Templated Self-Assembly of a Covalent Polymer Network for Intracellular Protein Delivery and Traceless Release

Polymer conjugation benefits proteins beyond simply extended half-life

Polymer conjugation is well known to extend the half-life of proteins in the bloodstream. The resulting protein-polymer conjugates have gained tremendous success due to this benefit, most prominently with the numerous PEGylated protein therapeutics that have been approved by the Food and Drug Administration (FDA). Prolonged half-life of protein therapeutics is usually accompanied by improved therapeutic outcome and patient compliance. However, simply extending the half-life of proteins is no longer sufficient to address the different therapeutic requirements of different diseases. Modern medicine has placed higher functional demands for protein therapeutics, such as biological barrier permeability, lower off-target effects, and higher biosafety. Indeed, the benefits of polymer conjugation for proteins have been greatly expanded beyond just extending the half-life, such as improving therapeutic index, facilitating intracellular delivery, remodeling biodistribution, penetrating the blood-brain barrier, and promoting oral absorption. Therefore, this short review will aim to systematically reveal the benefits of polymer conjugation for proteins at molecular, nanoscale, cellular, tissue, organ, and organ system level. The challenge and new direction for the development and clinical translation of protein-polymer conjugates are also covered. STATEMENT OF SIGNIFICANCE: Since the concept was pioneered by Frank Davis in the late 1960s, protein-polymer conjugates have gained tremendous success. Therapeutics based on protein-polymer conjugates have longer half-lives in the bloodstream compared to their native forms, which reduces dosing frequency and greatly enhances patient compliance. Indeed, beyond improved pharmacokinetic, protein-polymer conjugates have demonstrated multifaceted biological benefits, such as facilitating intracellular delivery, penetrating tissue barriers, remodeling biodistribution, and promoting oral absorption. This review aims to systematically reveal the benefits of polymer conjugation for proteins at the molecular, nanoscale, cellular, tissue, organ, and organ system level. Such comprehensive understanding will not only broaden the impact of protein-polymer conjugates, but also enable researchers to advance their development in the desired direction.

Efficient Direct Cytosolic Protein Delivery via Protein-Linker Co-engineering

Protein therapeutics have enormous potential for transforming the treatment of intracellular cell disorders, such as genetic disorders and cancers. Due to proteins' cell-membrane impermeability, protein-based drugs against intracellular targets require efficient cytosolic delivery strategies; however, none of the current approaches are optimal. Here, we present a simple approach to render proteins membrane-permeable. We use arginine-mimicking ligand N,N'-dimethyl-1,3-propanediamine (DMPA) to functionalize the surface of a few representative proteins, varying in isoelectric point and molecular weight. We show that when these proteins have a sufficient number of these ligands on their surface, they acquire the property of penetrating the cell cytosol. Uptake experiments at 37 and 4 °C indicate that one of the penetration pathways is energy independent, with no evidence of pore formation, with inhibition assays indicating the presence of other uptake pathways. Functional tests demonstrate that the modified proteins maintain their main cellular function; specifically, modified ovalbumin (OVA) leads to enhanced antigen presentation and modified cytochrome C (Cyto C) leads to enhanced cell apoptosis. We modified bovine serum albumin (BSA) with ligands featuring different hydrophobicity and end group charges and showed that, to confer cytosolic penetration, the ligands must be cationic and that some hydrophobic content improves the penetration efficiency. This study provides a simple strategy for efficiently delivering proteins directly to the cell cytosol and offers important insights into the design and development of arginine-rich cell-penetrating peptide mimetic small molecules for protein transduction.

Calixarene Modification Strategy for Efficient Intracellular Protein Delivery

Efficient intracellular protein delivery is of great importance for the development of protein-based therapy and modern biotechnologies. However, the hydrophilic and macromolecular nature of proteins greatly hinders their ability to cross cell membranes. Herein, a calixarene modification strategy for the intracellular delivery of protein drugs is developed. The decoration of sulfonate azocalix[4]arene (SAC4A) on proteins results in a nano-multivalent effect between Protein-S and amino acids on the cell surface, leading to efficient intracellular delivery of the protein via the clathrin-mediated endocytic pathway. By using SAC4A as a novel ligand, this calixarene modification strategy efficiently delivers 7 proteins, bovine serum albumin (BSA), trypsin (TRY), horseradish peroxidase (HRP), α-chymotrypsin (α-Chyt), lysozyme (LYZ), cytochrome C (Cyt C) and ribonuclease A (RNase A), into cells and significantly enhances the cytotoxicity of Cyt C and RNase A. Moreover, SAC4A-modified Cyt C demonstrates markedly enhanced antitumor efficacy in 4T1-bearing mice without notable side effects. Considering that these proteins are varied in molecular weight and isoelectric point, this calixarene modification strategy provides a platform technology for intracellular protein delivery and the development of protein drugs targeting intracellular pathways.

Engineering RAFT Polymers to the Protein-capped Gold Nanoclusters for Developing Fluorescent Polymeric Nanoconjugates

The synthesis of fluorescent hybrid nanomaterials engineered via the chain-end modification of reversible addition-fragmentation chain-transfer (RAFT) polymers on the surface of bovine serum albumin (BSA) protein-stabilized gold nanoclusters (AuNCs@BSA) is described. Based on the "grafting-to" approach the core-shell structured nanoconjugates AuNCs@BSA/polymer are generated via effective ligation of hydrophilic, and stimuli-responsive polymers. Such nanomaterials are characterized via various microscopic and spectroscopic studies and exhibit their size as ≈5 nm and emission peak at ≈650 nm. Interestingly, the conjugation of thermoresponsive polymer poly(diethylene glycol monomethyl ether methacrylate) (PDEGMA) transformed the nanoconjugates AuNCs@BSA/PDEGMA as dual thermo/pH-responsive nanomaterials.

