Sequentially Activatable Polypeptide Nanoparticles for Combinatory Photodynamic Chemotherapy of Breast Cancer

Stimuli-activatable nanomaterials hold significant promise for tumor-specific drug delivery by recognizing the internal or external stimulus. Herein, we reported a dual-responsive and biodegradable polypeptide nanoparticle (PPTP@PTX₂ NP) for combinatory chemotherapy and photodynamic therapy (PDT) of breast cancer. The NPs were engineered by encapsulating diselenide bond linked dimeric prodrug of paclitaxel (PTX₂) in an intracellular acidity-activatable polypeptide micelle. Specifically, the acid-responsive polypeptide was synthesized by grafting a tetraphenyl porphyrin (TPP) photosensitizer and N,N-diisopropylethylenediamine (DPA) onto the poly(ethylene glycol)-block-poly(glutamic acid) diblock copolymer by the amidation reaction, which self-assembled into micellar NPs and was activated inside the acidic endocytic vesicles to perform PDT. The paclitaxel dimer can be stably loaded into the polypeptide NPs and be restored by PDT inside the tumor cells. The formed PPTP@PTX₂ NPs remained inert during blood circulation and passively accumulated in the tumor foci, which could be activated within the endocytic vesicles via acid-triggered protonation of DPA groups to generate fluorescence signal and release PTX₂ in 4T1 murine breast tumor cells. Upon 660 nm laser irradiation, the activated NPs carried out PDT via TPP and chemotherapy via PTX to induce apoptosis of 4T1 cells and thereby efficiently inhibited 4T1 tumor growth and prevented metastasis of tumor cells.

Reaching High Stereoselectivity and Activity in Organocatalyzed Ring-Opening Polymerization of Racemic Lactide by the Combined Use of a Chiral (Thio)Urea and a N-Heterocyclic Carbene

Stereochemical control during polymerization is a key strategy of polymer chemistry to achieve semicrystalline engineered plastics. The stereoselective ring-opening polymerization (ROP) of racemic lactide (rac-LA), which can lead to highly isotactic polylactide (PLA), is one of the emblematic examples in this area. Surprisingly, stereoselective ROP of rac-LA employing chiral organocatalysts has been under-leveraged. Here we show that a commercially available chiral thiourea (TU1), or its urea homologue (U1), can be used in conjunction with an appropriately selected N-heterocyclic carbene (NHC) to trigger the stereoselective ROP of rac-LA at room temperature in toluene. Both a high organic catalysis activity (>90% monomer conversion in 5-9 h) and a high stereoselectivity (probability of formation of meso dyads, P_m, in the range 0.82-0.93) can be achieved by thus pairing a NHC and a chiral amino(thio)urea. The less sterically hindered and the more basic NHC, that is, a NHC bearing tert-butyl substituents (NHC_tBu), provides the highest stereoselectivity when employed in conjunction with the chiral TU1 or U1. This asymmetric organic catalysis strategy, as applied here in polymerization chemistry, further expands the field of possibilities to achieve bioplastics with adapted thermomechanical properties.

Intelligent poly(l-histidine)-based nanovehicles for controlled drug delivery

Stimuli-responsive drug delivery systems based on polymeric nanovehicles are among the most promising treatment regimens for malignant cancers. Such intelligent systems that release payloads in response to the physiological characteristics of tumor sites have several advantages over conventional drug carriers, offering, in particular, enhanced therapeutic effects and decreased toxicity. The tumor microenvironment (TME) is acidic, suggesting the potential of pH-responsive nanovehicles for enhancing treatment specificity and efficacy. The synthetic polypeptide poly(l-histidine) (PLH) is an appropriate candidate for the preparation of pH-responsive nanovehicles because the pK_a of PLH (approximately 6.0) is close to the pH of the acidic TME. In addition, the pendent imidazole rings of PLH yield pH-dependent hydrophobic-to-hydrophilic phase transitions in the acidic TME, triggering the destabilization of nanovehicles and the subsequent release of encapsulated chemotherapeutic agents. Herein, we highlight the state-of-the-art design and construction of pH-responsive nanovehicles based on PLH and discuss the future challenges and perspectives of this fascinating biomaterial for targeted cancer treatment and "benchtop-to-clinic" translation.

Atropisomerism in a polyglutamate-based thermoresponsive alignment medium

Structure elucidation via residual dipolar couplings (RDCs) relies on alignment media. We report on lyotropic liquid crystals (LLCs) of poly-γ-p-biphenyl(2'-methoxy-2-methyl)methyl-L-glutamate (PBPM³LG). Temperature dependent atropisomerism within the biphenyl group enables the acquisition of multiple RDC-datasets within one sample.

