Nucleophosmin Gene Mutations Exhibit High Spontaneous Apoptosis and Favorable Prognosis in Acute Myeloid Leukemia

Nucleophosmin gene mutations (NPM1-Mt) are the hallmark of a large adult acute myeloid leukemia (AML) subgroup with normal karyotype and interact with p53 and its regulatory molecules (Arf, Hdm2/Mdm2), thus lowering cell proliferation and increasing apoptosis (Falini, 2007). Moreover, AML pts show co-existing NPM1-Mt and internal tandem duplications of FLT3 (FLT3-ITD) which increase potential for cell proliferation. Furthermore, genes and proteins involved in apoptosis, such as bcl-2 and bax, have been demonstrated to be relevant in response to treatment and outcome (Del Poeta, 2003). Therefore, we analysed NPM1-Mt, FLT3-ITD and apoptosis proteins (bcl-2 and bax) in 222 pts, affected by de novo non-M3 AML, median age 60 years, treated with intensive chemotherapy regimens according to GIMEMA-EORTC protocols. The aims of our study were: to correlate NPM1-Mt or FLT3-ITD with bax/bcl-2 ratio levels, as a measure of spontaneous apoptosis; to assess the independent prognostic significance of NPM1-Mt and FLT3-ITD. Bcl-2 and bax proteins were determined by multicolor flow cytometry and bax/bcl-2 ratio was obtained by dividing mean fluorescence intensity (MFI) of bax/MFI bcl-2. The threshold of positivity was set at the median value >0.35 (range 0.01–9.1). NPM1 mutations and FLT3-ITD were detected by multiplex PCR and capillary gel electrophoresis. One hundred-twenty-one/222 (54.5%) pts were bax/bcl-2 ratio positive, 54/222 (24.3%) were NPM1-Mt and 52/222 (23.4%) presented FLT3-ITD; 17/222 (7.6%) pts carried both FLT3-ITD and NPM1-Mt. There was a strong correlation between higher WBC counts (>100x109/L) and FLT3-ITD (P0.35) and NPM1-Mt without FLT3-ITD were significantly associated (30/37; P=0.0001), demonstrating that NPM1-Mt alone express high amount of spontaneous apoptosis. Moreover, NPM1-Mt cases were significantly related to FAB M4 or M5 AML (P=0.03). A normal karyotype was found in 37/45 (82%) NPM1-Mt pts (P=0.00001) and almost all NPM1-Mt cases were CD34 negative (47/54; P