Open-vessel polymerization of N-carboxyanhydride (NCA) for polypeptide synthesis

Synthetic polypeptides, also known as poly(α-amino acids), have the same polyamide backbone structures as natural proteins and peptides. As an important class of biomaterials, polypeptides have been widely used because of their biocompatibility, bioactivity and biodegradability. Ring-opening polymerization of N-carboxyanhydride (NCA) is a classical and widely used method for the synthesis of polypeptides. The dominantly used primary amine-initiated NCA polymerization can yield well-defined polymers and complex macromolecular architectures, but the reaction is slow and sensitive to moisture, making it necessary to use anhydrous solvents and a glovebox. One solution is to use lithium hexamethyldisilazide (LiHMDS) as the initiator, as described in this protocol. LiHMDS-initiated NCA polymerization is less sensitive to moisture and can be carried out in an open vessel outside the glovebox. It is also very fast; the reaction can be complete within 5 min to produce 30-mer polypeptides. In this protocol, poly(γ-benzyl-L-glutamate) is prepared as an example, but the protocol can easily be adapted to the synthesis of other polypeptides by generating NCAs from different amino acids, making it particularly suitable for the efficient parallel synthesis of polypeptide libraries. We provide detailed procedures for NCA synthesis and purification, the method of polymer end-group modification and measurement of polymerization kinetics and reactivity ratio. The procedure for synthesis of monomers and polymerization to form polypeptides requires <1 d. The superfast and open-vessel NCA polymerization method described here will probably enable a wide range of applications in the synthesis and functional study of polypeptide biomaterials.

Magnetic silk fibroin nanospheres loaded with amphiphilic polypeptides and antibiotics for biofilm eradication

The eradication of established biofilms is a highly challenging task, due to the protective barrier effect of extracellular polymeric substances (EPS) and the presence of persister cells. Both increased drug permeability and elimination of persister cells are essential for the eradication of biofilms. Here, magnetic silk fibroin nanospheres loaded with antibiotics and host defense peptide (HDP) mimics (MPSN/S@P) were developed to demonstrate a new strategy for biofilm eradication. As an HDP mimic, an amphiphilic polypeptide containing 90% L-lysine and 10% L-valine (Lys90Val10) was selected for loading onto magnetic silk fibroin nanospheres via electrostatic interactions. Lys90Val10 exhibited excellent antibacterial activities against both planktonic and persister cells of Staphylococcus aureus (S. aureus). As a representative of the hydrophobic drug, spiramycin (SPM) was conveniently embedded into the β-sheet domain during the self-assembly process of silk fibroin. The sustained release of SPM during biofilm eradication enhanced the antibacterial efficacy of MPSN/S@P. The antibacterial test demonstrated that the extract from the MPSN/S@P suspension can kill both planktonic and persister cells of S. aureus, as well as inhibiting biofilm formation. Importantly, with the assistance of magnetic guidance and photothermal effects derived from Fe3O4 nanoparticles (Fe3O4 NPs), over 92% of bacteria in the biofilm were killed by MPSN/S@P, indicating the successful eradication of mature biofilms. The simple preparation method, integration of photothermal and magnetic responsiveness, and persister cell killing functions of MPSN/S@P provide an accessible strategy and illustrative paradigm for efficient biofilm eradication.

Emerging Trends in Dissolving-Microneedle Technology for Antimicrobial Skin-Infection Therapies

