Disclosed herein are methods and reagent kits for the quantitative in vitro determination of the functional determination of multi-drug resistance in cells, as well as for the clinical screening of potential modulators of multi-drug resistant transport activity in cells. The method of the invention is based on the measurement of the accumulation rate of free calcein within the cells of the specimen (advantageously by fluorescence measurement), after exposing the cells in vitro to a cell permeable form of calcein that is a good substrate for MDR proteins present in the sample. The cell permeable form of calcein is converted within the cell by intracellular enzymes to free calcein. Comparison of free calcein accumulation in the presence and absence of a potential inhibitor of transport activity permits the rapid screening of such inhibitors. Additionally, evaluation of free calcein accumulation rates in the presence of inhibitors of all MDR transport in comparison with calcein accumulation rates in the presence of selective inhibitors of MDR transport permits the evaluation of the functional type of MDR being exhibited.
This application is a division of application Ser. No. 09/203,553, filed Dec. 1, 1998, now U.S. Pat. No. 6,277,655, which is itself a continuation-in-part of application Ser. No. 08/928,528, filed Sep. 12, 1997, now U.S. Pat. No. 5,872,014, which is itself a continuation of application Ser. No. 08/322,702, filed Oct. 13, 1994, now abandoned, which claimed the priority of Hungarian application P94-02511, filed Aug. 31, 1994, which are each incorporated by reference.
