Abstract
Elderly AML patients have an unfavorable prognosis with frequent resistance of leukemic cells to chemotherapy. The expression of proteins related with apoptosis and multi-drug resistance have been involved in chemotherapeutic resistance in AML; however, these proteins are not only expressed on leukemic but also on normal cells. Moreover, within leukemic cells, different stages of maturation may occur. The aim of the present study was to evaluate the expression of proteins related to apoptosis (APO 2.7, bax, and bcl-2), and drug resistance (P-gp, MRP, LRP) in a series of 117 elderly AML patients (median age of 70) uniformly treated according with the Spanish Pethema cooperative group protocol (LMA >65). 63 patients (54%) achieved complete remission (CR), with a median relapse free survival (RFS) of 9.2 months. In the bone marrow (BM) pre-treatment, we performed a four-color staining technique (APO2.7, bax or bcl-2 with CD32/CD34/CD45; and P-gp, MRP, or LRP with CD34/CD19/CD33), allowing the identification of myeloid blast cells, and the discrimination between stages of maturation of blast cell subsets. Samples were acquired on a FACSCalibur flow cytometer (Becton/Dickinson), and appropriate controls were used in each individual sample and, accordingly, antigen expression in individual cell samples was quantified as relative fluorescence intensity (RFI) (ratio blast cell/control mean channel fluorescence value). Our results showed that the level of expression of MRP and LRP was significantly higher (mean±SD of MFI 2.0±0.75 vs 2.7±1.87 and 4.5±2.2 vs 7.0±6.2, respectively -p <0.03-) in cases that did not achieved CR with one or two cycles of chemotherapy. Although different patterns of expression of apoptosis or drug resistance-associated proteins were detected according with the stage of maturation on myeloid blast cells, we did’t found any other correlation between levels of bcl-2, bax, APO 2.7, bcl-2/bax ratio or MDR and probability of achieving morphological CR. In addition, CD34 expression on blast cells had also significant influence on response (CR was achieved in 81% of CD34 negative cases vs only 46% of CD34 positive cases; p= 0.005). We didn’t found any influence of apoptosis and/or drug-resistance proteins expression in relapse rate nor RFS. Variables influencing RFS were age (p=0.04), and number of cycles to achieve CR (p=0.01); while only WBC count (p=0.05) influenced overall survival (OS). We conclude that MRP and LRP could have a role in the resistance to induction treatment in elderly AML patients but not in RFS or OS.
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