Biodegradable Antimicrobial Polycarbonates with In Vivo Efficacy against Multidrug-Resistant MRSA Systemic Infection

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.

Recent Advances in Amphipathic Peptidomimetics as Antimicrobial Agents to Combat Drug Resistance

The development of antimicrobial drugs with novel structures and clear mechanisms of action that are active against drug-resistant bacteria has become an urgent need of safeguarding human health due to the rise of bacterial drug resistance. The discovery of AMPs and the development of amphipathic peptidomimetics have lay the foundation for novel antimicrobial agents to combat drug resistance due to their overall strong antimicrobial activities and unique membrane-active mechanisms. To break the limitation of AMPs, researchers have invested in great endeavors through various approaches in the past years. This review summarized the recent advances including the development of antibacterial small molecule peptidomimetics and peptide-mimic cationic oligomers/polymers, as well as mechanism-of-action studies. As this exciting interdisciplinary field is continuously expanding and growing, we hope this review will benefit researchers in the rational design of novel antimicrobial peptidomimetics in the future.

A novel indolylbenzoquinone compound HL-J6 suppresses biofilm formation and α-toxin secretion in methicillin-resistant Staphylococcus aureus

Eradication of methicillin-resistant Staphylococcus aureus (MRSA) is challenging due to multi-drug resistance of strains and biofilm formation, the latter of which is an important barrier to the penetration of antibiotics and host defences. As such, there is an urgent need to discover and develop novel agents to fight MRSA-associated infection. In this study, HL-J6, a novel indolylbenzoquinone compound, was shown to inhibit S. aureus strains, with a minimum inhibitory concentration against MRSA252 of 2 µg/mL. Moreover, HL-J6 exhibited potent antibiofilm activity in vitro and was able to kill bacteria in biofilm. In the mouse models of wound infection, HL-J6 treatment reduced the MRSA load significantly and inhibited biofilm formation on the wounds. The potent targets of its antibiofilm activity were explored by real-time reverse transcriptase polymerase chain rection, which indicated that HL-J6 downregulated the transcription levels of sarA, atlAE and icaADBC. Moreover, Western blot results showed that HL-J6 reduced the secretion level of α-toxin, a major virulence factor. These findings indicate that HL-J6 is a promising lead compound for the development of novel drugs against MRSA biofilm infections.

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.

Evaluation of the Efficiency of Random and Diblock Methacrylate-Based Amphiphilic Cationic Polymers against Major Bacterial Pathogens Associated with Cystic Fibrosis

Cystic fibrosis (CF) is associated with repeated lung bacterial infection, mainly by Pseudomonas aeruginosa, Staphylococcus aureus, and Mycobacterium abscessus, all known to be or becoming resistant to several antibiotics, often leading to therapeutic failure and death. In this context, antimicrobial peptides and antimicrobial polymers active against resistant strains and less prompt to cause resistance, appear as a good alternative to conventional antibiotics. In the present study, methacrylate-based copolymers obtained by radical chemistry were evaluated against CF-associated bacterial strains. Results showed that the type (Random versus Diblock) and the size of the copolymers affected their antibacterial activity and toxicity. Among the different copolymers tested, four (i.e., Random₁₀₂₀₀, Random₁₅₀₀₀, Random₂₃₉₀₀, and Diblock₉₅₀₀) were identified as the most active and the safest molecules and were further investigated. Data showed that they inserted into bacterial lipids, leading to a rapid membranolytic effect and killing of the bacterial. In relation with their fast bactericidal action and conversely to conventional antibiotics, those copolymers did not induce a resistance and remained active against antibiotic-resistant strains. Finally, the selected copolymers possessed a preventive effect on biofilm formation, although not exhibiting disruptive activity. Overall, the present study demonstrates that methacrylate-based copolymers are an interesting alternative to conventional antibiotics in the treatment of CF-associated bacterial infection.

