Effect of PEGylation on Protein Hydrodynamics

Hydrodynamic and thermodynamic analysis of PEGylated human serum albumin

Covalent labeling of therapeutic drugs and proteins with polyethylene glycol (PEGylation) is an important modification for improving stability, solubility, and half-life. PEGylation alters protein solution behavior through its impact on thermodynamic nonideality by increasing the excluded volume, and on hydrodynamic nonideality by increasing the frictional drag. To understand PEGylation's impact, we investigated the thermodynamic and hydrodynamic properties of a model system consisting of PEGylated human serum albumin derivatives using analytical ultracentrifugation (AUC) and dynamic light scattering (DLS). We constructed PEGylated human serum albumin derivatives of single, linear 5K, 10K, 20K, and 40K PEG chains and a single branched-chain PEG of 40K (2 × 20K). Sedimentation velocity (SV) experiments were analyzed using SEDANAL direct boundary fitting to extract ideal sedimentation coefficients so, hydrodynamic nonideality ks, and thermodynamic nonideality 2BM1SV terms. These quantities allow the determination of the Stokes radius Rs, the frictional ratio f/fo, and the swollen or entrained volume Vs/v, which measure size, shape, and solvent interaction. We performed sedimentation equilibrium experiments to obtain independent measurements of thermodynamic nonideality 2BM1SE. From DLS measurements, we determined the interaction parameter, kD, the concentration dependence of the apparent diffusion coefficient, D, and from extrapolation of D to c = 0 a second estimate of Rs. Rs values derived from SV and DLS measurements and ensemble model calculations (see complementary study) are then used to show that ks + kD = theoretical 2B22M1. In contrast, experimental BM1 values from SV and sedimentation equilibrium data collectively allow for similar analysis for protein-PEG conjugates and show that ks + kD = 1.02-1.07∗BM1, rather than the widely used ks + kD = 2BM1 developed for hard spheres. The random coil behavior of PEG dominates the colloidal properties of PEG-protein conjugates and exceeds the sum of a random coil and hard-sphere volume due to excess entrained water.

The molecular basis for hydrodynamic properties of PEGylated human serum albumin

Polyethylene glycol (PEG) conjugation provides a protective modification that enhances the pharmacokinetics and solubility of proteins for therapeutic use. A knowledge of the structural ensemble of these PEGylated proteins is necessary to understand the molecular details that contribute to their hydrodynamic and colligative properties. Because of the large size and dynamic flexibility of pharmaceutically important PEGylated proteins, the determination of structure is challenging. In addition, the hydration of these conjugates that contain large polymers is difficult to determine with traditional methods that identify only first shell hydration water, which does not account for the complete hydrodynamic volume of a macromolecule. Here, we demonstrate that structural ensembles, generated by coarse-grained simulations, can be analyzed with HullRad and used to predict sedimentation coefficients and concentration-dependent hydrodynamic and diffusion nonideality coefficients of PEGylated proteins. A knowledge of these concentration-dependent properties enhances the ability to design and analyze new modified protein therapeutics. HullRad accomplishes this analysis by effectively accounting for the complete hydration of a macromolecule, including that of flexible polymers.

The Effect of PEGylation on Drugs' Pharmacokinetic Parameters; from Absorption to Excretion

Until the drugs enter humans life, they may face problems in transportation, drug delivery, and metabolism. These problems can cause reducing drug's therapeutic effect and even increase its side effects. Together, these cases can reduce the patient's compliance with the treatment and complicate the treatment process. Much work has been done to solve or at least reduce these problems. For example, using different forms of a single drug molecule (like Citalopram and Escitalopram); slight changes in the drug's molecule like Meperidine and α-Prodine, and using carriers (like Tigerase®). PEGylation is a recently presented method that can use for many targets. Poly Ethylene Glycol or PEG is a polymer that can attach to drugs by using different methods and resulting sustained release, controlled metabolism, targeted delivery, and other cases. Although they will not necessarily lead to an increase in the effect of the drug, they will lead to the improvement of the treatment process in certain ways. In this article, the team of authors has tried to collect and carefully review the best cases based on the PEGylation of drugs that can help the readers of this article.

Lysozyme binding with amikacin and levofloxacin studied by tritium probe, fluorescence spectroscopy and molecular docking

Lysozyme complexes with amikacin and levofloxacin were studied by spectroscopy approaches as well as using a tritium probe. Tritium was used as a labeling agent to trace labeled compound concentration in a system of two immiscible liquids and in the atomic form to determine the possible position of the binding site. Co-adsorption of protein and drug at the liquid-liquid interface was analyzed by scintillation phase method that allowed us to directly determine the amount of protein and drug in the mixed adsorption layer. Also, tensiometric measuring of the interfacial tension was used for calculation of binding parameters accordingly to Fainerman model. The treatment of complexes with atomic tritium followed by trypsinolysis and analysis of tritium distribution in the lysozyme peptides reveals the binding sites, binding energies in which were analyzed using molecular docking. Formation of complexes with amikacin and levofloxacin preserves secondar structure of protein. However, the formation of complex with amikacin leads to the almost total loss of the enzymatic activity of lysozyme and the redshift of the maximum on the lysozyme fluorescence band. A slight decrease in the distribution coefficient of lysozyme in the presence of amikacin assumes that the complex has higher hydrophilicity in comparison to lysozyme without additives. The most favorable for binding were the positions of the active centers that included amino acids Asp52 and Glu35, as well as in the vicinity of peptide His15-Arg21, with the participation of amino acids Tyr20, Arg14. In the case of levofloxacin, the formation of lysozyme-ligand complex in aqueous solution is possible without changing the microenvironment of the active center of the protein. Binding of levofloxacin to the active center of the enzyme was the most favorable, but Asp52 and Glu35 that are responsible for the enzymatic activity of lysozyme, were not affected.

