Membrane reactor for continuous and selective protein mono-PEGylation

PEGylated proteins are value-added biopharmaceutical products obtained by conjugating poly (ethylene glycol) or PEG with proteins. It is difficult to simultaneously obtain both high selectivity and extent of synthesis of mono-PEGylated protein using a conventional batch reaction. This paper discusses a hollow-fiber membrane reactor (HMR) system suitable for addressing this issue. The HMR system was operated in a continuous mode with the protein being pumped directly into the lumen of the fiber and the PEG reagent being introduced in the hollow-fiber in a distributed manner along its length. The PEG concentration at any location within the reactor thereby was lower than the protein concentration, and thus the synthesis of higher PEGylated by-products was suppressed, leading to an increase in selectivity of mono-PEGylation. An additional factor that contributed towards the enhancement in selectivity was the radial concentration gradient of reactants and product within the hollow-fiber, which resulted in the diffusion of mono-PEGylated protein away from the reaction zone, thus further suppressing the synthesis of the higher PEGylated forms. The extent and selectivity of mono-PEGylation obtained with the HMR system were significantly higher than that obtained in equivalent batch reaction. Furthermore, a continuous process is much more desirable than a batch process from a manufacturing point of view.