Molecular Weight and Charge Density Effects of Guanidinylated Biodegradable Polycarbonates on Antimicrobial Activity and Selectivity

Synthesis and Characterization of Guanidinylated CO-Releasing Micelles Based on Biodegradable Polycarbonate

As one of the gaseous signals in living cells, carbon monoxide (CO) not only participates in many biological activities but also serves as a therapeutic agent for the treatment of diseases. However, the limited applicability of CO in gas therapy emerges from the inconvenience of direct administration of CO. Here we reported the construction of guanidinylated CO-releasing micelles, which are composed of poly(trimethylene carbonate) (PTMC)-based CO donors. The in vitro studies demonstrated that micelles in the presence of light irradiation can induce cancer death, whereas no obvious toxicity to normal cells was observed. Moreover, the functionalization of guanidine groups imparts improved cellular uptake efficiency to micelles owing to the specific interactions with the surface of cells, which synergistically increase the anticancer capacity of the system. The guanidine-functionalized CO-releasing micelles provide a new strategy for the construction of CO-releasing nanocarriers, which are expected to find applications in gas therapeutics.

Unlocking the Potential: PEGylation and Molecular Weight Reduction of Ionenes for Enhanced Antifungal Activity and Biocompatibility

Numerous synthetic polymers, imitating natural antimicrobial peptides, have demonstrated potent antimicrobial activity, positioning them as potential candidates for new antimicrobial drugs. However, the high activity of these molecules often comes at the cost of elevated toxicity against eukaryotic organisms. In this study, a series of cationic ionenes with varying molecular weights to assess the influence of polymer chain length on ionene activity is investigated. To enhance polymer antimicrobial activity and limit toxicity a PEG side chain is introduced into the repeating unit. The resulting molecules consistently exhibited high activity against three model organisms: E. coli, S. aureus and C. albicans. The incorporation of side PEG chain improves antifungal properties and biocompatibility, regardless of molecular weight. The most important finding of this work is that the reduction of polymer molecular mass led to increased antifungal activity and reduced cytotoxicity against HMF and MRC-5 cell lines simultaneously. As a result, the best-performing molecules reported herein displayed minimal inhibitory concentrations (MIC) as low as 2 and 0.0625 µg mL1 for C. albicans and C. tropicalis respectively, demonstrating exceptional selectivity. It is plausible that some of described herein molecules can serve as potential lead candidates for new antifungal drugs.

Antimicrobial Guanidinylate Polycarbonates Show Oral In Vivo Efficacy Against Clostridioides Difficile

The emerging antibiotic resistance has been named by the World Health Organization (WHO) as one of the top 10 threats to public health. Notably, methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecalis (VREF) are designated as serious threats, whereas Clostridioides difficile (C. difficile) is recognized as one of the most urgent threats to human health and unmet medical need. Herein, they report the design and application of novel biodegradable polymers - the lipidated antimicrobial guanidinylate polycarbonates. These polymers showed potent antimicrobial activity against a panel of bacteria with fast-killing kinetics and low resistance development tendency, mainly due to their bacterial membrane disruption mechanism. More importantly, the optimal polymer showed excellent antibacterial activity against C. difficile infection (CDI) in vivo via oral administration. In addition, compared with vancomycin, the polymer demonstrated a much-prolonged therapeutic effect and virtually diminished recurrence rate of CDI. The convenient synthesis, easy scale-up, low cost, as well as biodegradability of this class of polycarbonates, together with their in vitro broad-spectrum antimicrobial activity and orally in vivo efficacy against CDI, suggest the great potential of lipidated guandinylate polycarbonates as a new class of antibacterial biomaterials to treat CDI and combat emerging antibiotic resistance.

pH-Responsive Polymeric Micelle Dynamic Complexes for Selective Killing of Helicobacter pylori

Helicobacter pylori, the world's most common chronic infection-causing pathogen, is responsible for causing gastric ulcers, the fourth-leading cause of cancer-related death globally in 2020. In recent years, the effectiveness of the current treatment regimen (two antibiotics and one proton pump inhibitor) has often been plagued with problems such as resistance and the undesired elimination of commensal bacteria. Herein, we report the synthesis of block and random copolycarbonates, functionalized with cationic guanidinium and anionic acetate functional groups, aimed at selectively killing H. pylori in the acidic environment of the stomach, while remaining nontoxic to the commensal bacteria in the gut. The compositions of the polymers were fine-tuned so that the polymers were readily dispersed in water without any difficulty at both pH 3.0 and 7.4. The self-assembly behavior of the polymers at different pH values by dynamic light scattering showed that the random and block copolymers formed stable micelles in a simulated gastric environment (pH 3.0) while aggregated at pH 7.4. Both polymers demonstrated stronger antibacterial activity against H. pylori than the guanidinium-functionalized homopolymer without any acetate functional group at pH 3.0. The block copolymer was significantly more bactericidal at pH 3.0 across the concentrations tested, as compared to the random copolymer, while it did not show significant toxicity toward rat red blood cells (rRBCs) and HK-2 cells or bactericidal effect toward E. coli (a common gut bacterium) and nor caused aggregation of rRBCs at its effective concentration and at physiological pH of 7.4. Additionally, both the block and random copolymers were much more stable against hydrolysis at pH 3.0 than at pH 7.4. This study provides insight into the influence of both polymer architecture and dynamic assembly on the bioactivities of antimicrobial polymers, where the disassembly of coacervates into narrowly dispersed micelles at pH 3 make them potent antimicrobials aided by the protonated carboxylic acid block.

