VEGF signaling in acute leukemia: mitochondrial connections

The vascular endothelial growth factor (VEGF) signaling pathway regulates acute myeloid leukemia (AML) cell proliferation, survival and chemotherapy resistance. We have shown that VEGF/VEGFR2 signaling regulates leukemia cell survival by autocrine internal and external loops, with induction of pro-survival pathways and inhibition of apoptosis downstream of VEGFR2 internal signaling [1, 2]. Moreover, VEGF signaling can mediate paracrine vascular endothelial cell-controlled angiogenesis in AML, promoting vessel formation and leukemic blasts maintenance. As a consequence, aberrant VEGF signaling operates in the bone marrow of AML patients and is related to a poor prognosis, constituting an attractive target for therapeutic intervention in AML. Several therapeutic strategies (including monoclonal antibodies against VEGF-A and VEGFR-2 tyrosine kinase inhibitors) have been tested in clinical trials for refractory and relapsed AML with slight beneficial effects in combination with chemotherapy. The implication of VEGF/VEGFR2 signaling in multiple processes (including hematopoiesis and vascular growth in physiological and pathological situations) demands a deeper understanding of the VEGF/VEGFR2 downstream effectors operating specifically in leukemia cells as viable targets for combinatorial therapy particularly for relapsed AML patients