Feleucin-K3 Analogue with an α-(4-Pentenyl)-Ala Substitution at the Key Site Has More Potent Antimicrobial and Antibiofilm Activities in Vitro and in Vivo

An antifouling electrochemical sensor based on a U-shaped four-in-one peptide and poly(3,4-ethylenedioxythiophene) for vancomycin detection in fresh goat milk

Nonspecific adsorption of biomolecules (notably, proteins) and bacteria from unsterilized food may occur on sensor surfaces, which is still a challenge for food safety sensing. To achieve sensitive detection of unsterilized raw-food materials, in this study, a U-shaped four-in-one peptide with the sequence Ac-FLKLLKKLL-DOPA3-PPPPEEKDQDKEKaa that exhibited anchoring, antifouling, antibacterial, and recognition properties was designed. The peptide-modified sensor surface effectively prevented bacterial adhesion and proliferation while resisting biomolecule adsorption (signal inhibition rate as low as 0.51 % in single-protein solutions). A highly conductive polymer layer of poly(3,4-ethylenedioxythiophene) was introduced to improve the electrochemical performance before U-shaped four-in-one peptide anchoring. The proposed sensor could accurately detect vancomycin, with a wide linear range and limit of detection of 0.05-10 μg mL-1 and 2.06 ng mL-1 (S/N = 3), respectively. Satisfactory recovery rates (101.3-105.3 %) were achieved using diluted fresh goat milk.

Michael Addition Reaction between Dehydroalanines and Phosphites Enabled the Introduction of Phosphonates into Oligopeptides

A method for introducing a range of phosphonates into oligopeptides through a Michael addition reaction between dehydroalanine and phosphite is presented. The method offers a mild, cheap, and straightforward approach to peptide phosphorylation that has potential applications in chemical biology and medicinal chemistry. Moreover, the introduction of a phosphonate group into short antibacterial peptides is described to demonstrate its utility, leading to the discovery of phosphonated antibacterial peptides with potent broad-spectrum antibacterial activity.

Novel antimicrobial peptides modified with fluorinated sulfono-γ-AA having high stability and targeting multidrug-resistant bacteria infections

The emergence and increasing prevalence of multidrug-resistant (MDR) bacteria have posed an urgent demand for novel antibacterial drugs. Currently, antimicrobial peptides (AMPs), potential novel antimicrobial agents with rare antimicrobial resistance, represent an available strategy to combat MDR bacterial infections but suffer the limitation of protease degradation. In this study, we developed a highly effective method for optimizing the stability of AMPs by introducing fluorinated sulfono-γ-AApeptides, and successfully synthesized novel Feleucin-K3-analogs. The results demonstrated that the incorporation of fluorinated sulfono-γ-AA into Feleucin-K3 effectively improved stability and afforded optimal peptides, such as CF3-K11, which exhibited 8-9 times longer half-lives than Feleucin-K3. Moreover, CF3-K11 displayed potent antimicrobial activity against clinically isolated Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA), excellent biosafety, low resistance propensity, and possessed powerful antimicrobial efficacy for both local skin infection and pneumonia infection. The optimal CF3-K11 exhibited strong therapeutic potential and offered a superior approach for treating MDR bacterial infections.

Visible-Light Mediated Deoxygenation of Carboxylic Acid for Late-Stage Peptide Modification Targeting Dehydroalanine

A visible-light mediated deoxygenative radical addition of carboxylic acids to dehydroalanines has been disclosed. The method can be used in β-acyl alanine derivative synthesis, including those chiral and deuterated variants, and late-stage peptide modification with various functional groups, both in the homogeneous phase and on the resin in SPPS. It provides a new tool kit for rapid construction of bioactive peptide analogues, which has been demonstrated by modification of the antimicrobial peptide Feleucin-K3.

The novel peptide DR4penA attenuates the bleomycin- and paraquat-induced pulmonary fibrosis by suppressing the TGF-β/Smad signaling pathway

Pulmonary fibrosis (PF), which is caused by continuous alveolar epithelial cell injury and abnormal repair, is referred to as a difficult disease of the lung system by the World Health Organization due to its rapid progression, poor prognosis, and high mortality rate. However, there is still a lack of ideal therapeutic strategies. The peptide DR8 (DHNNPQIR-NH2 ), which is derived from rapeseed, exerted antifibrotic activity in the lung, liver, and kidney in our previous studies. By studying the structure-activity relationship and rational design, we introduced an unnatural hydrophobic amino acid (α-(4-pentenyl)-Ala) into DR8 and screened the novel peptide DR4penA (DHNα-(4-pentenyl)-APQIR-NH2 ), which had higher anti-PF activity, higher antioxidant activity and a longer half-life than DR8. Notably, DR4penA attenuated bleomycin- and paraquat-induced PF, and the anti-PF activity of DR4penA was equivalent to that of pirfenidone. Additionally, DR4penA suppressed the TGF-β/Smad pathway in TGF-β1-induced A549 cells and paraquat-induced rats. This study demonstrates that the novel peptide DR4penA is a potential candidate compound for PF therapy, and its antifibrotic activity in different preclinical models of PF provides a theoretical basis for further study.

