Molecular engineering of antimicrobial peptide (AMP)-polymer conjugates

A critical view of antimicrobial peptides: exploring their potential and the barriers to realization

The global rise of multidrug-resistant infections highlights the urgent need for innovative therapeutic strategies beyond traditional antibiotics. Antimicrobial peptides (AMPs), naturally occurring in all forms of life and synthetically producible, have garnered significant attention for their broad-spectrum antimicrobial properties and diverse mechanisms of action, including membrane disruption, immune modulation, and biofilm formation inhibition and disruption. Despite great potential, the clinical deployment of AMPs faces significant challenges, including cytotoxicity, low chemical stability, high production costs, and stringent regulatory demands. Innovative strategies, such as AMP-antibiotic conjugation, offer potential solutions to some of these challenges by enhancing efficacy, reducing toxicity, and broadening antimicrobial activity. This review critically evaluates the promise and limitations of AMPs as therapeutic antibacterial agents. We also explore the potential of AMP-antibiotic conjugates, highlighting their potential synergistic effects and the obstacles to their clinical application. Antimicrobial self-assembling peptides are also discussed, with their ability to form nanostructures that may disrupt biofilms and inhibit bacterial communication, representing a promising but complex avenue. A critical evaluation of these emerging strategies, grounded in their practical applicability and translational challenges, is essential to drive meaningful progress in combating antimicrobial resistance.

Anti-Candida Activity of Cysteine-Modified Amidated Decoralin in the Presence of Engineered Nanomaterials

Background: Candidiasis remains a chief concern in global healthcare. Drug safety issues and increasing resistance make it urgent to develop alternative antifungal agents, namely antimicrobial peptides. Amidated decoralin (Dec-CONH2) possesses considerable anti-Candida activity, and its association with nanocarriers could help in enhancing efficacy while reducing intrinsic toxicity to the host. Methods: We studied an N-terminal cysteine-modified version of the peptide (Cys-Dec-CONH2) and screened the effects of different nanosystems (polymeric nanoparticles (NPs), liposomes and gold NPs) on its activity against azole-sensitive and azole-resistant Candida species using a clinically relevant in vitro assay. Results: The antifungal activity of Cys-Dec-CONH2 was maintained (minimum inhibitory concentration (MIC) = 16-64 µg/mL), but the presence of poly(d,l-lactic-co-glycolic acid) (PLGA)- and polycaprolactone-based NPs impaired the antifungal effect of the peptide (MIC > 256 µg/mL). This effect was milder for polystyrene-based NPs, liposomes, and gold NPs (MIC ≤ 128 µg/mL). Additionally, the covalent surface functionalization of PLGA-based NPs with Cys-Dec-CONH2 or the presence of relevant biomolecules (albumin and mucin) resulted in complete inhibition of antifungal activity. Conclusions: Our data suggest that Cys-Dec-CONH2 is able to establish strong interfacial interactions with different nanomaterials, which need to be considered when developing nanomedicines based on this peptide for the management of candidiasis.

Presenting Antimicrobial Peptides on Poly(ethylene glycol): Star-Shaped vs Comb-Like Architectures

