Shaken, Not Stirred: Mechanical Stress Testing of an IgG1 Antibody

Protein aggregation is known to occur under different stress conditions and displays a wide variety of morphologies. In this work, the aggregation behavior of a monoclonal antibody (IgG1) was investigated using two different mechanical stress methods namley stirring and shaking at two temperatures, various fill volumes and headspaces and different amounts of polysorbate present in the formulation. The detection of aggregates in terms of size and number was carried out using various analytical techniques including visible particle inspection, turbidity, sub-visible particle analysis, size exclusion chromatography and dynamic light scattering. The data showed that shaking and stirring resulted in different species of aggregates both qualitatively and quantitatively, where stirring was found more stressful than shaking on the IgG1 formulation. Mechanical stress testing performed at 5 and 25°C only showed a difference on samples stressed by shaking and not by stirring. The headspace in the vials had great influence on the stability of the protein formulation when stressed by shaking. The presence of polysorbate had a protective effect on the antibody, however certain polysorbate concentrations even resulted in increased protein aggregation. An array of analytical methods was essential in order to cover the vast aggregate morphologies, which occured during agitation.