Protein PEPylation: A New Paradigm of Protein–Polymer Conjugation

Site-Specific Conjugation of Bottlebrush Polymers to Therapeutic Protein via Bioorthogonal Chemistry

Achieving efficient and site-specific conjugation of therapeutic protein to polymer is crucial to augment their applicability in the realms of biomedicine by improving their stability and enzymatic activity. In this study, we exploited tetrazine bioorthogonal chemistry to achieve the site-specific conjugation of bottlebrush polymers to urate oxidase (UOX), a therapeutic protein for gout treatment. An azido-functionalized zwitterionic bottlebrush polymer (N3-ZBP) using a "grafting-from" strategy involving RAFT and ATRP methods was synthesized, and a trans-cyclooctene (TCO) moiety was introduced at the polymer end through the strain-promoted azide-alkyne click (SPAAC) reaction. The subsequent coupling between TCO-incorporated bottlebrush polymer and tetrazine-labeled UOX using a fast and safe bioorthogonal reaction, inverse electron demand Diels-Alder (IEDDA), led to the formation of UOX-ZBP conjugates with a 52% yield. Importantly, the enzymatic activity of UOX remained unaffected following polymer conjugation, suggesting a minimal change in the folded structure of UOX. Moreover, UOX-ZBP conjugates exhibited enhanced proteolytic resistance and reduced antibody binding, compared to UOX-wild type. Overall, the present findings reveal an efficient and straightforward route for synthesizing protein-bottlebrush polymer conjugates without compromising the enzymatic activity while substantially reducing proteolytic degradation and antibody binding.

An organometallic swap strategy for bottlebrush polymer-protein conjugate synthesis

Polymer-protein bioconjugation offers a powerful strategy to alter the physical properties of proteins, and various synthetic polymer compositions and architectures have been investigated for this purpose. Nevertheless, conjugation of molecular bottlebrush polymers (BPs) to proteins remains an unsolved challenge due to the large size of BPs and a general lack of methods to transform the chain ends of BPs into functional groups suitable for bioconjugation. Here, we present a strategy to address this challenge in the context of BPs prepared by "graft-through" ring-opening metathesis polymerization (ROMP), one of the most powerful methods for BP synthesis. Quenching ROMP of PEGylated norbornene macromonomers with an activated enyne terminator facilitates the transformation of the BP Ru alkylidene chain ends into Pd oxidative addition complexes (OACs) for facile bioconjugation. This strategy is shown to be effective for the synthesis of two BP-protein conjugates (albumin and ERG), setting the stage for a new class of BP-protein conjugates for future therapeutic and imaging applications.

Recent progress on polySarcosine as an alternative to PEGylation: Synthesis and biomedical applications

Biotherapeutic PEGylation to prolong action of medications has gained popularity over the last decades. Various hydrophilic natural polymers have been developed to tackle the drawbacks of PEGylation, such as its accelerated blood clearance and non-biodegradability. Polypeptoides, such as polysarcosine (pSar), have been explored as hydrophilic substitutes for PEG. pSar has PEG-like physicochemical characteristics such as water solubility and no reported cytotoxicity and immunogenicity. This review discusses pSar derivatives, synthesis, characterization approaches, biomedical applications, in addition to the challenges and future perspectives of pSar based biomaterials as an alternative to PEG.

Precision Synthesis of Polysarcosine via Controlled Ring-Opening Polymerization of N-Carboxyanhydride: Fast Kinetics, Ultrahigh Molecular Weight, and Mechanistic Insights

The rapid and controlled synthesis of high-molecular-weight (HMW) polysarcosine (pSar), a potential polyethylene glycol (PEG) alternative, via the ring-opening polymerization (ROP) of N-carboxyanhydride (NCA) is rare and challenging. Here, we report the well-controlled ROP of sarcosine NCA (Sar-NCA) that is catalyzed by various carboxylic acids, which accelerate the polymerization rate up to 50 times, and enables the robust synthesis of pSar with an unprecedented ultrahigh molecular weight (UHMW) up to 586 kDa (DP ∼ 8200) and exceptionally narrow dispersity (D̵) below 1.05. Mechanistic experiments and density functional theory calculations together elucidate the role of carboxylic acid as a bifunctional catalyst that significantly facilitates proton transfer processes and avoids charge separation and suggest the ring opening of NCA, rather than decarboxylation, as the rate-determining step. UHMW pSar demonstrates improved thermal and mechanical properties over the low-molecular-weight counterparts. This work provides a simple yet highly efficient approach to UHMW pSar and generates a new fundamental understanding useful not only for the ROP of Sar-NCA but also for other NCAs.

