Comparative functional properties of engineered cationic antimicrobial peptides consisting exclusively of tryptophan and either lysine or arginine

Catalase-encapsulated matrix metalloproteinase-9 responsive nanogels for modulation of inflammatory response and treatment of neutrophilic asthma

Asthma is a chronic disease with typical pathological features such as airflow limitation, airway inflammation and remodeling. Of these, neutrophilic asthma is considered to be the more severe and corticosteroid-resistant subtype of asthma. Increasing evidence suggests that patients with neutrophilic asthma often accompany with dysbiosis of the internal microbiota, where the increased abundance of non-typeable Haemophilus influenzae (NTHi) is closely related to the neutrophilic asthma phenotype. Furthermore, emerging evidence suggests that reactive oxygen species (ROS) are pivotal in the pathogenesis of neutrophilic asthma. In this study, matrix metalloproteinase-9 (MMP-9)-responsive, catalase-loaded nanogels (M-CAT-NGs) were synthesized, which was composed of MMP-9-sensitive peptide (VPMS), arginine-grafted chitosan and maleimide (CS-Arg-Mal), catalase (CAT), sodium citrate (SC) and ε-poly(L-lysine) (ε-PLL). The M-CAT-NGs showed potent antimicrobial effects and exerted excellent therapeutic effects in the presence of MMP-9 by causing VPMS rupture and responsive release of CAT. In vitro experiments revealed that M-CAT-NGs effectively inhibited the proliferation of NTHi, Staphylococcus aureus (S. aureus), and Escherichia coli (E. coli), while also demonstrating the capacity to modulate the inflammatory response induced by lipopolysaccharide (LPS) and hydrogen peroxide (H2O2) stimulation. In vivo experiments demonstrated that nebulized inhalation of M-CAT-NGs was effective in reducing airway hyperresponsiveness (AHR), alleviating inflammation, downregulating the expression level of ROS in the lung tissues, thus enabling the effective management of neutrophilic asthma. Thus, the development of M-CAT-NGs has shown strong potential for the clinical management of neutrophilic asthma by modulating the inflammatory response.

LPS-enriched interaction drives spectrum conversion in antimicrobial peptides: Design and optimization of AA16 derivatives for targeting gram-negative bacteria

The increasing prevalence of antibiotic-resistant Gram-negative bacteria necessitates the development of novel antimicrobial agents with targeted specificity. In this study, we designed and optimized derivatives of the antimicrobial peptide AA16, which truncated from CD14 protein α-helical region, to selectively target Gram-negative bacteria by enhancing lipopolysaccharide (LPS)-enriched interactions, thereby achieving antibacterial spectrum conversion. Starting from the parent peptide AA16 (Ac-AARIPSRILFGALRVL-Amide), we performed strategic amino acid substitutions based on structure-activity relationship analysis. This led to the identification of AA16-10R, a derivative with a specific substitution at position 10, which demonstrated significantly enhanced antibacterial activity against Gram-negative strains such as Escherichia coli and Pseudomonas aeruginosa, while maintaining low hemolytic activity. Mechanistic studies revealed that AA16-10R exhibited a strong binding affinity to LPS (Kd = 0.15 μM), and its interaction with LPS induced the formation of an α-helical structure. This conformational change facilitated its accumulation on the bacterial outer membrane and disrupted membrane integrity. Our innovative approach of exploiting LPS-enriched interactions successfully converted the antimicrobial spectrum of AA16 derivatives from broad-spectrum to Gram-negative-specific. This study highlights a novel strategy for the rational design of antimicrobial peptides based on specific protein-protein interactions, offering a promising avenue for targeted antimicrobial therapy against Gram-negative pathogens.

Cyclization of Two Antimicrobial Peptides Improves Their Activity

One promising strategy to combat worldwide antimicrobial resistance involves using cyclic peptides as antibacterial agents. Cyclization of peptides can confer several advantages, including enhanced stability to proteolysis, decreased toxicity and increased bactericidal efficacy. This paper examines two cyclic peptides CE-03 (12 AAs) and CE-05 (16 AAs) and evaluates their effectiveness in combating bacterial infections, their stability and toxicity. We compare them to their linear versions. Circular dichroism (CD) reveals that CE-03 and CE-05 both adopt random coil and β-sheet structures in lipid model membranes (LMMs) mimicking G(-) and G(+) bacteria, where they are both bactericidal. Using X-ray diffuse scattering (XDS), their effects on lipid model membranes show a deep penetration of both peptides into eukaryotic LMMs where they are nontoxic, while a headgroup location in bacterial LMMs correlates with bacterial killing. Neutron reflectometry (NR) confirms the AMP locations determined using XDS. Further, solution small-angle X-ray scattering demonstrates that both peptides induce vesicle fusion in bacterial LMMs without affecting eukaryotic LMMs. Proteolytic degradation studies show that both CE-05 and CE-03 do not lose activity when incubated with the elastase enzyme, while the helical E2-35 AMP becomes inactive upon proteolysis.

Association of idealized amphiphiles and protease inhibitors: Conferring antimicrobial peptides with stable antibacterial activity under physiological conditions to combat multidrug-resistant bacteria

AIMS

The unstable antimicrobial activity of antimicrobial peptides (AMPs) under physiological conditions (especially the degradation instigated proteases) seems to be a persistent impediment for their successful implementation in clinical trials. Consequently, our objective was to devise AMP engineering frameworks that could sustain robust antibacterial efficacy within physiological environments.

METHODS

In this work, we harvested AMPs with stable antimicrobial activity under the physiological barriers through the combination of idealized amphiphiles and trypsin inhibitors.

RESULTS

We screened and identified the lead peptides IK3-A and IK3-S, which showed potent activity against Gram-negative bacteria, including multidrug-resistant (MDR) bacteria, and exhibited promising biocompatibility with mammalian cells. Remarkably, IK3-A and IK3-S maintained sustained antibacterial potency under physiological salts, serum, and protease conditions. Furthermore, both IK3-A and IK3-S kill Gram-negative bacteria by attacking the bacterial cell membrane and inducing oxidative damage (at high concentrations). Crucially, IK3-A and IK3-S have optimal safety and efficacy in mice.

CONCLUSIONS

This is the first work to compare the effects of different trypsin inhibitors on the resistance of AMPs to protease hydrolysis on the same sequence platform. In conclusion, these findings provide guidance for the molecular design of AMPs with stable antibacterial activity under physiological conditions and facilitates the process of clinical translation of AMPs as antimicrobial biomaterials against MDR bacteria. Moreover, this may stimulate a more general interest in protease inhibitors as molecular scaffolds in the creation of highly stable peptide-based biomaterials.

