MULTIDRUG-RESISTANCE IN ACUTE-LEUKEMIA - A COMPARISON OF DIFFERENT DIAGNOSTIC METHODS

Accurate measurement of P-glycoprotein (P-170) expression in clinical samples still remains a controversial issue. In this study tumor cell P-170 expression was assessed in 29 patients suffering from acute leuk emia (17 acute myeloid leukemia (AML) and 12 acute lymphoblastic leuke mia (ALL)) using three different techniques: flow cytometry measuring rhodamine 123 (Rh123) efflux (functional level), immunocytochemistry ( protein level) and RT-PCR (mRNA level). Rh123 efflux was detectable in 10/29 (34%) of all cases, in 9/17 (53%) of AML and in 1/12 (8%) of AL L samples. In AML patients a significant association of CD34 expressio n and P-170 activity was observed (P < 0.02). All AML patients with th e FAB subtype M5 were Rh123 negative (P < 0.007). Cytospin preparation s were analyzed for staining with monoclonal antibodies JSB1 and MM4.1 7. Eight of 16 (50%) AML and 0/9 (0%) ALL cases expressed the multidru g resistance (MDR) protein assessed by JSB1. With MM4.17 87% of AML an d 50% of ALL patients were scored positive. Agreement between both ant ibodies was found in only 13/23 (57%) samples. Extracted RNA from 12 p atients was analyzed by RT-PCR to evaluate the expression of MDR1 and multidrug resistance-associated protein (MRP) mRNA. An increased level of MDR1 mRNA was detectable in 4/7 AML and 0/5 ALL cases. MRP express ion was found in 3/7 AML and 0/5 ALL patients. Comparison of Rh123 ass ay and immunocytochemistry revealed a very good correlation when using MoAb JSB1 (P < 0.004) but not with MM4.17 (not significant (NS)). JSB 1 also showed a much better association with the PCR results (P < 0.05 ) than MM4.17 (NS). Finally, we compared the results of the functional Rh123 assay and RT-PCR and observed a high correlation for Rh123/MDR1 (r = 0.819, P < 0.001) but low for Rh123/MRP (r = 0.562, NS). We conc lude that measurement of Rh123 efflux and immunocytochemical staining of cytospin preparations with JSB1 allows the accurate monitoring of P -170 expression in acute leukemia. The simplicity of these two MDR ass ays suggests their use for routine MDR screening.