On the origin of the low immunogenicity and biosafety of a neutral α-helical polypeptide as an alternative to polyethylene glycol

Poly(ethylene glycol) (PEG) is a prominent synthetic polymer widely used in biomedicine. Despite its notable success, recent clinical evidence highlights concerns regarding the immunogenicity and adverse effects associated with PEG in PEGylated proteins and lipid nanoparticles. Previous studies have found a neutral helical polypeptide poly(γ-(2-(2-(2-methoxyethoxy)ethoxy)ethyl l-glutamate), namely L-P(EG3Glu), as a potential alternative to PEG, displaying lower immunogenicity. To comprehensively assess the immunogenicity, distribution, degradation, and biosafety of L-P(EG3Glu), herein, we employ assays including enzyme-linked immunosorbent assay, positron emission tomography-computed tomography, and fluorescent resonance energy transfer. Our investigations involve in vivo immune responses, biodistribution, and macrophage activation of interferon (IFN) conjugates tethered with helical L-P(EG3Glu) (L20k-IFN), random-coiled DL-P(EG3Glu) (DL20k-IFN), and PEG (PEG20k-IFN). Key findings encompass: minimal anti-IFN and anti-polymer antibodies elicited by L20k-IFN; length-dependent affinity of PEG to anti-PEG antibodies; accelerated clearance of DL20k-IFN and PEG20k-IFN linked to anti-IFN and anti-polymer IgG; complement activation for DL20k-IFN and PEG20k-IFN but not L20k-IFN; differential clearance with L20k-IFN kidney-based, and DL20k-IFN/PEG20k-IFN accumulation mainly in liver/spleen; enhanced macrophage activation by DL20k-IFN and PEG20k-IFN; L-P(EG3Glu) resistance to proteolysis; and safer repeated administrations of L-P(EG3Glu) in rats. Overall, this study offers comprehensive insights into the lower immunogenicity of L-P(EG3Glu) compared to DL-P(EG3Glu) and PEG, supporting its potential clinical use in protein conjugation and nanomedicines.

Self-Assembled Protein Nanostructures via Irreversible Peptide Assembly

The quaternary structure of proteins extends the functionality of monomeric proteins. Similarly, self-assembled protein nanostructures (SPrNs) have great potential to improve the functionality and complexity of proteins; however, the difficulty associated with the fabrication of SPrNs is far greater than that associated with the fabrication of self-assembled peptides or polymers and often requires sophisticated computational design. To make the process of SPrN formation simpler and more intuitive, herein, we devise a strategy to adopt an irreversible self-assembled peptide nanostructure (SPeN) process en route to the formation of SPrNs. The strategy employs three sequential steps: first, the formation of SPeNs (an equilibrium process); second, covalent capture of SPeNs (an irreversible process); third, the final assembly of SPrNs via protein-peptide interactions (an equilibrium process). This strategy allowed us to fabricate SPrNs in which the size of the protein was approximately 9 times higher than that of the self-assembling peptide. Furthermore, we demonstrated that the irreversible SPeN could be used as a primary building block for assembly into superstructures. Overall, this strategy is conceptually as simple as SPeN fabrication and is potentially applicable to any soluble protein.

Design of an Oxygen-Tolerant Photo-RAFT System for Protein-Polymer Conjugation Achieving High Bioactivity

Protein-polymer conjugates have significant potential in pharmaceutical and biomedical applications. To enable their widespread use, robust conjugation techniques are crucial. This study introduces a photo-initiated reversible addition-fragmentation chain-transfer (Photo-RAFT) polymerization system that exhibits excellent oxygen tolerance. This system allows for the synthesis of protein-polymer conjugates with high bioactivity under mild and aerobic conditions. Three photocatalytic systems utilizing Eosin Y (EY) as the photocatalyst with two different cocatalysts (ascorbic acid and triethanolamine) were investigated, each generating distinct reactive oxygen species (ROS) such as singlet oxygen, superoxide, hydrogen peroxide, and hydroxyl radicals. The impact of these ROS on three model proteins (lysozyme, albumin, and myoglobin) was evaluated, demonstrating varying bioactivities based on the ROS produced. The EY/TEOA system was identified as the optimal photo-RAFT initiating system, enabling the preparation of protein-polymer conjugates under aerobic conditions while maintaining high protein enzymatic activity. To showcase the potential of this approach, lysozyme-poly(dimethylaminoethyl acrylate) conjugates were successfully prepared and exhibited enhanced antimicrobial property against Gram-positive and Gram-negative bacteria.

Zwitterionic Polymer: A New Paradigm for Protein Conjugation beyond PEG

To render protein drugs more suitable for clinical treatment, PEGylation has been widely used to ameliorate their inherent deficiencies, such as poor stability, rapid elimination in the bloodstream, and high immunogenicity. While increasingly PEGylated protein drugs have been approved by the FDA, the non-degradability of PEG and the emergence of anti-PEG antibodies after injection raise concerns about their cumulative chronic toxicity and long-term therapeutic efficacy. Zwitterionic polymer, with a unique structure containing equal amounts of positively charged and negatively charged groups, shows a different hydration behavior to PEG, which may be a superior PEG alternative for protein conjugation. In this concept review, a series of features beyond that of PEGylated protein exhibited by protein-zwitterionic polymer conjugate are discussed and some suggestions are presented for their future direction.

Poly-l-glutamic acid modification modulates the bio-nano interface of a therapeutic anti-IGF-1R antibody in prostate cancer

Modifying biological agents with polymers such as polyethylene glycol (PEG) has demonstrated clinical benefits; however, post-market surveillance of PEGylated derivatives has revealed PEG-associated toxicity issues, prompting the search for alternatives. We explore how conjugating a poly-l-glutamic acid (PGA) to an anti-insulin growth factor 1 receptor antibody (AVE1642) modulates the bio-nano interface and anti-tumor activity in preclinical prostate cancer models. Native and PGA-modified AVE1642 display similar anti-tumor activity in vitro; however, AVE1642 prompts IGF-1R internalization while PGA conjugation prompts higher affinity IGF-1R binding, thereby inhibiting IGF-1R internalization and altering cell trafficking. AVE1642 attenuates phosphoinositide 3-kinase signaling, while PGA-AVE1642 inhibits phosphoinositide 3-kinase and mitogen-activated protein kinase signaling. PGA conjugation also enhances AVE1642's anti-tumor activity in an orthotopic prostate cancer mouse model, while PGA-AVE1642 induces more significant suppression of cancer cell proliferation/angiogenesis than AVE1642. These findings demonstrate that PGA conjugation modulates an antibody's bio-nano interface, mechanism of action, and therapeutic activity.

