One important mechanism of drug resistance in acute leukemia is the overexpression of the multi-drug
resistance (MDR1) gene that encodes a 170-kDa membrane protein called P-glycoprotein. To estimate the
incidence and role of MDR1 gene expression in patients with acute leukemia, we investigated the expression
of MDR1 by using the RT-PCR method in blast cells from 40 cases of de novo acute leukemia. We found a high
frequency of MDR1 gene expression: 10 out of 20 with de novo acute myeloid leukemia (AML), 8 out of 17 with
de novo acute lymphoblastic leukemia (ALL), and none of the 3 with de novo acute mixed leukemia, were MDR1
mRNA-positive. No correlation between cluster designation (CD) surface markers (CD19, CD7, CD13, CD33, CD34,
CD14, HLA-DR) and MDR1 gene expression in AML was found. The complete remission rate was correlated with
MDR1 gene expression. Among 40 evaluable patients examined, 17% (3 of 18) with MDR1 mRNA-positive reached
complete remission versus 77% (17 of 22) with MDR1 mRNA-negative (p=0.044). These results suggest that MDR1
gene expression can be used as a prognostic factor and may be helpful in determining chemotherapeutic
protocol for patients with acute leukemia.
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