Dias, S. et al. Inhibition of both paracrine and autocrine VEGF/ VEGFR-2 signaling pathways is essential to induce long-term remission of xenotransplanted human leukemias. Proc Natl. Acad. Sci. USA 98, 10857-10862

Division of Hematology-Oncology, Weill Medical College of Cornell University, New York, NY 10021, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 09/2001; 98(19):10857-10862. DOI: 10.1073/pnas.191117498


Antiangiogenic agents block the effects of tumor-derived angiogenic factors (paracrine factors), such as vascular endothelial
growth factor (VEGF), on endothelial cells (EC), inhibiting the growth of solid tumors. However, whether inhibition of angiogenesis
also may play a role in liquid tumors is not well established. We recently have shown that certain leukemias not only produce
VEGF but also selectively express functional VEGF receptors (VEGFRs), such as VEGFR-2 (Flk-1, KDR) and VEGFR1 (Flt1), resulting
in the generation of an autocrine loop. Here, we examined the relative contribution of paracrine (EC-dependent) and autocrine
(EC-independent) VEGF/VEGFR signaling pathways, by using a human leukemia model, where autocrine and paracrine VEGF/VEGFR
loops could be selectively inhibited by neutralizing mAbs specific for murine EC (paracrine pathway) or human tumor (autocrine)
VEGFRs. Blocking either the paracrine or the autocrine VEGF/VEGFR-2 pathway delayed leukemic growth and engraftment in vivo, but failed to cure inoculated mice. Long-term remission with no evidence of disease was achieved only if mice were treated
with mAbs against both murine and human VEGFR-2, whereas mAbs against human or murine VEGFR-1 had no effect on mice survival.
Therefore, effective antiangiogenic therapies to treat VEGF-producing, VEGFR-expressing leukemias may require blocking both
paracrine and autocrine VEGF/VEGFR-2 angiogenic loops to achieve remission and long-term cure.