Intracellular Delivery of Proteins by Protein-Recognizing Nanoparticles

Intracellular delivery of proteins can directly impact dysregulated and dysfunctional proteins and is a key step in the fast growing field of protein therapeutics. The vast majority of protein-delivery systems enter cells through endocytic pathways, but endosomal escape is a difficult and inefficient process, demanding fundamentally different methods of delivery. We report ultrasmall cationic molecularly imprinted nanoparticles that bind protein targets with high specificity through their uniquely distributed surface lysine groups. The nanoparticle-protein complexes enter cells even when energy-dependent endocytic pathways are inhibited. The micromolar binding affinities of the nanoparticle for the proteins are strong enough for the cargos to be bound during loading and transportation but weak enough to be released into cytosol for them to interact with the desired cellular targets. The nanoparticles display low cytotoxicity to cells and can be functionalized with fluorescent labels through click chemistry for easy tracking. Both the molecular imprinting and delivery work well for proteins with a range of molecular weights and isoelectric points, affording a convenient method to manipulate cellular functions and intracellular reactions through delivered proteins.

Chemoselective Reagents for the Traceless Bioreversible Modification of Native Proteins

Nature utilizes bioreversible post-translational modifications (PTMs) to spatiotemporally diversify protein function. Mimicking Nature's approach, chemists have developed a variety of chemoselective regents for traceless, bioreversible modification of native proteins. These strategies have found utility in the development of reversible covalent inhibitors and degraders as well as the synthesis of functional protein conjugates for delivery into cells. This Viewpoint provides a snapshot of such tools, which currently cover Cys, Ser, Thr, Lys, Asp, and Glu residues and the N terminus. Additionally, we explore how bioreversible reagents, originally developed by research communities with differing objectives, can be utilized synergistically. Looking forward, we discuss the need for developing bioreversible reagents for labeling His, Tyr, Arg, Trp, Asn, Gln, and Met residues and the C-terminus as well as the installation of dynamic PTMs. Finally, to broaden the applicability of these tools, we point out the importance of developing modular release scaffolds with tunable release times and responsiveness to multiple endogenous triggers. We anticipate that this Viewpoint will catalyze further research and technological breakthroughs in this rapidly evolving field.

3D-Printed Phenylboronic Acid-Bearing Hydrogels for Glucose-Triggered Drug Release

Diabetes is a major health concern that the next-generation of on-demand insulin releasing implants may overcome via personalized therapy. Therein, 3D-printed phenylboronic acid-containing implants with on-demand glucose-triggered drug release abilities are produced using high resolution stereolithography technology. To that end, the methacrylation of phenylboronic acid is targeted following a two-step reaction. The resulting photocurable phenylboronic acid derivative is accordingly incorporated within bioinert polyhydroxyethyl methacrylate-based hydrogels at varying loadings. The end result is a sub-centimeter scaled 3D-printed bioinert implant that can be remotely activated with 1,2-diols and 1,3-diols such as glucose for on-demand drug administration such as insulin. As a proof of concept, varying glucose concentration from hypoglycemic to hyperglycemic levels readily allow the release of pinacol, i.e., a 1,2-diol-containing model molecule, at respectively low and high rates. In addition, the results demonstrated that adjusting the geometry and size of the 3D-printed part is a simple and suitable method for tailoring the release behavior and dosage.

Protein Immobilization on Bacterial Cellulose for Biomedical Application

New carriers for protein immobilization are objects of interest in various fields of biomedicine. Immobilization is a technique used to stabilize and provide physical support for biological micro- and macromolecules and whole cells. Special efforts have been made to develop new materials for protein immobilization that are non-toxic to both the body and the environment, inexpensive, readily available, and easy to modify. Currently, biodegradable and non-toxic polymers, including cellulose, are widely used for protein immobilization. Bacterial cellulose (BC) is a natural polymer with excellent biocompatibility, purity, high porosity, high water uptake capacity, non-immunogenicity, and ease of production and modification. BC is composed of glucose units and does not contain lignin or hemicellulose, which is an advantage allowing the avoidance of the chemical purification step before use. Recently, BC-protein composites have been developed as wound dressings, tissue engineering scaffolds, three-dimensional (3D) cell culture systems, drug delivery systems, and enzyme immobilization matrices. Proteins or peptides are often added to polymeric scaffolds to improve their biocompatibility and biological, physical-chemical, and mechanical properties. To broaden BC applications, various ex situ and in situ modifications of native BC are used to improve its properties for a specific application. In vivo studies showed that several BC-protein composites exhibited excellent biocompatibility, demonstrated prolonged treatment time, and increased the survival of animals. Today, there are several patents and commercial BC-based composites for wounds and vascular grafts. Therefore, further research on BC-protein composites has great prospects. This review focuses on the major advances in protein immobilization on BC for biomedical applications.

Activable Nano-Immunomodulator Assembled from π-Extended Naphthalenediimide for Precision Photothermal Immunotherapy

A nano-immunomodulator (R-NPT NP) comprising a tumor microenvironment (TME) activable resiquimod (R848) and a π-extended NIR-absorbing naphthophenanthrolinetetraone (NPT) has been engineered for spatiotemporal controlled photothermal immunotherapy. R-NPT NP demonstrated excellent photostability, while R848 promoted synergistic immunity as a toll-like receptor 7/8 (TLR7/8) agonist. Upon accumulation at the tumor site, R-NPT NP released R848 in response to redox metabolite glutathione (GSH), triggering dendritic cell (DC) activation. The photothermal effect endowed by R-NPT NP can ablate tumors directly and trigger immunogenic cell death to augment immunity after photoirradiation. The synergistic effect of GSH-liable TLR7/8 agonist and released immunogenic factors leads to a robust evocation of systematic immunity through promoted DC maturation and T cell infiltration. Thus, R-NPT NP with photoirradiation achieved 99.3 % and 98.2 % growth inhibition against primary and distal tumors, respectively.

Sub-100 nm carriers by template polymerization for drug delivery applications

Size-controlled drug delivery systems (DDSs) have gained significant attention in the field of pharmaceutical sciences due to their potential to enhance drug efficacy, minimize side effects, and improve patient compliance. This review provides a concise overview of the preparation method, advancements, and applications of size-controlled drug delivery systems focusing on the sub-100 nm size DDSs. The importance of tailoring the size for achieving therapeutic goals is briefly mentioned. We highlight the concept of "template polymerization", a well-established method in covalent polymerization that offers precise control over molecular weight. We demonstrate the utility of this approach in crafting a monolayer of a polymer around biomolecule templates such as DNA, RNA, and protein, achieving the generation of DDSs with sizes ranging from several tens of nanometers. A few representative examples of small-size DDSs that share a conceptual similarity to "template polymerization" are also discussed. This review concludes by briefly discussing the drug release behaviors and the future prospects of "template polymerization" for the development of innovative size-controlled drug delivery systems, which promise to optimize drug delivery precision, efficacy, and safety.