Star-Peptide Polymers are Multi-Drug-Resistant Gram-Positive Bacteria Killers

Antibiotic resistance in bacteria, especially Gram-positive bacteria like Staphylococcus aureus, is gaining considerable momentum worldwide and unless checked will pose a global health crisis. With few new antibiotics coming on the market, there is a need for novel antimicrobial materials that target and kill multi-drug-resistant (MDR) Gram-positive pathogens like methicillin-resistant Staphylococcus aureus (MRSA). In this study, using a novel mixed-bacteria antimicrobial assay, we show that the star-peptide polymers preferentially target and kill Gram-positive pathogens including MRSA. A major effect on the activity of the star-peptide polymer was structure, with an eight-armed structure inducing the greatest bactericidal activity. The different star-peptide polymer structures were found to induce different mechanisms of bacterial death both in vitro and in vivo. These results highlight the potential utility of peptide/polymers to fabricate materials for therapeutic development against MDR Gram-positive bacterial infections.

An economical approach for peptide synthesis via regioselective C-N bond cleavage of lactams

An economical, solvent-free, and metal-free method for peptide synthesis via C-N bond cleavage using lactams has been developed. The method not only eliminates the need for condensation agents and their auxiliaries, which are essential for conventional peptide synthesis, but also exhibits high atom economy. The reaction is versatile because it can tolerate side chains bearing a range of functional groups, affording up to >99% yields of the corresponding peptides without racemisation or polymerisation. Moreover, the developed strategy enables peptide segment coupling, providing access to a hexapeptide that occurs as a repeat sequence in spider silk proteins.

An excited state intramolecular proton transfer induced phosphate ion targeted ratiometric fluorescent switch to monitor phosphate ions in human peripheral blood mononuclear cells

Detection of biological phosphate is very important for environmental and health care applications. In this study, a new ratiometric fluorescent probe (E)-N'-(3-(benzo[d]thiazol-2-yl)-2-hydroxybenzylidene) picolinohydrazide (BTP) is developed and exhibits a prominent excited-state intramolecular proton-transfer (ESIPT) mechanism. The probe BTP undergoes a unique phosphate induced hydrolytic reaction in mixed aqueous solution which produces a colorimetric change associated with a huge red-shift of ∼130 nm in the UV-visible absorption spectrum. Initially, BTP exhibits a strong fluorescence emission as the ESIPT process is 'on' and the tautomeric hydrogen remains flexible and is free to give two tautomeric forms. Eventually, after the addition of PO₄^3-, the two tautomeric forms break and thereby shift the equilibrium towards the 'enol' form. The phosphate ion binds with BTP which is associated with a ratiometric change and accounts for an enhancement in the fluorescence intensity with a large blue shift and the limit of detection value of 8.33 × 10^-8 M in a mixed aqueous medium. The binding constant (1.92 × 10⁵ M^-1) proportionally reflects the stability of the complexation between the binding sites of BTP with the guest PO₄^3- anion. The probable mechanism is supported by the NMR spectroscopy studies. The sensing phenomenon is found to be reversible towards Zn²⁺ and thus the sensor beautifully mimics the INHIBIT logic gate. Observations have been made in fluorescence imaging studies with human peripheral blood mononuclear cells (PBMCs) which indicates that BTP can be employed to successfully monitor the phosphate ion in human PBMCs.

Recent advances in post-polymerization modifications on polypeptides: synthesis and applications

Polypeptides, a kind of very promising biomaterial, have shown a wide range of applications due to their excellent biocompatibility, easy accessibility, and structural variability. To synthesize polypeptides with desired functions, post-polymerization modification (PPM) plays an important role in introducing novel chemical structure on their side-chains. The key of PPM strategy is to develop highly selective and efficient reactions that can couple the additional functional moieties with pre-installed side-chain functionalities on polypeptides. In this minireview, classic PPM reactions and especially their recent progresses are summarized, including different modification approaches for unsaturated alkyl group, oxygen-containing functional group, nitrogen-containing functional group, sulfur-containing functional group and other special functional group on side chains. In addition, this review also highlights the applications of structure-diversified polypeptides generated via PPM strategy in the field of biomaterial.

ROS-Responsive Selenopolypeptide Micelles: Preparation, Characterization, and Controlled Drug Release

Sulfur-containing polypeptides, capable of reactive oxygen species (ROS)-responsive structural change, are one of the most important building blocks for the construction of polypeptide-based drug delivery systems. However, the relatively low ROS sensitivity of side-chain thioethers limits the biomedical applications of these polypeptides because they usually require a high concentration of ROS beyond the pathological ROS level in the tumor microenvironment. Herein, we report the design and synthesis of a selenium-containing polypeptide, which undergoes random coil-to-extended helix and hydrophobic-to-hydrophilic transitions in the presence of 0.1% H₂O₂, a concentration that is much lower than the ROS requirement for thioether. ROS-responsive micelles were thus prepared from the amphiphilic copolymer consisting of the hydrophilic poly(ethylene glycol) (PEG) segment and hydrophobic selenopolypeptide segment and were used to encapsulate doxorubicin (DOX). The micelles could be sensitively dissociated inside tumor cells in consequence of ROS-triggered oxidation of side-chain selenoether and structural change of the micelles, thereby efficiently and selectively releasing the encapsulated DOX to kill cancer cells. This work provides an alternative design of ROS-responsive polypeptides with higher sensitivity than that of the existing sulfur-containing polypeptides, which may expand the biomedical applications of polypeptide materials.

