Biostimulation of Bacteria in Liquid Culture for Identification of New Antimicrobial Compounds

We hypothesized that environmental microbiomes contain a wide range of bacteria that produce yet uncharacterized antimicrobial compounds (AMCs) that can potentially be used to control pathogens. Over 600 bacterial strains were isolated from soil and food compost samples, and 68 biocontrol bacteria with antimicrobial activity were chosen for further studies based on inhibition assays against a wide range of food and plant pathogens. For further characterization of the bioactive compounds, a new method was established that used living pathogens in a liquid culture to stimulate bacteria to produce high amounts of AMCs in bacterial supernatants. A peptide gel electrophoresis microbial inhibition assay was used to concurrently achieve size separation of the antimicrobial peptides. Fifteen potential bioactive peptides were then further characterized by tandem MS, revealing cold-shock proteins and 50S ribosomal proteins. To identify non-peptidic AMCs, bacterial supernatants were analyzed by HPLC followed by GC/MS. Among the 14 identified bioactive compounds, 3-isobutylhexahydropyrrolo[1,2-a]pyrazine-1,4-dione and 2-acetyl-3-methyl-octahydropyrrolo[1,2-a]piperazine-1,4-dione were identified as new AMCs. Our work suggests that antimicrobial compound production in microbes is enhanced when faced with a threat from other microorganisms, and that this approach can rapidly lead to the development of new antimicrobials with the potential for upscaling.

CryoEM structure of the outer membrane secretin channel pIV from the f1 filamentous bacteriophage

The Ff family of filamentous bacteriophages infect gram-negative bacteria, but do not cause lysis of their host cell. Instead, new virions are extruded via the phage-encoded pIV protein, which has homology with bacterial secretins. Here, we determine the structure of pIV from the f1 filamentous bacteriophage at 2.7 Å resolution by cryo-electron microscopy, the first near-atomic structure of a phage secretin. Fifteen f1 pIV subunits assemble to form a gated channel in the bacterial outer membrane, with associated soluble domains projecting into the periplasm. We model channel opening and propose a mechanism for phage egress. By single-cell microfluidics experiments, we demonstrate the potential for secretins such as pIV to be used as adjuvants to increase the uptake and efficacy of antibiotics in bacteria. Finally, we compare the f1 pIV structure to its homologues to reveal similarities and differences between phage and bacterial secretins.

Instructive analysis of engineered carbon materials for potential application in water and wastewater treatment

Water remediation is an essential component for sustainable development. Increasing population and rapid industrialization have contributed to the deterioration of water resources. In particular, effluents from chemical, pharmaceutical, petroleum industries, and anthropogenic activities have led to severe ecological degradation. Many of these detrimental pollutants are highly toxic even at low concentrations, acting as carcinogens and inflicting severe long-lasting effects on human health. This review underscores the potential applications of engineered carbon-based materials for effective wastewater treatment. It focuses on the performance as well as efficiency of activated carbon, graphene nanomaterial, and carbon nanotubes, both with and without chemical functionalization. Plausible mechanisms of action between the chemically functionalized adsorbent and pollutants are also discussed. Based on the keywords from the literature published in the recent five years, a statistical practicality-vs-applicability analysis of these three materials is also provided. The review will provide a deep understanding of the physical or chemical interactions of the wastewater pollutants with carbon materials.

Platinum Cyclooctadiene Complexes with Activity against Gram-positive Bacteria

Antimicrobial resistance is a looming health crisis, and it is becoming increasingly clear that organic chemistry alone is not sufficient to continue to provide the world with novel and effective antibiotics. Recently there has been an increased number of reports describing promising antimicrobial properties of metal-containing compounds. Platinum complexes are well known in the field of inorganic medicinal chemistry for their tremendous success as anticancer agents. Here we report on the promising antibacterial properties of platinum cyclooctadiene (COD) complexes. Amongst the 15 compounds studied, the simplest compounds Pt(COD)X2 (X=Cl, I, Pt1 and Pt2) showed excellent activity against a panel of Gram-positive bacteria including vancomycin and methicillin resistant Staphylococcus aureus. Additionally, the lead compounds show no toxicity against mammalian cells or haemolytic properties at the highest tested concentrations, indicating that the observed activity is specific against bacteria. Finally, these compounds showed no toxicity against Galleria mellonella at the highest measured concentrations. However, preliminary efficacy studies in the same animal model found no decrease in bacterial load upon treatment with Pt1 and Pt2. Serum exchange studies suggest that these compounds exhibit high serum binding which reduces their bioavailability in vivo, mandating alternative administration routes such as e. g. topical application.

Design, synthesis and screening of a drug discovery library based on an Eremophila-derived serrulatane scaffold

Chemical studies of the aerial parts of the Australian desert plant Eremophila microtheca afforded the targeted and known diterpenoid scaffolds, 3,7,8-trihydroxyserrulat-14-en-19-oic acid and 3-acetoxy-7,8-dihydroxyserrulat-14-en-19-oic acid. The most abundant serrulatane scaffold was converted to the poly-methyl derivatives, 3-hydroxy-7,8-dimethoxyserrulat-14-en-19-oic acid methyl ester and 3,7,8-trimethoxyserrulat-14-en-19-oic acid methyl ester using simple and rapid methylation conditions consisting of DMSO, NaOH and MeI at room temperature. Subsequently a 12-membered amide library was synthesised by reacting the methylated scaffolds with a diverse series of commercial primary amines. The chemical structures of the 12 undescribed semi-synthetic analogues were fully characterised following 1D/2D NMR, MS, UV, ECD and [α]_D data analyses. All compounds were evaluated for their anthelmintic, anti-microbial and anti-viral activities. While none of the compounds significantly inhibited motility or development of the exsheathed third-stage larvae (xL3s) of a pathogenic ruminant parasite, Haemonchus contortus, the tri-methylated analogue induced a skinny phenotype in fourth-stage larvae (L4s) after seven days of treatment (IC₅₀ = 14 μM). Anti-bacterial and anti-fungal activities were not observed at concentrations up to 20 μM. Activity against HIV latency reversal was tested in inducible, chronically-infected cells, with the tri-methylated analogue being the most active (EC₅₀ = 38 μM).

Engineering mesoporous silica nanoparticles towards oral delivery of vancomycin

Vancomycin (Van) is a key antibiotic of choice for the treatment of systemic methicillin resistant Staphylococcus aureus (MRSA) infections. However, due to its poor membrane permeability, it is administered parenterally, adding to the cost and effort of treatment. The poor oral bioavailability of Van is mainly due to its physico-chemical properties that limit its paracellular and transcellular transport across gastrointestinal (GI) epithelium. Herein we report the development of silica nanoparticles (SNPs)-based formulations that are able to enhance the epithelial permeability of Van. We synthesized SNPs of different pore sizes (2 nm and 9 nm) and modified their surface charge and polarity by attaching different functional groups (-NH₂, -PO₃, and -CH₃). Van was loaded within these SNPs at a loading capacity in the range of ca. 18-29 wt%. The Van-loaded SNPs exhibited a controlled release behaviour when compared to un-encapsulated Van which showed rapid release due to its hydrophilic nature. Among Van-loaded SNPs, SNPs with large pores showed a prolonged release compared to SNPs with small pores while SNPs functionalised with -CH₃ groups exhibited a slowest release among the functionalised SNPs. Importantly, Van-loaded SNPs, especially the large pore SNPs with negative charge, enhanced the permeability of Van across an epithelial cell monolayer (Caco-2 cell model) by up to 6-fold, with P_app values up to 1.716 × 10^-5 cm s^-1 (vs. 0.304 × 10^-5 cm s^-1 for un-encapsulated Van) after 3 h. The enhancement was dependent on both the type of SNPs and their surface functionalisation. The permeation enhancing effect of SNPs was due to its ability to transiently open the tight junctions measured by decrease in transepithelial resistance (TEER) which was reversible after 3 h. All in all, our data highlights the potential of SNPs (especially SNPs with large pores) for oral delivery of Van or other antimicrobial peptides.

Serum Complement Activation by C4BP-IgM Fusion Protein Can Restore Susceptibility to Antibiotics in Neisseria gonorrhoeae

Neisseria gonorrhoeae is the etiological agent of gonorrhea, the second most common bacterial sexually transmitted infection worldwide. Reproductive sequelae of gonorrhea include infertility, ectopic pregnancy and chronic pelvic pain. Most antibiotics currently in clinical use have been rendered ineffective due to the rapid spread of antimicrobial resistance among gonococci. The developmental pipeline of new antibiotics is sparse and novel therapeutic approaches are urgently needed. Previously, we utilized the ability of N. gonorrhoeae to bind the complement inhibitor C4b-binding protein (C4BP) to evade killing by human complement to design a chimeric protein that linked the two N-terminal gonococcal binding domains of C4BP with the Fc domain of IgM. The resulting molecule, C4BP-IgM, enhanced complement-mediated killing of gonococci. Here we show that C4BP-IgM induced membrane perturbation through complement deposition and membrane attack complex pore insertion facilitates the access of antibiotics to their intracellular targets. Consequently, bacteria become more susceptible to killing by antibiotics. Remarkably, C4BP-IgM restored susceptibility to azithromycin of two azithromycin-resistant clinical gonococcal strains because of overexpression of the MtrC-MtrD-MtrE efflux pump. Our data show that complement activation can potentiate activity of antibiotics and suggest a role for C4BP-IgM as an adjuvant for antibiotic treatment of drug-resistant gonorrhea.

Mesoporous Silica Nanoparticles Improve Oral Delivery of Antitubercular Bicyclic Nitroimidazoles

Pretomanid and MCC7433, a novel nitroimidazopyrazinone analog, are promising antitubercular agents that belong to the bicyclic nitroimidazole family. Despite possessing high cell permeability, they suffer from poor aqueous solubility and require specialized formulations in order to be orally bioavailable. To address this limitation, we investigated the use of mesoporous silica nanoparticles (MCM-41) as drug carriers. MCM-41 nanoparticles were synthesized using a sol-gel method, and their surface was further modified with amine and phosphonate groups. A simple rotary evaporation method was used to incorporate the compounds of interest into the nanoparticles, leading to a high encapsulation efficiency of ≥86% with ∼10% loading (w/w). An overall significant improvement of solubility was also observed, and the pharmacological activity of pretomanid and MCC7433 was fully retained when tested in vitro against Mycobacterium tuberculosis using these nanocarriers. Amino-functionalized MCM-41 nanoparticles were found to enhance the systemic exposure of MCC7433 in mice (1.3-fold higher C_max) compared to MCC7433 alone. The current work highlights the potential of using nanoparticles such as mesoporous silica as a carrier for oral delivery of poorly soluble antibacterial agents against tuberculosis.

Targeted Protein Degradation: The New Frontier of Antimicrobial Discovery?

Targeted protein degradation aims to hijack endogenous protein quality control systems to achieve direct knockdown of protein targets. This exciting technology utilizes event-based pharmacology to produce therapeutic outcomes, a feature that distinguishes it from classical occupancy-based inhibitor agents. Early degrader candidates display resilience to mutations while possessing potent nanomolar activity and high target specificity. Paired with the rapid advancement of our knowledge in the factors driving targeted degradation, the expansion of this style of therapeutic agent to a range of disease indications is eagerly awaited. In particular, the area of antibiotic discovery is sorely lacking in novel approaches, with the Antimicrobial Resistance (AMR) crisis looming as the next potential global health calamity. Here, the current advances in targeted protein degradation are highlighted, and potential approaches for designing novel antimicrobial protein degraders are proposed, ranging from adaptations of current strategies to completely novel approaches to targeted protein degradation.