Biomimetic antimicrobial polymers—Design, characterization, antimicrobial, and novel applications

Biomimetic antimicrobial polymers have been an area of great interest as the need for novel antimicrobial compounds grows due to the development of resistance. These polymers were designed and developed to mimic naturally occurring antimicrobial peptides in both physicochemical composition and mechanism of action. These antimicrobial peptide mimetic polymers have been extensively investigated using chemical, biophysical, microbiological, and computational approaches to gain a deeper understanding of the molecular interactions that drive function. These studies have helped inform SARs, mechanism of action, and general physicochemical factors that influence the activity and properties of antimicrobial polymers. However, there are still lingering questions in this field regarding 3D structural patterning, bioavailability, and applicability to alternative targets. In this review, we present a perspective on the development and characterization of several antimicrobial polymers and discuss novel applications of these molecules emerging in the field. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Electrospun Polylactic Acid-Based Fibers Loaded with Multifunctional Antibacterial Biobased Polymers

Here, we report the development of antibacterial and compostable electrospun polylactic acid (PLA) fibers by incorporation of a multifunctional biobased polymer in the process. The multifunctional polymer was synthesized from the bio-sourced itaconic acid building block by radical polymerization followed by click chemistry reaction with hydantoin groups. The resulting polymer possesses triazole and hydantoin groups available for further N-alkylation and chlorination reaction, which provide antibacterial activity. This polymer was added to the electrospinning PLA solution at 10 wt %, and fiber mats were successfully prepared. The obtained fibers were surface-modified through the accessible functional groups, leading to the corresponding cationic triazolium and N-halamine groups. The fibers with both antibacterial functionalities demonstrated high antibacterial activity against Gram-positive and Gram-negative bacteria. While the fibers with cationic surface groups are only effective against Gram-positive bacteria (Staphylococcus epidermidis and Staphylococcus aureus), upon chlorination, the activity against Gram-negative Escherichia coli and Pseudomonas aeruginosa is significantly improved. In addition, the compostability of the electrospun fibers was tested under industrial composting conditions, showing that the incorporation of the antibacterial polymer does not impede the disintegrability of the material. Overall, this study demonstrates the feasibility of this biobased multifunctional polymer as an antibacterial agent for biodegradable polymeric materials with potential application in medical uses.

Guanidinium-rich lipopeptide functionalized bacteria-absorbing sponge as an effective trap-and-kill system for the elimination of focal bacterial infection

Focal bacterial infections are often difficult to treat due to the rapid emergence of antibiotic-resistant bacteria, high risk of relapse, and severe inflammation at local lesions. To address multidrug-resistant skin and soft tissue infections, a bacteria-absorbing sponge was prepared to involve a "trap-and-kill" mechanism. The system describes a guanidinium-rich lipopeptide functionalized lyotropic liquid-crystalline hydrogel with bicontinuous cubic networks. Amphiphilic lipopeptides can be spontaneously anchored to the lipid-water interface, exposing their bacterial targeting sequences to enhance antibacterial trapping/killing activity. Computational simulations supported our structural predictions, and the sponge was confirmed to successfully remove ∼98.8% of the bacteria in the medium. Release and degradation behavior studies indicated that the bacteria-absorbing sponge could degrade, mediate enzyme-responsive lipopeptide release, or generate ∼200 nm lipopeptide nanoparticles with environmental erosion. This implies that the sponge can effectively capture and isolate high concentrations of bacteria at the infected site and then sustainably release antimicrobial lipopeptides into deep tissues for the eradication of residual bacteria. In the animal experiment, we found that the antibacterial performance of the bacterial-absorbing sponge was significant, which demonstrated not only a long-term inhibition effect to disinfect and avoid bacterial rebound, but also a unique advantage to protect tissue from bacterial attack. STATEMENT OF SIGNIFICANCE: Host defense peptides/peptidomimetics (HDPs) have shown potential for the elimination of focal bacterial infections, but the application of their topical formulations suffers from time-consuming preparation processes, indistinctive toxicity reduction effects, and inefficient bacterial capture ability. To explore new avenues for the development of easily prepared, low-toxicity and high-efficiency topical antimicrobials, a guanidinium-rich lipopeptide was encapsulated in a lyotropic liquid-crystalline hydrogel (denoted as "bacteria-absorbing sponge") to achieve complementary superiorities. The superior characteristic of the bacteria-absorbing sponge involves a "trap-and-kill" mechanism, which undergoes not only a long-term inhibition effect to disinfect and avoid bacterial rebound, but also effective bacterial capture and isolating action to confine bacterial diffusion and protect tissues from bacterial attack.

