Prediction of the Viscosity Radius and the Size Exclusion Chromatography Behavior of PEGylated Proteins

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.

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.

A review on L-methioninase in cancer therapy: Precision targeting, advancements and diverse applications for a promising future

Cancer remains a global health challenge, demanding novel therapeutic options due to the debilitating side effects of conventional treatments on healthy tissues. The review highlights the potential of L-methioninase, a pyridoxal-5-phosphate (PLP)-dependent enzyme, as a promising avenue in alternative cancer therapy. L-methioninase offers a unique advantage, its ability to selectively target and inhibit the growth of cancer cells without harming healthy cells. This selectivity arises because tumor cells lack an essential enzyme called methionine synthase, which healthy cells use to make the vital amino acid L-methionine. Several sources harbor L-methioninase, including bacteria, fungi, plants, and protozoa. Future research efforts can explore and exploit this diverse range of sources to improve the therapeutic potential of L-methioninase in the fight against cancer. Despite challenges, research actively explores microbial L-methioninase for its anticancer potential. This review examines the enzyme's side effects, advancements in combination therapies, recombinant technologies, polymer conjugation and novel delivery methods like nanoparticles, while highlighting the success of oral administration in preclinical trials. Beyond its promising role in cancer therapy, L-methioninase holds potential applications in food science, antioxidants, and various health concerns like diabetes, cardiovascular issues, and neurodegenerative diseases. This review provides a piece of current knowledge and future prospects of L-methioninase, exploring its diverse therapeutic potential.

An Artificial Miniaturized Peroxidase for Signal Amplification in Lateral Flow Immunoassays

Signal amplification strategies are widely used for improving the sensitivity of lateral flow immunoassays (LFiAs). Herein, the artificial miniaturized peroxidase Fe(III)-MimochromeVI*a (FeMC6*a), immobilized on gold nanoparticles (AuNPs), is used as a strategy to obtain catalytic signal amplification in sandwich immunoassays on lateral flow strips. The assay scheme uses AuNPs decorated with the mini-peroxidase FeMC6*a and anti-human-IgG as a detection antibody (dAb), for the detection of human-IgG, as a model analyte. Recognition of the analyte by the capture and detection antibodies is first evidenced by the appearance of a red color in the test line (TL), due to the accumulation of AuNPs. Subsequent addition of 3,3',5,5'-tetramethylbenzidine (TMB) induces an increase of the test line color, due to the TMB being converted into an insoluble colored product, catalyzed by FeMC6*a. This work shows that FeMC6*a acts as an efficient catalyst in paper, increasing the sensitivity of an LFiA up to four times with respect to a conventional LFiA. Furthermore, FeMC6*a achieves lower limits of detection that are found in control experiments where it is replaced with horseradish peroxidase (HRP), its natural counterpart. This study represents a significant proof-of-concept for the development of more sensitive LFiAs, for different analytes, based on properly designed artificial metalloenzymes.

Analytical chromatography approaches during the synthesis and conjugation of methoxypolyethylene glycol-succinimidyl butanoate (mPEG-SBA) to epoetin beta

Conjugation of epoetin beta (EPO) with methoxypolyethylene glycol-succinimidyl butanoate (mPEG-SBA) was studied. The compound mPEG-SBA was synthesized from mPEG, and the obtained intermediates and final product were analyzed by a reversed-phase chromatographic system equipped with an evaporative light scattering detector. Labeling the hydroxyl group in PEGs with benzoyl chloride and succinimide with benzylamine was applied to resolve and characterize different PEGs. The synthesized mPEG-SBA was used for the PEGylation of EPO. A size-exclusion chromatographic method monitored the reaction, simultaneously determining the PEGylated and unreacted EPO and protein aggregates. A borate buffer (0.1 M, pH 7.8) and PEG/protein molar ratio of 3:1 produced a maximum amount of monoPEGylated EPO with the minimum amount of polyPEGylated EPO variants. Although EPO is considered a stable glycoprotein hormone that remains monomeric when refrigerated, PEGylation of EPO with mPEG-SBA resulted in the significant formation of EPO dimer. The formation of EPO dimer and polyPEGylated EPO was pH-dependent, showing higher amounts of aggregates and lower amounts of polyPEGylated forms in lower pH values. Accordingly, aggregated EPO should be considered a major PEGylation-related impurity. In conclusion, the present study highlighted the importance of having suitable analytical approaches in controlling mPEG-SBA synthesis and conjugation to EPO.