Main-Chain Cationic Bile Acid Polymers Mimicking Facially Amphiphilic Antimicrobial Peptides

Antibiotic-resistant bacterial infections have led to an increased demand for antibacterial agents that do not contribute to antimicrobial resistance. Antimicrobial peptides (AMPs) with the facially amphiphilic structures have demonstrated remarkable effectiveness, including the ability to suppress antibiotic resistance during bacterial treatment. Herein, inspired by the facially amphiphilic structure of AMPs, the facially amphiphilic skeletons of bile acids (BAs) are utilized as building blocks to create a main-chain cationic bile acid polymer (MCBAP) with macromolecular facial amphiphilicity via polycondensation and a subsequent quaternization. The optimal MCBAP displays an effective activity against Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative Escherichia coli, fast killing efficacy, superior bactericidal stability in vitro, and potent anti-infectious performance in vivo using the MRSA-infected wound model. MCBAP shows the low possibility to develop drug-resistant bacteria after repeated exposure, which may ascribe to the macromolecular facial amphiphilicity promoting bacterial membrane disruption and the generation of reactive oxygen species. The easy synthesis and low cost of MCBAP, the superior antimicrobial performance, and the therapeutic potential in treating MRSA infection altogether demonstrate that BAs are a promising group of building blocks to mimic the facially amphiphilic structure of AMPs in treating MRSA infection and alleviating antibiotic resistance.

Comparison of structure and neuroprotective ability of low molecular weight galactomannans from Sesbania cannabina obtained by different extraction technologies

Low-molecular-weight-galactomannan (LMW-GM) is an edible polysaccharide with various biological activities. However, it is used in the field of neuroprotection. In this study, two types of LMW-GMs from Sesbania cannabina were obtained by gluconic acid extraction (GA-LMW-GM) and enzymatic hydrolysis (GMOS). The structure of GA-LMW-GM and GMOS were identified using different nuclear magnetic resonance (NMR) techniques. The antioxidant and neuroprotective activities of GA-LMW-GM and GMOS were evaluated in vitro/vivo. The results showed that both GA-LMW-GM and GMOS possess good free radicals scavenging ability in vitro with IC₅₀ values of 1.9 mg/mL and 4.9 mg/mL for 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals 2.8 mg/mL and 4.4 mg/mL for O₂^•- radicals, respectively. However, GA-LMW-GM was more effective at scavenging reactive oxygen species (ROS) in vivo and protecting the fundamental growth (with a recovery capability of 62.5%) and locomotor functions (with recovery capability of 193.7%) of zebrafish with neurological damage induced by Bisphenol AF.

Biodegradable Polymers and Polymer Composites with Antibacterial Properties

Antibiotic resistance is one of the greatest threats to global health and food security today. It becomes increasingly difficult to treat infectious disorders because antibiotics, even the newest ones, are becoming less and less effective. One of the ways taken in the Global Plan of Action announced at the World Health Assembly in May 2015 is to ensure the prevention and treatment of infectious diseases. In order to do so, attempts are made to develop new antimicrobial therapeutics, including biomaterials with antibacterial activity, such as polycationic polymers, polypeptides, and polymeric systems, to provide non-antibiotic therapeutic agents, such as selected biologically active nanoparticles and chemical compounds. Another key issue is preventing food from contamination by developing antibacterial packaging materials, particularly based on degradable polymers and biocomposites. This review, in a cross-sectional way, describes the most significant research activities conducted in recent years in the field of the development of polymeric materials and polymer composites with antibacterial properties. We particularly focus on natural polymers, i.e., polysaccharides and polypeptides, which present a mechanism for combating many highly pathogenic microorganisms. We also attempt to use this knowledge to obtain synthetic polymers with similar antibacterial activity.

Dynamic helical cationic polyacetylenes for fast and highly efficient killing of bacteria