Syntheses of Polypeptides and Their Biomedical Application for Anti-Tumor Drug Delivery

Polypeptides have attracted considerable attention in recent decades due to their inherent biodegradability and biocompatibility. This mini-review focuses on various ways to synthesize polypeptides, as well as on their biomedical applications as anti-tumor drug carriers over the past five years. Various approaches to preparing polypeptides are summarized, including solid phase peptide synthesis, recombinant DNA techniques, and the polymerization of activated amino acid monomers. More details on the polymerization of specifically activated amino acid monomers, such as amino acid N-carboxyanhydrides (NCAs), amino acid N-thiocarboxyanhydrides (NTAs), and N-phenoxycarbonyl amino acids (NPCs), are introduced. Some stimuli-responsive polypeptide-based drug delivery systems that can undergo different transitions, including stability, surface, and size transition, to realize a better anti-tumor effect, are elaborated upon. Finally, the challenges and opportunities in this field are briefly discussed.

Recent Advances in Poly(α-L-glutamic acid)-Based Nanomaterials for Drug Delivery

Poly(α-L-glutamic acid) (PGA) is a class of synthetic polypeptides composed of the monomeric unit α-L-glutamic acid. Owing to their biocompatibility, biodegradability, and non-immunogenicity, PGA-based nanomaterials have been elaborately designed for drug delivery systems. Relevant studies including the latest research results on PGA-based nanomaterials for drug delivery have been discussed in this work. The following related topics are summarized as: (1) a brief description of the synthetic strategies of PGAs; (2) an elaborated presentation of the evolving applications of PGA in the areas of drug delivery, including the rational design, precise fabrication, and biological evaluation; (3) a profound discussion on the further development of PGA-based nanomaterials in drug delivery. In summary, the unique structures and superior properties enables PGA-based nanomaterials to represent as an enormous potential in biomaterials-related drug delivery areas.

Biocompatible Synthetic Polymers for Tissue Engineering Purposes

Synthetic polymers have been an integral part of modern society since the early 1960s. Besides their most well-known applications to the public, such as packaging, construction, textiles and electronics, synthetic polymers have also revolutionized the field of medicine. Starting with the first plastic syringe developed in 1955 to the complex polymeric materials used in the regeneration of tissues, their contributions have never been more prominent. Decades of research on polymeric materials, stem cells, and three-dimensional printing contributed to the rapid progress of tissue engineering and regenerative medicine that envisages the potential future of organ transplantations. This perspective discusses the role of synthetic polymers in tissue engineering, their design and properties in relation to each type of application. Additionally, selected recent achievements of tissue engineering using synthetic polymers are outlined to provide insight into how they will contribute to the advancement of the field in the near future. In this way, we aim to provide a guide that will help scientists with synthetic polymer design and selection for different tissue engineering applications.

Strategies for improving the safety and RNAi efficacy of noncovalent peptide/siRNA nanocomplexes

In the past decades, the striking development of cationic polypeptides and cell-penetrating peptides (CPPs) tailored for small interfering RNA (siRNA) delivery has been fuelled by the conception of nuclear acid therapy and precision medicine. Owing to their amino acid compositions, inherent secondary structures as well as diverse geometrical shapes, peptides or peptide-containing polymers exhibit good biodegradability, high flexibility, and bio-functional diversity as nonviral siRNA vectors. Also, a variety of noncovalent nanocomplexes could be built via self-assembling and electrostatic interactions between cationic peptides and siRNAs. Although the peptide/siRNA nanocomplex-based RNAi therapies, STP705 and MIR-19, are under clinical trials, a guideline addressing the current bottlenecks of peptide/siRNA nanocomplex delivery is in high demand for future research and development. In this review, we present strategies for improving the safety and RNAi efficacy of noncovalent peptide/siRNA nanocomplexes in the treatment of genetic disorders. Through thorough analysis of those RNAi formulations using different delivery strategies, we seek to shed light on the rationale of peptide design and modification in constructing robust siRNA delivery systems, including targeted and co-delivery systems. Based on this, we provide a timely and comprehensive understanding of how to engineer biocompatible and efficient peptide-based siRNA vectors.

