Vascular endothelial growth factor
Vascular endothelial growth factor (VEGF) is a signal protein produced by cells that stimulates vasculogenesis and angiogenesis. It is part of the system that restores the oxygen supply to tissues when blood circulation is inadequate. Serum concentration of VEGF is high in bronchial asthma and low in diabetes mellitus. VEGF's normal function is to create new blood vessels during embryonic development, new blood vessels after injury, muscle following exercise, and new vessels (collateral circulation) to bypass blocked vessels.
When VEGF is overexpressed, it can contribute to disease. Solid cancers cannot grow beyond a limited size without an adequate blood supply; cancers that can express VEGF are able to grow and metastasize. Overexpression of VEGF can cause vascular disease in the retina of the eye and other parts of the body. Drugs such as bevacizumab can inhibit VEGF and control or slow those diseases.
VEGF is a sub-family of growth factors, to be specific, the platelet-derived growth factor family of cystine-knot growth factors. They are important signaling proteins involved in both vasculogenesis (the de novo formation of the embryonic circulatory system) and angiogenesis (the growth of blood vessels from pre-existing vasculature).
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The most important member is VEGF-A. Other members are Placenta growth factor (PGF), VEGF-B, VEGF-C and VEGF-D. The latter ones were discovered later than VEGF-A, and, before their discovery, VEGF-A was called just VEGF.
|VEGF-B||Embryonic angiogenesis (myocardial tissue, specifically)|
|VEGF-D||Needed for the development of lymphatic vasculature surrounding lung bronchioles|
|PlGF||Important for Vasculogenesis, Also needed for angiogenesis during ischemia, inflammation, wound healing, and cancer.|
Activity of VEGF-A, as its name implies, has been studied mostly on cells of the vascular endothelium, although it does have effects on a number of other cell types (e.g., stimulation monocyte/macrophage migration, neurons, cancer cells, kidney epithelial cells). In vitro, VEGF-A has been shown to stimulate endothelial cell mitogenesis and cell migration. VEGF-A is also a vasodilator and increases microvascular permeability and was originally referred to as vascular permeability factor.
Alternative classification 
The broad term 'VEGF' covers a number of proteins from two families, that result from alternate splicing of mRNA from a single, 8-exon, VEGF gene. The two different families are referred to according to their terminal exon (exon 8) splice site - the proximal splice site (denoted VEGFxxx) or distal splice site (VEGFxxxb). In addition, alternate splicing of exon 6 and 7 alters their heparin-binding affinity, and amino acid number (in humans: VEGF121, VEGF121b, VEGF145, VEGF165, VEGF165b, VEGF189, VEGF206; the rodent orthologs of these proteins contain one fewer amino acid). These domains have important functional consequences for the VEGF splice variants, as the terminal (exon 8) splice site determines whether the proteins are pro-angiogenic (proximal splice site, expressed during angiogenesis) or anti-angiogenic (distal splice site, expressed in normal tissues). In addition, inclusion or exclusion of exons 6 and 7 mediate interactions with heparan sulfate proteoglycans (HSPGs) and neuropilin co-receptors on the cell surface, enhancing their ability to bind and activate the VEGF receptors (VEGFRs). Recently, VEGF-C has been shown to be an important inducer of neurogenesis in the murine subventricular zone, without exerting angiogenic effects.
All members of the VEGF family stimulate cellular responses by binding to tyrosine kinase receptors (the VEGFRs) on the cell surface, causing them to dimerize and become activated through transphosphorylation, although to different sites, times and extents. The VEGF receptors have an extracellular portion consisting of 7 immunoglobulin-like domains, a single transmembrane spanning region, and an intracellular portion containing a split tyrosine-kinase domain. VEGF-A binds to VEGFR-1 (Flt-1) and VEGFR-2 (KDR/Flk-1). VEGFR-2 appears to mediate almost all of the known cellular responses to VEGF. The function of VEGFR-1 is less well-defined, although it is thought to modulate VEGFR-2 signaling. Another function of VEGFR-1 may be to act as a dummy/decoy receptor, sequestering VEGF from VEGFR-2 binding (this appears to be particularly important during vasculogenesis in the embryo). VEGF-C and VEGF-D, but not VEGF-A, are ligands for a third receptor (VEGFR-3), which mediates lymphangiogenesis.