Bioreducible Amphiphilic Hyperbranched Polymer-Drug Conjugate for Intracellular Drug Delivery

This paper reports synthesis of a bioreducible hyperbranched (HB) polymer by A2+B3 approach from commercially available dithiothreitol (DTT) (A2) and an easily accessible trifunctional monomer (B3) containing three reactive pyridyl-disulfide groups. Highly efficient thiol-activated disulfide exchange reaction leads to the formation of the HB polymer (Mw = 21000; Đ = 2.3) with bioreducible disulfide linkages in the backbone and two different functional groups, namely, hydroxyl and pyridyl-disulfide in the core and periphery, respectively, of the HB-polymer. Postpolymerization functionalization of the hydroxyl-groups with camptothecin (CPT), a topoisomerase inhibitor and known anticancer drug, followed by replacing the terminal pyridyl-disulfide groups with oligo-oxyethylene-thiol resulted in easy access to an amphiphilic HB polydisulfide-CPT conjugate (P1) with a very high drug loading content of ∼40%. P1 aggregated in water (above ∼10 μg/mL) producing drug-loaded nanoparticles (Dh ∼ 135 nm), which showed highly efficient glutathione (GSH)-triggered release of the active CPT. Mass spectrometry analysis of the GSH-treated P1 showed the presence of the active CPT drug as well as a cyclic monothiocarbonate product, which underpins the cascade-degradation mechanism involving GSH-triggered cleavage of the labile disulfide linkage, followed by intramolecular nucleophilic attack by the in situ generated thiol to the neighboring carbonate linkage, resulting in release of the active CPT drug. The P1 nanoparticle showed excellent cellular uptake as tested by confocal fluorescence microscopy in HeLa cells by predominantly endocytosis mechanism, resulting in highly efficient cell killing (IC50 ∼ 0.6 μg/mL) as evident from the results of the MTT assay, as well as the apoptosis assay. Comparative studies with an analogous linear polymer-CPT conjugate showed much superior intracellular drug delivery potency of the hyperbranched polymer.

Structural Determinants of Stimuli-Responsiveness in Amphiphilic Macromolecular Nano-assemblies

Stimuli-responsive nano-assemblies from amphiphilic macromolecules could undergo controlled structural transformations and generate diverse macroscopic phenomenon under stimuli. Due to the controllable responsiveness, they have been applied for broad material and biomedical applications, such as biologics delivery, sensing, imaging, and catalysis. Understanding the mechanisms of the assembly-disassembly processes and structural determinants behind the responsive properties is fundamentally important for designing the next generation of nano-assemblies with programmable responsiveness. In this review, we focus on structural determinants of assemblies from amphiphilic macromolecules and their macromolecular level alterations under stimuli, such as the disruption of hydrophilic-lipophilic balance (HLB), depolymerization, decrosslinking, and changes of molecular packing in assemblies, which eventually lead to a series of macroscopic phenomenon for practical purposes. Applications of stimuli-responsive nano-assemblies in delivery, sensing and imaging were also summarized based on their structural features. We expect this review could provide readers an overview of the structural considerations in the design and applications of nanoassemblies and incentivize more explorations in stimuli-responsive soft matters.

Synthesis of bioactive hemoglobin-based oxygen carrier nanoparticles via metal-phenolic complexation

The transfusion of donor red blood cells (RBCs) is seriously hampered by important drawbacks that include limited availability and portability, the requirement of being stored in refrigerated conditions, a short shelf life or the need for RBC group typing and crossmatching. Thus, hemoglobin (Hb)-based oxygen (O2) carriers (HBOCs) which make use of the main component of RBCs and the responsible protein for O2 transport, hold a lot of promise in modern transfusion and emergency medicine. Despite the great progress achieved, it is still difficult to create HBOCs with a high Hb content to attain the high O2 demands of our body. Herein a metal-phenolic self-assembly approach that can be conducted in water and in one step to prepare nanoparticles (NPs) fully made of Hb (Hb-NPs) is presented. In particular, by combining Hb with polyethylene glycol, tannic acid (TA) and manganese ions, spherical Hb-NPs with a uniform size around 350-525 nm are obtained. The functionality of the Hb-NPs is preserved as shown by their ability to bind and release O2 over multiple rounds. The binding mechanism of TA and Hb is thoroughly investigated by UV-vis absorption and fluorescence spectroscopy. The binding site number, apparent binding constant at two different temperatures and the corresponding thermodynamic parameters are identified. The results demonstrate that the TA-Hb interaction takes place through a static mechanism in a spontaneous process as shown by the decrease in Gibbs free energy. The associated increase in entropy suggests that the TA-Hb binding is dominated by hydrophobic interactions.

Smart chemistry for traceless release of anticancer therapeutics

In the design of delivery strategies for anticancer therapeutics, the controlled release of intact cargo at the destined tumor and metastasis locations is of particular importance. To this end, stimuli-responsive chemical linkers have been extensively investigated owing to their ability to respond to tumor-specific physiological stimuli, such as lowered pH, altered redox conditions, increased radical oxygen species and pathological enzymatic activities. To prevent premature action and off-target effects, anticancer therapeutics are chemically modified to be transiently inactivated, a strategy known as prodrug development. Prodrugs are reactivated upon stimuli-dependent release at the sites of interest. As most drugs and therapeutic proteins have the optimal activity when released from carriers in their native and original forms, traceless release mechanisms are increasingly investigated. In this review, we summarize the chemical toolkit for developing innovative traceless prodrug strategies for stimuli-responsive drug delivery and discuss the applications of these chemical modifications in anticancer treatment including cancer immunotherapy.

