Antimicrobial and Hemolytic Activities of Copolymers with Cationic and Hydrophobic Groups: A Comparison of Block and Random Copolymers

Development of Low-Toxicity Antimicrobial Polycarbonates Bearing Lysine Residues

Antibiotic resistance has been threatening public health for a long period, while the COVID pandemic aggravated the scenario. To combat antibiotic resistance strains, host defense peptides (HDPs) mimicking molecules have attracted considerable attention. Herein, we reported a series of polycarbonates bearing cationic lysine amino acid residues that could mimic the mechanism of action of HDPs and possess broad-spectrum antimicrobial activity. Moreover, those polymers had negligible toxicity toward red blood cells and mammalian cells. The membrane-disruption mechanism endows the lysine-containing polycarbonates with low possibility of resistance development and the fast killing kinetics, making them promising candidates for antimicrobial development.

Selector of amino-acid scales set

Experimental and theoretical properties of amino acids as building blocks of peptides and proteins have been extensively researched. Each such method assigns a number to each amino acid, and one such assignment is called amino-acid scale. Their usage in bioinformatics to explain and predict behaviour of peptides and proteins is of essential value. The number of such scales is very large. There are more than a hundred scales related just to hydrophobicity. A large number of scales can be a computational burden for algorithms that try to define peptide descriptors combining several of these scales. Hence, it is of interest to construct a smaller, but still representative set of scales. Here, we present software that does this. We test it on the set of scales using a database constructed by Kawashima and collaborators and show that it is possible to significantly reduce the number of scales observed without losing much of the information. An algorithm is implemented in C#. As a result, we provide a smaller database that might be a very useful tool for the analyses and construction of new peptides. Another interesting application of this database would be to compare the artificial intelligence construction of peptides having as an input the complete Kawashima database and this reduced one. Obtaining in both cases similar results would give much credibility to the constructs of such AI algorithms.

Chronic aquatic toxicity assessment of diverse chemicals on Daphnia magna using QSAR and chemical read-across

We have modeled here chronic Daphnia toxicity taking pNOEC (negative logarithm of no observed effect concentration in mM) and pEC50 (negative logarithm of half-maximal effective concentration in mM) as endpoints using QSAR and chemical read-across approaches. The QSAR models were developed by strictly obeying the OECD guidelines and were found to be reliable, predictive, accurate, and robust. From the selected features in the developed models, we have found that an increase in lipophilicity and saturation, the presence of electrophilic or electronegative or heavy atoms, the presence of sulphur, amine, and their related functionality, an increase in mean atomic polarizability, and higher number of (thio-) carbamates (aromatic) groups are responsible for chronic toxicity. Therefore, this information might be useful for the development of environmentally friendly and safer chemicals and data-gap filling as well as reducing the use of identified toxic chemicals which have chronic toxic effects on aquatic ecosystems. Approved classes of drugs from DrugBank databases and diverse groups of chemicals from the Chemical and Product Categories (CPDat) database were also assessed through the developed models.

Evaluation of the Antimicrobial Activity in Host-Mimicking Media and In Vivo Toxicity of Antimicrobial Polymers as Functional Mimics of AMPs

Activity tests for synthetic antimicrobial compounds are often limited to the minimal inhibitory concentration assay using standard media and bacterial strains. In this study, a family of acrylamide copolymers that act as synthetic mimics of antimicrobial peptides were synthesized and shown to have a disruptive effect on bacterial membranes and structural integrity through microscopy techniques and membrane polarization experiments. The polymers were tested for their antimicrobial properties using media that mimic clinically relevant conditions. Additionally, their activity was compared in two different strains of the Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacterium Pseudomonas aeruginosa. We showed that the medium composition can have an important influence on the polymer activity as there was a considerable reduction in minimal inhibitory concentrations against S. aureus grown in synthetic wound fluid (SWF), and against P. aeruginosa grown in synthetic cystic fibrosis sputum media (SCFM), compared to the concentrations in standard testing media. In contrast, we observed a complete loss of activity against P. aeruginosa in the serum-containing SWF. Finally, we made use of an emerging invertebrate in vivo model, using Galleria mellonella larvae, to assess toxicity of the polymeric antimicrobials, showing a good correlation with cell line toxicity measurements and demonstrating its potential in the evaluation of novel antimicrobial materials.