Water-Assisted and Protein-Initiated Fast and Controlled Ring-Opening Polymerization of Proline N-Carboxyanhydride

The production of polypeptides via the ring-opening polymerization (ROP) of N-carboxyanhydride (NCA) is usually conducted under stringent anhydrous conditions. The ROP of proline NCA (ProNCA) for the synthesis of poly-_L-proline (PLP) is particularly challenging due to the premature product precipitation as polyproline type I helices, leading to slow reactions for up to one week, poor control of the molar mass and laborious workup. Here, we report the unexpected water-assisted controlled ROP of ProNCA, which affords well-defined PLP as polyproline II helices in 2–5 minutes and almost-quantitative yields. Experimental and theoretical studies together suggest the as-yet-unreported role of water in facilitating proton shift, which significantly lowers the energy barrier of the chain propagation. The scope of initiators can be expanded from hydrophobic amines to encompass hydrophilic amines and thiol-bearing nucleophiles, including complex biomacromolecules such as proteins. Protein-mediated ROP of ProNCA conveniently affords various protein-PLP conjugates via a grafting-from approach. PLP modification not only preserves the biological activities of the native proteins, but also enhances their resistance to extreme conditions. Moreover, PLP modification extends the elimination half-life of asparaginase (ASNase) 18-fold and mitigates the immunogenicity of wt ASNase >250-fold (ASNase is a first-line anticancer drug for lymphoma treatment). This work provides a simple solution to a long-standing problem in PLP synthesis, and offers valuable guidance for the development of water-resistant ROP of other proline-like NCAs. The facile access to PLP can greatly boost the application potential of PLP-based functional materials for engineering industry enzymes and therapeutic proteins.

Micro- and Nanocapsules Based on Artificial Peptides

The encapsulation of active ingredients into solid capsules from biodegradable materials has received significant attention over the last decades. In this short review, we focus on the formation of micro- and nano-sized capsules and emulsions based on artificial peptides as a fully degradable material. It deals with various approaches for the preparation of peptide-based capsules as well as with their crucial properties such as size and stability. We categorize all preparation procedures into three basic approaches: self-assembly, polymerization and crosslinking, and layer-by-layer technology. This article is meant to offer a short overview over all successful methods suitable for obtaining access to these very promising carrier systems.

Effect of Polymer Topology and Residue Chirality on Biodegradability of Polypeptide Hydrogels

Polypeptide-based injectable hydrogels have attracted the attention of biomedical researchers due to their unique biocompatibility and biodegradability, tunable residue chirality, and secondary conformation of polypeptide chains. In the present study, four types of poly(ethylene glycol)-block-poly(glutamic acid)s with different topological structures and residue chirality of polypeptide segments were developed, which were grafted with tyramine side groups for further cross-linking. The results demonstrated that the covalent conjugation between the tyramine groups in the presence of horseradish peroxidase and hydrogen peroxide could form porous hydrogels rapidly. Additionally, the gelation time and mechanical strength of the hydrogels were measured. All the polymer precursors and hydrogels exhibited good cytocompatibility in vitro. Further assessment of the enzymatic degradability of the hydrogels and copolymers in vitro revealed that the degradation rate was influenced by the adjustment of polymer topology or residue chirality of polypeptide copolymers. Subsequently, the effect of copolymer topology and polypeptide chirality on in vivo biodegradability and biocompatibility was assessed. This study will provide insights into the relationship between copolymer structures and hydrogel properties and benefit future polypeptide-based hydrogel studies in biomedical applications.

Antimicrobial Peptides and Macromolecules for Combating Microbial Infections: From Agents to Interfaces

Bacterial resistance caused by the overuse of antibiotics and the shelter of biofilms has evolved into a global health crisis, which drives researchers to continuously explore antimicrobial molecules and strategies to fight against drug-resistant bacteria and biofilm-associated infections. Cationic antimicrobial peptides (AMPs) are considered to be a category of potential alternative for antibiotics owing to their excellent bactericidal potency and lesser likelihood of inducing drug resistance through their distinctive antimicrobial mechanisms. In this review, the hitherto reported plentiful action modes of AMPs are systematically classified into 15 types and three categories (membrane destructive, nondestructive membrane disturbance, and intracellular targeting mechanisms). Besides natural AMPs, cationic polypeptides, synthetic polymers, and biopolymers enable to achieve tunable antimicrobial properties by optimizing their structures. Subsequently, the applications of these cationic antimicrobial agents at the biointerface as contact-active surface coatings and multifunctional wound dressings are also emphasized here. At last, we provide our perspectives on the development of clinically significant cationic antimicrobials and related challenges in the translation of these materials.

Charge reversal nano-systems for tumor therapy

Surface charge of biological and medical nanocarriers has been demonstrated to play an important role in cellular uptake. Owing to the unique physicochemical properties, charge-reversal delivery strategy has rapidly developed as a promising approach for drug delivery application, especially for cancer treatment. Charge-reversal nanocarriers are neutral/negatively charged at physiological conditions while could be triggered to positively charged by specific stimuli (i.e., pH, redox, ROS, enzyme, light or temperature) to achieve the prolonged blood circulation and enhanced tumor cellular uptake, thus to potentiate the antitumor effects of delivered therapeutic agents. In this review, we comprehensively summarized the recent advances of charge-reversal nanocarriers, including: (i) the effect of surface charge on cellular uptake; (ii) charge-conversion mechanisms responding to several specific stimuli; (iii) relation between the chemical structure and charge reversal activity; and (iv) polymeric materials that are commonly applied in the charge-reversal delivery systems.