Skin and soft-tissue infections require significant consideration because of their prolonged treatment duration and propensity to rapidly progress, resulting in severe complications. The primary challenge in their treatment stems from the involvement of drug-resistant microorganisms that can form impermeable biofilms, as well as the possibility of infection extending deep into tissues, thereby complicating drug delivery. Dissolving microneedle patches are an innovative transdermal drug-delivery system that effectively enhances drug penetration through the stratum corneum barrier, thereby increasing drug concentration at the site of infection. They offer highly efficient, safe, and patient-friendly alternatives to conventional topical formulations. This comprehensive review focuses on recent advances and emerging trends in dissolving-microneedle technology for antimicrobial skin-infection therapy. Conventional antibiotic microneedles are compared with those based on emerging antimicrobial agents, such as quorum-sensing inhibitors, antimicrobial peptides, and antimicrobial-matrix materials. The review also highlights the potential of innovative microneedles incorporating chemodynamic, nanoenzyme antimicrobial, photodynamic, and photothermal antibacterial therapies. This review explores the advantages of various antimicrobial therapies and emphasizes the potential of their combined application to improve the efficacy of microneedles. Finally, this review analyzes the druggability of different antimicrobial microneedles and discusses possible future developments.

Facile Construction of Antimicrobial Surface via One-Step Co-Deposition of Peptide Polymer and Dopamine

The infections associated with implantable medical devices can greatly affect the therapeutic effect and impose a heavy financial burden. Therefore, it is of great significance to develop antimicrobial biomaterials for the prevention and mitigation of healthcare-associated infections. Here, a facile construction of antimicrobial surface via one-step co-deposition of peptide polymer and dopamine is reported. The co-deposition of antimicrobial peptide polymer DLL60 BLG40 with dopamine (DA) on the surface of thermoplastic polyurethane (TPU) provides peptide polymer-modified TPU surface (TPU-DLL60 BLG40 ). The antimicrobial test shows that the TPU-DLL60 BLG40 surfaces of the sheet and the catheter both exhibit potent killing of 99.9% of methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli). In addition, the TPU-DLL60 BLG40 surface also exhibits excellent biocompatibility. This one-step antimicrobial modification method is fast and efficient, implies promising application in surface antimicrobial modification of implantable biomaterials and medical devices.

Paclitaxel prodrug-encapsulated polypeptide micelles with redox/pH dual responsiveness for cancer chemotherapy

Polypeptides are a highly promising carrier for delivering hydrophobic drugs, due to their excellent biocompatibility, non-toxicity, and non-immunogenicity. Herein, a redox and pH dual-responsive poly(ethylene glycol)-SS-b-polypeptide micelles encapsulated with disulfide bridged paclitaxel-pentadecanoic acid prodrug was developed for cancer chemotherapy. First of all, disulfide bridged paclitaxel-pentadecanoic acid prodrug (PTX-SS-COOH) and poly(ethylene glycol)-SS-b-polylysine-b-polyphenylalanine (mPEG-SS-b-PLys-b-PPhe, ESLP) were synthesized and confirmed via NMR, MS, FT-IR or GPC. After that, PTX-SS-COOH (PSH) embedded mPEG-SS-b-PLys-b-PPhe (ESLP/PSH) micelles were prepared by mixing method based on electrostatic interactions and hydrophobic forces. For comparison, mPEG-b-PLys-b-PPhe (ELP) was mixed with PTX-SS-COOH to generate another kind of micelles (ELP/PSH). The characterization of ESLP/PSH micelles through dynamic light scattering (DLS) and transmission electron microscopy (TEM) revealed a spherical structure with a diameter of approximately 170 nm. It is noteworthy that ESLP/PSH micelles displayed a high drug-loading rate of 22.84%, and excellent stability, which can be attributed to the specific interactions between the prodrug and copolymer. Drug release analysis demonstrated that the micelles exhibited a substantial release of PTX in the presence of GSH at pH 5.0, indicating a pH and redox dual responsiveness. In vivo pharmacokinetic study revealed the ESLP/PSH micelles had increased bioavailability and an extended circulation time. Ultimately, antitumor efficacy and systemic toxicity evaluation in 4 T1 tumor-bearing mice confirmed that ESLP/PSH micelles achieved the highest level of tumor growth inhibition (ca. 83%) and the lowest systemic toxicity in comparison with ELP/PSH micelles and commercialized Taxol®. Taken together, the dual responsive micelles represent a promising PTX formulation with potential clinical application in cancer chemotherapy.

