PEG-proteins: Reaction engineering and separation issues

Protein-polyelectrolyte complexation: effects of sterically repulsive groups, macromolecular architecture and hierarchical assembly

Self-assembly of proteins and polyelectrolytes in aqueous solutions is a promising approach for the development of advanced biotherapeutics and engineering efficient biotechnological processes. Synthetic polyions containing sterically repulsive ethylene oxide moieties are especially attractive as protein modifying agents, as they can potentially induce a PEGylation-like stabilizing effect without the need for complex covalent binding reactions. In this study, we investigated the protein-binding properties of anionic polyelectrolytes based on an inorganic polyphosphazene backbone, with ethylene oxide groups incorporated into both grafted and linear macromolecular topologies. The study was conducted in aqueous solutions using isothermal titration calorimetry, dynamic light scattering, and cryogenic electron microscopy to analyze the samples in their vitrified state. Our findings revealed that the stability of the resulting protein-polyion complexes and the thermodynamic profiles of these interactions were influenced by the molecular architecture of the polyions. Furthermore, the formation of hierarchical assemblies of polyions, through ionic crosslinking into nanogels, rapidly reduced or eliminated the ability of the polyelectrolyte to bind proteins. The comprehensive analysis, combining thermodynamic, spectroscopy and direct visualization techniques, provides valuable insights into the multivalent charge-charge interactions that are critical for the development of successful non-covalent protein modification methods.

Strategies for extending the half-life of biotherapeutics: successes and complications

INTRODUCTION

Engineering of the drug half-life in vivo has become an integral part of modern biopharmaceutical development due to the fact that many proteins/peptides with therapeutic potential are quickly cleared by kidney filtration after injection and, thus, circulate only a few hours in humans (or just minutes in mice).

AREAS COVERED

Looking at the growing list of clinically approved biologics that have been modified for prolonged activity, and also the plethora of such drugs under preclinical and clinical development, it is evident that not one solution fits all needs, owing to the vastly different structural features and functional properties of the pharmacologically active entities. This article provides an overview of established half-life extension strategies, as well as of emerging novel concepts for extending the in vivo stability of biologicals, and their pros and cons.

EXPERT OPINION

Beyond the classical and still dominating technologies for improving drug pharmacokinetics and bioavailability, Fc fusion and PEGylation, various innovative approaches that offer advantages in different respects have entered the clinical stage. While the Fc fusion partner may be gradually superseded by engineered albumin-binding domains, chemical PEGylation may be replaced by biodegradable recombinant amino-acid polymers like PASylation, thus also offering a purely biotechnological manufacturing route.

Reinforcement of the intestinal mucosal barrier via mucus-penetrating PEGylated bacteria

The breakdown of the gut's mucosal barrier that prevents the infiltration of microorganisms, inflammatory cytokines and toxins into bodily tissues can lead to inflammatory bowel disease and to metabolic and autoimmune diseases. Here we show that the intestinal mucosal barrier can be reinforced via the oral administration of commensal bacteria coated with poly(ethylene glycol) (PEG) to facilitate their penetration into mucus. In mice with intestinal homoeostatic imbalance, mucus-penetrating PEGylated bacteria preferentially localized in mucus at the lower gastrointestinal tract, inhibited the invasion of pathogenic bacteria, maintained homoeostasis of the gut microbiota, stimulated the secretion of mucus and the expression of tight junctions, and prevented the mice from developing colitis and diabetes. Orally delivered PEGylated bacteria may help prevent and treat gastrointestinal disorders.

Delivery of protein therapeutics and vaccines using their multivalent complexes with synthetic polyelectrolytes

Clinical applications of protein and peptide-based therapeutics and vaccines are rapidly expanding. However, the development of promising new product candidates is often hindered by unfavorable pharmacokinetic profiles, which necessitate the implementation of drug delivery systems to improve protein stability and bioavailability. Non-covalent modification of proteins with synthetic polyelectrolytes, which relies on the strength of cooperative multivalent interactions, may offer potential advantages. In contrast to commonly employed covalent conjugation or microencapsulation methodologies, this technology offers dynamic protection of the protein thereby minimizing the loss of its biological activity, enabling "mix-and-match" formulation approaches, reducing manufacturing costs and simplifying regulatory processes. The range of potential life sciences applications ranges from immunopotentiation and vaccine delivery systems to long-circulating stealth biotherapeutics. This review analyses current technology in the context of intended clinical indications and discusses various synthetic and formulation approaches leading to supramolecular complexation. It evaluates dynamic interactions of complexes with constituents of physiological compartments and attempts to identify critical factors that can affect future advancement of this paradigm-shifting protein delivery technology.

