De Novo Design of Flavonoid-Based Mimetics of Cationic Antimicrobial Peptides: Discovery, Development, and Applications

Bacterial cell death to overcome drug resistance with multitargeting bis-naphthalimides as potent antibacterial agents against Enterococcus faecalis

The increasing frequency of drug-resistant pathogens poses serious health issues to humans around the globe, leading to the development of new antibacterial agents to conquer drug resistance and bacterial infections. In view of this, we have synthesized a series of bis-naphthalimides to respond to awful drug resistance. Bioactivity assay and structure-activity relationship disclosed that compounds 5d and 5o exhibit potent antibacterial activity against E. faecalis, outperforming the marketed antibiotics. These drug candidates not only inhibit the biofilm formation of E. faecalis but also display rapid bactericidal properties, thus delaying the development of drug resistance within 20 passages. To explore the mechanism of antibacterial activity against E. faecalis, biofunctional examination was carried out which unveiled that 5d and 5o effectively disrupt bacterial cell membranes, causing the leakage of cytoplasmic contents and metabolic activity loss. Concurrently, 5d and 5o effectively intercalate with DNA to block DNA replication, causing the build-up of excessive reactive oxygen species and inhibiting the glutathione activity, ultimately leading to oxidative damage of E. faecalis and cell death. In addition, these compounds readily bind with HSA with a high binding constant, indicating that these drug candidates could be easily delivered to the target site. The above finding manifested that these newly synthesized bis-naphthalimides with multitargeting antibacterial properties offer a new prospect to overcome drug resistance.

Design, synthesis and antibacterial evaluation of low toxicity amphiphilic-cephalosporin derivatives

Global public health is facing a serious problem as a result of the rise in antibiotic resistance and the decline in the discovery of new antibiotics. In this study, two series of amphiphilic-cephalosporins were designed and synthesized, several of which showed good antibacterial activity against both Gram-positive and Gram-negative bacteria. Structure-activity relationships indicated that the length of the hydrophobic alkyl chain significantly affects the antibacterial activity against Gram-negative bacteria. The best compound 2d showed high activity against drug-susceptible Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) with MICs of 0.5 and 2-4 μg/mL, respectively. Furthermore, 2d remained active in complex mammalian body fluids and had a longer post-antibiotic effect (PAE) than vancomycin. Mechanism studies indicated that compound 2d lacks membrane-damaging properties and can target penicillin-binding proteins to disrupt bacterial cell wall structure, inhibit the metabolic activity and induce the accumulation of reactive oxygen species (ROS) in bacteria. Compound 2d showed minimal drug resistance and was nontoxic to HUVEC and HBZY-1 cells with CC50 > 128 μg/mL. These findings suggest that 2d is a promising drug candidate for treating bacterial infections.

Synthesis and antimicrobial activity of aminoalkyl resveratrol derivatives inspired by cationic peptides

Antimicrobial resistance is a global concern, far from being resolved. The need of new drugs against new targets is imminent. In this work, we present a family of aminoalkyl resveratrol derivatives with antibacterial activity inspired by the properties of cationic amphipathic antimicrobial peptides. Surprisingly, the newly designed molecules display modest activity against aerobically growing bacteria but show surprisingly good antimicrobial activity against anaerobic bacteria (Gram-negative and Gram-positive) suggesting specificity towards this bacterial group. Preliminary studies into the action mechanism suggest that activity takes place at the membrane level, while no cross-resistance with traditional antibiotics is observed. Actually, some good synergistic relations with existing antibiotics were found against Gram-negative pathogens. However, some cytotoxicity was observed, despite their low haemolytic activity. Our results show the importance of the balance between positively charged moieties and hydrophobicity to improve antimicrobial activity, setting the stage for the design of new drugs based on these molecules.

Design of phenothiazine-based cationic amphiphilic derivatives incorporating arginine residues: Potential membrane-active broad-spectrum antimicrobials combating pathogenic bacteria in vitro and in vivo