Assessment of structural behaviour of a new L-asparaginase and SAXS data-based evidence for catalytic activity in its monomeric form

The present study reports the structural and functional characterization of a new glutaminase-free recombinant L-asparaginase (PrASNase) from Pseudomonas resinovorans IGS-131. PrASNase showed substrate specificity to L-asparagine, and its kinetic parameters, Km, Vmax, and kcat were 9.49 × 10-3 M, 25.13 IUmL-1 min-1, and 3.01 × 103 s-1, respectively. The CD spectra showed that PrASNase consisted of 18.5 % helix, 21.5 % antiparallel sheets, 4.2 % parallel sheets, 14 % turns, and rest other structures. FTIR was used for the functional characterization, and molecular docking predicted that the substrate interacts with serine, alanine, and glutamine in the binding pocket of PrASNase. Differing from known asparaginases, structural characterization by small-angle X-ray scattering (SAXS) and analytical ultracentrifugation (AUC) unambiguously revealed PrASNase to exist as a monomer in solution at low temperatures and oligomerized to a higher state with temperature rise. Through SAXS studies and enzyme assay, PrASNase was found to be mostly monomer and catalytically active at 37 °C. Furthermore, this glutaminase-free PrASNase showed killing effects against WIL2-S and TF-1.28 cells with IC50 of 7.4 μg.mL-1 and 5.6 μg.mL-1, respectively. This is probably the first report with significant findings of fully active L-asparaginase in monomeric form using SAXS and AUC and demonstrated the potential of PrASNase in inhibiting cancerous cells, making it a potential therapeutic candidate.

Immunogenicity of Therapeutic Biological Modalities - Lessons from Hemophilia A Therapies

The introduction and development of biologics such as therapeutic proteins, gene-, and cell-based therapy have revolutionized the scope of treatment for many diseases. However, a significant portion of the patients develop unwanted immune reactions against these novel biological modalities, referred to as immunogenicity, and no longer benefit from the treatments. In the current review, using Hemophilia A (HA) therapy as an example, we will discuss the immunogenicity issue of multiple biological modalities. Currently, the number of therapeutic modalities that are approved or recently explored to treat HA, a hereditary bleeding disorder, is increasing rapidly. These include, but are not limited to, recombinant factor VIII proteins, PEGylated FVIII, FVIII Fc fusion protein, bispecific monoclonal antibodies, gene replacement therapy, gene editing therapy, and cell-based therapy. They offer the patients a broader range of more advanced and effective treatment options, yet immunogenicity remains the most critical complication in the management of this disorder. Recent advances in strategies to manage and mitigate immunogenicity will also be reviewed.

Optimization of Size of Nanosensitizers for Antitumor Radiotherapy Using Mathematical Modeling

The efficacy of antitumor radiotherapy can be enhanced by utilizing nonradioactive nanoparticles that emit secondary radiation when activated by a primary beam. They consist of small volumes of a radiosensitizing substance embedded within a polymer layer, which is coated with tumor-specific antibodies. The efficiency of nanosensitizers relies on their successful delivery to the tumor, which depends on their size. Increasing their size leads to a higher concentration of active substance; however, it hinders the penetration of nanosensitizers through tumor capillaries, slows down their movement through the tissue, and accelerates their clearance. In this study, we present a mathematical model of tumor growth and radiotherapy with the use of intravenously administered tumor-specific nanosensitizers. Our findings indicate that their optimal size for achieving maximum tumor radiosensitization following a single injection of their fixed total volume depends on the permeability of the tumor capillaries. Considering physiologically plausible spectra of capillary pore radii, with a nanoparticle polymer layer width of 7 nm, the optimal radius of nanoparticles falls within the range of 13-17 nm. The upper value is attained when considering an extreme spectrum of capillary pores.

PEG-Lipids: Quantitative Study of Unimers and Aggregates Thereof by the Methods of Molecular Hydrodynamics

Understanding the polymorphism of lipids in solution is the key to the development of intracellular delivery systems. Here, we study the dynamics of poly(ethylene glycol)-lipid (PEG-Lipid) conjugates aiming at a better understanding of their molecular properties and aggregation behavior in solution. Those PEG-Lipids are used as components of lipid nanoparticles (LNPs). LNPs are gaining increased popularity, e.g., by their utilization in modern vaccination strategies against SARS-CoV-2. Characterization of the systems is conducted by the classical methods of hydrodynamics in different solvents, such as ethanol and water, which are also commonly used for LNP formulation. We were able to elucidate the structurally associated hydrodynamic properties of isolated PEG-Lipids in ethanol, revealing the typically expected values of the hydrodynamic invariant for random coil polymers. By virtue of the same experimental setting, the PEG-Lipids' behavior in water was as well studied, which is a less good solvent than ethanol for the PEG-Lipids. Our experiments demonstrate that PEG-Lipids dissolved in water form well-defined micelles that can quantitatively be characterized in terms of their degree of aggregation of PEG-Lipid polymer unimers, their hydrodynamic size, and solvation, i.e., the quantitative determination of water contained or associated to the identified micelles. Quantitative results obtained from classical hydrodynamic analyses are fully supported by studies with standard dynamic light scattering (DLS). The obtained diffusion coefficients and hydrodynamic sizes are in excellent agreement with numerical results derived from analytical ultracentrifugation (AUC) data. Cryo-transmission electron microscopy (cryo-TEM) supports the structural insight from hydrodynamic studies, particularly, in terms of the observed spherical structure of the formed micelles. We demonstrate experimentally that the micelle systems can be considered as solvent-permeable, hydrated spheres.