Biodegradable Peptide Polymers as Alternatives to Antibiotics Used in Aquaculture

The pressure of antimicrobial resistance has forced many countries to reduce or even prohibit the use of antibiotics in feed. Therefore, it is in urgent need to develop alternatives to...

Plasma-Activated Saline Promotes Antibiotic Treatment of Systemic Methicillin-Resistant Staphylococcus aureus Infection

Systemic infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are life-threatening due to their strong multidrug resistance, especially since the biofilms formed by MRSA are more difficult to inactivate by antibiotics, causing long term recurrence of infection. Plasma-activated saline (PAS), a derived form of cold atmospheric-pressure plasma, can effectively inactivate bacteria and cancer cells and has been applied to sterilization and cancer treatment. Previous studies have demonstrated that the pretreatment of MRSA with PAS could promote the action of antibiotics. Here, the PAS was used as an antibiotic adjuvant to promote the inactivation of MRSA biofilms by rifampicin and vancomycin, and the combined treatment reduced approximately 6.0-log₁₀ MRSA cells in biofilms. The plasma-activated saline and rifampicin synergistically and effectively reduced the systemic infection in the murine model. The histochemical analysis and the blood hematological and biochemical test demonstrated that the combined treatment with plasma-activated saline and rifampicin improved the blood hematological and biochemical parameters of infected mice by reducing the infection. Therefore, PAS based on plasma technology represents a new strategy for the treatment of infectious disease caused by multidrug-resistant bacteria and alleviating antibiotic resistance.

Polymeric approach to combat drug-resistant methicillin-resistant Staphylococcus aureus

ABSTRACT

The current global death rate has threatened humans due to increase in deadly unknown infections caused by pathogenic microorganisms. On the contrary, the emergence of multidrug-resistant bacteria is also increasing which is leading to elevated lethality rate worldwide. Development of drug-resistant bacteria has become one of the daunting global challenges due to failure in approaching to combat against them. Methicillin-resistant Staphylococcus aureus (MRSA) is one of those drug-resistant bacteria which has led to increase in global mortality rate causing various lethal infections. Polymer synthesis can be one of the significant approaches to combat MRSA by fabricating polymeric coatings to prevent the spread of infections. This review provides last decade information in the development of various polymers against MRSA.

GRAPHICAL ABSTRACT

A soft anti-virulence liposome realizing the explosive release of antibiotics at an infectious site to improve antimicrobial therapy

Pore-forming toxins (PFTs), the most common virulence proteins, are promising therapeutic keys in bacterial infections. CAL02, consisting of sphingomyelin (Sm) and containing a maximum ratio of cholesterol (Ch), has been applied to sequester PFTs. However, Sm, a saturated phospholipid, leads to structural rigidity of the liposome, which does not benefit PFT combination. Therefore, in order to decrease the membrane rigidity and improve the fluidity of liposomes, we have introduced an unsaturated phospholipid, phosphatidylcholine (Pc), to the saturated Sm. In this report, a soft nanoliposome (called CSPL), composed of Ch, Sm and Pc, was artificially prepared. In order to further improve its antibacterial effect, vancomycin (Van) was loaded into the hydrophilic core of CSPL, where Van can be released radically at the infectious site through transmembrane pores formed by the PFTs in CSPL. This soft Van@CSPL nanoliposome with detoxification/drug release was able to inhibit the possibility of antibiotic resistance and could play a better role in treating severe invasive infections in mice.

A novel antimicrobial polymer efficiently treats multidrug-resistant MRSA-induced bloodstream infection

