Engineered synthetic polymer nanoparticles as IgG affinity ligands

Design of an Anti-HMGB1 Synthetic Antibody for In Vivo Ischemic/Reperfusion Injury Therapy

High-mobility group box 1 (HMGB1) is a multifunctional protein. Upon injury or infection, HMGB1 is passively released from necrotic and activated dendritic cells and macrophages, where it functions as a cytokine, acting as a ligand for RAGE, a major receptor of innate immunity stimulating inflammation responses including the pathogenesis of cerebral ischemia/reperfusion (I/R) injury. Blocking the HMGB1/RAGE axis offers a therapeutic approach to treating these inflammatory conditions. Here, we describe a synthetic antibody (SA), a copolymer nanoparticle (NP) that binds HMGB1. A lightly cross-linked N-isopropylacrylamide (NIPAm) hydrogel copolymer with nanomolar affinity for HMGB1 was selected from a small library containing trisulfated 3,4,6S-GlcNAc and hydrophobic N-tert-butylacrylamide (TBAm) monomers. Competition binding experiments with heparin established that the dominant interaction between SA and HMGB1 occurs at the heparin-binding domain. In vitro studies established that anti-HMGB1-SA inhibits HMGB1-dependent ICAM-1 expression and ERK phosphorylation of HUVECs, confirming that SA binding to HMGB1 inhibits the proteins' interaction with the RAGE receptor. Using temporary middle cerebral artery occlusion (t-MCAO) model rats, anti-HMGB1-SA was found to accumulate in the ischemic brain by crossing the blood-brain barrier. Significantly, administration of anti-HMGB1-SA to t-MCAO rats dramatically reduced brain damage caused by cerebral ischemia/reperfusion. These results establish that a statistical copolymer, selected from a small library of candidates synthesized using an "informed" selection of functional monomers, can yield a functional synthetic antibody. The knowledge gained from these experiments can facilitate the discovery, design, and development of a new category of drug.

Imprinted Hydrogel Nanoparticles for Protein Biosensing: A Review

Over the past decade, molecular imprinting (MI) technology has made tremendous progress, and the advancements in nanotechnology have been the major driving force behind the improvement of MI technology. The preparation of nanoscale imprinted materials, i.e., molecularly imprinted polymer nanoparticles (MIP NPs, also commonly called nanoMIPs), opened new horizons in terms of practical applications, including in the field of sensors. Currently, hydrogels are very promising for applications in bioanalytical assays and sensors due to their high biocompatibility and possibility to tune chemical composition, size (microgels, nanogels, etc.), and format (nanostructures, MIP film, fibers, etc.) to prepare optimized analyte-responsive imprinted materials. This review aims to highlight the recent progress on the use of hydrogel MIP NPs for biosensing purposes over the past decade, mainly focusing on their incorporation on sensing devices for detection of a fundamental class of biomolecules, the peptides and proteins. The review begins by directing its focus on the ability of MIPs to replace biological antibodies in (bio)analytical assays and highlight their great potential to face the current demands of chemical sensing in several fields, such as disease diagnosis, food safety, environmental monitoring, among others. After that, we address the general advantages of nanosized MIPs over macro/micro-MIP materials, such as higher affinity toward target analytes and improved binding kinetics. Then, we provide a general overview on hydrogel properties and their great advantages for applications in the field of Sensors, followed by a brief description on current popular routes for synthesis of imprinted hydrogel nanospheres targeting large biomolecules, namely precipitation polymerization and solid-phase synthesis, along with fruitful combination with epitope imprinting as reliable approaches for developing optimized protein-imprinted materials. In the second part of the review, we have provided the state of the art on the application of MIP nanogels for screening macromolecules with sensors having different transduction modes (optical, electrochemical, thermal, etc.) and design formats for single use, reusable, continuous monitoring, and even multiple analyte detection in specialized laboratories or in situ using mobile technology. Finally, we explore aspects about the development of this technology and its applications and discuss areas of future growth.

Abiotic Synthetic Antibody Inhibitor with Broad-Spectrum Neutralization and Antiviral Efficacy against Escaping SARS-CoV-2 Variants

The rapid emergence and spread of vaccine/antibody-escaping variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has posed serious challenges to our efforts in combating corona virus disease 2019 (COVID-19) pandemic. A potent and broad-spectrum neutralizing reagent against these escaping mutants is extremely important for the development of strategies for the prevention and treatment of SARS-CoV-2 infection. We herein report an abiotic synthetic antibody inhibitor as a potential anti-SARS-CoV-2 therapeutic agent. The inhibitor, Aphe-NP14, was selected from a synthetic hydrogel polymer nanoparticle library created by incorporating monomers with functionalities complementary to key residues of the SARS-CoV-2 spike glycoprotein receptor binding domain (RBD) involved in human angiotensin-converting enzyme 2 (ACE2) binding. It has high capacity, fast adsorption kinetics, strong affinity, and broad specificity in biologically relevant conditions to both the wild type and the current variants of concern, including Beta, Delta, and Omicron spike RBD. The Aphe-NP14 uptake of spike RBD results in strong blockage of spike RBD-ACE2 interaction and thus potent neutralization efficacy against these escaping spike protein variant pseudotyped viruses. It also inhibits live SARS-CoV-2 virus recognition, entry, replication, and infection in vitro and in vivo. The Aphe-NP14 intranasal administration is found to be safe due to its low in vitro and in vivo toxicity. These results establish a potential application of abiotic synthetic antibody inhibitors in the prevention and treatment of the infection of emerging or possibly future SARS-CoV-2 variants.

