The value of spray drying as stabilization process for proteins.

Protein stability in solution state is often poor due to the intrinsic instability of proteins. A solution is to solidify them by using techniques like freeze or spray drying (SD). To shield therapeutic proteins from stress (e.g., heat or shear stress) related to the solidification process, suitable buffers and excipients are added during formulation development. In this work, buffers and excipients were identified for the stabilization of three protein model compounds (BSA, IgG and lysozyme) in solution state using a design of experiments (DoE) approach based on screening results from differential scanning fluorimetry (DSF) combined with static light scattering (SLS). The aim was to investigate whether it is possible to predict protein stability in solid state using data from protein stabilization in solution state according to DSF/SLS. Therefore, three concepts per protein were analyzed after SD, two of which were expected to stabilize the protein, and one less stabilizing and compared these results to screening results obtained in solution state. Analytical techniques prior to and post SD were reversed-phase and size-exclusion chromatography (RPC and SEC, respectively), dynamic light scattering (DLS), UV and circular dichroism (CD). Furthermore, yield and residual moisture were analyzed. BSA and lysozyme showed high stability during SD and therefore only minor changes were observed. IgG was more affected by solidification which partly resulted in a loss of more than 15 % of the initial protein concentration in comparison to before SD. In future studies, the use of analytical techniques that do not require reconstitution would give additional value.