Challenges and progress toward tumor-targeted therapy by systemic delivery of polymer-complexed oncolytic adenoviruses

Oncolytic adenovirus (oAd) elicits antitumor activity by preferential viral replication in cancer cells. However, poor systemic administrability or suboptimal intratumoral retainment of the virus remains a major challenge toward maximizing the antitumor activity of oAd in a clinical environment. To surmount these issues, a variety of non-immunogenic polymers has been used to modify the surface of oAds chemically or physically. Complexation of oAd with polymers can effectively evade the host immune response and reduces nonspecific liver sequestration. The tumor-specific delivery of these complexes can be further improved upon by inclusion of tumor-targeting moieties on the surface. Therefore, modification of the Ad surface using polymers is viewed as a potential strategy to enhance the delivery of Ad via systemic administration. This review aims to provide a comprehensive overview of polymer-complexed Ads, their progress, and future challenges in cancer treatment.

PEtOxylated Interferon-α2a Bioconjugates Addressing H1N1 Influenza A Virus Infection

Influenza A viruses (IAV), including the pandemic 2009 (pdm09) H1N1 or avian influenza H5N1 virus, may advance into more pathogenic, potentially antiviral drug-resistant strains (including loss of susceptibility against oseltamivir). Such IAV strains fuel the risk of future global outbreaks, to which this study responds by re-engineering Interferon-α2a (IFN-α2a) bioconjugates into influenza therapeutics. Type-I interferons such as IFN-α2a play an essential role in influenza infection and may prevent serious disease courses. We site-specifically conjugated a genetically engineered IFN-α2a mutant to poly(2-ethyl-2-oxazoline)s (PEtOx) of different molecular weights by strain-promoted azide-alkyne cyclo-addition. The promising pharmacokinetic profile of the 25 kDa PEtOx bioconjugate in mice echoed an efficacy in IAV-infected ferrets. One intraperitoneal administration of this bioconjugate, but not the marketed IFN-α2a bioconjugate, changed the disease course similar to oseltamivir, given orally twice every study day. PEtOxylated IFN-α2a bioconjugates may expand our therapeutic arsenal against future influenza pandemics, particularly in light of rising first-line antiviral drug resistance to IAV.

Polymer selection impacts the pharmaceutical profile of site-specifically conjugated Interferon-α2a

Conjugation of poly(ethylene glycol) (PEG) to biologics is a successful strategy to favorably impact the pharmacokinetics and efficacy of the resulting bioconjugate. We compare bioconjugates synthesized by strain-promoted azide-alkyne cycloaddition (SPAAC) using PEG and linear polyglycerol (LPG) of about 20 kDa or 40 kDa, respectively, with an azido functionalized human Interferon-α2a (IFN-α2a) mutant. Site-specific PEGylation and LPGylation resulted in IFN-α2a bioconjugates with improved in vitro potency compared to commercial Pegasys. LPGylated bioconjugates had faster disposition kinetics despite comparable hydrodynamic radii to their PEGylated analogues. Overall exposure of the PEGylated IFN-α2a with a 40 kDa polymer exceeded Pegasys, which, in return, was similar to the 40 kDa LPGylated conjugates. The study points to an expanded polymer design space through which the selected polymer class may result in a different distribution of the studied bioconjugates.

Cyanine Masking: A Strategy to Test Functional Group Effects on Antibody Conjugate Targeting

Conjugates of small molecules and antibodies are broadly employed diagnostic and therapeutic agents. Appending a small molecule to an antibody often significantly impacts the properties of the resulting conjugate. Here, we detail a systematic study investigating the effect of various functional groups on the properties of antibody-fluorophore conjugates. This was done through the preparation and analysis of a series of masked heptamethine cyanines (CyMasks)-bearing amides with varied functional groups. These were designed to exhibit a broad range of physical properties, and include hydrophobic (-NMe2), pegylated (NH-PEG-8 or NH-PEG-24), cationic (NH-(CH2)2NMe3+), anionic (NH-(CH2)2SO3-), and zwitterionic (N-(CH2)2NMe3+)-(CH2)3SO3-) variants. The CyMask series was appended to monoclonal antibodies (mAbs) and analyzed for the effects on tumor targeting, clearance, and non-specific organ uptake. Among the series, zwitterionic and pegylated dye conjugates had the highest tumor-to-background ratio (TBR) and a low liver-to-background ratio. By contrast, the cationic and zwitterionic probes had high tumor signal and high TBR, although the latter also exhibited an elevated liver-to-background ratio (LBR). Overall, these studies provide a strategy to test the functional group effects and suggest that zwitterionic substituents possess an optimal combination of high tumor signal, TBR, and low LBR. These results suggest an appealing strategy to mask hydrophobic payloads, with the potential to improve the properties of bioconjugates in vivo.

Reincarnation of the Analytical Ultracentrifuge: Emerging Opportunities for Nanomedicine

The analytical ultracentrifuge (AUC) and the modern field of analytical ultracentrifugation found its inception approximately a century ago. We highlight the scope of its major experimental opportunities as a transport-based method, contemporary and up-and-coming investigation potential for polymers, polymer-drug conjugates, polymer assemblies, as well as medical nanoparticles. Special focus lies on molar mass estimates of unimeric polymeric species, self-assemblies in solution, and (co)localization of multicomponent systems in solution alongside the material-biofluid interactions. We close with present challenges and incentives for future research.