Conjugating antimicrobial peptides (AMPs) to nonlinear polymers is a promising strategy to overcome the translational challenges of AMPs toward treating infections caused by antibiotic-resistant bacteria. Nonlinear polymers, and therefore conjugates, can be prepared with various architectures (e.g., star-shaped, comb-like, hyperbranched, etc.), however, the effects of polymer architecture on antimicrobial performance and related properties, like size and morphology in solution and secondary structure, are not yet well-understood. Here, we compare conjugates of the human chemokine-derived AMP stapled P9 with poly(ethylene glycol) (PEG) prepared in two of the major nonlinear architectures: star-shaped and comb-like. At comparable molecular weights and compositions (peptide wt %), comb-like conjugates afford increased helicity, solubility, antimicrobial activity, and proteolytic stability compared to star-shaped analogs. We then leveraged the expansive design space of comb-like architectures to prepare conjugates with different backbone lengths and PEG side chain lengths, with shorter PEG side chains leading to increased helicity, yet potentially less shielding from proteolytic degradation and the longest backbone lengths furnishing the most potent antimicrobial activity. Both comb-like and star-shaped conjugates display high zeta potential, indicating that the cationic AMPs were accessible for electrostatic interactions with bacterial membranes. Yet, the comb-like conjugates showed a higher fraction of unimolecular structures indicative of a lower propensity for supramolecular assembly that could be encumbering the desired AMP-bacteria interactions in the star-shaped conjugates. Together, our work shows comb-like AMP-polymer conjugates to outperform analogous star-shaped conjugates, while adding design flexibility to access an expansive range of monomer chemistries, monomer distributions, and backbone lengths to modulate performance-determining properties and ultimately furnish an effective suite of AMP-polymer materials as alternatives to conventional antibiotics for combatting bacterial infections.

Microneedles in diabetic wound care: multifunctional solutions for enhanced healing

Diabetic wounds present a significant challenge in clinical treatment and are characterized by chronic inflammation, oxidative stress, impaired angiogenesis, peripheral neuropathy, and a heightened risk of infection during the healing process. By creating small channels in the surface of the skin, microneedle technology offers a minimally invasive and efficient approach for drug delivery and treatment. This article begins by outlining the biological foundation of normal skin wound healing and the unique pathophysiological mechanisms of diabetic wounds. It then delves into the various types, materials, and preparation processes of microneedles. The focus is on the application of multifunctional microneedles in diabetic wound treatment, highlighting their antibacterial, anti-inflammatory, immunomodulatory, antioxidant, angiogenic and neural repair properties. These multifunctional microneedles demonstrate synergistic therapeutic effects by directly influencing the wound microenvironment, ultimately accelerating the healing of diabetic wounds. The advancement of microneedle technology not only holds promise for enhancing the treatment outcomes of diabetic wounds but also offers new strategies for addressing other chronic wounds.

Hyaluronic acid based nanoparticles that mediate sustained thanatin release protect against NDM-1-resistant bacterial infections in a murine model

Thanatin, a potent cationic antimicrobial peptide, has demonstrated remarkable efficacy against new NDM-1 producing bacteria. However, its clinical application is hampered by suboptimal stability in circulation and limited bioavailability in the human body. To overcome these challenges, a novel thanatin nanomedicine has been developed, which encapsulated thanatin in nanoparticles formed by electrostatic interactions between negatively charged HA and PLGA. The obtained ThaNPs demonstrated good stability, low cytotoxicity, and good metabolic ratio. ThaNPs significantly improve the stability of thanatin in the circulation, increasing its half-life in 50 % serum from 0.6 h to 3.2 h. Notably, the protective effect of ThaNPs against sepsis induced by NDM-1-producing Escherichia coli. was 10-fold higher than that of unencapsulated thanatin. These findings suggest that hyaluronic acid-based nanoparticles have the potentiality to overcome the clinical limitations associated with cationic antimicrobial peptides, thereby providing a novel and effective strategy for treating severe infections caused by antibiotic-resistant bacteria.

Peptide-Based Biomaterials for Combatting Infections and Improving Drug Delivery

This review explores the potential of peptide-based biomaterials to enhance biomedical applications through self-assembly, biological responsiveness, and selective targeting. Peptides are presented as versatile agents for antimicrobial activity and drug delivery, with recent approaches incorporating antimicrobial peptides into self-assembling systems to improve effectiveness and reduce resistance. The review also covers peptide-based nanocarriers for cancer drug delivery, highlighting their improved stability, targeted delivery, and reduced side effects. The focus of this work is on the bioactive properties of peptides, particularly in infection control and drug delivery, rather than on their structural design or material characteristics. Additionally, it examines the role of peptidomimetics in broadening biomaterial applications and enhancing resistance to enzymatic degradation. Finally, the review discusses the commercial prospects and challenges of translating peptide biomaterials into clinical applications.

