HT29-MTX and Caco-2/TC7 monolayers as predictive models for human intestinal absorption: role of the mucus layer

The permeability of 19 compounds in both the Caco-2/TC7 and HT29-MTX models was determined, and the ability of each model to predict intestinal absorption in humans was compared. Similar apparent permeability values (log P(app)) were obtained in both models for the majority of compounds tested, and plots of log P(app) versus fraction absorbed in humans gave comparable sigmoidal curves. A linear correlation was also observed between the log P(app) values derived from these two models, which suggests that HT29-MTX is an alternative model for absorption prediction in humans. The similarity of both the diffusion coefficients and permeability values obtained for a range of hydrophilic and lipophilic compounds in the two models indicates that the mucus layer secreted by the human adenocarcinoma HT29-MTX goblet cells does not constitute a diffusion barrier to such compounds. The lack of P-glycoprotein (P-gp) in the HT29-MTX cell line may explain the higher permeability values obtained for cimetidine and sumatriptan in this model compared with those derived from the Caco-2/TC7 monolayers. The results suggest that the HT29-MTX model can be used to rank order the passive permeability of compounds, irrespective of their potential interaction with P-gp, which may facilitate optimization of the physicochemical features of compounds within a chemical series.