Multidrug-resistant bacteria infections pose an increasingly serious threat to human health, and the development of antimicrobials is far from meeting the clinical demand. It is urgent to discover and develop novel antibiotics to combat bacterial resistance. Currently, the development of membrane active antimicrobial agents is an attractive strategy to cope with antimicrobial resistance issues. In this study, the synthesis and biological evaluation of cationic amphiphilic phenothiazine-based derivatives were reported. Among them, the most promising compound 30 bearing a n-heptyl group and two arginine residues displayed potent bactericidal activity against both Gram-positive (MICs = 1.56 μg/mL) and Gram-negative bacteria (MICs = 3.125-6.25 μg/mL). Compound 30 showed low hemolysis activity (HC50 = 281.4 ± 1.6 μg/mL) and low cytotoxicity (CC50 ＞ 50 μg/mL) toward mammalian cells, as well as excellent salt resistance. Compound 30 rapidly killed bacteria by acting on the bacterial cell membrane and appeared less prone to resistance. Importantly, compound 30 showed potent in vivo efficacy in a murine model of bacterial keratitis. Hence, the results suggested compound 30 has a promising prospect as a broad-spectrum antibacterial agent for the treatment of drug-resistant bacterial infections.

Confronting the Threat: Designing Highly Effective bis-Benzimidazolium Agents to Overcome Biofilm Persistence and Antimicrobial Resistance

The objective of this study is to take the initial steps toward developing novel antibiotics to counteract the escalating problem of antimicrobial and bacterial persistence, particularly in relation to biofilms. Our approach involves emulating the structural characteristics of cationic antimicrobial peptides. To circumvent resistance development, we have designed a library of bis-benzimidazolium salts that selectively target the microbial membranes in a nonspecific manner. To explore their structure-activity relationship, we conducted experiments using these compounds on various pathogens known for their resistance to conventional antibiotics, including Gram-positive methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecium (VRE), and Gram-negative Escherichia coli (E. coli). Notably, two bis-benzimidazolium salts exhibited robust antimicrobial activity while maintaining a high level of selectivity compared with mammalian cells. Our investigations revealed significant antibiofilm activity, as these compounds rapidly acted against established biofilms. In addition, bis-benzimidazolium compounds exhibited consistent results in resistance development and cross-resistance studies. Consequently, amphiphilic bis-benzimidazolium salts hold promise as potential candidates to combat resistance-associated infections.

Ruthenium polypyridine complexes containing prenyl groups as antibacterial agents against Staphylococcus aureus through a membrane-disruption mechanism

Four new ruthenium polypyridyl complexes with prenyl groups, [Ru(bpy)2 (MHIP)](PF6 )2 (Ru(II)-1), [Ru(dtb)2 (MHIP)](PF6 )2 (Ru(II)-2), [Ru(dmb)2 (MHIP)](PF6 )2 (Ru(II)-3), and [Ru(dmob)2 (MHIP)](PF6 )2 (Ru(II)-4) (bpy = 2,2'-bipyridine, dtb = 4,4'-di-tert-butyl-2,2'-bipyridine, dmb = 4,4'-dimethyl-2,2'-bipyridine, dmob = 4,4'-dimethoxy-2,2'-bipyridine, and MHIP = 2-(2,6-dimethylhepta-1,5-dien-1-yl)-1H-imidazo[4,f][1,10]phenanthroline), were synthesized and characterized. Their antibacterial activities against Staphylococcus aureus were assessed, and the minimum inhibition concentration (MIC) value of Ru(II)-2 against S. aureus was only 0.5 µg/mL, showing the best antibacterial activity among them. S. aureus could be quickly killed by Ru(II)-2 in 30 min and Ru(II)-2 displayed an obvious inhibitive effect on the formation of a biofilm, which was essential to avoid the development of drug-resistance. Meanwhile, Ru(II)-2 exhibited a stable MIC value against antibiotic-resistant bacteria. The antibacterial mechanism of Ru(II)-2 was probably related to depolarization of the cell membrane, and a change of permeability was associated with the formation of reactive oxygen species, leading to leakage of nucleic acid and bacterial death. Furthermore, Ru(II)-2 hardly showed toxicity to mammalian cells and the Galleria mellonella worm. Finally, murine infection studies also illustrated that Ru(II)-2 was highly effective against S. aureus in vivo.

Enhanced Bacterial-Infected Wound Healing by Nitric Oxide-Releasing Topological Supramolecular Nanocarriers with Self-Optimized Cooperative Multi-Point Anchoring

Polymeric systems that provide cationic charges or biocide-release therapeutics are used to treat the bacteria-infected wound. However, most antibacterial polymers based on topologies with restricted molecular dynamics still do not satisfy the clinical requirements due to their limited antibacterial efficacy at safe concentrations in vivo. Here a NO-releasing topological supramolecular nanocarrier with rotatable and slidable molecular entities is reported to provide conformational freedom to promote the interactions between the carrier and the pathogenic microbes, hence greatly improving the antibacterial performance. With improved contacting-killing and efficient delivery of NO biocide from the molecularly dynamic cationic ligand design, the NO-loaded topological nanocarrier achieves excellent antibacterial and anti-biofilm effects via destroying the bacterial membrane and DNA. MRSA-infected rat model is also brought out to demonstrate its wound-healing effect with neglectable toxicity in vivo. Introducing flexible molecular motions into therapeutic polymeric systems is a general design to enhance the healing of a range of diseases.

