Evaluation of P-glycoprotein in drug trafficking across human bronchial epithelial cell culture models

Purpose: To assess the role of P-glycoprotein (P-gp) in drug transport across human bronchial epithelial cell layers in vitro.
Methods: The human bronchial epithelial cell line Calu-3 and normal human bronchial epithelial (NHBE) cells were cultured at an air-liquid interface on Transwell® inserts for 21 days. P-gp expression was characterised at both the gene and protein levels. Functionality was determined by measuring the permeability of the established P-gp substrate 3H-digoxin alone or in the presence of chemical and biomolecular inhibitors.
Results: Both Calu-3 and NHBE cell layers showed P-gp expression and net secretory transport of 3H-digoxin at 37°C. This was significantly reduced at 4°C, indicating the involvement of an active transport mechanism. In Calu-3 cells, the basolateral to apical transport of 3H-digoxin was reduced by the P-gp inhibitors verapamil and PSC833 but not in the presence of the P-gp inhibitory antibody UIC2 or the metabolic inhibitors sodium azide and sodium dichloroacetate.
Conclusions: The net secretory transport of 3H-digoxin in Calu-3 and NHBE cell layers demonstrated the presence of a functional apical efflux pump and/or a basolateral uptake drug transporter in both in vitro models. The transporter involved in 3H-digoxin trafficking is yet to be identified but as this was not affected by ATP-depletion or specific biomolecular inhibition, it is unlikely to be P-gp.