Expression of the multidrug transporter, P‐glycoprotein, in acute leukemia cells and correlation to clinical drug resistance

The overexpression of a cell‐surface glycoprotein termed P‐glycoprotein (P‐gp) is frequently associated with multi‐drug resistance (MDR) in cell lines in vitro. To evaluate the implications of P‐gp expression in clinical drug resistance, the authors examined the expression of P‐gp in leukemia cells from patients with acute myelogenous leukemia (AML) and those with acute lymphoblastic leukemia (ALL) at initial presentation and relapse, using immunoblotting with a monoclonal antibody against P‐gp, C219. Nine of 17 patients with AML and four of 11 patients with ALL had P‐gp‐positive results at the initial presentation, and most P‐gp‐positive patients did not respond to chemotherapy. Four of seven patients at the relapsed stage and all three patients with preceding myelodysplastic syndrome had P‐gp‐positive results. The expression of P‐gp and clinical refractoriness to chemotherapy were highly correlated. These data indicate that the expression of P‐gp is closely related to clinical drug resistance in acute leukemia.