Engineering Nucleotidoproteins for Base-Pairing-Assisted Cytosolic Delivery and Genome Editing

Protein therapeutics targeting intracellular machineries hold profound potential for disease treatment, and hence robust cytosolic protein delivery technologies are imperatively demanded. Inspired by the super-negatively charged, nucleotide-enriched structure of nucleic acids, adenylated pro-proteins (A-proteins) with dramatically enhanced negative surface charges have been engineered for the first time via facile green synthesis. Then, thymidine-modified polyethyleneimine is developed, which exhibits strong electrostatic attraction, complementary base pairing, and hydrophobic interaction with A-proteins to form salt-resistant nanocomplexes with robust cytosolic delivery efficiencies. The acidic endolysosomal environment enables traceless restoration of the A-proteins and consequently promotes the intracellular release of the native proteins. This strategy shows high efficiency and universality for a variety of proteins with different molecular weights and isoelectric points in mammalian cells. Moreover, it enables highly efficient delivery of CRISPR-Cas9 ribonucleoproteins targeting fusion oncogene EWSR1-FLI1, leading to pronounced anti-tumor efficacy against Ewing sarcoma. This study provides a potent and versatile platform for cytosolic protein delivery and gene editing, and may benefit the development of protein pharmaceuticals.

Protein-based Nanoparticles: From Drug Delivery to Imaging, Nanocatalysis and Protein Therapy

Proteins and enzymes are versatile biomaterials for a wide range of medical applications due to their high specificity for receptors and substrates, high degradability, low toxicity, and overall good biocompatibility. Protein nanoparticles are formed by the arrangement of several native or modified proteins into nanometer-sized assemblies. In this review, we will focus on artificial nanoparticle systems, where proteins are the main structural element and not just an encapsulated payload. While under natural conditions, only certain proteins form defined aggregates and nanoparticles, chemical modifications or a change in the physical environment can further extend the pool of available building blocks. This allows the assembly of many globular proteins and even enzymes. These advances in preparation methods led to the emergence of new generations of nanosystems that extend beyond transport vehicles to diverse applications, from multifunctional drug delivery to imaging, nanocatalysis and protein therapy.

Nucleic-Acid-Templated Synthesis of Smart Polymer Vectors for Gene Delivery

Nucleic acids are information-rich and readily available biomolecules, which can be used to template the polymerization of synthetic macromolecules. Here, we highlight the control over the size, composition, and sequence one can nowadays obtain by using this methodology. We also highlight how templated processes exploiting dynamic covalent polymerization can, in return, result in therapeutic nucleic acids fabricating their own dynamic delivery vector - a biomimicking concept that can provide original solutions for gene therapies.

Antibody Polymer Conjugates (APCs) for Active Targeted Therapeutic Delivery

Antibody drug conjugates (ADCs) are poised to have an enormous impact on targeted nanomedicine, especially in many cancer pathologies. The reach of the current format of ADCs is limited by their low drug-to-antibody ratio (DAR) because of the associated physiochemical instabilities. Here, we design antibody polymer conjugates (APCs) as a modular strategy to utilize polymers to address ADC's shortcomings. We show here that conjugation of polymer-based therapeutic molecules to antibodies helps increase the DAR, owing to the hydrophilic comonomer in the polymer that helps in masking the increased hydrophobicity caused by high drug loading. We show that the platform exhibits cell targetability and selective cell killing in multiple cell lines expressing disease-relevant antigens, viz., HER2 and EGFR. The ability to use different functionalities in the drug as the handle for polymer attachment further demonstrates the platform nature of APCs. The findings here could serve as an alternative design strategy for the next generation of active targeted nanomedicine.

Conferring liver selectivity to a thyromimetic using a novel nanoparticle increases therapeutic efficacy in a diet-induced obesity animal model

Optimization of metabolic regulation is a promising solution for many pathologies, including obesity, dyslipidemia, type 2 diabetes, and inflammatory liver disease. Synthetic thyroid hormone mimics-based regulation of metabolic balance in the liver showed promise but was hampered by the low biocompatibility and harmful effects on the extrahepatic axis. In this work, we show that specifically directing the thyromimetic to the liver utilizing a nanogel-based carrier substantially increased therapeutic efficacy in a diet-induced obesity mouse model, evidenced by the near-complete reversal of body weight gain, liver weight and inflammation, and cholesterol levels with no alteration in the thyroxine (T4) / thyroid stimulating hormone (TSH) axis. Mechanistically, the drug acts by binding to thyroid hormone receptor β (TRβ), a ligand-inducible transcription factor that interacts with thyroid hormone response elements and modulates target gene expression. The reverse cholesterol transport (RCT) pathway is specifically implicated in the observed therapeutic effect. Overall, the study demonstrates a unique approach to restoring metabolic regulation impacting obesity and related metabolic dysfunctions.

Functional L-Arginine Derivative as an Efficient Vector for Intracellular Protein Delivery for Potential Cancer Therapy

The utilization of cytosolic protein delivery is a promising approach for treating various diseases by replacing dysfunctional proteins. Despite the development of various nanoparticle-based intracellular protein delivery methods, the complicated chemical synthesis of the vector, loading efficiency and endosomal escape efficiency of proteins remain a great challenge. Recently, 9-fluorenylmethyloxycarbonyl (Fmoc)-modified amino acid derivatives have been used to self-assemble into supramolecular nanomaterials for drug delivery. However, the instability of the Fmoc group in aqueous medium restricts its application. To address this issue, the Fmoc ligand neighboring arginine was substituted for dibenzocyclooctyne (DBCO) with a similar structure to Fmoc to obtain stable DBCO-functionalized L-arginine derivative (DR). Azide-modified triethylamine (crosslinker C) was combined with DR to construct self-assembled DRC via a click chemical reaction for delivering various proteins, such as BSA and saporin (SA), into the cytosol of cells. The hyaluronic-acid-coated DRC/SA was able to not only shield the cationic toxicity, but also enhance the intracellular delivery efficiency of proteins by targeting CD44 overexpression on the cell membrane. The DRC/SA/HA exhibited higher growth inhibition efficiency and lower IC₅₀ compared to DRC/SA toward various cancer cell lines. In conclusion, DBCO-functionalized L-arginine derivative represents an excellent potential vector for protein-based cancer therapy.

Intracellular delivery of therapeutic proteins. New advancements and future directions

Achieving the full potential of therapeutic proteins to access and target intracellular receptors will have enormous benefits in advancing human health and fighting disease. Existing strategies for intracellular protein delivery, such as chemical modification and nanocarrier-based protein delivery approaches, have shown promise but with limited efficiency and safety concerns. The development of more effective and versatile delivery tools is crucial for the safe and effective use of protein drugs. Nanosystems that can trigger endocytosis and endosomal disruption, or directly deliver proteins into the cytosol, are essential for successful therapeutic effects. This article aims to provide a brief overview of the current methods for intracellular protein delivery to mammalian cells, highlighting current challenges, new developments, and future research opportunities.