Jellyfish-inspired smart tetraphenylethene lipids with unique AIE fluorescence, thermal response, and cell membrane interaction

Smart lipids with fluorescence emission, thermal response, and polyethylene glycolation (PEGylation) functions can be highly valuable for formulation, image-traceable delivery, and targeted release of payloads. Herein, a series of jellyfish-shaped amphiphiles with a tetraphenylethene (TPE) core and four symmetrical amphiphilic side chains were conveniently synthesized and systematically investigated as smart lipids. Compared with regular amphiphilic TPE lipids and phospholipids, the unprecedented jellyfish-shaped molecular geometry was found to enable a series of valuable capabilities, including sensitive and responsive aggregation-induced emission of fluorescence (AIE FL) and real-time FL monitoring of drug uptake. Furthermore, the jellyfish-shaped geometry facilitated the concentration-dependent aggregation from unimolecular micelles at low concentrations to "side-by-side" spherical aggregates at high concentrations and a unique mode of AIE. In addition, the size and the arrangement of the amphiphilic side chains were found to dominate the aggregate stability, cell uptake, and thus the cytotoxicity of the amphiphiles. This study has unprecedentedly developed versatile smart TPE lipids with precise structures, and unique physicochemical and biological properties while the peculiar structure-property relationship may shed new light on the design and application of AIE fluorophores and functional lipids in biomedicine and materials science.

Therapeutic synthetic and natural materials for immunoengineering

Immunoengineering is a rapidly evolving field that has been driving innovations in manipulating immune system for new treatment tools and methods. The need for materials for immunoengineering applications has gained significant attention in recent years due to the growing demand for effective therapies that can target and regulate the immune system. Biologics and biomaterials are emerging as promising tools for controlling immune responses, and a wide variety of materials, including proteins, polymers, nanoparticles, and hydrogels, are being developed for this purpose. In this review article, we explore the different types of materials used in immunoengineering applications, their properties and design principles, and highlight the latest therapeutic materials advancements. Recent works in adjuvants, vaccines, immune tolerance, immunotherapy, and tissue models for immunoengineering studies are discussed.

Noncovalent PEGylation of protein and peptide therapeutics

Clinical applications of protein therapeutics-an advanced generation of drugs characterized by high biological specificity-are rapidly expanding. However, their development is often impeded by unfavorable pharmacokinetic profiles and largely relies on the use of drug delivery systems to prolong their in vivo half-life and suppress undesirable immunogenicity. Although a commercially established PEGylation technology based on protein conjugation with poly(ethylene glycol) (PEG)-protective steric shield resolves some of the challenges, the search for alternatives continues. Noncovalent PEGylation, which mainly relies on multivalent (cooperative) interactions and high affinity (host-guest) complexes formed between protein and PEG offers a number of potential advantages. Among them are dynamic or reversible protection of the protein with minimal loss of biological activity, drastically lower manufacturing costs, "mix-and-match" formulations approaches, and expanded scope of PEGylation targets. While a great number of innovative chemical approaches have been proposed in recent years, the ability to effectively control the stability of noncovalently assembled protein-PEG complexes under physiological conditions presents a serious challenge for the commercial development of the technology. In an attempt to identify critical factors affecting pharmacological behavior of noncovalently linked complexes, this Review follows a hierarchical analysis of various experimental techniques and resulting supramolecular architectures. The importance of in vivo administration routes, degradation patterns of PEGylating agents, and a multitude of potential exchange reactions with constituents of physiological compartments are highlighted. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

A normalized differential sequence feature encoding method based on amino acid sequences

Protein interactions are the foundation of all metabolic activities of cells, such as apoptosis, the immune response, and metabolic pathways. In order to optimize the performance of protein interaction prediction, a coding method based on normalized difference sequence characteristics (NDSF) of amino acid sequences is proposed. By using the positional relationships between amino acids in the sequences and the correlation characteristics between sequence pairs, NDSF is jointly encoded. Using principal component analysis (PCA) and local linear embedding (LLE) dimensionality reduction methods, the coded 174-dimensional human protein sequence vector is extracted using sequence features. This study compares the classification performance of four ensemble learning methods (AdaBoost, Extra trees, LightGBM, XGBoost) applied to PCA and LLE features. Cross-validation and grid search methods are used to find the best combination of parameters. The results show that the accuracy of NDSF is generally higher than that of the sequence matrix-based coding method (MOS) coding method, and the loss and coding time can be greatly reduced. The bar chart of feature extraction shows that the classification accuracy is significantly higher when using the linear dimensionality reduction method, PCA, compared to the nonlinear dimensionality reduction method, LLE. After classification with XGBoost, the model accuracy reaches 99.2%, which provides the best performance among all models. This study suggests that NDSF combined with PCA and XGBoost may be an effective strategy for classifying different human protein interactions.