The present study aimed to ascertain if polymer 2a, a novel synthesized antimicrobial polyionene, could treat methicillin-resistant Staphylococcus aureus (MRSA)-induced bloodstream infection. The minimum inhibitory concentration (MIC) of polymer 2a against MRSA was detected. A time-kill assay was employed to determine the killing kinetic of polymer 2a. Potential antimicrobial mechanisms of polymer 2a, including membrane disruption and programmed cell death (PCD), were explored. A resistance development assay was introduced to determine the propensity of polymer 2a toward resistance against MRSA. A mouse model of MRSA bacteremia was established to assess in vivo efficacy of polymer 2a. Furthermore, in vivo toxicity of polymer 2a was also evaluated through injection by tail vein. Polymer 2a exhibited more superior antimicrobial activity and faster killing kinetic than the control antibiotics against clinically isolated MRSA strains. Polymer 2a resulted in an obvious leakage of cellular components (concentration more than 1× MIC). mRNA expression of PCD pathway-related gene (recA) was significantly up-regulated in the presence of polymer 2a with low concentration (concentration less than 1× MIC). Repeated use of polymer 2a did not lead to drug resistance. In a MRSA-induced bloodstream infection mouse model, polymer 2a displayed superior therapeutic efficacy with negligible systemic toxicity. Moreover, polymer 2a treatment by tail vein could evidently reduce MRSA counts in blood and major organs and markedly improve living conditions. In conclusion, all these findings presented in this work convincingly suggested that polymer 2a may be a promising therapeutic alternative for treating MRSA-induced infections, especially bloodstream infection.

Synthetic Polypeptide Polymers as Simplified Analogues of Antimicrobial Peptides

Antimicrobial peptides (AMPs) are naturally occurring macromolecules made of amino acids that are potent broad-spectrum antibiotics with potential as novel therapeutic agents. This review aims to summarize the fundamental principles concerning the structure and mechanism of action of these AMPs, in order to guide the design of polymeric analogues that organic chemistry can generate. Among those simplified analogues, this review particularly focuses on those made of amino acids called polypeptide polymers: they are showing great potential by providing one of the best biomimetic and bioactive structures for further biomaterials science applications.

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.

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.

Effects of infection of MRSA on the expression and activity of renal cytochrome P450s in mice

Methicillin-resistant Staphylococcus aureus (MRSA) leads to serious infections, but it is not known whether it changes the expression of kidney drug metabolizing enzymes during infection. The mice were infected with different doses of MRSA and the oxidative stress and inflammation levels in the kidney were examined. The mRNA expression and activity of cytochrome P450 enzyme was analysed. Mice infected with high levels of MRSA showed a decrease in renal antioxidant capability and an elevated level of oxidative metabolites, which was accompanied by the release of inflammatory cytokines. The levels of interleukin 1β, tumour necrosis factor alpha, and macrophage inflammatory protein-1α were significantly increased along with the levels of nitric oxide and malondialdehyde. On day 7, mRNA expression of Cyp1a2, 2d22, and 3a11 were decreased by the high level of MRSA, but the low level of MRSA increased their expressions. Cyp2e1 mRNA expression was increased by MRSA in the kidney of mice. High dose of MRSA infection increased the oxidative stress and inflammatory response in mouse kidney, leading to the decrease in the expression of renal drug-metabolizing enzymes and no recovery within 7 days.

Biodegradable Antibacterial Polymeric Nanosystems: A New Hope to Cope with Multidrug-Resistant Bacteria

The human society is faced with daunting threats from bacterial infections. Over decades, a variety of antibacterial polymeric nanosystems have exhibited great promise for the eradication of multidrug-resistant bacteria and persistent biofilms by enhancing bacterial recognition and binding capabilities. In this Review, the "state-of-the-art" biodegradable antibacterial polymeric nanosystems, which could respond to bacteria environments (e.g., acidity or bacterial enzymes) for controlled antibiotic release or multimodal antibacterial treatment, are summarized. The current antibacterial polymeric nanosystems can be categorized into antibiotic-containing and intrinsic antibacterial nanosystems. The antibiotic-containing polymeric nanosystems include antibiotic-encapsulated nanocarriers (e.g., polymeric micelles, vesicles, nanogels) and antibiotic-conjugated polymer nanosystems for the delivery of antibiotic drugs. On the other hand, the intrinsic antibacterial polymer nanosystems containing bactericidal moieties such as quaternary ammonium groups, phosphonium groups, polycations, antimicrobial peptides (AMPs), and their synthetic mimics, are also described. The biodegradability of the nanosystems can be rendered by the incorporation of labile chemical linkages, such as carbonate, ester, amide, and phosphoester bonds. The design and synthesis of the degradable polymeric building blocks and their fabrications into nanosystems are also explicated, together with their plausible action mechanisms and potential biomedical applications. The perspectives of the current research in this field are also described.