Thermoresponsive Polypeptide Fused L-Asparaginase with Mitigated Immunogenicity and Enhanced Efficacy in Treating Hematologic Malignancies

L-Asparaginase (ASP) is well-known for its excellent efficacy in treating hematological malignancies. Unfortunately, the intrinsic shortcomings of ASP, namely high immunogenicity, severe toxicity, short half-life, and poor stability, restrict its clinical usage. Poly(ethylene glycol) conjugation (PEGylation) of ASP is an effective strategy to address these issues, but it is not ideal in clinical applications due to complex chemical synthesis procedures, reduced ASP activity after conjugation, and pre-existing anti-PEG antibodies in humans. Herein, the authors genetically engineered an elastin-like polypeptide (ELP)-fused ASP (ASP-ELP), a core-shell structured tetramer predicted by AlphaFold2, to overcome the limitations of ASP and PEG-ASP. Notably, the unique thermosensitivity of ASP-ELP enables the in situ formation of a sustained-release depot post-injection with zero-order release kinetics over a long time. The in vitro and in vivo studies reveal that ASP-ELP possesses increased activity retention, improved stability, extended half-life, mitigated immunogenicity, reduced toxicity, and enhanced efficacy compared to ASP and PEG-ASP. Indeed, ASP-ELP treatment in leukemia or lymphoma mouse models of cell line-derived xenograft (CDX) shows potent anti-cancer effects with significantly prolonged survival. The findings also indicate that artificial intelligence (AI)-assisted genetic engineering is instructive in designing protein-polypeptide conjugates and may pave the way to develop next-generation biologics to enhance cancer treatment.

Design of lipid-based nanoparticles for delivery of therapeutic nucleic acids

The successful development of nonviral delivery systems for nucleic acids has been reported extensively over the past number of years. Among them, lipid-based nanoparticles (LNPs) represent the most advanced platform. This review provides an overview of the state-of-the-art in LNP technology, focusing on the delivery of a range of nucleic acids. Recent advances in the development of an efficient and safe lipid-based system are critically analyzed with a particular emphasis on the rationale behind the design of LNPs and on attempts to elucidate the resulting molecular assembly and structure, their interactions with cellular proteins and biodistribution. In addition, manufacturing methods including microfluidics and their potential to influence stability and scale-up are summarized.

Protein-supported transition metal catalysts: Preparation, catalytic applications, and prospects

The immobilization of transition metal catalysts onto supports enables their easier recycling and improves catalytic performance. Protein supports not only support and stabilize transition metal catalysts but also enable the incorporation of biocompatibility and enzymatic catalysis into these catalysts. Consequently, the engineering of protein-supported transition metal catalysts (PTMCs) has emerged as an effective approach to improving their catalytic performance and widening their catalytic applications. Here, we review the recent development of the preparation and applications of PTMCs. The preparation of PTMCs will be summarized and discussed in terms of the types of protein supports, including proteins, protein assemblies, protein-polymer conjugates, and cross-linked proteins. Then, their catalytic applications including organic synthesis, photocatalysis, polymerization, and biomedicine, will be surveyed and compared. Meanwhile, the established catalytic structures-function relationships will be summarized. Lastly, the remaining issues and prospects will be discussed. By surveying a wide range of PTMCs, we believe that this review will attract a broad readership and stimulate the development of PTMCs.

An immunomodulatory polypeptide hydrogel for osteochondral defect repair

Osteochondral injury is a common and frequent orthopedic disease that can lead to more serious degenerative joint disease. Tissue engineering is a promising modality for osteochondral repair, but the implanted scaffolds are often immunogenic and can induce unwanted foreign body reaction (FBR). Here, we prepare a polypept(o)ide-based PAA-RGD hydrogel using a novel thiol/thioester dual-functionalized hyperbranched polypeptide P(EG₃Glu-co-Cys) and maleimide-functionalized polysarcosine under biologically benign conditions. The PAA-RGD hydrogel shows suitable biodegradability, excellent biocompatibility, and low immunogenicity, which together lead to optimal performance for osteochondral repair in New Zealand white rabbits even at the early stage of implantation. Further in vitro and in vivo mechanistic studies corroborate the immunomodulatory role of the PAA-RGD hydrogel, which induces minimum FBR responses and a high level of polarization of macrophages into the immunosuppressive M2 subtypes. These findings demonstrate the promising potential of the PAA-RGD hydrogel for osteochondral regeneration and highlight the importance of immunomodulation. The results may inspire the development of PAA-based materials for not only osteochondral defect repair but also various other tissue engineering and bio-implantation applications.

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A polypept(o)ide-based hydrogel.

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Prominent and early osteochondral repair.

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Minimized immunogenicity.