Machine learning and genetic algorithm-guided directed evolution for the development of antimicrobial peptides

INTRODUCTION

Antimicrobial peptides (AMPs) are valuable alternatives to traditional antibiotics, possess a variety of potent biological activities and exhibit immunomodulatory effects that alleviate difficult-to-treat infections. Clarifying the structure-activity relationships of AMPs can direct the synthesis of desirable peptide therapeutics.

OBJECTIVES

In this study, the lipopolysaccharide-binding domain (LBD) was identified through machine learning-guided directed evolution, which acts as a functional domain of the anti-lipopolysaccharide factor family of AMPs identified from Marsupenaeus japonicus.

METHODS

LBDA-D was identified as an output of this algorithm, in which the original LBDMj sequence was the input, and the three-dimensional solution structure of LBDB was determined using nuclear magnetic resonance. Furthermore, our study involved a comprehensive series of experiments, including morphological studies and in vitro and in vivo antibacterial tests.

RESULTS

The NMR solution structure showed that LBDB possesses a circular extended structure with a disulfide crosslink at the terminus and two 310-helices and exhibits a broad antimicrobial spectrum. In addition, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that LBDB induced the formation of a cluster of bacteria wrapped in a flexible coating that ruptured and consequently killed the bacteria. Finally, coinjection of LBDB, Vibrio alginolyticus and Staphylococcus aureus in vivo improved the survival of M. japonicus, demonstrating the promising therapeutic role of LBDB for treating infectious disease.

CONCLUSIONS

The findings of this study pave the way for the rational drug design of activity-enhanced peptide antibiotics.

Novel Tree Shrew-Derived Antimicrobial Peptide with Broad-Spectrum Antibacterial Activity

The number of cationic residues and net charge are critical for the activity of antimicrobial peptides (AMPs) due to their role in facilitating initial electrostatic interactions with negatively charged bacterial membranes. A cathelicidin AMP (TC-33) has been identified from the Chinese tree shrew in our previous work, which exhibited weak antimicrobial activity, likely due to its moderately cationic nature. In the current study, based on TC-33, we designed a novel AMP by peptide truncation and Glu substitutions to increase its net cationic charge from +4 to +8. The resulting peptide, TC-LAR-18, showed 4-128-fold enhanced antimicrobial activity relative to TC-33 without causing hemolysis and cytotoxicity within 100 μg/mL. TC-LAR-18 effectively eliminated both planktonic and biofilm-associated bacteria, demonstrating rapid bactericidal effects due to its ability to quickly penetrate and disrupt bacterial cell membranes with a low propensity to induce resistance. Notably, TC-LAR-18 provided substantial protection against skin bacterial infection in mice, underscoring its therapeutic potential. These findings not only highlight the importance of positively charged residues for the antibacterial activity of AMPs but also present a useful drug candidate for combating multidrug-resistant bacteria.

How Unnatural Amino Acids in Antimicrobial Peptides Change Interactions with Lipid Model Membranes

This study investigates the potential of antimicrobial peptides (AMPs) as alternatives to combat antibiotic resistance, with a focus on two AMPs containing unnatural amino acids (UAAs), E2-53R (16 AAs) and LE-54R (14 AAs). In both peptides, valine is replaced by norvaline (Nva), and tryptophan is replaced by 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic). Microbiological studies reveal their potent activity against both Gram-negative (G(-)) and Gram-positive (G(+)) bacteria without any toxicity to eukaryotic cells at test concentrations up to 32 μM. Circular dichroism (CD) spectroscopy indicates that these peptides maintain α-helical structures when interacting with G(-) and G(+) lipid model membranes (LMMs), a feature linked to their efficacy. X-ray diffuse scattering (XDS) demonstrates a softening of G(-), G(+) and eukaryotic (Euk33) LMMs and a nonmonotonic decrease in chain order as a potential determinant for bacterial membrane destabilization. Additionally, XDS finds a significant link between both peptides' interfacial location in G(-) and G(+) LMMs and their efficacy. Neutron reflectometry (NR) confirms the AMP locations determined using XDS. Lack of toxicity in eukaryotic cells may be related to their loss of α-helicity and their hydrocarbon location in Euk33 LMMs. Both AMPs with UAAs offer a novel strategy to wipe out antibiotic-resistant strains while maintaining human cells. These findings are compared with previously published data on E2-35, which consists of the natural amino acids arginine, tryptophan, and valine.

Novel non-helical antimicrobial peptides insert into and fuse lipid model membranes

This research addresses the growing menace of antibiotic resistance by exploring antimicrobial peptides (AMPs) as alternatives to conventional antibiotics. Specifically, we investigate two linear amphipathic AMPs, LE-53 (12-mer) and LE-55 (16-mer), finding that the shorter LE-53 exhibits greater bactericidal activity against both Gram-negative (G(-)) and Gram-positive (G(+)) bacteria. Remarkably, both AMPs are non-toxic to eukaryotic cells. The heightened effectiveness of LE-53 is attributed to its increased hydrophobicity (H) compared to LE-55. Circular dichroism (CD) reveals that LE-53 and LE-55 both adopt β-sheet and random coil structures in lipid model membranes (LMMs) mimicking G(-) and G(+) bacteria, so secondary structure is not the cause of the potency difference. X-ray diffuse scattering (XDS) reveals increased lipid chain order in LE-53, a potential key distinction. Additionally, XDS study uncovers a significant link between LE-53's upper hydrocarbon location in G(-) and G(+) LMMs and its efficacy. Neutron reflectometry (NR) confirms the AMP locations determined using XDS. Solution small angle X-ray scattering (SAXS) demonstrates LE-53's ability to induce vesicle fusion in bacterial LMMs without affecting eukaryotic LMMs, offering a promising strategy to combat antibiotic-resistant strains while preserving human cell integrity, whereas LE-55 has a smaller ability to induce fusion.