Controlling Polymer Morphologies by Intramolecular and Intermolecular Dynamic Covalent Iron(III)/Catechol Complexation-From Polypeptide Single Chain Nanoparticles to Hydrogels

Responsive biomaterials, tunable from the molecular to the macroscopic scale, are attractive for various applications in nanotechnology. Herein, a long polypeptide chain derived from the abundant serum protein human serum albumin is cross-linked by dynamic-coordinative iron(III)/catechol bonds. By tuning the binding stoichiometry and the pH, reversible intramolecular folding into polypeptide nanoparticles with controllable sizes is achieved. Moreover, upon varying the stoichiometry, intermolecular cross-links become predominant yielding smart and tunable macroscopic protein hydrogels. By adjusting the intra- and intermolecular interactions, biocompatible and biodegradable materials are formed with varying morphologies and dimensions covering several lengths scales featuring rapid gelation without toxic reagents, fast and autonomous self-healing, tunable mechanical properties, and high adaptability to local environmental conditions. Such material characteristics can be particularly attractive for tissue engineering approaches to recreate soft tissues matrices with highly customizable features in a fast and simple fashion.

A structural perspective on the design of decoy immune modulators

Therapeutic mAbs have dominated the class of immunotherapeutics in general and immune checkpoint inhibitors in particular. The high specificity of mAbs to the target molecule as well as their extended half-life and (or) the effector functions raised by the Fc part are some of the important aspects that contribute to the success of this class of therapeutics. Equally potential candidates are decoys and their fusions that can address some of the inherent limitations of mAbs, like immunogenicity, resistance development, low bio-availability and so on, besides maintaining the advantages of mAbs. The decoys are molecules that trap the ligands and prevent them from interacting with the signaling receptors. Although a few FDA-approved decoy immune modulators are very successful, the potential of this class of drugs is yet to be fully realized. Here, we review various strategies employed in fusion protein therapeutics with a focus on the design of decoy immunomodulators from the structural perspective and discuss how the information on protein structure and function can strategically guide the development of next-generation immune modulators.

Simple Determination of Gold Nanocrystal Dimensions by Analytical Ultracentrifugation via Surface Ligand-Solvent Density Matching

Analytical ultracentrifugation (AUC) is a powerful technique to observe colloidal nanocrystals (NCs) directly in solution and obtain critical information about their physical-chemical properties. Nevertheless, a more comprehensive implementation of AUC for the characterisation of such a class of crystalline colloids has been traditionally impaired by the requirement of having a priori knowledge of the complex, multilayered structure formed by NC in solution. This includes the nature (density and mass) of the surface ligands (SLs) that provide NC colloidal stability and the shell of solvent molecules formed on it. Herein, we propose a methodology to determine the NCs size by using SLs with a density equal to that of the solvent. Thereby, the buoyancy force of the SL shell is neutral, and the density of the NCs is sufficient a priori knowledge to calculate their related mass and size distributions. The simplicity and reliability of the method are evaluated with cetyltrimethylammonium bromide (CTAB) stabilized spherical gold NCs (AuNCs) of dimensions ranging from 1 to 17 nm. The proposed method has great potential to be transferred to any non-crystalline and crystalline colloids of different nature and composition, which have a density that is equal to the bulk and can be stabilized by SLs having a density that matches that of the solvent.

Prolonged activity of exenatide: Detailed comparison of Site-specific linear polyglycerol- and poly(ethylene glycol)-conjugates

Exenatide is a small therapeutic peptide being currently used in clinic for the treatment of diabetes mellitus type II, however, displaying a short blood circulation time which makes two daily injections necessary. Covalent polymer modification of a protein is a well-known approach to overcome this limitation, resulting in steric shielding, an increased size and therefore a longer circulation half-life. In this study, we employed site-selective C-terminal polymer ligation of exenatide via copper-catalyzed azide-alkyne-cycloaddition (CuAAC) to yield 1:1-conjugates of either poly(ethylene glycol) (PEG) or linear polyglycerol (LPG) of different molecular weights. Our goal was to compare the impact of the two polymers on size, structure and activity of exenatide on the in vitro and in vivo level. Both polymers did not alter the secondary structure of exenatide and expectedly increased its hydrodynamic size, where the LPG-versions of exenatide showed slightly smaller values than their PEG-analogs of same molecular weight. Upon conjugation, GLP-1 receptor activation was diminished, however, still enabled maximum receptor response at slightly higher concentrations. Exenatide modified with a 40 kDa LPG (Ex-40-LPG) showed significant reduction of the blood glucose level in diabetic mice for up to 72 h, which was comparable to its PEG-analog, but 9-fold longer than native exenatide (8 h).

Polyglycerol for Half-Life Extension of Proteins-Alternative to PEGylation?

Since several decades, PEGylation is known to be the clinical standard to enhance pharmacokinetics of biotherapeutics. In this study, we introduce polyglycerol (PG) of different lengths and architectures (linear and hyperbranched) as an alternative polymer platform to poly(ethylene glycol) (PEG) for half-life extension (HLE). We designed site-selective N-terminally modified PG-protein conjugates of the therapeutic protein anakinra (IL-1ra, Kineret) and compared them systematically with PEG analogues of similar molecular weights. Linear PG and PEG conjugates showed comparable hydrodynamic sizes and retained their secondary structure, whereas binding affinity to IL-1 receptor 1 decreased with increasing polymer length, yet remained in the low nanomolar range for all conjugates. The terminal half-life of a 40 kDa linear PG-modified anakinra was extended 4-fold compared to the unmodified protein, close to its PEG analogue. Our results demonstrate similar performances of PEG- and PG-anakinra conjugates and therefore highlight the outstanding potential of polyglycerol as a PEG alternative for half-life extension of biotherapeutics.

