Structural and Biophysical Characterization of the 40 kDa PEG−Interferon-α2aand Its Individual Positional Isomers

Direct Assessment of Oligomerization of Chemically Modified Peptides and Proteins in Formulations using DLS and DOSY-NMR

PURPOSE

Protein higher order structure (HOS) including the oligomer distribution can be critical for efficacy, safety and stability of drug products (DP). Oligomerization is particularly relevant to chemically modified protein therapeutics that have an extended pharmacokinetics profile. Therefore, the direct assessment of protein oligomerization in drug formulation is desired for quality assurance and control.

METHODS

Here, two non-invasive methods, dynamic light scattering (DLS) and diffusion ordered spectroscopy (DOSY) NMR, were applied to measure translational diffusion coefficients (Ddls and Dnmr) of proteins in formulated drug products. The hydrodynamic molecular weights (MWhd), similar to hydrodynamic size, of protein therapeutics were derived based on a log(Ddls) vs log(MWhd) correlation model established using protein standards.

RESULTS

An exponent value of -0.40 ± 0.01 was established for DLS measured log(D) vs. log(MWhd) using protein standards and a theoretical exponent value of -0.6 was used for unstructured polyethylene glycol (PEG) chains. The analysis of DLS derived MWhd of the primary species showed the fatty acid linked glucagon-like peptide 1 (GLP-1) was in different oligomer states, but the fatty acid linked insulin and PEG linked proteins were in monomer states. Nevertheless, equilibrium and exchange between oligomers in formulations were universal and clearly evidenced from DOSY-NMR for all drugs except peginterferon alfa-2a.

CONCLUSION

The correlation models of log(D) vs. log(MWhd) could be a quick and efficient way to predict MWhd of protein, which directly informs on the state of protein folding and oligomerization in formulation.

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.

Protein Dynamics Is Altered by a High Surface Density of Atomic Transfer Radical Polymerization Polymers

The effect of atomic transfer radical polymerization (ATRP) polymers on the structure and dynamics of a 14.5 kDa RNA binding protein, Rho130, was assessed using NMR. A near-homogeneous sample was generated by optimizing initiator coupling to maximize the number of modified Lys residues. The reactivity of individual Lys residues was correlated with the average solvent accessible surface area from molecular dynamics (MD) simulations and influenced by local interactions. Larger structural changes were seen with the addition of the initiator alone than with polymer growth. Structural changes were localized to the N-terminal helical domain of the protein and MD simulations suggest stabilization of the terminus of one helix by the addition of the ATRP initiator and an initiator-induced change in interhelical angles. Relaxation dispersion shows that polymer addition, but not attachment of the initiator, causes a reduction in the microsecond-millisecond dynamics of the hydrophobic core.

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.

The Effects of p-Azidophenylalanine Incorporation on Protein Structure and Stability

Functionalization is often needed to harness the power of proteins for beneficial use but can cause losses to stability and/or activity. State of the art methods to limit these deleterious effects accomplish this by substituting an amino acid in the wild-type molecule into an unnatural amino acid, such as p-azidophenylalanine (pAz), but selecting the residue for substitution a priori remains an elusive goal of protein engineering. The results of this work indicate that all-atom molecular dynamics simulation can be used to determine whether substituting pAz for a natural amino acid will be detrimental to experimentally determined protein stability. These results offer significant hope that local deviations from wild-type structure caused by pAz incorporation observed in simulations can be a predictive metric used to reduce the number of costly experiments that must be done to find active proteins upon substitution with pAz and subsequent functionalization.