Antimicrobial resistance expansion in pathogens: a review of current mitigation strategies and advances towards innovative therapy

The escalating problem of antimicrobial resistance (AMR) proliferation in clinically important pathogens has become one of the biggest threats to human health and the global economy. Previous studies have estimated AMR-associated deaths and disability-adjusted life-years (DALYs) in many countries with a view to presenting a clearer picture of the global burden of AMR-related diseases. Recently, several novel strategies have been advanced to combat resistance spread. These include efflux activity inhibition, closing of mutant selection window (MSW), biofilm disruption, lytic bacteriophage particles, nanoantibiotics, engineered antimicrobial peptides, and the CRISPR-Cas9 gene-editing technique. The single or integrated deployment of these strategies has shown potentialities towards mitigating resistance and contributing to valuable therapeutic outcomes. Correspondingly, the new paradigm of personalized medicine demands innovative interventions such as improved and accurate point-of-care diagnosis and treatment to curtail AMR. The CRISPR-Cas system is a novel and highly promising nucleic acid detection and manipulating technology with the potential for application in the control of AMR. This review thus considers the specifics of some of the AMR-mitigating strategies, while noting their drawbacks, and discusses the advances in the CRISPR-based technology as an important point-of-care tool for tracking and curbing AMR in our fight against a looming 'post-antibiotic' era.

Amidine-Based Cationic Conjugated Oligoelectrolytes with Antimicrobial Activity against Pseudomonas aeruginosa Biofilms

Pseudomonas aeruginosa is an opportunistic Gram-negative bacterium that can cause high-morbidity infections. Due to its robust, flexible genome and ability to form biofilms, it can evade and rapidly develop resistance to antibiotics. Cationic conjugated oligoelectrolytes (COEs) have emerged as a promising class of antimicrobials. Herein, we report a series of amidine-containing COEs with high selectivity for bacteria. From this series, we identified 1b as the most active compound against P. aeruginosa (minimum inhibitory concentration (MIC) = 2 μg/mL) with low cytotoxicity (IC50 (HepG2) = 1024 μg/mL). The activity of 1b was not affected by known drug-resistant phenotypes of 100 diverse P. aeruginosa isolates. Moreover, 1b is bactericidal with a low propensity for P. aeruginosa to develop resistance. Furthermore, 1b is also able to inhibit biofilm formation at subinhibitory concentrations and kills P. aeruginosa in established biofilms. The in vivo efficacy of 1b was demonstrated in biofilm-associated murine wound infection models.

Combined charge and hydrophobicity-guided screening of antibacterial peptides: two-level approach to predict antibacterial activity and efficacy

Antibacterial peptides can be a potential game changer in the fight against antibiotic resistance. In order for these peptides to become successful antibiotic alternatives, it is essential that they possess high efficacy in addition to just being antibacterial. In this study, we have developed a two-level SVM-based binary classification approach to predict the antibacterial activity of a given peptide (model 1) and thereafter classify its antibacterial efficacy as high/low (model 2) with respect to minimum inhibitory concentration (MIC) values against Staphylococcus aureus, one of the most common pathogens. Based on charge and hydrophobicity of amino acids, we developed a sequence-based combined charge and hydrophobicity-guided triad (CHT) as a new method for obtaining features of any peptide. Model 1 with a combination of CHT and amino acid composition (AAC) as the feature representation method resulted in the highest accuracy of 96.7%. Model 2 with CHT as the feature representation method yielded the highest accuracy of 70.9%. Thus, CHT is found to be a potential feature representation method for classifying antibacterial peptides based on both activity and efficacy. Furthermore, we have also used an explainable machine learning algorithm to extract various insights from these models. These insights are found to be in excellent agreement with experimental findings reported in the literature, thus enhancing the dependability of the proposed models.

Novel Helical Trp- and Arg-Rich Antimicrobial Peptides Locate Near Membrane Surfaces and Rigidify Lipid Model Membranes

Antibiotics are losing effectiveness as bacteria become resistant to conventional drugs. To find new alternatives, antimicrobial peptides (AMPs) are rationally designed with different lengths, charges, hydrophobicities (H ), and hydrophobic moments (μH ), containing only three types of amino acids: arginine, tryptophan, and valine. Six AMPs with low minimum inhibitory concentrations (MICs) and <25% toxicity to mammalian cells are selected for biophysical studies. Their secondary structures are determined using circular dichroism (CD), which finds that the % α -helicity of AMPs depends on composition of the lipid model membranes (LMMs): gram-negative (G ( - ) ) inner membrane (IM) >gram-positive (G ( + ) ) > Euk33 (eukaryotic with 33 mol% cholesterol). The two most effective peptides, E2-35 (16 amino acid [AA] residues) and E2-05 (22 AAs), are predominantly helical in G ( - ) IM and G ( + ) LMMs. AMP/membrane interactions such as membrane elasticity, chain order parameter, and location of the peptides in the membrane are investigated by low-angle and wide-angle X-ray diffuse scattering (XDS). It is found that headgroup location correlates with efficacy and toxicity. The membrane bending modulus K C displays nonmonotonic changes due to increasing concentrations of E2-35 and E2-05 in G ( - ) and G ( + ) LMMs, suggesting a bacterial killing mechanism where domain formation causes ion and water leakage.

Efficient in planta production of amidated antimicrobial peptides that are active against drug-resistant ESKAPE pathogens

Antimicrobial peptides (AMPs) are promising next-generation antibiotics that can be used to combat drug-resistant pathogens. However, the high cost involved in AMP synthesis and their short plasma half-life render their clinical translation a challenge. To address these shortcomings, we report efficient production of bioactive amidated AMPs by transient expression of glycine-extended AMPs in Nicotiana benthamiana line expressing the mammalian enzyme peptidylglycine α-amidating mono-oxygenase (PAM). Cationic AMPs accumulate to substantial levels in PAM transgenic plants compare to nontransgenic N. benthamiana. Moreover, AMPs purified from plants exhibit robust killing activity against six highly virulent and antibiotic resistant ESKAPE pathogens, prevent their biofilm formation, analogous to their synthetic counterparts and synergize with antibiotics. We also perform a base case techno-economic analysis of our platform, demonstrating the potential economic advantages and scalability for industrial use. Taken together, our experimental data and techno-economic analysis demonstrate the potential use of plant chassis for large-scale production of clinical-grade AMPs.

KDEON WK-11: A short antipseudomonal peptide with promising potential

The plight of antimicrobial resistance continues to limit the availability of antibiotic treatment effective in combating resistant bacterial infections. Despite efforts made to rectify this issue and minimise its effects on both patients and the wider community, progress in this area remains minimal. Here, we de-novo designed a peptide named KDEON WK-11, building on previous work establishing effective residues and structures active in distinguished antimicrobial peptides such as lactoferrin. We assessed its antimicrobial activity against an array of bacterial strains and identified its most potent effect, against Pseudomonas aeruginosa with an MIC value of 3.12 μM, lower than its counterparts developed with similar residues and chain lengths. We then determined its anti-biofilm properties, potential mechanism of action and in vitro cytotoxicity. We identified that KDEON WK-11 had a broad range of antimicrobial activity and specific capabilities to fight Pseudomonas aeruginosa with low in vitro cytotoxicity and promising potential to express anti-lipopolysaccharide qualities, which could be exploited to expand its properties into an anti-sepsis agent.

Engineered peptide PLG0206 overcomes limitations of a challenging antimicrobial drug class

The absence of novel antibiotics for drug-resistant and biofilm-associated infections is a global public health crisis. Antimicrobial peptides explored to address this need have encountered significant development challenges associated with size, toxicity, safety profile, and pharmacokinetics. We designed PLG0206, an engineered antimicrobial peptide, to address these limitations. PLG0206 has broad-spectrum activity against >1,200 multidrug-resistant (MDR) ESKAPEE clinical isolates, is rapidly bactericidal, and displays potent anti-biofilm activity against diverse MDR pathogens. PLG0206 displays activity in diverse animal infection models following both systemic (urinary tract infection) and local (prosthetic joint infection) administration. These findings support continuing clinical development of PLG0206 and validate use of rational design for peptide therapeutics to overcome limitations associated with difficult-to-drug pharmaceutical targets.

3D printed scaffold for repairing bone defects in apical periodontitis

Objectives

To investigate the feasibility of the 3D printed scaffold for periapical bone defects.

Methods

In this study, antimicrobial peptide KSL-W-loaded PLGA sustainable-release microspheres (KSL-W@PLGA) were firstly prepared followed by assessing the drug release behavior and bacteriostatic ability against Enterococcus faecalis and Porphyromonas gingivalis. After that, we demonstrated that KSL-W@PLGA/collagen (COL)/silk fibroin (SF)/nano-hydroxyapatite (nHA) (COL/SF/nHA) scaffold via 3D-printing technique exhibited significantly good biocompatibility and osteoconductive property. The scaffold was characterized as to pore size, porosity, water absorption expansion rate and mechanical properties. Moreover, MC3T3-E1 cells were seeded into sterile scaffold materials and investigated by CCK-8, SEM and HE staining. In the animal experiment section, we constructed bone defect models of the mandible and evaluated its effect on bone formation. The Japanese white rabbits were killed at 1 and 2 months after surgery, the cone beam computerized tomography (CBCT) and micro-CT scanning, as well as HE and Masson staining analysis were performed on the samples of the operation area, respectively. Data analysis was done using ANOVA and LSD tests. (α = 0.05).

Results

We observed that the KSL-W@PLGA sustainable-release microspheres prepared in the experiment were uniform in morphology and could gradually release the antimicrobial peptide (KSL-W), which had a long-term antibacterial effect for at least up to 10 days. HE staining and SEM showed that the scaffold had good biocompatibility, which was conducive to the adhesion and proliferation of MC3T3-E1 cells. The porosity and water absorption of the scaffold were (81.96 ± 1.83)% and (458.29 ± 29.79)%, respectively. Histological and radiographic studies showed that the bone healing efficacy of the scaffold was satisfactory.

Conclusions

The KSL-W@PLGA/COL/SF/nHA scaffold possessed good biocompatibility and bone repairing ability, and had potential applications in repairing infected bone defects.

Clinical significance The 3D printed scaffold not only has an antibacterial effect, but can also promote bone tissue formation, which provides an alternative therapy option in apical periodontitis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-022-02362-4.

Rational Framework for the Design of Trp- and Arg-Rich Peptide Antibiotics Against Multidrug-Resistant Bacteria

The threat of antibiotic resistance warrants the discovery of agents with novel antimicrobial mechanisms. Antimicrobial peptides (AMPs) directly disrupting bacterial membranes may overcome resistance to traditional antibiotics. AMP development for clinical use has been mostly limited to topical application to date. We developed a rational framework for systematically addressing this challenge using libraries composed of 86 novel Trp- and Arg-rich engineered peptides tested against clinical strains of the most common multidrug-resistant bacteria known as ESKAPE pathogens. Structure-function correlations revealed minimum lengths (as low as 16 residues) and Trp positioning for maximum antibacterial potency with mean minimum inhibitory concentration (MIC) of 2–4 μM and corresponding negligible toxicity to mammalian cells. Twelve peptides were selected based on broad-spectrum activity against both gram-negative and -positive bacteria and <25% toxicity to mammalian cells at maximum test concentrations. Most of the selected PAX remained active against the colistin-resistant clinical strains. Of the selected peptides, the shortest (the 16-residue E35) was further investigated for antibacterial mechanism and proof-of-concept in vivo efficacy. E35 killed an extensively-resistant isolate of Pseudomonas aeruginosa (PA239 from the CDC, also resistant to colistin) by irreversibly disrupting the cell membranes as shown by propidium iodide incorporation, using flow cytometry and live cell imaging. As proof of concept, in vivo toxicity studies showed that mice tolerated a systemic dose of up to 30 mg/kg peptide and were protected with a single 5 mg/kg intravenous (IV) dose against an otherwise lethal intraperitoneal injection of PA239. Efficacy was also demonstrated in an immune-compromised Klebsiella pneumoniae infection model using a daily dose of 4mg/kg E35 systemically for 2 days. This framework defines the determinants of efficacy of helical AMPs composed of only cationic and hydrophobic amino acids and provides a path for a potential departure from the restriction to topical use of AMPs toward systemic application.

Synthetic Polypeptides with Cationic Arginine Moieties Showing High Antimicrobial Activity in Similar Mineral Environments to Blood Plasma

Translocation of cell-penetrating peptides is promoted by incorporated arginine or other guanidinium groups. However, relatively little research has considered the role of these functional groups on antimicrobial peptide activity. A series of cationic linear-, star- and multi-branched-poly(L-arginine-co-L-phenylalanine) have been synthesized via the ring-opening copolymerizations of corresponding N-carboxyanhydride monomers followed by further modifications using the N-heterocyclic carbene organocatalyst. All the polymers are characterized by the random coiled microstructure. Antibacterial efficacy, tested by the gram-positive B. subtilis bacteria and the gram-negative E. coli bacteria, was sensitive to the structure and relative composition of the copolymer and increased in the order of linear- < star- < multi-branched structure. The multi-branched-p[(L-arginine)23-co-(L-phenylalanine)7]8 polymer showed the best antibacterial property with the lowest minimum inhibitory concentration values of 48 μg mL−1 for E. coli and 32 μg mL−1 for B. subtilis. The efficacy was prominent for B. subtilis due to the anionic nature of its membrane. All of the resultant arginine moiety-containing polypeptides showed excellent blood compatibility. The antibiotic effect of the copolymers with arginine moieties was retained even in the environment bearing Ca2+, Mg2+, and Na+ ions similar to blood plasma. The cationic arginine-bearing copolypeptides were also effective for the sterilization of naturally occurring sources of water such as lakes, seas, rain, and sewage, showing a promising range of applicability.

Performance of Novel Antimicrobial Protein Bg_9562 and In Silico Predictions on Its Properties with Reference to Its Antimicrobial Efficiency against Rhizoctonia solani

Bg_9562 is a potential broad-spectrum antifungal effector protein derived from the bacteria Burkholderia gladioli strain NGJ1 and is effective against Rhizoctonia solani, the causal agent of sheath blight in rice. In the present study, in vitro antifungal assays showed that Bg_9562 was efficient at 35 °C and 45 °C and ineffective either at high acidic pH (3.0) or alkaline pH (9.5) conditions. Compatibility studies between the native bioagents Trichoderma asperellum TAIK1 and Bacillus subtilis BIK3 indicated that Bg_9562 was compatible with the bioagents. A field study using foliar spray of the Bg_9562 protein indicated the need of formulating the protein before its application. In silico analysis predicted that Bg_9562 possess 111 amino acid residues (46 hydrophobic residues, 12 positive and 8 negative residues) with the high aliphatic index of 89.92, attributing to its thermostability with a half-life of 30 h. Bg_9562 (C491H813N137O166S5) possessed a protein binding potential of 1.27 kcal/mol with a better possibility of interacting and perturbing the membrane, the main target for antimicrobial proteins. The secondary structure revealed the predominance of random coils in its structure, and the best 3D model of Bg_9562 was predicted using an ab initio method with Robetta and AlphaFold 2. The predicted binding ligands were nucleic acids and zinc with confidence scores of 0.07 and 0.05, respectively. The N-terminal region (1-14 residues) and C-terminal region (101 to 111) of Bg_9562 residues were predicted to be disordered regions. Stability and binding properties of the protein from the above studies would help to encapsulate Bg_9562 using a suitable carrier to maintain efficiency and improve delivery against Rhizoctonia solani in the most challenging rice ecosphere.

Design of Oligourea-Based Foldamers with Antibacterial and Antifungal Activities

There is an urgent need to develop new therapeutic strategies to fight the emergence of multidrug resistant bacteria. Many antimicrobial peptides (AMPs) have been identified and characterized, but clinical translation has been limited partly due to their structural instability and degradability in physiological environments. The use of unnatural backbones leading to foldamers can generate peptidomimetics with improved properties and conformational stability. We recently reported the successful design of urea-based eukaryotic cell-penetrating foldamers (CPFs). Since cell-penetrating peptides and AMPs generally share many common features, we prepared new sequences derived from CPFs by varying the distribution of histidine- and arginine-type residues at the surface of the oligourea helix, and evaluated their activity on both Gram-positive and Gram-negative bacteria as well as on fungi. In addition, we prepared and tested new amphiphilic block cofoldamers consisting of an oligourea and a peptide segment whereby polar and charged residues are located in the peptide segment and more hydrophobic residues in the oligourea segment. Several foldamer sequences were found to display potent antibacterial activities even in the presence of 50% serum. Importantly, we show that these urea-based foldamers also possess promising antifungal properties.

Antimicrobial Activity and Action Mechanisms of Arg-Rich Short Analog Peptides Designed from the C-Terminal Loop Region of American Oyster Defensin (AOD)

American oyster defensin (AOD) was previously purified from acidified gill extract of the American oyster, Crassostrea virginica. AOD is composed of 38 amino acids with three disulfide bonds and exhibits strong antimicrobial activity against Gram-positive bacteria as well as significant activity against Gram-negative bacteria. Here, to develop promising peptides into antibiotic candidates, we designed five arginine-rich analogs (A0, A1, A2, A3, and A4), predicted their loop and extended strand/random structures-including nine amino acids and a disulfide bond derived from the C-terminus of AOD-and described their antimicrobial and cytotoxic effects, as well as their modes of action. In our experimental results, the A3 and A4 analogs exhibited potent antimicrobial activity against all test organisms-including four Gram-positive bacteria, six Gram-negative bacteria, and Candida albicans-without cell toxicity. A sequence of experiments, including a membrane permeabilization assay, DNA binding study, and DNA polymerization inhibition test, indicated that the two analogs (A3 and A4) possibly did not act directly on the bacterial membrane but instead interacted with intracellular components such as DNA or DNA amplification reactions. AOD analogs also showed strong bacterial inhibition activity in the plasma environment. In addition, analog-treated microbial cells clearly exhibited membrane disruption, damage, and leakage of cytoplasmic contents. Collectively, our results suggest that two analogs, A3 and A4, have potent antimicrobial activity via DNA interaction and have the potential for development into novel antimicrobial agents.

Peptides to Tackle Leishmaniasis: Current Status and Future Directions

Peptide-based drugs are an attractive class of therapeutic agents, recently recognized by the pharmaceutical industry. These molecules are currently being used in the development of innovative therapies for diverse health conditions, including tropical diseases such as leishmaniasis. Despite its socioeconomic influence on public health, leishmaniasis remains long-neglected and categorized as a poverty-related disease, with limited treatment options. Peptides with antileishmanial effects encountered to date are a structurally heterogeneous group, which can be found in different natural sources—amphibians, reptiles, insects, bacteria, marine organisms, mammals, plants, and others—or inspired by natural toxins or proteins. This review details the biochemical and structural characteristics of over one hundred peptides and their potential use as molecular frameworks for the design of antileishmanial drug leads. Additionally, we detail the main chemical modifications or substitutions of amino acid residues carried out in the peptide sequence, and their implications in the development of antileishmanial candidates for clinical trials. Our bibliographic research highlights that the action of leishmanicidal peptides has been evaluated mainly using in vitro assays, with a special emphasis on the promastigote stage. In light of these findings, and considering the advances in the successful application of peptides in leishmaniasis chemotherapy, possible approaches and future directions are discussed here.

Evaluation of Peptide-Based Probes toward In Vivo Diagnostic Imaging of Bacterial Biofilm-Associated Infections

The clinical management of bacterial biofilm infections represents an enormous challenge in today's healthcare setting. The NIH estimates that 65% of bacterial infections are biofilm-related, and therapeutic outcomes are positively correlated with early intervention. Currently, there is no reliable imaging technique to detect biofilm infections in vivo, and current clinical protocols for accurate and direct biofilm identification are nonexistent. In orthopedic implant-associated biofilm infections, for example, current detection methods are based on nonspecific X-ray or radiolabeled white blood cell imaging, coupled with peri-prosthetic tissue or fluid samples taken invasively, and must be cultured. This approach is time-consuming and often fails to detect biofilm bacteria due to sampling errors and a lack of sensitivity. The ability to quantify bacterial biofilms by real-time noninvasive imaging is an urgent unmet clinical need that would revolutionize the management and treatment of these devastating types of infections. In the present study, we assembled a collection of fluorescently labeled peptide candidates to specifically explore their biofilm targeting properties. We evaluated these fluorescently labeled peptides using various in vitro assays for their ability to specifically and nondestructively target biofilms produced by model bacterial pathogen Pseudomonas aeruginosa. The lead candidate that emerged, 4Iphf-HN17, demonstrated rapid biofilm labeling kinetics, a lack of bactericidal activity, and biofilm targeting specificity in human cell infection models. In vivo fluorescently labeled 4Iphf-HN17 showed enhanced accumulation in biofilm-infected wounds, thus warranting further study.

Engineered Cationic Antimicrobial Peptides (eCAPs) to Combat Multidrug-Resistant Bacteria

The increasing rate of antibiotic resistance constitutes a global health crisis. Antimicrobial peptides (AMPs) have the property to selectively kill bacteria regardless of resistance to traditional antibiotics. However, several challenges (e.g., reduced activity in the presence of serum and lack of efficacy in vivo) to clinical development need to be overcome. In the last two decades, we have addressed many of those challenges by engineering cationic AMPs de novo for optimization under test conditions that typically inhibit the activities of natural AMPs, including systemic efficacy. We reviewed some of the most promising data of the last two decades in the context of the advancement of the field of helical AMPs toward clinical development.

Synthesis of Fmoc-Triazine Amino Acids and Its Application in the Synthesis of Short Antibacterial Peptidomimetics

To combat the escalating rise of antibacterial resistance, the development of antimicrobial peptides (AMPs) with a unique mode of action is considered an attractive strategy. However, proteolytic degradation of AMPs remains the greatest challenge in their transformation into therapeutics. Herein, we synthesized Fmoc-triazine amino acids that differ from each other by anchoring either cationic or hydrophobic residues. These unnatural amino acids were adopted for solid-phase peptide synthesis (SPPS) to synthesize a series of amphipathic antimicrobial peptidomimetics. From the antimicrobial screening, we found that the trimer, BJK-4 is the most potent short antimicrobial peptidomimetic without showing hemolytic activity and it displayed enhanced proteolytic stability. Moreover, the mechanism of action to kill bacteria was found to be an intracellular targeting.

Vogel H, Park Y. Antifungal and Antibiofilm Activities and the Mechanism of Action of Repeating Lysine-Tryptophan Peptides against Candida albicans

The rapid increase in the emergence of antifungal-resistant Candida albicans strains is becoming a serious health concern. Because antimicrobial peptides (AMPs) may provide a potential alternative to conventional antifungal agents, we have synthesized a series of peptides with a varying number of lysine and tryptophan repeats (KWn-NH2). The antifungal activity of these peptides increased with peptide length, but only the longest KW5 peptide displayed cytotoxicity towards a human keratinocyte cell line. The KW4 and KW5 peptides exhibited strong antifungal activity against C. albicans, even under conditions of high-salt and acidic pH, or the addition of fungal cell wall components. Moreover, KW4 inhibited biofilm formation by a fluconazole-resistant C. albicans strain. Circular dichroism and fluorescence spectroscopy indicated that fungal liposomes could interact with the longer peptides but that they did not release the fluorescent dye calcein. Subsequently, fluorescence assays with different dyes revealed that KW4 did not disrupt the membrane integrity of intact fungal cells. Scanning electron microscopy showed no changes in fungal morphology, while laser-scanning confocal microscopy indicated that KW4 can localize into the cytosol of C. albicans. Gel retardation assays revealed that KW4 can bind to fungal RNA as a potential intracellular target. Taken together, our data indicate that KW4 can inhibit cellular functions by binding to RNA and DNA after it has been translocated into the cell, resulting in the eradication of C. albicans.

Enhanced therapeutic index of an antimicrobial peptide in mice by increasing safety and activity against multidrug-resistant bacteria

The rising prevalence of antibiotic resistance underscores the urgent need for novel antimicrobial agents. Antimicrobial peptides (AMPs) are potentially effective therapeutics that disrupt bacterial membranes regardless of resistance to traditional antibiotics. We have developed engineered cationic AMPs (eCAPs) with broad activity against multidrug-resistant (MDR) bacteria, but stability remains an important concern. Therefore, we sought to enhance the clinical utility of eCAP WLBU2 in biological matrices relevant to respiratory infection. A designed substitution of d-Val for l-Val resulted in increased resistance to protease enzymatic degradation. We observed multiple gains of functions such as higher activity against bacteria in biofilm mode of growth, significantly lower toxicity to erythrocytes and white blood cells compared to WLBU2, with increased safety in mice. Direct airway delivery revealed a therapeutic index of >140 for the selected enantiomer compared to that of <35 for WLBU2. The data warrant clinical exploration by aerosolized delivery to mitigate MDR-related respiratory infection.

Structure-Activity Study of an All-d Antimicrobial Octapeptide D2D

The increasing emergence of multi-drug resistant bacteria is a serious threat to public health worldwide. Antimicrobial peptides have attracted attention as potential antibiotics since they are present in all multicellular organisms and act as a first line of defence against invading pathogens. We have previously identified a small all-d antimicrobial octapeptide amide kk(1-nal)fk(1-nal)k(nle)-NH2 (D2D) with promising antimicrobial activity. In this work, we have performed a structure-activity relationship study of D2D based on 36 analogues aimed at discovering which elements are important for antimicrobial activity and toxicity. These modifications include an alanine scan, probing variation of hydrophobicity at lys5 and lys7, manipulation of amphipathicity, N-and C-termini deletions and lys-arg substitutions. We found that the hydrophobic residues in position 3 (1-nal), 4 (phe), 6 (1-nal) and 8 (nle) are important for antimicrobial activity and to a lesser extent cationic lysine residues in position 1, 2, 5 and 7. Our best analogue 5, showed MICs of 4 µg/mL against A. baumannii, E. coli, P. aeruginosa and S. aureus with a hemolytic activity of 47% against red blood cells. Furthermore, compound 5 kills bacteria in a concentration-dependent manner as shown by time-kill kinetics. Circular dichroism (CD) spectra of D2D and compounds 1-8 showed that they likely fold into α-helical secondary structure. Small angle x-ray scattering (SAXS) experiments showed that a random unstructured polymer-like chains model could explain D2D and compounds 1, 3, 4, 6 and 8. Solution structure of compound 5 can be described with a nanotube structure model, compound 7 can be described with a filament-like structure model, while compound 2 can be described with both models. Lipid interaction probed by small angle X-ray scattering (SAXS) showed that a higher amount of compound 5 (~50-60%) inserts into the bilayer compared to D2D (~30-50%). D2D still remains the lead compound, however compound 5 is an interesting antimicrobial peptide for further investigations due to its nanotube structure and minor improvement to antimicrobial activity compared to D2D.