Targeting collagen damage for sustained in situ antimicrobial activities

Antimicrobial peptides (AMPs) are promising anti-infective drugs, but their use is restricted by their short-term retention at the infection site, non-targeted uptake, and adverse effects on normal tissues. Since infection often follows an injury (e.g., in a wound bed), directly immobilizing AMPs to the damaged collagenous matrix of the injured tissues may help overcome these limitations by transforming the extracellular matrix microenvironment of the infection site into a natural reservoir of AMPs for sustained in situ release. Here, we developed and demonstrated an AMP-delivery strategy by conjugating a dimeric construct of AMP Feleucin-K3 (Flc) and a collagen hybridizing peptide (CHP), which enabled selective and prolonged anchoring of the Flc-CHP conjugate to the damaged and denatured collagen in the infected wounds in vitro and in vivo. We found that the dimeric Flc and CHP conjugate design preserved the potent and broad-spectrum antimicrobial activities of Flc while significantly enhancing and extending its antimicrobial efficacy in vivo and facilitating tissue repair in a rat wound healing model. Because collagen damage is ubiquitous in almost all injuries and infections, our strategy of targeting collagen damage may open up new avenues for antimicrobial treatments in a range of infected tissues.

Cell selectivity and antibiofilm and anti-inflammatory activities and antibacterial mechanism of symmetric-end antimicrobial peptide centered on D-Pro-Pro

This study aimed to develop a new symmetric-end antimicrobial peptide (AMP) with cell selectivity, antibiofilm, and anti-inflammatory activities. Two symmetric-end AMPs, Lf6-pP and Lf6-GG, were designed based on the sequence RRWQWRzzRWQWRR, which contains two symmetric repeat sequences connected by a β-turn-promoting sequence (zz) that can be a rigid turn by D-Pro-Pro (pP) or a flexible turn by Gly-Gly (GG). Both Lf6-pP and Lf6-GG exhibited potent antibacterial activity without causing hemolysis, but Lf6-pP exhibited better cell selectivity, likely due to the more significant impact of the rigid pP turn. Compared to Lf6-GG, Lf6-pP demonstrated approximately three times higher antimicrobial activity against drug-resistant bacteria, had a low incidence of drug resistance, and maintained its activity in the presence of physiological salts and human serum. Additionally, Lf6-pP was more effective than Lf6-GG in inhibiting biofilm formation and eradicating mature biofilms. The BODIPY-cadaverine assay indicated that the potent anti-inflammatory activity of Lf6-pP may be attributed to its direct interaction with LPS, resulting in decreased TNF-α and IL-6 levels in LPS-stimulated macrophages. Mechanistic studies, including membrane depolarization, outer/inner membrane permeation, and membrane integrity change, demonstrated that Lf6-pP exerts its antibacterial action through an intracellular-target mechanism. Overall, we propose that Lf6-pP has potential as a novel antibacterial, antibiofilm, and anti-inflammatory agent against drug-resistant bacterial infections.

Bioactive compounds: a goldmine for defining new strategies against pathogenic bacterial biofilms?

Most human infectious diseases are caused by microorganisms growing as biofilms. These three-dimensional self-organized communities are embedded in a dense matrix allowing microorganisms to persistently inhabit abiotic and biotic surfaces due to increased resistance to both antibiotics and effectors of the immune system. Consequently, there is an urgent need for novel strategies to control biofilm-associated infections. Natural products offer a vast array of chemical structures and possess a wide variety of biological properties; therefore, they have been and continue to be exploited in the search for potential biofilm inhibitors with a specific or multi-locus mechanism of action. This review provides an updated discussion of the major bioactive compounds isolated from several natural sources - such as plants, lichens, algae, microorganisms, animals, and humans - with the potential to inhibit biofilm formation and/or to disperse established biofilms by bacterial pathogens. Despite the very large number of bioactive products, their exact mechanism of action often remains to be clarified and, in some cases, the identity of the active molecule is still unknown. This knowledge gap should be filled thus allowing development of these products not only as novel drugs to combat bacterial biofilms, but also as antibiotic adjuvants to restore the therapeutic efficacy of current antibiotics.

