Comparison of site-specific PEGylations of the N-terminus of interferon beta-1b: selectivity, efficiency, and in vivo/vitro activity.

PEGylation, including nonspecific and site-directed approaches, is a well-established and validated strategy to increase the stability, in vivo plasma retention time, and efficacy of protein pharmaceutics together with a reduction in immunogenicity and hydrophobicity. Site-directed conjugation by PEG-aldehyde is the most widely used method for N-terminal modification; however, the generation of multimodified products is inevitable because of lysine chemistry, which always leads to difficulties in purification and quantification. In this study, we developed a specific PEGylation strategy through the periodation of the N-terminus of interferon beta-1b (IFN-β-1b) followed by the coupling of PEG-hydrazide. The prolonged elimination half-life and significantly diminished immunogenicity of the PEG-hydrazide-modified protein indicated the development of an effective process for improving the pharmacology and immunogenicity of IFN-β-1b. We further conducted comparisons on the selectivity, velocity, yield, and pharmacokinetics of the two methods. The results demonstrated that the hydrazide-based conjugation was a highly specific coupling reaction that only produced homogeneous N-terminal mono-PEGylated conjugate but also generated heterogeneous multimodified products in the aldehyde-based process. In addition, a better PEGylation yield was found for the hydrazide conjugation compared with that of the aldehyde strategy. These investigations supply a practical approach for the site-specific modification of proteins with an N-terminal serine or threonine to achieve improved homogeneity of the conjugates as well as enhanced pharmacological properties.