In vitro permeability across Caco3 cells (colonic) can predict in vivo (small intestinal) absorption in man - Fact or myth

Purpose. To evaluate and optimize the use of Caco-2 cell monolayers to predict the in vivo absorption of a broad range of compounds in man. Methods. Caco-2 cells are derived from human adenocarcinoma colon cells and spontaneously differentiate when grown on porous polyethylene terephthalte membranes (PETP) in a 12 well format to form monolayers of polarized cells possessing function similar to intestinal enterocytes. Transport experiments were conducted using 21 day cultured cells in a shaking water bath at 37 degrees C. Radiolabeled mannitol was used to determine monolayer integrity. Apparent permeability coefficient (P-app) was calculated from the appearance of drug in the receiver side. Results. A strong correlation was observed between in vivo human absorption and in vitro P-app for a variety of compounds (R = 0.95, N = 35). For compounds that are substrates of p-glycoprotein (Pgp), use of a Pgp inhibitor resulted in a better estimate of absorption in humans. The results of this study suggest that the overall ranking of compounds with P-app < 1 x 10(-6) cm/sec, between 1-10 x 10(-6) cm/sec, and > 10 x 10(-6) cm/sec can be classified as poorly (0-20%), moderately (20-70%) and well (70-100%) absorbed compounds, respectively. Conclusions. These data suggest that Caco-2 cells developed under the culturing and transport conditions defined herein can be used to predict in vivo, human absorption of compounds regardless of transport mechanism, viz., transcellular, paracellular and carrier-mediated.