Synthesis and Biological Evaluation of Piperazine Hybridized Coumarin Indolylcyanoenones with Antibacterial Potential

A class of piperazine hybridized coumarin indolylcyanoenones was exploited as new structural antibacterial frameworks to combat intractable bacterial resistance. Bioactive assessment discovered that 4-chlorobenzyl derivative 11f showed a prominent inhibition on Pseudomonas aeruginosa ATCC 27853 with a low MIC of 1 μg/mL, which was four-fold more effective than norfloxacin. Importantly, the highly active 11f with inconspicuous hemolysis towards human red blood cells displayed quite low proneness to trigger bacterial resistance. Preliminary explorations on its antibacterial behavior disclosed that 11f possessed the ability to destroy bacterial cell membrane, leading to increased permeability of inner and outer membranes, the depolarization and fracture of membrane, and the effusion of intracellular components. Furthermore, bacterial oxidative stress and metabolic turbulence aroused by 11f also accelerated bacterial apoptosis. In particular, 11f could not only effectively inset into DNA, but also bind with DNA gyrase through forming supramolecular complex, thereby affecting the biological function of DNA. The above findings of new piperazine hybridized coumarin indolylcyanoenones provided an inspired possibility for the treatment of resistant bacterial infections.

Success stories of natural product-derived compounds from plants as multidrug resistance modulators in microorganisms

Microorganisms evolve resistance to antibiotics as a function of evolution. Antibiotics have accelerated bacterial resistance through mutations and acquired resistance through a combination of factors. In some cases, multiple antibiotic-resistant determinants are encoded in these genes, immediately making the recipient organism a "superbug". Current antimicrobials are no longer effective against infections caused by pathogens that have developed antimicrobial resistance (AMR), and the problem has become a crisis. Microorganisms that acquire resistance to chemotherapy (multidrug resistance) are a major obstacle for successful treatments. Pharmaceutical industries should be highly interested in natural product-derived compounds, as they offer new sources of chemical entities for the development of new drugs. Phytochemical research and recent experimental advances are discussed in this review in relation to the antimicrobial efficacy of selected natural product-derived compounds as well as details of synergistic mechanisms and structures. The present review recognizesand amplifies the importance of compounds with natural origins, which can be used to create safer and more effective antimicrobial drugs by combating microorganisms that are resistant to multiple types of drugs.

What Can De Novo Protein Design Bring to the Treatment of Hematological Disorders?

Protein therapeutics have been widely used to treat hematological disorders. With the advent of de novo protein design, protein therapeutics are not limited to ameliorating natural proteins but also produce novel protein sequences, folds, and functions with shapes and functions customized to bind to the therapeutic targets. De novo protein techniques have been widely used biomedically to design novel diagnostic and therapeutic drugs, novel vaccines, and novel biological materials. In addition, de novo protein design has provided new options for treating hematological disorders. Scientists have designed protein switches called Colocalization-dependent Latching Orthogonal Cage-Key pRoteins (Co-LOCKR) that perform computations on the surface of cells. De novo designed molecules exhibit a better capacity than the currently available tyrosine kinase inhibitors in chronic myeloid leukemia therapy. De novo designed protein neoleukin-2/15 enhances chimeric antigen receptor T-cell activity. This new technique has great biomedical potential, especially in exploring new treatment methods for hematological disorders. This review discusses the development of de novo protein design and its biological applications, with emphasis on the treatment of hematological disorders.