Characterisation of recombinant factor IX before and after GlycoPEGylation

The effect of the GlycoPEGylation process used for prolonging the half-life of recombinant factor IX (rFIX) has no impact on the primary and higher order structure of activated factor IX. Characterisation work performed on recombinant factor IX and on the GlycoPEGylated form of rFIX (N9-GP), confirm that the primary structure as well as the post translational modifications (PTMs) (disulphide bonds, γ-carboxylation, β-hydroxylation, sulphation and O- and N-linked glycan structures) were comparable for rFIX and N9-GP. Three O-linked glycan sites were identified in the activation peptide (Thr159, Thr163 and Thr169), where Thr163 has not been reported previously. For N9-GP, the mono GlycoPEGylation is directed toward one of the two N-linked glycans present at Asn157 and Asn167 in the activation peptide in a one to one ratio. Spectroscopic techniques, such as far and near UV Circular Dichroism studies show comparable secondary and tertiary structures of rFIX and N9-GP. The thermally induced unfolding of rFIX and N9-GP shows that the unfolding temperature is approximately 1 °C higher for N9-GP than that of the rFIX. Furthermore, the pH dependent degradation was reduced due to the GlycoPEGylation of rFIX. GlycoPEGylated rFIX (N9-GP) is used for the manufacturing of Refixia® (nonacog beta pegol, Rebinyn®, Novo Nordisk A/S, Bagsvaerd, Denmark).

Polymer Masked-Unmasked Protein Therapy: Identification of the Active Species after Amylase Activation of Dextrin-Colistin Conjugates

Polymer masked–unmasked protein therapy (PUMPT) uses conjugation of a biodegradable polymer, such as dextrin, hyaluronic acid, or poly(l-glutamic acid), to mask a protein or peptide’s activity; subsequent locally triggered degradation of the polymer at the target site regenerates bioactivity in a controllable fashion. Although the concept of PUMPT is well established, the relationship between protein unmasking and reinstatement of bioactivity is unclear. Here, we used dextrin–colistin conjugates to study the relationship between the molecular structure (degree of unmasking) and biological activity. Size exclusion chromatography was employed to collect fractions of differentially degraded conjugates and ultraperformance liquid chromatography–mass spectrometry (UPLC–MS) employed to characterize the corresponding structures. Antimicrobial activity was studied using a minimum inhibitory concentration (MIC) assay and confocal laser scanning microscopy of LIVE/DEAD-stained biofilms with COMSTAT analysis. In vitro toxicity of the degraded conjugate was assessed using an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. UPLC–MS revealed that the fully “unmasked” dextrin–colistin conjugate composed of colistin bound to at least one linker, whereas larger species were composed of colistin with varying lengths of glucose units attached. Increasing the degree of dextrin modification by succinoylation typically led to a greater number of linkers bound to colistin. Greater antimicrobial and antibiofilm activity were observed for the fully “unmasked” conjugate compared to the partially degraded species (MIC = 0.25 and 2–8 μg/mL, respectively), whereas dextrin conjugation reduced colistin’s in vitro toxicity toward kidney cells, even after complete unmasking. This study highlights the importance of defining the structure–antimicrobial activity relationship for novel antibiotic derivatives and demonstrates the suitability of LC–MS to aid the design of biodegradable polymer–antibiotic conjugates.

Measuring the Impact of PEGylation on a Protein-Polysaccharide Interaction

PEGylation is the most widely used half-life extension strategy for protein therapeutics. While it imparts a range of attractive attributes PEGylation can impede protein binding and reduce efficacy. A model system to probe the effects of PEGylation on protein binding has practical applications. Here, we present a system based on complex formation between a hexavalent lectin (RSL) and the globular polysaccharide Ficoll PM70 (a type of glycocluster). Mutants of the lectin were used to generate conjugates with 3, 6, or 12 PEG (1 kDa) chains. Using NMR spectroscopy we monitored how the degree of PEGylation impacted the lectin-Ficoll interaction. The binding propensity was observed to decrease with increasing polymer density. Apparently, the extended PEG chains sterically impede the lectin-Ficoll binding. This deduction was supported by molecular dynamics simulations of the protein-polymer conjugates. The implications for protein-surface interactions are discussed.