The antimicrobial activity of native antimicrobial peptides (AMPs) is often attributed to their helical structure, but the effectiveness of synthetic mimics with dynamic helical conformations, such as antimicrobial cationic polymers (ACPs), has not been well studied. Herein we demonstrate the antimicrobial activity of pyrrolidinium-pendant polyacetylenes (PAs) with dynamic helical conformations. The PAs exhibit fast and efficient antimicrobial activity against a wide range of pathogens, with low toxicity to mammalian cells and minimal risk of antibiotic resistance. In addition, the full-thickness wound infection model in mice has demonstrated the favorable biocompatibility and effective in vivo antibacterial capabilities of these PAs. Our data suggest that the dynamic helical structure of these PAs allows them to adapt and form pores in the bacterial membrane upon interaction, leading to their potent antimicrobial activity. This work investigated the antibacterial mechanism of dynamic helical ACPs, which provides valuable guidance for the rational design of high-performance antimicrobial agents. STATEMENT OF SIGNIFICANCE: Our study represents a significant contribution to the literature on antimicrobial cationic polymers (ACPs) as alternatives to antibiotics. Through a systematic investigation of the role of dynamic helical conformation in polyacetylenes (PAs) and the use of PAs with adaptive structure for the first time, we have provided valuable insights into the bacterial membrane action and killing mechanisms of these polymers. The results of our study, including fast killing rates and minimum inhibitory concentrations as low as 4-16 µg/mL against a broad range of pathogens and strong in vivo antibacterial activity, demonstrate the potential of these ACPs as high-performance antimicrobials. Our findings may guide the design of future ACPs with enhanced antimicrobial activity.

Guanidine-Containing Antifungal Agents against Human-Relevant Fungal Pathogens (2004-2022)-A Review

The guanidine moiety is typically a highly basic group, and can be found in a wide variety of drugs, such as zanamivir (Relenza) and metformin (Fortamet), as well as in biologically active compounds for numerous disease areas, including central nervous system (CNS) diseases and chemotherapeutics. This review will focus on antifungal agents which contain at least one guanidine group, for the treatment of human-related fungal pathogens, described in the literature between 2004 and 2022. These compounds include small molecules, steroids, polymers, metal complexes, sesquiterpenes, natural products, and polypeptides. It shall be made clear that a diverse range of guanidine-containing derivatives have been published in the literature and have antifungal activity, including efficacy in in vivo experiments.

Construction strategies and the development trend of antibacterial surfaces

The construction of antibacterial surfaces is an efficient way to respond to the problem of microbial contamination. In this review, we first describe the formation process and characteristics of microbial contamination and the current research status of antibacterial surfaces. Then, the passive antiadhesion, active killing, and combination construction strategies of the antibacterial surface are discussed in detail. Based on different antibacterial mechanisms and existing problems of current antibacterial strategies, we then discuss the future development trends of the next generation of antibacterial surfaces.

Addressing a future pandemic: how can non-biological complex drugs prepare us for antimicrobial resistance threats?

Loss of effective antibiotics through antimicrobial resistance (AMR) is one of the greatest threats to human health. By 2050, the annual death rate resulting from AMR infections is predicted to have climbed from 1.27 million per annum in 2019, up to 10 million per annum. It is therefore imperative to preserve the effectiveness of both existing and future antibiotics, such that they continue to save lives. One way to conserve the use of existing antibiotics and build further contingency against resistant strains is to develop alternatives. Non-biological complex drugs (NBCDs) are an emerging class of therapeutics that show multi-mechanistic antimicrobial activity and hold great promise as next generation antimicrobial agents. We critically outline the focal advancements for each key material class, including antimicrobial polymer materials, carbon nanomaterials, and inorganic nanomaterials, and highlight the potential for the development of antimicrobial resistance against each class. Finally, we outline remaining challenges for their clinical translation, including the need for specific regulatory pathways to be established in order to allow for more efficient clinical approval and adoption of these new technologies.

Preparation of CO2 -based Cationic Polycarbonate/Polyacrylonitrile Nanofibers with an Optimal Fibrous Microstructure for Antibacterial Applications

Utilizing CO₂ as one of the monomer resource, poly(vinylcyclohexene carbonates) (PVCHCs) are used as the precursor for preparing cationic PVCHCs (CPVCHCs) via thiol-ene click functionalization. Through the functionalization, CPVCHC-43 with a tertiary amine density of 43% relative to the backbone is able to display a significantly antibacterial ability against Staphylococcus aureus (S. aureus). Blending CPVCHC-43 with polyacrylonitrile (PAN), CPVCHC/PAN nanofiber meshes (NFMs) have been successfully prepared by electrospinning. More importantly, two crucial fibrous structural factors including CPVCHC/PAN weight ratio and fiber diameter have been systematically investigated for the effects on the antibacterial performance of the NFMs. Sequentially, a quaternization treatment has been employed on the NFMs with an optimal fibrous structure to enhance the antibacterial ability. The resulting quaternized NFMs have demonstrated the great biocidal effects against Gram-positive and Gram-negative bacteria. Moreover, the excellent biocompatibility of the quaternized NFMs have also been thoroughly evaluated and verified. This article is protected by copyright. All rights reserved.

Effects of Hydrophobicity on Antimicrobial Activity, Selectivity, and Functional Mechanism of Guanidinium-Functionalized Polymers

In this study, a series of guanidinium-functionalized polycarbonate random co-polymers is prepared from organocatalytic ring-opening polymerization to investigate the effect of the hydrophobic side chain (ethyl, propyl, isopropyl, benzyl, and hexyl) on their antimicrobial activity and selectivity. Although the polymers exhibit similar minimum inhibitory concentrations, the more hydrophobic polymers exhibit a faster rate of bacteria elimination. At higher percentage content (20 mol%), polymers with more hydrophobic side chains suffer from poor selectivity due to their high hemolytic activity. The highly hydrophobic co-polymer, containing the hydrophobic hexyl-functionalized cyclic carbonate, kills bacteria via a membrane-disruptive mechanism. Micelle formation leads to a lower extent of membrane disruption. This study unravels the effects of hydrophobic side chains on the activities of the polymers and their killing mechanism, providing insights into the design of new antimicrobial polymers.

