Prognostic Impact of Anti-Apoptotic and Multidrug Resistance Phenotypes in Elderly Acute Myeloid Leukemia Patients

Elderly patients with acute myeloid leukemia (AML) have an unfavorable outcome, which has been related to both the poor performance status of many of these patients and the biological characteristics of the malignant clone, including the expression of multidrug resistance (MDR) phenotypes. We have quantitatively analyzed by flow cytometry the expression of apoptosis- (bcl-2, bax, APO2.7) and MDR- (P-gp, MRP, LRP) associated proteins in a group of 117 elderly (>65 years) uniformly treated de novo AML patients according to the Pethema LMA-98 protocol. Upon analyzing factors influencing the response to induction therapy, as expected, patients with good and intermediate cytogenetics (n=76) more frequently achieved morphological complete remission (mCR) (63%) than patients having poor cytogenetics (n=23) (mCR: 30%). In addition, CD34 expression also influenced response; thus, 81% (21/26) of CD34-negative patients achieved mCR vs only 46% (42/91) of CD34-positive cases (p=0,008). Neither age nor WBC counts showed a significant influence in response rate. As far as apoptosis and MRD proteins is concerned, interestingly, responding cases showed a lower expression of the bcl-2, MRP and LRP proteins (bcl-2 RFI (relative fluorescence intensity) 10±5.5 vs 13±6, p=0.02; MRP RFI 1.9±0.8 vs 2.7±1.8, p=0.008; LRP RFI 6.2±4.9 vs 8.7±7.5, p=0.01 in responding vs non-responding patients). By contrast, expression of APO 2.7, Bax, and MDR-1 did not influenced response. Analysis of relapse free survival showed that only the number of cycles of chemotherapy required to achieve mCR had prognostic influence (p=0.008), with no significant influence for age, WBC counts, CD34 expression, or cytogenetics. In turn, a high percentage of early apoptotic cells in bone marrow at diagnosis (p=0.01), as well as a low bcl-2/bax ratio (p=0.05), and low MRP expression (p=0.04) were associated with a prolonged RFS. Moreover, upon grouping AML patients according to the expression of MRP and the bcl-2/bax ratio (> and < of the mean of both parameters), only patients with both low MRP expression and low bcl-2/bax ratio (n=16) achieved a plateau phase in the RFS curve after 20 months of follow-up, while the remaining patients showed a continuous relapse trend. In summary, our results show that, in addition to high bcl-2 and bcl-2/bax ratio, a high expression of the LRP and MRP multidrug resistant proteins have an adverse prognostic influence in elderly AML patients. The combination of these parameters contribute to identify distinct groups of patients at a different risk of relapse.