Background : The multidrug resistance(MDR) is a major obstacle in cancer chemotherapy. The best characterized mechanism of MDR involves the expression of P-glycoprotein. P-glycoprotein functions as an energy-dependent drug efflux pump lowering the intracellular drug concentration. The expression of P-glycoprotein is caused by the increased transcription and/or RNA stabilization of MDRI gene.
Methods: For the detection of MDRI gene RT-PCR was performed with the bone marrow or peripheral mononuclear cells obtained from 27 cases acute myeloid leukemia(AML), 9 cases of acute lymphoblastic leukemia(ALL) and 7 cases of multiple myeloma(MM). The immunophenotyping of acute leukemia and the cytogenetic study were also done.
Results: MDRI mRNA was detected in 4 cases(14.8%) among 27 cases of AML.
MDRI mRNA positive AML cases consist of M2 and M4, 2 cases each in FAB classification. MDRI mRNA was detected at the time of diagnosis(1 case), in partial remission(2 cases) and in relapse(1 case), and the patients died or were hopelessly discharged. The follow-up disclosed MDRI mRNA negative AML cases to be in complete remission(7/17, 41.2%) and in partial remission(2/17, 18.2%). MDRI mRNA
positive myeloid leukemic blasts showed the ectopic expression of CD3, CD5, CD7, and/or CDl9, and revealed normal karyotypes in 2 cases and trisomy 11 in 1 case.
MDRI mRNA was not detected in 9 cases of ALL, and detected in only one case(1/7, 14.3%) of MM which had 64% of myeloma cells in the bone marrow.
Conclusion: MDRI mRNA reflecting the expression P-glycoprotein was detected at the time of diagnosis, in partial remission and in relapse of AML. MDRI mRNA positive
AML cases terminated in the poor prognosis. The ectopic expression of T- and/or B-lymphoid antigens in MDRI mRNA positive AML cases suggests the correlation of MDR and the prematurity or abnormal differentiation of myeloblasts. The measurement of MDR in the hematologic malignancy including AML might contribute the establishment of therapeutic plan and the estimation of the prognosis.

Keywords: MDRI mRNA, Acute leukemia, Multiple myeloma