MEMBRANE-PERMEABILITY ASSAY USING CACO-2 CELLS IN DRUG DISCOVERY
2001 Volume 16 Issue supplement Pages 152-153
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2001 Volume 16 Issue supplement Pages 152-153
The Caco-2 human-epithelial cell line has been widely used as a tissue-culture model for permeability measurements to predict human oral absorption in the drug discovery stage. In my presentation I will address some of the strategic applications of the Caco-2 model. Physicochemical properties affect the permeability. For example, permeability tends to be underestimated in hydrophilic compounds. For determining the permeability of poorly soluble drugs, some solubilizing reagents or bovine serum albumin can be used. The expression of some carrier-mediated transport systems has been confirmed on Caco-2 cell monolayers; therefore, we should pay attention to evaluating compounds that may be substrates of the transporters. The pH of the medium also affects the result of this assay. Transport studies with an apical pH value at 6.0 or 6.5 showed better prediction of in vivo drug absorption in human. For compounds that are substrates of P-glycoprotein (Pgp), the use of a Pgp inhibitor resulted in a better estimate of absorption in humans. The results suggest that compounds can be ranked according to how well they are absorbed; namely, those with Papp less than 1×10-6cm/s (poorly absorbed), between 1×10-6cm/s and 1×10-5cm/s (moderately absorbed), and greater than 1×10-5cm/s (well absorbed). The data of the Caco-2 assays are sometimes different, however, from those in different laboratories due to fluctuations in permeability resulting from passages and culture conditions, even when using the same clone. For high throughput screening, the permeability in 96-well Caco-2 assay demonstrates a good correlation with known human absorption for a variety of compounds. This is comparable to a 24-well system. Automation machines can be successfully applied for Caco-2 assays. Several in silicostudies for the prediction of Caco-2 permeability have also been conducted. A database system to which scientists easily access should be developed in collaboration with information-technologyg roups.