Cooling-induced, localized release of cytotoxic peptides from engineered polymer nanoparticles in living mice for cancer therapy

Temperature-responsive polymers are often characterized by an abrupt change in the degree of swelling brought about by small changes in temperature. Polymers with a lower critical solution temperature (LCST) in particular, are important as drug and gene delivery vehicles. Drug molecules are taken up by the polymer in their solvent swollen state below their LCST. Increasing the temperature above the LCST, typically physiological temperatures, results in desolvation of polymer chains and microstructure collapse. The trapped drug is released slowly by passive diffusion through the collapsed polymer network. Since diffusion is dependent on many variables, localizing and control of the drug delivery rate can be challenging. Here, we report a fundamentally different approach for the rapid (seconds) tumor-specific delivery of a biomacromolecular drug. A copolymer nanoparticle (NP) was engineered with affinity for melittin, a peptide with potent anti-cancer activity, at physiological temperature. Intravenous injection of the NP-melittin complex results in its accumulation in organs and at the tumor. We demonstrate that by local cooling of the tumor the melittin is rapidly released from the NP-melittin complex. The release occurs only at the cooled tumor site. Importantly, tumor growth was significantly suppressed using this technique demonstrating therapeutically useful quantities of the drug can be delivered. This work reports the first example of an in vivo site-specific release of a macromolecular drug by local cooling for cancer therapy. In view of the increasing number of cryotherapeutic devices for in vivo applications, this work has the potential to stimulate cryotherapy for in vivo drug delivery.

Peptide-crosslinked molecularly imprinted polymers for efficient separation of immunoglobulin G from human serum

Low-cost and highly effective methods are highly desirable to replace the costly ethanol fractionation and affinity chromatography in IgG isolation from human plasma. Molecularly imprinted polymers (MIPs) of IgG are potential candidates, however, they still suffer from severe problems such as difficult template removal and low imprinting efficiency. Here, a recently developed strategy was adopted to overcome these problems. The MIPs were synthesized using poly(L-glutamic acid) (PLGA) peptide crosslinkers instead of commonly used crosslinkers, such as N,N-methylenebisacrylamide (BIS). Because of the pH-induced helix-coil transition and the precise folding of the peptide segments in the polymers, the imprint cavities can be enlarged by adjusting the pH from 5.0 to 7.0, but their original size and shape are restored when the pH is adjusted back. Therefore, the IgG template can be eluted completely under mild conditions, and significantly improved imprinting efficiency can be achieved. Compared with BIS-crosslinked MIP, 8.6 times more binding sites can be created by molecular imprinting PLGA-crosslinked MIP. The factors influencing the performance of the MIP were studied systematically. An optimized MIP with a high adsorption capacity (612.5 mg g^-1), high IF (4.92), and high selectivity was obtained. The adsorption capacity and selectivity of the MIP are much higher than the previously reported IgG MIPs. Because of its high adsorption capacity and selectivity, it can separate IgG from human serum effectively, affording high purity products.

Matrices and Affinity Ligands for Antibody Purification and Corresponding Applications in Radiotherapy

Antibodies have become an important class of biological products in cancer treatments such as radiotherapy. The growing therapeutic applications have driven a demand for high-purity antibodies. Affinity chromatography with a high affinity and specificity has always been utilized to separate antibodies from complex mixtures. Quality chromatographic components (matrices and affinity ligands) have either been found or generated to increase the purity and yield of antibodies. More importantly, some matrices (mainly particles) and affinity ligands (including design protocols) for antibody purification can act as radiosensitizers or carriers for therapeutic radionuclides (or for radiosensitizers) either directly or indirectly to improve the therapeutic efficiency of radiotherapy. This paper provides a brief overview on the matrices and ligands used in affinity chromatography that are involved in antibody purification and emphasizes their applications in radiotherapy to enrich potential approaches for improving the efficacy of radiotherapy.

Abiotic Synthetic Antibodies to Target a Specific Protein Domain and Inhibit Its Function

The Bacillus thuringiensis (Bt) Cry proteins are widely used in insect pest control. Despite their economic benefits, remaining concerns over potential ecological and health risks warrant their ongoing surveillance. Affinity reagents, most often antibodies, protein scaffolds, and aptamers, are the traditional tools used for protein binding and detection. We report a synthetic antibody (SA) alternative to traditional biological affinity reagents for binding Bt Cry proteins. Analysis of hotspots of the Bt Cry protein-insect midgut cadherin-like receptor complexes was used for the design of the SA. The SA was selected from a small focused library of hydrogel copolymers containing functional monomers complementary to key exposed hotspots of Bt Cry proteins. A directed chemical evolution identified a SA, APhe-NP23, with affinity and selectivity for Bt Cry1Ab/Ac proteins. The putative intermolecular polymer-protein interfaces were identified by the SA's uptake of Bt Cry1Ac pepsin hydrolysates, binding epitope mutation studies, and protein-protein inhibition studies of the toxin binding to its native insect receptor binding domains. The SA inhibitor binds to the same protein domains as the insect's cadherin-like receptors, Bt-R₁ and SeCad1b. The SA binds rapidly to Bt Cry1Ab/Ac with high capacity, is pH-responsive, and is synthesized reproducibly. We believe that a hotspot-directed approach is general for creation of abiotic protein affinity reagents that target functional protein domains. Affinity ligands are typically high-information content biologicals. Their structure and function are determined from their amino acid or oligo sequence. In contract, the SA described in this work is a statistical copolymer that lacks sequence specificity. These results are an important contribution to the concept that randomness and biospecificity are not mutually exclusive.

