[Development of Inhalable Dry Powder Formulations Loaded with Nanoparticles Maintaining Their Original Physical Properties and Functions].

Functional nanoparticles, such as liposomes and polymeric micelles, are attractive drug delivery systems for solubilization, stabilization, sustained release, prolonged tissue retention, and tissue targeting of various encapsulated drugs. For their clinical application in therapy for pulmonary diseases, the development of dry powder inhalation (DPI) formulations is considered practical due to such advantages as: (1) it is noninvasive and can be directly delivered into the lungs; (2) there are few biocomponents in the lungs that interact with nanoparticles; and (3) it shows high storage stability in the solid state against aggregation or precipitation of nanoparticles in water. However, in order to produce effective nanoparticle-loaded dry powders for inhalation, it is essential to pursue an innovative and comprehensive formulation strategy in relation to composition and powderization which can achieve (1) the particle design of dry powders with physical properties suitable for pulmonary delivery through inhalation, and (2) the effective reconstitution of nanoparticles that will maintain their original physical properties and functions after dissolution of the powders. Spray-freeze drying (SFD) is a relatively new powderization technique combining atomization and lyophilization, which can easily produce highly porous dry powders from an aqueous sample solution. Previously, we advanced the optimization of components and process conditions for the production of SFD powders suitable to DPI application. This review describes our recent results in the development of novel DPI formulations effectively loaded with various nanoparticles (electrostatic nanocomplexes for gene therapy, liposomes, and self-assembled lipid nanoparticles), based on SFD.