EGFL7 Antagonizes NOTCH Signaling and Represents a Novel Therapeutic Target in Acute Myeloid Leukemia (AML)

Epidermal growth factor-like domain 7 (EGFL7) is a secreted protein. We previously found that EGFL7 is up-regulated in primary AML blasts and that a high mRNA expression correlates with shorter event-free and overall survival in AML patients (Papaioannou et al. PNAS 2017;114(23)). However, the underlying mechanism by which EGFL7 promotes leukemogenesis is largely unknown. To identify EGFL7 binding partners, we took an unbiased high-throughput approach by using an antibody interaction-array to measure the ability of EGFL7 to bind directly ~400 proteins expressed by primary AML blasts. Using this strategy, we found in cell lysates of 3 AML patients that EGFL7 binds several signaling proteins important for normal and malignant hematopoiesis including NOTCH (in all patients P Next, we stimulated AML blasts from 3 patients with recombinant EGFL7 (rEGFL7) and found that it reduced NOTCH intracellular domain (NICD1/2, Figure 1A), indicating that EGFL7 inhibits NOTCH activation. In line with this, we found that stimulation of AML patients samples' with rEGFL7 resulted in a decreased expression of its well-known downstream target gene HES1 (Figure 1B; in all patients P On the other hand, treatment with an anti-EGFL7 blocking antibody (AB) caused increased levels of NICD1/2 (Figure 1C) and expression of HES1 (Figure 1D, in all patients P To determine whether blocking EGFL7 could provide a new targeted therapy for patients with AML, we treated 3 independent AML models (i.e. an AML cell line based xenotransplant model (n=4 mice per group), a primary murine AML model (n=7 mice per group), and a patient derived xenotransplant model (n=4 mice per group)) with anti-EGFL7 or IgG1 control to determine whether anti-EGFL7 could prolong survival in vivo. In all models, we demonstrated that in vivo treatment with anti-EGFL7 results in prolonged overall survival (cell line model: P In conclusion, our data demonstrate that EGFL7 contributes to NOTCH silencing in AML by antagonizing canonical NOTCH ligand binding. Reactivation of NOTCH signaling in vivo using anti-EGFL7 results in prolonged survival of leukemic mice, supporting EGFL7 might be a novel therapeutic target in AML. Figure 1 A AML patient blasts were cultured in the presence or absence (Unstim) of rEGFL7. Total proteins were extracted for immunoblotting with β-ACTIN as loading control. B Total RNA was extracted for quantitative real time (qRT-PCR) analysis of HES1 mRNA normalized to β-ACTIN control (*P Download : Download high-res image (416KB) Download : Download full-size image Disclosures No relevant conflicts of interest to declare.