Structural Exploration of Polycationic Nanoparticles for siRNA Delivery

RNA interference (RNAi) is a promising approach to the treatment of genetic diseases by the specific knockdown of target genes. Functional polymers are potential vehicles for the effective delivery of vulnerable small interfering RNA (siRNA), which is required for the broad application of RNAi-based therapeutics. The development of methods for the facile modulation of chemical structures of polymeric carriers and an elucidation of detailed delivery mechanisms remain important areas of research. In this paper, we synthesized a series of methacrylate-based polymers with controllable structures and narrow distributions by atom transfer radical polymerization using various combinations of cationic monomers (2-dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, and 2-dibutylaminoethyl methacrylate) and hydrophobic monomers (2-butyl methacrylate (BMA), cyclohexyl methacrylate, and 2-ethylhexyl methacrylate). These polymers exhibited varying hydrophobicities, charge densities, and pK_a values, enabling the discovery of effective carriers for siRNA by in vitro delivery assays. For the polymers with BMA segments, 50% of cationic segments were beneficial to the formation of siRNA nanoparticles (NPs) and the in vitro delivery of siRNA. The optimal ratio varied for different combinations of cationic and hydrophobic segments. In particular, 20k PMB 0.5, PME 0.5, and PEB 1.0 showed >75% luciferase knockdown. Efficacious delivery was dependent on high siRNA binding, the small size of NPs, and balanced hydrophobicity and charge density. Cellular uptake and endosomal escape experiments indicated that carboxybetaine modification of 20k PMB 0.5 did not remarkably affect the internalization of corresponding NPs after incubation for 6 h but significantly reduced the endosomal escape of NPs, which leads to the notable decrease in delivery efficacy of polymers. These results provide insights into the mechanism of polymer-based siRNA delivery and may inspire the development of novel polymeric carriers.

The Best Peptidomimetic Strategies to Undercover Antibacterial Peptides

Health-care systems that develop rapidly and efficiently may increase the lifespan of humans. Nevertheless, the older population is more fragile, and is at an increased risk of disease development. A concurrently growing number of surgeries and transplantations have caused antibiotics to be used much more frequently, and for much longer periods of time, which in turn increases microbial resistance. In 1945, Fleming warned against the abuse of antibiotics in his Nobel lecture: "The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug make them resistant". After 70 years, we are witnessing the fulfilment of Fleming's prophecy, as more than 700,000 people die each year due to drug-resistant diseases. Naturally occurring antimicrobial peptides protect all living matter against bacteria, and now different peptidomimetic strategies to engineer innovative antibiotics are being developed to defend humans against bacterial infections.

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.

Facial Amphiphilicity-Induced Polymer Nanostructures for Antimicrobial Applications

New antimicrobial agents are needed to address ever-increasing antimicrobial resistance and a growing epidemic of infections caused by multidrug resistant pathogens. We design nanostructured antimicrobial copolymers containing multicyclic natural products that bear facial amphiphilicity. Bile acid based macromolecular architectures of these nanostructures can interact preferentially with bacterial membranes. Incorporation of polyethylene glycol into the copolymers not only improved the colloidal stability of nanostructures but also increased the biocompatibility. This study investigated the effects of facial amphiphilicity, polymer architectures, and self-assembled nanostructures on antimicrobial activity. Advanced nanostructures such as spheres, vesicles, and rod-shaped aggregates are formed in water from the facial amphiphilic cationic copolymers via supramolecular interactions. These aggregates were particularly interactive toward Gram-positive and Gram-negative bacterial cell membranes and showed low hemolysis against mammalian cells.

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.