Engineered polymer nanoparticles incorporating l-amino acid groups as affinity reagents for fibrinogen

Synthetic polymer hydrogel nanoparticles (NPs) were developed to function as abiotic affinity reagents for fibrinogen. These NPs were made using both temperature-sensitive N-isopropyl acrylamide (NIPAm) and l-amino acid monomers. Five kinds of l-amino acids were acryloylated to obtain functional monomers: l-phenylalanine (Phe) and l-leucine (Leu) with hydrophobic side chains, l-glutamic acid (Glu) with negative charges, and l-lysine (Lys) and l-arginine (Arg) with positive charges. After incubating the NPs with fibrinogen, γ-globulin, and human serum albumin (HSA) respectively, the NPs that incorporated N-acryloyl-Arg monomers (AArg@NPs) showed the strongest and most specific binding affinity to fibrinogen, when compared with γ-globulin and HSA. Additionally, the fibrinogen-AArg binding model had the best docking scores, and this may be due to the interaction of positively charged AArg@NPs and the negatively charged fibrinogen D domain and the hydrophobic interaction between them. The specific adsorption of AArg@NPs to fibrinogen was also confirmed by the immunoprecipitation assay, as the AArg@NPs selectively trapped the fibrinogen from a human plasma protein mixture. AArg@NPs had a strong selectivity for, and specificity to, fibrinogen and may be developed as a potential human fibrinogen-specific affinity reagent.

Multimodal obstruction of tumorigenic energy supply via bionic nanocarriers for effective tumor therapy

Sufficient energy generation based on effective transport of nutrient via abundant blood vessels in tumor tissue and subsequent oxidative metabolism in mitochondria is critical for growth, proliferation and migration of tumor. Thus the strategy to cut off this transport pathway (blood vessels) and simultaneously close the power house (mitochondria) is highly desired for tumor treatment. Herein, we fabricated a bionic nanocarrier with core-shell-corona structure to give selective and effective tumor therapy via stepwise destruction of existed tumor vessel, inhibition of tumor angiogenesis and dysfunction of tumor mitochondria. The core of this bionic nanocarrier consists of combretastatin A4 phosphate (CA4P) and vitamin K₂ (VK₂) co-loaded mesoporous silica nanoparticle (MSNs), which is in charge of the vasculature destruction and mitochondrial dysfunction after cargos release. The N-tert-butylacrylamide (TBAM) and tri-sulfated N-acetylglucosamine (TSAG) shell served as artificial affinity reagent against vascular endothelial growth factor (VEGF) for angiogenesis inhibition. As to guarantee that these actions only happened in tumor, the hyaluronic acid (HA) corona was introduced to endow the nanocarrier with tumor targeting property and stimuli-responsiveness for accurate therapy. Both in vitro and in vivo results indicated that the CA4P/VK₂-MSNs-TBAM/TSAG-HA (CVM_MGH for short) nanocarrier combined well-controllable manipulation of tumor vasculature and tumor mitochondria to effectivly cut off the tumorigenic energy supply, which performed significant inhibition of tumor growth, demonstrating the great candidate of our strategy for effective tumor therapy.

Synthetic hydrogel nanoparticles for sepsis therapy

Sepsis is a life-threatening condition caused by the extreme release of inflammatory mediators into the blood in response to infection (e.g., bacterial infection, COVID-19), resulting in the dysfunction of multiple organs. Currently, there is no direct treatment for sepsis. Here we report an abiotic hydrogel nanoparticle (HNP) as a potential therapeutic agent for late-stage sepsis. The HNP captures and neutralizes all variants of histones, a major inflammatory mediator released during sepsis. The highly optimized HNP has high capacity and long-term circulation capability for the selective sequestration and neutralization of histones. Intravenous injection of the HNP protects mice against a lethal dose of histones through the inhibition of platelet aggregation and migration into the lungs. In vivo administration in murine sepsis model mice results in near complete survival. These results establish the potential for synthetic, nonbiological polymer hydrogel sequestrants as a new intervention strategy for sepsis therapy and adds to our understanding of the importance of histones to this condition.

Sepsis caused by the release of inflammatory mediators into the blood is a life threatening disease. Here, the authors report on the development of hydrogel nanoparticles for the capture and neutralisation of histones, major inflammatory mediators, and demonstrate sepsis treatment in a murine model.

[Design of Synthetic Polymer Nanoparticles That Capture and Neutralize Target Molecules]

Protein affinity reagents that specifically and strongly bind to target molecules are widely used in disease detection, diagnosis, and therapy. Although antibodies and their fragments are the gold standard in protein-protein inhibitors (PPIs), synthetic polymers such as linear polymers, dendrimers, and nanoparticles as cost-effective PPIs have attracted great attention as alternatives to antibodies. These polymers exhibit high affinity to the target by imitating natural protein-protein interactions. However, only a few in vivo applications have been reported. Here, our recent advances in the development of synthetic polymers for in vivo application are reviewed. Poly(N-isopropylacrylamide) (pNIPAm) was used as a model of synthetic affinity reagents. Incorporation of both sulfated carbohydrate and hydrophobic monomers into lightly crosslinked pNIPAm nanoparticles (NPs) captured and neutralized vascular endothelial growth factor (VEGF) and inhibited tumor growth upon intravenous injection into tumor-bearing mice. Modification of a liposome with the pNIPAm-based linear polymer increased the polymer circulation time after intravenous injection and improved the affinity for the target. The pNIPAm-based NPs delivered by oral administration captured the target small molecules and inhibited their absorption from the intestine. Our recent findings provide useful information for the design of synthetic polymers that capture target molecules in vivo.

Current approaches for the purification of antibody-drug conjugates

In the past two decades, antibody-drug conjugates have gained increasing attention because they expand the therapeutic index when compared with that of traditional chemotherapies. Antibody-drug conjugates are highly complex structures consisting of antibodies covalently conjugated with small-molecule cytotoxic drugs. The complex structure of antibody-drug conjugates makes chemistry, manufacturing, and control difficult. In contrast to antibody production, distinct purification methods following conjugation of antibodies with drug-linkers are required for the manufacturing. For process development of antibody drug conjugates, the drug-to-antibody ratio, free drug-linkers, and aggregates are critical quality attributes that must be strictly controlled and removed by appropriate purification techniques. In this review, features of various purification methods used to purify antibody drug conjugates are described and evaluated. The future landscape of the antibody-conjugates field is also discussed briefly.