PEGylation Strategy for Improving the Pharmacokinetic and Antitumoral Activity of the IL-2 No-alpha Mutein

BACKGROUND

In a previous work, an IL-2Rβγ biased mutant derived from human IL-2 and called IL-2noα, was designed and developed. Greater antitumor effects and lower toxicity were observed compared to native IL-2. Nevertheless, mutein has some disadvantages, such as a very short half-life of about 9-12 min, propensity for aggregation, and solubility problems.

OBJECTIVE

In this study, PEGylation was employed to improve the pharmacokinetic and antitumoral properties of the novel protein.

METHODS

Pegylated IL-2noα was characterized by polyacrylamide gel electrophoresis, size exclusion chromatography, in vitro cell proliferation and in vivo cell expansion bioassays, and pharmacokinetic and antitumor studies.

RESULTS

IL-2noα-conjugates with polyethylene glycol (PEG) of 1.2 kDa, 20 kDa, and 40 kDa were obtained by classical acylation. No significant changes in the secondary and tertiary structures of the modified protein were detected. A decrease in biological activity in vitro and a significant improvement in half-life were observed, especially for IL-2noα-PEG20K. PEGylation of IL-2noα with PEG20K did not affect the capacity of the mutant to induce preferential expansion of T effector cells over Treg cells. This pegylated IL-2noα exhibited a higher antimetastatic effect compared to unmodified IL-2noα in the B16F0 experimental metastases model, even when administered at lower doses and less frequently.

CONCLUSION

PEG20K was selected as the best modification strategy, to improve the blood circulation time of the IL-2noα with a superior antimetastatic effect achieved with lower doses.

Zwitterionic Biomaterials

The term "zwitterionic polymers" refers to polymers that bear a pair of oppositely charged groups in their repeating units. When these oppositely charged groups are equally distributed at the molecular level, the molecules exhibit an overall neutral charge with a strong hydration effect via ionic solvation. The strong hydration effect constitutes the foundation of a series of exceptional properties of zwitterionic materials, including resistance to protein adsorption, lubrication at interfaces, promotion of protein stabilities, antifreezing in solutions, etc. As a result, zwitterionic materials have drawn great attention in biomedical and engineering applications in recent years. In this review, we give a comprehensive and panoramic overview of zwitterionic materials, covering the fundamentals of hydration and nonfouling behaviors, different types of zwitterionic surfaces and polymers, and their biomedical applications.

Hydrophilic Natural Polylysine as Drug Nanocarrier for Preparation of Helical Delivery System

Polypeptide materials have clear secondary structure and biodegradability, which can be further modified and functionalized, so that they can be employed as therapeutic agents in clinical applications. PEGylation of polylysine (PEG-PLL) is a kind of safe and effective nanocarrier that is utilized for gene and drug delivery. However, PEG-PLL needs to be produced through chemical synthesis, which is expensive and difficult to obtain. We hope to simplify the nanocarrier and use hydrophilic natural polylysine (PLL) to develop a high-efficacy delivery system. To evaluate the possibility of PLL as nanocarriers, methotrexate (MTX) is selected as a model drug and PEG-PLL is utilized as control nanocarriers. The experimental results showed that PLL is an ideal polypeptide to prepare MTX-loaded PLL nanoparticles (PLL/MTX NPs). Compared with PEG-PLL as nanocarriers, PLL/MTX NPs showed higher drug-loading content (58.9%) and smaller particle sizes (113.7 nm). Moreover, the shape of PLL/MTX NPs was a unique helical nanorod. The PLL/MTX NPs had good storage stability, media stability, and sustained release effect. Animal research demonstrated that PLL/MTX NPs could improve the anti-tumor activity of MTX, the antitumor efficacy is enhanced 1.9-fold and 1.2-fold compared with MTX injection and PEG-PLL/MTX NPs, respectively. To sum up, natural polymer PLL is an ideal nano drug delivery carrier which has potential clinical applications.

Preparation of Temperature-Responsive Antibody–Nanoparticles by RAFT-Mediated Grafting from Polymerization

Herein, we report the preparation of temperature-responsive antibody–nanoparticles by the direct polymerization of N-isopropylacrylamide (NIPAAm) from immunoglobulin G (IgG). To this end, a chain transfer agent (CTA) was introduced into IgG, followed by the precipitation polymerization of NIPAAm in an aqueous medium via reversible addition–fragmentation chain transfer polymerization above the lower critical solution temperature (LCST). Consequently, antibody–polymer particles with diameters of approximately 100–200 nm were formed. Owing to the entanglement of the grafted polymers via partial chemical crosslinking, the antibody–nanoparticles maintained their stability even at temperatures below the LCST. Further, the dispersed nanoparticles could be collected by thermal precipitation above the LCST. Additionally, the antibody–nanoparticles formulation could maintain its binding constant and exhibited a good resistance against enzymatic treatment. Thus, the proposed antibody–nanoparticles can be useful for maximizing the therapeutic potential of antibody–drug conjugates or efficacies of immunoassays and antibody recovery and recycling.