Protein adsorption on core-shell resins for flow-through purifications: Effect of protein molecular size, shape, and salt concentration

This work addresses the functional properties of the core-shell resins Capto Core 400 and 700 for a broad range of proteins spanning 66.5 to 660 kDa in molecular mass, including bovine serum albumin (BSA) in monomer and dimer form, fibronectin, thyroglobulin, and BSA conjugates with 10 and 30 kDa poly(ethylene glycol) chains. Negatively charged latex nanoparticles (NPs) with nominal diameters of 20, 40, and 100 nm are also studied as surrogates for bioparticles. Protein binding and its trends with respect to salt concentration depend on the protein size and are different for the two agarose-based multimodal resins. For the smaller proteins, the amount of protein bound over practical time scales is limited by the resin surface area and is larger for Capto Core 400 compared with Capto Core 700. For the larger proteins, diffusion is severely restricted in Capto Core 400, resulting in lower binding capacities than those observed for Capto Core 700 despite the larger surface area. Adding 500 mM NaCl reduces the local bound protein concentration and diffusional hindrance resulting in higher binding capacities for the large proteins in Capto Core 400 compared with low ionic strength conditions. The NPs are essentially completely excluded from the Capto Core 400 pores. However, 20 and 40 nm NPs bind significantly to Capto Core 700, further hindering protein diffusion. A model is provided to predict the dynamic binding capacities as a function of residence time.

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.

Oral inhalation for delivery of proteins and peptides to the lungs

Oral inhalation is the preferred route for delivery of small molecules to the lungs, because high tissue levels can be achieved shortly after application. Biologics are mainly administered by intravenous injection but inhalation might be beneficial for the treatment of lung diseases (e.g. asthma). This review discusses biological and pharmaceutical challenges for delivery of biologics and describes promising candidates. Insufficient stability of the proteins during aerosolization and the biological environment of the lung are the main obstacles for pulmonary delivery of biologics. Novel nebulizers will improve delivery by inducing less shear stress and administration as dry powder appears suitable for delivery of biologics. Other promising strategies include pegylation and development of antibody fragments, while carrier-encapsulated systems currently play no major role in pulmonary delivery of biologics for lung disease. While development of various biologics has been halted or has shown little effects, AIR DNase, alpha1-proteinase inhibitor, recombinant neuraminidase, and heparin are currently being evaluated in phase III trials. Several biologics are being tested for the treatment of coronavirus disease (COVID)-19, and it is expected that these trials will lead to improvements in pulmonary delivery of biologics.

Pegylated catalase as a potential alternative to treat vitiligo and UV induced skin damage

The metabolic function of catalase (CAT) is to prevent oxidative damage to tissues through the hydrolysis of hydrogen peroxide, which is a strong oxidizing agent. It has been suggested as an alternative to treat skin diseases related to oxidative stress, such as vitiligo. Owing to the instability associated to the protein nature, topical use of CAT is challenging and, in this sense, PEGylation can be an interesting alternative. Here, we conjugated CAT to methoxy-poly(ethylene oxide) (mPEG) of 10, 20 and 40 kDa, by means of a nucleophilic attack of ε-amino groups to an electron-deficient carbonyl group of the reactive PEG, resulting in site specifically PEGylated bioconjugates. PEGylation yields ranged from 31% ± 2% for CAT-PEG40 to 59% ± 4% for CAT-PEG20 and were strongly affected by the reaction pH owing to the protonation/deprotonation state of primary amines of lysine and N-terminal residues. PEGylated conjugates were purified by size-exclusion chromatography (purity > 95%) and characterized by circular dichroism. Irrespectively of MW, PEG did not affected CAT secondary and tertiary structure, but a decrease in specific activity was observed, more pronounced when PEGs of higher MWs were used. However, this loss of activity is compensated by the increased long-term stability, with a gain of >5 times in t_1/2. In vitro antioxidant activity of CAT-PEG20 showed complete elimination of lipid peroxidation at the skin upper layer (stratum corneum) suitable for a topical use to treat vitiligo, as well as other skin conditions related to oxidative stress.