Synthesis, Characterization, and Antimicrobial Properties of Peptides Mimicking Copolymers of Maleic Anhydride and 4-Methyl-1-pentene

Synthetic amphiphilic copolymers with strong antimicrobial properties mimicking natural antimicrobial peptides were obtained via synthesis of an alternating copolymer of maleic anhydride and 4-methyl-1-pentene. The obtained copolymer was modified by grafting with 3-(dimethylamino)-1-propylamine (DMAPA) and imidized in a one-pot synthesis. The obtained copolymer was modified further to yield polycationic copolymers by means of quaternization with methyl iodide and dodecyl iodide, as well as by being sequentially quaternized with both of them. The antimicrobial properties of obtained copolymers were tested against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis, and Staphylococcus aureus. Both tested quaternized copolymers were more active against the Gram-negative E. coli than against the Gram-positive S. aureus. The copolymer modified with both iodides was best when tested against E. coli and, comparing all three copolymers, also exhibited the best effect against S. aureus. Moreover, it shows (limited) selectivity to differentiate between mammalian cells and bacterial cell walls. Comparing the minimum inhibitory concentration (MIC) of Nisin against the Gram-positive bacteria on the molar basis instead on the weight basis, the difference between the effect of Nisin and the copolymer is significantly lower.

Novel Antibacterial Polyglycidols: Relationship between Structure and Properties

Antimicrobial polymers are an attractive alternative to low molecular weight biocides, because they are non-volatile, chemically stable, and can be used as non-releasing additives. Polymers with pendant quaternary ammonium groups and hydrophobic chains exhibit antimicrobial properties due to the electrostatic interaction between polymer and cell wall, and the membrane disruptive capabilities of the hydrophobic moiety. Herein, the synthesis of cationic⁻hydrophobic polyglycidols with varying structures by post-polymerization modification is presented. The antimicrobial properties of the prepared polyglycidols against E. coli and S. aureus are examined. Polyglycidol with statistically distributed cationic and hydrophobic groups (cationic⁻hydrophobic balance of 1:1) is compared to (i) polyglycidol with a hydrophilic modification at the cationic functionality; (ii) polyglycidol with both-cationic and hydrophobic groups-at every repeating unit; and (iii) polyglycidol with a cationic⁻hydrophobic balance of 1:2. A relationship between structure and properties is presented.

The effects of polymer topology and chain length on the antimicrobial activity and hemocompatibility of amphiphilic ternary copolymers

Hyperbranched random copolymers that consist of ethylhexyl hydrophobic groups have the best selectivity compared to linear random and block copolymers.

Elaboration of antimicrobial polymeric materials by dispersion of well-defined amphiphilic methacrylic SG1-based copolymers

Towards a versatile and easy method of elaboration of solid polymeric antimicrobial materials.

Sequence Control as a Powerful Tool for Improving the Selectivity of Antimicrobial Polymers

Antimicrobial polymers appear as a promising alternative to tackle the current development of bacterial resistance against conventional antibiotics as they rely on bacterial membrane disruption. This study investigates the effect of segmentation of hydrophobic and cationic functionalities on antimicrobial polymers over their selectivity between bacteria and mammalian cells. Using RAFT technology, statistical, diblock, and highly segmented multiblock copolymers were synthesized in a controlled manner. Polymers were analyzed by HPLC, and the segmentation was found to have a significant influence on their overall hydrophobicity. In addition, the amount of incorporated cationic comonomer was varied to yield a small library of bioactive macromolecules. The antimicrobial properties of these compounds were probed against pathogenic bacteria (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis), and their biocompatibility was tested using hemolysis and erythrocyte aggregation assays, as well as mammalian cell viability assays. In all cases, diblock and multiblock copolymers were found to outperform statistical copolymers, and for polymers with a low content of cationic comonomer, the multiblock showed a tremendously increased selectivity for P. aeruginosa and S. epidermidis compared to its statistical and diblock analogue. This work highlights the remarkable effect of segmentation on both the physical properties of the materials as well as their interaction with biological systems. Due to the outstanding selectivity of multiblock copolymers toward certain bacteria strains, the presented materials are a promising platform for the treatment of infections and a valuable tool to combat antimicrobial resistance.

