Competitive reverse transcription-polymerase chain reaction assay for quantification of human multidrug resistance 1 (MDR1) gene expression in fresh leukemic cells

We have analyzed MDR1 gene expression in 69 clinical samples obtained from 64 patients with leukemic hematologic malignancies by using a competitive r everse transcription-polymerase chain reaction assay with a heterologous co mpetitor RNA, To exclude a false-positive result caused by concomitant norm al lymphocytes that physiologically express MDR1, in samples we determined a cut-off value of 8 amol MDR1 transcript per microgram of RNA by simultane ous measurement of rhodamine 123 dye efflux either in lymphocyte or gated l eukemic cell populations. Consequently, 23 of 69 samples were concluded to be MDR1-positive in leukemic cells per se. The MDR1 expression rate was sig nificantly correlated with factors such as a history of preceding chemother apy, elder age of the patient, and certain disease types (eg, leukemia prog ressed from myelodysplastic syndrome). Moreover, the complete response rate after chemotherapy was significantly higher in MDR1-negative patients than in MDR1-positive patients (52% vs 17%, respectively; P=.01), The assay est ablished will enable the quantification of MDR1 gene expression in blood sa mples from patients with leukemic hematologic malignancies and will be appl icable to clinical laboratories as a routine test.