Potential use of 13-mer peptides based on phospholipase and oligoarginine as leishmanicidal agents

Phospholipase A₂ toxins present in snake venoms interact with biological membranes and serve as structural models for the design of small peptides with anticancer, antibacterial and antiparasitic properties. Oligoarginine peptides are capable of increasing cell membrane permeability (cell penetrating peptides), and for this reason are interesting delivery systems for compounds of pharmacological interest. Inspired by these two families of bioactive molecules, we have synthesized two 13-mer peptides as potential antileishmanial leads gaining insights into structural features useful for the future design of more potent peptides. The peptides included p-Acl, reproducing a natural segment of a Lys49 PLA₂ from Agkistrodon contortrix laticinctus snake venom, and its p-AclR7 analogue where all seven lysine residues were replaced by arginines. Both peptides were active against promastigote and amastigote forms of Leishmania (L.) amazonensis and L. (L.) infantum, while displaying low cytotoxicity for primary murine macrophages. Spectrofluorimetric studies suggest that permeabilization of the parasite's cell membrane is the probable mechanism of action of these biomolecules. Relevantly, the engineered peptide p-AclR7 was more active in both life stages of Leishmania and induced higher rates of ethidium bromide incorporation than its native template p-Acl. Taken together, the results suggest that short peptides based on phospholipase toxins are potential scaffolds for development of antileishmanial candidates. Moreover, specific amino acid substitutions, such those herein employed, may enhance the antiparasitic action of these cationic peptides, encouraging their future biomedical applications.

Acellular and cellular approaches to improve diabetic wound healing

Chronic diabetic wounds represent a huge socioeconomic burden for both affected individuals and the entire healthcare system. Although the number of available treatment options as well as our understanding of wound healing mechanisms associated with diabetes has vastly improved over the past decades, there still remains a great need for additional therapeutic options. Tissue engineering and regenerative medicine approaches provide great advantages over conventional treatment options, which are mainly aimed at wound closure rather than addressing the underlying pathophysiology of diabetic wounds. Recent advances in biomaterials and stem cell research presented in this review provide novel ways to tackle different molecular and cellular culprits responsible for chronic and nonhealing wounds by delivering therapeutic agents in direct or indirect ways. Careful integration of different approaches presented in the current article could lead to the development of new therapeutic platforms that can address multiple pathophysiologic abnormalities and facilitate wound healing in patients with diabetes.

Inhibitory effect of four novel synthetic peptides on food spoilage yeasts

The spoilage of foods caused by the growth of undesirable yeast species is a problem in the food industry. Yeast species such as Zygosaccharomyces bailii, Zygosaccharomyces rouxii, Debaryomyces hansenii, Kluyveromyces lactis and Saccharomyces cerevisiae have been encountered in foods such as high sugar products, fruit juices, wine, mayonnaise, chocolate and soft drinks. The demand for new methods of preservations has increased because of the negative association attached to chemical preservatives. The sequence of a novel short peptide (KKFFRAWWAPRFLK-NH2) was modified to generate three versions of this original peptide. These peptides were tested for the inhibition of the yeasts mentioned above, allowing for the better understanding of their residue modifications. The range of the minimum inhibitory concentration was between 25 and 200 μg/mL. Zygosaccharomyces bailii was the most sensitive strain to the peptides, while Zygosaccharomyces rouxii was the most resistant. Membrane permeabilisation was found to be responsible for yeast inhibition at a level which was a two-fold increase of the MIC (400 μg/mL). The possibility of the production of reactive oxygen species was also assessed but was not recognised as a factor involved for the peptides' mode of action. Their stability in different environments was also tested, focusing on high salt, pH and thermal stability. The newly designed peptides showed good antifungal activity against some common food spoilage yeasts and has been proven effective in the application in Fanta Orange. These efficient novel peptides represent a new source of food preservation that can be used as an alternative for current controversial preservatives used in the food industry.

Antibacterial Properties and Efficacy of a Novel SPLUNC1-Derived Antimicrobial Peptide, α4-Short, in a Murine Model of Respiratory Infection

The rise of superbugs underscores the urgent need for novel antimicrobial agents. Antimicrobial peptides (AMPs) have the ability to kill superbugs regardless of resistance to traditional antibiotics. However, AMPs often display a lack of efficacy in vivo. Sequence optimization and engineering are promising but may result in increased host toxicity. We report here the optimization of a novel AMP (α4-short) derived from the multifunctional respiratory protein SPLUNC1. The AMP α4-short demonstrated broad-spectrum activity against superbugs as well as in vivo efficacy in the P. aeruginosa pneumonia model. Further exploration for clinical development is warranted.

Multidrug resistance (MDR) by bacterial pathogens constitutes a global health crisis, and resistance to treatment displayed by biofilm-associated infections (e.g., cystic fibrosis, surgical sites, and medical implants) only exacerbates a problem that is already difficult to overcome. Antimicrobial peptides (AMPs) are a promising class of therapeutics that may be useful in the battle against antibiotic resistance, although certain limitations have hindered their clinical development. The goal of this study was to examine the therapeutic potential of novel AMPs derived from the multifunctional respiratory host defense protein SPLUNC1. Using standard growth inhibition and antibiofilm assays, we demonstrated that a novel structurally optimized AMP, α4-short, was highly effective against the most common group of MDR bacteria while showing broad-spectrum bactericidal and antibiofilm activities. With negligible hemolysis and toxicity to white blood cells, the new peptide also demonstrated in vivo efficacy when delivered directly into the airway in a murine model of Pseudomonas aeruginosa-induced respiratory infection. The data warrant further exploration of SPLUNC1-derived AMPs with optimized structures to assess the potential application to difficult-to-cure biofilm-associated infections.

