In Vitro Activity of the Novel Antimicrobial Peptide Dendrimer G3KL against Multidrug-Resistant Acinetobacter baumannii and Pseudomonas aeruginosa.

The in vitro activity of the novel antimicrobial peptide dendrimer G3KL was evaluated against 32 Acinetobacter baumannii (including 10 OXA-23, 7 OXA-24, and 11 OXA-58 carbapenemase producers) and 35 Pseudomonas aeruginosa (including 18 VIM and 3 IMP carbapenemase producers) strains and compared to the activities of standard antibiotics. Overall, both species collections showed MIC50/90 values of 8/8 μg/ml and minimum bactericidal concentrations at which 50% or 90% of strains tested are killed (MBC50/90) of 8/8 μg/ml. G3KL is a promising molecule with antibacterial activity against multidrug-resistant and extensively drug-resistant A. baumannii and P. aeruginosa isolates.

Membrane disrupting antimicrobial peptide dendrimers with multiple amino termini

Antimicrobial peptide dendrimer H1 Leu8(Lys-Leu)4(Lys-Phe)2Lys-LysNH2 (Lys = branching lysine) was identified by screening a 6750-membered combinatorial library by the bead-diffusion assay. Sequence variations also revealed dendrimer bH1 Leu8(Dap-Leu)4(Dap-Phe)2Dap-LysNH2 (Dap = branching 2,3-diaminopropanoic acid) as a more potent analog. H1 and bH1 showed good antimicrobial activities mediated by membrane disruption (MIC = 2–4 μg mL−1 on Bacillus subtilis and Escherichia coli) but low hemolytic activity (MHC = 310 μg mL−1 respectively >2000 μg mL−1).

Dendritic glycopeptides as Pseudomonas aeruginosa biofilm inhibitors, Oral presentation, 32nd European Peptide symposium, Athens, Greece, 2-7 September 2012

Glycopeptide dendrimers as Pseudomonas aeruginosa biofilm inhibitors. Glycopeptide dendrimers are being developed for inhibition of pathogen adhesion to host cells, a process mediated by carbohydrate-lectins interactions. Such compounds could be used in the treatment of infections by pathogenic bacteria such as Pseudomonas aeruginosa that can be resistant to known antibiotics. Pseudomonas aeruginosa produces two lectins, the fucose binding LecB and the galactose binding LecA. Both lectins have been shown to be virulence factors, involved in cell adhesion and biofilms formation. Screening combinatorial libraries of fucosylated peptide dendrimers led to the glycopeptide dendrimer (C-Fuc-LysProLeu)4(LysPheLysIle)2 LysHisIleNH2. This dendrimer binds the lectin LecB with submicromolar IC50 and shows potent inhibition of P. aeruginosa biofilms for both the laboratory strain PAO1 and for clinical isolates [1]. Appending the peptide dendrimer portion of FD2 with galactosy endgroups gave galactosylpeptide dendrimers as potent ligands for LecA which also act as biofilm inhibitors. Structure-activity relationship studies demonstrated that multivalency was essential for strong binding and biofilm inhibition. [2]The results open the way to develop therapeutic agents based on glycopeptide dendrimers. Peptide dendrimers with antimicrobial properties and good cell penetration are other applications of dendritic peptides we are now investigating.

Functionalization of PAMAM dendrimers with nitronyl nitroxide radicals as models for the outer-sphere relaxation in dentritic potential MRI contrast agents

PAMAM dendrimers functionalized with nitronyl nitroxide radicals were characterized. Quantitative determination of substitution with radicals was performed using EPR and electrochemical methods. The study of the 1H NMR relaxation of the surrounding water showed how the outer-sphere contribution to the relaxivity may be limited by the presence of the dendrimer core.

Structural Insight into Multivalent Galactoside Binding to Pseudomonas aeroginosa 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.

Multivalency effects in Pseudomonas aeruginosa biofilm inhibition and dispersal by glycopeptide dendrimers targeting lectin LecA

The galactose specific lectin LecA partly mediates the formation of antibiotic resistant biofilms by Pseudomonas aeruginosa, an opportunistic pathogen causing lethal airways infections in immunocompromised and cystic fibrosis patients, suggesting that preventing LecA binding to natural saccharides might provide new opportunities for treatment. Here 8-fold (G3) and 16-fold (G4) galactosylated analogs of GalAG2, a tetravalent G2 glycopeptide dendrimer LecA ligand and P. aeruginosa biofilm inhibitor, were obtained by convergent chloroacetyl thioether (ClAc) ligation between 4-fold or 8-fold chloroacetylated dendrimer cores and digalactosylated dendritic arms. Hemagglutination inhibition, isothermal titration calorimetry and biofilm inhibition assays showed that G3 dendrimers bind LecA slightly better than their parent G2 dendrimers and induce complete biofilm inhibition and dispersal of P. aeruginosa biofilms, while G4 dendrimers show reduced binding and no biofilm inhibition. A binding model accounting for the observed saturation of glycopeptide dendrimer galactosyl groups and LecA binding sites is proposed based on the crystal structure of a G3 dendrimer LecA complex.

Liquid-Crystalline Dendrimers Designed by Click Chemistry

Liquid-crystalline dendrimers have been prepared from second-generation Percec-type poly(benzyl ether) dendrons or second-generation poly(aryl ester) dendrons carrying cyanobiphenyl mesogens. The Janus dendrimer, which combines the two types of dendromesogens, has also been synthesized. Those compounds have been prepared under copper-catalyzed azide–alkyne cycloaddition conditions. The mesomorphic properties have been studied by thermal analysis (POM, DSC) and small-angle X-ray scattering. Smectic A, nematic, and columnar phases have been observed depending on the dendritic building blocks. The click reaction has proven to be a powerful and elegant synthetic tool for the design of complex dendritic liquid-crystalline architectures.