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.

Structural and functional characterization of Solanum tuberosum VDAC36

As it forms water-filled channel in the mitochondria outer membrane and diffuses essential metabolites such as NADH and ATP, the voltage-dependent anion channel (VDAC) protein family plays a central role in all eukaryotic cells. In comparison with their mammalian homologues, little is known about the structural and functional properties of plant VDACs. In the present contribution, one of the two VDACs isoforms of Solanum tuberosum, stVDAC36, has been successfully overexpressed and refolded by an in-house method, as demonstrated by the information on its secondary and tertiary structure gathered from circular dichroism and intrinsic fluorescence. Cross-linking and molecular modeling studies have evidenced the presence of dimers and tetramers, and they suggest the formation of an intermolecular disulfide bond between two stVDAC36 monomers. The pore-forming activity was also assessed by liposome swelling assays, indicating a typical pore diameter between 2.0 and 2.7 nm. Finally, insights about the ATP binding inside the pore are given by docking studies and electrostatic calculations.

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.

Probing Polymer Chain Conformation and Fibril Formation of Peptide Conjugates

Covalent conjugates between a synthetic polymer and a peptide hormone were used to probe the molecular extension of these macromolecules and how the polymer modifies the fibril formation of the hormone. NMR spectroscopy of ¹⁵ N labeled parathyroid hormone (PTH) was employed to visualize the conformation of the conjugated synthetic polymer, triggered by small temperature changes via its lower critical solution temperature. A shroud-like polymer conformation dominated the molecular architecture of the conjugated chimeras. PTH readily forms amyloid fibrils, which is probably the physiological storage form of the hormone. The polyacrylate based polymers stimulated the nucleation processes of the peptide.

Dendrimer-encapsulated nanoparticle-core micelles as a modular strategy for particle-in-a-box-in-a-box nanostructures

The hierarchically controlled synthesis and characterization of self-assembling macromolecules and particles are key to explore and exploit new nanomaterials. Here we present a versatile strategy for constructing particle-in-a-box-in-a-box systems by assembling dendrimer-encapsulated gold nanoparticles (DENs) into dendrimicelles. This is realized by combining positively charged PAMAM dendrimers with a negative-neutral block copolymer. The number of particles per dendrimicelle can be controlled by mixing DENs with empty PAMAM dendrimers. The dendrimicelles are stable in solution for months and provide improved resistance for the nanoparticles against degradation. The dendrimicelle strategy provides a flexible platform with a plethora of options for variation in the type of nanoparticles, dendrimers and block copolymers used, and hence is tunable for applications ranging from nanomedicine to catalysis.

Comparative Study of In Situ Loaded Antibody and PEG-Fab NIPAAM Gels

Hydrogels can potentially prolong the release of a therapeutic protein, especially to treat blinding conditions. One challenge is to ensure that the protein and hydrogel are intimately mixed by better protein entanglement within the hydrogel. N-isopropylacrylamide (NIPAAM) gels are optimized with poly(ethylene glycol) diacrylate (PEDGA) crosslinker in the presence of either bevacizumab or PEG conjugated ranibizumab (PEG₁₀ -Fab_rani ). The release profiles of the hydrogels are evaluated using an outflow model of the eye, which is previously validated for human clearance of proteins. Release kinetics of in situ loaded bevacizumab-NIPAAM gels displays a prolonged bimodal release profile in phosphate buffered saline compared to bevacizumab loaded into a preformed NIPAAM gel. Bevacizumab release in simulated vitreous from in situ loaded gels is similar to bevacizumab control indicating that diffusion through the vitreous rather than from the gel is rate limiting. Ranibizumab is site-specifically PEGylated by disulfide rebridging conjugation. Prolonged and continuous release is observed with the in situ loaded PEG₁₀ -Fab_rani -NIPAAM gels compared to PEG₁₀ -Fab_rani injection (control). Compared to an unmodified protein, there is better mixing due to PEG entanglement and compatibility of PEG₁₀ -Fab_rani within the NIPAAM-PEDGA hydrogel. These encouraging results suggest that the extended release of PEGylated proteins in the vitreous can be achieved using injectable hydrogels.