Novel Method for the Isolation of Proteins and Small Target Molecules from Biological and Aqueous Media by Salt-Assisted Phase Transformation of Their PEGylated Recognition Counterparts

An efficient and simple method for the application of PEGylated affinity ligands in precipitative isolation of protein target molecules (TMs) from a biological fluid such as blood serum or small target molecules from an aqueous medium is presented for the first time. This approach is based on the high binding specificity of PEGylated recognition molecules (PEG-RMs) to their TMs and the unique physicochemical properties of PEG that result in their salt-assisted phase transformation. Addition of PEG-RM to blood serum results in the formation of an RM-specific macromolecular complex (PEG-RM + TM → PEG-RM.TM) that undergoes facile salt-assisted phase transformation to a separable semisolid with ammonium sulfate. PEG-RM.TM is then dissociated into its components by pH reduction or an increase of ionic strength (PEG-RM.TM → PEG-RM + TM). PEG-RM is salted out to afford pure TM in solution. The same phenomenon is observed when RM or TM are small molecules. The general applicability of the method was validated by PEGylation of two proteins (protein A, sheep antihuman IgG) and a small molecule (salicylic acid) used as model RMs for the isolation of Igs, IgG, and serum albumin from blood serum. The isolated protein TMs were shown to be pure and aggregate-free by gel electrophoresis and dynamic light scattering (DLS). IgG isolated by this method was further characterized by peptide mass fingerprinting. PEGylated protein A was used to demonstrate the recyclability and scale-up potential of PEG-RM. IgG isolated by this method from blood serum of a hepatitis C-vaccinated individual was tested for its binding to sheep antihuman IgG by UV spectroscopy, and its bioactivity was ascertained by comparison of its enzyme-linked immunosorbent assay (ELISA) result to that of a blood sample from the same individual. Reciprocity of RM and TM was ascertained using PEGylated salicylic acid to obtain pure serum albumin, and PEGylated serum albumin was utilized for near-exclusive isolation of one drug from an aqueous equimolar mixture of three drugs (salicylic acid, 91%; capecitabine, 6%; and deferiprone, 3%). Advantages of this approach, including target specificity and general applicability and celerity, over other affinity methods for the isolation of proteins are discussed at a molecular level.

Molecular simulation of zwitterionic polypeptides on protecting glucagon-like peptide-1 (GLP-1)

Owing to their anti-fouling properties, zwitterionic polypeptides demonstrate great advantage on protecting protein drugs. When conjugated to glucagon-like peptide-1 (GLP-1), a drug for type-II diabetes, zwitterionic polypeptides confer better pharmacokinetics than uncharged counterparts. However, its microscopic mechanism is still unclear due to the complicated conformational space. To address this challenge, this work explored the interaction modes of GLP-1 with the unconnected repeat units, instead of the full-length polypeptides. The three repeat units are two zwitterionic pentapeptides VPKEG and VPREG, and one uncharged control VPGAG. Our molecular simulations revealed that the helical conformation of GLP-1 was stabilized by adding 40 polypeptides. Both VPGAG and VPREG formed dense packing shells around GLP-1, but the driving forces were hydrophobic and electrostatic interactions, respectively. In contrast, the packing shell composed of VPKEG was most loose, while could still stabilize GLP-1. The moderate electrostatic interactions endowed VPKEG an anti-fouling property, thereby avoiding non-specific interaction with other amino acids. The strong electrostatic interactions exerted by arginine promoted atomic contacts between VPREG and other residues, making it as "hydrophobic" as VPGAG. In summary, the combination of hydrophobic and moderate electrostatic interactions in VPKEG brings about a subtle balance between stabilizing GLP-1 and avoiding non-specific interaction.

Polymeric nanoparticles functionalized with muscle-homing peptides for targeted delivery of phosphatase and tensin homolog inhibitor to skeletal muscle

Phosphatase and tensin homolog (PTEN) antagonizes muscle growth and repair, and inhibition of PTEN has been shown to improve the pathophysiology and dystrophic muscle function in a mouse model of Duchenne muscular dystrophy (DMD). However, conventional pharmacological delivery of PTEN inhibitors carries a high risk of off-target side effects in other non-muscle organs due to broad targeting spectrums. Here we report a muscle-targeted nanoparticulate platform for cell-specific delivery of a PTEN inhibitor. Poly(lactide-co-glycolide)-b-poly(ethylene glycol) nanoparticles (NPs) are functionalized with a muscle-homing peptide M12 to promote the selective uptake by muscle cells/tissue in vitro and in vivo. Moreover, the NPs are formulated to slowly release the PTEN inhibitor, preventing cytotoxicity associated with direct exposure to the drug and facilitating sustained inhibition of PTEN. This advanced delivery approach taking advantages of polymeric nanomaterials and muscle-homing peptides opens a new avenue for the development of long-term therapeutic strategies in DMD treatment.