The Antimicrobial Resistance Crisis: An Inadvertent, Unfortunate but Nevertheless Informative Experiment in Evolutionary Biology

The global rise of antimicrobial resistance (AMR) phenotypes is an exemplar for rapid evolutionary response. Resistance arises as a consequence of humanity’s widespread and largely indiscriminate use of antimicrobial compounds. However, some features of this crisis remain perplexing. The remarkably widespread and rapid rise of diverse, novel and effective resistance phenotypes is in stark contrast to the apparent paucity of antimicrobial producers in the global microbiota. From the viewpoint of evolutionary theory, it should be possible to use selection coefficients to examine these phenomena. In this work we introduce an elaboration on the selection coefficient s termed selective efficiency, considering the genetic, metabolic, ecological and evolutionary impacts that accompany selective phenotypes. We then demonstrate the utility of the selective efficiency concept using AMR and antimicrobial production phenotypes as ‘worked examples’ of the concept. In accomplishing this objective, we also put forward cogent hypotheses to explain currently puzzling aspects of the AMR crisis. Finally, we extend the selective efficiency concept into a consideration of the ongoing management of the AMR crisis.

Repurposing a neurodegenerative disease drug to treat Gram-negative antibiotic-resistant bacterial sepsis

The emergence of polymyxin resistance in carbapenem-resistant and extended-spectrum β-lactamase (ESBL)-producing bacteria is a critical threat to human health, and alternative treatment strategies are urgently required. We investigated the ability of the hydroxyquinoline analog ionophore PBT2 to restore antibiotic sensitivity in polymyxin-resistant, ESBL-producing, carbapenem-resistant Gram-negative human pathogens. PBT2 resensitized Klebsiella pneumoniae, Escherichia coli, Acinetobacter baumannii, and Pseudomonas aeruginosa to last-resort polymyxin class antibiotics, including the less toxic next-generation polymyxin derivative FADDI-287, in vitro. We were unable to select for mutants resistant to PBT2 + FADDI-287 in polymyxin-resistant E. coli containing a plasmid-borne mcr-1 gene or K. pneumoniae carrying a chromosomal mgrB mutation. Using a highly invasive K. pneumoniae strain engineered for polymyxin resistance through mgrB mutation, we successfully demonstrated the efficacy of PBT2 + polymyxin (colistin or FADDI-287) for the treatment of Gram-negative sepsis in immunocompetent mice. In comparison to polymyxin alone, the combination of PBT2 + polymyxin improved survival and reduced bacterial dissemination to the lungs and spleen of infected mice. These data present a treatment modality to break antibiotic resistance in high-priority polymyxin-resistant Gram-negative pathogens.

Chemical Synthesis of TFF3 Reveals Novel Mechanistic Insights and a Gut-Stable Metabolite

TFF3 regulates essential gastro- and neuroprotective functions, but its molecular mode of action remains poorly understood. Synthetic intractability and lack of reliable bioassays and validated receptors are bottlenecks for mechanistic and structure–activity relationship studies. Here, we report the chemical synthesis of TFF3 and its homodimer via native chemical ligation followed by oxidative folding. Correct folding was confirmed by NMR and circular dichroism, and TFF3 and its homodimer were not cytotoxic or hemolytic. TFF3, its homodimer, and the trefoil domain (TFF3_10-50) were susceptible to gastrointestinal degradation, revealing a gut-stable metabolite (TFF3_7-54; t_1/2 > 24 h) that retained its trefoil structure and antiapoptotic bioactivity. We tried to validate the putative TFF3 receptors CXCR4 and LINGO2, but neither TFF3 nor its homodimer displayed any activity up to 10 μM. The discovery of a gut-stable bioactive metabolite and reliable synthetic accessibility to TFF3 and its analogues are cornerstones for future molecular probe development and structure–activity relationship studies.

