Mucus overproduction is a feature of chronic inflammatory airway diseases and inhaled drugs are usually delivered to such diseased airways. Due to a lack of bio-relevant in vitro models, the effect of the mucus on drug and particulate dissolution and absorption is rarely considered in the development of inhaled drugs and drug delivery systems. The mucus-secreting UNCN3T airway cell line was compared with the Calu-3 cell line to explore whether it can provide a better model of the airways with which to study drug transport in the presence of mucus.
An optimized enzyme-linked lectin assay (ELLA) showed that both cell lines cultured at air-liquid interface on Transwells™ secreted mature, glycosylated mucins. A non-hydrolysable analogue of the physiological mucin secretagogue ATP, adenylyl-imidodiphosphate (AMP-PNP) (100 mM), was shown to increase mucin secretion in UNCN3T (~2-fold) cells but not in Calu-3 cells. However, a greater fold difference in mucus between control and test cultures was achieved by the development of a mucus-depleted (MD) method, in which control cells were washed repeatedly to deplete the mucus layer. The amount of mucus was 3- and 4-fold higher in the unwashed cultures of Calu-3 and UNCN3T cells respectively. It was found that the permeability of ‘high mucus’ cells to testosterone was significantly less in UNCN3T cells (P < 0.05) but not in Calu-3 cells.
The UNCN3T cells were better able to model the effect of mucus on drug absorption and are proposed for use in considering drug-mucus interactions in inhaled drug and formulation development.
This study indicates that the UNCN3T cell line is more suitable than the Calu-3 cell line for studying the effect of mucus on the delivery of drugs and particulates to the airways. It should therefore be used when considering drug-mucus interactions in inhaled drug and formulation development.