Conjugated therapeutic proteins as a treatment for bacteria which trigger cancer development

In recent years, an increasing amount of research has focused on the intricate and complex correlation between bacterial infections and the development of cancer. Some studies even identified specific bacterial species as potential culprits in the initiation of carcinogenesis, which generated a great deal of interest in the creation of innovative therapeutic strategies aimed at addressing both the infection and the subsequent risk of cancer. Among these strategies, there has been a recent emergence of the use of conjugated therapeutic proteins, which represent a highly promising avenue in the field of cancer therapeutics. These proteins offer a dual-targeting approach that seeks to effectively combat both the bacterial infection and the resulting malignancies that may arise because of such infections. This review delves into the landscape of conjugated therapeutic proteins that have been intricately designed with the purpose of specifically targeting bacteria that have been implicated in the induction of cancer.

Rejuvenation of Meropenem by Conjugation with Tilapia Piscidin-4 Peptide Targeting NDM-1 Escherichia coli

Gram-negative pathogens that produce β-lactamases pose a serious public health threat as they can render β-lactam antibiotics inactive via hydrolysis. This action contributes to the waning effectiveness of clinical antibiotics and creates an urgent need for new antimicrobials. Antimicrobial peptides (AMPs) exhibiting multimodal functions serve as a potential source in spite of a few limitations. Thus, the conjugation of conventional antibiotics with AMPs may be an effective strategy to leverage the advantages of each component. In this study, we conjugated meropenem to the AMP Tilapia piscidin 4 (TP4) using a typical coupling reaction. The conjugate was characterized by using HPLC-MS, HR-MS, and MS-MS fragmentation analysis. It was then evaluated in terms of antibacterial potency, hemolysis, and cytotoxicity toward RAW264.7 and CCD-966SK cell lines. The conjugation of meropenem with TP4 significantly reduced the cytotoxicity compared to TP4. Conjugation of unprotected TP4 with meropenem resulted in cross-linking at the N-terminal and lysine sites. The structural activity relationship of the two isomers of the TP4-meropenem conjugate was investigated. Both the isomers showed notable antibacterial activities against NDM-1 Escherichia coli and reduced red blood cell hemolysis as compared to TP4. Lysine conjugate (TP4-K-Mero) showed lesser hemolysis than the N-terminal conjugate (TP4-N-Mero). Molecular modeling further revealed that the conjugates can bind to lipopolysaccharides and inhibit NDM-1 β-lactamase. Together, these data show that conjugation of antibiotics with AMP can be a feasible approach to increase the therapeutic profile and effectively target multidrug-resistant pathogens. Furthermore, antibiotic conjugation at different AMP sites tends to show unique biological properties.

How can biomaterial-conjugated antimicrobial peptides fight bacteria and be protected from degradation?

The emergence of antibiotic-resistant bacteria is a serious threat to public health. Antimicrobial peptides (AMP) are a powerful alternative to antibiotics due to their low propensity to induce bacterial resistance. However, cytotoxicity and short half-lives have limited their clinical translation. To overcome these problems, AMP conjugation has gained relevance in the biomaterials field. Nevertheless, few studies describe the influence of conjugation on enzymatic protection, mechanism of action and antimicrobial efficacy. This review addresses this gap by providing a detailed comparison between conjugated and soluble AMP. Additionally, commonly employed chemical reactions and factors to consider when promoting AMP conjugation are reviewed. The overall results suggested that AMP conjugated onto biomaterials are specifically protected from degradation by trypsin and/or pepsin. However, sometimes, their antimicrobial efficacy was reduced. Due to limited conformational freedom in conjugated AMP, compared to their soluble forms, they appear to act initially by creating small protuberances on bacterial membranes that may lead to the alteration of membrane potential and/or formation of holes, triggering cell death. Overall, AMP conjugation onto biomaterials is a promising strategy to fight infection, particularly associated to the use of medical devices. Nonetheless, some details need to be addressed before conjugated AMP reach clinical practice. STATEMENT OF SIGNIFICANCE: Covalent conjugation of antimicrobial peptides (AMP) has been one of the most widely used strategies by bioengineers, in an attempt to not only protect AMP from proteolytic degradation, but also to prolong their residence time at the target tissue. However, an explanation for the mode of action of conjugated AMP is still lacking. This review extensively gathers works on AMP conjugation and puts forward a mechanism of action for AMP when conjugated onto biomaterials. The implications of AMP conjugation on antimicrobial activity, cytotoxicity and resistance to proteases are all discussed. A thorough review of commonly employed chemical reactions for this conjugation is also provided. Finally, details that need to be addressed for conjugated AMP to reach clinical practice are discussed.

