(586p) Optimization of Protein Pegylation

Corbett, B., McMaster University
Shang, X., McMaster University
Ghosh, R., McMaster University
Mhaskar, P., McMaster University

PEGylation is a generic term for chemical conjugation of polyethylene glycol (or PEG) to biomacromolecules such as proteins. PEGylation is frequently used to improve the properties of therapeutic proteins. While this type of chemical reaction is easy to carry out, it typically results in the synthesis of complex mixtures of different PEGylated forms, i.e. mono-, di-, tri-, and higher-PEGylated protein. With many PEGylated therapeutic protein products the mono-PEGylated protein is usually the desired form. Formation of by-products in a PEGylation reaction represents material loss as well as the inconvenience of a challenging purification process that would follow. The problem of low selectivity of mono-PEGylation could be addressed through the use of specific reactions such as N-terminal PEGylation. However, even with such specific reactions, significant amounts of by-products are typically synthesized. Generally speaking, a trade-off between selectivity and yield of desired product is observed in most PEGylation reactions. We present a systematic attempt at optimization of batch protein PEGylation. To this end, initially a first principles model (with the associated reaction network) is presented with kinetic rate constants determined using the experimental data. The dynamic model captures the effect of variation in initial condition as well as the pH at which the experiment is run. Having established the validity of the model beyond the fit data by additional experiments, the model is then utilized to determine the optimal pH, duration and initial recipe that maximize the formation of the mono-PEGylated product. The benefits of operating at the conditions suggested by the optimization problem are finally demonstrated though additional experiments.