Advanced engineering of third-generation lysins and formulation strategies for clinical applications

One of the possible solutions for the current antibiotic resistance crisis may be found in (often bacteriophage-derived) peptidoglycan hydrolases. The first clinical trials of these natural enzymes, coined here as first-generation lysins, are currently ongoing. Moving beyond natural endolysins with protein engineering established the second generation of lysins. In second-generation lysins, the focus lies on improving antibacterial and biochemical properties such as antimicrobial activity and stability, as well as expanding their activities towards Gram-negative pathogens. However, solutions to particular key challenges regarding clinical applications are only beginning to emerge in the third generation of lysins, in which protein and biochemical engineering efforts focus on improving properties relevant under clinical conditions. In addition, increasingly advanced formulation strategies are developed to increase the bioavailability, antibacterial activity, and half-life, and to reduce pro-inflammatory responses. This review focuses on third-generation and advanced formulation strategies that are developed to treat infections, ranging from topical to systemic applications. Together, these efforts may fully unlock the potential of lysin therapy and will propel it as a true antibiotic alternative or supplement.

From Synthesis to Characterization of Site-Selective PEGylated Proteins

Covalent attachment of therapeutic proteins to polyethylene glycol (PEG) is widely used for the improvement of its pharmacokinetic and pharmacological properties, as well as the reduction in reactogenicity and related side effects. This technique named PEGylation has been successfully employed in several approved drugs to treat various diseases, even cancer. Some methods have been developed to obtain PEGylated proteins, both in multiple protein sites or in a selected amino acid residue. This review focuses mainly on traditional and novel examples of chemical and enzymatic methods for site-selective PEGylation, emphasizing in N-terminal PEGylation, that make it possible to obtain products with a high degree of homogeneity and preserve bioactivity. In addition, the main assay methods that can be applied for the characterization of PEGylated molecules in complex biological samples are also summarized in this paper.

PEGylation within a confined hydrophobic cavity of a protein

The conjugation of polyethylene glycol (PEG) to proteins, known as PEGylation, has increasingly been employed to expand the efficacy of therapeutic drugs. Recently, research has emphasized the effect of the conjugation site on protein-polymer interactions. In this study, we performed atomistic molecular dynamics (MD) simulations of lysine 116 PEGylated bovine serum albumin (BSA) to illustrate how conjugation near a hydrophobic pocket affects the conjugate's dynamics and observed altered low mode vibrations in the protein. MD simulations were performed for a total of 1.5 μs for each PEG chain molecular mass from 2 to 20 kDa. Analysis of preferential PEG-BSA interactions showed that polymer behavior was also affected as proximity to the attractive protein surface patches promoted interactions in small (2 kDa) PEG chains, while the confined environment of the conjugation site reduced the expected BSA surface coverage when the polymer molecular mass increased to 10 kDa. This thorough analysis of PEG-BSA interactions and polymer dynamics increases the molecular understanding of site-specific PEGylation and enhances the use of protein-polymer conjugates as therapeutics.

Application of N-Dodecyl l-Peptide to Enhance Serum Stability while Maintaining Inhibitory Effects on Myometrial Contractions Ex Vivo

N-Alkylation and N-acylation of the prostaglandin-F_2α allosteric modulator l-PDC31 were performed to install various alkyl, PEG and isoprenoid groups onto the l-enantiomer of the peptide. Among the different bio-conjugates studied, the N-dodecyl analog reduced prostaglandin-F_2α-induced mouse myometrium contractions ex vivo. Furthermore, N-dodecyl-l-PDC31 exhibited improved stability in a mouse serum assay, likely due to protection from protease degradation by the lipid chain.

Hydrodynamic and Electrophoretic Properties of Trastuzumab/HER2 Extracellular Domain Complexes as Revealed by Experimental Techniques and Computational Simulations

The combination of hydrodynamic and electrophoretic experiments and computer simulations is a powerful approach to study the interaction between proteins. In this work, we present hydrodynamic and electrophoretic experiments in an aqueous solution along with molecular dynamics and hydrodynamic modeling to monitor and compute biophysical properties of the interactions between the extracellular domain of the HER2 protein (eHER2) and the monoclonal antibody trastuzumab (TZM). The importance of this system relies on the fact that the overexpression of HER2 protein is related with the poor prognosis breast cancers (HER2++ positives), while the TZM is a monoclonal antibody for the treatment of this cancer. We have found and characterized two different complexes between the TZM and eHER2 proteins (1:1 and 1:2 TZM:eHER2 complexes). The conformational features of these complexes regulate their hydrodynamic and electrostatic properties. Thus, the results indicate a high degree of molecular flexibility in the systems that ultimately leads to higher values of the intrinsic viscosity, as well as lower values of diffusion coefficient than those expected for simple globular proteins. A highly asymmetric charge distribution is detected for the monovalent complex (1:1 complex), which has strong implications in correlations between the experimental electrophoretic mobility and the modeled net charge. In order to understand the dynamics of these systems and the role of the specific domains involved, it is essential to find biophysical correlations between dynamics, macroscopic transport and electrostatic properties. The results should be of general interest for researchers working in this area.

Novel site-specific PEGylated L-asparaginase

L-asparaginase (ASNase) from Escherichia coli is currently used in some countries in its PEGylated form (ONCASPAR, pegaspargase) to treat acute lymphoblastic leukemia (ALL). PEGylation refers to the covalent attachment of poly(ethylene) glycol to the protein drug and it not only reduces the immune system activation but also decreases degradation by plasmatic proteases. However, pegaspargase is randomly PEGylated and, consequently, with a high degree of polydispersity in its final formulation. In this work we developed a site-specific N-terminus PEGylation protocol for ASNase. The monoPEG-ASNase was purified by anionic followed by size exclusion chromatography to a final purity of 99%. The highest yield of monoPEG-ASNase of 42% was obtained by the protein reaction with methoxy polyethylene glycol-carboxymethyl N-hydroxysuccinimidyl ester (10kDa) in 100 mM PBS at pH 7.5 and PEG:ASNase ratio of 25:1. The monoPEG-ASNase was found to maintain enzymatic stability for more days than ASNase, also was resistant to the plasma proteases like asparaginyl endopeptidase and cathepsin B. Additionally, monoPEG-ASNase was found to be potent against leukemic cell lines (MOLT-4 and REH) in vitro like polyPEG-ASNase. monoPEG-ASNase demonstrates its potential as a novel option for ALL treatment, being an inventive novelty that maintains the benefits of the current enzyme and solves challenges.