Sequence-Defined Backbone Modifications Regulate Antibacterial Activity of OligoTEAs

In response to the urgent need for new antibiotic development strategies, antimicrobial peptides (AMPs) and other synthetic polymers are being actively investigated as promising alternatives to traditional antibiotics. Although most AMPs display lytic activity against several types of bacteria, they have poor toxicology profiles and are susceptible to proteolysis in vivo. While many synthetic variants have been created to mimic AMPs by tuning the hydrophobic to cationic ratio of the side-chain groups, few have decoupled the effects of charge from hydrophobicity in discrete systems, and none have investigated the effect of backbone hydrophobicity. We recently developed a rapid and efficient approach for the assembly of synthetic sequence-defined oligothioetheramides (oligoTEAs) that are resistant to protease activity. Our oligoTEA assembly scheme allows direct access to the oligomer backbone, which enables precise tuning of oligoTEA hydrophobicity while keeping charge constant. In this study, we synthesized a new class of antibacterial oligoTEAs (AOTs) with precise control over backbone hydrophobicity and composition. Our studies suggest that AOTs lyse cells via membrane permeabilization and that hydrophobicity and macromolecular conformation are key properties that regulate AOT activity. Some of our AOTs show highly promising antibacterial activity (MIC ∼ 0.5-5 μM) against clinically relevant pathogens in the presence of serum, with little to no toxicity against RBCs and HEK293 cells. Taken together, our data identify design parameters and criteria that may be useful for assembling the next generation of potent and selective AOTs.

A Cationic Amphiphilic Random Copolymer with pH-Responsive Activity against Methicillin-Resistant Staphylococcus aureus

In this report, we demonstrate the pH-dependent, in vitro antimicrobial activity of a cationic, amphiphilic random copolymer against clinical isolates of drug-resistant Staphylococcus aureus. The polymer was developed toward a long-term goal of potential utility in the treatment of skin infections. The proposed mechanism of action of the polymer is through selectively binding to bacterial membranes and subsequent disruption of the membrane structure/integrity, ultimately resulting in bacterial cell death. The polymer showed bactericidal activity against clinical isolates of methicillin-resistant or vancomycin-intermediate S. aureus. The polymer was effective in killing S. aureus at neutral pH, but inactive under acidic conditions (pH 5.5). The polymer did not exhibit any significant hemolytic activity against human red blood cells or display cytotoxicity to human dermal fibroblasts over a range of pH values (5.5–7.4). These results indicate that the polymer activity was selective against bacteria over human cells. Using this polymer, we propose a new potential strategy for treatment of skin infections using the pH-sensitive antimicrobial polymer agent that would selectively target infections at pH-neutral wound sites, but not the acidic, healthy skin.

Evaluation of antimicrobial efficacy of quaternized poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea] against targeted pathogenic and multi-drug-resistant bacteria

Here, we have investigated in vitro antimicrobial efficacy of a quaternized cationic polymer, poly[bis(2-chloroethyl)ether- alt-1,3-bis[3-(dimethylamino)propyl]urea] (polyquaternium-2), against gram-positive as well as gram-negative bacteria along with several multi-drug-resistant bacterial strains. The antimicrobial efficacy of this polymer was first tested against some clinical pathogens followed by microorganisms isolated from acne lesions. Interestingly, polyquaternium-2 exhibited significant antimicrobial activity against methicillin-resistant Staphylococcus aureus, for which very limited drugs are available. Most importantly, the polymer displayed low haemolytic activity and non-toxic behaviour against mammalian cells. The results showed the promising potential of the projected polymer to be utilized as an antibacterial agent for various biomedical applications.

