Targeting Multiple Active Kinase Pathways In 11q23 Translocated Pediatric Acute Myeloid Leukemia Using a VEGFR2 Antibody Together with a MEK Inhibitor.
Authors: Elst Arja ter , Kampen Kim R , Diks Sander H , Scherpen Frank JG , Haas Válerie de , Peppelenbosch Maikel P , Bont Evelina S. De 
Published: October 2019

Abstract
Abstract 3626
One of the major pathways involved in the angiogenic process is the VEGF/VEGFR signaling pathway. VEGFA was found to be an independent prognostic factor for therapeutic outcome in AML (de Bont et al, 2002;Aguayo et al, 1999). Moreover, it has been shown that after chemotherapy the expression level of VEGFR2 is restored to normal in the bone marrow of AML patients in complete remission (Padro et al, 2002). Both VEGF and its receptors Flt-1(VEGFR1) and KDR (VEGFR2) are expressed by leukemic blasts which results in both a paracrine and an autocrine VEGF/VEGFR2 pathway in AML (Dias et al, 2001). In response to VEGF stimulation, VEGFR2 has been shown to transmit intracellular signals leading to activation of multiple downstream signaling pathways including the mitogen-activated protein (MAP) kinases, JAK)STAT, and Phosphoinositide 3-kinases (PI3 kinases). In AML it has been described that simultaneous activation of these pathways results in a poor prognosis (Kornblau et al, 2006). Chromosomal translocations involving the Mixed Lineage Leukemia (MLL) gene at locus 11q23 are associated with a poor outcome. These MLL translocations represent 15–20% of pediatric acute myeloid leukemia's. In this study we show that VEGFR2 expression is significantly higher on blasts of 11q23 translocated acute myeloid leukemia's compared to blasts of AML patients with another karyotype. In addition, using peptide arrays and proteome profiler arrays we have found that the VEGF receptor signaling pathway and part of the MAP kinase signaling pathway are active and or phosphorylated in blasts of 11q23 translocated patients (Fig. 1). Proteins from these active pathway are potential targets in the treatment of pediatric 11q23 translocated AML. To further investigate these potential targets we have performed ex vivo drug target assays using an inhibitor and an antibody against two key proteins from the major signal transduction pathways, VEGFR2 antibody (IMC1121b) and MEK inhibitor (U0126). No effect of VEGFR2 inhibition was measured in two AML cell lines (HL-60 and THP-1). Whereas, MEK inhibition had an effect on both cell lines, LC50 8.7 μM and 7.5 μM for HL-60 and THP-1 respectively. Cell survival of the THP-1 cell line (containing a 11q23 translocation) was substantially inhibited after addition of a combination therapy with an inhibitor against MEK and a antibody against VEGFR2 (LC50 2.9 μM). In contrast, the VEGFR2 antibody in combination with the MEK inhibitor had only a marginal effect on the HL-60 cell line (LC50 7.7 μM). Future experiments to investigate the effect of the combination therapy on primary patient material are underway. Overall these data show for the first time that targeting multiple active pathways in pediatric 11q23 AML could result in promising opportunities concerning future therapy options.
Figure 1. Provisional scheme of active kinases and phosphorylated proteins in AML. Green-white, active kinase; Yellow, phosphorylated protein; Green-Yellow, active kinase and phosphorylated protein; thick lining, bold receptors and, bold cell cycle proteins, kinase activity higher in AML cells compared to normal bone marrow. Red arrows, site of inhibition. Figure 1. Provisional scheme of active kinases and phosphorylated proteins in AML. Green-white, active kinase; Yellow, phosphorylated protein; Green-Yellow, active kinase and phosphorylated protein; thick lining, bold receptors and, bold cell cycle proteins, kinase activity higher in AML cells compared to normal bone marrow. Red arrows, site of inhibition.

Disclosures:
No relevant conflicts of interest to declare.