Membrane-Active Nonivamide Derivatives as Effective Broad-Spectrum Antimicrobials: Rational Design, Synthesis, and Biological Evaluation

Antibiotic resistance is emerging as a "global public health concern". To address the growing epidemic of multidrug-resistant pathogens, the development of novel antimicrobials is urgently needed. In this study, by biomimicking cationic antibacterial peptides, we designed and synthesized a series of new membrane-active nonivamide and capsaicin derivatives as peptidomimetic antimicrobials. Through modulating charge/hydrophobicity balance and rationalizing structure-activity relationships of these peptidomimetics, compound 51 was identified as the lead compound. Compound 51 exhibited potent antibacterial activity against both Gram-positive bacteria (MICs = 0.39-0.78 μg/mL) and Gram-negative bacteria (MICs = 1.56-6.25 μg/mL), with low hemolytic activity and low cytotoxicity. Compound 51 displayed a faster bactericidal action through a membrane-disruptive mechanism and avoided bacterial resistance development. Furthermore, compound 51 significantly reduced the microbial burden in a murine model of keratitis infected by Staphylococcus aureus or Pseudomonas aeruginosa. Hence, this design strategy can provide a promising and effective solution to overcome antibiotic resistance.

Identification of Novel Antifungal Skeleton of Hydroxyethyl Naphthalimides with Synergistic Potential for Chemical and Dynamic Treatments

The invasion of pathogenic fungi poses nonnegligible threats to the human health and agricultural industry. This work exploited a family of hydroxyethyl naphthalimides as novel antifungal species with synergistic potential of chemical and dynamic treatment to combat the fungal resistance. These prepared naphthalimides showed better antifungal potency than fluconazole towards some tested fungi including Aspergillus fumigatus, Candida tropicalis and Candida parapsilosis 22019. Especially, thioether benzimidazole derivative 7f with excellent anti-Candida tropicalis efficacy (MIC = 4 μg/mL) possessed low cytotoxicity, safe hemolysis level and less susceptibility to induce resistance. Biochemical interactions displayed that 7f could form a supramolecular complex with DNA to block DNA replication, and constitute a biosupermolecule with cytochrome P450 reductase (CPR) from Candida tropicalis to hinder CPR biological function. Additionally, 7f presented strong lipase affinity, which facilitated its permeation into cell membrane. Moreover, 7f with dynamic antifungal potency promoted the production and accumulation of reactive oxygen species (ROS) in cells, which destroyed the antioxidant defence system, led to oxidative stress with lipid peroxidation, loss of glutathione, membrane dysfunction and metabolic inactivation, and eventually caused cell death. The chemical and dynamic antifungal synergistic effect initiated by hydroxyethyl naphthalimides was a reasonable treatment window for prospective development.

An unanticipated discovery of novel naphthalimidopropanediols as potential broad-spectrum antibacterial members

Constructing a new antibacterial structural framework is an effective strategy to combat drug resistance. This work discovered a class of naphthalimidopropanediols (NIOLs) as a novel structural type of potential broad-spectrum antibacterial agents. Especially, NIOLs 9u, 12i, 15 against Staphylococcus aureus and NIOLs 9l, 13a against Pseudomonas aeruginosa showed excellent inhibitory activities, and they displayed high membrane selectivity from an electrostatic distinction on the membranes between bacteria and mammalian cells. These highly active NIOLs could effectually inhibit the bacterial growths, and relieve the resistance developments. Moreover, the facts of membrane depolarization, outer/inner membrane permeabilization and leakage of intracellular materials, demonstrated that these NIOLs could target and destroy the S. aureus or P. aeruginosa membranes. In particular, they could disrupt the antioxidant defense systems of S. aureus or P. aeruginosa through up-regulation of reactive oxygen species. Simultaneously, they could render the metabolic inactivation of the tested strains, and eradicate the formed biofilms and efficiently kill the strains within the biofilms. The in vitro and in vivo cytotoxicity assay indicated that these compounds possessed low toxicity. These findings of novel NIOLs as potential broad-spectrum antibacterial members provided a bright hope for conquering drug resistance.

Design and Synthesis of Phenyl Sulfide-Based Cationic Amphiphiles as Membrane-Targeting Antimicrobial Agents against Gram-Positive Pathogens

Due to the emergence of antimicrobial resistance and the lack of new antibacterial agents, it has become urgent to discover and develop new antibacterial agents against multidrug-resistant pathogens. Antimicrobial peptides (AMPs) serve as the first line of defense for the host. In this work, we have designed, synthesized, and biologically evaluated a series of phenyl sulfide derivatives by biomimicking the structural features and biological functions of AMPs. Among these derivatives, the most promising compound 17 exhibited potent antibacterial activity against Gram-positive bacteria (minimum inhibitory concentrations = 0.39-1.56 μg/mL), low hemolytic activity (HC₅₀ > 200 μg/mL), and high membrane selectivity. In addition, 17 can rapidly kill Gram-positive bacteria within 0.5 h through membrane-targeting action and avoid antibiotic resistance. More importantly, 17 showed high in vivo efficacy against Staphylococcus aureus in a murine corneal infection model. Therefore, 17 has great potential as a lead compound for the treatment of Gram-positive bacterial infections.

