Short Guanidinium-Functionalized Poly(2-oxazoline)s Displaying Potent Therapeutic Efficacy on Drug-Resistant Fungal Infections.

New antifungals are urgently needed to combat invasive fungal infections, due to limited types of available antifungal drugs and frequently encountered side effects, as well as the quick emergence of drug-resistance. We previously developed amine-pendent poly(2-oxazoline)s (POXs) as synthetic mimics of host defense peptides (HDPs) to have antibacterial properties, but with poor antifungal activity. Hereby, we report the finding of short guanidinium-pendent POXs, inspired by cell-penetrating peptides, as synthetic mimics of HDPs to display potent antifungal activity, superior mammalian cells versus fungi selectivity, and strong therapeutic efficacy in treating local and systemic fungal infections. Moreover, the unique antifungal mechanism of fungal cell membrane penetration and organelle disruption explains the insusceptibility of POXs to antifungal resistance. The easy synthesis and structural diversity of POXs imply their potential as a class of promising antifungal agents.

Superfast and Water-Insensitive Polymerization on α-Amino Acid N-Carboxyanhydrides to Prepare Polypeptides Using Tetraalkylammonium Carboxylate as the Initiator.

We design the tetraalkylammonium carboxylate-initiated superfast polymerization on α-amino acid N-carboxyanhydrides (NCA) for efficient synthesis of polypeptides. Carboxylates, as a new class of initiator for NCA polymerization, can initiate the superfast NCA polymerization without the need of extra catalysts and the polymerization can be operated in open vessels at ambient condition without the use of glove box. Tetraalkylammonium carboxylate-initiated polymerization on NCA easily affords block copolymers with at least 15 blocks. Moreover, this method avoids tedious purification steps and enables direct polymerization on crude NCAs in aqueous environments to prepare polypeptides and one-pot synthesis of polypeptide nanoparticles. These advantages and the mild polymerization condition of tetraalkylammonium carboxylate-initiated NCA polymerization imply its great potential in functional exploration and application of polypeptides.

Poly(2-Oxazoline)-Based Functional Peptide Mimics: Eradicating MRSA Infections and Persisters while Alleviating Antimicrobial Resistance.

Peptides have important biological functions. However, their susceptibility to proteolysis limits their applications. We demonstrated here for the first time, that poly(2-oxazoline) (POX) can work as a functional mimic of peptides. POX-based glycine pseudopeptides, a host defense peptide mimic, had potent activities against methicillin-resistant S. aureus, which causes formidable infections. The POX mimic showed potent activity against persisters that are highly resistant to antibiotics. S. aureus did not develop resistance to POX owning to the reactive oxygen species related antimicrobial mechanism. POX-treated S. aureus is sensitive to common antibiotics, demonstrating no observable antimicrobial pressure or cross-resistance in using antimicrobial POX. This study highlights POX as a new type of functional mimic of peptides and opens new avenues in designing and exploring peptide mimetics for biological functions and applications.

Host defense peptide mimicking cyclic peptoid polymers exerting strong activity against drug-resistant bacteria.

Extensive use of antibiotics accelerates the emergence of drug-resistant bacteria and related infections. Host defense peptides (HDPs) have been studied as promising and potential therapeutic candidates. However, their clinical applications of HDPs are limited due to their high cost of synthesis and low stability upon proteolysis. Therefore, HDP mimics have become a new approach to address the challenge of bacterial resistance. In this work, we design the amphiphilic peptoid polymers by mimicking the positively charged and hydrophobic structures of HDPs and synthesize a series of cyclic peptoid polymers efficiently via the polymerization on α-amino acid N-substituted glycine N-carboxyanhydrides (α-NNCAs) using 1,8-diazabicycloundec-7-ene (DBU) as the initiator. The optimal cyclic peptoid polymer, poly(Naeg0.7Npfbg0.3)20, displays strong antibacterial activities against drug-resistant bacteria, but low hemolysis and cytotoxicity. In addition, the mode-of-action study indicates that the antibacterial mechanism is associated with bacterial membrane interaction. Our study implies that HDP mimicking cyclic peptoid polymers have potential application in treating drug-resistant bacterial infections.

Peptide-Mimicking Poly(2-oxazoline)s Displaying Potent Antimicrobial Properties.

Poly(2-oxazoline)s have excellent biocompatibility and have been used as FDA-approved indirect food additives. The inert property of the hydrophilic poly(2-oxazoline)s suggests them as promising substitutes for poly(ethylene glycol) (PEG) in various applications such as anti-biofouling agents. It was recently reported that poly(2-oxazoline)s themselves have antimicrobial properties as synthetic mimics of host defense peptides. These studies revealed the bioactive properties of poly(2-oxazoline)s as a new class of functional peptide mimics, by mimicking host defense peptides to display potent and selective antimicrobial activities against methicillin-resistant Staphylococcus aureus both in vitro and in vivo, without concerns about antimicrobial resistance. The high structural diversity, facile synthesis, and potent and tunable antimicrobial properties underscore the great potential of poly(2-oxazoline)s as a class of novel antimicrobial agents in dealing with drug-resistant microbial infections and antimicrobial resistance.

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

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

Addressing MRSA infection and antibacterial resistance with peptoid polymers.

Methicillin-Resistant Staphylococcus aureus (MRSA) induced infection calls for antibacterial agents that are not prone to antimicrobial resistance. We prepare protease-resistant peptoid polymers with variable C-terminal functional groups using a ring-opening polymerization of N-substituted N-carboxyanhydrides (NNCA), which can provide peptoid polymers easily from the one-pot synthesis. We study the optimal polymer that displays effective activity against MRSA planktonic and persister cells, effective eradication of highly antibiotic-resistant MRSA biofilms, and potent anti-infectious performance in vivo using the wound infection model, the mouse keratitis model, and the mouse peritonitis model. Peptoid polymers show insusceptibility to antimicrobial resistance, which is a prominent merit of these antimicrobial agents. The low cost, convenient synthesis and structure diversity of peptoid polymers, the superior antimicrobial performance and therapeutic potential in treating MRSA infection altogether imply great potential of peptoid polymers as promising antibacterial agents in treating MRSA infection and alleviating antibiotic resistance.

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

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

An alpha/beta chimeric peptide molecular brush for eradicating MRSA biofilms and persister cells to mitigate antimicrobial resistance.

Infections involving methicillin-resistant Staphylococcus aureus present great challenges, especially when biofilms and persister cells are involved. In this work, an α/ß chimeric polypeptide molecular brush (α/ß CPMB) is reported to show excellent performance in inhibiting the formation of biofilms and eradicating established biofilms. Additionally, the polymer brush efficiently killed metabolically inactive persister cells that are antibiotic-insensitive. Antimicrobial mechanism studies showed that α/ß CPMB causes membrane disturbance and a substantial increase in reactive oxygen species (ROS) levels to kill bacteria, and mesosome-like structure formation was also observed. Furthermore, the polymer brush was able to kill clinically isolated multidrug resistant Gram-positive bacteria with no risk of antimicrobial resistance. The α/ß CPMB has demonstrated great potential in addressing the great challenge of eradicating multidrug resistant Gram-positive bacterial infections.