Expression of the Human ATP-Binding Cassette Transporter Superfamily in Acute Myeloid Leukemia.

Members of the ATP-Binding-Cassette (ABC) transporter superfamily of proteins are involved in resistance to multiple chemotherapeutic drugs ( Multidrug Resistance or MDR) in a variety of malignant cells including leukemic blasts. Overexpression of some ABC transporters has been demonstrated in acute myeloid leukemia (AML) and is associated with clinical MDR and failure of conventional chemotherapy, which occurs frequently in this leukemia. Recent studies have also demonstrated ABC transporter expression in primitive normal hematopoietic cells, including progenitors which may give rise to AML after malignant transformation. In this study we used quantitative Real-Time PCR to assess and compare the expression level of all 47 known human ABC transporters in AML blasts and normal peripheral blood. Peripheral blood blasts from 17 patients with newly-diagnosed AML who subsequently received conventional remission induction therapy with cytosine arabinoside and daunorubicin were studied; 11 of these subsequently achieved complete remission of their leukemia while the remaining 6 had chemotherapy refractory disease. Contrary to expectations, no consistent difference in mRNA levels was found between the chemotherapy responsive and refractory groups of patient samples for any ABC transporter, including known MDR-related members such as MDR-1 and BCRP. Profiling of the 47 ABC transporters in 12 normal peripheral blood samples (6 mobilized with G-CSF, 6 non-mobilized) showed that TAP1 and MRP3 were 3.3-fold (P = 0.032) and 24-fold (P = 0.012), respectively, higher in normal donors as compared to AML patients. ABCA7, ABCB8, MRP3, MRP7, ALDP, PMP70 and PMP69 were greater than 3-fold higher (P < 0.05) in G-CSF-mobilized as compared to steady state normal blood. These results suggest that levels of ABC transporter mRNA expression in AML blasts prior to chemotherapy are not predictive of treatment response. This raises questions regarding the role of ABC transporters in intrinsic as opposed to induced or acquired chemotherapy drug resistance, which in turn has important implications in clinical usage of ABC-reversal agents. In addition, we identified expression of a variety of ABC transporters in both AML blasts and normal blood cells suggesting that this class of transporter proteins may have importance in both normal and malignant hematopoiesis.