They shed light on protein conformations in the solid state
23 September 2020, 12:55
The presence of an even small amount of water in the freeze-drying biotherapeutic formulations can have a negative impact on their long-term stability and storage. Using a synchrotron-based technique, researchers from MAU together with partners within NBF (SOBI, RISE, MAXIV) can now provide a new way to extract the structural information of proteins in the solid state and during the rehydration, which is an important piece of puzzle to better understanding the relation between the moisture content and protein stability in solid state formulations.
The stability of biologically produced pharmaceuticals is a limiting factor for commercialization. This can be improved by production in solid state, mostly via lyophilization. Solid formulations involve stages where they are exposed to low levels of hydration. The presence and behaviour of residual water after drying are however not well understood and yet they most likely affect the physical and chemical stability of the biological drug. Understanding the mechanisms of destabilization of proteins in the dry/semi dry state is essential to the development of more stable and effective drugs.
The new study, recently published in the journal of Molecular Pharmaceutics, on a model protein, lysozyme in the presence of water from very low amount (few percent as in freeze-dry powder) up to highly diluted solution. The study is important in that it provides structural information that is complementary to studies using other techniques such as DSC and Raman and appears to confirm what has been suspected, i.e., proteins undergo distortion upon drying and pack to fill the space that was occupied by water.
The data presented in the article show that below 35 wt % water, the lysozyme molecules are distorted to fulfill the space-filling requirements. The distortion of the overall structure in the dry conditions, together with other stresses during/upon dehydration, reversibly changes the native structure of the protein. The researchers developed a new method using small and wide-angle X-ray scattering techniques to study powder to make results available down to intramolecular length scales.
The next step for the researchers is to apply the method to investigate other biotherapeutic products in the presence of excipients as well as in real time processing.