N-terminal site-specific mono-PEGylation of epidermal growth factor

Purpose. N-terminal site-specific mono-PEGylation of recombinant human epidermal growth factor (EGF) was accomplished using poly-ethyleneglycol (PEG) derivatives (Mw = 2000 and 5000) through a reactive terminal aldehyde group. Methods. The site-specific PEG conjugation was conducted at a slightly acidic pH condition (pH 5.5). The mono-PEGylation was targeted to an α-amine group at the N-terminal end of EGF to minimize reduction of biologic activity. Tryptic digestion mapping and MALDI-TOF MS techniques were applied to show the occurrence of mono-PEGylation at the N-terminus of EGF. Results. The site-specific mono-PEGylated EGF, when compared with native EGF, fully retained its in vitro biologic activities such as cell proliferation and intracellular signal transduction. This revealed that although a synthetic polymer of a PEG was covalently conjugated to EGF, the internalized complex of PEGylated EGF-receptor within cells did not hamper the intracellular signal transduction events. The PEGylated EGF also exhibited a prolonged circulation in blood stream in vivo and markedly enhanced physical stability when incubated with tissue homogenate. Conclusion. N-terminally mono-PEGylated EGF shows increased physical stability while retaining its biologic activity.