A 3D Model of the Human Lung Airway for Evaluating Permeability of Inhaled Drugs

Current in vitro cell-based methods, relying on single cell types, have structural and functional limitations in determining lung drug permeability, which is a contributing factor affecting both local and systemic drug levels. To address this issue, we investigated a 3D human lung airway model generated using a cell culture insert, wherein primary human lung epithelial and endothelial cells were cocultured at an air-liquid interface (ALI). To ensure that the cell culture mimics the physiological and functional characteristics of airway tissue, the model was characterized by evaluating several parameters such as cellular confluency, ciliation, tight junctions, mucus-layer formation, transepithelial electrical resistance, and barrier function through assaying fluorescein isothiocyanate-dextran permeability. To understand how the characterized ALI quality attributes influenced the absorption of inhaled drugs through the epithelial-endothelial barrier, we measured the permeability and epithelial intracellular concentrations of albuterol sulfate (AL), formoterol fumarate (FO), and fluticasone furoate (FL). The presented characterization results overall demonstrate that this culture platform mimicked the airway-specific structure and barrier function. An apparent permeability (<i>P</i> _app) of 5.7 × 10^-6 cm/s and an intracellular concentration below 1% were quantified for AL over 3 h. The <i>P</i> _app of FO was 8.5 × 10^-6 cm/s, with an intracellular concentration of 3.8%. Due to its high lipophilicity, FL showed a higher intracellular concentration (17.4%) compared to AL and FO, but also a 73.1% loss of the compound over 3 h due to nonspecific binding, with a <i>P</i> _app as low as 1.3 × 10^-7 cm/s. While the model exhibited physiologically relevant properties, its utility in estimating the permeability of inhaled drugs may be drug-specific, warranting further optimization and study.