A novel and low-toxic peptide DR3penA alleviates pulmonary fibrosis by regulating the MAPK/miR-23b-5p/AQP5 signaling axis

Pulmonary fibrosis (PF) is a pathological change caused by repeated injuries and repair dysfunction of the alveolar epithelium. Our previous study revealed that the residues Asn3 and Asn4 of peptide DR8 (DHNNPQIR-NH₂) could be modified to improve stability and antifibrotic activity, and the unnatural hydrophobic amino acids α-(4-pentenyl)-Ala and d-Ala were considered in this study. DR3penA (DHα-(4-pentenyl)-ANPQIR-NH₂) was verified to have a longer half-life in serum and to significantly inhibit oxidative damage, epithelial-mesenchymal transition (EMT) and fibrogenesis in vitro and in vivo. Moreover, DR3penA has a dosage advantage over pirfenidone through the conversion of drug bioavailability under different routes of administration. A mechanistic study revealed that DR3penA increased the expression of aquaporin 5 (AQP5) by inhibiting the upregulation of miR-23b-5p and the mitogen-activated protein kinase (MAPK) pathway, indicating that DR3penA may alleviate PF by regulating MAPK/miR-23b-5p/AQP5. Safety evaluation showed that DR3penA is a peptide drug without obvious toxicity or acute side effects and has significantly improved safety compared to DR8. Thus, our findings suggest that DR3penA, as a novel and low-toxic peptide, has the potential to be a leading compound for PF therapy, which provides a foundation for the development of peptide drugs for fibrosis-related diseases.

Novel Feleucin-K3-Derived Peptides Modified with Sulfono-γ-AA Building Blocks Targeting Pseudomonas aeruginosa and Methicillin-Resistant Staphylococcus aureus Infections

The prevalence of multidrug-resistant bacterial infections has led to dramatically increased morbidity and mortality. Antimicrobial peptides (AMPs) have great potential as new therapeutic agents to reverse this dangerous trend. Herein, a series of novel AMP Feleucin-K3 analogues modified with unnatural peptidomimetic sulfono-γ-AA building blocks were designed and synthesized. The structure-activity, structure-toxicity, and structure-stability relationships were investigated to discover the optimal antimicrobial candidates. Among them, K122 exhibited potent and broad-spectrum antimicrobial activity and high selectivity. K122 had a rapid bactericidal effect and a low tendency to induce resistance. Surprisingly, K122 showed excellent effectiveness against bacterial pneumonia. For biofilm and local skin infections, K122 significantly decreased the bacterial load and improved tissue injury at a dose of only 0.25 mg/kg, which was 160 times lower than the concentration deemed to be safe for local dermal applications. In summary, K122 is an outstanding candidate for the treatment of multidrug-resistant bacteria and biofilm infections.

Short, mirror-symmetric antimicrobial peptides centered on "RRR" have broad-spectrum antibacterial activity with low drug resistance and toxicity

The increasingly severe bacterial resistance worldwide pushes people to discover and design potential antibacterial drugs unavoidably. In this work, a series of short, mirror-symmetric peptides were designed and successfully synthesized, centered on "RRR" and labeled with hydrophobic amino acids at both ends. Based on the structure-activity relationship analysis, LWWR (LWWRRRWWL-NH₂) was screened as a desirable mirror-symmetric peptide for further study. As expected, LWWR displayed broad-spectrum antibacterial activity against the standard bacteria and antibiotic-resistant strains. Undoubtedly, the high stability of LWWR in a complex physiological environment was an essential guarantee to maximizing its antibacterial activity. Indeed, LWWR also exhibited a rapid bactericidal speed and a low tendency to develop bacterial resistance, based on the multiple actions of non-receptor-mediated membrane actions and intra-cellular mechanisms. Surprisingly, although LWWR showed similar in vivo antibacterial activity compared with Polymyxin B and Melittin, the in vivo safety of LWWR was far higher than that of them, so LWWR had better therapeutic potential. In summary, the desirable mirror-symmetric peptide LWWR was promised as a potential antibacterial agent to confront the antibiotics resistance crisis. STATEMENT OF SIGNIFICANCE: Witnessing the growing problem of antibiotic resistance, a series of short, mirror-symmetric peptides based on the symmetric center "RRR" and hydrophobic terminals were designed and synthesized in this study. Among, LWWR (LWWRRRWWL-NH₂) presented broad-spectrum antibacterial activity both in vitro and in vivo due to its multiple mechanisms and good stability. Meanwhile, the low drug resistance and toxicity of LWWR also suggested its potential for clinical application. The findings of this study will provide some inspiration for the design and development of potential antibacterial agents, and contribute to the elimination of bacterial infections worldwide as soon as possible.

