Relaxation Processes in Freeze-Dried Monoclonal Antibody Formulations─The Role of Sucrose Concentration

Sucrose is the most common stabilizer used in freeze-dried protein formulations. We have investigated, using several methods, the effect of monoclonal antibody (mAb) to sucrose weight ratio on the thermal, relaxation, and water sorption behavior of freeze-dried formulations. The influence of the sucrose content on the miscibility and retention of the native structure of mAb was also investigated. With decreasing mAb-to-sucrose weight ratio, the following effects were observed. Differential scanning calorimetry revealed a progressive decrease in the glass transition temperature of the formulation, while, based on dielectric spectroscopy, the α-relaxation time decreased, whereas both the β- and γ-relaxation times increased. The ¹H T₁ relaxation time of the antibody, determined by solid-state nuclear magnetic resonance spectroscopy, followed the same trend as the β-relaxation time. Finally, infrared spectroscopy indicated that the optimal retention of the native-like secondary structure of the antibody was achieved at a 4:1 mAb-to-sucrose weight ratio. At mAb-to-sucrose weight ratios of 1:1 and lower, there was no evidence of phase separation in the 20-50 nm scale. Taken together, the results provide new insights into the solid-state behavior of the antibody-sucrose system.