Random peptide mixtures inhibit and eradicate methicillin-resistant Staphylococcus aureus biofilms

Sequence-random hydrophobic-cationic peptides are capable of controlling and managing methicillin-resistantStaphylococcus aureusbiofilms and might be used as lead biofilm inhibitor candidates for further studies.

Block versus Random Amphiphilic Glycopolymer Nanopaticles as Glucose-Responsive Vehicles

To explore the effect of polymer structure on their self-assembled aggregates and their unique characteristics, this study was devoted to developing a series of amphiphilic block and random phenylboronic acid-based glycopolymers by RAFT polymerization. The amphiphilic glycopolymers were successfully self-assembled into spherically shaped nanoparticles with narrow size distribution in aqueous solution. For block and random copolymers with similar monomer compositions, block copolymer nanoparticles exhibited a more regular transmittance change with the increasing glucose level, while a more evident variation of size and quicker decreasing tendency in I/I0 behavior in different glucose media were observed for random copolymer nanoparticles. Cell viability of all the polymer nanoparticles investigated by MTT assay was higher than 80%, indicating that both block and random copolymers had good cytocompatibility. Insulin could be encapsulated into both nanoparticles, and insulin release rate for random glycopolymer was slightly quicker than that for the block ones. We speculate that different chain conformations between block and random glycopolymers play an important role in self-assembled nanoaggregates and underlying glucose-sensitive behavior.

Antimicrobial and antioxidant amphiphilic random copolymers to address medical device-centered infections

Microbial biofilms are known to support a number of human infections, including those related to medical devices. This work is focused on the development of novel dual-function amphiphilic random copolymers to be employed as coatings for medical devices. Particularly, copolymers were obtained by polymerization of an antimicrobial cationic monomer (bearing tertiary amine) and an antioxidant and antimicrobial hydrophobic monomer (containing hydroxytyrosol, HTy). To obtain copolymers with various amphiphilic balance, different molar ratios of the two monomers were used. (1)H NMR and DSC analyses evidenced that HTy aromatic rings are able to interact with each other leading to a supra-macromolecular re-arrangement and decrease the copolymer size in water. All copolymers showed good antioxidant activity and Fe(2+) chelating ability. Cytotoxicity and hemolytic tests evidenced that the amphiphilic balance, cationic charge density and polymer size in solution are key determinants for polymer biocompatibility. As for the antimicrobial properties, the lowest minimal inhibitory concentration (MIC = 40 μg/mL) against Staphylococcus epidermidis was shown by the water-soluble copolymer having the highest HTy molar content (0.3). This copolymer layered onto catheter surfaces was also able to prevent staphylococcal adhesion. This approach permits not only prevention of biofilm infections but also reduction of the risk of emergence of drug-resistant bacteria. Indeed, the combination of two active compounds in the same polymer can provide a synergistic action against biofilms and suppress reactive species oxygen (ROS), known to promote the occurrence of antibiotic resistance.

Nonhemolytic and Antibacterial Acrylic Copolymers with Hexamethyleneamine and Poly(ethylene glycol) Side Chains

Amphiphilic acrylic copolymers with hexamethyleneamine and poly(ethylene glycol) side chains can show >100-fold selectivity toward Escherichia coli over red blood cells. Homopolymer with cationic pendant amine groups is highly hemolytic and antibacterial. Incorporation of approximately 33 mol % of poly(ethylene glycol) methyl ether methacrylate (PEGMA) led to 1300 times reduction in hemolytic activity, while maintaining high levels of antibacterial activity. The hemolytic activity of these PEGylated copolymers depends on the overall content and spatial distribution of the PEGMA units. Higher activity against Escherichia coli than Staphylococcus aureus was observed for this polymer system, likely due to hydrogen bonding ability of the PEG side chains with polysaccharide cell wall of the bacteria. Field emission scanning electron microscopy analysis confirmed the bacterial membrane rupture activity exerted by these copolymers, whereas time-kill studies revealed significantly different bactericidal kinetics toward the Gram-negative Escherichia coli and the Gram-positive Staphylococcus aureus.