Peptide Dendrimer-Based Antibacterial Agents: Synthesis and Applications

Pathogenic bacteria cause the deaths of millions of people every year. With the development of antibiotics, hundreds and thousands of people's lives have been saved. Nevertheless, bacteria can develop resistance to antibiotics, rendering them insensitive to antibiotics over time. Peptides containing specific amino acids can be used as antibacterial agents; however, they can be easily degraded by proteases in vivo. To address these issues, branched peptide dendrimers are now being considered as good antibacterial agents due to their high efficacy, resistance to protease degradation, and low cytotoxicity. The ease with which peptide dendrimers can be synthesized and modified makes them accessible for use in various biological and nonbiological fields. That is, peptide dendrimers hold a promising future as antibacterial agents with prolonged efficacy without bacterial resistance development. Their in vivo stability and multivalence allow them to effectively target multi-drug-resistant strains and prevent biofilm formation. Thus, it is interesting to have an overview of the development and applications of peptide dendrimers in antibacterial research, including the possibility of employing machine learning approaches for the design of AMPs and dendrimers. This review summarizes the synthesis and applications of peptide dendrimers as antibacterial agents. The challenges and perspectives of using peptide dendrimers as the antibacterial agents are also discussed.

Current status of development and biomedical applications of peptide-based antimicrobial hydrogels

Microbial contamination poses a serious threat to human life and health. Through the intersection of material science and modern medicine, advanced bionic hydrogels have shown great potential for biomedical applications due to their unique bioactivity and ability to mimic the extracellular matrix environment. In particular, as a promising antimicrobial material, the synthesis and practical biomedical applications of peptide-based antimicrobial hydrogels have drawn increasing research interest. The synergistic effect of peptides and hydrogels facilitate the controlled release of antimicrobial agents and mitigation of their biotoxicity while achieving antimicrobial effects and protecting the active agents from degradation. This review reports on the progress and trends of researches in the last five years and provides a brief outlook, aiming to provide theoretical background on peptide-based antimicrobial hydrogels and make suggestions for future related work.

A Versatile Elastin-Like Carrier for Bioactive Antimicrobial Peptide Production and Delivery

Elastin-like polypeptides are biotechnological protein and peptide carriers that offer a vast scope of applicability. This work aims to build a model for the expression of antimicrobial peptides (AMPs) by genetically engineering the Human Elastin-like Polypeptide platform developed in the lab. The well-characterized AMP indolicidin is selected as an example of an antimicrobial domain for the recombinant fusion at the C-terminus of the carrier. The fusion construct has been designed to allow the release of the antimicrobial domain. The expression product has been purified and its physicochemical and antimicrobial properties has been characterized. Taking advantage of the self-assembling and matrix-forming properties of the recombinant biopolymer, the materials that are obtained have been evaluated for antimicrobial activity toward bacterial-strain models. This approach represents a cost-effective strategy for the production of smart components and materials endowed with antimicrobial capacity triggered by external stimuli.

