Large-Scale Biophysical Evaluation of Protein PEGylation Effects: In Vitro Properties of 61 Protein Entities

Molecular Engineering of Efficacious Mono-Valent Ultra-Long Acting Two-Chain Insulin-Fc Conjugates

Here, we describe molecular engineering of monovalent ultra-long acting two-chain insulin-Fc conjugates. Insulin-Fc conjugates were synthesized using trifunctional linkers with one amino reactive group for reaction with a lysine residue of insulin and two thiol reactive groups used for re-bridging of a disulfide bond within the Fc molecule. The ultra-long pharmacokinetic profile of the insulin-Fc conjugates was the result of concertedly slowing insulin receptor-mediated clearance by (1) introduction of amino acid substitutions that lowered the insulin receptor affinity and (2) conjugating insulin to the Fc element. Fc conjugation leads to recycling by the neonatal Fc receptor and increase in the molecular size, both contributing to the ultra-long pharmacokinetic and pharmacodynamic profiles.

Towards toxin PEGylation: The example of rCollinein-1, a snake venom thrombin-like enzyme, as a PEGylated biopharmaceutical prototype

PEGylation was firstly described around 50 years ago and has been used for more than 30 years as a strategy to improve the drugability of biopharmaceuticals. However, it remains poorly employed in toxinology, even though it may be a promising strategy to empower these compounds in therapeutics. This work reports the PEGylation of rCollinein-1, a recombinant snake venom serine protease (SVSP), able to degrade fibrinogen and inhibit the hEAG1 potassium channel. We compared the functional, structural, and immunogenic properties of the non-PEGylated (rCollinein-1) and PEGylated (PEG-rCollinein-1) forms. PEG-rCollinein-1 shares similar kinetic parameters with rCollinein-1, maintaining its capability of degrading fibrinogen, but with reduced activity on hEAG1 channel. CD analysis revealed the maintenance of protein conformation after PEGylation, and thermal shift assays demonstrated similar thermostability. Both forms of the enzyme showed to be non-toxic to peripheral blood mononuclear cells (PBMC). In silico epitope prediction indicated three putative immunogenic peptides. However, immune response on mice showed PEG-rCollinein-1 was devoid of immunogenicity. PEGylation directed rCollinein-1 activity towards hemostasis control, broadening its possibilities to be employed as a defibrinogenant agent.

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.

Science and art of protein formulation development

Protein pharmaceuticals have become a significant class of marketed drug products and are expected to grow steadily over the next decade. Development of a commercial protein product is, however, a rather complex process. A critical step in this process is formulation development, enabling the final product configuration. A number of challenges still exist in the formulation development process. This review is intended to discuss these challenges, to illustrate the basic formulation development processes, and to compare the options and strategies in practical formulation development.

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.

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.