A Biomimetic of Endogenous Tissue Inhibitors of Metalloproteinases: Inhibition Mechanism and Contribution of Composition, Polymer Size, and Shape to the Inhibitory Effect

A biomimetic of endogenous tissue inhibitors of metalloproteinases (TIMPs) was engineered by introducing three binding elements to a synthetic tetrapolymer. We evaluated the contribution of composition, size, and shape of the TIMP-mimicking polymers to the inhibition of BaP1, a P-I class snake venom metalloproteinase (SVMP). Inhibition was achieved when the size of the linear polymer (LP) was comparable to or greater than that of the enzyme, indicating the efficacy requires binding to a significant portion of the enzyme surface in the vicinity of the active site. The efficacy of a low cross-linked polymer hydrogel nanoparticle (NP) of substantially greater molecular weight was comparable to that of the LPs despite differences in size and shape, an important finding for in vivo applications. The abiotic TIMP was effective against two classes of SVMPs in whole snake venom. The results can serve as a design principle for biomimetic polymer inhibitors of enzymes.

Enhancement of target toxin neutralization effect in vivo by PEGylation of multifunctionalized lipid nanoparticles

Protein-protein (e.g., antibody-antigen) interactions comprise multiple weak interactions. We have previously reported that lipid nanoparticles (LNPs) bind to and neutralize target toxic peptides after multifunctionalization of the LNP surface (MF-LNPs) with amino acid derivatives that induce weak interactions; however, the MF-LNPs aggregated after target capture and showed short blood circulation times. Here we optimized polyethylene glycol (PEG)-modified MF-LNPs (PEG-MF-LNPs) to inhibit the aggregation and increase the blood circulation time. Melittin was used as a target toxin, and MF-LNPs were prepared with negatively charged, hydrophobic, and neutral amino-acid-derivative-conjugated functional lipids. In this study, MF-LNPs modified with only PEG5k (PEG5k-MF-LNPs) and with both PEG5k and PEG2k (PEGmix-MF-LNPs) were prepared, where PEG5k and PEG2k represent PEG with a molecular weight of 5000 and 2000, respectively. PEGylation of the MF-LNPs did not decrease the melittin neutralization ability of nonPEGylated MF-LNPs, as tested by hemolysis assay. The PEGmix-MF-LNPs showed better blood circulation characteristics than the PEG5k-MF-LNPs. Although the nonPEGylated MF-LNPs immediately aggregated when mixed with melittin, the PEGmix-MF-LNPs did not aggregate. The PEGmix-MF-LNPs dramatically increased the survival rate of melittin-treated mice, whereas the nonPEGylated MF-LNPs increased slightly. These results provide a fundamental strategy to improve the in vivo toxin neutralization ability of MF-LNPs.

Abiotic Stimuli-Responsive Protein Affinity Reagent for IgG

We describe an approach for the discovery of protein affinity reagents (PARs). Abiotic synthetic hydrogel copolymers can be "tuned" for selective protein capture by the type and ratios of functional monomers included in their polymerization and by the polymerization conditions (i.e., pH). By screening libraries of hydrogel nanoparticles (NPs) containing charged and hydrophobic groups against a protein target (IgG), a stimuli-responsive PAR is selected. The robust carbon backbone synthetic copolymer is rapidly synthesized in the chemistry laboratory from readily available monomers. The production of the PAR does not require living cells and is free from biological contamination. The capture and release of the protein by the copolymer NP is reversible. IgG is sequestered from human serum at pH 6.5 and following a wash step, the purified protein is released by elevating the pH to 7.3. The binding and release of the protein occur without denaturation. The abiotic material functions as a selective PAR for the F(ab')₂ domain of IgG for pull-down and immunoprecipitation experiments and for isolation and purification of proteins from complex biological mixtures.

Design of Functional Nanoparticles for Intractable Disease Therapy

Protein affinity reagents are widely used for basic research, diagnostics, and disease therapy. Antibodies and their fragments are known as the most common protein affinity reagents. They specifically and strongly bind to target molecules and inhibit their functions. Thus, antibody drugs have increased in the recent two decades for disease therapy, such as cancer. These strong protein-protein interactions are composed of a nexus of multiple weak interactions. Synthetic polymers that bind to target molecules have been developed by the imitation of protein-protein interactions. These polymers show nanomolar affinity for the target and neutralize their functions; thus, they are of significant interest as a cost-effective protein affinity reagent. We have been developing synthetic polymer nanoparticles (NPs) that bind to target peptides and proteins by the inclusion of several functional monomers, such as charged and hydrophobic monomers. In this review, the focus is on the design of synthetic polymer NPs that bind to target molecules for disease therapy. We succeeded in neutralization of toxic peptides and signaling proteins both in vitro and in vivo. Additionally, linear polymers were modified on a lipid nanoparticle surface to improve polymer biodistribution. Our recent findings should provide useful information for the development of abiotic protein affinity reagents.

Complex polymer architectures through free-radical polymerization of multivinyl monomers

The construction of complex polymer architectures with well-defined topology, composition and functionality has been extensively explored as the molecular basis for the development of modern polymer materials. The unique reaction kinetics of free-radical polymerization leads to the concurrent formation of crosslinks between polymer chains and rings within an individual chain and, thus, free-radical (co)polymerization of multivinyl monomers provides a facile method to manipulate chain topology and functionality. Regulating the relative contribution of these intermolecular and intramolecular chain-propagation reactions is the key to the construction of architecturally complex polymers. This can be achieved through the design of new monomers or by spatially or kinetically controlling crosslinking reactions. These mechanisms enable the synthesis of various polymer architectures, including linear, cyclized, branched and star polymer chains, as well as crosslinked networks. In this Review, we highlight some of the contemporary experimental strategies to prepare complex polymer architectures using radical polymerization of multivinyl monomers. We also examine the recent development of characterization techniques for sub-chain connections in such complex macromolecules. Finally, we discuss how these crosslinking reactions have been engineered to generate advanced polymer materials for use in a variety of biomedical applications.