Research progress of nanoparticle targeting delivery systems in bacterial infections

Bacterial infection is a huge threat to the health of human beings and animals. The abuse of antibiotics have led to the occurrence of bacterial multidrug resistance, which have become a difficult problem in the treatment of clinical infections. Given the outstanding advantages of nanodrug delivery systems in cancer treatment, many scholars have begun to pay attention to their application in bacterial infections. However, due to the similarity of the microenvironment between bacterial infection lesions and cancer sites, the targeting and accuracy of traditional microenvironment-responsive nanocarriers are questionable. Therefore, finding new specific targets has become a new development direction of nanocarriers in bacterial prevention and treatment. This article reviews the infectious microenvironment induced by bacteria and a series of virulence factors of common pathogenic bacteria and their physiological functions, which may be used as potential targets to improve the targeting accuracy of nanocarriers in lesions.

A natural polyphenol-functionalized chitosan/gelatin sponge for accelerating hemostasis and infected wound healing

Natural polymers have been particularly appealing for constructing hemostatic materials/devices, but it is still desirable to develop new natural polymer-based biomaterials with balanced hemostatic and wound-healing performance. In this work, a natural polyphenol-functionalized chitosan/gelatin sponge (PCGS) was prepared by the lyophilization of a chitosan/gelatin mixture solution (under a self-foaming condition to prepare the CGS) and subsequent chemical cross-linking with procyanidin (PC). Compared with the original CGS, PCGS exhibited an enhanced liquid-absorption ability, reduced surface charges, and similar/low hemolysis rate. Benefiting from such a liquid-absorption ability (∼4000% for whole blood and normal saline) and moderate surface charges, PCGS exhibited high in vitro hemostatic property and promising hemostatic performance in an in vivo femoral-artery-injury model. In addition, PCGS possessed higher antioxidant property and slightly decreased antibacterial ability than CGS, owing to the incorporation of PC. The feasibility of PCGS for treating infected wounds was further confirmed in an in vivo infected-tooth-extraction model, as the typical complication of intractable tooth-extraction bleeding. The present work demonstrated a facile approach for developing multifunctional hemostatic materials through the flexible management of natural polymers and polyphenols.

Switching from membrane disrupting to membrane crossing, an effective strategy in designing antibacterial polypeptide

Drug-resistant bacterial infections have caused serious threats to human health and call for effective antibacterial agents that have low propensity to induce antimicrobial resistance. Host defense peptide-mimicking peptides are actively explored, among which poly-β-l-lysine displays potent antibacterial activity but high cytotoxicity due to the helical structure and strong membrane disruption effect. Here, we report an effective strategy to optimize antimicrobial peptides by switching membrane disrupting to membrane penetrating and intracellular targeting by breaking the helical structure using racemic residues. Introducing β-homo-glycine into poly-β-lysine effectively reduces the toxicity of resulting poly-β-peptides and affords the optimal poly-β-peptide, βLys₅₀HG₅₀, which shows potent antibacterial activity against clinically isolated methicillin-resistant Staphylococcus aureus (MRSA) and MRSA persister cells, excellent biosafety, no antimicrobial resistance, and strong therapeutic potential in both local and systemic MRSA infections. The optimal poly-β-peptide demonstrates strong therapeutic potential and implies the success of our approach as a generalizable strategy in designing promising antibacterial polypeptides.

Peptide–Polymer Conjugates: A Promising Therapeutic Solution for Drug-Resistant Bacteria

By 2050, it is estimated that 10 million people will die of drug-resistant bacterial infection caused by antibiotic abuse. Antimicrobial peptide (AMP) is widely used to prevent such circumstances, for the positively charged AMPs can kill drug-resistant bacteria by destroying negatively charged bacterial cell membrane, and has excellent antibacterial efficiency and low drug resistance. However, due to the defects in low in vivo stability, easy degradation, and certain cytotoxicity, its practical clinical application is limited. The emergence of peptide–polymer conjugates (PPC) helps AMPs overcome these shortcomings. By combining with functional polymers, the positive charge of AMPs is partially shielded, and its stability and water solubility are improved, so as to prolong the in vivo circulation time of AMPs and reduce its cytotoxicity. At the same time, the self-assembly ability of PPC enables it to assemble into different nanostructures to undertake specific antibacterial tasks. At present, PPC is mainly used in wound dressing, bone tissue repair, antibacterial coating of medical devices, nerve repair, tumor treatment, and oral health maintenance. In this study, we summarize the structure, synthesis methods, and the clinical applications of PPC, so as to present the current challenges and discuss the future prospects of antibacterial therapeutic materials.

