Pulmonary delivery of protein therapeutics has considerable clinical potential for treating both local and systemic diseases. However, poor protein conformational stability, immunogenicity and protein degradation by proteolytic enzymes in the lung are major challenges to overcome for the development of effective therapeutics. To address these, a family of structurally related copolymers comprising polyethylene glycol, mPEG2k, and poly(glutamic acid) with linear A-B (mPEG2k-lin-GA) and miktoarm A-B3 (mPEG2k-mik-(GA)3) macromolecular architectures was investigated as potential protein stabilisers. These copolymers form non-covalent nanocomplexes with a model protein (lysozyme) which can be formulated into dry powders by spray-drying using common aerosol excipients (mannitol, trehalose and leucine). Powder formulations with excellent aerodynamic properties (fine particle fraction of up to 68%) were obtained with particle size (D50) in the 2.5 µm range, low moisture content (<5%), and high glass transitions temperatures, i.e. formulation attributes all suitable for inhalation application. In aqueous medium, dry powders rapidly disintegrated into the original polymer-protein nanocomplexes which provided protection towards proteolytic degradation. Taken together, the present study shows that dry powders based on (mPEG2k-polyGA)-protein nanocomplexes possess potentials as an inhalation delivery system.
In the present study we demonstrated that a non-covalent protein complexes with mPEG2k- polyGA copolymers, with either linear or miktoarm architecture, can be successfully formulated into spray-dried powders with product attributes appropriate for inhalation delivery. Typical inhalable aerosol excipients such as trehalose, mannitol and leucine were employed in the production, whereby the presence of leucine was found to be critical in obtaining a dry powder with spherical shape and particle size (D50 ̃ 2.5 μm) optimal for inhalation. The moisture content was found to be between 0.5- 5.0 %, a range appropriate for the stability of protein formulations. The best aerodynamic properties were observed for dry powders composed of trehalose+leucine+polymer-protein nanocomplexes, with FPFs as high as 68%, without any significant negative effect of nanocomplexes on powder properties. ‘Original’ protein-polymer nanocomplexes could be recovered from dry powder formulations, with protein retaining its enzymatic activity, especially when mPEG2k-lin-GA30 copolymer was employed in the complexation. The same copolymer also provided the best protection to the complexed protein against enzymatic degradation. Hence, dry powder formulations incorporating non-covalent polymer-protein nanocomplexes have attributes appropriate for efficient and protective inhalation delivery of proteins.