Solid state chemistry of proteins: II. The correlation of storage stability of freeze-dried human growth hormone (hGH) with structure and dynamics in the glassy solid

This research presents storage stability of human growth hormone, hGH, in lyophilized di-saccharide formulations. Stability via HPLC assay was assessed at 40 and 50 degrees C. Structure of the protein in the solids was assessed by infrared spectroscopy. Molecular mobility was characterized by structural relaxation times estimated from DSC data and by measurement of atomic motion on a nanosecond time scale by neutron scattering. Very large stability differences were observed among the various formulations, with both chemical and aggregation stability showing the same qualitative trends with formulation. Near the T(g), T(g) appeared to be a relevant stability parameter, but for storage well below T(g), stability seems unrelated to T(g). Stability (chemical and aggregation) was weakly correlated with secondary structure of the protein, and there was a partial quantitative correlation between degradation rate and the structural relaxation time. However, at equivalent levels of disaccharide relative to protein, sucrose systems were about a factor of two more stable than trehalose formulations, but yet had greater mobility as measured by structural relaxation time. Secondary structure was equivalent in both formulations. Neutron scattering results documented greater suppression of fast dynamics by sucrose than by trehalose, suggesting that well below T(g), fast dynamics are important to stability.