Preparation of antibacterial polypeptides with different topologies and their antibacterial properties

Antimicrobial peptides (AMPs) are attractive antimicrobial agents used to combat bacterial infections, and have been advanced to be one of the most promising alternatives to conventional antibiotics. They stand out for their attractive broad-spectrum activity, unmatched antibacterial mechanism that is not prone to develop drug resistance and diversified topologies, which can be fabricated with manifold amino acid blocks. In this study, using n-hexylamine and amine-terminated polyamidoamine dendrimers (Gx-PAMAM, x = 1-2) as initiators, a series of AMPs with linear and star-shaped topological structures were constructed via the controllable ring-opening polymerization (ROP) of N-carboxyanhydrides (NCAs). The antibacterial performances of the tailored linear and star-shaped AMPs were comprehensively evaluated in both solution states and surface-bonded states. The results indicated that the star-shaped AMPs exhibited enhanced bactericidal activity against Gram-negative E. coli and similar bactericidal activity against Gram-positive S. aureus when compared with the linear AMPs. It is worth mentioning that star-shaped AMPs demonstrated a significantly faster bactericidal efficiency (completely killed bacteria within 5 min at a concentration of 2 × MIC for S. aureus) than their linear analogues (took 15 min to achieve the same effect). However, when the AMPs were immobilized to the surface, they similarly exhibited superior antibacterial activity and fast bactericidal efficiency towards S. aureus and E. coli in the case of the same surface grafting amount. In addition, both the surfaces grafted with AMPs of different topologies demonstrated favorable biocompatibility in vitro.

Influence of the block copolypeptide surfactant structure on the size of polypeptide nanoparticles obtained by mini emulsion polymerisation

Polypetide nanoparticles obtained by miniemulsion polymerisation of amino acid N-carboxyanhydrides (NCA) are a novel class of tuneable bio-derived functional nano materials for potential applications in nutraceutics, agriculture, and medicine. This...

Versatile fully-substituted triazole-functionalized polypeptides with a stable α-helical conformation for gene delivery

A library of polypeptides bearing fully-substituted triazoles (FT) was developed via a Cu-catalyzed multicomponent reaction (MCR), which avoided the undesired hydrogen bonding and stabilized the α-helix in a broad pH range.

The chiral pyridoxal-catalyzed biomimetic Mannich reaction: the mechanism and origin of stereoselectivity

A biomimetic organocatalyst with a pyridoxal-like structure is one of the most successful examples of catalyzing organic reactions under mild conditions in an asymmetric synthesis field.

Star-like poly(peptoid)s with selective antibacterial activity

We developed new macromolecular engineering approaches enabling the preparation of star-shaped and antimicrobial polypeptoids by ring-opening polymerization.

Fluorescent homopolypeptide toroids

Toroids are important ring-like nanostructures in living systems; intrinsically luminogenic toroids are promising in bioimaging but it is challenging to synthesize such nanoparticles. Herein, we report a fluorescent toroid that...

Peptide Multimerization as Leads for Therapeutic Development

Multimerization of peptide structures has been a logical evolution in their development as potential therapeutic molecules. The multivalent properties of these assemblies have attracted much attention from researchers in the past and the development of more complex branching dendrimeric structures, with a wide array of biocompatible building blocks is revealing previously unseen properties and activities. These branching multimer and dendrimer structures can induce greater effect on cellular targets than monomeric forms and act as potent antimicrobials, potential vaccine alternatives and promising candidates in biomedical imaging and drug delivery applications. This review aims to outline the chemical synthetic innovations for the development of these highly complex structures and highlight the extensive capabilities of these molecules to rival those of natural biomolecules.

Poly(l-cysteine) Peptide Amphiphile Derivatives Containing Disulfide Bonds: Synthesis, Self-Assembly-Induced β-Sheet Nanostructures, pH/Reduction Dual Response, and Drug Release

