Lymphoid Enhancer Binding Factor-1 (LEF1) Expression As a Prognostic Factor In Adult Acute Promyelocytic Leukemia

Lymphoid enhancer-binding factor 1 (LEF1) is a downstream effector of the Wnt/ β-catenin signaling pathway, which controls cell growth and differentiation. In normal hematopoiesis, LEF1 plays a pivotal role in the development of B- and T-lymphocytes as well as granulocyte progenitor cells. High LEF1 expression has been reported as a favorable prognostic marker in cytogenetically normal acute myeloid leukemia whereas it is associated with poor prognosis in adult B precursor acute lymphoblastic leukemia and in chronic lymphocytic leukemia. Moreover, marked downregulation of LEF1 is associated with disease progression in myelodysplastic syndromes. Given the functional role of LEF1 in hematopoiesis and its putative prognostic impact in several hematological malignancies, we evaluated the prognostic significance of LEF1 expression in adult acute promyelocytic leukemia (APL).

One hundred and three consecutive patients with newly diagnosed APL were observed and treated with ATRA-based regimens (AIDA04937 and AIDA2000 GIMEMA protocols), between January 1996 and December 2012. LEF1 expression was measured by real-time qPCR in 78 patients (median age 45 years, range 16 to 88 years) with sufficient available material from the primary cohort. Advanced relative quantification analysis was performed using LightCycler 480 Software 1.5.1, based on the ΔΔCt method. APL samples were dichotomized at the median value and divided into two expression groups: low LEF1 (39 patients) with LEF1 values below the median value (LEF1^low) and high LEF1 (39 patients) with LEF1 values above the median value (LEF1^high). Clinical and biological features of the two groups were compared. A p value <0.05 was considered significant. Multivariable Cox proportional hazards models were used to study factors (LEF1 expression, FLT3 mutation status, and relapse risk grade) associated with survival endpoints. To evaluate the biological impact of the differential expression of LEF1 in APL, a dataset (GSE13159, including 37 samples of APL patients ) was identified and downloaded from the Gene Expression Omnibus.

Patients with LEF1^high expression had lower white blood cell counts at baseline (1.8 vs 12.0 x10⁹/L; p < 0 .0001), and were less likely to carry a FLT3-ITD than LEF1^low patients (12.8% vs 35.9%, respectively, p=0.02). The association between LEF1^low and the presence of FLT3-ITD was also confirmed when the 11 patients with FLT3-TKD were included among patients with FLT3 mutations (p=0.03), or the group of FLT3 wild type patients, as compared to those bearing FLT3-ITD (p=0.03). Early death (defined as death during induction treatment) occurred in nine cases (23%) of the LEF1^low group versus no case in the LEF1^high group (OR = 0.04; p= 0.002). LEF1^low expression was associated with a high relapse risk score (53.9% vs 7.7%, OR=0.07; p < 0.0001). The LEF1^high group showed a trend toward a statistically significant association with a lower median age (p = 0.08). No significant differences were observed regarding CD34, CD2, bcr3 positivity and LEF1 expression. Survival analysis of 61 APL patients < 60 years revealed that the LEF1^high group had significantly longer overall survival (OS) (p = 0.03), whereas no differences were observed between the two groups in terms of relapse-free survival. Cox analysis for OS confirmed only LEF1 expression as an independent prognostic factor (HR=5.4; 95% CI, 1.0 – 27.5, p =0.04). Among the 17 patients over the age of 60, those with LEF1^high expression showed a higher median survival than those in the LEF1^low group (6.5 vs 0.04 y.rs, p = 0.05). In silico analysis of the differential expression of LEF1 in APL identified 9 differentially expressed, up-modulated genes associated with a high expression of LEF1 (ETS1, FAIM3, CCR7, IL7R, LCK, IL2RB, ITK, RASGRP1, TRBC1); the majority of these genes is involved in the regulation of apoptosis

Our study provides, for the first time, evidence that LEF1 expression is an independent prognostic factor in APL and that it could be used in patients risk stratification. The observation provided by in silico gene expression analysis that LEF1 expression in APL is associated with biologic changes, mostly in terms of apoptosis regulation, will need to be confirmed experimentally.

No relevant conflicts of interest to declare.