Optimizing Conjugation Chemistry, Antibody Conjugation Site, and Surface Density in Antibody-Nanogel Conjugates (ANCs) for Cell-Specific Drug Delivery

Targeted delivery of therapeutics using antibody-nanogel conjugates (ANCs) with a high drug-to-antibody ratio has the potential to overcome some of the inherent limitations of antibody-drug conjugates (ADCs). ANC platforms with simple preparation methods and precise tunability to evaluate structure-activity relationships will greatly contribute to translating this promise into clinical reality. In this work, using trastuzumab as a model antibody, we demonstrate a block copolymer-based ANC platform that allows highly efficient antibody conjugation and formulation. In addition to showcasing the advantages of using an inverse electron-demand Diels-Alder (iEDDA)-based antibody conjugation, we evaluate the influence of antibody surface density and conjugation site on the nanogels upon the targeting capability of ANCs. We show that compared to traditional strain-promoted alkyne-azide cycloadditions, the preparation of ANCs using iEDDA provides significantly higher efficiency, which results in a shortened reaction time, simplified purification process, and enhanced targeting toward cancer cells. We also find that a site-specific disulfide-rebridging method in antibodies offers similar targeting abilities as the more indiscriminate lysine-based conjugation method. The more efficient bioconjugation using iEDDA allows us to optimize the avidity by fine-tuning the surface density of antibodies on the nanogel. Finally, with trastuzumab-mertansine (DM1) antibody-drug combination, our ANC demonstrates superior activities in vitro compared to the corresponding ADC, further highlighting the potential of ANCs in future clinical translation.

A light-activated polymer with excellent serum tolerance for intracellular protein delivery

The design of efficient materials for intracellular protein delivery has attracted great interest in recent years; however, most current materials for this purpose are limited by poor serum stability due to the early release of cargoes triggered by abundant serum proteins. Here, we propose a light-activated crosslinking (LAC) strategy to prepare efficient polymers with excellent serum tolerance for intracellular protein delivery. A cationic dendrimer engineered with photoactivatable O-nitrobenzene moieties co-assembles with cargo proteins via ionic interactions, followed by light activation to yield aldehyde groups on the dendrimer and the formation of imine bonds with cargo proteins. The light-activated complexes show high stability in buffer and serum solutions, but dis-assemble under low pH conditions. As a result, the polymer successfully delivers cargo proteins green fluorescent protein and β-galactosidase into cells with maintained bioactivity even in the presence of 50% serum. The LAC strategy proposed in this study provides a new insight to improve the serum stability of polymers for intracellular protein delivery.

Mucus-Inspired Dynamic Hydrogels: Synthesis and Future Perspectives

Mucus hydrogels at biointerfaces are crucial for protecting against foreign pathogens and for the biological functions of the underlying cells. Since mucus can bind to and host both viruses and bacteria, establishing a synthetic model system that can emulate the properties and functions of native mucus and can be synthesized at large scale would revolutionize the mucus-related research that is essential for understanding the pathways of many infectious diseases. The synthesis of such biofunctional hydrogels in the laboratory is highly challenging, owing to their complex chemical compositions and the specific chemical interactions that occur throughout the gel network. In this perspective, we discuss the basic chemical structures and diverse physicochemical interactions responsible for the unique properties and functions of mucus hydrogels. We scrutinize the different approaches for preparing mucus-inspired hydrogels, with specific examples. We also discuss recent research and what it reveals about the challenges that must be addressed and the opportunities to be considered to achieve desirable de novo synthetic mucus hydrogels.

Magnetic torque–driven living microrobots for increased tumor infiltration

Biohybrid bacteria–based microrobots are increasingly recognized as promising externally controllable vehicles for targeted cancer therapy. Magnetic fields in particular have been used as a safe means to transfer energy and direct their motion. Thus far, the magnetic control strategies used in this context rely on poorly scalable magnetic field gradients, require active position feedback, or are ill-suited to diffuse distributions within the body. Here, we present a magnetic torque–driven control scheme for enhanced transport through biological barriers that complements the innate taxis toward tumor cores exhibited by a range of bacteria, shown for Magnetospirillum magneticum as a magnetically responsive model organism. This hybrid control strategy is readily scalable, independent of position feedback, and applicable to bacterial microrobots dispersed by the circulatory system. We observed a fourfold increase in translocation of magnetically responsive bacteria across a model of the vascular endothelium and found that the primary mechanism driving increased transport is torque-driven surface exploration at the cell interface. Using spheroids as a three-dimensional tumor model, fluorescently labeled bacteria colonized their core regions with up to 21-fold higher signal in samples exposed to rotating magnetic fields. In addition to enhanced transport, we demonstrated that our control scheme offers further advantages, including the possibility for closed-loop optimization based on inductive detection, as well as spatially selective actuation to reduce off-target effects. Last, after systemic intravenous injection in mice, we showed significantly increased bacterial tumor accumulation, supporting the feasibility of deploying this control scheme clinically for magnetically responsive biohybrid microrobots.

Self-assembling nanocarriers from engineered proteins: Design, functionalization, and application for drug delivery

Self-assembling proteins are valuable building blocks for constructing drug nanocarriers due to their self-assembly behavior, monodispersity, biocompatibility, and biodegradability. Genetic and chemical modifications allow for modular design of protein nanocarriers with effective drug encapsulation, targetability, stimuli responsiveness, and in vivo half-life. Protein nanocarriers have been developed to deliver various therapeutic molecules including small molecules, proteins, and nucleic acids with proven in vitro and in vivo efficacy. This article reviews recent advances in protein nanocarriers that are not derived from natural protein nanostructures, such as protein cages or virus like particles. The protein nanocarriers described here are self-assembled from rationally or de novo designed recombinant proteins, as well as recombinant proteins complexed with other biomolecules, presenting properties that are unique from those of natural protein carriers. Design, functionalization, and therapeutic application of protein nanocarriers will be discussed.