There is no market for new antibiotics: this allows an open approach to research and development

There is an increasingly urgent need for new antibiotics, yet there is a significant and persistent economic problem when it comes to developing such medicines. The problem stems from the perceived need for a "market" to drive commercial antibiotic development. In this article, we explore abandoning the market as a prerequisite for successful antibiotic research and development. Once one stops trying to fix a market model that has stopped functioning, one is free to carry out research and development (R&D) in ways that are more openly collaborative, a mechanism that has been demonstrably effective for the R&D underpinning the response to the COVID pandemic. New "open source" research models have great potential for the development of medicines for areas of public health where the traditional profit-driven model struggles to deliver. New financial initiatives, including major push/pull incentives, aimed at fixing the broken antibiotics market provide one possible means for funding an openly collaborative approach to drug development. We argue that now is therefore the time to evaluate, at scale, whether such methods can deliver new medicines through to patients, in a timely manner.

Syzygium cumini(L.),Skeels fruit extracts: In vitro and in vivo anti-inflammatory properties

ETHNOPHARMACOLOGICAL RELEVANCE

Syzygium cumini (L.) Skeels is an important medicinal plant utilized in the health care systems of Pakistan, India, Sri Lanka, and Bangladesh. S. cumini have been used to treat renal issues, indigestion, diabetes, dysentery, and employed in folk medicine to treat inflammations. It is known to anticipate antioxidant, anti-inflammatory, anticancer, anti-diabetic, anti-bacterial, antifungal, activities, and radioprotective activities.

MATERIAL AND METHODS

We examined the in vitro anti-inflammatory activities of S. cumini fruit extracts, evaluated using membrane stabilization, egg albumin denaturation, and bovine serum albumin denaturation assays. In vivo anti-inflammatory activity was also assessed, using murine models of carrageenan, formaldehyde, and PGE2 induced paw edema. Fractionation of active extracts was performed using HPLC, followed by LC-ESI-MS/MS analysis to identify the bioactive compounds responsible for anti-inflammatory activity.

RESULTS

The crude methanolic extract showed stronger in vitro and in vivo anti-inflammatory activities compared to other extracts. The most potent effects were observed in the formaldehyde induced paw edema assay wherein methanolic extract and standard indomethacin induced 72% and 88% inhibition against paw edema volume in comparison to control (normal saline) respectively. In the bovine serum albumin denaturation assay the methanolic extract induced 82% inhibition against denaturation as compared to control (phosphate buffer) while standard diclofenac sodium induced 98% inhibition. In contrast, 50% v/v MeOH:H2O or 100% dichloromethane extracts displayed moderate to weak effects in the anti-inflammatory models. HPLC fractionation provided 6 active sub-fractions, four (MF2, MF3, MF6, MF7) from the 100% methanolic extract and two (HAF1, HAF3) from the 50% methanolic extract. The MF2, MF7, and HAF1 sub-fractions displayed potent activity in all studied in vitro assays. LC-ESI-MS-MS analysis tentatively identified delphinidin 3-glucoside, peonidin-3,5-diglucoside, gallic acid, liquitrigenin, scopoletin, umbelliferon, and rosmanol from the 100% methanolic fractions. Myricetin, catechin, quinic acid, chlorogenic acid, ellagic acid, gallic acid, and caffeic acid were identified in the 50% methanolic fractions.

CONCLUSIONS

These results demonstrate that S. cumini fruit extracts are a rich source of bioactive compounds that are worthy of further investigation as leads for anti-inflammatory drug discovery.

Antimicrobial and Anticancer Properties of Synthetic Peptides Derived from the Wasp Parachartergus fraternus

Agelaia-MPI and protonectin are antimicrobial peptides isolated from the wasp Parachartergus fraternus that show antimicrobial and neuroactive activities. Previously, two analogues of these peptides, neuroVAL and protonectin-F, were designed to reduce nonspecific toxicity and improve potency. Here, the three-dimensional structures of neuroVAL, protonectin and protonectin-F were determined by using circular dichroism and NMR spectroscopy. Antibacterial, antifungal, cytotoxic and hemolytic activities were tested for the parent peptides and analogues. All peptides showed moderate antimicrobial activity against Gram-positive bacteria, with agelaia-MPI being the most active. Protonectin and protonectin-F were found to be toxic to cancerous and noncancerous cell lines. Internalization experiments revealed that these peptides accumulate inside both cell types. By contrast, neuroVAL was nontoxic to all tested cells and was able to enter cells without accumulating. In summary, neuroVAL has potential as a nontoxic cell-penetrating peptide, while protonectin-F needs further modification to realize its potential as an antitumor peptide.