VEGFxxx production can be induced in cells that are not receiving enough oxygen. When a cell is deficient in oxygen, it produces HIF, hypoxia-inducible factor, a transcription factor. HIF stimulates the release of VEGFxxx, among other functions (including modulation of erythropoeisis). Circulating VEGFxxx then binds to VEGF Receptors on endothelial cells, triggering a Tyrosine Kinase Pathway leading to angiogenesis.
HIF1 alpha and HIF1 beta are constantly being produced but HIF1 alpha is highly O2 labile, so, in aerobic conditions, it is degraded. When the cell becomes hypoxic, HIF1 alpha persists and the HIF1alpha/beta complex stimulates VEGF release.
Clinical significance 
VEGF in disease 
VEGFxxx has been implicated with poor prognosis in breast cancer. Numerous studies show a decreased overall survival and disease-free survival in those tumors overexpressing VEGF. The overexpression of VEGFxxx may be an early step in the process of metastasis, a step that is involved in the "angiogenic" switch. Although VEGFxxx has been correlated with poor survival, its exact mechanism of action in the progression of tumors remains unclear.
VEGFxxx is also released in rheumatoid arthritis in response to TNF-α, increasing endothelial permeability and swelling and also stimulating angiogenesis (formation of capillaries).
VEGFxxx is also important in diabetic retinopathy (DR). The microcirculatory problems in the retina of people with diabetes can cause retinal ischaemia, which results in the release of VEGFxxx, and a switch in the balance of pro-angiogenic VEGFxxx isoforms over the normally expressed VEGFxxxb isoforms. VEGFxxx may then cause the creation of new blood vessels in the retina and elsewhere in the eye, heralding changes that may threaten the sight.
VEGFxxx plays a role in the disease pathology of the wet form age-related macular degeneration (AMD), which is the leading cause of blindness for the elderly of the industrialized world. The vascular pathology of AMD shares certain similarities with diabetic retinopathy, although the cause of disease and the typical source of neovascularization differs between the two diseases.
Once released, VEGFxxx may elicit several responses. It may cause a cell to survive, move, or further differentiate. Hence, VEGF is a potential target for the treatment of cancer. The first anti-VEGF drug, a monoclonal antibody named bevacizumab, was approved in 2004. Approximately 10-15% of patients benefit from bevacizumab therapy; however, biomarkers for bevacizumab efficacy are not yet known.
Current studies show that VEGFs are not the only promoters of angiogenesis. In particular FGF2 and HGF are potent angiogenic factors.
Patients suffering from pulmonary emphysema have been found to have decreased levels of VEGF in the pulmonary arteries.
Anti-VEGF therapies 
Anti-VEGF therapies are important in the treatment of certain cancers and in age-related macular degeneration. They can involve monoclonal antibodies such as bevacizumab (Avastin), antibody derivatives such as ranibizumab (Lucentis), or orally-available small molecules that inhibit the tyrosine kinases stimulated by VEGF: lapatinib (Tykerb), sunitinib (Sutent), sorafenib (Nexavar), axitinib, and pazopanib. (Some of these therapies target VEGF receptors rather than the VEGFs.) THC and Cannabidiol both inhibit VEGF and slow Glioma growth.
Both antibody-based compounds are commercialized. The first three orally available compounds are commercialized, as well. The latter two (axitinib and pazopanib) are in clinical trials, the results of which were presented (June 7) at the American Society of Clinical Oncology meeting.
