Peptidomimetic antibiotics disrupt the lipopolysaccharide transport bridge of drug-resistant Enterobacteriaceae.

The rise of antimicrobial resistance poses a substantial threat to our health system, and, hence, development of drugs against novel targets is urgently needed. The natural peptide thanatin kills Gram-negative bacteria by targeting proteins of the lipopolysaccharide transport (Lpt) machinery. Using the thanatin scaffold together with phenotypic medicinal chemistry, structural data, and a target-focused approach, we developed antimicrobial peptides with drug-like properties. They exhibit potent activity against Enterobacteriaceae both in vitro and in vivo while eliciting low frequencies of resistance. We show that the peptides bind LptA of both wild-type and thanatin-resistant Escherichia coli and Klebsiella pneumoniae strains with low-nanomolar affinities. Mode of action studies revealed that the antimicrobial activity involves the specific disruption of the Lpt periplasmic protein bridge.

Antibiotic polymyxin arranges lipopolysaccharide into crystalline structures to solidify the bacterial membrane.

Polymyxins are last-resort antibiotics with potent activity against multi-drug resistant pathogens. They interact with lipopolysaccharide (LPS) in bacterial membranes, but mechanistic details at the molecular level remain unclear. Here, we characterize the interaction of polymyxins with native, LPS-containing outer membrane patches of Escherichia coli by high-resolution atomic force microscopy imaging, along with structural and biochemical assays. We find that polymyxins arrange LPS into hexagonal assemblies to form crystalline structures. Formation of the crystalline structures is correlated with the antibiotic activity, and absent in polymyxin-resistant strains. Crystal lattice parameters alter with variations of the LPS and polymyxin molecules. Quantitative measurements show that the crystalline structures decrease membrane thickness and increase membrane area as well as stiffness. Together, these findings suggest the formation of rigid LPS-polymyxin crystals and subsequent membrane disruption as the mechanism of polymyxin action and provide a benchmark for optimization and de novo design of LPS-targeting antimicrobials.

Emerging peptide antibiotics with therapeutic potential.

This review covers some of the recent progress in the field of peptide antibiotics with a focus on compounds with novel or established mode of action and with demonstrated efficacy in animal infection models. Novel drug discovery approaches, linear and macrocyclic peptide antibiotics, lipopeptides like the polymyxins as well as peptides addressing targets located in the plasma membrane or in the outer membrane of bacterial cells are discussed.

Author Correction: Chimeric peptidomimetic antibiotics against Gram-negative bacteria.

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

Chimeric peptidomimetic antibiotics against Gram-negative bacteria.

There is an urgent need for new antibiotics against Gram-negative pathogens that are resistant to carbapenem and third-generation cephalosporins, against which antibiotics of last resort have lost most of their efficacy. Here we describe a class of synthetic antibiotics inspired by scaffolds derived from natural products. These chimeric antibiotics contain a ß-hairpin peptide macrocycle linked to the macrocycle found in the polymyxin and colistin family of natural products. They are bactericidal and have a mechanism of action that involves binding to both lipopolysaccharide and the main component (BamA) of the ß-barrel folding complex (BAM) that is required for the folding and insertion of ß-barrel proteins into the outer membrane of Gram-negative bacteria. Extensively optimized derivatives show potent activity against multidrug-resistant pathogens, including all of the Gram-negative members of the ESKAPE pathogens1. These derivatives also show favourable drug properties and overcome colistin resistance, both in vitro and in vivo. The lead candidate is currently in preclinical toxicology studies that-if successful-will allow progress into clinical studies that have the potential to address life-threatening infections by the Gram-negative pathogens, and thus to resolve a considerable unmet medical need.

Frontier Between Cyclic Peptides and Macrocycles.

This review describes a selection of macrocyclic natural products and structurally modified analogs containing peptidic and non-peptidic elements as structural features that potentially modulate cellular permeability. Examples range from exclusively peptidic structures like cyclosporin A or phepropeptins to compounds with mostly non-peptidic character, such as telomestatin or largazole. Furthermore, semisynthetic approaches and synthesis platforms to generate general and focused libraries of compounds at the interface of cyclic peptides and non-peptidic macrocycles are discussed.

Advances in macrocyclic peptide-based antibiotics.

Macrocyclic peptide-based natural products have provided powerful new antibiotic drugs, drug candidates, and scaffolds for medicinal chemists as a source of inspiration to design novel antibiotics. While most of those natural products are active mainly against Gram-positive pathogens, novel macrocyclic peptide-based compounds have recently been described, which exhibit potent and specific activity against some of the most problematic Gram-negative ESKAPE pathogens. This mini-review gives an up-date on recent developments.

Protein epitope mimetic macrocycles as biopharmaceuticals.

Fully synthetic medium-sized macrocyclic peptides mimicking the key ß-hairpin and α-helical protein epitopes relevant in many protein-protein interactions have emerged as a novel class of drugs with the potential to fill an important gap between small molecules and proteins. Conformationally stabilized macrocyclic scaffolds represent ideal templates for medicinal chemists to incorporate bioactive peptide and protein pharmacophores in order to generate novel drugs to treat diseases with high unmet medical need. This review describes recent approaches to design and generate large libraries of such macrocycles, for hit identification, and for their efficient optimization. Finally, this review describes some of the most advanced protein epitope mimetic (PEM) macrocycles in clinical development.

Spontaneous head-to-tail cyclization of unprotected linear peptides with the KAHA ligation.

The α-ketoacid-hydroxylamine (KAHA) ligation with 5-oxaproline enables the direct cyclization of peptides upon cleavage from a solid support, without coupling reagents, protecting groups, or purification of the linear precursors. This Fmoc SPPS-based method was applied to the synthesis of a library of 24 homoserine-containing cyclic peptides and was compared side-by-side with the synthesis of the same products using a standard method for cyclizing side-chain protected substrates. A detailed mechanistic study including 2H and 18O labeling experiments and the characterization of reaction intermediates by NMR and mass spectrometry is reported.