Antimicrobial and Anti-Inflammatory Activities of MAF-1-Derived Antimicrobial Peptide Mt6 and Its D-Enantiomer D-Mt6 against Acinetobacter baumannii by Targeting Cell Membranes and Lipopolysaccharide Interaction

Antibiotic resistance in Acinetobacter baumannii is on the rise around the world, highlighting the urgent need for novel antimicrobial drugs. Antimicrobial peptides (AMPs) contribute to effective protection against infections by pathogens, making them the most promising options for next-generation antibiotics. Here, we report two designed, cationic, antimicrobial-derived peptides: Mt6, and its dextroisomer D-Mt6, belonging to the analogs of MAF-1, which is isolated from the instar larvae of houseflies. Both Mt6 and D-Mt6 have a broad-spectrum antimicrobial activity that is accompanied by strong antibacterial activities, especially against A. baumannii planktonic bacteria and biofilms. Additionally, the effect of D-Mt6 against A. baumannii is stable in a variety of physiological settings, including enzyme, salt ion, and hydrogen ion environments. Importantly, D-Mt6 cleans the bacteria on Caenorhabditis elegans without causing apparent toxicity and exhibits good activity in vivo. Both Mt6 and D-Mt6 demonstrated synergistic or additive capabilities with traditional antibiotics against A. baumannii, demonstrating their characteristics as potential complements to combination therapy. Scanning electron microscopy (SEM) and laser scanning confocal microscope (LSCM) experiments revealed that two analogs displayed rapid bactericidal activity by destroying cell membrane integrity. Furthermore, in lipopolysaccharide (LPS)-stimulated macrophage cells, these AMPs drastically decreased IL-1β and TNF-a gene expression and protein secretion, implying anti-inflammatory characteristics. This trait is likely due to its dual function of directly binding LPS and inhibiting the LPS-activated mitogen-activated protein kinase (MAPK) signaling pathways in macrophages. Our findings suggested that D-Mt6 could be further developed as a novel antimicrobial/anti-inflammatory agent and used in the treatment of A. baumannii infections. IMPORTANCE Around 700,000 people worldwide die each year from antibiotic-resistant pathogens. Acinetobacter baumannii in clinical specimens increases year by year, and it is developing a strong resistance to clinical drugs, which is resulting in A. baumannii becoming the main opportunistic pathogen. Antimicrobial peptides show great potential as new antibacterial drugs that can replace traditional antibiotics. In our study, Mt6 and D-Mt6, two new antimicrobial peptides, were designed based on a natural peptide that we first discovered in the hemlymphocytes of housefly larvae. Both Mt6 and D-Mt6 showed broad-spectrum antimicrobial activity, especially against A. baumannii, by damaging membrane integrity. Moreover, D-Mt6 showed better immunoregulatory activity against LPS induced inflammation through its LPS-neutralizing and suppression on MAPK signaling. This study suggested that D-Mt6 is a promising candidate drug as a derived peptide against A. baumannii.