Design, synthesis, and biological evaluation of tetrahydroquinoline amphiphiles as membrane-targeting antimicrobials against pathogenic bacteria and fungi

The rising prevalence of drug-resistant pathogens is one of the biggest threats to human health. The development of new antibiotics that can overcome drug resistance is in urgent need. Herein, we designed and synthesized a series of amphiphilic tetrahydroquinoline derivatives as small-molecule-based antimicrobial peptidomimetics. Two lead compounds 36 and 52 which contained the tetrahydroquinoline core, hydrophobic alkyl chains (n-nonyl or isoprenyl group), different spacer lengths (n = 4 or 8), and cationic guanidine moiety, showed poor hemolytic activity, low cytotoxicity, and potent broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria, as well as fungi. The further biological evaluation revealed that compounds 36 and 52 can kill bacteria and fungi rapidly via membrane-targeting action and avoid drug resistance development. More importantly, compounds 36 and 52 exhibited similarly potent in vivo antimicrobial activities in a murine corneal infection caused by Staphylococcus aureus ATCC29213 or Pseudomonas aeruginosa ATCC9027, as compared to vancomycin or gatifloxacin. These results suggest that compounds 36 and 52 have great potential as new broad-spectrum antimicrobial agents to combat microbial resistance.

N-Arylimidazoliums as Highly Selective Biomimetic Antimicrobial Agents

Antibiotic resistance has become one of the greatest health threats in the world. In this study, a charge-dispersed dimerization strategy is described for the antimicrobial peptide (AMP) mimics via a tunable cationic charge to improve the selectivity between prokaryotic microbes and eukaryotic cells. This strategy is demonstrated with a series of charge-dispersed AMP mimics based on N-arylimidazolium skeletons. These N-arylimidazolium AMP mimics show potent antibacterial activity against strains along with a low rate of drug resistance, good hemocompatibility, and low cytotoxicity. In addition to the elimination of planktonic bacteria, N-arylimidazolium AMP mimics can also inhibit biofilm formation and destroy the established biofilm. More importantly, methicillin-resistant Staphylococcus aureus (MRSA)-induced lung-infected mice can be effectively treated by the intravenous administration of N-arylimidazolium AMP mimic, which enable the design of N-arylimidazolium AMP mimics to offer an alternative avenue to eradicate drug-resistant bacterial infection.

Aloe emodin-conjugated sulfonyl hydrazones as novel type of antibacterial modulators against S. aureus 25923 through multifaceted synergistic effects

Aloe emodin-conjugated sulfonyl hydrazones were designed and synthesized as novel type of antibacterial modulators. Aloe emodin benzenesulfonyl hydrazone 5a (AEBH-5a) was preponderant for the treatment of S. aureus 25923 (MIC = 0.5 μg/mL) over norfloxacin and presented high selectivity between bacterial membranes and mammalian membranes. Especially, AEBH-5a could eliminate the formed biofilms and relieve the development of S. aureus 25923 resistance. The antibacterial mechanism of AEBH-5a from extracellularity to intracellularity illustrated that AEBH-5a could destroy bacterial membrane integrity, leading to the leakage of protein and nucleic acid. Besides, AEBH-5a could not only interact with DNA and induce oxidative stress but also inhibit lactate dehydrogenase (LDH) activity as well as render metabolic inactivation. In silico ADME studies prediction of AEBH-5a revealed a favorable bioavailability score and prominent drug-likeness profile. This research showed that the multifaceted synergistic effect initiated by aloe emodin-conjugated sulfonyl hydrazones is a reasonable and effective tactic to combat menacing bacterial infections.

Evaluation of the Acute and Sub-Acute Oral Toxicity of Jaranol in Kunming Mice

Background: Jaranol has shown a wide range of pharmacological activities; however, no study has yet examined in vivo toxicity. The study aimed to investigate the oral acute and sub-acute toxicity of jaranol in mice.

Methods: The acute toxicity was determined by a single oral dose of jaranol (2000 mg/kg). Therein animal behaviour and mortality rate were observed for 14 days. The jaranol (50, 100 and 200 mg/kg BW·d⁻¹) was given by gavage for 28 days daily in the sub-acute study. The mouse body weight (BW), organ weight, food, water intake, biochemical, haematological parameters, and histopathology were studied in acute and sub-acute toxicity.