Nontoxic Cobalt(III) Schiff Base Complexes with Broad-Spectrum Antifungal Activity

Resistance to currently available antifungal drugs has quietly been on the rise but overshadowed by the alarming spread of antibacterial resistance. There is a striking lack of attention to the threat of drug-resistant fungal infections, with only a handful of new drugs currently in development. Given that metal complexes have proven to be useful new chemotypes in the fight against diseases such as cancer, malaria, and bacterial infections, it is reasonable to explore their possible utility in treating fungal infections. Herein we report a series of cobalt(III) Schiff base complexes with broad-spectrum antifungal activity. Some of these complexes show minimum inhibitory concentrations (MIC) in the low micro- to nanomolar range against a series of Candida and Cryptococcus yeasts. Additionally, we demonstrate that these compounds show no cytotoxicity against both bacterial and human cells. Finally, we report the first in vivo toxicity data on these compounds in Galleria mellonella, showing that doses as high as 266 mg kg-1 are tolerated without adverse effects, paving the way for further in vivo studies of these complexes.

The antimicrobial potential of cannabidiol

Antimicrobial resistance threatens the viability of modern medicine, which is largely dependent on the successful prevention and treatment of bacterial infections. Unfortunately, there are few new therapeutics in the clinical pipeline, particularly for Gram-negative bacteria. We now present a detailed evaluation of the antimicrobial activity of cannabidiol, the main non-psychoactive component of cannabis. We confirm previous reports of Gram-positive activity and expand the breadth of pathogens tested, including highly resistant Staphylococcus aureus, Streptococcus pneumoniae, and Clostridioides difficile. Our results demonstrate that cannabidiol has excellent activity against biofilms, little propensity to induce resistance, and topical in vivo efficacy. Multiple mode-of-action studies point to membrane disruption as cannabidiol's primary mechanism. More importantly, we now report for the first time that cannabidiol can selectively kill a subset of Gram-negative bacteria that includes the 'urgent threat' pathogen Neisseria gonorrhoeae. Structure-activity relationship studies demonstrate the potential to advance cannabidiol analogs as a much-needed new class of antibiotics.

Multi-Institution Research and Education Collaboration Identifies New Antimicrobial Compounds

New antibiotics are urgently needed to address increasing rates of multidrug resistant infections. Seventy-six diversely functionalized compounds, comprising five structural scaffolds, were synthesized and tested for their ability to inhibit microbial growth. Twenty-six compounds showed activity in the primary phenotypic screen at the Community for Open Antimicrobial Drug Discovery (CO-ADD). Follow-up testing of active molecules confirmed that two unnatural dipeptides inhibit the growth of Cryptococcus neoformans with a minimum inhibitory concentration (MIC) ≤ 8 μg/mL. Syntheses were carried out by undergraduate students at five schools implementing Distributed Drug Discovery (D3) programs. This report showcases that a collaborative research and educational process is a powerful approach to discover new molecules inhibiting microbial growth. Educational gains for students engaged in this project are highlighted in parallel to the research advances. Aspects of D3 that contribute to its success, including an emphasis on reproducibility of procedures, are discussed to underscore the power of this approach to solve important research problems and to inform other coupled chemical biology research and teaching endeavors.