Three disulfide bond-containing peptide amphiphiles (PA1-3) with different lengths of alkyl tails (PA1 for C₆, PA2 for C₁₂, and PA3 for C₁₈) were synthesized by ring-opening polymerization of α-amino acid N-carboxyanhydride followed by post-polymerization modification. The peptide segments were composed of 3-mercaptopropionic acid-modified poly(l-cysteine) [P(Cys-SS-CH₂CH₂COOH)]. We characterized the chemical structure and molecular parameters by ¹H NMR, ¹³C NMR, gel permeation chromatography, Fourier transform infrared spectroscopy, and circular dichroism spectroscopy. It is found that alkyl-P(Cys-SS-CH₂CH₂COOH) mainly presents a β-sheet conformation at the solid state. However, the PAs present predominant random coils at pH 7.4 in aqueous solutions. The β-sheet conformation increased dramatically when the concentration of the PA exceeded its critical micelle concentration (ca. 0.3 mg/mL for PA3), indicating the formation of self-assembly-induced β-sheet nanostructures. Elongation of the alkyl chain length or a decrease of the pH of the PA solution can promote the formation of the β-sheet conformation. The three PAs can self-assemble into spherical micelles or nanofibrous hydrogels, which can be utilized as nanocarriers for systemic drug delivery or implants for localized drug delivery, respectively. Cisplatin (CDDP) was loaded as a model medicine to examine the drug delivery potential of PA3. We found that the CDDP-loaded PA3 micelles are stable at pH 7.4, have a spherical morphology with a hydrodynamic diameter of ca. 52 nm, and accomplish pH/reduction dual-responsive release of CDDP. In addition, alkyl-P(Cys-SS-CH₂CH₂COOH) can self-assemble into nanofibrous hydrogels at pH 5.0-6.0 or upon the addition of certain metal ions and show excellent dynamic reversibility. Moreover, the CDDP-loaded PA3 hydrogel exhibits a sustained release profile and a nearly linear release over 48 h. In vitro cytotoxicity of PA3 also indicates its nontoxicity. Thus, our findings suggest that alkyl-P(Cys-SS-CH₂CH₂COOH) has great potential for both systemic and localized delivery of therapeutics.

Site-Specific Conjugation of a Selenopolypeptide to Alpha-1-antitrypsin Enhances Oxidation Resistance and Pharmacological Properties

Human alpha-1-antitrypsin (A1AT), a native serine-protease inhibitor that protects tissue damage from excessive protease activities, is used as an augmentation therapy to treat A1AT-deficienct patients. However, A1AT is sensitive to oxidation-mediated deactivation and has a short circulating half-life. Currently, there is no method that can effectively protect therapeutic proteins from oxidative damage in vivo. Here we developed a novel biocompatible selenopolypeptide and site-specifically conjugated it with A1AT. The conjugated A1AT fully retained its inhibitory activity on neutrophil elastase, enhanced oxidation resistance, extended the serum half-life, and afforded long-lasting protective efficacy in a mouse model of acute lung injury. These results demonstrated that conjugating A1AT with the designed selenopolymer is a viable strategy to improve its pharmacological properties, which could potentially further be applied to a variety of oxidation sensitive biotherapeutics.

Dynamic Glycopeptide Dendrimers: Synthesis and Their Controllable Self-Assembly into Varied Glyco-Nanostructures for the Biomimicry of Glycans

A library of 14 dynamic glycopeptide amphiphilic dendrimers composed of 14 hydrophilic and bioactive saccharides (seven kinds) as dendrons and 7 hydrophobic peptides (di- and tetrapeptides) as arms with β-cyclodextrin (CD) as a core were facially designed and synthesized in several steps. Fourteen saccharides were first conjugated to the C-2 and C-3 positions of CD, forming glycodendrons. Subsequently, seven oligopeptide arms were introduced at the C-6 positions of a CD moiety by an acylhydrazone dynamic covalent bond, resulting in unique Janus amphiphilic glycopeptide dendrimers with precise and varied molecular structures. The kinds of hydrophilic parts of saccharides and hydrophobic parts of peptides were easily varied to prepare a series of amphiphilic Janus glycopeptide dendrimers. Intriguingly, these obtained amphiphilic glycopeptide dendrimers showcased very different self-assembly behaviors from the traditional amphiphilic linear block-copolymers and self-assembled into different glyco-nanostructures with controllable morphologies including glycospheres, worm-like micelles, and fibers depending upon the repeat unit ratio of saccharides and phenylalanine. Both glycodendrons and glycopeptide assemblies displayed strong and specific recognitions with C-type mannose-specific lectin. Moreover, these glycopeptide nanomaterials can encapsulate exemplary hydrophobic molecules such as Nile red (NR). The dye-loaded glycopeptide nanostructures showed a pH-controllable release behavior around the physiological and acidic tumor environment. Furthermore, cell experiments demonstrated that such glyco-nanostructures can further facilitate the functions of a model drug of the pyridone agent to reduce the expression of monocyte chemotactic protein-1 (MCP-1) and interleukin -1beta (IL-1β) in the primary peritoneal macrophages via encapsulating drugs. Considering all the abovementioned advantages including unique and precise structures, bioactivity, targeting, and controllable cargo release, we believe that these findings can not only enrich the library of glycopeptides but also provide a new avenue to the fabrication of smart and structure-controllable glyco-nanomaterials which hold great potential biological applications such as targeted delivery and release of therapeutic and bioactive molecules.

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.