Emerging functional materials based on chemically designed molecular recognition

The specific interactions responsible for molecular recognition play a crucial role in the fundamental functions of biological systems. Mimicking these interactions remains one of the overriding challenges for advances in both fundamental research in biochemistry and applications in material science. However, current molecular recognition systems based on host–guest supramolecular chemistry rely on familiar platforms (e.g., cyclodextrins, crown ethers, cucurbiturils, calixarenes, etc.) for orienting functionality. These platforms limit the opportunity for diversification of function, especially considering the vast demands in modern material science. Rational design of novel receptor-like systems for both biological and chemical recognition is important for the development of diverse functional materials. In this review, we focus on recent progress in chemically designed molecular recognition and their applications in material science. After a brief introduction to representative strategies, we describe selected advances in these emerging fields. The developed functional materials with dynamic properties including molecular assembly, enzyme-like and bio-recognition abilities are highlighted. We have also selected materials with dynamic properties in contract to traditional supramolecular host–guest systems. Finally, the current limitations and some future trends of these systems are discussed.

Mimicking Molecular Chaperones to Regulate Protein Folding

Folding and unfolding are essential ways for a protein to regulate its biological activity. The misfolding of proteins usually reduces or completely compromises their biological functions, which eventually causes a wide range of diseases including neurodegeneration diseases, type II diabetes, and cancers. Therefore, materials that can regulate protein folding and maintain proteostasis are of significant biological and medical importance. In living organisms, molecular chaperones are a family of proteins that maintain proteostasis by interacting with, stabilizing, and repairing various non-native proteins. In the past few decades, efforts have been made to create artificial systems to mimic the structure and biological functions of nature chaperonins. Herein, recent progress in the design and construction of materials that mimic different kinds of natural molecular chaperones is summarized. The fabrication methods, construction rules, and working mechanisms of these artificial chaperone systems are described. The application of these materials in enhancing the thermal stability of proteins, assisting de novo folding of proteins, and preventing formation of toxic protein aggregates is also highlighted and explored. Finally, the challenges and potential in the field of chaperone-mimetic materials are discussed.

Nanoparticle-supported temperature responsive polymer brushes for affinity separation of histidine-tagged recombinant proteins

We developed a modular approach for the preparation of nanoparticle-supported polymer brushes carrying repeating iminodiacetate units for affinity separation of histidine-tagged recombinant proteins. The nanoparticle-supported polymer brushes were prepared via the combination of surface-initiated atom transfer radical polymerization with Cu(I)-catalyzed azide-alkyne cycloaddition reaction. The nanocomposite materials were characterized to determine the particle size, morphology, organic content, densities of polymer chains and the affinity ligand. Protein binding assay illustrated that the iminodiacetate-rich polymer brushes enable to selectively bind histidine-tagged recombinant proteins in the presence of abundant interfering proteins. More importantly, the protein binding capacity can be tuned by adjusting the environmental temperature. STATEMENT OF SIGNIFICANCE: The nanoparticle core-polymer brush structure enables selective binding of histidine-tagged recombinant proteins via multiple metal-coordination interactions. The soft and flexible structure of the polymer brushes was found beneficial for lowering the steric hindrance in protein binding. Taking advantage of the conformational changes of the polymer brushes at different temperatures, it is possible to modulate the protein binding on the nanocomposite by adjusting the environmental temperature. In general, the iminodiacetate-rich core-brush nano adsorbents are attractive for purifying histidine-tagged recombinant proteins practically. The synthetic approach reported here may be expanded to develop other advanced functional materials for applications in various biomedical fields ranging from biosensors to drug delivery.

Downstream Processing Technologies/Capturing and Final Purification : Opportunities for Innovation, Change, and Improvement. A Review of Downstream Processing Developments in Protein Purification

Increased pressure on upstream processes to maximize productivity has been crowned with great success, although at the cost of shifting the bottleneck to purification. As drivers were economical, focus is on now on debottlenecking downstream processes as the main drivers of high manufacturing cost. Devising a holistically efficient and economical process remains a key challenge. Traditional and emerging protein purification strategies with particular emphasis on methodologies implemented for the production of recombinant proteins of biopharmaceutical importance are reviewed. The breadth of innovation is addressed, as well as the challenges the industry faces today, with an eye to remaining impartial, fair, and balanced. In addition, the scope encompasses both chromatographic and non-chromatographic separations directed at the purification of proteins, with a strong emphasis on antibodies. Complete solutions such as integrated USP/DSP strategies (i.e., continuous processing) are discussed as well as gains in data quantity and quality arising from automation and high-throughput screening (HTS). Best practices and advantages through design of experiments (DOE) to access a complex design space such as multi-modal chromatography are reviewed with an outlook on potential future trends. A discussion of single-use technology, its impact and opportunities for further growth, and the exciting developments in modeling and simulation of DSP rounds out the overview. Lastly, emerging trends such as 3D printing and nanotechnology are covered. Graphical Abstract Workflow of high-throughput screening, design of experiments, and high-throughput analytics to understand design space and design space boundaries quickly. (Reproduced with permission from Gregory Barker, Process Development, Bristol-Myers Squibb).