Strategies employed in the design of antimicrobial peptides with enhanced proteolytic stability

Due to the alarming developing rate of multidrug-resistant bacterial pathogens, the development and modification of antimicrobial peptides (AMPs) are unprecedentedly active. Despite the fact that considerable efforts have been expended on the discovery and design strategies of AMPs, the clinical translation of peptide antibiotics remains inadequate. A large number of articles and reviews credited the limited success of AMPs to their poor stability in the biological environment, particularly their poor proteolytic stability. In the past forty years, various design strategies have been used to improve the proteolytic stability of AMPs, such as sequence modification, cyclization, peptidomimetics, and nanotechnology. Herein, we focus our discussion on the progress made in improving the proteolytic stability of AMPs and the principle, successes, and limitations of various anti-proteolytic design strategies. It is of prospective significance to extend current insights into the degradation-related inactivation of AMPs and also alleviate/overcome the problem.

NDTP Mediated Direct Rapid Amide and Peptide Synthesis without Epimerization

Herein, we explored an unprecedented mild, nonirritating, conveniently available, and recyclable coupling reagent NDTP, which could activate the carboxylic acids via acyl thiocyanide and enable the rapid amide and peptide synthesis at very mild conditions. In addition, the methodology was compatible with Fmoc-SPPS, which may provide an alternative to peptide manufacturing.

Molecular design and preparation of 2-aminothiazole sulfanilamide oximes as membrane active antibacterial agents for drug resistant Acinetobacter baumannii

A series of 2-aminothiazole sulfanilamide oximes were developed as new membrane active antibacterial agents to conquer the microbial infection. Benzoyl derivative 10c was preponderant for the treatment of drug-resistant A. baumannii infection in contrast to norfloxacin and exerted excellent biocompatibility against mammalian cells including erythrocyte and LO2 cell line. Meanwhile, it had ability to eradicate established biofilm to alleviate the resistance burden. Mechanism investigation elucidated that compound 10c was able to disturb the membrane effectively and inhibit lactic dehydrogenase, which led to cytoplasmic content leakage. The cellular redox homeostasis was interfered via the production of reactive oxygen and nitrogen species (RONS), which further contributed to respiratory pathway inactivation and reduction of GSH activity. This work indicated that 2-aminothiazole sulfanilamide oximes could be a promising start for the exploitation of novel antibacterial agents against pathogens.

Potent Antimicrobial and Antibiofilm Activities of Feleucin-K3 Analogs Modified by α-(4-Pentenyl)-Ala against Multidrug-Resistant Bacteria

The dramatic increase in antimicrobial resistance (AMR) highlights an urgent need to develop new antimicrobial therapies. Thus, antimicrobial peptides (AMPs) have emerged as promising novel antibiotic alternatives. Feleucin-K3 is an amphiphilic α-helical nonapeptide that has powerful antimicrobial activity. In our previous study, it was found that the fourth residue of Feleucin-K3 is important for antimicrobial activity. After α-(4-pentenyl)-Ala was introduced into this position, both the antimicrobial activity and stability were greatly improved. Herein, to improve the limitations of Feleucin-K3, this unnatural amino acid was further introduced into different positions of Feleucin-K3. Among these synthetic Feleucin-K3 analogs, the N-terminal-substituted analog Feleucin-K65 (K65) and C-terminal-substituted analog Feleucin-K70 (K70) had preferable antimicrobial activity. In particular, their antimicrobial activities against multidrug-resistant bacteria were more potent than that of antibiotics. The stabilities of these peptides in salt and serum environments were improved compared with those of Feleucin-K3. In addition, these analogs had low hemolytic activity and AMR. More importantly, they effectively inhibited biofilm formation and exhibited considerable efficacy compared with traditional antibiotics against biofilm infection caused by methicillin-resistant Staphylococcus aureus (MRSA). In antimicrobial mechanism studies, K65 and K70 mainly permeated the outer membrane and depolarized the cytoplasmic membrane, resulting in cellular component leakage and cell death. In summary, analogs K65 and K70 are potential antimicrobial alternatives to solve the antibiotic crisis.