Engineering High-Performance Inhalable Monoclonal Antibody Powders via Spray Freeze Drying

Spray freeze-drying (SFD) is a cutting-edge technique for producing dry powders, ideal for pulmonary drug delivery, owing to its ability to generate porous microparticles with low density and excellent aerodynamic properties. The SFD process, involving atomisation, freezing, and drying, is particularly suited for formulating biologics, e.g., monoclonal antibodies (mAbs), due to its low-temperature conditions. However, the method poses challenges, including the potential denaturation of mAbs due to shear, freezing, and dehydration stresses during processing. Here, we investigated how formulation modulates mAb stability and delivery performance during and after SFD processing. A model mAb was spray freeze-dried in the presence of selected stabilizing excipients, including sugars/polyols, amino acids, cyclodextrins, and surfactants. MAb chemical stability was assessed by size exclusion chromatography after the SFD process to study the strength of the formulations in each stage. The resulting inhalable mAb powders demonstrated favourable aerodynamic properties, rapid dissolution rates, and stability under various storage conditions. Notably, trehalose combined with either leucine or HPβCD effectively preserved mAb stability throughout the SFD process, ensuring high fine particle fractions (50-60%), and good physical stability of the powders. The optimised dry powder was successfully administered to rats via inhalation, as evidenced by lung deposition and systemic exposure, supporting the suitability of inhaled mAb-based therapeutics. This work elucidates key formulation-process interactions governing the pulmonary delivery of inhalable mAbs and demonstrates how rational excipient design enables the production of stable, inhalable biologic dry powders via SFD.