Design of Synthetic Polymer Nanoparticles Specifically Capturing Indole, a Small Toxic Molecule

Synthetic polymers are of interest as stable and cost-effective biomolecule-affinity reagents, since these polymers interact with target biomolecules both in vitro and in the bloodstream. However, little has been reported about orally administered polymers capable of capturing a target molecule and inhibiting its intestinal absorption. Here, we describe the design of synthetic polymer nanoparticles (NPs) specifically capturing indole, a major factor exacerbating chronic kidney disease, in the intestine. N-isopropylacrylamide-based NPs were prepared with various hydrophobic monomers. The amounts of indole captured by NPs depended on the structures and feed ratios of the hydrophobic monomers and the polymer density but not on the particle size. The combination of hydrophobic and quadrupole interaction was effective to enhance the affinity and specificity of NPs for indole. The optimized NPs specifically inhibited intestinal absorption of orally administered indole in mice. These results showed the potential of synthetic polymer NPs for inhibiting the intestinal absorption of a target molecule.

Sequestering and inhibiting a vascular endothelial growth factor in vivo by systemic administration of a synthetic polymer nanoparticle

Protein affinity reagents (PARs), frequently antibodies, are essential tools for basic research, diagnostics, separations and for clinical applications. However, there is growing concern about the reproducibility, quality and cost of recombinant and animal-derived antibodies. This has prompted the development of alternatives that could offer economic, and time-saving advantages without the use of living organisms. Synthetic copolymer nanoparticles (NPs), engineered with affinity for specific protein targets, are potential alternatives to PARs. Although there are now a number of examples of abiotic protein affinity reagents (APARs), most have been evaluated in vitro limiting a realistic assessment of their potential for more demanding, practical in vivo applications. We demonstrate for the first time that an abiotic copolymer hydrogel nanoparticle (NP1) engineered to bind a key signaling protein, vascular endothelial growth factor (VEGF₁₆₅), functions in vivo to suppress tumor growth by regulating angiogenesis. Lightly cross-linked N-isopropylacrylamide based NPs that incorporate both sulfated N-acetylglucosamine and hydrophobic monomers were optimized by dynamic chemical evolution for VEGF₁₆₅ affinity. NP1 efficacy in vivo was evaluated by systemic administration to tumor-bearing mice. The study found that NP1 suppresses tumor growth and reduces tumor vasculature density. Combination therapy with doxorubicin resulted in increased doxorubicin concentration in the tumor and dramatic inhibition of tumor growth. NP1 treatment did not show off target anti-coagulant activity. In addition, >97% of injected NPs are rapidly excreted from the body following IV injection. These results establish the use of APARs as inhibitors of protein-protein interactions in vivo and may point the way to their broader use as abiotic, cost effective protein affinity reagents for the treatment of certain cancers and more broadly for regulating signal transduction.

Sealing hyaluronic acid microgels with oppositely-charged polypeptides: A simple strategy for packaging hydrophilic drugs with on-demand release

A simple route to deliver on demand hydrosoluble molecules such as peptides, packaged in biocompatible and biodegradable microgels, is presented. Hyaluronic acid hydrogel particles with a controlled structure are prepared using a microfluidic approach. Their porosity and their rigidity can be tuned by changing the crosslinking density. These negatively-charged polyelectrolytes interact strongly with positively-charged linear peptides such as poly-l-lysine (PLL). Their interactions induce microgel deswelling and inhibit microgel enzymatic degradability by hyaluronidase. While small PLL penetrate the whole volume of the microgel, PLL larger than the mesh size of the network remain confined at its periphery. They make a complexed layer with reduced pore size, which insulates the microgel inner core from the outer medium. Consequently, enzymatic degradation of the matrix is fully inhibited and non-affinity hydrophilic species can be trapped in the core. Indeed, negatively-charged or small neutral peptides, without interactions with the network, usually diffuse freely across the network. By simple addition of large PLL, they are packaged in the core and can be released on demand, upon introduction of an enzyme that degrades selectively the capping agent. Single polyelectrolyte layer appears as a simple generic method to coat hydrogel-based materials of various scales for encapsulation and controlled delivery of hydrosoluble molecules.

Functionalized Nano-adsorbent for Affinity Separation of Proteins

Thiol-functionalized silica nanospheres (SiO₂-SH NSs) with an average diameter of 460 nm were synthesized through a hydrothermal route. Subsequently, the prepared SiO₂-SH NSs were modified by SnO₂ quantum dots to afford SnO₂/SiO₂ composite NSs possessing obvious fluorescence, which could be used to trace the target protein. The SnO₂/SiO₂ NSs were further modified by reduced glutathione (GSH) to obtain SnO₂/SiO₂-GSH NSs, which can specifically separate glutathione S-transferase-tagged (GST-tagged) protein. Moreover, the peroxidase activity of glutathione peroxidase 3 (GPX3) separated from SnO₂/SiO₂-GSH NSs in vitro was evaluated. Results show that the prepared SnO₂/SiO₂-GSH NSs exhibit negligible nonspecific adsorption, high concentration of protein binding (7.4 mg/g), and good reused properties. In the meantime, the GST-tagged GPX3 separated by these NSs can retain its redox state and peroxidase activity. Therefore, the prepared SnO₂/SiO₂-GSH NSs might find promising application in the rapid separation and purification of GST-tagged proteins.

Thermodynamic and conformational analysis of the interaction between antibody binding proteins and IgG

Studying interaction of IgG with bacterial proteins such as proA (Protein A) and proG is essential for development in the areas of drug discovery and biotechnology. Some solution studies in the past have hinted at the possibility of variable binding ratios for IgG with proA and proG. Since earlier crystallographic studies focussed mostly on monomeric complexes, the knowledge about the binding interfaces and protein conformational changes involved in multimeric complexes is scarce. In this paper, we observed that single proA molecule was able to bind to three IgG molecules (1:3, proA:IgG) in ITC accentuating the presence of conformational flexibility in proA, corroborated also by CD results. By contrast, proG binds with 1:1 stoichiometry to IgG, which also involves key structural rearrangement within the binding interface of IgG-proG complex, confirmed by fluorescence KI quenching study. It is implicit from CD and fluorescence results that IgG does not undergo any significant conformational changes, which further suggests that proA and proG dictate the phenomenon of recognition in antibody complexes. ANS as a hydrophobic probe helped in revealing the distinctive antibody binding mechanism of proA and proG. Additionally, the binding competition experiments using ITC established that proA and proG cannot bind IgG concurrently.