Reactive oxygen species-responsive branched poly (β-amino ester) with robust efficiency for cytosolic protein delivery

Protein therapy targeting the intracellular machinery holds great potentials for disease treatment, and therefore, effective cytosolic protein delivery technologies are highly demanded. Herein, we developed reactive oxygen species (ROS)-degradable, branched poly(β-amino ester) (PBAE) with built-in phenylboronic acid (PBA) in the backbone and terminal-pendent arginine for the efficient cytosolic protein delivery. The PBAE could form stable and cell-ingestible nanocomplexes (NCs) with proteins via electrostatic interaction, nitrogen-boronate (N-B) coordination, and hydrogen bonding, while it can be degraded into small segments by the over-produced H₂O₂ in tumor cells to enable cytoplasmic protein release. As thus, PBAE exhibited high efficiency in delivering varieties of proteins with distinct molecular weights (12.4-430 kDa) and isoelectric points (4.7-10.5) into tumor cells, including enzymes, toxins, and antibodies. Moreover, PBAE mediated efficient delivery of saporin into tumor cells in vivo, provoking pronounced anti-tumor outcomes. This study provides a robust and versatile platform for cytosolic protein delivery, and the elaborately tailored PBAE may find promising applications for protein-based biological research and disease management. STATEMENT OF SIGNIFICANCE: Cytosolic delivery of native proteins holds great therapeutic potentials, which however, is limited by the lack of robust delivery carriers that can simultaneously feature strong protein encapsulation yet effective intracellular protein release. Herein, ROS-degradable, branched poly(β-amino ester) (PBAE) with backbone-embedded phenylboronic acid (PBA) and terminal-pendent arginine was developed to synchronize these two processes. PBA and arginine moieties allowed PBAE to encapsulate proteins via N-B coordination, electrostatic interaction, hydrogen bonding, and salt bridging, while PBA could be oxidized by over-produced H₂O₂ inside cancer cells to trigger PBAE degradation and intracellular protein release. As thus, the top-performing PBAE mediated efficient cytosolic delivery of various proteins including enzymes, toxins, and antibodies. This study provides a powerful platform for cytosolic protein delivery, and may find promising utilities toward intracellular protein therapy against cancer and other diseases such as inflammation.

Controlled Covalent Self-Assembly of a Homopolymer for Multiscale Materials Engineering

Polymer self-assembly is a crucial process in materials engineering. Currently, almost all polymer self-assembly is limited to non-covalent bonding methods, even though these methods have drawbacks as they require complicated synthesis techniques and produce relatively unstable structures. Here, a novel mechanism of covalent polymer self-assembly is discovered and employed to address drawbacks of non-covalent polymer self-assembly. A simple ketone homopolymer is found to self-assemble into nano- to macroscale hydrogels during covalent crosslinking. In contrast to non-covalent self-assembly, the covalent self-assembly is independent of and unaffected by solvent conditions (e.g., polarity and ionic strength) and does not require additional agents, e.g., organic solvents and surfactants. The covalent polymer self-assembly is subjected to a new mechanism of control by tuning the covalent crosslinking rate. This leads to nanogels with an unprecedented and tightly controlled range of dimensions from less than 10 nm to above 100 nm. Moreover, the crosslinking rate also regulates the assembly behavior of microgels fabricated by microfluidics. The microgels self-assemble into granular fibers, which is 3D printed into stable porous scaffolds. The novel covalent polymer assembly method has enormous potential to revolutionize multiscale materials fabrication for applications in drug delivery, tissue engineering, and many other fields.

Endocytosis-Independent and Cancer-Selective Cytosolic Protein Delivery via Reversible Tagging with LAT1 substrate

Protein drugs targeting intracellular machineries have shown profound therapeutic potentials, but their clinical utilities are greatly hampered by the lack of efficient cytosolic delivery techniques. Existing strategies mainly rely on nanocarriers or conjugated cell-penetrating peptides (CPPs), which often have drawbacks such as materials complexity/toxicity, lack of cell specificity, and endolysosomal entrapment. Herein, a unique carrier-free approach is reported for mediating cancer-selective and endocytosis-free cytosolic protein delivery. Proteins are sequentially modified with 4-nitrophenyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) benzyl carbonate as the H₂ O₂ -responsive domain and 3,4-dihydroxy-l-phenylalanine as the substrate of l-type amino acid transporter 1 (LAT1). Thus, the pro-protein can be directly transported into tumor cells by overexpressed LAT1 on cell membranes, bypassing endocytosis and endolysosomal entrapment. In the cytosol, overproduced H₂ O₂ restores the protein structure and activity. Using this technique, versatile proteins are delivered into tumor cells with robust efficiency, including toxins, enzymes, CRISPR-Cas9 ribonucleoprotein, and antibodies. Furthermore, intravenously injected pro-protein of saporin shows potent anticancer efficacy in 4T1-tumor-bearing mice, without provoking systemic toxicity. Such a facile and versatile pro-protein platform may benefit the development of protein pharmaceuticals.

Multiplexed Analysis of the Cellular Uptake of Polymeric Nanocarriers

Polymeric nanocarriers (PNCs) are versatile drug delivery vehicles capable of delivering a variety of therapeutics. Quantitatively monitoring their uptake in biological systems is essential for realizing their potential as next-generation delivery systems; however, existing quantification strategies are limited due to the challenges of detecting polymeric materials in complex biological samples. Here, we describe a metal-coded mass tagging approach that enables the multiplexed quantification of the PNC uptake in cells using mass spectrometry (MS). In this approach, PNCs are conjugated with ligands that bind strongly to lanthanide ions, allowing the PNCs to be sensitively quantitated by inductively coupled plasma-MS. The metal-coded tags have little effect on the properties or toxicity of the PNCs, making them biocompatible. We demonstrate that the conjugation of different metals to the PNCs enables the multiplexed analysis of cellular uptake of multiple distinct PNCs at the same time. This multiplexing capability should improve the design and optimization of PNCs by minimizing biological variability and reducing analysis time, effort, and cost.

Amphipathic poly-β-peptides for intracellular protein delivery

A series of amphipathic poly-β-peptides are designed for intracellular protein delivery. The poly-β-peptides with higher molecular weight and hydrophobic contents exhibit higher protein loading and superior delivery efficiency. The lead material efficiently delivers proteins into cells with reserved bioactivity.