Membrane-Based Hybrid Method for Purifying PEGylated Proteins

PEGylated proteins are usually purified using chromatographic methods, which are limited in terms of both speed and scalability. In this paper, we describe a microfiltration membrane-based hybrid method for purifying PEGylated proteins. Polyethylene glycol (or PEG) is a lower critical solution temperature polymer which undergoes phase transition in the presence of a lyotropic salt and forms micelle-like structures which are several microns in size. In the proposed hybrid method, the PEGylated proteins are first converted to their micellar form by the addition of a lyotropic salt (1.65 M ammonium sulfate). While the micelles are retained using a microfiltration membrane, soluble impurities such as the unmodified protein are washed out through the membrane. The PEGylated proteins thus retained by the membrane are recovered by solubilizing them by removing the lyotropic salt. Further, by precisely controlling the salt removal, the different PEGylated forms of the protein, i.e., mono-PEGylated and di-PEGylated forms, are fractionated from each other. Hybrid separation using two different types of microfiltration membrane devices, i.e., a stirred cell and a tangential flow filtration device, are examined in this paper. The membrane-based hybrid method for purifying PEGylated proteins is both fast and scalable.

PEGylation of genistein-loaded bovine serum albumin nanoparticles and its effect on in vitro cell viability and genotoxicity properties

Self-assembled bovine serum albumin nanoparticles loaded with the isoflavone genistein have shown apoptosis-mediated cytotoxicity against murine mammary adenocarcinoma F3II cells. Due to their protein nature and small particle size (13-15 nm), their parenteral administration could be affected by possible immunogenic reactions and rapid clearance from the bloodstream. To avoid these problems, PEGylation of the systems was achieved in this work by using a 30 kDa methoxy-polyethylene glycol carbonyl imidazole derivative through the reaction between the carbonyl imidazole group and the amino groups of Lys residues on the protein surface, which was confirmed by a 17% reduction in the available amino groups content measured by the o-phthaldialdehyde method. PEGylated isoforms were obtained, showing an increase of particle size from 13 to 15 nm to around 260 nm, and were purified by SEC-FPLC and characterized by SDS-PAGE, DLS and AFM techniques. The effect of PEGylation on BSAnp-Gen cytotoxicity and genotoxicity against F3II cells was evaluated in vitro by MTT assay, flow cytometry analysis and micronucleus assay. From the results, PEGylation produced an improvement of the biological properties of genistein-loaded nanoparticles in terms of cytotoxicity (lower IC₅₀), not affecting the induction of apoptosis, decreasing the genotoxicity of the systems (less induction of micronucleus formation).

The Effect of Length and Structure of Attached Polyethylene Glycol Chain on Hydrodynamic Radius, and Separation of PEGylated Human Serum Albumin by Chromatography

Purpose: This study focuses on the effect of length and structure of attached polyethylene glycol (PEG) chain on hydrodynamic radius (R_h ) and chromatographic retention of PEGylated protein. To this aim human serum albumin (HSA) as a standard protein was PEGylated site specifically with mPEG-maleimide. Methods: Separated PEG_HSA fractions were analyzed by size exclusion and anion exchange chromatography (AExC). The purity of fractions and the relative mobility of PEGylated and native proteins were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Hydrodynamic radius was determined based on the retention time of fractions on size exclusion chromatography (SEC), and also according to the previously reported equations. Results: A linear relation was shown between the molecular weight of attached PEG and R_h of PEGylated HSA. No significant difference between R_h of proteins modified with linear and branched PEG was shown. In SDS-PAGE, the delaying effect of branched PEG on movement of PEGylated protein was higher than that of linear PEG. Conclusion: As PEGylated HSA and dimer HSA have almost the same size and in SEC they elute at very close retention times, so in this case ion exchange chromatography (IExC) is more effective than SEC in separation of PEGylated HSA. Branched PEG- HSA showed earlier elution on anion exchange chromatography compared to linear PEG-HSA, that this can explain the different shielding effect of various structures of attached PEGs. The smaller size of PEGylated HSA in compare to the sum of the hydrodynamic radiuses of native HSA and attached PEG could be as a result of shielded attachment of polymer around protein.

