesized several ciprofloxacin-carbohydrate conjugates and established a structure-activity relationship. Conjugation of ciprofloxacin to lectin probes enabled biofilm accumulation in vitro, reduced the antibiotic's cytotoxicity, but also reduced its antibiotic activity against planktonic cells due to a reduced cell permeability and on target activity. This work defines the starting point for new biofilm/lectin-targeted drugs to modulate antibiotic properties and ultimately break antimicrobial resistance.

Design, Synthesis and Characterization of Cyclic NU172 Analogues: A Biophysical and Biological Insight

NU172—a 26-mer oligonucleotide able to bind exosite I of human thrombin and inhibit its activity—was the first aptamer to reach Phase II clinical studies as an anticoagulant in heart disease treatments. With the aim of favoring its functional duplex-quadruplex conformation and thus improving its enzymatic stability, as well as its thrombin inhibitory activity, herein a focused set of cyclic NU172 analogues—obtained by connecting its 5′- and 3′-extremities with flexible linkers—was synthesized. Two different chemical approaches were exploited in the cyclization procedure, one based on the oxime ligation method and the other on Cu(I)-assisted azide-alkyne cycloaddition (CuAAC), affording NU172 analogues including circularizing linkers with different length and chemical nature. The resulting cyclic NU172 derivatives were characterized using several biophysical techniques (ultraviolet (UV) and circular dichroism (CD) spectroscopies, gel electrophoresis) and then investigated for their serum resistance and anticoagulant activity in vitro. All the cyclic NU172 analogues showed higher thermal stability and nuclease resistance compared to unmodified NU172. These favorable properties were, however, associated with reduced—even though still significant—anticoagulant activity, suggesting that the conformational constraints introduced upon cyclization were somehow detrimental for protein recognition. These results provide useful information for the design of improved analogues of NU172 and related duplex-quadruplex structures.

AS, Mukherjee R, Tiwari VK. An expeditious click approach towards the synthesis of galactose coated novel glyco-dendrimers and dentromers utilizing a double stage convergent method

The primary motive behind this article is to bring to the forefront a unique kind of dendrimer which has remained a dark horse since its discovery, namely dentromer. We herein report the synthesis of glycodendrimers and glycodentromers crowned with galactose units by harnessing an expeditious synthesis of dendrimer core 18 and dentromer core 19, divergently with branching directionality (1 → 2) and (1 → 3), respectively. A competent, double stage convergent synthetic path was chosen to facilitate ease of refining and spectroscopic elucidations. By exploiting a Cu(i)-catalyzed azide–alkyne cycloaddition (CuAAC) reaction strategy, we successfully developed a new series of galactosylated dendrimers 20, 21, 22, and 24 containing 6, 12, 18, and 18 peripheral galactose units, respectively. We are first to report the practical synthesis of 9-peripheral galactose coated glycodentromer 23 (0^th generation) and 27-peripheral galactose coated glycodentromer 25 (1^st generation). These synthesized scaffolds were characterized by spectral studies such as ¹H, ¹³C NMR, FT-IR, MALDI-TOF MS, HRMS and SEC analysis. Additionally, gel permeation chromatography depicted the regular progression in size from 6 to 27-peripheral galactose coated glycodendrimers along with glycodentromers, with their high monodispersity. Also, the glyco-dendrimers and dentromers synthesized from two different hypercore units i.e. dendrimers core (18) and dentromer core (19), have been supported by their UV-visible absorbance and emission spectroscopy.

A proficient double stage convergent approach has been exploited for an easy access of galactose coated novel glycodendrimers and dentromers under CuAAC click condition.

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.

Pathoblockers or antivirulence drugs as a new option for the treatment of bacterial infections

The rapid development of antimicrobial resistance is threatening mankind to such an extent that the World Health Organization expects more deaths from infections than from cancer in 2050 if current trends continue. To avoid this scenario, new classes of anti-infectives must urgently be developed. Antibiotics with new modes of action are needed, but other concepts are also currently being pursued. Targeting bacterial virulence as a means of blocking pathogenicity is a promising new strategy for disarming pathogens. Furthermore, it is believed that this new approach is less susceptible towards resistance development. In this review, recent examples of anti-infective compounds acting on several types of bacterial targets, e.g., adhesins, toxins and bacterial communication, are described.

