Lia M. Bersin

A significant challenge for pharmaceutical scientists during protein therapeutic development is maintaining the molecule’s native structure, which ensures safety and efficacy of the drug product. For this reason, understanding and controlling protein degradation is critical. Large molecules, such as therapeutic proteins, monoclonal antibodies (mAbs), and antibody drug conjugates (ADCs), are particularly challenging because of their immense size and complexity. To overcome these instabilities, protein therapeutics are often freeze-dried and stored in the solid form. The removal of water and decreased molecular mobility is thought to minimize degradation potential. However, reactivity is still often sufficient to cause instability. Formulating in the solid state is particularly challenging because there are significant gaps in the understanding of chemical degradation reactions in this phase. The effect of pH is often an important factor in the solution state, however there is no true definition of pH in the absence of water. It is often assumed that solid-state reactions simply parallel those of the solution state, but that is not always the case. Therefore, the objective of this work is to gain a better understanding of two chemical degradation reactions in the solid state: pyroglutamate formation and asparagine deamidation. Specific attention will be given to the influence of solution pH prior to freeze-drying. Using these two reactions as models, this work will also investigate the use of solid-state hydrogen deuterium exchange mass spectrometry (ssHDX-MS) as a means to measure hydrogen ion activity in solids, and thus serve as a surrogate for solid pH measurement.