Chain-folding regulated self-assembly, outstanding bactericidal activity and biofilm eradication by biomimetic amphiphilic polymers

Chain-folding regulated hierarchical self-assembly of cationic host defense peptide mimicking amphiphilic polyurethanes exhibit excellent antibacterial activity and biofilm killing.

Main-Chain Sulfonium-Containing Homopolymers with Negligible Hemolytic Toxicity for Eradication of Bacterial and Fungal Biofilms

Antimicrobials against planktonic cells and established biofilms at low doses are in increasing demand to tackle antibiotic-resistant biofilm infections. As a promising alternative to antibiotics, cationic polymers can effectively kill planktonic microbes but usually require high concentrations to eradicate the established biofilms. Herein, we developed a series of sulfonium-based homopolymers with cationic sulfoniums and alkane spacers in the main chain. These polysulfoniums presented effective activity against planktonic fungi (Candida albicans) and bacteria (Escherichia coli and Staphylococcus aureus) with minimum inhibition concentrations (MICs) of 0.5-32 μg/mL, and the optimal composition can provide an 80-90% reduction in biofilm mass and >99% killing of Candida albicans and Escherichia coli cells in 3-day mature biofilms at 2 × MIC as well as steadily low hemolytic toxicity. The influence of amphiphilicity and charge density of polysulfonium homopolymers on their antimicrobial activity against planktonic microbes and mature biofilms was investigated to provide insights for effective antimicrobial polymer design.

Elucidating the anticancer activities of guanidinium-functionalized amphiphilic random copolymers by varying the structure and composition in the hydrophobic monomer

Rationale: Use of traditional anticancer chemotherapeutics has been hindered by the multifactorial nature of multi-drug resistance (MDR) development and metastasis. Recently, cationic polycarbonates were reported as novel unconventional anticancer agents that mitigated MDR and inhibited metastasis. The aim of this study is to explore structure-anticancer activity relationship. Specifically, a series of cationic guanidinium-based random copolymers of varying hydrophobicity was synthesized with a narrow polydispersity (Ð = 1.12-1.27) via organocatalytic ring-opening polymerization (OROP) of functional cyclic carbonate monomers, and evaluated for anticancer activity, killing kinetics, degradability and functional mechanism. Methods: Linear, branched and aromatic hydrophobic side chain units, such as ethyl, benzyl, butyl, isobutyl and hexyl moieties were explored as comonomer units for modulating anticancer activity. As hydrophobicity/hydrophilicity balance of the polymers determines their anticancer efficacy, the feed ratio between the two monomers was varied to tune their hydrophobicity. Results: Notably, incorporating the hexyl moiety greatly enhanced anticancer efficiency and killing kinetics on cancer cells. Degradation studies showed that the polymers degraded completely within 4-6 days. Flow cytometry and lactate dehydrogenase (LDH) release analyses demonstrated that anticancer mechanism of the copolymers containing a hydrophobic co-monomer was concentration dependent, apoptosis at IC50, and both apoptosis and necrosis at 2 × IC50. In contrast, the homopolymer without a hydrophobic comonomer killed cancer cells predominantly via apoptotic mechanism. Conclusion: The hydrophobicity of the polymers played an important role in anticancer efficacy, killing kinetics and anticancer mechanism. This study provides valuable insights into designing novel anticancer agents utilizing polymers.

Macromolecular Nanotherapeutics and Antibiotic Adjuvants to Tackle Bacterial and Fungal Infections

The escalating rise in the population of multidrug-resistant (MDR) pathogens coupled with their biofilm forming ability has struck the global health as nightmare. Alongwith the threat of aforementioned menace, the sluggish development of new antibiotics and the continuous deterioration of the antibiotic pipeline has stimulated the scientific community toward the search of smart and innovative alternatives. In near future, membrane targeting antimicrobial polymers, inspired from antimicrobial peptides, can stand out significantly to combat against the MDR superbugs. Many of these amphiphilic polymers can form nanoaggregates through self-assembly with superior and selective antimicrobial efficacy. Additionally, these macromolecular nanoaggregrates can be utilized to engineer smart antibiotic-delivery system for on-demand drug-release, exploiting the infection site's micoenvironment. This strategy substantially increases the local concentration of antibiotics and reduces the associated off-target toxicity. Furthermore, amphiphilc macromolecules can be utilized to rejuvinate obsolete antibiotics to tackle the drug-resistant infections. This review article highlights the recent developments in macromolecular architecture to design numerous nanostructures with broad-spectrum antimicrobial activity, their application in fabricating smart drug delivery systems and their efficacy as antibiotic adjuvants to circumvent antimicrobial resistance. Finally, the current challenges and future prospects are briefly discussed for further exploration and their practical application in clinical settings.