Bergers and Hanahan concluded in 2008 that anti-VEGF drugs can show therapeutic efficacy in mouse models of cancer and in an increasing number of human cancers. But, "the benefits are at best transitory and are followed by a restoration of tumour growth and progression."
Later studies into the consequences of VEGF inhibitor use have shown that, although they can reduce the growth of primary tumours, VEGF inhibitors can concomitantly promote invasiveness and metastasis of tumours.  
AZ2171 (Cediranib), a multi-targeted tyrosine kinase inhibitor has been shown to have anti-edema effects by reducing the permeability and aiding in vascular normalization.
VEGF is also inhibited by thiazolidinediones (used for diabetes mellitus type 2 and related disease), and this effect on granulosa cells gives the potential of thiazolidinediones to be used in ovarian hyperstimulation syndrome.
Ranibizumab, a monoclonal antibody fragment (Fab) derived from bevacizumab, has been developed by Genetech for intraocular use. In 2006, FDA approved the drug for the treatment of neovascular age-related macular degeneration (wet AMD). The drug had undergone three successful clinical trials by then.
In the October 2006 issue of the New England Journal of Medicine (NEJM), Rosenfield, et al. reported that monthly intravitreal injection of ranibizumab led to significant increase in the level of mean visual acuity compared to that of sham injection. It was concluded from the two year, phase III study that ranibizumab is very effective in the treatment of minimally classic (MC) or occult wet AMD (age-related macular degeneration) with low rates of ocular adverse effects.
Another study published in the January 2009 issue of Ophthalmology provides the evidence for the efficacy of ranibizumab. Brown, et al. reported that monthly intravitreal injection of ranibizumab led to significant increase in the level of mean visual acuity compared to that of photodynamic therapy with verteporfin. It was concluded from the two year, phase III study that ranibizumab was superior to photodynamic therapy with verteporfin in the treatment of predominantly classic (PC) Wet AMD with low rates of ocular adverse effects.
Although the efficacy of ranibizumab is well supported by extensive clinical trials, the cost effectiveness of the drug is questioned. Since the drug merely stabilizes patient conditions, ranibizumab must be administered monthly. At a cost of $2,000.00 per injection, the cost to treat wet AMD patients in the United States is greater than $10.00 billion per year. Due to high cost, many ophthalmologists have turned to bevacizumab as the alternative intravitreal agent in the treatment of wet AMD. The drug costs $15.00 to 50.00 in the United States.
In 2007, Raftery, et al. reported in the British Journal of Ophthalmology that, unless ranibizumab is 2.5 times more effective the bevacizumab, ranibizumab is not cost effective. It was concluded that the price of ranibizumab would have to be drastically reduced for the drug to be cost effective.
Off-label use of intravitreal bevacizumab has become a widespread treatment for neovascular age-related macular degeneration. Although the drug is not FDA approved for non-oncologic uses, some studies[which?] suggest that bevacizumab is effective in increasing visual acuity with low rates of ocular adverse effects. However, due to small sample size and lack of randomized control trial, the result is not conclusive.
In October 2006, the National Eye Institute (NEI) of the National Institutes of Health (NIH) announced that it would fund a comparative study trial of ranibizumab and bevacizumab to assess the relative efficacy and ocular adversity in treating wet AMD. This study, called the Comparison of Age-Related Macular Degeneration Treatment Trials (CATT Study), will enroll about 1,200 patients with newly diagnosed wet AMD, randomly assigning the patients to different treatment groups.
By May 2012, anti-VEGF treatment with Avastin has been accepted by Medicare, is quite reasonably priced, and effective. Lucentis has a similar but smaller molecular structure to Avastin, and is FDA approved (2006) for treating MacD, yet remains more costly, as is the more recent (2011 approved) EYELEA. Tests are ongoing as the efficacy of one over another as to these treatments.