Antimicrobial Peptide-Poly(ethylene glycol) Conjugates: Connecting Molecular Architecture, Solution Properties, and Functional Performance

Antimicrobial peptides (AMPs) are promising alternatives to conventional antibiotics for treating infections caused by drug-resistant bacteria; yet, many peptides are limited by toxicity to eukaryotic cells and instability in biological environments. Conjugation to linear polymers that reduce cytotoxicity and improve stability, however, often decreases antimicrobial activity. In this work, we combine the biocompatibility advantages of poly(ethylene glycol) (PEG) with the efficacy merits of nonlinear polymer architectures that accommodate multiple AMPs per molecule. By conjugating a chemokine-derived AMP, stapled Ac-P9, to linear and star-shaped PEG with various arm numbers and lengths, we investigated the role of molecular architecture in solution properties (i.e., ζ-potential, size, and morphology) and performance (i.e., antimicrobial activity, hemolysis, and protease resistance). Linear, 4-arm, and 8-arm conjugates with 2-2.5 kDa PEG arms were found to form nanoscale structures in solution with lower ζ-potentials relative to the unconjugated AMP, suggesting that the polymer partially shields the cationic AMP. Reducing the length of the PEG arms of the 8-arm conjugate to 1.25 kDa appeared to better reveal the peptide, seen by the increased ζ-potential, and promote assembly into particles with a larger size and defined spherical morphology. The antimicrobial effects exerted by the short 8-arm conjugate rivaled that of the unconjugated peptide, and the AMP constituents of the short 8-arm conjugate were protected from proteolytic degradation. All other conjugates examined also imparted a degree of protease resistance, but exhibited some reduced level of antimicrobial activity as compared to the AMP alone. None of the conjugates caused significant cytotoxic effects, which bodes well for their future potential to treat infections. While enhancing proteolytic stability often comes with the cost of lower antimicrobial activity, we have found that presenting AMPs at high density on a neutral nonlinear polymer strikes a favorable balance, exhibiting both enhanced stability and high antimicrobial activity.

Advances of Antimicrobial Peptide-Based Biomaterials for the Treatment of Bacterial Infections

Owing to the increase in multidrug-resistant bacterial isolates in hospitals globally and the lack of truly effective antimicrobial agents, antibiotic resistant bacterial infections have increased substantially. There is thus an urgent need to develop new antimicrobial drugs and their related formulations. In recent years, natural antimicrobial peptides (AMPs), AMP optimization, self-assembled AMPs, AMP hydrogels, and biomaterial-assisted delivery of AMPs have shown great potential in the treatment of bacterial infections. In this review, it is focused on the development prospects and shortcomings of various AMP-based biomaterials for treating animal model infections, such as abdominal, skin, and eye infections. It is hoped that this review will inspire further innovations in the design of AMP-based biomaterials for the treatment of bacterial infections and accelerate their commercialization.

Smart tools for antimicrobial peptides expression and application: The elastic perspective

In recent years, antimicrobial peptides (AMPs) have become a promising alternative to the use of conventional and chemically synthesized antibiotics, especially after the emergence of multidrug-resistant organisms. Thus, this review aims to provide an updated overview of the state-of-the-art for producing antimicrobial peptides fused or conjugated with the elastin-like (ELP) peculiar carriers, and that are mostly intended for biomedical application. The elastin-like biopolymers are thermosensitive proteins with unique properties. Due to the flexibility of their modular structure, their features can be tuned and customized to improve the production of the antimicrobial domain while reducing their toxic effects on the host cells. Both fields of research faced a huge rise in interest in the last decade, as witnessed by the increasing number of publications on these topics, and several recombinant fusion proteins made of these two domains have been already described but they still present a limited variability. Herein, the approaches described to recombinantly fuse and chemically conjugate diverse AMPs with ELPs are reviewed, and the nature of the AMPs and the ELPs used, as well as the main features of the expression and production systems are summarized.

