Multidrug Resistance in Acute Leukaemia: A Comparative Study of Immunocytochemical and RNA Slot Blot Detection of P-glycoprotein Expression

We have analysed and compared the applicability of mRNA quantitation and immunocytochemistry to the detection of the multidrug resistant gene mdr1 and its protein product P-glycoprotein (PGP) in patients with acute leukaemia. Elevated mdr1 mRNA was detected in 12 of 55 patients and PGP expression by immunocytochemistry in 10 of 27. Raised mdr1 transcript was associated with immunocytochemical positivity in 6 of 8 cases studied. 4 of 10 cases of immunocytochemical positivity were not associated with elevated mdr1 mRNA. Immunocytochemistry showed PGP expression to be heterogeneous within blast populations. In 4 cases PGP positivity was most marked in differentiated leukaemic subpopulations. PGP expression was increased in secondary acute myeloid leukaemia (AML) compared to other disease groups. No association with disease stage was detected except within the secondary leukaemias. In 40 patients studied mdr3 mRNA was raised in one patient with AML and in two remission marrows. These results indicate that further prospective studies in acute leukaemias are required using combined immunocytochemical and RNA quantitation of PGP expression.