Site-selective protein conjugation at histidine

Site-selective conjugation generally requires both (i) molecular engineering of the protein of interest to introduce a conjugation site at a defined location and (ii) a site-specific conjugation technology. Three N-terminal interferon α2-a (IFN) variants with truncated histidine tags were prepared and conjugation was examined using a bis-alkylation reagent, PEG(10kDa)-mono-sulfone 3. A histidine tag comprised of two histidines separated by a glycine (His2-tag) underwent PEGylation. Two more IFN variants were then prepared with the His2-tag engineered at different locations in IFN. Another IFN variant was prepared with the His-tag introduced in an α-helix, and required three contiguous histidines to ensure that two histidine residues in the correct conformation would be available for conjugation. Since histidine is a natural amino acid, routine methods of site-directed mutagenesis were used to generate the IFN variants from E. coli in soluble form at titres comparable to native IFN. PEGylation conversions ranged from 28-39%. A single step purification process gave essentially the pure PEG-IFN variant (>97% by RP-HPLC) in high recovery with isolated yields ranging from 21-33%. The level of retained bioactivity was strongly dependent on the site of PEG conjugation. The highest biological activity of 74% was retained for the PEG10-106(HGHG)-IFN variant which is unprecedented for a PEGylated IFN. The His2-tag at 106(HGHG)-IFN is engineered at the flexible loop most distant from IFN interaction with its dimeric receptor. The biological activity for the PEG10-5(HGH)-IFN variant was determined to be 17% which is comparable to other PEGylated IFN conjugates achieved at or near the N-terminus that have been previously described. The lowest retained activity (10%) was reported for PEG10-120(HHH)-IFN which was prepared as a negative control targeting a IFN site thought to be involved in receptor binding. The presence of two histidines as a His2-tag to generate a site-selective target for bis-alkylating PEGylation is a feasible approach for achieving site-selective PEGylation. The use of a His2-tag to strategically engineer a conjugation site in a protein location can result in maximising the retention of the biological activity following protein modification.

The Locational Impact of Site-Specific PEGylation: Streamlined Screening with Cell-Free Protein Expression and Coarse-Grain Simulation

Although polyethylene glycol (PEG) is commonly used to improve protein stability and therapeutic efficacy, the optimal location for attaching PEG onto proteins is not well understood. Here, we present a cell-free protein synthesis-based screening platform that facilitates site-specific PEGylation and efficient evaluation of PEG attachment efficiency, thermal stability, and activity for different variants of PEGylated T4 lysozyme, including a di-PEGylated variant. We also report developing a computationally efficient coarse-grain simulation model as a potential tool to narrow experimental screening candidates. We use this simulation method as a novel tool to evaluate the locational impact of PEGylation. Using this screen, we also evaluated the predictive impact of PEGylation site solvent accessibility, conjugation site structure, PEG size, and double PEGylation. Our findings indicate that PEGylation efficiency, protein stability, and protein activity varied considerably with PEGylation site, variations that were not well predicted by common PEGylation guidelines. Overall our results suggest current guidelines are insufficiently predictive, highlighting the need for experimental and simulation screening systems such as the one presented here.

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

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

Macrocyclization of Interferon-Poly(α-amino acid) Conjugates Significantly Improves the Tumor Retention, Penetration, and Antitumor Efficacy

Cyclization and polymer conjugation are two commonly used approaches for enhancing the pharmacological properties of protein drugs. However, cyclization of parental proteins often only affords a modest improvement in biochemical or cell-based in vitro assays. Moreover, very few studies have included a systematic pharmacological evaluation of cyclized protein-based therapeutics in live animals. On the other hand, polymer-conjugated proteins have longer circulation half-lives but usually show poor tumor penetration and suboptimal pharmacodynamics due to increased steric hindrance. We herein report the generation of a head-to-tail interferon-poly(α-amino acid) macrocycle conjugate circ-P(EG₃Glu)₂₀-IFN by combining the aforementioned two approaches. We then compared the antitumor pharmacological activity of this macrocycle conjugate against its linear counterparts, N-P(EG₃Glu)₂₀-IFN, C-IFN-P(EG₃Glu)₂₀, and C-IFN-PEG. Our results found circ-P(EG₃Glu)₂₀-IFN to show considerably greater stability, binding affinity, and in vitro antiproliferative activity toward OVCAR3 cells than the three linear conjugates. More importantly, circ-P(EG₃Glu)₂₀-IFN exhibited longer circulation half-life, remarkably higher tumor retention, and deeper tumor penetration in vivo. As a result, administration of the macrocyclic conjugate could effectively inhibit tumor progression and extend survival in mice bearing established xenograft human OVCAR3 or SKOV3 tumors without causing severe paraneoplastic syndromes. Taken together, our study provided until now the most relevant experimental evidence in strong support of the in vivo benefit of macrocyclization of protein-polymer conjugates and for its application in next-generation therapeutics.

