Following the successful development of the first once-daily GLP-1 analog liraglutide we aimed to discover analogs suitable for once-weekly dosing through acylation with fatty acids, enabling binding to serum albumin in vivo. This technology allows a drug molecule that is structurally near human GLP-1, which is not possible with fusion protein strategies. To go from once-daily to once-weekly dosing, the aim of our studies were to increase albumin affinity and obtain full stability against DPP-4 degradation, without compromising a high GLP-1 receptor (GLP-1R) affinity. The human GLP-1R was used for testing of receptor and albumin affinity. Pharmacokinetic properties were investigated in rats and pigs. Alterations in the peptide sequence as well as the fatty acid “sidechain” were explored. The latter was the key feature to secure the combination of high albumin affinity and high GLP-1R potency. Length and type of fatty acid as well as the linking chemistry between the fatty acid and GLP-1 were the parameters investigated.
Semaglutide has a peptide backbone with two substitutions compared to human GLP-1 (gamma-aminobutyric acid in position 8, arginine in 34) and is derivatized with a fatty acid “sidechain” at lysine 26. The GLP-1R affinity (0.38±0.06nM, without albumin) was slightly decreased compared to liraglutide (0.11±0.01nM), whereas the receptor affinity with albumin present was decreased more for semaglutide than liraglutide (357±98nM for semaglutide; 4.78±1.01nM for liraglutide), indicating a stronger albumin affinity for semaglutide. Plasma half-life in rats was 8.9 hours(h) (s.c. dosing), 47 h in mini pigs and 63 h in Cynomolgus monkeys. These data underscore the need for large animal models with subcutaneous tissue more similar to man in order to find compounds suitable for once-weekly administration in man. The half-life of semaglutide in man was 160 h. In conclusion, semaglutide was designed for once-weekly human use through the same technology as liraglutide, with affinity for albumin obtained though acylation.