Discovery and characterization of taspoglutide, a novel analogue of human glucagon-like peptide-1, engineered for sustained therapeutic activity in type 2 diabetes

Aim: Glucagon-like peptide-1 (GLP-1) receptor agonists for the treatment of type 2 diabetes are administered by daily injection because of short plasma half-lives, which result partly from the biochemical instability of these peptides. There is a medical need for GLP-1 analogues that can be administered less frequently for patient convenience. Methods: We synthesized a series of human GLP-1 (hGLP-1(7-36)NH2) derivatives containing alpha-aminoisobutyric acid (Aib) substitutions, analysed their enzymatic stabilities and evaluated their secondary structures using circular dichroism (CD) and nuclear magnetic resonance (NMR). Results: Plasma stability experiments showed that only the analogue containing Aib substitutions in both the N-terminus (position 8) and the C-terminus (position 35), [Aib(8,35)]hGLP-1(7-36)NH2 (BIM-51077), was fully resistant to enzymatic cleavage. Incubation with human plasma kallikrein or plasmin confirmed that the Aib substitution at position 35 prevented protease cleavage around this residue, which contributes to the significantly enhanced plasma stability and increased plasma half-life. CD revealed increased C-terminal alpha-helicity in Aib(35)-substituted analogues compared with both hGLP-1(7-36)NH2 and analogues containing only Aib8 substitutions. Based on NMR studies, the secondary structure of BIM-51077 is similar to hGLP-1(7-36)NH2 with a slight increase in alpha-helicity in the C-terminus. Compared with hGLP-1(7-36)NH2, BIM-51077 had similar binding affinity for the human GLP-1 receptor and activated this receptor with similar potency. Conclusions: We have discovered an Aib(8,35)-substituted analogue of native hGLP-1(7-36)NH2 (BIM-51077) that retains the structure of the native peptide, and has similar activity and enhanced stability. A sustained-release formulation of this molecule (taspoglutide) is in phase-3 clinical development.