Identification of Agitation-Induced Unfolding Events Causing Aggregation of Monoclonal Antibodies Using Hydrogen Exchange-Mass Spectrometry.

Due to significant safety tolerances on maximum levels of visible and sub-visible particles in parenterally dosed drug products like monoclonal antibodies (mAbs), particle formation rates must be determined during development and minimized. Agitation stress, encountered during transportation and manufacturing, increases particle formation rates in a protein and formulation dependent fashion in a phenomenon thought to be partially mediated by mAb adsorption to the continuously regenerating air-water interface that results from agitation. The goal of this study was to explore the structural dynamics of three mAbs with variable sensitivity to agitation to develop a mechanistic understanding of exactly what occurs at the air-water interface that leads to aggregation and particle formation. We observed preferential orientation at the interface and subsequent cooperative unfolding for the molecule which aggregates most extensively under agitation, and also that the magnitude of destabilization appears to scale with particle formation rates. We also show that polysorbate, a widely-used excipient in parenteral formulations to protect against particle formation, eliminates interface-induced destabilization. This study provides direct evidence that local unfolding events resulting from interface exposure precede particle formation and may play a causal role in the process.