Changes in the Structure of A Monoclonal Antibody Adsorbed to Silica Particles

Aggregation leading to visible particulates in protein therapeutics is not desirable. The mechanisms leading to the appearance of visible particulates or aggregates in some final formulations of protein therapeutics upon storage are not completely understood. However, adsorption to surfaces has been suggested as a potential cause of protein aggregation or visible particle formation.

The purpose of this work was to investigate the tertiary structure of a model, non-therapeutic monoclonal antibody (IgG1 - antistreptavidin, generously donated by Amgen Inc.) after adsorption to silica microparticles, which were used as a model foreign particulate contaminant. The effect of common formulation excipients added to 10 mM pH 5.0 acetate buffered solutions was examined. A novel combination of front-face fluorescence and tryptophan quenching was used to detect the subtle changes in tertiary structure of adsorbed protein versus free protein. The small increase in tryptophan fluorescence quenching when adsorbed versus free indicated that there was only a minor change in the protein's tertiary structure upon adsorption. The presence of salt, sucrose, and polysorbate 20 were found to modulate changes in tertiary structure of the protein upon adsorption to silica microparticles.