See also 
- Claesson-Welsh, L. (20 August 2008). "VEGF-B Taken to Our Hearts: Specific Effect of VEGF-B in Myocardial Ischemia". Arteriosclerosis, Thrombosis, and Vascular Biology 28 (9): 1575–1576. doi:10.1161/ATVBAHA.108.170878.
- A VEGF-A splice variant defective for heparan sulfate and neuropilin-1 binding shows attenuated signaling through VEGFR-2 doi:10.1007/s00018-006-6254-9
- Shin, Y. J., J. S. Choi, et al. (2010). "Induction of vascular endothelial growth factor receptor-3 mRNA in glial cells following focal cerebral ischemia in rats." J Neuroimmunol 229(1-2): 81-90.
- Holmes, Katherine; Roberts, Owain Ll; Thomas, Angharad M.; Cross, Michael J. (2007). "Vascular endothelial growth factor receptor-2: Structure, function, intracellular signalling and therapeutic inhibition". Cellular Signalling 19 (10): 2003–12. doi:10.1016/j.cellsig.2007.05.013. PMID 17658244.
- Amo, Y.; Masuzawa, M.; Hamada, Y.; Katsuoka, K. (2004). "Serum concentrations of vascular endothelial growth factor-D in angiosarcoma patients". British Journal of Dermatology 150 (1): 160–1. doi:10.1111/j.1365-2133.2004.05751.x. PMID 14746640.
- Liu, E.; Morimoto, M.; Kitajima, S.; Koike, T.; Yu, Y.; Shiiki, H.; Nagata, M.; Watanabe, T. et al. (2007). "Increased Expression of Vascular Endothelial Growth Factor in Kidney Leads to Progressive Impairment of Glomerular Functions". Journal of the American Society of Nephrology 18 (7): 2094–104. doi:10.1681/ASN.2006010075. PMID 17554151.
- Andraweera, P. H.; Dekker, G. A.; Roberts, C. T. (2012). "The vascular endothelial growth factor family in adverse pregnancy outcomes". Human Reproduction Update 18 (4): 436–457. doi:10.1093/humupd/dms011. PMID 22495259.
- Bergers G, Hanahan D (August 2008). "Modes of resistance to anti-angiogenic therapy". Nat. Rev. Cancer 8 (8): 592–603. doi:10.1038/nrc2442. PMC 2874834. PMID 18650835.
- Ebos, John; Christina R. Lee, William Cruz-Munoz, Georg A. Bjarnason, James G. Christensen, and Robert S. Kerbel (March 2009). "Accelerated Metastasis after Short-Term Treatment with a Potent Inhibitor of Tumor Angiogenesis". Cancer Cell 15: 232–239. doi:10.1016/j.ccr.2009.01.021. Retrieved 22 October 2012.
- Pa` ez-Ribes, Marta; Elizabeth Allen, James Hudock, Takaaki Takeda, Hiroaki Okuyama, Francesc Vin˜ als, Masahiro Inoue, Gabriele Bergers, Douglas Hanahan and Oriol Casanovas (March 2009). "Antiangiogenic Therapy Elicits Malignant Progression of Tumors to Increased Local Invasion and Distant Metastasis". Cancer Cell 15: 220–231. doi:10.1016/j.ccr.2009.01.027. Retrieved 22 October 2012.
- Shah DK, Menon KM, Cabrera LM, Vahratian A, Kavoussi SK, Lebovic DI (April 2010). "Thiazolidinediones decrease vascular endothelial growth factor (VEGF) production by human luteinized granulosa cells in vitro". Fertil. Steril. 93 (6): 2042–7. doi:10.1016/j.fertnstert.2009.02.059. PMC 2847675. PMID 19342033.
- "FDA Approves New Biologic Treatment for Wet Age-Related Macular Degeneration". FDA News & Events. June 30, 2006. Retrieved 17 April 2013.