Facile Synthesis of Imidazolium-Based Block Copolypeptides with Excellent Antimicrobial Activity

Antimicrobial polypeptides are promising mimics of antimicrobial peptides (AMPs) with low risks of antimicrobial resistance (AMR). Polypeptides with facile and efficient production, high antimicrobial activity, and low toxicity toward mammalian cells are highly desirable for practical applications. Herein, triblock copolypeptides with chloro groups (PPG_n-PCPBLG_m) and different main-chain lengths were synthesized via an ultrafast ring-opening polymerization (ROP) using a macroinitiator, namely poly(propylene glycol) bis(2-aminopropyl ether), and purified or nonpurified monomer (i.e., CPBLG-NCA). PPG_n-PCPBLG_m with 90 amino acid residues can be readily prepared within 300 s. Imidazolium-based block copolypeptides (PPG_n-PIL_m) were facilely prepared via nucleophilic substitution of PPG_n-PCPBLG_m with NaN₃ and subsequent "click" chemistry. α-Helical PPG_n-PIL_m can self-assemble into nanostructured and cationic micelles which displayed highly potent antimicrobial activity and low hemolysis. The top-performing material, namely PPG₃₄-PIL₇₀, showed low minimum inhibitory concentration (MIC) against both Gram-positive S. aureus and Gram-negative E. coli (25 μg mL^-1). It also displayed low toxicity against mouse embryonic fibroblast (NIH 3T3) and human embryonic kidney (293T) cells at 2× MIC.

Recent Progress in Bile Acid-Based Antimicrobials

With the emergence of drug-resistant bacteria and the formation of biofilms by bacteria and fungi, microbial infections gradually threaten global health. Natural antimicrobial peptides (AMPs) have low susceptibility for developing resistance due to the membrane targeted mechanism, but instability and high manufacturing cost limit their applications in clinic. Bile acids, a group of steroids in the human body, with high stability, biocompatibility, and inherent facial amphiphilic structure similar to the characteristics of AMPs, have been applied to the biological field, such as drug delivery systems, self-healing hydrogels, antimicrobials, and so on. In this review, we mainly focus on the different classes of bile acid-based antimicrobials in recent years. Various designs and methods for the preparation of unimolecular antimicrobials with bile acid skeletons are first introduced, including coupling of primary amine, quaternary ammonium, and amino acid units with bile acid skeletons. Some representative oligomeric antimicrobials, including dimers of bile acids, are summarized. Finally, macromolecular antimicrobials bearing some positive charges at the main chain or side chain and interaction mechanisms of these bile acid-based antimicrobials are discussed.

Cyclic peptides bearing the d-Phe-2-Abz turn motif: Structural characterization and antimicrobial potential

The effect on secondary structure and antimicrobial activity of introducing different cyclic constraints in linear β-hairpin antimicrobial peptides has been investigated with the intention of generating cyclic β sheets as promising antimicrobials with improved therapeutic potential. The linear peptides were cyclized head to tail either directly or after the addition of either a second turn motif or a disulfide bridge. The propensity of these peptides to adopt a cyclic β-sheet structure has been correlated to their antibacterial activity. All cyclic peptides showed enhanced activity, compared with their linear counterparts against methicillin-resistant Staphylococcus aureus. Scanning electron microscopy and transmission electron microscopy studies showed that this family kills bacteria through membrane lysis. The peptide that showed the best efficacy against all strains (exhibiting nanomolar activity), while retaining low haemolysis, bears two symmetrical, homochiral d-phe-2-Abz-d-ala turns and adopted a flexible structure. Its twin peptide that bears heterochiral turns (one with d-ala and one with L-Ala) showed reduced antibacterial activity and higher percentage of haemolysis. Circular dichroism and nuclear magnetic resonance spectroscopy indicate that heterochirality in the two turns leads to oligomerization of the peptide at higher concentrations, stabilizing the β-sheet secondary structure. More rigid secondary structure is associated with lower activity against bacteria and loss of selectivity.

l-Arginine Grafted Poly(Glycerol Sebacate) Materials: An Antimicrobial Material for Wound Dressing

This study focuses on the development and evaluation of a novel wound dressing material. l-arginine grafted poly(glycerol sebacate) materials (PGS-g-Arg) are developed by chemical conjugation of l-arginine on poly(glycerol sebacate) chains and the mechanical property, water vapor transmission rate, antimicrobial functions and biocompatibility are investigated. At various l-arginine grafting ratio, the mechanical properties are tunable. It was found that between 7-13% l-arginine grafting ratios, the tensile strengths of PGS-g-Arg were similar to that of natural skin. These materials are shown with a low water vapor transmission rate, 6.1 to 10.3 g/m²/h, which may form a barrier and assist in the closure of wounds. Inhibition in the growth of Pseudomonas aeruginosa and Staphylococcus aureus was observed on PGS-g-Arg, and a series of experiments were conducted to confirm its biocompatibility. In summary, l -arginine grafted poly(glycerol sebacate) may offer a novel option for wound dressing.

