Abstract. We report on the results of multidrug-resistance transporters (P-glycoprotein, LRP, and MDR1), and apoptosis-related proteins (Fas, Bcl-2, Bax, p53, and Bcl-X L ) expression analysis of 56 acute myeloid leukemia (AML) patients by flow cytometry. Of these, there were 21 persons exposed to ionizing radiation due to the Chornobyl accident with radiation-associated and 35 patients with spontaneous AML. Leukemic cells in patients with radiation-associated AML more often overexpressed antiapoptotic protein Bcl-2 (12/21 vs. 6/35, р < 0.005) and less often demonstrated expression of Fas receptor (12/21 vs. 30/35, р < 0.05). Moreover, leukemic cells were simultaneously Fas negative and Bcl-2 positive in 4 out of 21 patients exposed to ionizing radiation but none of spontaneous cases had similar phenotype (р < 0.05). Patients with radiation-associated AML compared to spontaneous cases more often were P-glycoprotein positive (12/20 vs. 9/31, р < 0.05). P-glycoprotein overexpression significantly correlated with the resistance of the disease to chemotherapy in patients with radiation-associated AML (р < 0.05).

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