- Brown, David M.; Michels, Mark; Kaiser, Peter K.; Heier, Jeffrey S.; Sy, Judy P.; Ianchulev, Tsontcho; Anchor Study, Group (2009). "Ranibizumab versus Verteporfin Photodynamic Therapy for Neovascular Age-Related Macular Degeneration: Two-Year Results of the ANCHOR Study". Ophthalmology 116 (1): 57–65. doi:10.1016/j.ophtha.2008.10.018. PMID 19118696.
- Rosenfeld, Philip J.; Brown, David M.; Heier, Jeffrey S.; Boyer, David S.; Kaiser, Peter K.; Chung, Carol Y.; Kim, Robert Y.; Marina Study, Group (2006). "Ranibizumab for Neovascular Age-Related Macular Degeneration". New England Journal of Medicine 355 (14): 1419–31. doi:10.1056/NEJMoa054481. PMID 17021318.
- Raftery, J.; Clegg, A.; Jones, J.; Tan, S. C.; Lotery, A. (2007). "Ranibizumab (Lucentis) versus bevacizumab (Avastin): modelling cost effectiveness". British Journal of Ophthalmology 91 (9): 1244–6. doi:10.1136/bjo.2007.116616. PMC 1954941. PMID 17431015.
- Vascular Endothelial Growth Factors at the US National Library of Medicine Medical Subject Headings (MeSH)
- Proteopedia Vascular_Endothelial_Growth_Factor - the Vascular Endothelial Growth Factor Structure in Interactive 3D
Further reading 
- Bengoetxea H, Argandoña EG, Lafuente JV (2008). "Effects of Visual Experience on Vascular Endothelial Growth Factor Expression during the Postnatal Development of the Rat Visual Cortex". Cerebral Cortex. 18 (7): 1630–39. doi:10.1093/cercor/bhm190. PMC 2430152. PMID 17986606.
- Ferrara N, Gerber HP (2002). "The role of vascular endothelial growth factor in angiogenesis". Acta Haematol. 106 (4): 148–56. doi:10.1159/000046610. PMID 11815711.
- Orpana A, Salven P (2003). "Angiogenic and lymphangiogenic molecules in hematological malignancies". Leuk. Lymphoma 43 (2): 219–24. doi:10.1080/10428190290005964. PMID 11999550.
- Afuwape AO, Kiriakidis S, Paleolog EM (2003). "The role of the angiogenic molecule VEGF in the pathogenesis of rheumatoid arthritis". Histol. Histopathol. 17 (3): 961–72. PMID 12168808.
- de Bont ES, Neefjes VM, Rosati S et al. (2003). "New vessel formation and aberrant VEGF/VEGFR signaling in acute leukemia: does it matter?". Leuk. Lymphoma 43 (10): 1901–9. doi:10.1080/1042819021000015844. PMID 12481883.
- Ria R, Roccaro AM, Merchionne F et al. (2003). "Vascular endothelial growth factor and its receptors in multiple myeloma". Leukemia 17 (10): 1961–6. doi:10.1038/sj.leu.2403076. PMID 14513045.
- Caldwell RB, Bartoli M, Behzadian MA et al. (2004). "Vascular endothelial growth factor and diabetic retinopathy: pathophysiological mechanisms and treatment perspectives". Diabetes Metab. Res. Rev. 19 (6): 442–55. doi:10.1002/dmrr.415. PMID 14648803.
- Patan S (2004). "Vasculogenesis and angiogenesis". Cancer Treat. Res. Cancer Treatment and Research 117: 3–32. doi:10.1007/978-1-4419-8871-3_1. ISBN 978-1-4020-7704-3. PMID 15015550.
- Machein MR, Plate KH (2004). "Role of VEGF in developmental angiogenesis and in tumor angiogenesis in the brain". Cancer Treat. Res. Cancer Treatment and Research 117: 191–218. doi:10.1007/978-1-4419-8871-3_13. ISBN 978-1-4020-7704-3. PMID 15015562.