Strategies from nature: polycaprolactone-based mimetic antimicrobial peptide block copolymers with low cytotoxicity and excellent antibacterial efficiency

PCL₁₆-b-K_n diblock copolymers exhibit excellent antibacterial activities and low cytotoxicity. Meanwhile, they act by the pore-forming bactericidal mechanism without inducement of drug resistance.

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

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

Dynamically crosslinked polymer nanocomposites to treat multidrug-resistant bacterial biofilms

Multidrug-resistant biofilms are highly resistant to current antimicrobial therapies. We have developed an antimicrobial platform that integrates the bacteria-killing phytochemical carvacrol into dynamically crosslinked polymer nanocomposites (DCPNs). Taking advantage of a reversibly crosslinked Schiff-base scaffold throughout the engineered emulsions, DCPNs exhibited long-term shelf-life and good stability in serum, while readily disassembling in acidic microenvironments. Furthermore, we demonstrated that DCPNs efficiently penetrate the biofilm matrix, eradicating both Gram-negative/positive bacteria enclosed within. Moreover, DCPNs showed no observable toxicity to fibroblast mammalian cells with the same antimicrobial concentrations necessary to eradicate MDR biofilms. Given their potent antimicrobial and stimuli-responsive dissociation characteristics in a biofilm setting, DCPNs are a suitable therapeutic platform for combating MDR bacterial infections.

Polyprodrug Antimicrobials: Remarkable Membrane Damage and Concurrent Drug Release to Combat Antibiotic Resistance of Methicillin-Resistant Staphylococcus aureus

The increased threat of antibiotic resistance has created an urgent need for new strategies. Herein, polyprodrug antimicrobials are proposed to mimic antimicrobial peptides appended with a concurrent drug release property, exhibiting broad-spectrum antibacterial activity and especially high potency to inhibit methicillin-resistant Staphylococcus aureus (MRSA) without inducing resistance. Two series of polyprodrug antimicrobials are fabricated by facile polymerization of triclosan prodrug monomer (TMA) and subsequent quaternization of hydrophilic poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA), affording PDMAEMA-b-PTMA and PQDMA-b-PTMA, respectively. Optimized samples with proper hydrophobic ratio are screened out, which exhibit remarkable bacterial inhibition and low hemolysis toward red blood cells. Furthermore, synergistic antibacterial mechanisms contribute to the bacteria killing, including serious membrane damage, increased out-diffusion of cytosolic milieu across the membrane, and intracellular reductive milieu-mediated triclosan release. No detectable resistance is observed for polyprodrug antimicrobials against MRSA, which is demonstrated to be better than commercial triclosan and vancomycin against in vivo MRSA-infected burn models and a promising approach to the hurdle of antibiotic resistance in biomedicine.

Antimicrobial polymers as therapeutics for treatment of multidrug-resistant Klebsiella pneumoniae lung infection

Klebsiella pneumoniae (K. pneumoniae) is one of the most common pathogens in hospital-acquired infections. It is often resistant to multiple antibiotics (including carbapenems), and can cause severe pneumonia. In search of effective antimicrobials, we recently developed polyionenes that were demonstrated to be potent against a broad-spectrum of microbes in vitro. In this study, polyionenes containing rigid amide bonds were synthesized to treat multidrug-resistant (MDR) K. pneumoniae lung infection. The polyionene exhibited broad-spectrum activity against clinically-isolated MDR bacteria with low minimum inhibitory concentrations (MICs). It also demonstrated stronger antimicrobial activity against 20 clinical strains of K. pneumoniae and more rapid killing kinetics than imipenem and other commonly used antibiotics. Multiple treatments with imipenem and gentamycin led to drug resistance in K. pneumoniae, while repeated use of the polymer did not cause resistance development due to its membrane-disruption antimicrobial mechanism. Additionally, the polymer showed potent anti-biofilm activity. In a MDR K. pneumoniae lung infection mouse model, the polymer demonstrated lower effective dose than imipenem with negligible systemic toxicity. The polymer treatment significantly alleviated lung injury, markedly reduced K. pneumoniae counts in the blood and major organs, and decreased mortality. Given its potent in vivo antimicrobial activity, negligible toxicity and ability of mitigating resistance development, the polyionene may be used to treat MDR K. pneumoniae lung infection.

