MDR1 gene expression in acute myeloid leukemia: clinical correlation

Acute myeloid leukemia (AML) has a poor long-term prognosis, with a disease-free survival rate of only 20%. Drug resistance remains the major obstacle in this disease, although relatively little data are available on the correlation of multi-drug resistance (MDR) and clinical outcome. We examined 28 bone marrow samples from 24 patients with AML. The MDR1 RNA levels were determined by slot blot analysis. The incidence of positive expression of MDR1 mRNA in patients was 64.7% in samples from newly-diagnosed patients and 85.7% in relapse samples. The overall complete remission rate was 45%. However, the complete remission rate was lower for patients in the MDR1 RNA positive group than in the negative group. In three cases, the MDR1 RNA expression steadily rose during the period of disease progression and after several courses of chemotherapy. We suggest that a high frequency of MDR1 gene expression in patients with AML and higher MDR1 RNA levels are associated with a lower incidence of complete remission as well as a shorter disease-free time. The expression of MDR1 is a poor prognostic factor for AML treatment and it may play an important role in resistance to chemotherapy.