Lipidation and conformational constraining for prolonging the effects of peptides: Xenopus glucagon-like peptide 1 analogues with potent and long-acting hypoglycemic activity

The main disadvantages of glucagon-like peptide 1 (GLP-1) are its rapid degradation and excretion. These bottlenecks can be overcome by lipidation or other structural modification. The aim of this study was to design a series of long-acting GLP-1 analogues based on our previously discovered Xenopus GLP-1 analogs (1-3). The structure-activity relationship around lipidated 1-3 derivatives (1a-3l) with respect to in vitro potency as well as protraction was firstly explored. Compound 3g was selected for further modification. The Gly(2) of 3g was replaced with Aib(2), and a lactam constraint between Glu(16) and Lys(20) (i to i + 4) was introduced to further improve the in vivo activity and stability, affording compound 4. The receptor activation capability and in vitro stability of 4 were better than 3g and liraglutide. In addition, the hypoglycemic and insulinotropic activity of 4 was significantly better than liraglutide in db/db mice. Moreover, the enhanced in vitro stability of 4 translated into improved in vivo pharmacokinetic profiles and a prolonged antidiabetic duration. Administration of 4 twice daily for one week in diet-induced obese mice caused a significant decrease in food intake, body fat and body weight. The five-week treatment study on db/db mice of 4 further demonstrated the therapeutic effects of 4 on body weight, HbA1c and glucose tolerance. These preclinical studies demonstrate the therapeutic potential of 4 for type 2 diabetes and obesity. The present study also suggests that combined lipidation and conformational constraint strategy has potential to be used for improving the therapeutic properties of peptides.