Mechano-bioconjugation Strategy Empowering Fusion Protein Therapeutics with Aggregation Resistance, Prolonged Circulation, and Enhanced Antitumor Efficacy

Bioconjugation is a powerful protein modification strategy to improve protein properties. Herein, we report mechano-bioconjugation as a novel approach to empower fusion protein therapeutics and demonstrate its utility by a protein heterocatenane (cat-IFN-ABD) containing interferon-α2b (IFN) mechanically interlocked with a consensus albumin-binding domain (ABD). The conjugate was selectively synthesized in cellulo following a cascade of post-translational events using a pair of heterodimerizing p53dim variants and two orthogonal split-intein reactions. The catenane topology was proven by combined techniques of LC-MS, SDS-PAGE, SEC, and controlled proteolytic digestion. Not only did cat-IFN-ABD retain activities comparable to those of the wild-type IFN and ABD, the conjugate also exhibited enhanced aggregation resistance and prolonged circulation time over the simple linear and cyclic fusions. Consequently, cat-IFN-ABD potently inhibited tumor growth in the mouse xenograft model. Therefore, mechano-bioconjugation by catenation accomplishes function integration with additional benefits, providing an alternative pathway for developing advanced protein therapeutics.

Polymer-drug conjugates: Design principles, emerging synthetic strategies and clinical overview

Adagen, an enzyme replacement treatment for adenosine deaminase deficiency, was the first protein-polymer conjugate to be approved in early 1990s. Post this regulatory approval, numerous polymeric drugs and polymeric nanoparticles have entered the market as advanced or next-generation polymer-based therapeutics, while many others have currently been tested clinically. The polymer conjugation to therapeutic moiety offers several advantages, like enhanced solubilization of drug, controlled release, reduced immunogenicity, and prolonged circulation. The present review intends to highlight considerations in the design of therapeutically effective polymer-drug conjugates (PDCs), including the choice of linker chemistry. The potential synthetic strategies to formulate PDCs have been discussed along with recent advancements in the different types of PDCs, i.e., polymer-small molecular weight drug conjugates, polymer-protein conjugates, and stimuli-responsive PDCs, which are under clinical/preclinical investigation. Current impediments and regulatory hurdles hindering the clinical translation of PDC into effective therapeutic regimens for the amelioration of disease conditions have been addressed.

Multivalent Polypeptide and Tannic Acid Cooperatively Iron-Coordinated Nanohybrids for Synergistic Cancer Photothermal Ferroptosis Therapy

Owing to having a unique mechanism to kill cancer cells via the membrane accumulation of lipid peroxide (LPO) and the downregulation of glutathione peroxidase-4 (GPX-4), the ferroptosis therapy (FT) of tumors based on the Fenton reaction of iron nanoparticles has been receiving much attention in the past decade; however, there are some hurdles including the uncontrollable release of iron ions, slower kinetics of the intracellular Fenton reaction, and poor efficacy of FT that need to be overcome. Considering cooperative coordination of a multivalent thiol-pendant polypeptide ligand with iron ions, we put forward a facile strategy for constructing the iron-coordinated nanohybrid of methacryloyloxyethyl phosphorylcholine-grafted polycysteine/iron ions/tannic acid (i.e., PCFT), which could deliver a higher concentration of iron ions into cells. The dynamic and unsaturated coordination in PCFT is favorable for the intracellular stimuli-triggered release and fast Fenton reaction to realize efficient FT, while its intrinsic photothermia would boost the Fenton reaction to induce a synergistic effect between FT and photothermal therapy (PTT). Both immunofluorescence analyses of reactive oxygen species (ROS) and LPO confirmed that the intracellular Fenton reaction resulted in efficient FT, during which process the photothermia greatly boosted ferroptosis, and the Western blot assay corroborated that the expression level of GPX-4 was downregulated by FT and highly degraded by the photothermia to induce synergistic PTT-FT in vitro. Excitingly, by a single intravenous dose of PCFT plus one NIR irradiation, in vivo PTT-FT treatment completely eradicated 4T1 tumors without skin scar and tumor recurrence for 16 days, demonstrating prominent antitumor efficacy, as evidenced by the GPX-4, H&E, and TUNEL assays.

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.

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.

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.

Polymeric Nanostructures Containing Proteins and Peptides for Pharmaceutical Applications

Over the last three decades, proteins and peptides have attracted great interest as drugs of choice for combating a broad spectrum of diseases, including diabetes mellitus, cancer, and infectious and neurological diseases. However, the delivery of therapeutic proteins to target sites should take into account the obstacles and limitations related to their intrinsic sensitivity to different environmental conditions, fragile tertiary structures, and short half-life. Polymeric nanostructures have emerged as competent vehicles for protein delivery, as they are multifunctional and can be tailored according to their peculiarities. Thus, the enhanced bioavailability and biocompatibility, the adjustable control of physicochemical features, and the colloidal stability of polymer-based nanostructures further enable either the embedding or conjugation of hydrophobic or hydrophilic bioactive molecules, which are some of the features of paramount importance that they possess and which contribute to their selection as vehicles. The present review aims to discuss the prevalent nanostructures composed of block copolymers from the viewpoint of efficient protein hospitality and administration, as well as the up-to-date scientific publications and anticipated applications of polymeric nanovehicles containing proteins and peptides.

