In Situ Characterization of the Microstructural Evolution of Biopharmaceutical Solid-State Formulations with Implications for Protein Stability

Lyophilized
and spray-dried biopharmaceutical formulations are
used to provide long-term stability for storage and transport, but
questions remain about the molecular structure in these solid formulations
and how this structure may be responsible for protein stability. Small-angle
neutron scattering with a humidity control environment is used to
characterize protein-scale microstructural changes in such solid-state
formulations as they are humidified and dried in situ. The findings
indicate that irreversible protein aggregates of stressed formulations
do not form within the solid-state but do emerge upon reconstitution
of the formulation. After plasticization of the solid-state matrix
by exposure to humidity, the formation of reversibly self-associating
aggregates can be detected in situ. The characterization of the protein-scale
microstructure in these solid-state formulations facilitates further
efforts to understand the underlying mechanisms that promote long-term
protein stability.