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Testa et al. J Cancer Metastasis Treat 2020;6:53 I http://dx.doi.org/10.20517/2394-4722.2020.111 Page 11 of 17
[73]
In line with this initial study, Imai et al. showed that t(8;21) AML cells are responsive to exogenous
VEGF stimulation with activation of AKT pathway. Furthermore, t(8;21)-positive AML cell lines are

inhibited in their proliferation by VEGF-R2 kinase inhibitors. The gene AML1/RUNX1 located on
chromosome 21 is frequently involved in genetic alterations, such as chromosomal translocation events
(AML1/ETO or AML1/EVI1) resulting in the formation of fusion proteins, associated with a loss of
function of AML1/RUNX1. The analysis of a large dataset of gene expression arrays relative to AML
samples showed the existence of an inverse correlation between expression of VEGF and AML1/RUNX1,
[73]
with the highest VEGF levels being observed in leukemic blasts bearing t(8;21) . Gene expression and
transfection experiments provided evidence that AML1/RUNX1 acts as a repressor of VEGFA expression,
through its direct binding at the level of three sites present on the promoter of the VEGF gene; AML1/ETO
[72]
fails to exert this repressive effect on VEGF expression and results in a stimulation of its expression . In
line with this interpretation, silencing of AML1/ETO expression in t(8;21) leukemic cell lines resulted in an
[74]
inhibition of VEGF expression .
Studies carried out in APLs have led to similar conclusions concerning the mechanisms through which the
fusion protein observed in t(15;17) AMLs stimulates angiogenesis. Saulle et al. through the analysis of a
[75]
large TCGA dataset on gene expression in AMLs, confirmed that the highest expression of VEGF-A mRNA
was observed in M3 t(15;17) AMLs. The molecular mechanism through which PML/RARA stimulates
VEGF expression is related to its capacity to induce a significant downmodulation of Hematopoietically
Expressed Homeobox (HHEX) expression, a homeobox transcription factor exerting a repressive effect
on VEGF gene expression. The downmodulation of HHEX was also responsible for the stimulation of the
expression of other genes involved in the control of angiogenesis .
[75]

EXPRESSION OF ENDOTHLIEL GROWTH FACTOR RECEPTORS IN AMLS
The receptors for various endothelial growth factors are frequently expressed on leukemic blasts and several
studies have characterized the properties of AMLs expressing these receptors.

Padrò and coworkers explored VEGF-R1 and VEGF-R2 expression in AML bone marrow biopsies and
observed that VEGF-R2 but not VEGF-R1 expression in AMLs was increased compared to normal bone
marrow; VEGF-R2 expression was mostly increased in AMLs with an immature myeloid phenotype,
[54]
classified as M1 and M2 in the FAB classification system or those with a monocytic phenotype (M5 AMLs) .
Studies in a model of mice xenotransplanted with human AML cells showed that inhibition of paracrine
(dependent on endothelial cells present in the bone marrow microenvironment) and autocrine (dependent
on leukemic cells) VEGF/VEGF-R2 signaling pathway was essential to induce long-term remission of these
[76]
mice . This study provided a rationale to investigate in humans the antileukemic potential of VEGF-R2
inhibitors. Other preclinical studies supported an inhibitory effect of anti-VEGF-R2 monoclonal antibodies
on human AML development in leukemia animal models .
[77]
Zahiragic et al. treated nine AML patients with refractory/relapsing disease with the anti-VEGF
[78]
monoclonal antibody bevacizumab. Bevacizumab treatment reduced VEGF expression at the level of bone
[78]
marrow but failed to show any significant clinical antileukemic activity . It is interesting to note that,
while bevacizumab reduced VEGF expression at the level of bone marrow, it was unable to modify bone
[66]
marrow MVD . Other clinical trials incorporating anti-VEGF or anti-VEGF-R2 antibodies have not
produced results supporting a significant clinical benefit [79,80] .

More recent studies have reevaluated the role of VEGF-R2 in leukemia development and its targeting with
new VEGF-R2 inhibitors. Nobrega-Pereira provided evidence that VEGF-R2 signaling is involved in the
[81]
mechanism of AML chemoresistance . Treatment of chemoresistant AML cells with a VEGF-R2 inhibitor