Substituent position effect on the crystal structures of N-phenyl-2-phthalimidoethanesulfonamide derivatives

In order to determine the impact of different substituents and their positions on intermolecular interactions and ultimately on the crystal packing, unsubstituted N-phenyl-2-phthalimidoethanesulfonamide, C16H14N2O4S, (I), and the N-(4-nitrophenyl)-, C16H13N3O6S, (II), N-(4-methoxyphenyl)-, C16H16N3O6S, (III), and N-(2-ethylphenyl)-, as the monohydrate, C18H18N2O4S·H2O, (IV), derivatives have been characterized by single-crystal X-ray crystallography. Sulfonamides (I) and (II) have triclinic crystal systems, while (III) and (IV) are monoclinic. Although the molecules differ from each other only with respect to small substituents and their positions, they crystallized in different space groups as a result of differing intra- and intermolecular hydrogen-bond interactions. The structures of (I), (II) and (III) are stabilized by intermolecular N—H...O and C—H...O hydrogen bonds, while that of (IV) is stabilized by intermolecular O—H...O and C—H...O hydrogen bonds. All four structures are of interest with respect to their biological activities and have been studied as part of a program to develop anticonvulsant drugs for the treatment of epilepsy.

Real-time observation of protein aggregates in pharmaceutical formulations using liquid cell electron microscopy

Understanding the properties of protein-based therapeutics is a common goal of biologists and physicians. Technical barriers in the direct observation of small proteins or therapeutic agents can limit our knowledge of how they function in solution and in the body. Electron microscopy (EM) imaging performed in a liquid environment permits us to peer into the active world of cells and molecules at the nanoscale. Here, we employ liquid cell EM to directly visualize a protein-based therapeutic in its native conformation and aggregate state in a time-resolved manner. In combination with quantitative analyses, information from this work contributes new molecular insights toward understanding the behaviours of immunotherapies in a solution state that mimics the human body.

Poly(ethylene glycol) modified Mn2+ complexes as contrast agents with a prolonged observation window in rat MRA

PEGylated Mn²⁺ complexes show higher relaxivity and longer blood circulation time than free Mn²⁺ complexes.

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.

Site-Specific Transglutaminase-Mediated Conjugation of Interferon α-2b at Glutamine or Lysine Residues

Interferon α (IFN α) subtypes are important protein drugs that have been used to treat infectious diseases and cancers. Here, we studied the reactivity of IFN α-2b to microbial transglutaminase (TGase) with the aim of obtaining a site-specific conjugation of this protein drug. Interestingly, TGase allowed the production of two monoderivatized isomers of IFN with high yields. Characterization by mass spectrometry of the two conjugates indicated that they are exclusively modified at the level of Gln101 if the protein is reacted in the presence of an amino-containing ligand (i.e., dansylcadaverine) or at the level of Lys164 if a glutamine-containing molecule is used (i.e., carbobenzoxy-l-glutaminyl-glycine, ZQG). We explained the extraordinary specificity of the TGase-mediated reaction on the basis of the conformational features of IFN. Indeed, among the 10 Lys and 12 Gln residues of the protein, only Gln101 and Lys164 are located in highly flexible protein regions. The TGase-mediated derivatization of IFN was then applied to the production of IFN derivatives conjugated to a 20 kDa polyethylene glycol (PEG), using PEG-NH₂ for Gln101 derivatization and PEG modified with ZQG for Lys164 derivatization. The two mono-PEGylated isomers of IFN were obtained in good yields, purified, and characterized in terms of protein conformation, antiviral activity, and pharmacokinetics. Both conjugates maintained a native-like secondary structure, as indicated by far-UV circular dichroism spectra. Importantly, they disclosed good in vitro antiviral activity retention (about only 1.6- to 1.8-fold lower than that of IFN) and half-lives longer (about 5-fold) than that of IFN after intravenous administration to rats. Overall, these results provide evidence that TGase can be used for the development of site-specific derivatives of IFN α-2b possessing interesting antiviral and pharmacokinetic properties.