Guanidinylated Amphiphilic Polycarbonates with Enhanced Antimicrobial Activity by Extending the Length of the Spacer Arm and Micelle Self-Assembly

Nine guanidinylated amphiphilic polycarbonates are rationally designed and synthesized. Each polymer has the same biodegradable backbone but different side groups. The influence of the hydrophobic/hydrophilic effect on antimicrobial activities and cytotoxicity is systematically investigated. The results verify that tuning the length of the spacer arm between the cationic guanidine group and the polycarbonate backbone is an efficient design strategy to alter the hydrophobic/hydrophilic balance without changing the cationic charge density. A spacer arm of six methylene units (CH₂ )₆ shows the best antimicrobial activity (minimum inhibitory concentration, MIC = 40 µg mL^-1 against Escherichia coli, MIC = 20 µg mL^-1 against Staphylococcus aureus, MIC = 40 µg mL^-1 against Candida albicans) with low hemolytic activity (HC₅₀ > 2560 µg mL^-1 ). Furthermore, the guanidinylated polycarbonates exhibit the ability to self-assemble and present micelle-like nanostructure due to their intrinsic amphiphilic macromolecular structure. Transmission electron microscopy and dynamic light scattering measurements confirm polymer micelle formation in aqueous solution with sizes ranging from 82 to 288 nm.

Synthetic macromolecules as therapeutics that overcome resistance in cancer and microbial infection

Synthetic macromolecular antimicrobials have shown efficacy in the treatment of multidrug resistant (MDR) pathogens. These synthetic macromolecules, inspired by Nature's antimicrobial peptides (AMPs), mitigate resistance by disrupting microbial cell membrane or targeting multiple intracellular proteins or genes. Unlike AMPs, these polymers are less prone to degradation by proteases and are easier to synthesize on a large scale. Recently, various studies have revealed that cancer cell membrane, like that of microbes, is negatively charged, and AMPs can be used as anticancer agents. Nevertheless, efforts in developing polymers as anticancer agents has remained limited. This review highlights the recent advancement in the development of synthetic biodegradable antimicrobial polymers (e.g. polycarbonates, polyesters and polypeptides) and anticancer macromolecules including peptides and polymers. Additionally, strategies to improve their in vivo bioavailability and selectivity towards bacteria and cancer cells are examined. Lastly, future perspectives, including use of artificial intelligence or machine learning, in the development of antimicrobial and anticancer macromolecules are discussed.

A shear-thinning electrostatic hydrogel with antibacterial activity by nanoengineering of polyelectrolytes

Injectable shear-thinning hydrogels can be prepared by the non-covalent interactions between hydrophilic polymers. Although electrostatic force is a typical non-covalent interaction, direct mixing of two oppositely charged polyelectrolytes usually leads to a complex coacervate rather than an injectable hydrogel. Herein, a facile approach is proposed to prepare a shear-thinning hydrogel by nanoengineering of polyelectrolytes. Nanosized cationic micelles with electroneutral shells were prepared by mixing methoxyl poly(ethylene glycol)-block-poly(ε-caprolactone) and poly(ε-caprolactone)-block-poly(hexamethylene guanidine) hydrochloride-block-poly(ε-caprolactone) in an aqueous solution. When sodium carboxymethyl cellulose was added into the micellar solution, the outer poly(ethylene glycol) shell of mixed micelles prevented the instant electrostatic interaction between poly(hexamethylene guanidine) hydrochloride segments and sodium carboxymethyl cellulose, resulting in a homogenous shear-thinning electrostatic (STES) hydrogel. Because of the cationic poly(hexamethylene guanidine) hydrochloride segments, this hydrogel exhibits strong antibacterial activity against both Gram-positive and Gram-negative bacteria. Furthermore, the poly(ε-caprolactone) core of the mixed micelles can efficiently encapsulate a hydrophobic drug. In this work, curcumin-loaded STES hydrogel prepared by this method was used as wound dressing material that can promote wound healing even in infected wounds by further reducing bacterial infection via releasing curcumin. The present study provides a facile strategy to prepare shear-thinning antibacterial hydrogels from polyelectrolytes, which has great potential in biomedical application.

An on-demand nanoplatform for enhanced elimination of drug-resistant bacteria

We establish an “on-demand” nanoplatform based on acid-degradable scaffolds by conjugating glycomimetic-based galactose ligands to target a key lectin on P. aeruginosa and guanidine moieties.

Bioactive Aliphatic Polycarbonates Carrying Guanidinium Functions: An Innovative Approach for Myotonic Dystrophy Type 1 Therapy

Dystrophia myotonica type 1 (DM1) results from nuclear sequestration of splicing factors by a messenger RNA (mRNA) harboring a large (CUG) _n repeat array transcribed from the causal (CTG) _n DNA amplification. Several compounds were previously shown to bind the (CUG) _n RNA and release the splicing factors. We now investigated for the first time the interaction of an aliphatic polycarbonate carrying guanidinium functions to DM1 DNA/RNA model probes by affinity capillary electrophoresis. The apparent association constants (K _a) were in the range described for reference compounds such as pentamidine. Further macromolecular engineering could improve association specificity. The polymer presented no toxicity in cell culture at concentrations of 1.6-100.0 μg/mL as evaluated both by MTT and real-time monitoring xCELLigence method. These promising results may lay the foundation for a new branch of potential therapeutic agents for DM1.

