Friederike Roth, Regina Scherließ
Department of Pharmaceutics and Biopharmaceutics Kiel University, Grasweg 9a, Kiel, 24118, Germany
Summary
Protein formulations are especially challenging since proteins tend to aggregate or denaturise easily, resulting in a possible function loss. Most protein drugs are parenteral solutions having several disadvantages; an alternative would be a dry powder formulation for inhalation. Being a dry powder the drug should be more stable and, since sterility is not necessary for inhalation, easier to formulate. In this study, chymotrypsin as model protein and mannitol as stabilising excipient were investigated to examine the influence of the drying process in a Nano Spray Dryer B-90 HP on the protein structure. The focus laid on the impact of the different stress factors during the stages of spray drying on the protein. During pumping shear forces and adsorption to tubing material, during atomisation shear forces and ultrasonic sound and during drying, air-liquid-interfaces, thermal stress and dehydration occur. All stress factors can possibly lead to denaturation or aggregation. To detect structural changes the chymotrypsin activity assay and the measurement of changes in the fluorescence emission spectra of the fluorescent dye anilinonaphthalene-8-sulfonic-acid were used. It was found that mannitol stabilises the protein against high temperatures. Different results occurred for the stages of spray-drying. The pumping process did not cause structural changes. Atomisation, however, seems to influence the protein structure, although the enzyme activity did not change. The drying did not only influence the protein structure but also caused a small decrease in enzyme activity. Further studies will be conducted to find the best production parameters to get a stable product.
Key Message
To achieve stable protein DPI products, it is important to identify destabilising factors during production to address these with stabilising excipients. Individual stages in spray drying caused different structural changes, drying even decreased enzyme activity. Mannitol stabilised the protein against heat, whereas for other stress factors excipient selection is ongoing.