Beyond nylon 6: polyamides via ring opening polymerization of designer lactam monomers for biomedical applications

Ring opening polymerization (ROP) of lactams is a highly efficient and versatile method to synthesize polyamides. Within the last ten years, significant advances in polymerization methodology and monomer diversity are ushering in a new era of polyamide chemistry. We begin with a discussion of polymerization techniques including the most widely used anionic ring opening polymerization (AROP), and less prevalent cationic ROP and enzyme-catalyzed ROP. Next, we describe new monomers being explored for ROP with increased functionality and stereochemistry. We emphasize the relationships between composition, structure, and properties, and how chemists can control composition and structure to dictate a desired property or performance. Finally, we discuss biomedical applications of the synthesized polyamides, specifically as biomaterials and pharmaceuticals, with examples to include as antimicrobial agents, cell adhesion substrates, and drug delivery scaffolds.

Silver loaded biodegradable carboxymethyl chitin films with long-lasting antibacterial activity for infected wound healing

Bacteria-related infections are one of the main causes of human skin infections, which are associated with the delay of wound healing and secondary complications. In this work, a series of novel biodegradable films based on thermosensitive carboxymethyl chitin were prepared without using any crosslinkers. All the carboxymethyl chitin films had good flexibility, high transparency, and appropriate water absorption capacity, and could provide a moist environment for wound healing. The silver ions (Ag⁺) were incorporated on the LTCF-5 film, which had the best mechanical strength (56.39 MPa in the dry state and 0.66 MPa in the wet state) among the carboxymethyl chitin films and was higher than those of the reported biodegradable dressings and commercially available dressings. Compared with the commercial hydrofiber dressing with silver (AQUACEL®), the composite film could provide slow and sustained release of Ag⁺ with good strength and biodegradability, and displayed excellent long-lasting antibacterial activity in vitro against both S. aureus and E. coli without obvious cytotoxicity, which still possessed good antibacterial activity with almost 100% bacteriostatic rates after soaking in phosphate buffered saline for 7 days. More importantly, the Ag⁺ loaded carboxymethyl chitin film could promote infected cutaneous wound healing in a S. aureus infected full-thickness cutaneous defect in vivo model because of its long-lasting antibacterial activity, good biocompatibility, exudate absorption and ability to maintain a moist environment. Thus Ag⁺ loaded carboxymethyl chitin films are excellent candidates for infected wound healing.

Intelligent poly(l-histidine)-based nanovehicles for controlled drug delivery

Stimuli-responsive drug delivery systems based on polymeric nanovehicles are among the most promising treatment regimens for malignant cancers. Such intelligent systems that release payloads in response to the physiological characteristics of tumor sites have several advantages over conventional drug carriers, offering, in particular, enhanced therapeutic effects and decreased toxicity. The tumor microenvironment (TME) is acidic, suggesting the potential of pH-responsive nanovehicles for enhancing treatment specificity and efficacy. The synthetic polypeptide poly(l-histidine) (PLH) is an appropriate candidate for the preparation of pH-responsive nanovehicles because the pK_a of PLH (approximately 6.0) is close to the pH of the acidic TME. In addition, the pendent imidazole rings of PLH yield pH-dependent hydrophobic-to-hydrophilic phase transitions in the acidic TME, triggering the destabilization of nanovehicles and the subsequent release of encapsulated chemotherapeutic agents. Herein, we highlight the state-of-the-art design and construction of pH-responsive nanovehicles based on PLH and discuss the future challenges and perspectives of this fascinating biomaterial for targeted cancer treatment and "benchtop-to-clinic" translation.

Secondary Ammonium-Based Hyperbranched Poly(amidoamine) with Excellent Membrane-Active Property for Multidrug-Resistant Bacterial Infection

