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

Abstract

eThe 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 MIC 50/90 values of 8/8 g/ml and minimum bactericidal concentrations at which 50% or 90% of strains tested are killed (MBC 50/90 ) of 8/8 g/ml. G3KL is a promising molecule with antibacterial activity against multidrug-resistant and extensively drug-resistant A. baumannii and P. aeruginosa isolates. The spread of Acinetobacter baumannii and Pseudomonas aeruginosa isolates that are resistant to carbapenem antibiotics due to the production of carbapenemases represents a serious threat (1). These strains are usually multidrug-resistant (MDR) due to the coexpression of mechanisms involving other classes of antibiotics, thus drastically limiting our therapeutic armamentarium (2-4). In particular, extensively drug-resistant (XDR) isolates are commonly detected worldwide (5), whereas the prevalence of pandrug-resistant (PDR) isolates is increasing worryingly in several countries (6-8). Therefore, novel antimicrobial strategies need to be rapidly developed.Recently, there has been a rising interest in evaluating naturally occurring or synthetic antimicrobial peptides (AMPs) with activity against prokaryotic membranes. This attention is due to their wide spectrum of activity against both Gram-positive and Gramnegative species, potent bactericidal activity, and ability to bypass common mechanisms of resistance that affect standard antibiotics (9, 10). However, several reasons have so far limited the clinical implementation of AMPs: (i) high susceptibility to degradation by endogenous and microbial proteases; (ii) toxicity due to the high concentration necessary to inhibit bacteria; and (iii) short half-life because of high protein binding (11). Several authors have modified AMPs to obtain proteolytically resistant versions, mostly by sequence variations and the use of D-amino acids (12-15). However, redesigning the peptide chain topology, in particular by introducing multiple branching points to obtain synthetic AMP dendrimers (AMPDs), seems a promising solution to overcome all of the the aforementioned problems (16-18).G3KL is a novel AMP dendrimer (AMPD) developed at the Department of Chemistry and Biochemistry of the University of Bern (Switzerland) by sequence optimization of an initial hit compound identified by screening a combinatorial library of dendrimers using a tailored high-throughput screening assay and presumed to act as a membrane-disrupting agent (19)(20)(21)(22). Its activity requires a dendritic topology and only natural lysine and leucine residues alternating in the branches (Fig. 1). This novel AMPD has demonstrated in vitro activity against several Gram-negative strains, low toxicity to human red blood cells (minimal hemolytic ...

Alternatives to antibiotics—a pipeline portfolio review

“…Chemical modifications, hybrid peptides and chemical mimetics could be explored. 134,135 Project creation and translational research in this area could be accelerated by committing £85m/year for 5 years. This would provide a powerful incentive to build capacity and to progress towards clinical validation of these peptide based approaches.…”

Antimicrobial Dendrimeric Peptides: Structure, Activity and New Therapeutic Applications

“…As noted by the researchers, both arginine (Arg) and tryptophan (Trp) residues occur frequently in AMPs, often in the same sequence (e.g., indolicidin), with Arg providing cationic charges that are crucial for peptide binding to the negatively-charged cell walls and membranes of bacterial targets and the lipophilic Trp anchoring peptides to the outer leaflet of the membrane and perturbing its integrity. More recently, the activity of the novel antimicrobial peptide dendrimer G3KL, with natural lysine and leucine residues alternating in the branches, against a number of Acinetobacter baumannii and Pseudomonas aeruginosa strains was reported as compared to the activities of standard antibiotics [25]. Overall, G3KL displayed a promising antibacterial activity against a large collection of difficult-to-treat isolates, including several producing carbapenemases, that are frequently faced in the contemporary international clinical scenario; in addition, the compound had little toxicity for red blood cells in vitro [25].…”

“…More recently, the activity of the novel antimicrobial peptide dendrimer G3KL, with natural lysine and leucine residues alternating in the branches, against a number of Acinetobacter baumannii and Pseudomonas aeruginosa strains was reported as compared to the activities of standard antibiotics [25]. Overall, G3KL displayed a promising antibacterial activity against a large collection of difficult-to-treat isolates, including several producing carbapenemases, that are frequently faced in the contemporary international clinical scenario; in addition, the compound had little toxicity for red blood cells in vitro [25]. G3KL, which is believed to act as a membrane-disrupting compound, is a peptide dendrimer of third generation with the sequence (KL) 8 ( K KL) 4 ( K KL) 2 K KL ( K = branching lysine), structured as multiple short dipeptides connected by branching Lys residues, and has been derived through a process of sequence optimization of a hit compound spotted by screening a combinatorial library of dendrimers, by means of a custom-made high-throughput screening assay [26,27].…”

Branched peptides as bioactive molecules for drug design

“…It showed in vitro activity against several Gram‐negative strains, low toxicity to human red blood cells (minimal hemolytic concentration 840 μg/mL vs >2000 μg/mL for polymyxin B), stability in human serum (half‐life >18 hours; MIC 2 and 4 μg/mL for P. aeruginosa ) and easy preparation by standard solid‐phase peptide synthesis. Attempts to identify G3KL‐resistant strains were also unsuccessful …”