Development of next generation adeno-associated viral vectors capable of selective tropism and efficient gene delivery

Virus-based nanoparticles have shown promise as vehicles for delivering therapeutic genes. However, the rational design of viral vectors that enable selective tropism towards particular types of cells and tissues remains challenging. Here, we explored structural-functional relationships of the adeno-associated virus 2 (AAV2) vector by expanding its genetic code during production. As a proof-of-principle, an azide moiety was strategically displayed on the vector capsid as a bioorthogonal chemical reporter. Upon bioorthogonal conjugation of AAV2 with fluorophores and cyclic arginyl-glycyl-aspartic acid ligands at certain modifiable sites, we characterized in vitro and in vivo AAV2 movement and enhanced tropism selectivity towards integrin-expressing tumor cells. Targeting AAV2 vectors resulted in selective killing of U87 glioblastoma cells and derived xenografts via the herpes simplex virus suicide gene thymidine kinase, with the potency of ganciclovir being increased by 25-fold. Our results demonstrated successful rational modification of AAV2 as a targeting delivery vehicle, establishing a facile platform for precision engineering of virus-based nanoparticles in basic research and therapeutic applications.

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.

Positional isomeric effect on the crystallization of chlorine-substituted N-phenyl-2-phthalimidoethanesulfonamide derivatives

The ortho-, para- and meta-chloro-substituted N-chlorophenyl-2-phthalimidoethanesulfonamide derivatives, C16H13ClN2O4S, have been structurally characterized by single-crystal X-ray crystallography. N-(2-Chlorophenyl)-2-phthalimidoethanesulfonamide, (I), has orthorhombic (P2(1)2(1)2(1)) symmetry, N-(4-chlorophenyl)-2-phthalimidoethanesulfonamide, (II), has triclinic (P1¯) symmetry and N-(3-chlorophenyl)-2-phthalimidoethanesulfonamide, (III), has monoclinic (P2(1)/c) symmetry. The molecules of (I)-(III) are regioisomers which have crystallized in different space groups as a result of the differing intra- and intermolecular hydrogen-bond interactions which are present in each structure. Compounds (I) and (II) are stabilized by N-H···O and C-H···O hydrogen bonds, while (III) is stabilized by N-H···O, C-H···O and C-H···Cl hydrogen-bond interactions. The structure of (II) also displays π-π stacking interactions between the isoindole and benzene rings. All three structures are of interest with respect to their biological activities and have been studied as part of a programme to develop anticonvulsant drugs for the treatment of epilepsy.

Development of next generation of therapeutic IFN-α2b via genetic code expansion

With the aim to overcome the heterogeneity associated with marketed IFN-α2b PEGylates and optimize the size of the PEG moiety and the site of PEGylation, we develop a viable and facile platform through genetic code expansion for PEGylation of IFN-α2b at any chosen site(s). This approach includes site-specific incorporation of an azide-bearing amino acid into IFN-α2b followed by orthogonal and stoichiometric conjugation of a variety of PEGs via a copper-free click reaction. By this approach, only the chosen site(s) within IFN-α2b is consistently PEGylated under mild conditions, leading to a single and homogenous conjugate. Furthermore, it makes the structure-activity relationship study of IFN-α2b possible by which the opposite effects of PEGylation on the biological and pharmacological properties are optimized. Upon re-examination of the PEGylated IFN-α2b isomers carrying different sizes of PEG at different sites, we find mono-PEGylates at H34, A74 and E107 with a 20-, 10- and 10-kDa PEG moiety, respectively, have both higher biological activities and better PK profiles than others. These might represent the direction for development of the next generation of PEGylated IFN-α2b.

Pegylation of biological molecules and potential benefits: pharmacological properties of certolizumab pegol

