Evaluation of a vincristine resistant Caco-2 cell line for use in a calcein AM extrusion screening assay for P-glycoprotein interaction

Aim: To develop a fast fluorometric screening assay based on vincristine re sistant Caco-2 cells (Caco-2VCR) in order to elucidate potential P-glycopro tein (Pgp) interactions of compounds, and to characterise Caco-2VCR cells w ith regard to their expression of the efflux transporters Pgp, MRP1 and MRP 2. Methods: We applied the Caco-2VCR cells to a 96-well plate-based calcein AM extrusion assay. The Caco-2VCR cells were cultured as monolayers and in cubated with calcein AM with/without addition of Pgp modulators. Fourteen k nown Pgp modulators were tested in the assay (chloropromazine, cyclosporin A, domperidone, digoxin, ivermectin, ketoconazole, loperamide, metoprolol, propranolol, progesterone, quinidine, quinine, verapamil and vincristine). For each compound an EC50 value was calculated. Protein and mRNA levels of the efflux transporters were analysed by Western blot and polymerase chain reaction techniques. Results: All compounds with the exception of digoxin d isplayed increased calcein levels. Protein and mRNA analysis showed increas ed levels of Pgp after vincristine exposure, while expression of the efflux transporters MRP1 and MRP2 remained unchanged. Conclusions: The calcein AM extrusion assay applied to Caco-2VCR cells can be a valuable tool as a scr eening assay for new compounds and their potential interaction with P-glyco protein. (C) 2001 Elsevier Science B.V. All rights reserved.