Degradable antimicrobial polycarbonates with unexpected activity and selectivity for treating multidrug-resistant Klebsiella pneumoniae lung infection in mice

Multidrug resistant (MDR) Klebsiella pneumoniae is a major cause of healthcare-associated infections around the world, with attendant high rates of morbidity and mortality. Progressive reduction in potency of antibiotics capable of treating MDR K. pneumoniae infections - including lung infection - as a consequence of escalating drug resistance provides the motivation to develop drug candidates targeting MDR K. pneumoniae. We recently reported degradable broad-spectrum antimicrobial guanidinium-functionalized polycarbonates with unique antimicrobial mechanism - membrane translocation followed by precipitation of cytosolic materials. These polymers exhibited high potency against bacteria with negligible toxicity. The polymer with ethyl spacer between the quanidinium group and the polymer backbone (pEt_20) showed excellent in vivo efficacy for treating MDR K. pneumoniae-caused peritonitis in mice. In this study, the structures of the polymers were optimized for the treatment of MDR Klebsiella pneumoniae lung infection. Specifically, in vitro antimicrobial activity and selectivity of guanidinium-functionalized polycarbonates containing the same number of guanidinium groups but of a shorter chain length and a structural analogue containing a thiouronium moiety as the pendent cationic group were evaluated. The polymers with optimal compositions and varying hydrophobicity were assessed against 25 clinically isolated K. pneumonia strains for antimicrobial activity and killing kinetics. The results showed that the polymers killed the bacteria more efficiently than clinically used antibiotics, and repeated use of the polymers did not cause drug resistance in K. pneumonia. Particularly, the polymer with butyl spacer (pBut_20) self-assembled into micelles at high concentrations, where the hydrophobic component was shielded in the micellar core, preventing interacting with mammalian cells. A subtle change in the hydrophobicity increased the antimicrobial activity while reducing in vivo toxicity. The in vivo efficacy studies showed that pBut_20 alleviated K. pneumonia lung infection without inducing damage to major organs. Taken together, pBut_20 is promising for treating MDR Klebsiella pneumoniae lung infection in vivo. STATEMENT OF SIGNIFICANCE: Multidrug resistant (MDR) Klebsiella pneumoniae is a major cause of healthcare-associated infections, with attendant high rates of morbidity and mortality. The progressive reduction in antibiotics capable of treating MDR K. pneumoniae infections - including lung infection - as a consequence of escalating drug resistance rates provides the motivation to develop drug candidates. In this study, we report a degradable guanidinium-functionalized polycarbonate with unexpected antimicrobial activity and selectivity towards MDR Klebsiella pneumoniae. A subtle change in polymer hydrophobicity increases antimicrobial activity while reducing in vivo toxicity due to self-assembly at high concentrations. The polymer with optimal composition alleviates Klebsiella pneumonia lung infection without inducing damage to major organs. The polymer is promising for treating MDR Klebsiella pneumoniae lung infection in vivo.

Design, Synthesis, Antibacterial Potential, and Structural Characterization of N-Acylated Derivatives of the Human Autophagy 16 Polypeptide

A synthetic antimicrobial peptide library based on the human autophagy 16 polypeptide has been developed. Designed acetylated peptides bearing lipids of different chain lengths resulted in peptides with enhanced potency compared to the parent Atg16. A 21-residue fragment of Atg16 conjugated to 4-methylhexanoic acid (K30) emerged as the most potent antibacterial, with negligible hemolysis. Several studies, including microscopy, dye leakage, and ITC, were conducted to gain insight into the antibacterial mechanism of action of the peptide. Visual inspection using both SEM and TEM revealed the membranolytic effect of the peptide on bacterial cells. The selectivity of the peptide against bacterial cell membranes was also proven using dye leakage assays. ITC analysis revealed the exothermic nature of the binding interaction of the peptide to D8PG micelles. The three-dimensional solution NMR structure of K30 in complex with dioctanoylphosphatidylglycerol (D8PG) micelles revealed that the peptide adopts a helix-loop-helix structure in the presence of anionic membrane lipids mimicking bacterial membranes. Intermolecular NOEs between the peptide and lipid deciphered the location of the peptide in the bound state, which was subsequently supported by the paramagnetic relaxation enhancement (PRE) NMR experiment. Collectively, these results describe the structure-function relationship of the peptide in the bacterial membrane.