A polymer nanoparticle with engineered affinity for a vascular endothelial growth factor (VEGF165)

Protein affinity reagents are widely used in basic research, diagnostics and separations and for clinical applications, the most common of which are antibodies. However, they often suffer from high cost, and difficulties in their development, production and storage. Here we show that a synthetic polymer nanoparticle (NP) can be engineered to have many of the functions of a protein affinity reagent. Polymer NPs with nM affinity to a key vascular endothelial growth factor (VEGF₁₆₅) inhibit binding of the signalling protein to its receptor VEGFR-2, preventing receptor phosphorylation and downstream VEGF₁₆₅-dependent endothelial cell migration and invasion into the extracellular matrix. In addition, the NPs inhibit VEGF-mediated new blood vessel formation in Matrigel plugs in vivo. Importantly, the non-toxic NPs were not found to exhibit off-target activity. These results support the assertion that synthetic polymers offer a new paradigm in the search for abiotic protein affinity reagents by providing many of the functions of their protein counterparts.

Wide-range pKa tuning of proton imprinted nanoparticles for reversible protonation of target molecules via thermal stimuli

pK_a tuning of Brønsted acids in synthetic nano-materials is of great importance for the design of ion exchange and bio-/molecular-separation media and polymer catalysis.

Self-assembly and the hemolysis effect of monodisperse N,N-diethylacrylamide/acrylic acid nanogels with high contents of acrylic acid

Monodisperse temperature/pH sensitive poly(N,N-diethylacrylamide/acrylic acid) (P(DEA/AAc)) nanogels with high contents of AAc up to 40 wt% have been prepared. In this study, it was unexpectedly found that the polydispersity of the nanogels with 40 wt% AAc strongly depended on the initiator concentration. Monodisperse P(DEA/AA) nanogels were synthesized only at a very low concentration of initiator. The phase transition behavior of the nanogels in water can be tuned by pH and temperature. Due to low polydispersity, the nanogels self-assembled into colloidal crystals at different temperatures below the volume phase transition temperature (VPTT). The sharp Bragg peaks of the crystals were significantly blue-shifted as the concentration of the nanogels was increased. In contrast, the condensed suspensions without crystals still exhibited clear colours resulting from a short-range order structure. The reflection spectra of the coloured suspensions showed that the peak wavelength became a bit longer and much broader. And the reflection intensity of the coloured suspensions was much weaker. Elastic and coloured crosslinked nanogel networks prepared by a one-pot and rapid light-initiated crosslinking method showed responses to pH and temperature. Furthermore, the interaction between the nanogels and peptide melittin was investigated. The results showed that an increasing AAc composition led to more efficient inhibition of the hemolytic activity of melittin. The nanogels with 40 wt% AAc composition completely inhibited hemolytic activity at a nanogel concentration of 400 µg ml(-1). Thus, monodisperse P(DEA/AAc) nanogels of high AAc composition may be developed as efficient substitutes for antibody-based antidotes. Owing to the combined influence of the periodic structure of the crystals of the nanogels and an efficient neutralization effect, the P(DEA/AAc) nanogels show promise to become an integral step for preparing valuable naked-eye biosensors as simple, cheap and stable substitutes for antibody-based antidotes.

Tuning the Protein Corona of Hydrogel Nanoparticles: The Synthesis of Abiotic Protein and Peptide Affinity Reagents

Nanomaterials, when introduced into a complex, protein-rich environment, rapidly acquire a protein corona. The type and amount of proteins that constitute the corona depend significantly on the synthetic identity of the nanomaterial. For example, hydrogel nanoparticles (NPs) such as poly(N-isopropylacrylamide) (NIPAm) have little affinity for plasma proteins; in contrast, carboxylated poly(styrene) NPs acquire a dense protein corona. This range of protein adsorption suggests that the protein corona might be "tuned" by controlling the chemical composition of the NP. In this Account, we demonstrate that small libraries of synthetic polymer NPs incorporating a diverse pool of functional monomers can be screened for candidates with high affinity and selectivity to targeted biomacromolecules. Through directed synthetic evolution of NP compositions, one can tailor the protein corona to create synthetic organic hydrogel polymer NPs with high affinity and specificity to peptide toxins, enzymes, and other functional proteins, as well as to specific domains of large proteins. In addition, many NIPAm NPs undergo a change in morphology as a function of temperature. This transformation often correlates with a significant change in NP-biomacromolecule affinity, resulting in a temperature-dependent protein corona. This temperature dependence has been used to develop NP hydrogels with autonomous affinity switching for the protection of proteins from thermal stress and as a method of biomacromolecule purification through a selective thermally induced catch and release. In addition to temperature, changes in pH or buffer can also alter a NP protein corona composition, a property that has been exploited for protein purification. Finally, synthetic polymer nanoparticles with low nanomolar affinity for a peptide toxin were shown to capture and neutralize the toxin in the bloodstream of living mice. While the development of synthetic polymer alternatives to protein affinity reagents is in its early stages, these recent successes using only small libraries of functional monomers are most encouraging. It is likely that by expanding the chemical diversity of functional hydrogels and other polymers, a much broader range of NP-biomacromolecule affinity pairs will result. Since these robust, nontoxic polymers are readily synthesized in the chemistry laboratory, we believe the results presented in this Account offer a promising future for the development of low cost alternatives to more traditional protein affinity reagents such as antibodies.

Selective removal of IgG from the urine of patients with proteinuria using a polymer coated core–shell magnetic nanoparticle

A synthetic monomer ofN-methacryloyl-l-aspartic acid plays a specific recognition role in magnetic separation of IgG from urinary protein sample using Fe₃O₄@SiO₂@MAsp-HEMA nanoparticles.