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Available from: Shahin Rafii, Apr 27, 2015
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    • "It has been shown that VEGF stimulates a mitogenic response in hematologic malignancies and promotes self-renewal of leukemia progenitors [17,18]. The role of VEGF-A as a proangiogenic factor in AML has been well documented [19]. Furthermore, recent studies have revealed the contribution of VEGF-C in hematological malignancies’ progression [20,21,22]. "
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    ABSTRACT: Objective: The crucial role of angiogenesis in the pathophysiology of acute myeloid leukemia (AML) has been proposed. One of the key regulators of angiogenesis is the vascular endothelial growth factor (VEGF). Among the VEGF family, it has been observed that VEGF-A and VEGF-C are expressed by AML cells and mediate leukemic cell proliferation, survival, and resistance to chemotherapy. Emerging evidence, however, suggests that elevated levels of VEGF or a proangiogenic phenotype may impede, rather than promote, early tumor development and progression. As the significance of VEGF-A and VEGF-C levels in the pathogenesis of AML has not been clarified well, the aim of this study is to evaluate gene expression of these angiogenesis promoters and its possible prognostic value in peripheral blood mononuclear cells of Iranian patients with AML. Materials and Methods: We investigated the mRNA expression of VEGF-A and VEGF-C in peripheral blood mononuclear cells of 27 patients with newly diagnosed AML and 28 healthy controls by quantitative real-time PCR. Results: Expression of VEGF-C mRNA was significantly lower in AML patients than in healthy controls (p<0.001). However, there was no significant decrement in expression of VEGF-A mRNA of AML patients compared to the control group (p=0.861). VEGF-A and VEGF-C expression were not able to predict clinical outcome. Conclusion: Our data showed that AML is associated with a decreased expression of VEGF-C mRNA. However, expression levels did not influence the clinical outcome in our study. It seems that angiogenesis is affected by different cytokines other than VEGF-C or VEGF-A, and VEGF is also affected by different cytokines. Taken together, these findings help to provide new insights into the investigation of other angiogenic factors and cytokines that may play roles in the pathogenesis of AML. Conflict of interest:None declared.
    Turkish Journal of Haematology 06/2013; 30(2):137-43. DOI:10.4274/Tjh.2011.0023 · 0.36 Impact Factor
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    • "Intracrine VEGF/VEGFR2 signaling that allows cancer cells to stimulate their own survival pathways without the need for exogenous secreted factors has been demonstrated for subsets of acute leukemia cells [21] [26] [37]. VEGF is also reported to act as an intracrine survival factor in breast cancer cells through its binding to VEGFR1 [30]. "
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    ABSTRACT: Receptors for the angiogenic factor VEGF are expressed by tumor cancer cells including melanoma, although their functionality remains unclear. Paired human melanoma cell lines WM115 and WM239 were used to investigate differences in expression and functionality of VEGF and VEGFR2 in vitro and in vivo with the anti-VEGF antibody bevacizumab. Both WM115 and WM239 cells expressed VEGF and VEGFR2, the levels of which were modulated by hypoxia. Detection of native and phosphorylated VEGFR2 in subcellular fractions under serum-free conditions showed the presence of a functional autocrine as well as intracrine VEGF/VEGFR2 signaling loops. Interestingly, treatment of WM115 and WM239 cells with increasing doses of bevacizumab (0-300 µg/ml) in vitro did not show any significant inhibition of VEGFR2 phosphorylation. Small-molecule tyrosine kinase inhibitor, sunitinib, caused an inhibition of VEGFR2 phosphorylation in WM239 but not in WM115 cells. An increase in cell proliferation was observed in WM115 cells treated with bevacizumab, whereas sunitinib inhibited proliferation. When xenografted to immune-deficient mice, we found bevacizumab to be an effective antiangiogenic but not antitumorigenic agent for both cell lines. Because bevacizumab is unable to neutralize murine VEGF, this supports a paracrine angiogenic response. We propose that the failure of bevacizumab to generate an antitumorigenic effect may be related to its generation of enhanced autocrine/intracrine signaling in the cancer cells themselves. Collectively, these results suggest that, for cancers with intracrine VEGF/ VEGFR2 signaling loops, small-molecule inhibitors of VEGFR2 may be more effective than neutralizing antibodies at disease control.
    Neoplasia (New York, N.Y.) 07/2012; 14(7):612-23. DOI:10.1593/neo.11948 · 4.25 Impact Factor
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    • "The VEGF-Rs KDR (VEGF-R2) and FLT4 (VEGF-R3) are not only expressed on blood endothelial and lymphendothelial cells, but also on solid tumors and leukemias. Leukemia-derived VEGFs may induce the growth of leukemic cells in an autocrine or paracrine fashion [7,10,18,19]. The promoters of VEGF-Rs and their ligands contain CpG islands, regulatory regions that are typically methylated in epigenetically silenced genes [14]. "
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    ABSTRACT: Vascular Endothelial Growth Factors (VEGFs) and their receptors (VEGF-Rs) are important regulators for angiogenesis and lymphangiogenesis. VEGFs and VEGF-Rs are not only expressed on endothelial cells but also on various subtypes of solid tumors and leukemias contributing to the growth of the malignant cells. This study was performed to examine whether VEGF-R2 (KDR) and VEGF-R3 (FLT4) are regulated by DNA methylation. Real-time (RT) PCR analysis was performed to quantify KDR and FLT4 expression in some ninety leukemia/lymphoma cell lines, human umbilical vein endothelial cells (HUVECs) and dermal microvascular endothelial cells (HDMECs). Western blot analyses and flow cytometric analyses confirmed results at the protein level. After bisulfite conversion of DNA we determined the methylation status of KDR and FLT4 by DNA sequencing and by methylation specific PCR (MSP). Western blot analyses were performed to examine the effect of VEGF-C on p42/44 MAPK activation. Expression of KDR and FLT4 was observed in cell lines from various leukemic entities, but not in lymphoma cell lines: 16% (10/62) of the leukemia cell lines expressed KDR, 42% (27/65) were FLT4 positive. None of thirty cell lines representing six lymphoma subtypes showed more than marginal expression of KDR or FLT4. Western blot analyses confirmed KDR and FLT4 protein expression in HDMECs, HUVECs and in cell lines with high VEGF-R mRNA levels. Mature VEGF-C induced p42/44 MAPK activation in the KDR- /FLT4(+) cell line OCI-AML1 verifying the model character of this cell line for VEGF-C signal transduction studies. Bisulfite sequencing and MSP revealed that GpG islands in the promoter regions of KDR and FLT4 were unmethylated in HUVECs, HDMECs and KDR(+) and FLT4(+) cell lines, whereas methylated cell lines did not express these genes. In hypermethylated cell lines, KDR and FLT4 were re-inducible by treatment with the DNA demethylating agent 5-Aza-2'deoxycytidine, confirming epigenetic regulation of both genes. Our data show that VEGF-Rs KDR and FLT4 are silenced by DNA methylation. However, if the promoters are unmethylated, other factors (e.g. transactivation factors) determine the extent of KDR and FLT4 expression.
    BMC Cancer 01/2012; 12(1):19. DOI:10.1186/1471-2407-12-19 · 3.36 Impact Factor
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