Impact of polymer geometry on the interactions of protein-PEG conjugates

The conjugation of high molecular weight polyethylene glycol (PEG) to an active pharmaceutical ingredient (API) is an attractive strategy for the modification of biophysical and biodistribution properties of the API. Indeed, several therapeutic proteins conjugated to PEG have been safely administered in the clinic. While there have been studies on the configuration of these conjugates in solution, investigations on the impact of PEG geometry on protein-PEG conjugate interactions is limited. In this study, we use dynamic light scattering (DLS), rheology, and small-angle neutron scattering (SANS) to investigate the biophysical solution and interaction behavior of a 50kDa Fab protein attached to either a linear or tetrameric (branched) 40kDa PEG molecule. The hydrodynamic radii, diffusivity, viscosity and pair distance distribution function (PDDF) were obtained for the protein-PEG conjugates in solution. An analysis revealed that interactions between unconjugated proteins were quite attractive, however linear PEG-protein conjugates exhibited net repulsive interactions, similar to that of the unconjugated polymer. Tetramer PEG-protein conjugates on the other hand, exhibited a net weak attractive interaction, indicating a more balanced distribution of repulsive and attractive interaction states. Further analysis of the SANS data using geometric models consistent with the PDDF elucidated the conjugates' equilibrium configuration in solution. Insights gained from measurements and analysis used here can also be useful in predicting how conjugate geometries affect viscosity and aggregation behavior, which are important in determining suitable protein-polymer drug formulations.

Optimizing the Bioavailability of Subcutaneously Administered Biotherapeutics Through Mechanochemical Drivers

The subcutaneous route offers myriad benefits for the administration of biotherapeutics in both acute and chronic diseases, including convenience, cost effectiveness and the potential for automation through closed-loop systems. Recent advances in parenteral administration devices and the use of additives which enhance drug dispersion have generated substantial additional interest in IV to SQ switching studies. Designing pre-clinical and clinical studies using SQ mediated delivery however requires deep understanding of complex inter-related physiologies and transport pathways governing the interstitial matrix, vascular system and lymphatic channels. This expert review will highlight key structural features which contribute to transport and biodistribution in the subcutaneous space and also assess the impact of drug formulations. Based on the rapidly growing interest in the SQ delivery route, a number of potential areas for future development are highlighted, which are likely to allow continued evolution and innovation in this important area.

Assessment of the structure of pegylated-recombinant protein therapeutics by the NMR fingerprint assay

A number of recombinant protein therapeutic products, such as filgrastim (methionyl granulocyte colony stimulating factor [Met-GCSF] used to boost the immune system in chemotherapy treated cancer patients), and interferon alpha-2 (used for the treatment of various viral infections), have been chemically modified with the addition of a polyethylene glycol (PEG) chain. This modification prolongs residency of the drug in the body and reduces metabolic degradation, which allows less frequent administration of the products. Here we show how NMR spectroscopy methods can assess the higher order structure (HOS) of pegylated-filgrastim (Neulasta®), pegylated interferon-α2a (Pegasys®) pegylated interferon-α2b (PEG-Intron®) purchased from the marketplace. The addition of the PEG moiety effectively doubles the molecular weight of the three products. This presents a significant challenge for the application of NMR techniques. Nevertheless, the results showed that high-resolution spectra could be recorded for two of the three products. Comparison of the spectra of the pegylated protein and the non-pegylated protein shows that the chemical modification did not alter the HOS of these proteins.

PEGylation of Biopharmaceuticals: A Review of Chemistry and Nonclinical Safety Information of Approved Drugs

Modification of biopharmaceutical molecules by covalent conjugation of polyethylene glycol (PEG) molecules is known to enhance pharmacologic and pharmaceutical properties of proteins and other large molecules and has been used successfully in 12 approved drugs. Both linear and branched-chain PEG reagents with molecular sizes of up to 40 kDa have been used with a variety of different PEG derivatives with different linker chemistries. This review describes the properties of PEG itself, the history and evolution of PEGylation chemistry, and provides examples of PEGylated drugs with an established medical history. A trend toward the use of complex PEG architectures and larger PEG polymers, but with very pure and well-characterized PEG reagents is described. Nonclinical toxicology findings related to PEG in approved PEGylated biopharmaceuticals are summarized. The effect attributed to the PEG part of the molecules as observed in 5 of the 12 marketed products was cellular vacuolation seen microscopically mainly in phagocytic cells which is likely related to their biological function to absorb and remove particles and macromolecules from blood and tissues. Experience with marketed PEGylated products indicates that adverse effects in toxicology studies are usually related to the active part of the drug but not to the PEG moiety.

Addition of 20-kDa PEG to Insulin Lispro Alters Absorption and Decreases Clearance in Animals

PURPOSE

Determine the pharmacokinetics of insulin peglispro (BIL) in 5/6-nephrectomized rats and study the absorption in lymph duct cannulated (LDC) sheep.

