Simulation modelling of human intestinal absorption using Caco-2 permeability and kinetic solubility data for early drug discovery.

Measurement of permeation across a monolayer of the human adenocarcinoma cell line, Caco-2, is a popular surrogate for a compound's permeation across the human intestinal epithelium. Taken alone, however, Caco-2 permeability has certain limitations in the prediction of the extent of absorption of an orally-administered compound, because it does not take into account confounding factors such as solubility and dissolution in the gastrointestinal (GI) tract fluids. A simulation model is described that uses Caco-2 permeability measured in the apical to basolateral direction plus kinetic solubility in buffered solution (both measured at pH 7.4) to predict human intestinal absorption. The model features novel treatment of time-varying fluid volume in the GI tract, as a consequence of secretions into, and absorption of fluid from, the upper part of the GI tract. The model has been trained and cross-validated with data for 120 combinations of compound and dose. It has superior predictive power to recently published simulation and quantitative structure property relationship models, and is suitable for high-throughput screening during lead identification and lead optimisation in drug discovery. (c) 2008 Wiley-Liss, Inc. and the American Pharmacists Association