Recovery of monosaccharides from lignocellulosic hydrolysates by ion exclusion chromatography

The production of sugars from lignocellulosic biomass is the key to a sustainable, renewable chemical industry. Glucose, xylose and other monosaccharides can be easily produced by hydrolyzing cellulose and hemicellulose, the primary polysaccharides in biomass. However, the hydrolysis of biomass generates byproducts that, together with the mineral acid normally added in the hydrolysis step, have to be removed before the downstream conversion processes. In this work, the recovery of monosaccharides from lignocellulosic hydrolysates by means of Ion Exclusion Chromatography (IEC) has been studied. The analyzed process relies on new pretreatment and hydrolysis steps, involving the neutralization of the hydrolysate with sodium hydroxide. The adsorption behavior of the main components involved in the separation has been experimentally investigated. Pulse tests at the high loading encountered in preparative conditions have been performed for a selected group of model components found in the hydrolysates. For all the electrolytes, the retention volume fraction was always between the interparticle porosity and the total column porosity, confirming that ion exclusion was the dominant retention mechanism. On the other hand, sugars eluted before the total column porosity, indicating partial steric exclusion from the resin pores. This observation was then confirmed by size-exclusion experiments with polyethylene glycol standards, from which the distribution coefficient of the studied sugars has been determined. The comparison between the elution profiles of the same sugars in pure form and as a mixture present in the hydrolysate showed differences in both peak shape and retention times. Therefore, an investigation of the influence of the main electrolytes contained in the hydrolysates on sugars adsorption has been performed through the pulse on a plateau method. The electrolytes were found to enhance the sugars retention by promoting their adsorption onto the resin. However, this effect was not sufficient to explain the observed differences, which were effectively explained in terms of viscous fingering, due to the high viscosity differences between the eluent and the sample. A previously developed model for IEC has been updated to take into account all the observed phenomena and applied to simulate the experimental results. The proposed model was in good agreement with the batch-column elution profiles both for the pure components and for the actual hydrolysate, allowing a quantitative description of the separation.

Effect of PEG molecular weight and PEGylation degree on the physical stability of PEGylated lysozyme

During production, purification, formulation, and storage proteins for pharmaceutical or biotechnological applications face solution conditions that are unfavorable for their stability. Such harmful conditions include extreme pH changes, high ionic strengths or elevated temperatures. The characterization of the main influencing factors promoting undesired changes of protein conformation and aggregation, as well as the manipulation and selective control of protein stabilities are crucially important to biopharmaceutical research and process development. In this context PEGylation, i.e. the covalent attachment of polyethylene glycol (PEG) to proteins, represents a valuable strategy to improve the physico-chemical properties of proteins. In this work, the influence of PEG molecular weight and PEGylation degree on the physical stability of PEGylated lysozyme is investigated. Specifically, conformational and colloidal properties were studied by means of high-throughput melting point determination and automated generation of protein phase diagrams, respectively. Lysozyme from chicken egg-white as a model protein was randomly conjugated to 2kDa, 5kDa and 10kDa mPEG-aldehyde and resulting PEGamer species were purified by chromatographic separation. Besides protein stability assessment, residual enzyme activities were evaluated employing a Micrococcus lysodeikticus based activity assay. PEG molecules with lower molecular weights and lower PEGylation degrees resulted in higher residual activities. Changes in enzyme activities upon PEGylation have shown to result from a combination of steric hindrance and molecular flexibility. In contrast, higher PEG molecular weights and PEGylation degrees enhanced conformational and colloidal stability. By PEGylating lysozyme an increase of the protein solubility by more than 11-fold was achieved.

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.