METHODS

BIL is insulin lispro modified with 20-kDa linear PEG at lysine B28 increasing the hydrodynamic size to 4-fold larger than insulin lispro. Pharmacokinetics of BIL and insulin lispro after IV administration were compared in 5/6-nephrectomized and sham rats. BIL was administered IV or SC into the interdigital space of the hind leg, and peripheral lymph and/or serum samples were collected from both LDC and non-LDC sheep to determine pharmacokinetics and absorption route of BIL.

RESULTS

The clearance of BIL was similar in 5/6-nephrectomized and sham rats, while the clearance of insulin lispro was 3.3-fold slower in 5/6-nephrectomized rats than in the sham rats. In non-LDC sheep, the terminal half-life after SC was about twice as long vs IV suggesting flip-flop pharmacokinetics. In LDC sheep, bioavailability decreased to <2%; most of the dose was absorbed via the lymphatic system, with 88% ± 19% of the dose collected in the lymph after SC administration.

CONCLUSION

This work demonstrates that increasing the hydrodynamic size of insulin lispro through PEGylation can impact both absorption and clearance to prolong drug action.

Solid-State NMR of PEGylated Proteins

PEGylated proteins are widely used in biomedicine but, in spite of their importance, no atomic-level information is available since they are generally resistant to structural characterization approaches. PEGylated proteins are shown here to yield highly resolved solid-state NMR spectra, which allows assessment of the structural integrity of proteins when PEGylated for therapeutic or diagnostic use.

Investigation into the Relaxation Dynamics of Polymer-Protein Conjugates Reveals Surprising Role of Polymer Solvation on Inherent Protein Flexibility

Fully biodegradable protein-polymer conjugates, namely, MBP-PMeEP (maltose binding protein-poly methyl-ethylene phosphonate), have been investigated in order to understand the role of polymer solvation on protein flexibility. Using elastic and quasi-elastic incoherent neutron scattering, in combination with partially deuterated conjugate systems, we are able to disentangle the polymer dynamics from the protein dynamics and meaningfully address the coupling between both components. We highlight that, in the dry state, the protein-polymer conjugates lack any dynamical transition in accordance with the generally observed behavior for dry proteins. In addition, we observe a larger flexibility of the conjugated protein, compared to the native protein, as well as a lack of polymer-glass transition. Only upon water hydration does the conjugate recover its dynamical transition, leading to the conclusion that exclusive polymer solvation is insufficient to unfreeze fluctuations on the picosecond-nanosecond time scale in biomolecules. Our results also confirm the established coupling between polymer and protein dynamics in the conjugate.

Comparison of Ensemble and Single Molecule Methods for Particle Characterization and Binding Analysis of a PEGylated Single-Domain Antibody

Domain antibodies (dAbs) are single immunoglobulin domains that form the smallest functional unit of an antibody. This study investigates the behavior of these small proteins when covalently attached to the polyethylene glycol (PEG) moiety that is necessary for extending the half-life of a dAb. The effect of the 40 kDa PEG on hydrodynamic properties, particle behavior, and receptor binding of the dAb has been compared by both ensemble solution and surface methods [light scattering, isothermal titration calorimetry (ITC), surface Plasmon resonance (SPR)] and single-molecule atomic force microscopy (AFM) methods (topography, recognition imaging, and force microscopy). The large PEG dominates the properties of the dAb-PEG conjugate such as a hydrodynamic radius that corresponds to a globular protein over four times its size and a much reduced association rate. We have used AFM single-molecule studies to determine the mechanism of PEG-dependent reductions in the effectiveness of the dAb observed by SPR kinetic studies. Recognition imaging showed that all of the PEGylated dAb molecules are active, suggesting that some may transiently become inactive if PEG sterically blocks binding. This helps explain the disconnect between the SPR, determined kinetically, and the force microscopy and ITC results that demonstrated that PEG does not change the binding energy.

Conjugation of PolyPEG to interferon alpha extends serum half-life while maintaining low viscosity of the conjugate

The covalent attachment of poly(ethylene glycol) (PEG) to therapeutic proteins is a commonly used approach for extending in vivo half-lives. A potential limitation of this PEGylation strategy is the adverse effect of PEG on conjugate viscosity. Interferon-alpha (IFN) was conjugated via its N-terminal amino group by reductive amination to α-aldehyde functional comb-shaped PolyPEG polymers (50 and 70 kDa) and to linear PEG (30 kDa). In vitro potencies of the purified PEGylated IFN conjugates were measured by reporter gene assay using a HEK293P/ISRE-SEAP cell line. IFN levels were measured in rats following intravenous injection. Viscosities of various linear PEG and PolyPEG polymers along with the polymer-IFN conjugates were determined using a rotational rheometer with cone-and-plate geometry. In vitro potencies and half-lives of the PEGylated IFN conjugates were compared with those of the marketed branched PEG-IFN conjugate PEGASYS. Both PolyPEG-IFN conjugates retained a similar potency as that of the marketed comparator, whereas the linear PEG-IFN conjugate potency was greater. All conjugates showed extended half-lives compared to that of naked IFN, with the PolyPEG conjugates exhibiting the longest half-lives and the linear PEG conjugate, the shortest. Viscosity analysis showed that the linear PEG-IFN conjugate was over twice as viscous as both PolyPEG conjugates. Taken together, this work demonstrates the potential of PolyPEG conjugation to therapeutic proteins as a novel tool for optimizing pharmacokinetic profiles in a way that potentially allows administration of high-dose formulations because of lower conjugate viscosity.