Chemosensitization and drug accumulation assays as complementary methods for the screening of multidrug resistance reversal agents

Two methods based on the reversion of adriamycin-resistance or the increase of Rhodamine 123 accumulation in a multidrug resistant (MDR) cell line have been simplified and adapted for the screening of MDR reversal agents. Both methods are carried out in microtiter plates, are highly sensitive and can be easily automated. In both assays verapamil and the cyclosporine derivative PSC 833 could be detected at concentrations lower than 1 and 0.05 μM, respectively. Depending on the MDR cell line used, drugs exhibiting the collateral sensitivity phenomenon can be selected in the cytotoxicity assay, while interferences due to sample toxicity are easily avoided in the dye accumulation assay.