PEGylation of biological proteins, defined as the covalent conjugation of proteins with polyethylene glycol (PEG), leads to a number of biopharmaceutical improvements, including increased half-life, increased solubility and reduced aggregation, and reduced immunogenicity. Since their introduction in 1990, PEGylated proteins have significantly improved the management of various chronic diseases, including rheumatoid arthritis (RA) and Crohn's disease. Certolizumab pegol is the only PEGylated anti-tumour necrosis factor (TNF)-α agent. It is a PEGylated, humanised, antigen-binding fragment of an anti-TNF monoclonal antibody. Unlike other anti-TNF agents, it has no crystallisable fragment (Fc) domain. Because of its novel structure, certolizumab pegol may have a different mechanism of action to the other anti-TNF agents, and also has different pharmacodynamic properties, which could possibly translate to a different safety profile. Pharmacodynamic studies have shown that certolizumab pegol binds to TNF with a higher affinity than adalimumab and infliximab. Certolizumab pegol is also more potent at neutralising soluble TNF-mediated signalling than adalimumab and infliximab, and has similar or lesser potency to etanercept. Certolizumab pegol does not cause detrimental in vitro effects such as degranulation, loss of cell integrity, apoptosis, complement-dependent cytotoxicity and antibody-dependent cell-mediated cytotoxicity. Certolizumab pegol may also penetrate more effectively into inflamed arthritic tissue than other anti-TNF agents, and is not actively transported across the placenta during pregnancy. Pharmacokinetic studies in healthy volunteers demonstrated that single intravenous and subcutaneous doses of certolizumab pegol had predictable pharmacokinetics. The pharmacokinetics of certolizumab pegol in patients with RA and Crohn's disease were consistent with pharmacokinetics in healthy volunteers.

Broadening the versatility of lentiviral vectors as a tool in nucleic acid research via genetic code expansion

With the aim of broadening the versatility of lentiviral vectors as a tool in nucleic acid research, we expanded the genetic code in the propagation of lentiviral vectors for site-specific incorporation of chemical moieties with unique properties. Through systematic exploration of the structure–function relationship of lentiviral VSVg envelope by site-specific mutagenesis and incorporation of residues displaying azide- and diazirine-moieties, the modifiable sites on the vector surface were identified, with most at the PH domain that neither affects the expression of envelope protein nor propagation or infectivity of the progeny virus. Furthermore, via the incorporation of such chemical moieties, a variety of fluorescence probes, ligands, PEG and other functional molecules are conjugated, orthogonally and stoichiometrically, to the lentiviral vector. Using this methodology, a facile platform is established that is useful for tracking virus movement, targeting gene delivery and detecting virus–host interactions. This study may provide a new direction for rational design of lentiviral vectors, with significant impact on both basic research and therapeutic applications.

Effect of polyethylene glycol conjugation on conformational and colloidal stability of a monoclonal antibody antigen-binding fragment (Fab')

We have investigated the effects of site specific "hinge" polyethylene glycol conjugation (PEGylation) on thermal, pH, and colloidal stability of a monoclonal antibody antigen-binding fragment (Fab') using a variety of biophysical techniques. The results obtained by circular dichroism (CD), ultraviolet (UV) absorbance, and fluorescence spectroscopy suggested that the physical stability of the Fab' is maximized at pH 6-7 with no apparent differences due to PEGylation. Temperature-induced aggregation experiments revealed that PEGylation was able to increase the transition temperature, as well as prevent the formation of visible and subvisible aggregates. Statistical comparison of the three-index empirical phase diagram (EPD) revealed significant differences in thermal and pH stability signatures between Fab' and PEG-Fab'. Upon mechanical stress, micro-flow imaging (MFI) and measurement of the optical density at 360 nm showed that the PEG-Fab' had significantly higher resistance to surface-induced aggregation compared to the Fab'. Analysis of the interaction parameter, kD, indicated repulsive intermolecular forces for PEG-Fab' and attractive forces for Fab'. In conclusion, PEGylation appears to protect Fab' against thermal and mechanical stress-induced aggregation, likely due to a steric hindrance mechanism.

Head to head comparison of the formulation and stability of concentrated solutions of HESylated versus PEGylated anakinra

Although PEGylation of biologics is currently the gold standard for half-life extension, the technology has a number of limitations, most importantly the non-biodegradability of PEG and the extremely high viscosity at high concentrations. HESylation is a promising alternative based on coupling to the biodegradable polymer hydroxyethyl starch (HES). In this study, we are comparing HESylation with PEGylation regarding the effect on the protein's physicochemical properties, as well as on formulation at high concentrations, where protein stability and viscosity can be compromised. For this purpose, the model protein anakinra is coupled to HES or PEG by reductive amination. Results show that coupling of HES or PEG had practically no effect on the protein's secondary structure, and that it reduced protein affinity by one order of magnitude, with HESylated anakinra more affine than the PEGylated protein. The viscosity of HESylated anakinra at protein concentrations up to 75 mg/mL was approximately 40% lower than that of PEG-anakinra. Both conjugates increased the apparent melting temperature of anakinra in concentrated solutions. Finally, HESylated anakinra was superior to PEG-anakinra regarding monomer recovery after 8 weeks of storage at 40°C. These results show that HESylating anakinra offers formulation advantages compared with PEGylation, especially for concentrated protein solutions.

