Use of MALDI-MS with solid-state hydrogen deuterium exchange for semi-automated assessment of peptide and protein physical stability in lyophilized solids

Highlights: • There is a concerted effort in the biopharmaceutical industry for orally available peptides. • The physical stability of lyophilized peptides formulated with excipients was assessed. • Well studied solid-dose excipients and model peptides/proteins to used validate this method. • Automated robotics and Hydrogen Deuterium Exchange coupled to MALDI-MS provided a high throughput method for this measurement. -- Abstract: Biological therapeutics are established as major contributors to the pharmaceutical pipeline. Many of these biological drugs are lyophilized to preserve their conformation and reduce decomposition during storage and shipping. Therefore, understanding and controlling the effects of lyophilization on protein higher order structure is critical for commercialization of biologics. Hydrogen Deuterium Exchange Mass Spectrometry (HDX-MS) is a well-established technique for studying protein higher order structure. Previous publications have demonstrated a solid state HDX (ssHDX) method for labeling formulated, lyophilized proteins to assess their physical stability during, but this process still suffered from low throughput and undesired back exchange. Recently, our group described a method combining HDX-MS with MALDI to greatly reduce the time of analysis and nearly eliminate H/D back-exchange, but that method was not suited for interrogating solid samples. This work integrates the two techniques to assess and predict the stability of peptides and proteins following mixing and lyophilization with various excipient formulations. Sample mixing and handling were performed through the use of a bench-top robotics and programmed data MALDI-MS acquisition allowed for monitoring deuterium incorporation for dried peptides and protein samples following continuous labeling with D₂O vapor. Effects of excipients upon peptide stability were also tracked and compared to a control for a three day labeling time course. This workflow is automated and free from back-exchange. As demonstrated by deuterium retention of bradykinin, these features serve to reduce experimental error normally associated with conventional deuterium exchange experiments. The proposed union of MALDI-MS and ssHDX can be applied to study higher order structure of proteins and peptides and the effects of added excipients in an environment that closely resembles the storage and shipping conditions of biopharmaceuticals and may be beneficial in giving insights studying protein structural dynamics in solids.