STATEMENT OF SIGNIFICANCE

Klebsiella pneumoniae (K. pneumoniae) is one of the most common pathogens in hospital-acquired infections, is often resistant to multiple antibiotics including carbapenems and can cause severe pneumonia. In this study, we report synthesis of antimicrobial polymers (polyionenes) and their use as antimicrobial agents for treatment of K. pneumoniae-caused pneumonia. The polymers have broad spectrum antibacterial activity against clinically isolated MDR bacteria, and eliminate MDR K. pneumoniae more effectively and rapidly than clinically used antibiotics. The polymer treatment also provides higher survival rate and faster bacterial removal from the major organs and the blood than the antibiotics. Repeated use of the polymer does not lead to resistance development. More importantly, at the therapeutic dose, the polymer treatment does not cause acute toxicity. Given its in vivo efficacy and negligible toxicity, the polymer is a promising candidate for the treatment of MDR K. pneumoniae-caused pneumonia.

Green Fabrication of Amphiphilic Quaternized β-Chitin Derivatives with Excellent Biocompatibility and Antibacterial Activities for Wound Healing

Bacterial infection has always been a great threat to public health, and new antimicrobials to combat it are urgently needed. Here, a series of quaternized β-chitin derivatives is prepared simply and homogeneously in an aqueous KOH/urea solution, which is a high-efficiency, energy-saving, and "green" route for the modification of chitin. The mild reaction conditions keep the acetamido groups of β-chitin intact and introduce quaternary ammonium groups on the primary hydroxyl at the C-6 position of the chitin backbone, allowing the quaternized β-chitin derivatives (QCs) to easily form micelles. These QCs are found to exhibit excellent antimicrobial activities against Escherichia coli, Staphylococcus aureus, Candida albicans, and Rhizopus oryzae with minimum inhibitory concentrations (MICs) of 8, 12, 60, and 40 µg mL-1 , respectively. As a specific highlight, their inherent outstanding biocompatibility and significant accelerating effects on the healing of uninfected, E. coli-infected, and S. aureus-infected wounds imply that these novel polysaccharide-based materials can be used as dressings for clinical skin regeneration, particularly for infected wounds.

Dynamic Ureas with Fast and pH-Independent Hydrolytic Kinetics

Low cost, high performance hydrolysable polymers are of great importance in biomedical applications and materials industries. While many applications require materials to have a degradation profile insensitive to external pH to achieve consistent release profiles under varying conditions, hydrolysable chemistry techniques developed so far have pH-dependent hydrolytic kinetics. This work reports the design and synthesis of a new type of hydrolysable polymer that has identical hydrolysis kinetics from pH 3 to 11. The unprecedented pH independent hydrolytic kinetics of the aryl ureas were shown to be related to the dynamic bond dissociation controlled hydrolysis mechanism; the resulting hindered poly(aryl urea) can be degraded with a hydrolysis half-life of 10 min in solution. More importantly, these fast degradable hindered aromatic polyureas can be easily prepared by addition polymerization from commercially available monomers and are resistant to hydrolysis in solid form for months under ambient storage conditions. The combined features of good stability in solid state and fast hydrolysis at various pH values is unprecedented in polyurea material, and will have implications for materials design and applications, such as sacrificial coatings and biomaterials.

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.

Engineering Polymersomes for Diagnostics and Therapy

Engineered polymer vesicles, termed as polymersomes, confer a flexibility to control their structure, properties, and functionality. Self-assembly of amphiphilic copolymers leads to vesicles consisting of a hydrophobic bilayer membrane and hydrophilic core, each of which is loaded with a wide array of small and large molecules of interests. As such, polymersomes are increasingly being studied as carriers of imaging probes and therapeutic drugs. Effective delivery of polymersomes necessitates careful design of polymersomes. Therefore, this review article discusses the design strategies of polymersomes developed for enhanced transport and efficacy of imaging probes and therapeutic drugs. In particular, the article focuses on overviewing technologies to regulate the size, structure, shape, surface activity, and stimuli- responsiveness of polymersomes and discussing the extent to which these properties and structure of polymersomes influence the efficacy of cargo molecules. Taken together with future considerations, this article will serve to improve the controllability of polymersome functions and accelerate the use of polymersomes in biomedical applications.