Role of benzyl alcohol in the unfolding and aggregation of interferon α-2a

Benzyl alcohol (BA) is the most widely used antimicrobial preservative in multidose protein formulations, and has been shown to cause protein aggregation. Our previous work on a model protein cytochrome c demonstrated that this phenomenon occurs via partial unfolding. Here, we examine the validity of these results by investigating the effect of BA on a pharmaceutically relevant protein, interferon α-2a (IFNA2). IFNA2 therapeutic formulations available on the pharmaceutical market contain BA as a preservative. Isothermal aggregation kinetics and temperature scanning demonstrated that BA induced IFNA2 aggregation in a concentration-dependent manner. With increasing concentration of BA, the apparent aggregation temperature of IFNA2 linearly decreased. Denaturant melts measured using protein intrinsic fluorescence and that of the 1-anilinonaphthalene-8-sulfonic acid dye indicated that IFNA2 stability decreased with increasing BA concentration, populating a partially unfolded intermediate. Changes in nuclear magnetic resonance chemical shifts and hydrogen exchange rates identified the structural nature of this intermediate, which correlated with an aggregation "hot-spot" predicted by computational methods. These results indicate that BA induces IFNA2 aggregation by partial unfolding rather than global unfolding of the entire protein, and is consistent with our earlier conclusions from model protein studies.

Effect of pegylation on self-association of IFN-α2b

Pegylation of therapeutic proteins is an established technology used to enhance the bioavailability of an active pharmaceutical ingredient in the body of patients. While the physiochemical properties of pegylated monomeric proteins have been extensively described, there is still limited information on the characterization of pegylated oligomeric proteins. In this study, we report the characterization of a pegylated interferon alpha2b (PEGIFN-α2b) concentration-dependent oligomerization by a series of orthogonal biochemical and biophysical methods. These methods include sedimentation velocity and sedimentation equilibrium analytical ultracentrifugation, matrix-assisted laser desorption ionization, and size exclusion chromatography of bissulfosuccinimidyl suberate cross-linked PEGIFN. We report here that PEGIFN-α2b self-associates in a concentration-dependent manner into mainly monomers, dimers, and trimers. In the presence of the chemical cross-linker, PEGIFN-α2b is primarily monomeric (57%) at concentration lower than 0.3 mg/mL and contains about equal amount of monomers and dimers (47.0% and 37.7%, respectively), about 15% of trimers, and up to 4% of higher molecular weight species at 0.7 mg/mL and above.

Building better drugs: developing and regulating engineered therapeutic proteins

Most native proteins do not make optimal drugs and thus a second- and third-generation of therapeutic proteins, which have been engineered to improve product attributes or to enhance process characteristics, are rapidly becoming the norm. There has been unprecedented progress, during the past decade, in the development of platform technologies that further these ends. Although the advantages of engineered therapeutic proteins are considerable, the alterations can affect the safety and efficacy of the drugs. We discuss both the key technological innovations with respect to engineered therapeutic proteins and advancements in the underlying basic science. The latter would permit the design of science-based criteria for the prediction and assessment of potential risks and the development of appropriate risk management plans. This in turn holds promise for more predictable criteria for the licensure of a class of products that are extremely challenging to develop but represent an increasingly important component of modern medical practice.

Long-acting preparations of exenatide

Exenatide has been widely used for the treatment of type 2 diabetes mellitus. However, its short plasma half-life of 2.4 hours has limited its clinical application. The exenatide products on the market, twice-daily Byetta™ and once-weekly Bydureon™ (both Amylin Pharmaceuticals, San Diego, CA, USA), are still not perfect. Many researchers have attempted to prolong the acting time of exenatide by preparing sustained-release dosage forms, modifying its structure, gene therapies, and other means. This review summarizes recent advances in long-acting exenatide preparations.