Results: During the acute toxicity test, a single oral dose (2000 mg/kg) jaranol did not cause significant alteration in majority of the hematological indices. However, jaranol decreased the level of serum alanine aminotransferase and aspartate aminotransferase. Those results showed that the oral lethal dose 50 (LD₅₀) of jaranol was higher than 2000 mg/kg BW, regardless of sex. In repeated daily oral doses (50, 100 and 200 mg/kg BW·d⁻¹), no mortality was recorded in the various experimental groups. The jaranol reduced body weight gain (200 mg/kg BW·d⁻¹), the relative spleen weight (all doses) and serum alanine aminotransferase activity (200 mg/kg BW·d⁻¹). On the other hand, jaranol significantly elevated red blood cell count (100 and 200 mg/kg BW·d⁻¹) and serum creatinine levels (200 mg/kg BW·d⁻¹). Histological study revealed that spleen bleeding was identified in 200 mg/kg jaranol-treated mice.

Conclusion: Jaranol was relatively safe in Kunming Mice when repetitively administered orally in small doses for a prolonged period of time. We recommend more chronic toxicity studies and clinical trials on jaranol to ensure that its use is free of potential toxicity to humans.

Antimicrobial Peptide Mimics for Clinical Use: Does Size Matter?

The search for efficient antimicrobial therapies that can alleviate suffering caused by infections from resistant bacteria is more urgent than ever before. Infections caused by multi-resistant pathogens represent a significant and increasing burden to healthcare and society and researcher are investigating new classes of bioactive compounds to slow down this development. Antimicrobial peptides from the innate immune system represent one promising class that offers a potential solution to the antibiotic resistance problem due to their mode of action on the microbial membranes. However, challenges associated with pharmacokinetics, bioavailability and off-target toxicity are slowing down the advancement and use of innate defensive peptides. Improving the therapeutic properties of these peptides is a strategy for reducing the clinical limitations and synthetic mimics of antimicrobial peptides are emerging as a promising class of molecules for a variety of antimicrobial applications. These compounds can be made significantly shorter while maintaining, or even improving antimicrobial properties, and several downsized synthetic mimics are now in clinical development for a range of infectious diseases. A variety of strategies can be employed to prepare these small compounds and this review describes the different compounds developed to date by adhering to a minimum pharmacophore based on an amphiphilic balance between cationic charge and hydrophobicity. These compounds can be made as small as dipeptides, circumventing the need for large compounds with elaborate three-dimensional structures to generate simplified and potent antimicrobial mimics for a range of medical applications. This review highlight key and recent development in the field of small antimicrobial peptide mimics as a promising class of antimicrobials, illustrating just how small you can go.

Human defensin-inspired discovery of peptidomimetic antibiotics

We report the development of peptidomimetic antibiotics derived from a natural antimicrobial peptide, human α-defensin 5. By engaging multiple bacterial targets, the lead compound is efficacious in vitro and in vivo against bacteria with highly inducible antibiotic resistance, promising a useful therapeutic agent for the treatment of infections caused by antibiotic-resistant bacteria.

Antibiotics with multiple mechanisms of action and broad-spectrum are urgently required to combat the growing health threat posed by resistant pathogenic microorganisms. Combining computational and medicinal chemistry tools, we used the structure of human α-defensin 5 (HD5) to design a class of peptidomimetic antibiotics with improved activity against both gram-negative and gram-positive bacteria. The most promising lead, compound 10, showed potent killing of multiple drug-resistant gram-negative bacteria isolated from patients. Compound 10 exhibited a multiplex mechanism of action through targeting membrane components—outer membrane protein A and lipopolysaccharide, as well as a potential intracellular target—70S ribosome, thus causing membrane perturbation and inhibition of protein synthesis. In vivo efficacy, stability, and safety of compound 10 were also validated. This human defensin-inspired synthetic peptidomimetic could help solve the serious problem of drug resistance to conventional antibiotics.