With the rapid emergence of microbial infections induced by "superbugs", public health and the global economy are threatened by the lack of effective and biocompatible antibacterial agents. Herein, we systematically design a series of secondary ammonium-based hyperbranched poly(amidoamine) (SAHBP) with different alkyl chain lengths for probing high-efficacy antibacterial agents. SAHBP modified with alkyl tails at the hyperbranched core could efficiently kill Escherichia coli and Staphylococcus aureus, two types of clinically important bacteria worldwide. The best SAHBP with 12-carbon-long alkyl tails (SAHBP-12) also showed high activity against problematic multidrug-resistant bacteria, including Pseudomonas aeruginosa and methicillin-resistant S. aureus (MRSA). Based on ζ potential, isothermal titration microcalorimetry (ITC), and membrane integrity assays, it is found that SAHBP-12 could attach to the cell membrane via electrostatic adsorption and hydrophobic interactions, following which the integrity of the bacterial cell wall and the cell membrane is disrupted, resulting in severe cell membrane damage and the leakage of cytoplasmic contents, finally causing bacterial cell death. Impressively, benefiting from excellent membrane-active property, SAHBP-12 exhibited robust therapeutic efficacy in MRSA-infected mice wounds. Moreover, SAHBP-12 also showed excellent biosafety in vitro and in vivo, which undoubtedly distinguished it as a potent weapon in combating the growing threat of problematic multidrug-resistant bacterial infections.

An Effective Strategy to Develop Potent and Selective Antifungal Agents from Cell Penetrating Peptides in Tackling Drug-Resistant Invasive Fungal Infections

The high mortality rate of invasive fungal infections and quick emergence of drug-resistant fungal pathogens urgently call for potent antifungal agents. Inspired by the cell penetrating peptide (CPP) octaarginine (R8), we elongated to 28 residues poly(d,l-homoarginine) to obtain potent toxicity against both fungi and mammalian cells. Further incorporation of glutamic acid residues shields positive charge density and introduces partial zwitterions in the obtained optimal peptide polymer that displays potent antifungal activity against drug-resistant fungi superior to antifungal drugs, excellent stability upon heating and UV exposure, negligible in vitro and in vivo toxicity, and strong therapeutic effects in treating invasive fungal infections. Moreover, the peptide polymer is insusceptible to antifungal resistance owing to the unique CPP-related antifungal mechanism of fungal membrane penetration followed by disruption of organelles within fungal cells. All these merits imply the effectiveness of our strategy to develop promising antifungal agents.

Photosensitizer-Polypeptides Conjugate with Synergistic Antibacterial Efficacy

Recently, continuous emergence of resistant bacteria has appeared as one of the most serious threats to human health. Therefore, systematic exploration of new antibacterial materials is of guiding significance. In this study, a series of photosensitizer-polypeptides conjugate (PPa-cP) was readily synthesized through the simple ring-opening reactions to realize the synergistic antibacterial effects toward Staphylococcus aureus (S. aureus) and methicillin-resistant Staphylococcus aureus (MRSA) under light irradiation. Compared with free PPa, the cationic PPa-cP showed enhanced binding ability with the negative surface of S. aureus through electrostatic interaction, exhibiting effective antibacterial activity against both S. aureus and MRSA in vitro under light irradiation. Among the synthesized PPa-cP, PPa-cP5 with the degree of polymerization of 37 and modified with 1-methylimidazole side group exhibited the best antibacterial activity with a minimum inhibitory concentration (MIC) value of 2 μM without light irradiation and 0.25 μM with light irradiation. Moreover, PPa-cP5 showed good hemocompatibility. The above-mentioned results elucidate that the positively charged PPa-cP5 could significantly increase the efficiency of photodynamic therapy and effectively eradicate S. aureus biofilm due to its potent penetration ability into S. aureus biofilms. Overall, the present study establishes an efficient strategy for treatment of S. aureus and S. aureus biofilm infections. This article is protected by copyright. All rights reserved.

Microbial Metabolite Inspired β-Peptide Polymers Displaying Potent and Selective Antifungal Activity

Potent and selective antifungal agents are urgently needed due to the quick increase of serious invasive fungal infections and the limited antifungal drugs available. Microbial metabolites have been a rich source of antimicrobial agents and have inspired the authors to design and obtain potent and selective antifungal agents, poly(DL-diaminopropionic acid) (PDAP) from the ring-opening polymerization of β-amino acid N-thiocarboxyanhydrides, by mimicking ε-poly-lysine. PDAP kills fungal cells by penetrating the fungal cytoplasm, generating reactive oxygen, and inducing fungal apoptosis. The optimal PDAP displays potent antifungal activity with minimum inhibitory concentration as low as 0.4 µg mL-1 against Candida albicans, negligible hemolysis and cytotoxicity, and no susceptibility to antifungal resistance. In addition, PDAP effectively inhibits the formation of fungal biofilms and eradicates the mature biofilms. In vivo studies show that PDAP is safe and effective in treating fungal keratitis, which suggests PDAPs as promising new antifungal agents.