Molecular insight into the steric shielding effect of PEG on the conjugated staphylokinase: biochemical characterization and molecular dynamics simulation

PEGylation is a successful approach to improve potency of a therapeutic protein. The improved therapeutic potency is mainly due to the steric shielding effect of PEG. However, the underlying mechanism of this effect on the protein is not well understood, especially on the protein interaction with its high molecular weight substrate or receptor. Here, experimental study and molecular dynamics simulation were used to provide molecular insight into the interaction between the PEGylated protein and its receptor. Staphylokinase (Sak), a therapeutic protein for coronary thrombolysis, was used as a model protein. Four PEGylated Saks were prepared by site-specific conjugation of 5 kDa/20 kDa PEG to N-terminus and C-terminus of Sak, respectively. Experimental study suggests that the native conformation of Sak is essentially not altered by PEGylation. In contrast, the bioactivity, the hydrodynamic volume and the molecular symmetric shape of the PEGylated Sak are altered and dependent on the PEG chain length and the PEGylation site. Molecular modeling of the PEGylated Saks suggests that the PEG chain remains highly flexible and can form a distinctive hydrated layer, thereby resulting in the steric shielding effect of PEG. Docking analyses indicate that the binding affinity of Sak to its receptor is dependent on the PEG chain length and the PEGylation site. Computational simulation results explain experimental data well. Our present study clarifies molecular details of PEG chain on protein surface and may be essential to the rational design, fabrication and clinical application of PEGylated proteins.

Impact of site-specific PEGylation on the conformational stability and folding rate of the Pin WW domain depends strongly on PEG oligomer length

Protein PEGylation is an effective method for reducing the proteolytic susceptibility, aggregation propensity, and immunogenicity of protein drugs. These pharmacokinetic challenges are fundamentally related to protein conformational stability, and become much worse for proteins that populate the unfolded state under ambient conditions. If PEGylation consistently led to increased conformational stability, its beneficial pharmacokinetic effects could be extended and enhanced. However, the impact of PEGylation on protein conformational stability is currently unpredictable. Here we show that appending a short PEG oligomer to a single Asn side chain within a reverse turn in the WW domain of the human protein Pin 1 increases WW conformational stability in a manner that depends strongly on the length of the PEG oligomer: shorter oligomers increase folding rate, whereas longer oligomers increase folding rate and reduce unfolding rate. This strong length dependence is consistent with the possibility that the PEG oligomer stabilizes the transition and folded states of WW relative to the unfolded state by interacting favorably with side-chain or backbone groups on the WW surface.

Injectable hyaluronic acid-tyramine hydrogels incorporating interferon-α2a for liver cancer therapy

We report an injectable hydrogel system that incorporates interferon-α2a (IFN-α2a) for liver cancer therapy. IFN-α2a was incorporated in hydrogels composed of hyaluronic acid-tyramine (HA-Tyr) conjugates through the oxidative coupling of Tyr moieties with hydrogen peroxide (H2O2) and horseradish peroxidase (HRP). IFN-α2a-incorporated HA-Tyr hydrogels of varying stiffness were formed by changing the H2O2 concentration. The incorporation of IFN-α2a did not affect the rheological properties of the hydrogels. The activity of IFN-α2a was furthermore well-maintained in the hydrogels with lower stiffness. Through the caspase-3/7 pathway in vitro, IFN-α2a released from HA-Tyr hydrogels inhibited the proliferation of liver cancer cells and induced apoptosis. In the study of the pharmacokinetics, a higher concentration of IFN-α2a was shown in the plasma of mice treated with IFN-α2a-incorporated hydrogels after 4h post injection, with a much higher amount of IFN-α2a delivered at the tumor tissue comparing to that of injecting an IFN-α2a solution. The tumor regression study revealed that IFN-α2a-incorporated HA-Tyr hydrogels effectively inhibited tumor growth, while the injection of an IFN-α2a solution did not demonstrate antitumor efficacy. Histological studies confirmed that tumor tissues in mice treated with IFN-α2a-incorporated HA-Tyr hydrogels showed lower cell density, with more apoptotic and less proliferating cells compared with tissues treated with an IFN-α2a solution. In addition, the IFN-α2a-incorporated hydrogel treatment greatly inhibited the angiogenesis of tumor tissues.