Heptyl α-D-mannosides grafted on a ß-cyclodextrin core to interfere with Escherichia coli adhesion: an in vivo multivalent effect.

n-Heptyl α-D-mannoside (HM) has previously been identified as a nanomolar FimH antagonist able to prevent Escherichia coli adhesion. We have designed mono- and heptavalent glycoconjugates in which HM is tethered to ß-cyclodextrin (ß-CD) through short and long spacers. One-pot click or co-clicking procedures were developed to directly obtain the glycoconjugates from unprotected HM and ß-CD precursors. These FimH antagonists were examined biophysically and in vivo. Reverse titrations by isothermal calorimetry led to trapping of the short-tethered heptavalent ß-CD in a complex with three FimH lectins. Combined dynamic light scattering and small-angle X-ray solution scattering data allowed the construction of a model of the FimH trimer. The heptavalent ß-CDs were shown to capture and aggregate living bacteria in solution and are therefore also able to aggregate FimH when attached to different bacteria pili. The first in vivo evaluation of multivalent FimH inhibitors has been performed. The heptavalent ß-CDs proved to be much more effective anti-adhesive agents than monovalent references with doses of around 2 µg instilled in the mouse bladder leading to a significantly decreased E. coli load. Intravenously injected radiolabeled glycoconjugates can rapidly reach the mouse bladder and >2 µg concentrations can easily be retained over 24 h to prevent fluxing bacteria from rebinding.

Probing the nature of the cluster effect observed with synthetic multivalent galactosides and peanut agglutinin lectin.

We designed a set of multi-galactosides with valencies ranging from one to seven and different spacer-arm lengths. The compounds display a high structural homology for a strict assessment of multivalent phenomena. The multimers were first evaluated by an enzyme-linked lectin assay (ELLA) toward the peanut agglutinin (PNA). The binding affinity was shown to be dependent on the spacer-arm length, and cluster effects were observed for the galactosides bearing the shortest and the longest linkers. The latter compounds were shown to be much more potent PNA cross-linkers in a "sandwich assay". Dynamic light scattering (DLS) experiments also revealed the formation of soluble aggregates between heptavalent derivatives with medium or long linkers and the labeled PNA. ELLA experiments performed with valency-controlled clusters and labeled lectins are therefore not always devoid from aggregative processes. The precise nature of the multivalent interaction observed by ELLA for the compounds bearing the shortest linkers, which are unable to form PNA aggregates, was further investigated by atomic force microscopy (AFM). The galactosides were grafted onto the tip of a cantilever and the PNA lectin onto a gold surface. Similar unbinding forces were registered when the valency of the ligands was increased, thus showing that the multimers cannot interact more strongly with PNA. Multiple binding events to the PNA were also never observed, thus confirming that a chelate binding mode does not operate with the multivalent galactosides, probably because the linkers are too short. Altogether, these results suggest that the cluster effect that operates in ELLA with the multimers is not related to additional PNA stabilizations and can be ascribed to local concentration effects that favor a dynamic turnover of the tethered galactosides in the PNA binding sites.

Clustering of Escherichia coli type-1 fimbrial adhesins by using multimeric heptyl α-D-mannoside probes with a carbohydrate core.

Heptyl α-D-mannoside (HM) is a strong inhibitor of the FimH lectin that mediates the initial adhesion of the uropathogenic Escherichia coli (E. coli) to the bladder cells. We designed a set of multivalent HM ligands based on carbohydrate cores with structural valencies that range from 1 to 7. The chemical strategy used to construct the regular hydrophilic structures consisted of the repetition of a critical glucoside fragment. A primary amino group was grafted at the sugar reducing end to couple the multimers to a fluorescent label. A one-pot synthetic approach was developed to tether the ligands and the fluorescein isothiocyanate (FITC) probe to the scaffold simultaneously. Isothermal calorimetry with the monomeric FimH lectin revealed nanomolar affinities and saturation of all structurally available binding sites on the multivalent HM ligands. Direct titrations domain showed almost strict correlation of enthalpy-entropy compensation with increasing valency of the ligand, whereas reverse titration calorimetry demonstrated negative cooperativity between the first and the second binding site of the divalent heptyl mannoside. A multivalency effect was nevertheless observed by inhibiting the haemagglutination of type-1 piliated UTI89 E. coli, with a titer as low as 60 nM for the heptavalent HM ligand. An FITC-labeled HM trimer showed capture and cross-linking of living bacteria in solution, a phenomenon not previously described with low-valency ligands.

A click procedure with heterogeneous copper to tether technetium-99m chelating agents and rhenium complexes. Evaluation of the chelating properties and biodistribution of the new radiolabelled glucose conjugates.

An efficient protocol was developed to tether chelating agents and rhenium complexes onto a glucoside scaffold with a heterogeneous copper catalyst via click chemistry. The supported catalyst avoids the formation of unwanted copper complexes during the cyclisation step. The possibility to graft a pre-chelated M(CO)(3) core by click chemistry onto a biomolecule was highlighted for the first time. (99m)Tc(CO)(3)-glucoconjugates displayed excellent in vitro stability, a fast in vivo blood clearance and a low specific organ uptake or long-term retention in spleen and stomach.