Structure-function relationships of nonviral gene vectors: Lessons from antimicrobial polymers

In recent years, substantial advances have been achieved in the design and synthesis of nonviral gene vectors. However, lack of effective and biocompatible vectors still remains a major challenge that hinders their application in clinical settings. In the past decade, there has been a rapid expansion of cationic antimicrobial polymers, due to their potent, rapid, and broad-spectrum biocidal activity against resistant microbes, and biocompatible features. Given that antimicrobial polymers share common features with nonviral gene vectors in various aspects, such as membrane affinity, functional groups, physicochemical characteristics, and unique macromolecular architectures, these polymers may provide us with inspirations to overcome challenges in the design of novel vectors toward more safe and efficient gene delivery in clinic. Building off these observations, we provide here an overview of the structure-function relationships of polymers for both antimicrobial applications and gene delivery by elaborating some key structural parameters, including functional groups, charge density, hydrophobic/hydrophilic balance, MW, and macromolecular architectures. By borrowing a leaf from antimicrobial agents, great advancement in the development of newer nonviral gene vectors with high transfection efficiency and biocompatibility will be more promising. STATEMENT OF SIGNIFICANCE: The development of gene delivery is still in the preclinical stage for the lack of effective and biocompatible vectors. Given that antimicrobial polymers share common features with gene vectors in various aspects, such as membrane affinity, functional groups, physicochemical characteristics, and unique macromolecular architectures, these polymers may provide us with inspirations to overcome challenges in the design of novel vectors toward more safe and efficient gene delivery in clinic. In this review, we systematically summarized the structure-function relationships of antimicrobial polymers and gene vectors, with which the design of more advanced nonviral gene vectors is anticipated to be further boosted in the future.

Increasing the Antimicrobial Activity of Amphiphilic Cationic Copolymers by the Facile Synthesis of High Molecular Weight Stars by Supplemental Activator and Reducing Agent Atom Transfer Radical Polymerization

Infections caused by bacteria represent a great motif of concern in the health area. Therefore, there is a huge demand for more efficient antimicrobial agents. Antimicrobial polymers have attracted special attention as promising materials to prevent infectious diseases. In this study, a new polymeric system exhibiting antimicrobial activity against a range of Gram-positive and Gram-negative bacterial strains at micromolar concentrations (e.g., 0.8 μM) was developed. Controlled linear and star-shaped copolymers, comprising hydrophobic poly(butyl acrylate) (PBA) and cationic poly(3-acrylamidopropyl)trimethylammonium chloride) (PAMPTMA) segments, were obtained by supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) at 30 °C. The antibacterial activity of the polymers was studied by varying systematically the molecular weight (MW), hydrophilic/hydrophobic balance, and architecture. The MW was found to exert the greatest influence on the antimicrobial activity of the polymers, with minimum inhibitory concentration values decreasing with increasing MW. Live/dead membrane integrity assays and scanning electron microscopy analysis confirmed the bactericidal character of the synthesized PAMPTMA- (b)co-PBA polymers.

Modulating bioactivities of primary ammonium-tagged antimicrobial aliphatic polycarbonates by varying length, sequence and hydrophobic side chain structure

A highly antimicrobial, biocompatible, and fast biodegradable polycarbonate has been developed by incorporating primary ammonium and monoether side chains.

Cationic polycarbonates via ring-opening polymerization: design, synthesis, and applications

The synthetic methods and applications of cationic polycarbonates via ring-opening polymerization are highlighted.

Enhanced anti-microbial effect through cationization of a mono-triazatricyclodecane substituted asymmetric phthalocyanine

Antimicrobial photodynamic therapy (aPDT) is an effective way to combat infectious diseases and antibiotic resistance. Photosensitizer is a key factor of aPDT and has triggered extensive research interest. In this study, a new asymmetric Zn(II) phthalocyanine mono-substituted with a triazatricyclodecane moiety (compound 3) and its cationic N-methylated derivative (compound 4) were synthesized. Their photodynamic antimicrobial activities were evaluated using bioluminescent bacterial strains. Compound 3 showed phototoxicity only toward the Gram-positive bacteria, whereas the cationic derivative compound 4 exhibited strong anti-bacterial activity against both Gram-positive and Gram-negative strains. These bacterial species were eradicated (>4.0 logs or 99.99% killing) at appropriate concentrations of compound 4 with 12.7 J/cm² of red light, demonstrating compound 4 as a potent aPDT agent.

Recent Progress in Polymer Research to Tackle Infections and Antimicrobial Resistance

Global health is increasingly being threatened by the rapid emergence of drug-resistant microbes. The ability of these microbes to form biofilms has further exacerbated the scenario leading to notorious infections that are almost impossible to treat. For addressing this clinical threat, various antimicrobial polymers, polymer-based antimicrobial hydrogels and polymer-coated antimicrobial surfaces have been developed in the recent past. This review aims to discuss such polymer-based antimicrobial strategies with a focus on their current advancement in the field. Antimicrobial polymers, whose designs are inspired from antimicrobial peptides (AMPs), are described with an emphasis on structure-activity analysis. Additionally, antibiofilm activity and in vivo efficacy are delineated to elucidate the real potential of these antimicrobial polymers as possible therapeutics. Antimicrobial hydrogels, prepared from either inherently antimicrobial polymers or biocide-loaded into polymer-derived hydrogel matrix, are elaborated followed by various strategies to engineer polymer-coated antimicrobial surfaces. In the end, the current challenges are accentuated along with future directions for further expansion of the field toward tackling infections and antimicrobial resistance.