FUNCTIONAL-STUDY OF MULTIDRUG-RESISTANCE WITH FLUORESCENT DYES - LIMITS OF THE ASSAY FOR LOW-LEVELS OF RESISTANCE AND APPLICATION IN CLINICAL-SAMPLES

Fluorescent dyes such as rhodamine 123 (R123) and Hoechst 33342 (Ho342 ) have been widely used to characterize multidrug-resistance (MDR) phe notype cells in cell populations, on the basis of their reduced accumu lation in resistant cells. Taking advantage of the high fluorescence q uantum yield of R123 and Ho342 compared with that of anthracyclines, w e investigated the limits of fluorescence image cytometry in detecting MDR by the level of R123 and Ho342 accumulation and efflux. We were a ble to separate with this technique a cell line with a level of resist ance as low as 3. We then studied the presence of MDR cells in lymphoc ytes isolated from patients with hematological malignancies.