Peptide Design and Self-assembly into Targeted Nanostructure and Functional Materials

Peptides have been extensively utilized to construct nanomaterials that display targeted structure through hierarchical assembly. The self-assembly of both rationally designed peptides derived from naturally occurring domains in proteins as well as intuitively or computationally designed peptides that form β-sheets and helical secondary structures have been widely successful in constructing nanoscale morphologies with well-defined 1-d, 2-d, and 3-d architectures. In this review, we discuss these successes of peptide self-assembly, especially in the context of designing hierarchical materials. In particular, we emphasize the differences in the level of peptide design as an indicator of complexity within the targeted self-assembled materials and highlight future avenues for scientific and technological advances in this field.

A Guideline for the Synthesis of Amino-Acid-Functionalized Monomers and Their Polymerizations

Amino acids have emerged as a sustainable source for the design of functional polymers. Besides their wide availability, especially their high degree of biocompatibility makes them appealing for a broad range of applications in the biomedical research field. In addition to these favorable characteristics, the versatility of reactive functional groups in amino acids (i.e., carboxylic acids, amines, thiols, and hydroxyl groups) makes them suitable starting materials for various polymerization approaches, which include step- and chain-growth reactions. This review aims to provide an overview of strategies to incorporate amino acids into polymers. To this end, it focuses on the preparation of polymerizable monomers from amino acids, which yield main chain or side chain-functionalized polymers. Furthermore, postpolymerization modification approaches for polymer side chain functionalization are discussed. Amino acids are presented as a versatile platform for the development of polymers with tailored properties.

N-Heterocyclic Carbene-Catalyzed Random Copolymerization of N-Carboxyanhydrides of α-Amino Acids

Synthetic polypeptides prepared from N-carboxyanhydrides (NCAs) of α-amino acids are useful for elucidating the relationship between the primary structure of natural peptides and their immunogenicity. In this study, complex copolypeptide sequences were prepared using a recently developed technique; specifically, the random copolymerization of l-alanine NCA with NCAs of l-glutamic acid 5-benzylester (Bn-Glu NCA), S-benzyl-cysteine (Bn-Cys NCA), O-benzyl-l-serine (Bn-Ser NCA), and l-phenylalanine (Phe NCA) was performed using N-heterocyclic carbene (NHC) catalysts. The NHC-initiated Ala NCA/Bn-Glu NCA and Ala NCA/Bn-Cys NCA copolymerization reactions achieved 90% conversion within 30 min. The reactivity ratio values estimated using the Kelen and Tüdos method show that poly(Bn-Glu-co-Ala) and poly(Bn-Cys-co-Ala) have random repeating units with rich alternating sequences, whereas poly(Bn-Ser-co-Ala) and poly(Phe-co-Ala) contain a larger proportion of Ala-repeating units than Bn-Ser and Phe in random placement.

Synthesis of poly-α/β-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/β-peptide has proven to be an effective strategy to address the stability issue, the synthesis of poly-α/β-peptide from polymerization is not available yet. Hereby, we demonstrate a living and controlled copolymerization on α-NCA and β-NTA to prepare sequence-tunable poly-α/β-peptides. This polymerization strategy shows a prominent solvent-driven characteristic, providing random-like copolymers of poly-α/β-peptides in THF and block-like copolymers of poly-α/β-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/β-peptides for diverse applications.

•

Realizing controlled synthesis of poly-α/β-peptides via one-pot polymerization

•

Sequence-tunable copolymerization via solvent-dependent polymerization kinetics

•

Adjustable proteolytic stability and antibacterial activity of poly-α/β-peptides

•

Tunable self-assembly behavior of poly-α/β-peptides via one-pot polymerization

Self-assembled PEGylated amphiphilic polypeptides for gene transfection

In the present study, three biodegradable block copolymers composed of a poly(ethylene glycol) block and a copolypeptide block with varying compositions of cationic L-lysine (L-Lys) and hydrophobic benzyl-L-glutamate (Bzl-L-Glu) were designed for gene delivery applications. The polypeptides were synthesized by ring opening polymerization (ROP) and after orthogonal deprotection of Boc-L-Lys side chains, the polymer exhibited an amphiphilic character. To bind or encapsulate plasmid DNA (pDNA), different formulations were investigated: a nanoprecipitation and an emulsion technique using various organic solvents as well as an aqueous pH-controlled formulation method. The complex and nanoparticle (NP) formations were monitored by dynamic light scattering (DLS), and pDNA interaction was shown by gel electrophoresis and subsequent controlled release with heparin. The polypeptides were further tested for their cytotoxicity as well as biodegradability. The complexes and NPs presenting the most promising size distributions and pDNA binding ability were subsequently evaluated for their transfection efficiency in HEK293T cells. The highest transfection efficiencies were obtained with an aqueous formulation of the polypeptide containing the highest L-Lys content and lowest proportion of hydrophobic, helical structures (P1*), which is therefore a promising candidate for efficient gene delivery by biodegradable gene delivery vectors.