Assembly of Bioactive Nanoparticles via Metal-Phenolic Complexation

The integration of bioactive materials (e.g., proteins and genes) into nanoparticles holds promise in fields ranging from catalysis to biomedicine. However, it is challenging to develop a simple and broadly applicable nanoparticle platform that can readily incorporate distinct biomacromolecules without affecting their intrinsic activity. Herein, a metal-phenolic assembly approach is presented whereby diverse functional nanoparticles can be readily assembled in water by combining various synthetic and natural building blocks, including poly(ethylene glycol), phenolic ligands, metal ions, and bioactive macromolecules. The assembly process is primarily mediated by metal-phenolic complexes through coordination and hydrophobic interactions, which yields uniform and spherical nanoparticles (mostly <200 nm), while preserving the function of the incorporated biomacromolecules (siRNA and five different proteins used). The functionality of the assembled nanoparticles is demonstrated through cancer cell apoptosis, RNA degradation, catalysis, and gene downregulation studies. Furthermore, the resulting nanoparticles can be used as building blocks for the secondary engineering of superstructures via templating and cross-linking with metal ions. The bioactivity and versatility of the platform can potentially be used for the streamlined and rational design of future bioactive materials.

Tailoring Hyperbranched Poly(β-amino ester) as a Robust and Universal Platform for Cytosolic Protein Delivery

Cytosolic protein delivery is a prerequisite for protein-based biotechnologies and therapeutics on intracellular targets. Polymers that can complex with proteins to form nano-assemblies represent one of the most important categories of materials, because of the ease of nano-fabrication, high protein loading efficiency, no need for purification, and maintenance of protein bioactivity. Stable protein encapsulation and efficient intracellular liberation are two critical yet opposite processes toward cytosolic delivery, and polymers that can resolve these two conflicting challenges are still lacking. Herein, hyperbranched poly(β-amino ester) (HPAE) with backbone-embedded phenylboronic acid (PBA) is developed to synchronize these two processes, wherein PBA enhanced protein encapsulation via nitrogen-boronate (N-B) coordination while triggered polymer degradation and protein release upon oxidation by H₂ O₂ in cancer cells. Upon optimization of the branching degree, charge density, and PBA distribution, the best-performing A2-B3-C2-S₂ -P₂ is identified, which mediates robust delivery of various native proteins/peptides with distinct molecular weights (1.6-430 kDa) and isoelectric points (4.1-10.3) into cancer cells, including enzymes, toxins, antibodies, and CRISPR-Cas9 ribonucleoproteins (RNPs). Moreover, A2-B3-C2-S₂ -P₂ mediates effective cytosolic delivery of saporin both in vitro and in vivo to provoke remarkable anti-tumor efficacy. Such a potent and universal platform holds transformative potentials for protein pharmaceuticals.

Dynamic-Responsive Virus-Mimetic Nanocapsules Facilitate Protein Drug Penetration and Extracellular-Specific Unpacking for Antitumor Treatment

Protein-based drugs have been demonstrating great potential on the treatment of various diseases, but most of them encounter many difficulties in clinical trials or uses, such as instability, low bioavailability,...

“Spear and Shield in One” Nanochaperone Enables Protein to Navigate Multiple Biological Barriers for Enhanced Tumor Synergistic Therapy

Protein therapeutics have been viewed as powerful candidates for cancer treatment by virtue of highly specific bioactivity and minimized adverse effects. However, the intracellular delivery of protein drugs remains enormously...

Confinements of Thermoresponsive Dendronized Polymers to Proteins

Crowding environment created by host polymers plays crucial roles in manipulating interactions with proteins and modulating their bioactivity. Here, we report our investigation on interactions between polymers and proteins in...

Protein Binding and Release by Polymeric Cell-Penetrating Peptide Mimics

There is significant potential in exploiting antibody specificity to develop new therapeutic treatments. However, intracellular protein delivery is a paramount challenge because of the difficulty in transporting large, polar molecules across cell membranes. Cell-penetrating peptide mimics (CPPMs) are synthetic polymers that are versatile materials for intracellular delivery of biological molecules, including nucleic acids and proteins, with superior performance compared to their natural counterparts and commercially available peptide-based reagents. Studies have demonstrated that noncovalent complexation with these synthetic carriers is necessary for the delivery of proteins, but the fundamental interactions dominating CPPM-protein complexation are not well understood. Beyond these interactions, the mechanism of release for many noncovalent carriers is not well established. Herein, interactions expected to be critical in CPPM-protein binding and unbinding were explored, including hydrogen bonding, electrostatics, and hydrophobic interactions. Despite the guanidinium-rich functionality of these polymeric carriers, hydrogen bonding was shown not to be a dominant interaction in CPPM-protein binding. Fluorescence quenching assays were used to decouple the effect of electrostatic and hydrophobic interactions between amphiphilic CPPMs and proteins. Furthermore, by conducting competition assays with other proteins, unbinding of protein cargoes from CPPM-protein complexes was demonstrated and provided insight into mechanisms of protein release. This work offers understanding toward the role of carrier and cargo binding and unbinding in intracellular outcomes. In turn, an improved fundamental understanding of noncovalent polymer-protein complexation will enable more effective methods for intracellular protein delivery.

Poly(disulfide)s: From Synthesis to Drug Delivery

Bioresponsive polymers have been widely used in drug delivery because of their degradability. For example, poly(disulfide)s with repeating disulfide bonds in the main chain have attracted considerable research attention. The characteristics of the disulfide bonds, including their dynamic and reversible properties and their responsiveness to stimuli such as reductants, light, heat, and mechanical force, make them ideal platforms for on-demand drug delivery. This review introduces the synthesis methods and applications of poly(disulfide)s. Furthermore, the synthesis methods of poly(disulfide)s are classified on the basis of the monomers used: oxidative step-growth polymerization with dithiols, ring-opening polymerization with cyclic disulfides, and polymerization with linear disulfides. In addition, recent advances in poly(disulfide)s for the delivery of small-molecule or biomacromolecular drugs are discussed. Quantum-dot-loaded poly(disulfide) delivery systems for imaging are also included. This review provides an overview of the various design strategies employed in the construction of poly(disulfide) platforms to inspire new applications in the field of drug delivery.