Disparate Regions of the Human Chemokine CXCL10 Exhibit Broad-Spectrum Antimicrobial Activity against Biodefense and Antibiotic-Resistant Bacterial Pathogens

CXCL10 is a pro-inflammatory chemokine produced by the host in response to microbial infection. In addition to canonical, receptor-dependent actions affecting immune-cell migration and activation, CXCL10 has also been found to directly kill a broad range of pathogenic bacteria. Prior investigations suggest that the bactericidal effects of CXCL10 occur through two distinct pathways that compromise the cell envelope. These observations raise the intriguing notion that CXCL10 features a separable pair of antimicrobial domains. Herein, we affirm this possibility through peptide-based mapping and structure/function analyses, which demonstrate that discrete peptides derived from the N- and C-terminal regions of CXCL10 mediate bacterial killing. The N-terminal derivative, peptide P1, exhibited marked antimicrobial activity against Bacillus anthracis vegetative bacilli and spores, as well as antibiotic-resistant clinical isolates of Klebsiella pneumoniae, Acinetobacter baumannii, Enterococcus faecium, and Staphylococcus aureus, among others. At bactericidal concentrations, peptide P1 had a minimal degree of chemotactic activity, but did not cause red blood cell hemolysis or cytotoxic effects against primary human cells. The C-terminal derivative, peptide P9, exhibited antimicrobial effects, but only against Gram-negative bacteria in low-salt medium─conditions under which the peptide can adopt an α-helical conformation. The introduction of a hydrocarbon staple induced and stabilized α-helicity; accordingly, stapled peptide P9 displayed significantly improved bactericidal effects against both Gram-positive and Gram-negative bacteria in media containing physiologic levels of salt. Together, our findings identify and characterize the antimicrobial regions of CXCL10 and functionalize these novel determinants as discrete peptides with potential therapeutic utility against difficult-to-treat pathogens.

Targeting Multidrug Resistance With Antimicrobial Peptide-Decorated Nanoparticles and Polymers

As a category of small peptides frequently found in nature, antimicrobial peptides (AMPs) constitute a major part of the innate immune system of various organisms. Antimicrobial peptides feature various inhibitory effects against fungi, bacteria, viruses, and parasites. Due to the increasing concerns of antibiotic resistance among microorganisms, development of antimicrobial peptides is an emerging tool as a favorable applicability prospect in food, medicine, aquaculture, animal husbandry, and agriculture. This review presents the latest research progress made in the field of antimicrobial peptides, such as their mechanism of action, classification, application status, design techniques, and a review on decoration of nanoparticles and polymers with AMPs that are used in treating multidrug resistance. Lastly, we will highlight recent progress in antiviral peptides to treat emerging viral diseases (e.g., anti-coronavirus peptides) and discuss the outlook of AMP applications.

Polymer Conjugates of Antimicrobial Peptides (AMPs) with d-Amino Acids (d-aa): State of the Art and Future Opportunities

In recent years, antimicrobial peptides (AMPs) have enjoyed a renaissance, as the world is currently facing an emergency in terms of severe infections that evade antibiotics’ treatment. This is due to the increasing emergence and spread of resistance mechanisms. Covalent conjugation with polymers is an interesting strategy to modulate the pharmacokinetic profile of AMPs and enhance their biocompatibility profile. It can also be an effective approach to develop active coatings for medical implants and devices, and to avoid biofilm formation on their surface. In this concise review, we focus on the last 5 years’ progress in this area, pertaining in particular to AMPs that contain d-amino acids, as well as their role, and the advantages that may arise from their introduction into AMPs.

Quaternized Amphiphilic Block Copolymers as Antimicrobial Agents

In this study, a novel polystyrene-block-quaternized polyisoprene amphipathic block copolymer (PS-b-PIN) is derived from anionic polymerization. Quaternized polymers are prepared through post-quaternization on a functionalized polymer side chain. Moreover, the antibacterial activity of quaternized polymers without red blood cell (RBCs) hemolysis can be controlled by block composition, side chain length, and polymer morphology. The solvent environment is highly related to the polymer morphology, forming micelles or other structures. The polymersome formation would decrease the hemolysis and increase the electron density or quaternized groups density as previous research and our experiment revealed. Herein, the PS-b-PIN with N,N-dimethyldodecylamine as side chain would form a polymersome structure in the aqueous solution to display the best inhibiting bacterial growth efficiency without hemolytic effect. Therefore, the different single-chain quaternized groups play an important role in the antibacterial action, and act as a controllable factor.