Substrate-based near-infrared imaging sensors enable fluorescence lifetime contrast via built-in dynamic fluorescence quenching elements

Enzymatic activity sensing in fluorescence lifetime (FLT) mode with "self-quenched" macromolecular near-infrared (NIR) sensors is a highly promising strategy for in vivo imaging of proteolysis. However, the mechanisms of FLT changes in such substrate-based NIR sensors have not yet been studied. We synthesized two types of sensors by linking the near-infrared fluorophore IRDye 800CW to macromolecular graft copolymers of methoxy polyethylene glycol and polylysine (MPEG-gPLL) with varying degrees of MPEGylation and studied their fragmentation induced by trypsin, elastase, plasmin and cathepsins (B,S,L,K). We determined that the efficiency of such NIR sensors in FLT mode depends on sensor composition. While MPEG-gPLL with a high degree of MPEGylation showed rapid (τ1/2=0.1-0.2 min) FLT increase (Δτ=0.25 ns) upon model proteinase-mediated hydrolysis in vivo, lower MPEGylation density resulted in no such FLT increase. Temperature-dependence of fluorescence de-quenching of NIR sensors pointed to a mixed dynamic/static-quenching mode of MPEG-gPLL-linked fluorophores. We further demonstrated that although the bulk of sensor-linked fluorophores were de-quenched due to the elimination of static quenching, proteolysis-mediated deletion of a fraction of short (8-10kD) negatively charged fragments of highly MPEGylated NIR sensor is the most likely event leading to a rapid FLT increase phenomenon in quenched NIR sensors. Therefore, the optimization of "built-in" dynamic quenching elements of macromolecular NIR sensors is a potential avenue for improving their response in FLT mode.

Pegylated Trastuzumab Fragments Acquire an Increased in Vivo Stability but Show a Largely Reduced Affinity for the Target Antigen

PEGylation of biomolecules is a major approach to increase blood stream half-life, stability and solubility of biotherapeutics and to reduce their immunogenicity, aggregation potential and unspecific interactions with other proteins and tissues. Antibodies have generally long half-lives due to high molecular mass and stability toward proteases, however their size lowers to some extent their potential because of a reduced ability to penetrate tissues, especially those of tumor origin. Fab or otherwise engineered smaller fragments are an alternative but are less stable and are much less well retained in circulation. We have here investigated the effects of various PEGylations on the binding properties and in vivo half-life of Fab fragments derived from the enzymatic splitting of Trastuzumab. We find that PEGylation increases the half-life of the molecules but also strongly affects the ability to recognize the target antigen in a way that is dependent on the extent and position of the chemical modification. Data thus support the concept that polyethylene glycol (PEG) conjugation on Trastuzumab Fabs increases half-life but reduces their affinity and this is a fine balance, which must be carefully considered for the design of strategies based on the use of antibody fragments.

Nanoparticle dosage-a nontrivial task of utmost importance for quantitative nanosafety research

For a detailed and correct understanding of effects of colloidal nanoparticles exposed to organisms, a correlation of such effects to the physicochemical properties of the nanoparticles is a necessity. Such correlation is complex by the fact that many physicochemical parameters such as size, shape, surface charge, and colloidal stability are interlinked, and nontrivial to experimentally determine. This review aims to give an overview regarding such correlations. Particular focus will be given on the role of determining nanoparticle concentrations, which is the basis for most quantitative toxicity evaluations. A comparison of mass versus particle number concentrations is given, and their respective differences are highlighted. WIREs Nanomed Nanobiotechnol 2016, 8:479-492. doi: 10.1002/wnan.1378 For further resources related to this article, please visit the WIREs website.

Branched Polymer-Drug Conjugates for Multivalent Blockade of Angiotensin II Receptors

The use of angiotensin receptor blockers (ARBs) for treatment of ocular diseases associated with neovascularizations, such as proliferative diabetic retinopathy, shows tremendous promise but is presently limited due to short intravitreal half-life. Conjugation of ARB molecules to branched polymers could vastly augment their therapeutic efficacy. EXP3174, a potent non-peptide ARB, was conjugated to branched poly(ethylene glycol) (PEG) and poly(amido amine) (PAMAM) dendrimers: 7.8 ligand molecules were tethered to each 40 kDa PEG molecule whereas 16.7 ligand molecules were linked to each PAMAM generation 5 dendrimer. The multivalent PEG and PAMAM conjugates blocked AT1R signaling with an IC50 of 224 and 36.3 nM, respectively. The 6-fold higher affinity of the multivalent ligand-conjugated PAMAM dendrimers was due to their unique microarchitecture and ability to suppress polymer-drug interactions. Remarkably, both polymer-drug conjugates exhibited no cytotoxicity, in stark contrast to plain PAMAM dendrimers. With sufficiently long vitreous half-lives, both synthesized polymer-ARB conjugates have the potential to pave a new path for the therapy of ocular diseases accompanied by retinal neovascularizations.

