Inhibition of both paracrine and autocrine VEGF/ VEGFR-2 signaling pathways is essential to induce long-term remission of xenotransplanted human leukemias

Division of Hematology-Oncology, Weill Medical College of Cornell University, New York, NY 10021, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 09/2001; 98(19):10857-10862. DOI: 10.1073/pnas.191117498

ABSTRACT 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.

Download full-text


Available from: Shahin Rafii, Apr 27, 2015
  • Source
    • "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]. "
    [Show abstract] [Hide abstract]
    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 · 5.40 Impact Factor
  • Source
    • "). Inhibition of VEGF receptors reduces angiogenic activity and appears to either directly or indirectly inhibit the growth of leukaemic cells (Dias et al, 2001; Zhu et al, 2003). The findings of the present study add new elements and complexity to our understanding of the cell signalling generated by the activation of VEGF-R in AML cells, showing a cross-talk between VEGF-R from one side and IL-3R and GM-CSFR from the other side. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Previous studies suggested an important role for vascular endothelial growth factor (VEGF) and its receptors in postnatal haemopoiesis. However, it is unclear how VEGF receptor (VEGFR) signalling could interact with that issued from the activation of haematopoietic growth factor receptors. To elucidate this point we explored VEGF-R2 and granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR) membrane localization and cell signalling in TF1-KDR cells (TF1 leukaemic cells that overexpress VEGF-R2/KDR). Activation of either GM-CSFR or VEGF-R2 was shown to determine the migration of both receptor elements (VEGF-R2 and the common beta-chain of the GM-CSFR) to lipid rafts. The study of receptor phosphorylation showed that GM-CSF induced the phosphorylation of its own receptor and the transphosphorylation of VEGF-R2; on the other hand, VEGF triggered the phosphorylation of its receptor and transphosphorylated the beta-chain of the GM-CSFR. Co-stimulation of TF1-KDR cells with both GM-CSF and VEGF-A resulted in massive migration of both the common GM-CSFR beta-chain and VEGF-R2 to lipid rafts and sustained p38 mitogen-activated protein kinase activation. Disruption of lipid rafts inhibited the capacity of both GM-CSF and VEGF-A to activate p38. Experiments with specific p38 inhibitors showed that p38 activation was required to sustain the VEGF- and GM-CSF-dependent proliferation of TF1-KDR and the survival of primary acute myeloid leukaemia blasts.
    British Journal of Haematology 03/2009; 145(3):399-411. DOI:10.1111/j.1365-2141.2009.07627.x · 4.96 Impact Factor
  • Source
    • "While the functions of VEGFRs on tumour cells are not completely understood, the concomitant production of VEGF and VEGFR expression by tumour cells suggests the possibility that these receptors mediate biologic functions in tumour cells. Indeed, in cancers of the breast and skin (melanoma) and in some leukaemias, VEGF/VEGFR autocrine signalling loops have been identified (Bellamy et al, 1999; Dias et al, 2000, 2001; Lacal et al, 2000), but the elucidation of the contribution of individual VEGF/ VEGFR family members to biologic functions mediated by individual receptors is only beginning to emerge. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Vascular endothelial growth factor (VEGF) is the predominant pro-angiogenic cytokine in human malignancy, and its expression correlates with disease recurrence and poor outcomes in patients with colorectal cancer. Recently, expression of vascular endothelial growth factor receptors (VEGFRs) has been observed on tumours of epithelial origin, including those arising in the colon, but the molecular mechanisms governing potential VEGF-driven biologic functioning in these tumours are not well characterised. In this report, we investigated the role of Src family kinases (SFKs) in VEGF-mediated signalling in human colorectal carcinoma (CRC) cell lines. Vascular endothelial growth factor specifically activated SFKs in HT29 and KM12L4 CRC cell lines. Further, VEGF stimulation resulted in enhanced cellular migration, which was effectively blocked by pharmacologic inhibition of VEGFR-1 or Src kinase. Correspondingly, migration studies using siRNA clones with reduced Src expression confirmed the requirement for Src in VEGF-induced migration in these cells. Furthermore, VEGF treatment enhanced VEGFR-1/SFK complex formation and increased tyrosine phosphorylation of focal adhesion kinase, p130 cas and paxillin. Finally, we demonstrate that VEGF-induced migration is not due, at least in part, to VEGF acting as a mitogen. These results suggest that VEGFR-1 promotes migration of tumour cells through a Src-dependent pathway linked to activation of focal adhesion components that regulate this process.
    British Journal of Cancer 07/2006; 94(11):1710-7. DOI:10.1038/sj.bjc.6603143 · 4.82 Impact Factor
Show more