Effect of pH, sucrose and mannitol on structure and long-term stability of a model IgG1 antibody upon freeze-drying

Purpose. The purpose of this study is to investigate the effect of pH and potential stabilizers on structure and long-term stability of an IgG1 monoclonal antibody in the solid state after freeze-drying. The inter-relationships between preservation of secondary and tertiary structure of the protein in the solid state and long term storage stability under different formulation conditions and temperatures was obtained from examining data collected using spectroscopic techniques and stability-indicating assays, respectively.;Methods. Anti-Streptavidin IgG1 antibody was formulated with mannitol at pH 3.0, 5.0 and 7.0 in the presence and absence of sucrose as a stabilizer. All samples were stored at 4 ºC, 25 ºC, and 37 ºC up to 12 months and at 50 ºC for 6 months. Physical degradation of each lyophilized formulation was monitored using size-exclusion chromatography (SEC), covalent degradation was monitored using cation-exchange chromatography (CEX), and sub-visible particle counts (SbVP) were measured by HIAC. The secondary structure of the protein in the solid state was characterized using Fourier transform infrared (FTIR) spectroscopy and tertiary structure was monitored using fluorescence spectroscopy. Raman spectroscopy was also used to determine changes in secondary and tertiary structure spectral features.;Results. The IgG1 antibody underwent significant secondary structural perturbations at pH 3.0 regardless of excipients, and all formulations without sucrose also showed decreased structural stability in the solid state. Based on observation of structural changes, formulation at pH 5.0, showed the least change over time and at elevated temperatures. This correlated with long-term stability upon reconstitution with respect to protein aggregate formation and sub-visible particle counts.;Conclusions. The results of the study show that protein secondary and tertiary structural preservation in the solid state correlates to improved long-term stability of the monoclonal antibody in the different lyophilized formulations.