Design of a UCST Polymer with Strong Hydrogen Bonds and Reactive Moieties for Facile Polymer-Protein Hybridization

Polymer-protein hybrids have been extensively used in biomedical fields. Polymers with upper critical solution temperature (UCST) behaviors can form a hydrated coacervate phase below the cloud point (T_cp), providing themselves the opportunity to directly capture hydrophilic proteins and form hybrids in aqueous solutions. However, it is always a challenge to obtain a UCST polymer that could aggregate at a high temperature at a relatively low concentration and also efficiently bind with proteins. In this work, a UCST polymer reactive with proteins was designed, and its temperature responsiveness and protein-capture ability were investigated in detail. The polymer was synthesized by the reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylamide (AAm) and N-acryloxysuccinimide (NAS). Interestingly, taking advantage of the partial hydrolysis of NAS into acrylic acid (AAc), the obtained P(AAm-co-NAS-co-AAc) polymer exhibited an excellent UCST behavior and possessed good protein-capture ability. It showed a relatively higher T_cp (81 °C) at a lower concentration (0.1 wt %) and quickly formed polymer-protein hybrids with high protein loading and without losing protein bioactivity, and both the polymer and polymer-protein nanoparticles showed good cytocompatibility. All the findings are attributed to the unique structure of the polymer, which provided not only the strong and stable hydrogen bonds but also the quick and mild reactivity. The work offers an easy and mild strategy for polymer-protein hybridization directly in aqueous solutions, which may find applications in biomedical fields.

Molecular Simulations of Zwitterlation-induced Conformation and Dynamics Variation of Glucagon-like Peptide-1 and Insulin

Zwitterionic materials have shown their ability to improve the circulation time and stability of proteins. Zwitterionic peptides present unique potential because genetic technology can fuse them to any wild-type protein....

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.

Chemoselective cysteine or disulfide modification via single atom substitution in chloromethyl acryl reagents

The development of bioconjugation chemistry has enabled the combination of various synthetic functionalities to proteins, giving rise to new classes of protein conjugates with functions well beyond what Nature can provide. Despite the progress in bioconjugation chemistry, there are no reagents developed to date where the reactivity can be tuned in a user-defined fashion to address different amino acid residues in proteins. Here, we report that 2-chloromethyl acryl reagents can serve as a simple yet versatile platform for selective protein modification at cysteine or disulfide sites by tuning their inherent electronic properties through the amide or ester linkage. Specifically, the 2-chloromethyl derivatives (acrylamide or acrylate) can be obtained via a simple and easily implemented one-pot reaction based on the coupling reaction between commercially available starting materials with different end-group functionalities (amino group or hydroxyl group). 2-Chloromethyl acrylamide reagents with an amide linkage favor selective modification at the cysteine site with fast reaction kinetics and near quantitative conversations. In contrast, 2-chloromethyl acrylate reagents bearing an ester linkage can undergo two successive Michael reactions, allowing the selective modification of disulfides bonds with high labeling efficiency and good conjugate stability.

2-Chloromethyl acryl derivatives (acrylamides and acrylates) can serve as simple and versatile bioconjugation reagents to achieve site-selective cysteine and disulfide modification on demand and with high efficiency.

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.

Nanohybrids as Protein-Polymer Conjugate Multimodal Therapeutics

Protein therapeutic formulations are being widely explored as multifunctional nanotherapeutics. Challenges in ensuring susceptibility and efficacy of nanoformulation still prevail owing to various interactions with biological fluids before reaching the target site. Smart polymers with the capability of masking drugs, ease of chemical modification, and multi-stimuli responsiveness can assist controlled delivery. An active moiety like therapeutic protein has started to be known as an important biological formulation with a diverse medicinal prospect. The delivery of proteins and peptides with high target specificity has however been tedious, due to their tendency to aggregate formation in different environmental conditions. Proteins due to high chemical reactivity and poor bioavailability are being researched widely in the field of nanomedicine. Clinically, multiple nano-based formulations have been explored for delivering protein with different carrier systems. A biocompatible and non-toxic polymer-based delivery system serves to tailor the polymer or drug better. Polymers not only aid delivery to the target site but are also responsible for proper stearic orientation of proteins thus protecting them from internal hindrances. Polymers have been shown to conjugate with proteins through covalent linkage rendering stability and enhancing therapeutic efficacy prominently when dealing with the systemic route. Here, we present the recent developments in polymer-protein/drug-linked systems. We aim to address questions by assessing the properties of the conjugate system and optimized delivery approaches. Since thorough characterization is the key aspect for technology to enter into the market, correlating laboratory research with commercially available formulations will also be presented in this review. By examining characteristics including morphology, surface properties, and functionalization, we will expand different hybrid applications from a biomaterial stance applied in in vivo complex biological conditions. Further, we explore understanding related to design criteria and strategies for polymer-protein smart nanomedicines with their potential prophylactic theranostic applications. Overall, we intend to highlight protein-drug delivery through multifunctional smart polymers.

Weaving Enzymes with Polymeric Shells for Biomedical Applications

Enzyme therapeutics have received increasing attention due to their high biological specificity, outstanding catalytic efficiency, and impressive therapeutic outcomes. Protecting and delivering enzymes into target cells while retaining enzyme catalytic efficiency is a big challenge. Wrapping of enzymes with rational designed polymer shells, rather than trapping them into large nanoparticles such as liposomes, have been widely explored because they can protect the folded state of the enzyme and make post-functionalization easier. In this review, the methods for wrapping up enzymes with protective polymer shells are mainly focused on. It is aimed to provide a toolbox for the rational design of polymeric enzymes by introducing methods for the preparation of polymeric enzymes including physical adsorption and chemical conjugation with specific examples of these conjugates/hybrid applications. Finally, a conclusion is drawn and key points are emphasized.

