Site-specific PEGylated exendin-4 modified with a high molecular weight trimeric PEG reduces steric hindrance and increases type 2 antidiabetic therapeutic effects

The purpose of this study was to optimize an Exendin-4 (Ex4-Cys) site-specific PEGylation method with a high-molecular-weight trimeric PEG. Here, we describe the preparation of C-terminal specific PEGylated Ex4-Cys (C40-tPEG-Ex4-Cys), which was performed using cysteine and amine residue specific coupling reactions between Ex4-Cys and activated trimeric PEG. The C40-PEG-Ex4-Cys was obtained at high yields (∼83%) and characterized by MALDI-TOF mass spectrometry. The receptor binding affinity of C40-PEG _5K-Ex4-Cys was 3.5-fold higher than that of N-terminal PEGylated Ex4-Cys (N_ter-PEG_5K-Ex4-Cys), and receptor binding by the trimeric PEG (tPEG; 23, 50 kDa) adduct was much higher than that of branched PEG (20 kDa). Furthermore, C40-tPEG_50K-Ex4-Cys was found to have greater blood circulating t_1/2 and AUC_inf values than native Ex4-Cys by 7.53- and 45.61-fold, respectively. Accordingly, its hypoglycemic duration was much greater at 59.2 h than that of native Ex4-Cys at 7.3 h, with a dose of 25 nM/kg. The results of this study show that C-terminal specific PEGylation using trimeric PEG is effective when applied to Ex4-Cys and suggest that C40-tPEG_50K-Ex4-Cys has considerable potential as a type 2 antidiabetic agent.