Purification of Modified Therapeutic Proteins Available on the Market: An Analysis of Chromatography-Based Strategies

Proteins, which have inherent biorecognition properties, have long been used as therapeutic agents for the treatment of a wide variety of clinical indications. Protein modification through covalent attachment to different moieties improves the therapeutic's pharmacokinetic properties, affinity, stability, confers protection against proteolytic degradation, and increases circulation half-life. Nowadays, several modified therapeutic proteins, including PEGylated, Fc-fused, lipidated, albumin-fused, and glycosylated proteins have obtained regulatory approval for commercialization. During its manufacturing, the purification steps of the therapeutic agent are decisive to ensure the quality, effectiveness, potency, and safety of the final product. Due to the robustness, selectivity, and high resolution of chromatographic methods, these are recognized as the gold standard in the downstream processing of therapeutic proteins. Moreover, depending on the modification strategy, the protein will suffer different physicochemical changes, which must be considered to define a purification approach. This review aims to deeply analyze the purification methods employed for modified therapeutic proteins that are currently available on the market, to understand why the selected strategies were successful. Emphasis is placed on chromatographic methods since they govern the purification processes within the pharmaceutical industry. Furthermore, to discuss how the modification type strongly influences the purification strategy, the purification processes of three different modified versions of coagulation factor IX are contrasted.

Influence of excipients in Protein A chromatography and virus inactivation

The purification of monoclonal antibodies and Fc fusion proteins consist of several unit operations operated commonly as a platform approach, starting with Protein A chromatography. The first capture step, the following low pH virus inactivation, and subsequent ion exchange chromatography steps are mostly able to remove any impurities, like host cell proteins, aggregates, and viruses. The changes in pH and conductivity during these steps can lead to additional unwanted product species like aggregates. In this study, excipients with stabilizing abilities, like polyols, were used as buffer system additives to study their impact on several aspects during Protein A chromatography, low pH virus inactivation, and cation exchange chromatography. The results show that excipients, like PEG4000, influence antibody elution behavior, as well as host-cell protein elution behavior in a pH-gradient setup. Sugar excipients, like Sucrose, stabilize the antibody during low pH virus inactivation. All excipients tested show no negative impact on virus inactivation and dynamic binding capacity in a subsequent cation exchange chromatography step. This study indicates that excipients and, possibly excipient combinations, can have a beneficial effect on purification without harming subsequent downstream processing steps.

Fast and high-resolution purification of a PEGylated protein using a z2 laterally-fed membrane chromatography device

PEGylated proteins comprise a class of value-added biopharmaceuticals. High-resolution separation techniques are required for the purification of these molecules. In this study, we discuss the application of a newly developed z² laterally-fed membrane chromatography (or z²LFMC) device for carrying out high-resolution purification of a PEGylated protein drug. The device used in the current study contained a stack of anion exchange (Q) membranes. The membrane bed-height of this z²LFMC device being small, it could be operated at very high flow rates, at relatively low back pressures. The primary goal was to speedily and efficiently separate a mono-PEGylated protein from impurities present in the PEGylation reaction mixture. A resin-based anion exchange column having the same ligand and bed-volume was used as the control device. The purification performance of the z²LFMC device and the control column were compared terms of resolution, recovery and purity. The z²LFMC device outperformed the control column in terms of every metric compared in this study. Higher purity (85.4% as opposed to 77.9%) and higher recovery (28% greater) of the target mono-PEGylated protein were obtained using the z²LFMC device at 20-time higher speed. These results clearly demonstrate that the z²LFMC device could be a faster and more efficient alternative to resin-based columns for purification of biopharmaceuticals.

Atomistic insight towards the impact of polymer architecture and grafting density on structure-dynamics of PEGylated bovine serum albumin and their applications

Macromolecules such as proteins conjugated to polyethylene glycol (PEG) have been employed in therapeutic drug applications, and recent research has emphasized the potential of varying polymer architectures and conjugation strategies to achieve improved efficacy. In this study, we performed atomistic molecular dynamics simulations of bovine serum albumin (BSA) conjugated to 5 kDa PEG polymers in an array of schemes, including varied numbers of attached chains, grafting density, and nonlinear architectures. Nonlinear architectures included U-shaped PEG, Y-shaped PEG, and poly(oligoethylene glycol methacrylate) (POEGMA). Buried surface area calculations and polymer volume map analyses revealed that volume exclusion behaviors of the high grafting density conjugate promoted additional protein-polymer interactions when compared to simply increasing numbers of conjugated chains uniformly across the protein surface. Investigation of nonlinear polymer architectures showed that stable polymer-lysine loop-like conformations seen in previous conjugate designs were more variable in prevalence, especially in POEGMA, which contained short oligomer PEG chains. The findings of this comprehensive study of alternate PEGylation schemes of BSA provide critical insight into molecular patterns of interaction within bioconjugates and highlight their importance in the future of controlled modification of conjugate system parameters.