PEGylation and its impact on the design of new protein-based medicines

PEGylation is the covalent conjugation of PEG to therapeutic molecules. Protein PEGylation is a clinically proven approach for extending the circulation half-life and reducing the immunogenicity of protein therapeutics. Most clinically used PEGylated proteins are heterogeneous mixtures of PEG positional isomers conjugated to different residues on the protein main chain. Current research is focused to reduce product heterogeneity and to preserve bioactivity. Recent advances and possible future directions in PEGylation are described in this review. So far protein PEGylation has yielded more than 10 marketed products and in view of the lack of equally successful alternatives to extend the circulation half-life of proteins, PEGylation will still play a major role in drug delivery for many years to come.

Design Rationale and Development Approach for Pegfilgrastim as a Long-Acting Granulocyte Colony-Stimulating Factor

Filgrastim, a recombinant methionyl human granulocyte colony-stimulating factor (G-CSF) (r-metHuG-CSF), is efficacious in stimulating neutrophil production and maturation to prevent febrile neutropenia (FN) in response to chemotherapy. Because of its relatively short circulating half-life, daily filgrastim injections are required to stimulate neutrophil recovery. In an effort to develop a long-acting form of filgrastim that was as safe and efficacious as filgrastim but had a longer in vivo residence time, a number of strategies were considered. Ultimately, fusion of filgrastim to polyethylene glycol (PEG) was selected. Following extensive analysis of conjugation chemistries as well as in vitro and in vivo characterization of a panel of PEGylated proteins, a construct containing a 20 kDa PEG moiety covalently conjugated to the N-terminus of filgrastim was chosen for advancement as pegfilgrastim. Pegfilgrastim is primarily cleared by neutrophils and neutrophil precursors (rather than the kidneys), meaning that clearance from the circulation is self-regulating and pegfilgrastim is eliminated only after neutrophils start to recover. Importantly, addition of PEG did not alter the mechanism of action and safety profile compared to filgrastim. Clinical evaluation revealed that a single 6 mg dose effectively reduces the duration of neutropenia and risk of FN in patients receiving chemotherapy. This work demonstrates the benefit of using PEGylation to generate pegfilgrastim, which allows for once-per-chemotherapy cycle administration while maintaining similar safety and efficacy profiles as those for multiple daily administration of filgrastim. Approaches that may provide advances for therapeutic agonists of G-CSF receptor are also discussed.

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.

Coupled protein diffusion and folding in the cell

When a protein unfolds in the cell, its diffusion coefficient is affected by its increased hydrodynamic radius and by interactions of exposed hydrophobic residues with the cytoplasmic matrix, including chaperones. We characterize protein diffusion by photobleaching whole cells at a single point, and imaging the concentration change of fluorescent-labeled protein throughout the cell as a function of time. As a folded reference protein we use green fluorescent protein. The resulting region-dependent anomalous diffusion is well characterized by 2-D or 3-D diffusion equations coupled to a clustering algorithm that accounts for position-dependent diffusion. Then we study diffusion of a destabilized mutant of the enzyme phosphoglycerate kinase (PGK) and of its stable control inside the cell. Unlike the green fluorescent protein control's diffusion coefficient, PGK's diffusion coefficient is a non-monotonic function of temperature, signaling ‘sticking’ of the protein in the cytosol as it begins to unfold. The temperature-dependent increase and subsequent decrease of the PGK diffusion coefficient in the cytosol is greater than a simple size-scaling model suggests. Chaperone binding of the unfolding protein inside the cell is one plausible candidate for even slower diffusion of PGK, and we test the plausibility of this hypothesis experimentally, although we do not rule out other candidates.