Intracellular Delivery of Proteins into Living Cells by Low-Molecular-Weight Polyethyleneimine

Introduction

Intracellular protein delivery is emerging as a potential strategy to revolutionize therapeutics in the field of biomedicine, aiming at treating a wide range of diseases including cancer, inflammatory diseases and other oxidative stress-related disorders with high specificity. However, the current challenges and limitations are addressed to either synthetically or biologically through multipotency of engineering, such as protein modification, insufficient delivery of large-size proteins, deficiency or mutation of proteins, and high cytotoxicity.

Methods

We prepared the nanocomposites by mixing protein with PEI1200 at a certain molar ratio and demonstrated that it can deliver proteins into living cells in high efficiency and safety through the following experiments, such as dynamic light scattering, fluorescent detection, agarose gel electrophoresis, ß-Galactosidase activity detection, immunofluorescence staining, digital fluorescent detection, cell viability assay and flow cytometry.

Results

The self-assembly of PEI1200/protein nanocomposites with appropriate molar ratio (4:1 and 8:1) could provide efficiently delivery of active proteins to a variety of cell types in the presence of serum. The nanocomposites could continuously release protein up to 96 h in their desired intracellular locations. In addition, these nanocomposites were able to preserve protein activity while maintain low cytotoxicity (when final concentration <1 μg/mL).

Conclusion

Collectively, PEI1200-based delivery system provided an alternative strategy to direct protein delivery in high efficiency and safety, offering increased potential applications in clinical biomedicine.

Polypeptides-Drug Conjugates for Anticancer Therapy

Polypeptides are an important class of biodegradable polymers that have been widely used in drug delivery field. Owing to the controllable synthesis and robust side chain-functionalization ability, polypeptides have long been ideal candidates for conjugation with anticancer drugs. The chemical conjugation of anticancer drugs with polypeptides, termed polypeptides-drug conjugates, has demonstrated several advantages in improving pharmacokinetics, enhancing drug targeting, and controlling drug release, thereby leading to enhanced therapeutic outcomes with reduced side toxicities. This review focuses on the recent advances in the design and preparation of polypeptides-drug conjugates for enhanced anticancer therapy. Strategies for conjugation of different types of drugs, including small-molecule chemotherapeutic drugs, proteins, vascular disrupting agents, and gas molecules, onto polypeptides backbone are summarized. Finally, the challenges and future perspectives on the development of innovative polypeptides-drug conjugates for clinical cancer treatment are also presented.

Sustained Release Systems for Delivery of Therapeutic Peptide/Protein

Peptide/protein therapeutics have been significantly applied in the clinical treatment of various diseases such as cancer, diabetes, etc. owing to their high biocompatibility, specificity, and therapeutic efficacy. However, due to their immunogenicity, instability stemming from its complex tertiary and quaternary structure, vulnerability to enzyme degradation, and rapid renal clearance, the clinical application of protein/peptide therapeutics is significantly confined. Though nanotechnology has been demonstrated to prevent enzyme degradation of the protein therapeutics and thus enhance the half-life, issues such as initial burst release and uncontrollable release kinetics are still unsolved. Moreover, the traditional administration method results in poor patient compliance, limiting the clinical application of protein/peptide therapeutics. Exploiting the sustained-release formulations for more controllable delivery of protein/peptide therapeutics to decrease the frequency of injection and enhance patient compliance is thus greatly meaningful. In this review, we comprehensively summarize the substantial advancements of protein/peptide sustained-release systems in the past decades. In addition, the advantages and disadvantages of all these sustained-release systems in clinical application together with their future challenges are also discussed in this review.

α-Amino acid N-carboxyanhydride (NCA)-derived synthetic polypeptides for nucleic acids delivery

In recent years, gene therapy has come into the spotlight for the prevention and treatment of a wide range of diseases. Polypeptides have been widely used in mediating nucleic acid delivery, due to their versatilities in chemical structures, desired biodegradability, and low cytotoxicity. Chemistry plays an essential role in the development of innovative polypeptides to address the challenges of producing efficient and safe gene vectors. In this Review, we mainly focused on the latest chemical advances in the design and preparation of polypeptide-based nucleic acid delivery vehicles. We first discussed the synthetic approach of polypeptides via ring-opening polymerization (ROP) of N-carboxyanhydrides (NCAs), and introduced the various types of polypeptide-based gene delivery systems. The extracellular and intracellular barriers against nucleic acid delivery were then outlined, followed by detailed review on the recent advances in polypeptide-based delivery systems that can overcome these barriers to enable in vitro and in vivo gene transfection. Finally, we concluded this review with perspectives in this field.

Biological applications of water-soluble polypeptides with ordered secondary structures

Water-soluble polypeptides are a class of synthetic polymers with peptide bond frameworks imitating natural proteins and have broad prospects in biological applications. The regulation and dynamic transition of the secondary structures of water-soluble polypeptides have a great impact on their physio-chemical properties and biological functions. In this review article, we briefly introduce the current strategies to synthesize polypeptides and modulate their secondary structures. We then discuss the factors affecting the conformational stability/transition of polypeptides and the potential impact of side-chain functionalization on the ordered secondary structures, such as α-helix and β-sheet. We then summarize the biological applications of water-soluble polypeptides such as cell penetration, gene delivery, and antimicrobial treatment, highlighting the important roles of ordered secondary structures therein.