High-resolution purification of a therapeutic PEGylated protein using a cuboid packed-bed device

PEGylated proteins which are a class of protein-synthetic polymer conjugates that have shown significant promise in the area of biotherapeutics are difficult to purify. A cuboid packed-bed device was used to purify a mono-PEGylated therapeutic protein from impurities such as high molecular weight (HMW) species (e.g., tri- and/or di-PEGylated forms), and low molecular weight (LMW) species such as unreacted protein and polyethylene glycol (or PEG). The separation efficiency of this device was compared with that of an equivalent cylindrical column. The effects of operating conditions such as flow rate, buffer composition, elution gradient, and column loading were systematically compared. An equivalent column with the same bed volume, same resin and same bed height was served as control. In mono-PEGylated protein purifications experiments, the cuboid packed-bed device exhibited sharper peaks and gave better resolution at all conditions examined in this study. The purity of mono-PEGylated protein in the samples collected from the cuboid packed-bed device and the column were comparable, i.e., 98.1% and 97.9% respectively. The recovery of mono-PEGylated protein in the pooled eluate from the cuboid packed-bed device was 31.7% greater than that recovered in the pooled eluate from the column. Therefore, significantly higher recovery of mono-PEGylated protein was obtained with the cuboid packed-bed device while maintaining the same purity specification as obtained with the column.

Peptidic Monodisperse PEG "Comb" as Multifunctional "Add-On" Module for Imaging-Traceable and Thermo-Responsive Theranostics

Monodisperse polyethylene glycols-modified (M-PEGylated) biomaterials exhibit high structural accuracy, biocompatibility, and fine-tunable physicochemical properties. To develop "smart" drug delivery systems in a controllable and convenient manner, a peptidic M-PEG "comb" with fluorinated L-lysine side chains and a fluorescent N-terminal is conveniently prepared as a ¹⁹ F magnetic resonance imaging (¹⁹ F MRI) and fluorescence dual-imaging traceable and thermo-responsive "add-on" module for liposomal theranostics in cancer therapy. The peptidic M-PEG "comb" has high biocompatibility, thermo-responsivity with a sharp lower critical solution temperature, an aggregation-induced emission fluorescence, and high ¹⁹ F MRI sensitivity. As a highly branched amphiphile, it self-assembles and firmly anchors on the doxorubicin-loaded liposomal nanoparticles, which M-PEGylates the liposomes and facilitates the thermo-responsive drug release and drug tracking with dual-imaging technologies. In a rodent xenograft model of human liver cancer HepG2 cells, the M-PEGylated liposomes exhibit long in vivo half time, low toxicity, high tumor accumulation, "hot spot" ¹⁹ F MRI, and therapeutic efficacy. With accurately programmable chemical structure, fine-tunable physicochemical and biological properties to meet the demands of diagnosis, drug delivery, and therapy, the M-PEG "comb" is promising as a versatile "add-on" module for rapid and convenient formulation of various "smart" theranostics.

Perspectives, Tendencies, and Guidelines in Affinity-Based Strategies for the Recovery and Purification of PEGylated Proteins

In recent years, the effective purification of PEGylated therapeutic proteins from reaction media has received particular attention. Although several techniques have been used, affinity-based strategies have been scarcely explored despite the fact that, after PEGylation, marked changes in the molecular affinity parameters of the modified molecules are observed. With this in mind, future contributions in the bioseparation of these polymer-protein conjugates are expected to exploit affinity in chromatographic and nonchromatographic techniques which will surely derive in the integration of different operations. However, this will only occur as novel ligands which are simultaneously found. As it will be mentioned, these novel ligands may be screened or designed. In both cases, computer-aided tools will support their identification or development. Additionally, ligand discovery by high-throughput screening (HTS) is believed to become a fast, economic, and informative technology that will aid in the mass production of ligands along with genetic engineering and related technologies. Therefore, besides analyzing the state of the art in affinity separation strategies for PEGylated molecules, this review proposes a basic guideline for the selection of adequate ligands to provide information and prospective on the future of affinity operations in solving this particular bioengineering problem.

