Aerosolizable Plasmid DNA Dry Powders Engineered by Thin-film Freezing

PURPOSE: This study was designed to test the feasibility of using thin-film freezing (TFF) to prepare aerosolizable dry powders of plasmid DNA (pDNA) for pulmonary delivery. METHODS: Dry powders of pDNA formulated with mannitol/leucine (70/30, w/w) with various drug loadings, solid contents, and solvents were prepared using TFF, their aerosol properties (i.e., mass median aerodynamic diameter (MMAD) and fine particle fraction (FPF)) were determined, and selected powders were used for further characterization. RESULTS: Of the nine dry powders prepared, their MMAD values were about 1–2 µm, with FPF values (delivered) of 40–80%. The aerosol properties of the powders were inversely correlated with the pDNA loading and the solid content in the pDNA solution before TFF. Powders prepared with Tris–EDTA buffer or cosolvents (i.e., 1,4-dioxane or tert-butanol in water), instead of water, showed slightly reduced aerosol properties. Ultimately, powders prepared with pDNA loading at 5% (w/w), 0.25% of solid content, with or without Tris–EDTA were selected for further characterization due to their overall good aerosol performance. The pDNA powders exhibited a porous matrix structure, with a moisture content of < 2% (w/w). Agarose gel electrophoresis confirmed the chemical integrity of the pDNA after it was subjected to TFF and after the TFF powder was actuated. A cell transfection study confirmed that the activity of the pDNA did not change after it was subjected to TFF. CONCLUSION: It is feasible to use TFF to produce aerosolizable pDNA dry powder for pulmonary delivery, while preserving the integrity and activity of the pDNA.