The MTT cell viability assay for cytotoxicity testing in multidrug-resistant human leukemic cells

The MTT cell viability assay is widely used in determining drug sensitivity profiles for patients with hematological malignancies and in primary screening of potential chemotherapeutic drugs. Because the multidrug resistance (MDR) phenotype is associated with these malignancies, and since many vital dyes are effluxed from MDR expressing cells, we have investigated whether the MDR phenotype interferes with the MTT assay. In CCRF-CEM and K562 human leukemic cell lines and drug-resistant sub-lines developed from them, comparison of the MTT assay with other cell viability assays showed significant variation in IC50 concentrations, although the resistance relative to the sensitive parent cell was correlated. Inclusion of verapamil, an inhibitor of drug efflux activity, had no effect on the MTT assay.