Impact of Site-Specific Bioconjugation on the Interfacial Activity of a Protein Biosurfactant

Biosurfactants are surface active molecules that can be produced by renewable, industrially scalable biologic processes. DAMP4, a designer biosurfactant, enables the modification of interfaces via genetic or chemical fusion to functional moieties. However, bioconjugation of addressable amines introduces heterogeneity that limits the precision of functionalization as well as the resolution of interfacial characterization. Here, we designed DAMP4 variants with cysteine point mutations to allow for site-specific bioconjugation. The DAMP4 variants were shown to retain the structural stability and interfacial activity characteristic of the parent molecule, while permitting efficient and specific conjugation of polyethylene glycol (PEG). PEGylation results in a considerable reduction on the interfacial activity of both single and double mutants. Comparison of conjugates with one or two conjugation sites shows that both the number of conjugates as well as the mass of conjugated material impact the interfacial activity of DAMP4. As a result, the ability of DAMP4 variants with multiple PEG conjugates to impart colloidal stability on peptide-stabilized emulsions is reduced. We suggest that this is due to steric constraints on the structures of amphiphilic helices at the interface. Specific and efficient bioconjugation permits the exploration and investigation of the interfacial properties of designer protein biosurfactants with molecular precision. Our findings should therefore inform the design and modification of biosurfactants for their increasing use in industrial processes and nutritional and pharmaceutical formulations.

Evaluating the ion exchange chromatography for matrix-assisted PEGylation and purification of consensus interferon

Scientists have implemented protein-PEGylation technology for boosting-up the pharmacokinetics and stability of recombinant therapeutic proteins. In the present study, (a) matrix-assisted PEGylation was compared with solution-phase PEGylation and (b) matrix-assisted PEGylation was performed with different ion exchange resins for impact of chromatography medium on yield and purity of PEGylated product. DEAE Sepharose CL 6B, DEAE Fracto gel, and Macro cap Q ion exchange chromatography medium were compared for on column PEGylation and purification of cIFN. A MSC-PEG of 12.0 KDa was selected. cIFN was bound to ion exchange medium, and PEG solution was passed through resin for 180 Min, and protein was eluted by sodium chloride linear gradient. Yield and purity for mono-PEGylated cIFN with Macro cap Q matrix was 75% and 99%, respectively, whereas for DEAE Sepharose was 45% and 60%. DEAE Fracto gel^TM purity was 85% with 50% yield of mono-PEGylated cIFN. Further investigation of in vitro biological activities demonstrated that about 30% antiviral activity was reduced as compared to unmodified cIFN. However, thermal stability was significantly improved. The present study proved that matrix-assisted PEGylation can improve the yield and purity of mono-PEGylated product, and Macro Cap resin provided the highest yield of a homogeneous product. In present study, (a) matrix-assisted PEGylation was compared with solution-phase PEGylation and (b) matrix-assisted PEGylation was performed with different ion exchange resins for impact of chromatography medium on yield and purity of PEGylated product. Matrix-assisted PEGylation increases the yield of mono-PEGylated product and further Macro Cap^TM produced highest yield and purity of PEGylated cIFN.

Rational surface engineering of an arginine deiminase (an antitumor enzyme) for increased PEGylation efficiency

Arginine deiminase (ADI) is a therapeutic protein for cancer therapy of arginine-auxotrophic tumors. However, its application as anticancer drug is hampered by its poor stability under physiological conditions in the bloodstream. Commonly, random PEGylation is being used for increasing the stability of ADI and in turn the improved half-life. However, the traditional random PEGylation usually leads to poor PEGylation efficiency due to the limited number of Lys on the protein surface. To boost the PEGylation efficiency and enhance the stability of ADI further, surface engineering of PpADI (an ADI from Pseudomonas plecoglossicida) to increase the suitable PEGylation sites was carried out. A new in silico approach for increasing the PEGylation sites was developed. The validation of this approach was performed on previously identified PpADI variant M31 to increase potential PEGylation sites. Four Arg residues on the surface of PpADI M31 were selected through three criteria and subsequently substituted to Lys, aiming for providing primary amines for PEGylation. Two out of the four substitutions (R299K and R382K) enhanced the stability of PEGylated PpADI in human serum. The average numbers of PEGylation sites were increased from ~12 (tetrameric PpADI M31, starting point) to ~20 (tetrameric PpADI M36, final variant). Importantly, the PEGylated PpADI M36 after PEGylation exhibited significantly improved T_m values (M31: 40°C; M36: 40°C; polyethylene glycol [PEG]-M31: 54°C; PEG-M36: 64°C) and half-life in human serum (M31: 1.9 days; M36: 2.0 days; PEG-M31: 3.2 days; PEG-M36: 4.8 days). These proved that surface engineering is an effective approach to increase the PEGylation efficiency which therefore enhances the stability of therapeutic enzymes. Furthermore, the PEGylated PpADI M36 represents a highly attractive candidate for the treatment of arginine-auxotrophic tumors.

