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Functional Activity of P-gp in Patients with Acute Myeloid Leukemia and Its Correlation with Karyotype Findings


, : Functional Activity of P-gp in Patients with Acute Myeloid Leukemia and Its Correlation with Karyotype Findings. Blood 100(11): Abstract No 4416, November 16

Background: Intensive chemotherapy (CT) in acute myeloid leukemia (AML) results in CR rate as high as 60-70%. Nevertheless the 5 year-disease free survival ranges from only 25 to 35%, due predominantly to relapse of the disease caused by resistance to CT. Both transporter proteins P-glycoprotein (P-gp) and multidrug resistance protein (MRP) are considered as major causes of cross-resistance to functionally and structurally unrelated drugs. The functional activity of P-gp has been evaluated through flow cytometric assays using Rhodamine 123 (Rh-123). Patients and Methods:In the present study, Rh-123 efflux was assayed in bone marrow cells of 37 consecutive patients with AML. Diagnosis of AML was established through FAB morphological classification and Immunophenotyping using a large panel of monoclonal antibodies by multiparametric flow cytometry. Rh-123 efflux assays were performed on a FACScalibur cytometer using Cell Quest software (Becton Dickinson, San Jose, CA), by analysing cellular fluorescence of gated leukemic blasts after efflux in the presence and absence of Verapamil. Differences in fluorescence were analysed with Kolmogorov-Smirnov (KS) statistics and a D value was determined and the efflux rate in percentage was also analysed. The karyotype was studied in bone marrow samples submitted to short term culture without mitogens. At least 15 to 20 G-banded metaphases were analysed and abnormalities described following ISCN 1995. Translocation t(9;22)(q34.1;q11.2); t(1;2)(p31;q34); +8,+9; +11, complex karyotype, and +8 were considered unfavorable markers, according to previous defined criteria. The mean values of D and efflux percentages were compared according to the following parameters: patient age, WBC count at diagnosis, pan myeloid (pan-M) antigen expression ( + for CD117, 13, 33, 65 and myeloperoxidase) and karyotype. Results:The Rh-123 efflux did not correlate with patients age, WBC count at diagnosis or pan myeloid antigens expression on blast cells. In contrast, patients with unfavorable cytogenetics abnormalities showed higher values of D and efflux percentage than other ones (meanD=0,47+-0,25 x 0,24+-0,12 (p=0,022)) and (mean efflux =47,8%+- 19,1 x 0,24+-0,12(p= 0,0167)), respectively. Conclusions:Our results demonstrate a positive correlation between high P-gp activity and unfavorable cytogenetics findings . P-gp activity can be used as another parameter to stratify risk groups at diagnosis and it is also a valuable data when cytogenetis is not available.

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