Membrane Active Peptides and Their Biophysical Characterization

In the last 20 years, an increasing number of studies have been reported on membrane active peptides. These peptides exert their biological activity by interacting with the cell membrane, either to disrupt it and lead to cell lysis or to translocate through it to deliver cargos into the cell and reach their target. Membrane active peptides are attractive alternatives to currently used pharmaceuticals and the number of antimicrobial peptides (AMPs) and peptides designed for drug and gene delivery in the drug pipeline is increasing. Here, we focus on two most prominent classes of membrane active peptides; AMPs and cell-penetrating peptides (CPPs). Antimicrobial peptides are a group of membrane active peptides that disrupt the membrane integrity or inhibit the cellular functions of bacteria, virus, and fungi. Cell penetrating peptides are another group of membrane active peptides that mainly function as cargo-carriers even though they may also show antimicrobial activity. Biophysical techniques shed light on peptide–membrane interactions at higher resolution due to the advances in optics, image processing, and computational resources. Structural investigation of membrane active peptides in the presence of the membrane provides important clues on the effect of the membrane environment on peptide conformations. Live imaging techniques allow examination of peptide action at a single cell or single molecule level. In addition to these experimental biophysical techniques, molecular dynamics simulations provide clues on the peptide–lipid interactions and dynamics of the cell entry process at atomic detail. In this review, we summarize the recent advances in experimental and computational investigation of membrane active peptides with particular emphasis on two amphipathic membrane active peptides, the AMP melittin and the CPP pVEC.

Improving the Activity of Trp-Rich Antimicrobial Peptides by Arg/Lys Substitutions and Changing the Length of Cationic Residues

Antimicrobial peptides (AMPs) constitute a promising alternative for the development of new antibiotics that could potentially counteract the growing number of antibiotic-resistant bacteria. However, the AMP structure⁻function relationships remain unclear and detailed studies are still necessary. The positively charged amino acid residues (Arg and Lys) play a crucial role in the activity of most AMPs due to the promotion of electrostatic interactions between the peptides and bacterial membranes. In this work we have analyzed the antimicrobial and structural properties of several Trp-rich AMPs containing exclusively either Arg or Lys as the positively charged residues. Their antimicrobial activity and mechanism of action were investigated, showing that Lys residues give rise to a reduced antimicrobial potency for most peptides, which was correlated, in turn, with a decrease in their ability to permeabilize the cytoplasmic membrane of Escherichia coli. Additionally, the presence of Arg and Lys renders the peptides susceptible to degradation by proteases, such as trypsin, limiting their therapeutic use. Therefore, modifications of the side chain length of Arg and Lys were investigated in an attempt to improve the protease resistance of AMPs. This approach resulted in enhanced stability to trypsin digestion, and in several cases, shorter sidechains conserved or even improved the antimicrobial activity. All together, these results suggest that Arg-to-Lys substitutions, coupled with side chain length modifications, can be extremely useful for improving the activity and stability of AMPs.

Antimicrobial peptides with selective antitumor mechanisms: prospect for anticancer applications

In the last several decades, there have been significant advances in anticancer therapy. However, the development of resistance to cancer drugs and the lack of specificity related to actively dividing cells leading to toxic side effects have undermined these achievements. As a result, there is considerable interest in alternative drugs with novel antitumor mechanisms. In addition to the recent approach using immunotherapy, an effective but much cheaper therapeutic option of pharmaceutical drugs would still provide the best choice for cancer patients as the first line treatment. Ribosomally synthesized cationic antimicrobial peptides (AMPs) or host defense peptides (HDP) display broad-spectrum activity against bacteria based on electrostatic interactions with negatively charged lipids on the bacterial surface. Because of increased proportions of phosphatidylserine (negatively charged) on the surface of cancer cells compared to normal cells, cationic amphipathic peptides could be an effective source of anticancer agents that are both selective and refractory to current resistance mechanisms. We reviewed herein the prospect for AMP application to cancer treatment, with a focus on modes of action of cationic AMPs.

Antimicrobial Peptides: A Potential Therapeutic Option for Surgical Site Infections

Surgical Site Infections (SSI) represents one of the most common hospital-associated infections worldwide, and many cases of SSI are due to multidrug-resistant bacteria with the propensity to attach to tissues and form biofilm on post-surgical sites. While systemic antibiotic treatment (prophylactically and therapeutically) is usually effective, SSI can be difficult to treat when associated with drug resistance. Antimicrobial Peptides (AMPs) are an untapped resource that could serve as an effective therapeutic option, as they display broad-spectrum antimicrobial activity regardless of antibiotic resistance. In the last decade, it has become increasingly clear that AMPs also display antibiofilm properties. We reviewed herein the potential of AMPs as promising therapeutics for SSI and the need for structural optimization to develop AMPs for clinical applications.

Enhanced efficacy of the engineered antimicrobial peptide WLBU2 via direct airway delivery in a murine model of Pseudomonas aeruginosa pneumonia

OBJECTIVES

Pseudomonas aeruginosa is a common cause of pneumonia in patients with cystic fibrosis with the property to generate multidrug resistance against clinically used antibiotics. Antimicrobial peptides (AMPs) are a diverse group of effector molecules of the innate immune system that protect the host against pathogens. However, the lack of activity in common biological matrices has hampered efforts towards clinical development. In this study, we evaluated the therapeutic potential of the engineered AMP WLBU2 via direct airway delivery in a murine model of P. aeruginosa infection.

METHODS

The human AMPs LL37 and WLBU2 were compared for (i) antibiofilm activity using P. aeruginosa on polarized human bronchial epithelial cells, and (ii) efficacy in P. aeruginosa pneumonia in mice using intratracheal instillation of bacteria and AMPs.

RESULTS

WLBU2 (16 μM) prevents biofilm formation by up to 3-log compared with 1-log reduction by LL37. With a single dose of 1 μg (0.05 mg/kg) delivered intratracheally, the initial effect of LL37 was moderate and transitory, as bacterial load and inflammatory cytokines increased at 24 h with observed signs of disease such as lethargy and hypothermia, consistent with moribund state requiring euthanasia. In sharp contrast, WLBU2 reduced bacterial burden (by 2 logs) and bacteria-induced inflammation (leucocytic infiltrates, cytokine and chemokine gene expression) at 6 h and 24 h post-exposure, with no observed signs of disease or host toxicity.

CONCLUSION

These promising results now establish a much lower minimum therapeutic dose of WLBU2 (a net gain of 80-fold) compared with the previously reported 4 mg/kg systemic minimum therapeutic dose, with significant implications for clinical development.