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

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.

Deinococcus radiodurans Exopolysaccharide Inhibits Staphylococcus aureus Biofilm Formation

Deinococcus radiodurans is an extremely resistant bacterium against extracellular stress owing to on its unique physiological functions and the structure of its cellular constituents. Interestingly, it has been reported that the pattern of alteration in Deinococcus proportion on the skin is negatively correlated with skin inflammatory diseases, whereas the proportion of Staphylococcus aureus was increased in patients with chronic skin inflammatory diseases. However, the biological mechanisms of deinococcal interactions with other skin commensal bacteria have not been studied. In this study, we hypothesized that deinococcal cellular constituents play a pivotal role in preventing S. aureus colonization by inhibiting biofilm formation. To prove this, we first isolated cellular constituents, such as exopolysaccharide (DeinoPol), cell wall (DeinoWall), and cell membrane (DeinoMem), from D. radiodurans and investigated their inhibitory effects on S. aureus colonization and biofilm formation in vitro and in vivo. Among them, only DeinoPol exhibited an anti-biofilm effect without affecting bacterial growth and inhibiting staphylococcal colonization and inflammation in a mouse skin infection model. Moreover, the inhibitory effect was impaired in the Δdra0033 strain, a mutant that cannot produce DeinoPol. Remarkably, DeinoPol not only interfered with S. aureus biofilm formation at early and late stages but also disrupted a preexisting biofilm by inhibiting the production of poly-N-acetylglucosamine (PNAG), a key molecule required for S. aureus biofilm formation. Taken together, the present study suggests that DeinoPol is a key molecule in the negative regulation of S. aureus biofilm formation by D. radiodurans. Therefore, DeinoPol could be applied to prevent and/or treat infections or inflammatory diseases associated with S. aureus biofilms.

Pillar[5]arene-Based Polycationic Glyco[2]rotaxanes Designed as Pseudomonas aeruginosa Antibiofilm Agents

Pseudomonas aeruginosa (P.A.) is a human pathogen belonging to the top priorities for the discovery of new therapeutic solutions. Its propensity to generate biofilms strongly complicates the treatments required to cure P.A. infections. Herein, we describe the synthesis of a series of novel rotaxanes composed of a central galactosylated pillar[5]arene, a tetrafucosylated dendron, and a tetraguanidinium subunit. Besides the high affinity of the final glycorotaxanes for the two P.A. lectins LecA and LecB, potent inhibition levels of biofilm growth were evidenced, showing that their three subunits work synergistically. An antibiofilm assay using a double ΔlecAΔlecB mutant compared to the wild type demonstrated that the antibiofilm activity of the best glycorotaxane is lectin-mediated. Such antibiofilm potency had rarely been reached in the literature. Importantly, none of the final rotaxanes was bactericidal, showing that their antibiofilm activity does not depend on bacteria killing, which is a rare feature for antibiofilm agents.

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.

Carbohydrate supramolecular chemistry: beyond the multivalent effect

(Hetero)multivalency acts as a multichannel switch that shapes the supramolecular properties of carbohydrates in an intrinsically multifactorial biological context.

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.

An efficient and controlled synthesis of persulfonylated G1 dendrimers via click reaction

A controlled synthesis for persulfonylated G1 dendrimers has been standardized at room temperature through click reaction using Cu(PPh₃)₃Br complex in the presence of tridentate chelating ligands.

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.

Biofilms and human health

A biofilm can be defined as a surface-attached (sessile) community of microorganisms embedded and growing in a self-produced matrix of extracellular polymeric substances. These biofilm communities can be found in medical, industrial and natural environments, and can also be engineered in vitro for various biotechnological applications. Biofilms play a significant role in the transmission and persistence of human disease especially for diseases associated with inert surfaces, including medical devices for internal or external use. Biofilm infections on implants or in-dwelling devices are difficult to eradicate because of their much better protection against macrophages and antibiotics, compared to free living cells, leading to severe clinical complications often with lethal outcome. Recent developments in nanotechnology have provided novel approaches to preventing and dispersing biofilm related infections and potentially providing a novel method for fighting infections that is nondrug related.

Recent advances in click chemistry applied to dendrimer synthesis

Dendrimers are monodisperse polymers grown in a fractal manner from a central point. They are poised to become the cornerstone of nanoscale devices in several fields, ranging from biomedicine to light-harvesting. Technical difficulties in obtaining these molecules has slowed their transfer from academia to industry. In 2001, the arrival of the "click chemistry" concept gave the field a major boost. The flagship reaction, a modified Hüisgen cycloaddition, allowed researchers greater freedom in designing and building dendrimers. In the last five years, advances in click chemistry saw a wider use of other click reactions and a notable increase in the complexity of the reported structures. This review covers key developments in the click chemistry field applied to dendrimer synthesis from 2010 to 2015. Even though this is an expert review, basic notions and references have been included to help newcomers to the field.

Pseudomonas Aeruginosa Lectins As Targets for Novel Antibacterials

Pseudomonas aeruginosa is one of the most widespread and troublesome opportunistic pathogens that is capable of colonizing various human tissues and organs and is often resistant to many currently used antibiotics. This resistance is caused by different factors, including the acquisition of specific resistance genes, intrinsic capability to diminish antibiotic penetration into the bacterial cell, and the ability to form biofilms. This situation has prompted the development of novel compounds differing in their mechanism of action from traditional antibiotics that suppress the growth of microorganisms or directly kill bacteria. Instead, these new compounds should decrease the pathogens' ability to colonize and damage human tissues by inhibiting the virulence factors and biofilm formation. The lectins LecA and LecB that bind galactose and fucose, as well as oligo- and polysaccharides containing these sugars, are among the most thoroughly-studied targets for such novel antibacterials. In this review, we summarize the results of experiments highlighting the importance of these proteins for P. aeruginosa pathogenicity and provide information on existing lectins inhibitors and their effectiveness in various experimental models. Particular attention is paid to the effects of lectins inhibition in animal models of infection and in clinical practice. We argue that lectins inhibition is a perspective approach to combating P. aeruginosa. However, despite the existence of highly effective in vitro inhibitors, further experiments are required in order to advance these inhibitors into pre-clinical studies.