Dynamic Polymer Amphiphiles for Efficient Intracellular and In Vivo Protein Delivery

Intracellular delivery of proteins is receiving considerable attention in biotherapeutics for various diseases by replacing dysfunctional proteins. Successful intracellular protein delivery highly relies on the development of efficient and safe polymeric carriers, which remains a grand challenge due to the lack of strong binding sites on proteins and their distinct molecular sizes and polarities. In this work, a strategy is proposed for efficient intracellular protein delivery by using dynamic polymer supra-amphiphiles, which are prepared by grafting boronated polylysine with a series of lipidated catechols via dynamic covalent catechol-boronate ester bonds. The prepared supra-amphiphiles can coassemble with proteins to form stable nanoparticles in water and also enable the release of bound proteins in cells due to their dynamic features, thereby strongly promoting the intracellular delivery process. The lead supra-amphiphiles screened in the library demonstrate high efficiency in the delivery of various proteins including bovine serum albumin, β-galactosidase, α-chymotrypsin, saporin, R-phycoerythrin, ovalbumin, catalase, and superoxide dismutase, and show great potency in delivering superoxide dismutase to treat ulcerative colitis in vivo. This work provides new opportunities for rational design and facile construction of robust intracellular protein delivery materials by the integration of polymer chemistry and supramolecular engineering strategies.

Oral delivery of infliximab using nano-in-microparticles for the treatment of inflammatory bowel disease

The anti-tumor necrosis factor-α (anti-TNF-α) blocker, has shown great efficacy for the treatment of inflammatory bowel disease (IBD). However, systemic exposure to it can cause considerable safety problems due to reduced suppression of the systemic immune response and loss of response to the production of anti-drug antibodies. Thus, we try to devise a targeted vehicle system for oral administration of anti-TNF-α antibodies for the treatment of IBD. In the present study, we developed an oral Infliximab (IFX) loaded nano-in-microparticles, based on chitosan (CS)/carboxymethyl chitosan (CMC) and alginate (Alg), which could protect IFX from the harsh environment of the gastrointestinal tract and produce targeted drug delivery to the inflamed intestine. In vivo studies demonstrated that the IFX loaded nano-in-micro vehicle can alleviate colitis by ameliorating inflammation and maintaining the intestinal epithelial barrier.

Immobilization of Enzymes by Polymeric Materials

Enzymes are the highly efficient biocatalyst in modern biotechnological industries. Due to the fragile property exposed to the external stimulus, the application of enzymes is highly limited. The immobilized enzyme by polymer has become a research hotspot to empower enzymes with more extraordinary properties and broader usage. Compared with free enzyme, polymer immobilized enzymes improve thermal and operational stability in harsh environments, such as extreme pH, temperature and concentration. Furthermore, good reusability is also highly expected. The first part of this study reviews the three primary immobilization methods: physical adsorption, covalent binding and entrapment, with their advantages and drawbacks. The second part of this paper includes some polymer applications and their derivatives in the immobilization of enzymes.

Exogenous Introduction of Initiator and Executioner Caspases Results in Different Apoptotic Outcomes

The balance of pro-apoptotic and pro-survival proteins defines a cell's fate. These processes are controlled through an interdependent and finely tuned protein network that enables survival or leads to apoptotic cell death. The caspase family of proteases is central to this apoptotic network, with initiator and executioner caspases, and their interaction partners, regulating and executing apoptosis. In this work, we interrogate and modulate this network by exogenously introducing specific initiator or executioner caspase proteins. Each caspase is exogenously introduced using redox-responsive polymeric nanogels. Although caspase-3 might be expected to be the most effective due to the centrality of its role in apoptosis and its heightened catalytic efficiency relative to other family members, we observed that caspase-7 and caspase-9 are the most effective at inducing apoptotic cell death. By critically analyzing the introduced activity of the delivered caspase, the pattern of substrate cleavage, as well as the ability to activate endogenous caspases, we conclude that the efficacy of each caspase correlated with the levels of pro-survival factors that both directly and indirectly impact the introduced caspase. These findings lay the groundwork for developing methods for exogenous introduction of caspases as a therapeutic option that can be tuned to the apoptotic balance in a proliferating cell.

In-Situ Encapsulation of Protein into Nanoscale Hydrogen-Bonded Organic Frameworks for Intracellular Biocatalysis

Hydrogen-bonded organic frameworks (HOFs) are porous materials with great potential for biological applications. The self-assembly of HOFs and biomacromolecules, however, is challenging. We report herein the self-assembly of nanoscale HOFs (nHOFs) to encapsulate protein for intracellular biocatalysis. The self-assembly of tetrakis(4-amidiniumphenyl)methane and azobenzenedicarboxylate can encapsulate protein in situ to form protein@nHOFs under mild conditions. This strategy is applicable to proteins with different surface charge and molecular weight, showing a high protein encapsulation efficiency and minimal effect on protein activity. A cellular delivery study shows that the protein@TA-HOFs can efficiently enter cells and retain enzyme activity for biochemical catalysis in living cells for neuroprotection. Our strategy paves new avenues for interfacing nHOFs with biological settings and sheds light on expanding nHOFs as a platform for biomacromolecule delivery and disease treatment.

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.

Nanogel-facilitated Protein Intracellular Specific Degradation through Trim-Away

Recently discovered "Trim-Away" mechanism opens a new window for fast and selective degradation of endogenous proteins. However, the in vivo and clinical application of this approach is stuck by the requirement of special skills and equipment needed for the intracellular delivery of antibodies. Hereby, an antibody conjugated polymer nanogel system, Nano-ERASER, for intracellular delivery and release of antibody, and degradation of a specific endogenous protein has been developed. After being delivered into cells, the antibody is released and forms complex with its target protein, and subsequently binds to the Fc receptor of TRIM21. The resulted complex of target protein/antibody/TRIM21 is then degraded by the proteasome. The efficacy of Nano-ERASER has been validated by depleting GFP protein in a GFP expressing cell line. Furthermore, Nano-ERASER successfully degrades COPZ1, a vital protein for cancer cells, and kills those cells while sparing normal cells. Benefit from its convenience and targeted delivery merit, Nano-ERASER technique is promising in providing a reliable tool for endogenous protein function study as well as paves the way for novel antibody-based Trim-Away therapeutic modalities for cancer and other diseases.