Kinetic Optimization and Scale-Up of Site-Specific Thiol-PEGylation of Loxenatide from Laboratory to Pilot Scale

Moving Protein PEGylation from an Art to a Data Science

PEGylation is a well-established and clinically proven half-life extension strategy for protein delivery. Protein modification with amine-reactive poly(ethylene glycol) (PEG) generates heterogeneous and complex bioconjugate mixtures, often composed of several PEG positional isomers with varied therapeutic efficacy. Laborious and costly experiments for reaction optimization and purification are needed to generate a therapeutically useful PEG conjugate. Kinetic models which accurately predict the outcome of so-called “random” PEGylation reactions provide an opportunity to bypass extensive wet lab experimentation and streamline the bioconjugation process. In this study, we propose a protein tertiary structure-dependent reactivity model that describes the rate of protein-amine PEGylation and introduces “PEG chain coverage” as a tangible metric to assess the shielding effect of PEG chains. This structure-dependent reactivity model was implemented into three models (linear, structure-based, and machine-learned) to gain insight into how protein-specific molecular descriptors (exposed surface areas, pK_a, and surface charge) impacted amine reactivity at each site. Linear and machine-learned models demonstrated over 75% prediction accuracy with butylcholinesterase. Model validation with Somavert, PEGASYS, and phenylalanine ammonia lyase showed good correlation between predicted and experimentally determined degrees of modification. Our structure-dependent reactivity model was also able to simulate PEGylation progress curves and estimate “PEGmer” distribution with accurate predictions across different proteins, PEG linker chemistry, and PEG molecular weights. Moreover, in-depth analysis of these simulated reaction curves highlighted possible PEG conformational transitions (from dumbbell to brush) on the surface of lysozyme, as a function of PEG molecular weight.

Recycling reaction and separation for FACylation of loxenatide by trade-off between miscibility and immiscibility of reactants and product in methanol solution

The growing demand and scale of production for fatty acid chain modified (FACylated) polypeptide has sparked the interest in novel production technologies. In this study, a recycling reaction and separation process was proposed and applied to the fatty acid chain modification (FACylation) of loxenatide (LOX), which was based on the difference in solubility between reactants and FACylated product. Especially, the mixed PBS-Methanol (MeOH) solution was designed to meet the demands for FACylation of LOX as well as separation of FACylated LOX and residual modifier. In order to ensure the efficient FACylation, a mixed 10% PBS-90% MeOH (v/v) solution was chosen to provide a good miscibility for two reactants, LOX and N-tetradecylmaleimide (C₁₄-MAL). On the other hand, the immiscibility between reactant (C₁₄-MAL) and FACylated product (N-tetradecyl-Loxenatide (C₁₄-LOX)) could realize the separation of C₁₄-LOX when the MeOH concentration was less than 30% (v/v). Based on this strategy, the recycling reaction and separation process for FACylation of LOX was established by adjusting the MeOH concentration in the mixed solution. The reaction yield and recovery of C₁₄-LOX exceeded 97% and 94%, and the excess reactant C₁₄-MAL could be recycled with a recovery of more than 80%. Furthermore, after purification by reversed-phase chromatography, C₁₄-LOX showed good pharmacokinetic and pharmacodynamic properties in vivo. This study will have great application prospects in industrial production of C₁₄-LOX.

The evolution of polymer conjugation and drug targeting for the delivery of proteins and bioactive molecules

Polymer conjugation can be considered one of the leading approaches within the vast field of nanotechnology-based drug delivery systems. In fact, such technology can be exploited for delivering an active molecule, such as a small drug, a protein, or genetic material, or it can be applied to other drug delivery systems as a strategy to improve their in vivo behavior or pharmacokinetic activities such as prolonging the half-life of a drug, conferring stealth properties, providing external stimuli responsiveness, and so on. If on the one hand, polymer conjugation with biotech drug is considered the linchpin of the protein delivery field boasting several products in clinical use, on the other, despite dedicated research, conjugation with low molecular weight drugs has not yet achieved the milestone of the first clinical approval. Some of the primary reasons for this debacle are the difficulties connected to achieving selective targeting to diseased tissue, organs, or cells, which is the main goal not only of polymer conjugation but of all delivery systems of small drugs. In light of the need to achieve better drug targeting, researchers are striving to identify more sophisticated, biocompatible delivery approaches and to open new horizons for drug targeting methodologies leading to successful clinical applications. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine.