Multidrug resistance protein expression in chronic myeloid leukemia: associations and significance.

Background: Overexpression of the multidrug resistance gene (MDR1) product, the MDR1 protein (MDR1), has been associated with poor prognosis in several hematologic malignancies. The significance of MDR1 levels in patients with chronic myeloid leukemia (CML) has not been established.

Methods: The authors investigated MDR1 levels and their association with patient and tumor characteristics, responsiveness to therapy, and long term prognosis in 198 CML patients. These included 127 patients in early chronic phase (ECP) CML, 31 patients in late chronic phase (LCP) CML, and 40 patients in accelerated or blastic phase CML. MDR1 expression was analyzed by Western blot analysis and quantitative solid-phase plate radioimmunoassay. MDR1 levels were measured on cell lysates obtained from the bone marrow mononuclear cell fraction. Expression was compared in relation to the median derived from 36 normal control samples.

Results: Among patients with CML, high levels of MDR1 were found in 73 of 127 ECP (57%), 20 of 31 LCP (65%), 8 of 27 in accelerated phase (30%), and 8 of 13 in blastic phase (62%) (P value not significant). Furthermore, among the 127 ECP CML patients, high MDR1 levels were associated with age >/=50 years (69% vs. 51%; P < 0. 05), thrombocytosis >700 x 10(9)/L (84% vs. 53%; P < 0.01), and leukocyte counts

Conclusions: The results of the current study demonstrate that MDR1 overexpression was not associated with disease progression, responsiveness to IFN-alpha therapy, or survival in patients with ECP CML.