EVALUATION OF MULTIDRUG-RESISTANT PHENOTYPE BY NOW CYTOMETRY WITH MONOCLONAL-ANTIBODIES AND FUNCTIONAL TESTS

Multidrug resistant (MDR) phenotype is characterized by a defect in dr ug accumulation caused by overexpression of a transmembrane glycoprote in, the P-glycoprotein (P-gp). MDR phenotype can be characterized eith er with monoclonal antibodies raised against P-gp or with functional t ests, most often based on the incorporation of fluorescent compounds. In the present study, data obtained with the monoclonal antibodies C21 9, JSB1 and MRK16 are compared to those of functional tests performed by flow cytometry including uptake of daunorubicin (DNR), Rhodamine 12 3 (Rh 123) or Hoechst 33342. Sensitive and resistant cell lines K562S, K562R, KBA1 and KB31, derived either from a human chronic myeloid leu kemia or from a human epithelial carcinoma, were used. In resistant ce lls, P-gp expression was revealed with either the monoclonal antibodie s C219, JSB1 or MRK-16. The most specific results were obtained with M RK-16. With functional tests, no matter which dyes were used, the fluo rescence was always stronger in sensitive than in resistant cells. How ever, with DNR and Hoechst 33342, an incorporation of these dyes was e xhibited in resistant cells. This phenomenon was not observed with Ph 123, which makes it possible to distinguish clearly between sensitive and resistant cells and to detect as few as 1% of resistant cells. Bec ause of its high sensitivity, the functional test involving incorporat ion of Ph 123 was successfully used in acute myeloid leukemia to detec t multichemoresistant cells.