The use of differential scanning fluorimetry in the rational design of plastic antibodies for protein targets

Predicted interactions between acrylic monomers and proteins, and melting profiles using DSF in the rational design of MIP-NPs for proteins.

Tailor-Made Boronic Acid Functionalized Magnetic Nanoparticles with a Tunable Polymer Shell-Assisted for the Selective Enrichment of Glycoproteins/Glycopeptides

Biomedical sciences, and in particular biomarker research, demand efficient glycoproteins enrichment platforms. In this work, we present a facile and time-saving method to synthesize phenylboronic acid and copolymer multifunctionalized magnetic nanoparticles (NPs) using a distillation-precipitation polymerization (DPP) technique. The polymer shell is obtained through copolymerization of two monomers-affinity ligand 3-acrylaminophenylboronic acid (AAPBA) and a hydrophilic functional monomer. The resulting hydrophilic Fe3O4@P(AAPBA-co-monomer) NPs exhibit an enhanced binding capacity toward glycoproteins by an additional functional monomer complementary to the surface presentation of the target protein. The effects of monomer ratio of AAPBA to hydrophilic comonomers on the binding of glycoproteins are systematically investigated. The morphology, structure, and composition of all the synthesized microspheres are characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and vibrating sample magnetometer (VSM). The hydrophilic Fe3O4@P(AAPBA-co-monomer) microspheres show an excellent performance in the separation of glycoproteins with high binding capacity; And strong magnetic response allows them to be easily separated from solution in the presence of an external magnetic field. Moreover, both synthetic Fe3O4@P(AAPBA) and copolymeric NPs show good adsorption to glycoproteins in physiological conditions (pH 7.4). The Fe3O4@P(AAPBA-co-monomer) NPs are successfully utilized to selectively capture and identify the low-abundance glycopeptides from the tryptic digest of horseradish peroxidase (HRP). In addition, the selective isolation and enrichment of glycoproteins from the egg white samples at physiological condition is obtained by Fe3O4@P(AAPBA-co-monomer) NPs as adsorbents.

Surface plasmon resonance based on molecularly imprinted nanoparticles for the picomolar detection of the iron regulating hormone Hepcidin-25

BACKGROUND

Molecularly imprinted polymer (MIP) technique is a powerful mean to produce tailor made synthetic recognition sites. Here precipitation polymerization was exploited to produce a library of MIP nanoparticles (NPs) targeting the N terminus of the hormone Hepcidin-25, whose serum levels correlate with iron dis-metabolisms and doping. Biotinylated MIP NPs were immobilized to NeutrAvidin™ SPR sensor chip. The response of the MIP NP sensor to Hepcidin-25 was studied.

FINDINGS

Morphological analysis showed MIP NPs of 20-50 nm; MIP NP exhibited high affinity and selectivity for the target analyte: low nanomolar Kds for the interaction NP/Hepcidin-25, but none for the NP/non regulative Hepcidin-20. The MIP NP were integrated as recognition element in SPR allowing the detection of Hepcidin-25 in 3 min. Linearity was observed with the logarithm of Hepcidin-25 concentration in the range 7.2-720 pM. LOD was 5 pM. The response for Hepcidin-20 was limited. Hepcidin-25 determination in real serum samples spiked with known analyte concentrations was also attempted.

CONCLUSION

The integration of MIP NP to SPR allowed the determination of Hepcidin-25 at picomolar concentrations in short times outperforming the actual state of art. Optimization is still needed for real sample measurements in view of future clinical applications.

Synthesis of surfactant-free hydroxypropylcellulose nanogel and its dual-responsive properties

Surfactant-free hydroxypropylcellulose (HPC) nanogels were synthesized by using thermo-sensitive HPC as a template to form HPC/PMAA nanoscale complex. The formation mechanism was owing to the interpolymer hydrogen bonding between HPC and PMAA induced phase transition of HPC in aqueous media. The average size of the resulting HPC nanogels ranges from about 98 to 241 nm. It was found that the average size of HPC nanogels changed little with increasing polymerization temperature below 26 °C, whereas it greatly increased above 26 °C. When the concentration of HPC was increased from 0.1 to 0.9 wt.%, the diameter of nanogels decreased firstly and then increased. Besides, an increasing crosslinker BIS concentration led to a reduced size of HPC nanogels, and the nanogels had the narrowest size distribution when its concentration was 0.1 wt.%. In addition to intrinsic thermo-sensitivity, HPC nanogels also display pH-induced phase transition due to pH-responsive PMAA contained in HPC nanogels. Surfactant-free, dual-responsive HPC nanogels would have promising applications in biotechnology and nanomedicine.

Optical sensing of phenylalanine in urine via extraction with magnetic molecularly imprinted poly(ethylene-co-vinyl alcohol) nanoparticles

Incorporation of superparamagnetic nanoparticles into molecularly imprinted polymers (MIPs) is useful for both bioseparations and for concentration and sensing of biomedically relevant target molecules in physiological fluids, through the application of a magnetic field. In this study, we combined the separation and concentration of a target (phenylalanine) in urine, using magnetic molecularly imprinted polymeric composite nanoparticles, with optical sensing, to improve assay sensitivity. This target is important as a catecholamine precursor, and as an important amino acid constituent of proteins. Poly(ethylene-co-vinyl alcohol)s were imprinted with target molecules, and showed a high imprinting effectiveness (target binding compared with binding to non-imprinted polymer particles.) Fluorescence spectrophotometry was used to measure binding of the target, and also binding of possible interfering compounds. These measurements suggest that functional groups on phenylalanine dominate the selectivity of the synthesized MIPs. Finally, the composite nanoparticles were used to separate and sense the target molecule in urine by Raman scattering microscopy.