Recent advances in the design of antimicrobial peptide conjugates

Antimicrobial peptides (AMPs) are ubiquitous host defense peptides characterized by antibiotic activity and lower propensity for developing resistance compared to classic antibiotics. While several AMPs have shown activity against antibiotic-sensitive...

Polymeric Nanomaterials for Efficient Delivery of Antimicrobial Agents

Bacterial infections have threatened the lives of human beings for thousands of years either as major diseases or complications. The elimination of bacterial infections has always occupied a pivotal position in our history. For a long period of time, people were devoted to finding natural antimicrobial agents such as antimicrobial peptides (AMPs), antibiotics and silver ions or synthetic active antimicrobial substances including antimicrobial peptoids, metal oxides and polymers to combat bacterial infections. However, with the emergence of multidrug resistance (MDR), bacterial infection has become one of the most urgent problems worldwide. The efficient delivery of antimicrobial agents to the site of infection precisely is a promising strategy for reducing bacterial resistance. Polymeric nanomaterials have been widely studied as carriers for constructing antimicrobial agent delivery systems and have shown advantages including high biocompatibility, sustained release, targeting and improved bioavailability. In this review, we will highlight recent advances in highly efficient delivery of antimicrobial agents by polymeric nanomaterials such as micelles, vesicles, dendrimers, nanogels, nanofibers and so forth. The biomedical applications of polymeric nanomaterial-based delivery systems in combating MDR bacteria, anti-biofilms, wound healing, tissue engineering and anticancer are demonstrated. Moreover, conclusions and future perspectives are also proposed.

Host Defense Peptide-Mimicking Polymers and Polymeric-Brush-Tethered Host Defense Peptides: Recent Developments, Limitations, and Potential Success

Amphiphilic antimicrobial polymers have attracted considerable interest as structural mimics of host defense peptides (HDPs) that provide a broad spectrum of activity and do not induce bacterial-drug resistance. Likewise, surface engineered polymeric-brush-tethered HDP is considered a promising coating strategy that prevents infections and endows implantable materials and medical devices with antifouling and antibacterial properties. While each strategy takes a different approach, both aim to circumvent limitations of HDPs, enhance physicochemical properties, therapeutic performance, and enable solutions to unmet therapeutic needs. In this review, we discuss the recent advances in each approach, spotlight the fundamental principles, describe current developments with examples, discuss benefits and limitations, and highlight potential success. The review intends to summarize our knowledge in this research area and stimulate further work on antimicrobial polymers and functionalized polymeric biomaterials as strategies to fight infectious diseases.

Biodegradable polycaprolactone metallopolymer-antibiotic bioconjugates containing phenylboronic acid and cobaltocenium for antimicrobial application

This paper reports antimicrobial metallopolymers containing biodegradable polycaprolactone as the backbone with boronic acid and cobaltocenium as the side chain. While boronic acid promotes interactions with bacterial cells via boronolectin with lipopolysaccharides, cationic cobaltocenium facilitates the unique complexation with anionic β-lactam antibiotics. The synergistic interactions in these metallopolymer-antibiotic bioconjugates were evidenced by re-sensitized efficacy of penicillin-G against four different Gram-negative bacteria (E. coli, P. vulgaris, P. aeruginosa and K. pneumoniae). The degradability of the polyester backbone was validated through tests under physiological pH (7.4) and acidic pH (5.5) or under enzymatic conditions. These metallopolymers exhibited time-dependent uptake and reduction of cobalt metals in different organs of mice via in vivo absorption, distribution, metabolism, and excretion (ADME) tests.

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.