Synthesis of poly-α/β-peptides with tunable sequence via the copolymerization on N-carboxyanhydride and N-thiocarboxyanhydride

The fascinating functions of proteins and peptides in biological systems have attracted intense interest to explore their mimics using polymers, including polypeptides synthesized from polymerization. The folding, structures and functions of proteins and polypeptides are largely dependent on their sequence. However, sequence-tunable polymerization for polypeptide synthesis is a long-lasting challenge. The application of polypeptides is also greatly hindered by their susceptibility to enzymatic degradation. Although poly-α/β-peptide has proven to be an effective strategy to address the stability issue, the synthesis of poly-α/β-peptide from polymerization is not available yet. Hereby, we demonstrate a living and controlled copolymerization on α-NCA and β-NTA to prepare sequence-tunable poly-α/β-peptides. This polymerization strategy shows a prominent solvent-driven characteristic, providing random-like copolymers of poly-α/β-peptides in THF and block-like copolymers of poly-α/β-peptides in a mixed solvent of CHCl₃/H₂O (95/5, v/v), and opens new avenues for sequence-tunable polymerization and enables facile synthesis of proteolysis tunable poly-α/β-peptides for diverse applications.

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Realizing controlled synthesis of poly-α/β-peptides via one-pot polymerization

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Sequence-tunable copolymerization via solvent-dependent polymerization kinetics

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Adjustable proteolytic stability and antibacterial activity of poly-α/β-peptides

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Tunable self-assembly behavior of poly-α/β-peptides via one-pot polymerization

Membrane-disruptive peptides/peptidomimetics-based therapeutics: Promising systems to combat bacteria and cancer in the drug-resistant era

Membrane-disruptive peptides/peptidomimetics (MDPs) are antimicrobials or anticarcinogens that present a general killing mechanism through the physical disruption of cell membranes, in contrast to conventional chemotherapeutic drugs, which act on precise targets such as DNA or specific enzymes. Owing to their rapid action, broad-spectrum activity, and mechanisms of action that potentially hinder the development of resistance, MDPs have been increasingly considered as future therapeutics in the drug-resistant era. Recently, growing experimental evidence has demonstrated that MDPs can also be utilized as adjuvants to enhance the therapeutic effects of other agents. In this review, we evaluate the literature around the broad-spectrum antimicrobial properties and anticancer activity of MDPs, and summarize the current development and mechanisms of MDPs alone or in combination with other agents. Notably, this review highlights recent advances in the design of various MDP-based drug delivery systems that can improve the therapeutic effect of MDPs, minimize side effects, and promote the co-delivery of multiple chemotherapeutics, for more efficient antimicrobial and anticancer therapy.

Polypeptides-Drug Conjugates for Anticancer Therapy

Polypeptides are an important class of biodegradable polymers that have been widely used in drug delivery field. Owing to the controllable synthesis and robust side chain-functionalization ability, polypeptides have long been ideal candidates for conjugation with anticancer drugs. The chemical conjugation of anticancer drugs with polypeptides, termed polypeptides-drug conjugates, has demonstrated several advantages in improving pharmacokinetics, enhancing drug targeting, and controlling drug release, thereby leading to enhanced therapeutic outcomes with reduced side toxicities. This review focuses on the recent advances in the design and preparation of polypeptides-drug conjugates for enhanced anticancer therapy. Strategies for conjugation of different types of drugs, including small-molecule chemotherapeutic drugs, proteins, vascular disrupting agents, and gas molecules, onto polypeptides backbone are summarized. Finally, the challenges and future perspectives on the development of innovative polypeptides-drug conjugates for clinical cancer treatment are also presented.

