In vitro Caco-2 permeability

The Caco-2 permeability assay measures the permeability of compounds through a human intestinal epithelial cell barrier. Therefore, the endpoint measured is intestinal permeability (expressed as apparent permeability - Papp value).

The test method appears more relevant for drug permeability studies. The use of in vitro epithelial cell culture methods to estimate intestinal permeability is already foreseen in the FDA Guidance for Industry "Waiver of In Vivo Bioavailability and Bioequivalence Studies for Immediate-Release Solid Oral Dosage Forms Based on a Biopharmaceutics Classification System (BCS)". This guideline explains how to demonstrate the suitability of a permeability method intended for application of the BCS.

The permeability coefficient across Caco-2 cell monolayer may be used to assign a drug substance to BCS class. It may also be used to estimate the oral absorption of new chemical entities. Compounds exhibiting apparent permeability < 1x10-6 [cm/s], 1-10x10-6 [cm/s] and > 10x10-6 [cm/s], can be classified as poorly (0-20%), moderately (20-70%) and well (70-100%) absorbed drugs, respectively.

It is claimed that in some cases (presumably drugs) the method may replace the use of preliminary in vivo bioavailability or bioequivalence tests on animals.