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.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

Galactose Derivative-Modified Nanoparticles for Efficient siRNA Delivery to Hepatocellular Carcinoma

Successful siRNA therapy requires suitable delivery systems with targeting moieties such as small molecules, peptides, antibodies, or aptamers. Galactose (Gal) residues recognized by the asialoglycoprotein receptor (ASGPR) can serve as potent targeting moieties for hepatocellular carcinoma (HCC) cells. However, efficient targeting to HCC via galactose moieties rather than normal liver tissues in HCC patients remains a challenge. To achieve more efficient siRNA delivery in HCC, we synthesized various galactoside derivatives and investigated the siRNA delivery capability of nanoparticles modified with those galactoside derivatives. In this study, we assembled lipid/calcium/phosphate nanoparticles (LCP NPs) conjugated with eight types of galactoside derivatives and demonstrated that phenyl β-d-galactoside-decorated LCP NPs (L4-LCP NPs) exhibited a superior siRNA delivery into HCC cells compared to normal hepatocytes. VEGF siRNAs delivered by L4-LCP NPs downregulated VEGF expression in HCC in vitro and in vivo and led to a potent antiangiogenic effect in the tumor microenvironment of a murine orthotopic HCC model. The efficient delivery of VEGF siRNA by L4-LCP NPs that resulted in significant tumor regression indicates that phenyl galactoside could be a promising HCC-targeting ligand for therapeutic siRNA delivery to treat liver cancer.

“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.

Perylenediimide-based glycoclusters as high affinity ligands of bacterial lectins: synthesis, binding studies and anti-adhesive properties

Rapid access to perylenediimide-based glycoclusters allowed their evaluation as high affinity ligands of bacterial lectins and their potential as anti-adhesive antibacterials.

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.

Toward the Rational Design of Galactosylated Glycoclusters That Target Pseudomonas aeruginosa Lectin A (LecA): Influence of Linker Arms That Lead to Low-Nanomolar Multivalent Ligands

Anti-infectious strategies against pathogen infections can be achieved through antiadhesive strategies by using multivalent ligands of bacterial virulence factors. LecA and LecB are lectins of Pseudomonas aeruginosa implicated in biofilm formation. A series of 27 LecA-targeting glycoclusters have been synthesized. Nine aromatic galactose aglycons were investigated with three different linker arms that connect the central mannopyranoside core. A low-nanomolar (Kd =19 nm, microarray) ligand with a tyrosine-based linker arm could be identified in a structure-activity relationship study. Molecular modeling of the glycoclusters bound to the lectin tetramer was also used to rationalize the binding properties observed.

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.

Importance of topology for glycocluster binding to Pseudomonas aeruginosa and Burkholderia ambifaria bacterial lectins

Pseudomonas aeruginosa (PA) and Burkholderia ambifaria (BA) are two opportunistic Gram negative bacteria and major infectious agents involved in lung infection of cystic fibrosis patients. Both bacteria can develop resistance to conventional antibiotherapies. An alternative strategy consists of targeting virulence factors in particular lectins with high affinity ligands such as multivalent glycoclusters. LecA (PA-IL) and LecB (PA-IIL) are two tetravalent lectins from PA that recognise galactose and fucose respectively. BambL lectin from BA is trimeric with 2 binding sites per monomer and is also specific for fucose. These three lectins are potential therapeutic targets in an anti-adhesive anti-bacterial approach. Herein, we report the synthesis of 18 oligonucleotide pentofuranose-centered or mannitol-centered glycoclusters leading to tri-, penta- or decavalent clusters with different topologies. The linker arm length between the core and the carbohydrate epitope was also varied leading to 9 galactoclusters targeting LecA and 9 fucoclusters targeting both LecB and BambL. Their dissociation constants (Kd) were determined using a DNA-based carbohydrate microarray technology. The trivalent xylo-centered galactocluster and the ribo-centered fucocluster exhibited the best affinity for LecA and LecB respectively while the mannitol-centered decafucocluster displayed the best affinity to BambL. These data demonstrated that the topology and nature of linkers were the predominant factors for achieving high affinity rather than valency.