Structure–property relationships of antibacterial amphiphilic polymers derived from 2-aminoethyl acrylate

The effects of variation in the topographical position of the cationic center and hydrophobic segments on the antibacterial and hemolytic activities of polyacrylates.

Nanoengineered drug delivery systems for enhancing antibiotic therapy

Formulation scientists are recognizing nanoengineered drug delivery systems as an effective strategy to overcome limitations associated with antibiotic drug therapy. Antibiotics encapsulated into nanodelivery systems will contribute to improved management of patients with various infectious diseases and to overcoming the serious global burden of antibiotic resistance. An extensive review of several antibiotic-loaded nanocarriers that have been formulated to target drugs to infectious sites, achieve controlled drug release profiles, and address formulation challenges, such as low-drug entrapment efficiencies, poor solubility and stability is presented in this paper. The physicochemical properties and the in vitro/in vivo performances of various antibiotic-loaded delivery systems, such as polymeric nanoparticles, micelles, dendrimers, liposomes, solid lipid nanoparticles, lipid-polymer hybrid nanoparticles, nanohybirds, nanofibers/scaffolds, nanosheets, nanoplexes, and nanotubes/horn/rods and nanoemulsions, are highlighted and evaluated. Future studies that will be essential to optimize formulation and commercialization of these antibiotic-loaded nanosystems are also identified. The review presented emphasizes the significant formulation progress achieved and potential that novel nanoengineered antibiotic drug delivery systems have for enhancing the treatment of patients with a range of infections.

Synthetic polymers active against Clostridium difficile vegetative cell growth and spore outgrowth

Nylon-3 polymers (poly-β-peptides) have been investigated as synthetic mimics of host-defense peptides in recent years. These polymers are attractive because they are much easier to synthesize than are the peptides themselves, and the polymers resist proteolysis. Here we describe in vitro analysis of selected nylon-3 copolymers against Clostridium difficile, an important nosocomial pathogen that causes highly infectious diarrheal disease. The best polymers match the human host-defense peptide LL-37 in blocking vegetative cell growth and inhibiting spore outgrowth. The polymers and LL-37 were effective against both the epidemic 027 ribotype and the 012 ribotype. In contrast, neither vancomycin nor nisin inhibited outgrowth for the 012 ribotype. The best polymer was less hemolytic than LL-37. Overall, these findings suggest that nylon-3 copolymers may be useful for combatting C. difficle.

Tuning the biological activity profile of antibacterial polymers via subunit substitution pattern

Binary nylon-3 copolymers containing cationic and hydrophobic subunits can mimic the biological properties of host-defense peptides, but relationships between composition and activity are not yet well understood for these materials. Hydrophobic subunits in previously studied examples have been limited mostly to cycloalkane-derived structures, with cyclohexyl proving to be particularly promising. The present study evaluates alternative hydrophobic subunits that are isomeric or nearly isomeric with the cyclohexyl example; each has four sp(3) carbons in the side chains. The results show that varying the substitution pattern of the hydrophobic subunit leads to relatively small changes in antibacterial activity but causes significant changes in hemolytic activity. We hypothesize that these differences in biological activity profile arise, at least in part, from variations among the conformational propensities of the hydrophobic subunits. The α,α,β,β-tetramethyl unit is optimal among the subunits we have examined, providing copolymers with potent antibacterial activity and excellent prokaryote vs eukaryote selectivity. Bacteria do not readily develop resistance to the new antibacterial nylon-3 copolymers. These findings suggest that variation in subunit conformational properties could be generally valuable in the development of synthetic polymers for biological applications.