Antibacterial activities of plant-derived xanthones

The increasing threat to global health posed by antibiotic resistance remains a serious concern. This troublesome scenario has steered a need for the discovery and evaluation of novel antibacterial agents. Natural products are the main sources of antimicrobials used in clinical practice, serving as a rich reservoir for the discovery of new antibiotics. Pharmaceutical phenolics especially xanthones widely exist in the plant kingdom, and are important plant metabolites. They possess versatile biological activities, including antiviral, antibacterial, neurotrophic, and anticancer. In the present study, we focus on the antibacterial activities of phytoxanthones and summarize their structures and sources, categories and drug-likeness evaluations, and antibacterial activities. A total of 226 different plant xanthones are identified through the NETs screening, and most of them are distributed in Clusiaceae family. These phytoxanthones are divided into four groups according to the intrinsic structural properties, including the most common simple xanthones and the majority of biprenylated ones. Moreover, their physicochemical parameters are calculated and the structure-activity relationships are discussed as well. These results indicate that the biprenylated xanthone derivatives may be promising antibacterial candidates and that the natural products of plants may be a poorly understood repository for the discovery of novel antibacterial agents.

Multiple roles of ribosomal antimicrobial peptides in tackling global antimicrobial resistance

In the last century, conventional antibiotics have played a significant role in global healthcare. Antibiotics support the body in controlling bacterial infection and simultaneously increase the tendency of drug resistance. Consequently, there is a severe concern regarding the regression of the antibiotic era. Despite the use of antibiotics, host defence systems are vital in fighting infectious diseases. In fact, the expression of ribosomal antimicrobial peptides (AMPs) has been crucial in the evolution of innate host defences and has been irreplaceable to date. Therefore, this valuable source is considered to have great potential in tackling the antimicrobial resistance (AMR) crisis. Furthermore, the possibility of bacterial resistance to AMPs has been intensively investigated. Here, we summarize all aspects related to the multiple applications of ribosomal AMPs and their derivatives in combating AMR.

Short Peptides and Their Mimetics as Potent Antibacterial Agents and Antibiotic Adjuvants

Antimicrobial resistance (AMR) has been increasing unrelentingly worldwide, thus negatively impacting human health. The discovery and development of novel antibiotics is an urgent unmet need of the hour. However, it has become more challenging, requiring increasingly time-consuming efforts with increased commercial risks. Hence, alternative strategies are urgently needed to potentiate the existing antibiotics. In this context, short cationic peptides or peptide-based antimicrobials that mimic the activity of naturally occurring antimicrobial peptides (AMPs) could overcome the disadvantages of AMPs having evolved as potent antibacterial agents. Besides their potent antibacterial efficacy, short peptide conjugates have also gained attention as potent adjuvants to conventional antibiotics. Such peptide antibiotic combinations have become an increasingly cost-effective therapeutic option to tackle AMR. This Review summarizes the recent progress for peptide-based small molecules as promising antimicrobials and as adjuvants for conventional antibiotics to counter multidrug resistant (MDR) pathogens.

Advances on chemically modified antimicrobial peptides for generating peptide antibiotics

Antimicrobial peptides (AMPs) are pinpointed as promising molecules against antibiotic-resistant bacterial infections. Nevertheless, there is a discrepancy between the AMP sequences generated and the tangible outcomes in clinical trials. AMPs' limitations include enzymatic degradation, chemical/physical instability and toxicity toward healthy human cells. These factors compromise AMPs' bioavailability, resulting in limited therapeutic potential. To overcome such obstacles, peptidomimetic approaches, including glycosylation, PEGylation, lipidation, cyclization, grafting, D-amino acid insertion, stapling and dendrimers are promising strategies to fine-tune AMPs. Here we focused on chemical modifications applied for AMP optimization and how they have helped these peptide-based antibiotic candidates' design and translational potential.

Host Defense Peptides: Dual Antimicrobial and Immunomodulatory Action

The rapid rise of multidrug-resistant (MDR) bacteria has once again caused bacterial infections to become a global health concern. Antimicrobial peptides (AMPs), also known as host defense peptides (HDPs), offer a viable solution to these pathogens due to their diverse mechanisms of actions, which include direct killing as well as immunomodulatory properties (e.g., anti-inflammatory activity). HDPs may hence provide a more robust treatment of bacterial infections. In this review, the advent of and the mechanisms that lead to antibiotic resistance will be described. HDP mechanisms of antibacterial and immunomodulatory action will be presented, with specific examples of how the HDP aurein 2.2 and a few of its derivatives, namely peptide 73 and cG4L73, function. Finally, resistance that may arise from a broader use of HDPs in a clinical setting and methods to improve biocompatibility will be briefly discussed.