A macromolecular approach to eradicate multidrug resistant bacterial infections while mitigating drug resistance onset

Polymyxins remain the last line treatment for multidrug-resistant (MDR) infections. As polymyxins resistance emerges, there is an urgent need to develop effective antimicrobial agents capable of mitigating MDR. Here, we report biodegradable guanidinium-functionalized polycarbonates with a distinctive mechanism that does not induce drug resistance. Unlike conventional antibiotics, repeated use of the polymers does not lead to drug resistance. Transcriptomic analysis of bacteria further supports development of resistance to antibiotics but not to the macromolecules after 30 treatments. Importantly, high in vivo treatment efficacy of the macromolecules is achieved in MDR A. baumannii-, E. coli-, K. pneumoniae-, methicillin-resistant S. aureus-, cecal ligation and puncture-induced polymicrobial peritonitis, and P. aeruginosa lung infection mouse models while remaining non-toxic (e.g., therapeutic index—ED₅₀/LD₅₀: 1473 for A. baumannii infection). These biodegradable synthetic macromolecules have been demonstrated to have broad spectrum in vivo antimicrobial activity, and have excellent potential as systemic antimicrobials against MDR infections.

Antibiotic resistance is a major threat across the whole healthcare spectrum. Here, the authors report on the development of biodegradable guanidinium functionalized polycarbonates and demonstrate antimicrobial activity against drug resistant infections.

Biomimetic antimicrobial polymers: recent advances in molecular design

The increasing prevalence of antibiotic-resistant bacterial infections, coupled with the decline in the number of new antibiotic drug approvals, has created a therapeutic gap that portends an emergent public health crisis.

Broad Spectrum Macromolecular Antimicrobials with Biofilm Disruption Capability and In Vivo Efficacy

In this study, antimicrobial polymers are synthesized by the organocatalytic ring-opening polymerization of an eight-membered heterocyclic carbonate monomer that is subsequently quaternized with methyl iodide. These polymers demonstrate activity against clinically relevant Gram-positive Staphylococcus epidermidis and Staphylococcus aureus, Gram-negative Escherichia coli and Pseudomonas aeruginosa, and fungus Candida albicans with fast killing kinetics. Importantly, the polymer efficiently inhibits biofilm growth and lyses existing biofilm, leading to a reduction in biomass and cell viability. In addition, the macromolecular antimicrobial is less likely to induce resistance as it acts via a membrane-lytic mechanism. The polymer is not cytotoxic toward mammalian cells with LD₅₀ of 99.0 ± 11.6 mg kg^-1 in mice through i.v. injection. In an S. aureus blood stream infection mouse model, the polymer removes bacteria from the blood more rapidly than the antibiotic Augmentin. At the effective dose, the polymer treatment does not damage liver and kidney tissues or functions. In addition, blood electrolyte balance remains unchanged after the treatment. The low cost of starting materials, ease of synthesis, nontoxicity, broad spectrum activity with fast killing kinetics, and in vivo antimicrobial activity make these macromolecular antimicrobials ideal candidates for prevention of sepsis and treatment of infections.

Prevention of Bacterial Colonization on Catheters by a One-Step Coating Process Involving an Antibiofouling Polymer in Water

As reports of multidrug resistant pathogens have increased, patients with implanted medical catheters increasingly need alternative solutions to antibiotic treatments. As most catheter-related infections are directly associated with biofilm formation on the catheter surface, which, once formed, is difficult to eliminate, a promising approach to biofilm prevention involves inhibiting the initial adhesion of bacteria to the surface. In this study, we report an amphiphilic, antifouling polymer, poly(DMA-mPEGMA-AA) that can facilely coat the surfaces of commercially available catheter materials in water and prevent bacterial adhesion to and subsequent colonization of the surface, giving rise to an antibiofilm surface. The antifouling coating layer was formed simply by dipping a model substrate (polystyrene, PET, PDMS, or silicon-based urinary catheter) in water containing poly(DMA-mPEGMA-AA), followed by characterization by X-ray photoelectron spectroscopy (XPS). The antibacterial adhesion properties of the polymer-coated surface were assessed for Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) growth under static (incubation in the presence of a bacterial suspension) and dynamic (bacteria suspended in a solution under flow) conditions. Regardless of the conditions, the polymer-coated surface displayed significantly reduced attachment of the bacteria (antiadhesion effect > ∼8-fold) compared to the bare noncoated substrates. Treatment of the implanted catheters with S. aureus in vivo further confirmed that the polymer-coated silicon urinary catheters could significantly reduce bacterial adhesion and biofilm formation in a bacterial infection animal model. Furthermore, the polymer-coated catheters did not induce hemolysis and were resistant to the adhesion of blood-circulating cells, indicative of high biocompatibility. Collectively, the present amphiphilic antifouling polymer is potentially useful as a coating platform that renders existing medical devices resistant to biofilm formation.