Structure-activity relationships among antifungal nylon-3 polymers: identification of materials active against drug-resistant strains of Candida albicans

Fungal infections are a major challenge to human health that is heightened by pathogen resistance to current therapeutic agents. Previously, we were inspired by host-defense peptides to develop nylon-3 polymers (poly-β-peptides) that are toxic toward the fungal pathogen Candida albicans but exert little effect on mammalian cells. Based on subsequent analysis of structure-activity relationships among antifungal nylon-3 polymers, we have now identified readily prepared cationic homopolymers active against strains of C. albicans that are resistant to the antifungal drugs fluconazole and amphotericin B. These nylon-3 polymers are nonhemolytic. In addition, we have identified cationic-hydrophobic copolymers that are highly active against a second fungal pathogen, Cryptococcus neoformans, and moderately active against a third pathogen, Aspergillus fumigatus.

Antibacterial polymeric nanostructures for biomedical applications

A topical review on recent advances in the research and applications of antimicrobial polymeric nanostructures, such as silver-decorated polymeric nanostructures, and polymeric micelles and vesicles based on antimicrobial polymers and antimicrobial peptides.

Enzyme-coated mesoporous silica nanoparticles as efficient antibacterial agents in vivo

Despite the fact that pathogenic infections are widely treated by antibiotics in the clinic nowadays, the increasing risk of multidrug-resistance associated with abuse of antibiotics is becoming a major concern in global public health. The increased death toll caused by pathogenic bacterial infection calls for effective antibiotic alternatives. Lysozyme-coated mesoporous silica nanoparticles (MSNs⊂Lys) are reported as antibacterial agents that exhibit efficient antibacterial activity both in vitro and in vivo with low cytotoxicity and negligible hemolytic side effect. The Lys corona provides multivalent interaction between MSNs⊂Lys and bacterial walls and consequently raises the local concentration of Lys on the surface of cell walls, which promotes hydrolysis of peptidoglycans and increases membrane-perturbation abilities. The minimal inhibition concentration (MIC) of MSNs⊂Lys is fivefold lower than that of free Lys in vitro. The antibacterial efficacy of MSNs⊂Lys is evaluated in vivo by using an intestine-infected mouse model. Experimental results indicate that the number of bacteria surviving in the colon is three orders of magnitude lower than in the untreated group. These natural antibacterial enzyme-modified nanoparticles open up a new avenue for design and synthesis of next-generation antibacterial agents as alternatives to antibiotics.

Nylon-3 polymers with selective antifungal activity

Host-defense peptides inhibit bacterial growth but show little toxicity toward mammalian cells. A variety of synthetic polymers have been reported to mimic this antibacterial selectivity; however, achieving comparable selectivity for fungi is more difficult because these pathogens are eukaryotes. Here we report nylon-3 polymers based on a novel subunit that display potent antifungal activity (MIC = 3.1 μg/mL for Candida albicans ) and favorable selectivity (IC10 > 400 μg/mL for 3T3 fibroblast toxicity; HC10 > 400 μg/mL for hemolysis).

Antimicrobial polymers as synthetic mimics of host-defense peptides

Antibiotic-resistant bacteria 'superbugs' are an emerging threat to public health due to the decrease in effective antibiotics as well as the slowed pace of development of new antibiotics to replace those that become ineffective. The need for new antimicrobial agents is a well-documented issue relating to world health. Tremendous efforts have been given to developing compounds that not only show high efficacy, but also those that are less susceptible to resistance development in the bacteria. However, the development of newer, stronger antibiotics which can overcome these acquired resistances is still a scientific challenge because a new mode of antimicrobial action is likely required. To that end, amphiphilic, cationic polymers have emerged as a promising candidate for further development as an antimicrobial agent with decreased potential for resistance development. These polymers are designed to mimic naturally occurring host-defense antimicrobial peptides which act on bacterial cell walls or membranes. Antimicrobial-peptide mimetic polymers display antibacterial activity against a broad spectrum of bacteria including drug-resistant strains and are less susceptible to resistance development in bacteria. These polymers also showed selective activity to bacteria over mammalian cells. Antimicrobial polymers provide a new molecular framework for chemical modification and adaptation to tune their biological functions. The peptide-mimetic design of antimicrobial polymers will be versatile, generating a new generation of antibiotics toward implementation of polymers in biomedical applications.