Efficient synthesis and excellent antimicrobial activity of star-shaped cationic polypeptides with improved biocompatibility

Antimicrobial peptides (AMPs) have been considered as a promising new tool to combat the antimicrobial resistance (AMR) crisis. However, the high toxicity and high cost of AMPs hampered their further development. Herein, a series of star poly(_L-lysine) (PLL) homo- and copolymers with excellent antimicrobial activity and improved biocompatibility were prepared by the combination of ultra-fast ring opening polymerization (ROP) and side-chain modification. The amine-terminated polyamidoamine dendrimer (Gx-PAMAM) mediated ROP of Nε-tert-butyloxycarbonyl-_L-lysine N-carboxyanhydride (Boc-_L-Lys-NCA) and γ-benzyl-_L-glutamic acid-based N-carboxyanhydride (PBLG-NCA) was able to prepare star PLL homo- and copolymers with 400 residues within 50 min. While the star PLL homopolymers exhibited low minimum inhibitory concentration (MIC = 50-200 μg mL^-1) against both Gram-positive and Gram-negative bacteria (i.e., S. aureus and E. coli), they showed high toxicity against various mammalian cell lines. The star PLL copolymers with low contents of hydrophobic and hydroxyl groups showed enhanced antimicrobial activity (MIC = 25-50 μg mL^-1) and improved mammalian cell viability. Both SEM and CLSM results indicated the antimicrobial mechanism of membrane disruption.

The membrane-targeting mechanism of host defense peptides inspiring the design of polypeptide-conjugated gold nanoparticles exhibiting effective antibacterial activity against methicillin-resistant Staphylococcus aureus

Multidrug-resistant bacterial infections are a grand challenge to global medical and health systems. Therefore, it is urgent to develop versatile antibacterial strategies that can combat bacterial resistance without displaying toxicity. Here, we synthesize antibacterial polypeptide-conjugated gold nanoparticles that exhibit potent antibacterial activities against clinically isolated multiple drug resistance Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus, and excellent in vitro and in vivo biocompatibility. The antibacterial mechanism study indicates that over-production of reactive oxygen species results in the killing of bacteria. The overall antibacterial performance of these polypeptide-conjugated gold nanoparticles and the convenient synthesis of these polypeptides via lithium hexamethyldisilazide-initiated fast ring-opening polymerization on α-amino acid N-carboxyanhydride imply the potential application of this strategy in treating bacterial infections.

Antibacterial and Anti-Inflammatory Activity of an Antimicrobial Peptide Synthesized with D Amino Acids

The peptide SET-M33 is a molecule synthesized in tetra-branched form which is being developed as a new antibiotic against Gram-negative bacteria. Its isomeric form with D amino acids instead of the L version (SET-M33D) is also able to kill Gram-positive bacteria because of its higher resistance to bacterial proteases (Falciani et al., PLoS ONE, 2012, 7, e46259). Here we report the strong in vitro activity of SET-M33D (MIC range 0.7-6.0 µM) against multiresistant pathogens of clinical interest, including Gram-positives Staphylococcus aureus, Staphylococcus saprophyticus, and Enterococcus faecalis, and various Gram-negative enterobacteriaceae. SET-M33D antibacterial activity is also confirmed in vivo against a MRSA strain of S. aureus with doses perfectly compatible with clinical use (5 and 2.5 mg/Kg). Moreover, SET-M33D strongly neutralized lipopolysaccharide (LPS) and lipoteichoic acid (LTA), thus exerting a strong anti-inflammatory effect, reducing expression of cytokines, enzymes, and transcription factors (TNF-α, IL6, COX-2, KC, MIP-1, IP10, iNOS, NF-κB) involved in the onset and evolution of the inflammatory process. These results, along with in vitro and in vivo toxicity data and the low frequency of resistance selection reported here, make SET-M33D a strong candidate for the development of a new broad spectrum antibiotic.