Thermo-separating polymer-based aqueous two-phase systems for the recovery of PEGylated lysozyme species

Fractionation of native, mono and di-PEGylated lysozyme was performed in 36 different polymer-polymer aqueous two-phase systems using UCON as a phase-forming component. After a discrete partition analysis, dextran 75 kDa-UCON, volume ratio 3, tie-line length 35% w/w; ficoll 70 kDa-UCON, volume ratio 1, tie-line length 45% w/w and a PEG 8 kDa-UCON volume ratio 3, tie-line length 65% w/w systems were selected for optimization via salt addition and to observe the behavior of the lysozyme species in mixtures. The dextran-UCON and the PEG-UCON systems with 75 mM NaCl showed effectiveness in separating 75% and 87% of mono-PEGylated lysozyme from the rest of the lysozyme species in the top and bottom phases, respectively. These results are an advancement in incorporating these extractions in different processes since the use of UCON simplifies the removal of the polymers, providing the opportunity of recycling it to the operation.

One-pot synthesis of monodisperse dual-functionalized polyethylene glycols through macrocyclic sulfates

Dual-functionalization of monodisperse oligoethylene glycols, especially hetero-functionalization, provides a series of highly valuable intermediates for life and materials sciences. However, the existing methods for the preparation of these compounds suffer excessive protecting and activating group manipulation as well as tedious purification. Here, a one-pot dual-substitution strategy with macrocyclic sulfates of polyethylene glycols as the key intermediates was developed for the convenient and scalable preparation of a series of homo-functionalized and hetero-functionalized oligoethylene glycols in just 1 step. A high synthetic efficacy was achieved by avoiding the protecting and activating group manipulation and the intermediate purification.

Hydrolytically Degradable PEGylated Polyelectrolyte Nanocomplexes for Protein Delivery

Novel oppositely charged polyphosphazene polyelectrolytes containing grafted poly(ethylene glycol) (PEG) chains were synthesized as modular components for the assembly of biodegradable PEGylated protein delivery vehicles. These macromolecular counterparts, which contained either carboxylic acid or tertiary amino groups, were then formulated at near physiological conditions into supramolecular assemblies of nanoscale level, below 100 nm. Nanocomplexes with electroneutral surface charge, as assessed by zeta potential measurements, were stable in aqueous solutions, which suggests their compact polyelectrolyte complex "core"-hydrophilic PEG "shell" structure. Investigation of PEGylated polyphosphazene nanocomplexes as agents for noncovalent PEGylation of the therapeutic protein l-asparaginase (L-ASP) in vitro demonstrated their ability to dramatically reduce protein antigenicity, as measured by antibody binding using enzyme linked immunosorbent assay (ELISA). Encapsulation in nanocomplexes did not affect enzymatic activity of L-ASP, but improved its thermal stability and proteolytic resistance. Gel permeation chromatography (GPC) experiments revealed that all synthesized polyphosphazenes exhibited composition controlled hydrolytic degradability in aqueous solutions at neutral pH and showed greater stability at lower temperatures. Overall, novel hydrolytically degradable polyphosphazene polyelectrolytes capable of spontaneous self-assembly into PEGylated nanoparticulates in aqueous solutions can potentially enable a simple and effective approach to modifying therapeutic proteins without the need for their covalent modification.

Continuous flow microreactor for protein PEGylation

PEGylation is increasingly being utilized to enhance the therapeutic efficacy of biopharmaceuticals. Various chemistries and reaction conditions have been established to synthesize PEGylated proteins and more are being developed. Both the extent of conversion and selectivity of protein PEGylation are highly sensitive to process variables and parameters. Therefore, microfluidic-based high-throughput screening platforms would be highly suitable for optimization of protein PEGylation. As part of this study, a poly-dimethylsiloxane-based continuous flow microreactor system was designed and its performance was compared head-to-head with a batch reactor. The reactants within the microreactor were contacted by passive micromixing based on chaotic advection generated by staggered herringbone grooves embedded in serpentine microchannels. The microreactor system was provided with means for on-chip reaction quenching. Lysozyme was used as the model protein while methoxy-polyethylene glycol-(CH2)5COO-NHS was used as the PEGylation reagent. Full mixing was achieved close to the microreactor inlet, making the device suitable for protein PEGylation. The effect of mixing type, i.e., simple stirring versus chaotic laminar mixing on PEGylation, was investigated. Higher selectivity (as high as 100% selectivity) was obtained with the microreactor while the conversion was marginally lower.

Nanotechnological Strategies for Protein Delivery

The use of therapeutic proteins plays a fundamental role in the treatment of numerous diseases. The low physico-chemical stability of proteins in physiological conditions put their function at risk in the human body until they reach their target. Moreover, several proteins are unable to cross the cell membrane. All these facts strongly hinder their therapeutic effect. Nanomedicine has emerged as a powerful tool which can provide solutions to solve these limitations and improve the efficacy of treatments based on protein administration. This review discusses the advantages and limitations of different types of strategies employed for protein delivery, such as PEGylation, transport within liposomes or inorganic nanoparticles or their in situ encapsulation.

Reaction-Mediated Desorption of Macromolecules: Novel Phenomenon Enabling Simultaneous Reaction and Separation

Combining chemical reaction with separation offers several advantages. In this work possibility to induce spontaneous desorption of adsorbed macromolecules, once being PEGylated, through adjustment of the reagent composition is investigated. Bovine serum albumin (BSA) and activated oligonucleotide, 9T, are used as the test molecules and 20 kDa linear activated PEG is used for their PEGylation. BSA solid-phase PEGylation is performed on Q Sepharose HP. Distribution coefficient of BSA and PEG-BSA as a function of NaCl is determined using linear gradient elution (LGE) experiments and Yamamoto model. According to the distribution coefficient the selectivity between BSA and PEG - BSA of around 15 is adjusted by using NaCl. Spontaneous desorption of PEG - BSA is detected with no presence of BSA. However, due to a rather low selectivity, also desorption of BSA occurred at high elution volume. A similar procedure is applied for activated 9T oligonucleotide, this time using monolithic CIM QA disk monolithic column for adsorption. Selectivity of over 2000 is obtained by proper adjustment of PEG reagent composition. High selectivity enables spontaneous desorption of PEG-9T without any desorption of activated 9T. Both experiments demonstrates that reaction-mediated desorption of macromolecules is possible when the reaction conditions are properly tuned.

Enzymatically cleavable traceless biotin tags for protein PEGylation and purification

Immobilized lipase was successfully employed for the rapid removal of a biotin tag from a protein–PEG conjugate under mild conditions.

Insights into the interfacial structure-function of poly(ethylene glycol)-decorated peptide-stabilised nanoscale emulsions

The interfacial properties of nanoscale materials have profound influence on biodistribution and stability as well as the effectiveness of sophisticated surface-encoded properties such as active targeting to cell surface receptors. Tailorable nanocarrier emulsions (TNEs) are a novel class of oil-in-water emulsions stabilised by molecularly-engineered biosurfactants that permit single-pot stepwise surface modification with related polypeptides that may be chemically conjugated or genetically fused to biofunctional moieties. We have probed the structure and function of poly(ethylene glycol) (PEG) used to decorate TNEs in this way. The molecular weight of PEG decorating TNEs has considerable impact on the ζ-potential of the emulsion particles, related to differential interfacial thickness of the PEG layer as determined by X-ray reflectometry. By co-modifying TNEs with an antibody fragment, we show that the molecular weight and density of PEG governs the competing parameters of accessibility of the targeting moiety and of shielding the interface from non-specific interactions with the environment. The fundamental understanding of the molecular details of the PEG layer that we present provides valuable insights into the structure-function relationship for soft nanomaterial interfaces. This work therefore paves the way for further rational design of TNEs and other nanocarriers that must interact with their environment in controlled and predictable ways.

Soft Nanotubes Derivatized with Short PEG Chains for Thermally Controllable Extraction and Separation of Peptides

By means of a two-step self-assembly process involving three components, including short poly(ethylene glycol) (PEG) chains, we produced two different types of molecular monolayer nanotubes: nanotubes densely functionalized with PEG chains on the outer surface and nanotubes densely functionalized with PEG chains in the nanochannel. Turbidity measurements and fluorescence spectroscopy with an environmentally responsive probe suggested that the PEG chains underwent dehydration when the nanotubes were heated above 44-57 °C and rehydration when they were cooled back to 25 °C. Dehydration of the exterior or interior PEG chains rendered them hydrophobic and thus able to effectively extract hydrophobic amino acids from the bulk solution. Rehydration of the PEG chains restored their hydrophilicity, thus allowing the extracted amino acids to be squeezed out into the bulk solutions. The nanotubes with exterior PEG chains exhibited selectivity for all of the hydrophobic amino acids, whereas the interior PEG chains were selective for hydrophobic amino acids with an aliphatic side chain over hydrophobic amino acids with an aromatic side chain. The higher selectivity of the latter system is attributable that the extraction and back-extraction processes involve encapsulation and transportation of the amino acids in the nanotube channel. As the result, the latter system was useful for separation of peptides that differed by only a single amino acid, whereas the former system showed no such separation ability.