Single-Chain Nanoparticle-Based Coatings with Improved Bactericidal Activity and Antifouling Properties

Dual-function antibacterial surfaces have exhibited promising potential in addressing implant-associated infections. However, both bactericidal and antifouling properties need to be further improved prior to practical uses. Herein, we report the preparation and properties of a linear block copolymer coating (LP-KF) and a single-chain nanoparticle coating (NP-KF) with poly(ethylene glycol) (PEG) and cationic polypeptide segments. NP-KF with cyclic PEG segments and densely charged polypeptide segments was expected to display improved bactericidal and antifouling properties. LP-KF was prepared by the combination of ring-opening polymerization of N-carboxyanhydride (NCA) monomers and subsequent deprotection. NP-KF was prepared by intramolecular cross-linking of LP-KF in diluted solutions. Both LP-KF- and NP-KF-coated PDMS surfaces were prepared by dipping with polydopamine-coated surfaces. They showed superior in vitro bactericidal activity against both Staphylococcus aureus and Escherichia coli with >99.9% killing efficacy, excellent protein adsorption resistance, antibacterial adhesion, and low cytotoxicity. The NP-KF coating showed higher bactericidal activity and antifouling properties than its linear counterpart. It also showed significant anti-infective property and histocompatibility in vivo, which makes it a good candidate for implants and biomedical device applications.

Poly(l-ornithine)-Grafted Zinc Phthalocyanines as Dual-Functional Antimicrobial Agents with Intrinsic Membrane Damage and Photothermal Ablation Capacity

Multifunctional antimicrobial peptides that combine the intrinsic microbicidal property of cationic polypeptide chains and additional antibacterial strategy hold promising applications for the treatment of infections caused by antibiotic-resistant bacteria, especially "superbugs". In the present study, star-shaped copolymers ZnPc-g-PLO with a zinc phthalocyanine (ZnPc) core and four poly(l-ornithine) (PLO) arms were designed, synthesized, and evaluated as dual-functional antimicrobial agents, that is, intrinsic membrane damage and photothermal ablation capacity. In an aqueous solution, amphiphilic ZnPc-g-PLO molecules self-assemble into nanosized polymeric micelles with an aggregated ZnPc core and star-shaped PLO periphery, where the ZnPc core exhibits appreciable aggregation-induced photothermal conversion efficiency. In the absence of laser irradiation, ZnPc-g-PLO micelles display potent and broad-spectrum antibacterial activities via physical bacterial membrane disruption as a result of the high cationic charge density of the star-shaped PLO. Upon laser irradiation, significant improvement in bactericidal potency was realized due to the efficacious photothermal sterilization from the ZnPc core. Notably, ZnPc-g-PLO micelles did not induce drug-resistance upon subinhibitory passages. In summary, dual-functional ZnPc-g-PLO copolymers can serve as promising antibacterial agents for the treatment of infectious diseases caused by antibiotic-resistant bacteria.

A moisture-tolerant route to unprotected α/β-amino acid N-carboxyanhydrides and facile synthesis of hyperbranched polypeptides

A great hurdle in the production of synthetic polypeptides lies in the access of N-carboxyanhydrides (NCA) monomers, which requires dry solvents, Schlenk line/gloveboxe, and protection of side-chain functional groups. Here we report a robust method for preparing unprotected NCA monomers in air and under moisture. The method employs epoxy compounds as ultra-fast scavengers of hydrogen chloride to allow assisted ring-closure and prevent NCA from acid-catalyzed decomposition under moist conditions. The broad scope and functional group tolerance of the method are demonstrated by the facile synthesis of over 30 different α/β-amino acid NCAs, including many otherwise inaccessible compounds with reactive functional groups, at high yield, high purity, and up to decagram scales. The utility of the method and the unprotected NCAs is demonstrated by the facile synthesis of two water-soluble polypeptides that are promising candidates for drug delivery and protein modification. Overall, our strategy holds great potential for facilitating the synthesis of NCA and expanding the industrial application of synthetic polypeptides.

A sulfonate-based polypeptide toward infection-resistant coatings

Multifunctional coatings have gained significant attention for their promising potential to address the issue of medical device-related infections. However, they usually have multiple components in one layer which decreases the density of functional groups on surfaces and hence reduces the biological properties. Herein, we report a mono-component and sulfonate-based anionic polypeptide coating with on-demand antibacterial activity, antifouling property, and biocompatibility. The anionic polypeptide was prepared by ring-opening polymerization of L-cysteine-based N-carboxyanhydride (NCA) with allyl groups and a subsequent thiol-ene reaction to incorporate the sulfonate pendants. It adopted a 17.1-19.5% β-sheet conformation and self-assembled into a spherical nanoparticle. The polypeptide coating showed excellent in vitro antibacterial activity against both Gram-positive (i.e., S. aureus) and Gram-negative bacteria (i.e., E. coli) with >99% killing efficacy after acidic solution treatment and prominent antifouling property and biocompatibility after weak base treatment. An in vivo study revealed that the sulfonate-based polypeptide-coated polydimethylsiloxane (PDMS) exhibited good anti-infection property and histocompatibility.