Solution structures of long‐acting insulin analogues and their complexes with albumin.

The lipidation of peptide drugs is one strategy to obtain extended half‐lives, enabling once‐daily or even less frequent injections for patients. The half‐life extension results from a combination of self‐association and association with human serum albumin (albumin). The self‐association and association with albumin of two insulin analogues, insulin detemir and insulin degludec, were investigated by small‐angle X‐ray scattering (SAXS) and dynamic light scattering (DLS) in phenolic buffers. Detemir shows concentration‐dependent self‐association, with an equilibrium between hexamer, dihexamer, trihexamer and larger species, while degludec appears as a dihexamer independent of concentration. The solution structure of the detemir trihexamer has a bent shape. The stoichiometry of the association with albumin was studied using DLS. For albumin–detemir the molar stoichiometry was determined to be 1:6 (albumin:detemir ratio) and for albumin–degludec it was between 1:6 and 1:12 (albumin:degludec ratio). Batch SAXS measurements of a 1:6 albumin:detemir concentration series revealed a concentration dependence of complex formation. The data allowed the modelling of a complex between albumin and a detemir hexamer and a complex consisting of two albumins binding to opposite ends of a detemir dihexamer. Measurements of size‐exclusion chromatography coupled to SAXS revealed a complex between a degludec dihexamer and albumin. Based on the results, equilibria for the albumin–detemir and albumin–degludec mixtures are proposed. Solution structures of complexes between human serum albumin and the two lipidated insulin analogues detemir and degludec are presented and models for the equilibria are suggested. [ABSTRACT FROM AUTHOR]