- Eremina V, Quaggin SE (2004). "The role of VEGF-A in glomerular development and function". Curr. Opin. Nephrol. Hypertens. 13 (1): 9–15. doi:10.1097/00041552-200401000-00002. PMID 15090854.
- Storkebaum E, Lambrechts D, Carmeliet P (2004). "VEGF: once regarded as a specific angiogenic factor, now implicated in neuroprotection". BioEssays 26 (9): 943–54. doi:10.1002/bies.20092. PMID 15351965.
- Ribatti D (2005). "The crucial role of vascular permeability factor/vascular endothelial growth factor in angiogenesis: a historical review". Br. J. Haematol. 128 (3): 303–9. doi:10.1111/j.1365-2141.2004.05291.x. PMID 15667531.
- Loureiro RM, D'Amore PA (2005). "Transcriptional regulation of vascular endothelial growth factor in cancer". Cytokine Growth Factor Rev. 16 (1): 77–89. doi:10.1016/j.cytogfr.2005.01.005. PMID 15733833.
- Herbst RS, Onn A, Sandler A (2005). "Angiogenesis and lung cancer: prognostic and therapeutic implications". J. Clin. Oncol. 23 (14): 3243–56. doi:10.1200/JCO.2005.18.853. PMID 15886312.
- Pufe T, Kurz B, Petersen W et al. (2006). "The influence of biomechanical parameters on the expression of VEGF and endostatin in the bone and joint system". Ann. Anat. 187 (5–6): 461–72. doi:10.1016/j.aanat.2005.06.008. PMID 16320826.
- Tong JP, Yao YF (2006). "Contribution of VEGF and PEDF to choroidal angiogenesis: a need for balanced expressions". Clin. Biochem. 39 (3): 267–76. doi:10.1016/j.clinbiochem.2005.11.013. PMID 16409998.
- Lambrechts D, Carmeliet P (2007). "VEGF at the neurovascular interface: therapeutic implications for motor neuron disease". Biochim. Biophys. Acta 1762 (11–12): 1109–21. doi:10.1016/j.bbadis.2006.04.005. PMID 16784838.
- Matsumoto T, Mugishima H (2006). "Signal transduction via vascular endothelial growth factor (VEGF) receptors and their roles in atherogenesis". J. Atheroscler. Thromb. 13 (3): 130–5. doi:10.5551/jat.13.130. PMID 16835467.
- Bogaert E, Van Damme P, Van Den Bosch L, Robberecht W (2006). "Vascular endothelial growth factor in amyotrophic lateral sclerosis and other neurodegenerative diseases". Muscle Nerve 34 (4): 391–405. doi:10.1002/mus.20609. PMID 16856151.
- Mercurio AM, Lipscomb EA, Bachelder RE (2006). "Non-angiogenic functions of VEGF in breast cancer". Journal of Mammary Gland Biology and Neoplasia 10 (4): 283–90. doi:10.1007/s10911-006-9001-9. PMID 16924371.
- Makinde T, Murphy RF, Agrawal DK (2007). "Immunomodulatory role of vascular endothelial growth factor and angiopoietin-1 in airway remodeling". Curr. Mol. Med. 6 (8): 831–41. doi:10.2174/156652406779010795. PMID 17168735.
- Rini BI, Rathmell WK (2007). "Biological aspects and binding strategies of vascular endothelial growth factor in renal cell carcinoma". Clin. Cancer Res. 13 (2 Pt 2): 741s–746s. doi:10.1158/1078-0432.CCR-06-2110. PMID 17255303.
- Rodgers LS, Lalani S, Hardy KM, Xiang X, Broka D, Antin PB, Camenisch TD. (2006). "Depolymerized hyaluronan induces vascular endothelial growth factor, a negative regulator of developmental epithelial-to-mesenchymal transformation". Circ Res. 99 (6): 583–9. doi:10.1161/01.RES.0000242561.95978.43. PMID 16931798.