Fluorescent macrolide probes - synthesis and use in evaluation of bacterial resistance

The emerging crisis of antibiotic resistance requires a multi-pronged approach in order to avert the onset of a post-antibiotic age. Studies of antibiotic uptake and localisation in live cells may inform the design of improved drugs and help develop a better understanding of bacterial resistance and persistence. To facilitate this research, we have synthesised fluorescent derivatives of the macrolide antibiotic erythromycin. These analogues exhibit a similar spectrum of antibiotic activity to the parent drug and are capable of labelling both Gram-positive and -negative bacteria for microscopy. The probes localise intracellularly, with uptake in Gram-negative bacteria dependent on the level of efflux pump activity. A plate-based assay established to quantify bacterial labelling and localisation demonstrated that the probes were taken up by both susceptible and resistant bacteria. Significant intra-strain and -species differences were observed in these preliminary studies. In order to examine uptake in real-time, the probe was used in single-cell microfluidic microscopy, revealing previously unseen heterogeneity of uptake in populations of susceptible bacteria. These studies illustrate the potential of fluorescent macrolide probes to characterise and explore drug uptake and efflux in bacteria.

Macrolide fluorescent probes illuminate the interactions between antibiotics and bacteria, providing new insight into mechanisms of resistance.

Antitubercular and Antiparasitic 2-Nitroimidazopyrazinones with Improved Potency and Solubility

Following the approval of delamanid and pretomanid as new drugs to treat drug-resistant tuberculosis, there is now a renewed interest in bicyclic nitroimidazole scaffolds as a source of therapeutics against infectious diseases. We recently described a nitroimidazopyrazinone bicyclic subclass with promising antitubercular and antiparasitic activity, prompting additional efforts to generate analogs with improved solubility and enhanced potency. The key pendant aryl substituent was modified by (i) introducing polar functionality to the methylene linker, (ii) replacing the terminal phenyl group with less lipophilic heterocycles, or (iii) generating extended biaryl side chains. Improved antitubercular and antitrypanosomal activity was observed with the biaryl side chains, with most analogs achieved 2- to 175-fold higher activity than the monoaryl parent compounds, with encouraging improvements in solubility when pyridyl groups were incorporated. This study has contributed to understanding the existing structure–activity relationship (SAR) of the nitroimidazopyrazinone scaffold against a panel of disease-causing organisms to support future lead optimization.

An amphipathic peptide with antibiotic activity against multidrug-resistant Gram-negative bacteria

Peptide antibiotics are an abundant and synthetically tractable source of molecular diversity, but they are often cationic and can be cytotoxic, nephrotoxic and/or ototoxic, which has limited their clinical development. Here we report structure-guided optimization of an amphipathic peptide, arenicin-3, originally isolated from the marine lugworm Arenicola marina. The peptide induces bacterial membrane permeability and ATP release, with serial passaging resulting in a mutation in mlaC, a phospholipid transport gene. Structure-based design led to AA139, an antibiotic with broad-spectrum in vitro activity against multidrug-resistant and extensively drug-resistant bacteria, including ESBL, carbapenem- and colistin-resistant clinical isolates. The antibiotic induces a 3–4 log reduction in bacterial burden in mouse models of peritonitis, pneumonia and urinary tract infection. Cytotoxicity and haemolysis of the progenitor peptide is ameliorated with AA139, and the ‘no observable adverse effect level’ (NOAEL) dose in mice is ~10-fold greater than the dose generally required for efficacy in the infection models.

Peptide antibiotics often display a very narrow therapeutic index. Here, the authors present an optimized peptide antibiotic with broad-spectrum in vitro activities, in vivo efficacy in multiple disease models against multidrug-resistant Gram-negative infections, and reduced toxicity.

Chemical synthesis of human trefoil factor 1 (TFF1) and its homodimer provides novel insights into their mechanisms of action

TFF1 is a key peptide for gastrointestinal protection and repair. Its molecular mechanism of action remains poorly understood with synthetic intractability a recognised bottleneck. Here we describe the synthesis of TFF1 and its homodimer and their interactions with mucins and Helicobacter pylori. Synthetic access to TFF1 is an important milestone for probe and therapeutic development.