Conformation of Myoglobin-Poly(Ethyl Ethylene Phosphate) Conjugates Probed by SANS: Correlation with Polymer Grafting Density and Interaction

One can take advantage of the influence of a polymer conjugated with a protein to control the thermal stability and the deployment of the protein. Here, the structural properties are reported of the protein-polymer conjugate myoglobin (Mb)-poly(ethyl ethylene phosphate) (PEEP) in the native and unfolded conformations, in order to understand the respective roles of the protein and of the polymer size in the stability of the conjugate. The effect is also investigated of the grafting density of the linear biodegradable polyphosphoesters covalently attached to the protein. It is observed that, while the conjugation process at room temperature does not modify the secondary and tertiary structure of the Mb, the unfolding process, as a function of temperature, depends on the grafting density. Small angle neutron scattering reveals that, at room temperature, conjugation does not alter the size of the native protein and that the thickness of the polymer shell around the protein increases as a function of grafting density and of polymer molecular weight. The denatured form of all conjugates is described by an unfolded chain and a correlation length due to the presence of local stiffness.

A zwitterionic polypeptide nanocomposite with unique NIR-I/II photoacoustic imaging for NIR-I/II cancer photothermal therapy

The second near infrared photoacoustic imaging (NIR-II PAI) and photothermal therapy (NIR-II PTT) have attracted wide interest in cancer theranostics because of maximum permission exposure (MPE), deep penetration, and lower scattering and background noise compared to NIR-I counterparts; however, it is imperative to develop biocompatible nanomaterials having NIR-II response. By utilizing multivalent Au-S coordination bonds, we constructed a zwitterionic polypeptide nanocomposite of PMC@AuNP with a suitable size of 48 ± 2 nm, which possessed a strong and broad absorbance at 650-1100 nm and an excellent photothermal conversion efficiency of 49.5%. In vitro biological studies demonstrated that NIR-II PTT within MPE was more effective than NIR-I PTT beyond MPE. Along with X-ray computed tomography and photothermal imaging functions, PMC@AuNP in vivo presented unique NIR-I/II PAI with 2.6-5.9 times signal enhancement compared to the contrast. By single dose and NIR-II irradiation (1064 nm, 1 W cm-2, 10 min), NIR-II PTT within MPE completely eradicated MCF-7 tumors without tissue damage and tumor recurrence within 24 days, inducing a better antitumor efficacy than NIR-I PTT beyond MPE. Importantly, this study provides an innovative method for the fabrication of biocompatible zwitterionic polypeptide nanocomposites with unique NIR-I/II PAI and NIR-II PTT attributes, thus holding great potential for precise cancer theranostics and further clinical transitions.

Mechanistic Understanding From Molecular Dynamics Simulation in Pharmaceutical Research 1: Drug Delivery

In this review, we outline the growing role that molecular dynamics simulation is able to play as a design tool in drug delivery. We cover both the pharmaceutical and computational backgrounds, in a pedagogical fashion, as this review is designed to be equally accessible to pharmaceutical researchers interested in what this new computational tool is capable of and experts in molecular modeling who wish to pursue pharmaceutical applications as a context for their research. The field has become too broad for us to concisely describe all work that has been carried out; many comprehensive reviews on subtopics of this area are cited. We discuss the insight molecular dynamics modeling has provided in dissolution and solubility, however, the majority of the discussion is focused on nanomedicine: the development of nanoscale drug delivery vehicles. Here we focus on three areas where molecular dynamics modeling has had a particularly strong impact: (1) behavior in the bloodstream and protective polymer corona, (2) Drug loading and controlled release, and (3) Nanoparticle interaction with both model and biological membranes. We conclude with some thoughts on the role that molecular dynamics simulation can grow to play in the development of new drug delivery systems.

Strategies to expand the therapeutic potential of superoxide dismutase by exploiting delivery approaches

The overproduction of free radicals can cause oxidative-stress damage to a range of biomolecules, and thus potentially contribute to several pathologies, from neurodegenerative disorders to cardiovascular diseases and metabolic disorders. Endogenous antioxidant enzymes, such as superoxide dismutase (SOD), play an important role in diminishing oxidative stress. SOD supplementation could therefore be an effective preventive strategy to reduce the risk of free-radical overproduction. However, the efficacy of SOD administration is hampered by its rapid clearance. Several different approaches to improve the bioavailability of SOD have been explored in recent decades. This review intends to describe the rationale that underlie the various approaches and chemical strategies that have led to the most recent advances in SOD delivery. This critical description includes SOD conjugates, SOD loaded into particulate carriers (micelles, liposomes, nanoparticles, microparticles) and the most promising and suitable formulations for oral delivery, with a particular emphasis on reports of preclinical/clinical results. Likely future directions are also considered and reported.

Biomolecular Densely Grafted Brush Polymers: Oligonucleotides, Oligosaccharides and Oligopeptides

In this Minireview, we describe synthetic polymers densely functionalized with sequence-defined biomolecular sidechains. We focus on synthetic brush polymers of oligonucleotides, oligosaccharides, and oligopeptides, prepared via graft-through polymerization from biomolecule functionalized monomers. The resulting structures are brush polymers wherein a biomolecular graft is positioned at each monomer backbone unit. We describe key synthetic milestones, identify synthetic opportunities, and highlight recent advances in the field, including biological applications.