Purpose: To determine the effect of moisture and the role of the glass transition temperature (Tg) on the stability of a high concentration, lyophilized, monoclonal antibody.
Methods: A humanized monoclonal antibody was lyophilized in a sucrose/histidine/polysorbate 20 formulation. Residual moistures were from 1 to 8%. Tg values were measured by modulated DSC. Vials were stored at temperatures from 5 to 50 degrees C for 6 or 12 months. Aggregation was monitored by size exclusion chromatography and Asp isomerization by hydrophobic interaction chromatography. Changes in secondary structure were monitored by Fourier transform infrared (FTIR).
Results: T. values varied from 80 degrees C at 1% moisture to 25 degrees C at 8% moisture, there was no cake collapse and were no differences in the secondary structure by FTIR. All formulations were stable at 5 degrees C. High moisture cakes had higher aggregation rates than drier samples if stored above their Tg values. Intermediate moisture vials were more stable to aggregation than dry vials. High moisture samples had increased rates of Asp isomerization at elevated temperatures both above and below their Tg values. Chemical and physical degradation pathways followed Arrhenius kinetics during storage in the glassy state. Only Asp isomerization followed the Arrhenius model above the Tg value. Both chemical and physical stability at T > or = Tg were fitted to Williams-Landel-Ferry (WLF) kinetics. The WLF constants were dependent on the nature of the degradation system and were not characteristic of the solid system.
Conclusion: High moisture levels decreased chemical stability of the formulation regardless of whether the protein was in a glassy or rubbery state. In contrast, physical stability was not compromised, and may even be enhanced, by increasing residual moisture if storage is below the Tg value.