ISAC XX Abstracts on Disc Presented by Purdue University Cytometry Laboratories

Clinical significance of the apoptotic proteins in acute myeloid leukemia (AML)

Giovanni DEL POETA, Luca Maurillo, Adriano Venditti, Francesco Buccisano, Anna Tamburini, Beatrice Del Moro, Anna Maria Epiceno, Sergio Amadori Dept of Hematology Ospedale S. Eugenio P.le Umanesimo, 10 Roma, Roma, ITALY, 00144

Abstract Number: 6273     Clinical Cytometry  –  Leukemia/Lymphoma

The involvement of mitochondria in apoptosis is demonstrated by the crucial interactions between bcl-2 and pro-apoptotic related oncoproteins (bax, bad and bak). Moreover, the monoclonal antibody (MoAb) APO2.7 which reacts with a 38 kDa mitochondrial membrane protein (7A6 antigen) highlights an early event of apoptosis. In order to evaluate the clinical significance of spontaneous apoptosis in AML, we investigated 7A6 and bcl-2 expression in 60 patients, 26 females and 34 males, median age 56 years. All patients were treated with intensive chemotherapy regimens (EORTC/GIMEMA AML10 and AML13 protocols), except for the FAB M3 cases, treated according to the GIMEMA AIDA protocol. Bcl-2 and 7A6 expressions were determined on flow cytometer (Epics XL, Coulter) using an anti-bcl-2 124 FITC MoAb (Dako) and APO2.7 PE Moab (Immunotech), respectively. Bcl-2 and APO2.7 were evaluated as mean fluorescence intensities (MFI), calculated as the ratio of bcl-2 or APO2.7 MoAbs mean/negative controls mean. The results were expressed as an index (APO) obtained by dividing MFI APO2.7/ MFI bcl-2. The threshold for considering AML cases as ½apoptoticƒ was set at the APO median value > 1.5. APO < 1.5 patients were associated both with immature FAB M0-M1 classes (P=0.039) and with CD34 positivity (20/29; P=0.018). There was a significant correlation between low or high cytogenetic risk class and APO index > or < 1.5 (P=0.009). With regard to clinical outcome, a significant difference in complete remission (CR) rate was found between APO < 1.5 and APO > 1.5 patients (51.7% v. 88.5%; P=0.003). Overall survival and CR duration were significantly longer (P=0.017 and = 0.007, respectively) in APO >1.5 patients. In multivariate analysis, only APO (P=0.003), age (0.009) and WBC (P=0.043) were confirmed independent prognostic factors for CR achievement. In conclusion, low 7A6/bcl-2 ratio might explain the poor outcome of patients treated with very intensive regimens and might induce to treat the APO <1.5 cases with apoptosis enhancer drugs.

Keywords: Apoptosis; bcl-2; APO 2.7; Flow cytometry; AML prognosis