Short Synthetic β-Sheet Antimicrobial Peptides for the Treatment of Multidrug-Resistant Pseudomonas aeruginosa Burn Wound Infections

Pseudomonas aeruginosa is often implicated in burn wound infections; its inherent drug resistance often renders these infections extremely challenging to treat. This is further compounded by the problem of emerging drug resistance and the dearth of novel antimicrobial drug discovery in recent years. In the perennial search for effective antimicrobial compounds, the authors identify short synthetic β-sheet folding peptides, IRIKIRIK (IK8L), IRIkIrIK (IK8-2D), and irikirik (IK8D) as prime candidates owing to their high potency against Gram-negative bacteria. In this study, the peptides are first assayed against 20 clinically isolated multidrug-resistant P. aeruginosa strains in comparison with the conventional antibiotics imipenem and ceftazidime, and IK8L is demonstrated to be the most effective. IK8L also exhibits superior antibacterial killing kinetics compared to imipenem and ceftazidime. From transmission electron microscopy, confocal microscopy, and protein release analyses, IK8L shows membrane-lytic antimicrobial mechanism. Repeated use of IK8L does not induce drug resistance, while the bacteria develop resistance against the antibiotics after several times of treatment at sublethal doses. Analysis of mouse blood serum chemistry reveals that peptide does not induce systemic toxicity. The potential utility of IK8L in the in vivo treatment of P. aeruginosa-infected burn wounds is further demonstrated in a mouse model.

Zinc versus Magnesium: Orthogonal Catalyst Reactivity in Selective Polymerizations of Epoxides, Bio-derived Anhydrides and Carbon Dioxide

Developing selective polymerizations from complex monomer mixtures is an important challenge. Here, dinuclear catalysts allow selective polymerization from mixtures of sterically hindered tricyclic anhydrides, carbon dioxide and epoxides to yield well-controlled copoly(ester-carbonates). Surprisingly, two very similar homogeneous catalysts differing only in the central metal, zinc versus magnesium, show very high but diametrically opposite monomer selectivity. The selectivity is attributed to different polymerization kinetics and to steric factors associated with the anhydrides.

Cationic peptidopolysaccharides synthesized by ‘click’ chemistry with enhanced broad-spectrum antimicrobial activities

A series of broad-spectrum antimicrobial cationic peptidopolysaccharides have been synthesized using a facile thiol–ene ‘click’ chemistry.

Self-assembled cationic amphiphiles as antimicrobial peptides mimics: Role of hydrophobicity, linkage type, and assembly state

Inspired by high promise using naturally occurring antimicrobial peptides (AMPs) to treat infections caused by antimicrobial-resistant bacteria, cationic amphiphiles (CAms) were strategically designed as synthetic mimics to overcome associated limitations, including high manufacture cost and low metabolic stability. CAms with facially amphiphilic conformation were expected to demonstrate membrane-lytic properties and thus reduce tendency of resistance development. By systematically tuning the hydrophobicity, CAms with optimized compositions exhibited potent broad-spectrum antimicrobial activity (with minimum inhibitory concentrations in low μg/mL range) as well as negligible hemolytic activity. Electron microscope images revealed the morphological and ultrastructure changes of bacterial membranes induced by CAm treatment and validated their membrane-disrupting mechanism. Additionally, an all-atom molecular dynamics simulation was employed to understand the CAm-membrane interaction on molecular level. This study shows that these CAms can serve as viable scaffolds for designing next generation of AMP mimics as antimicrobial alternatives to combat drug-resistant pathogens.