Development of Amphiphilic Coumarin Derivatives as Membrane-Active Antimicrobial Agents with Potent In Vivo Efficacy against Gram-Positive Pathogenic Bacteria

Increases in drug-resistant pathogens are becoming a serious detriment to human health. To combat pathogen infections, a new series of amphiphilic coumarin derivatives were designed and synthesized as antimicrobial agents with membrane-targeting action. We herein report a lead compound, 25, that displayed potent antibacterial activity against Gram-positive bacteria, including MRSA. Compound 25 exhibited weak hemolytic activity and low toxicity to mammalian cells and can kill Gram-positive bacteria quickly (within 0.5 h) by directly disrupting the bacterial cell membranes. Additionally, compound 25 demonstrated excellent efficacy in a murine corneal infection caused by Staphylococcus aureus. These results suggest that 25 has great potential to be a potent antimicrobial agent for treating drug-resistant Gram-positive bacterial infections.

Plant Natural Flavonoids Against Multidrug Resistant Pathogens

The increasing emergence and dissemination of multidrug resistant (MDR) bacterial pathogens accelerate the desires for new antibiotics. Natural products dominate the preferred chemical scaffolds for the discovery of antibacterial agents. Here, the potential of natural flavonoids from plants against MDR bacteria, is demonstrated. Structure-activity relationship analysis shows the prenylation modulates the activity of flavonoids and obtains two compounds, α-mangostin (AMG) and isobavachalcone (IBC). AMG and IBC not only display rapid bactericidal activity against Gram-positive bacteria, but also restore the susceptibility of colistin against Gram-negative pathogens. Mechanistic studies generally show such compounds bind to the phospholipids of bacterial membrane, and result in the dissipation of proton motive force and metabolic perturbations, through distinctive modes of action. The efficacy of AMG and IBC in four models associated with infection or contamination, is demonstrated. These results suggest that natural products of plants may be a promising and underappreciated reservoir to circumvent the existing antibiotic resistance.

Self-assembly of virulent amyloid-derived peptides into nanoantibacterials

Current strategies for the design of antibacterial peptides show limitations in the development of assembled antibacterial peptides due to the challenges in simultaneously balancing the antibacterial activity and assembling behavior. Herein, we report on one strategy for the design of antibacterial peptides derived from virulent amyloids and investigate their self-assembly into nanostructures with remarkable antibacterial activity. The peptides were either directly truncated from virulent amyloid peptide PSM α3 or mutated from the original sequence by replacing the lysine and phenylalanine residues with arginine or tryptophan, leading to three undecapeptides. Conformational and morphological results indicated the formation of nanotubes and twisted nanoribbons by the truncated peptide and the mutated peptide, respectively, predominately driven by anti-parallel β-sheets. Bacterial culturing experiments revealed that the two mutated peptides possessed remarkable antibacterial activity against both Gram-positive and Gram-negative bacteria by disrupting the bacterial membrane at a concentration above their critical aggregation concentrations, thus leading to two nanoantibacterials. Our findings demonstrate that biomimetic peptides originated from virulent amyloids exhibit great potential in the development of assembled antibacterial peptides, thus providing a new strategy for simultaneously addressing the antibacterial activity and pharmacokinetics of natural antibacterial peptides in the future.

Amphipathic Peptide Antibiotics with Potent Activity against Multidrug-Resistant Pathogens

The emergence and prevalence of multidrug-resistant (MDR) bacteria have posed a serious threat to public health. Of particular concern are methicillin-resistant Staphylococcus aureus (MRSA) and blaNDM, mcr-1 and tet(X)-positive Gram-negative pathogens. The fact that few new antibiotics have been approved in recent years exacerbates this global crisis, thus, new alternatives are urgently needed. Antimicrobial peptides (AMPs) originated from host defense peptides with a wide range of sources and multiple functions, are less prone to achieve resistance. All these characteristics laid the foundation for AMPs to become potential antibiotic candidates. In this study, we revealed that peptide WW307 displayed potent antibacterial and bactericidal activity against MDR bacteria, including MRSA and Gram-negative bacteria carrying blaNDM-5, mcr-1 or tet(X4). In addition, WW307 exhibited great biofilm inhibition and eradication activity. Safety and stability experiments showed that WW307 had a strong resistance against various physiological conditions and displayed relatively low toxicity. Mechanistic experiments showed that WW307 resulted in membrane damage by selectively targeting bacterial membrane-specific components, including lipopolysaccharide (LPS), phosphatidylglycerol (PG), and cardiolipin (CL). Moreover, WW307 dissipated membrane potential and triggered the production of reactive oxygen species (ROS). Collectively, these results demonstrated that WW307 represents a promising candidate for combating MDR pathogens.