Angiogenesis in health and disease.
TL;DR: Molecular insights into the formation of new blood vessels are being generated at a rapidly increasing pace, offering new therapeutic opportunities that are currently being evaluated.
Abstract: Blood vessels constitute the first organ in the embryo and form the largest network in our body but, sadly, are also often deadly. When dysregulated, the formation of new blood vessels contributes to numerous malignant, ischemic, inflammatory, infectious and immune disorders. Molecular insights into these processes are being generated at a rapidly increasing pace, offering new therapeutic opportunities that are currently being evaluated.
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TL;DR: Emerging evidence supporting an alternative hypothesis is reviewed—that certain antiangiogenic agents can also transiently “normalize” the abnormal structure and function of tumor vasculature to make it more efficient for oxygen and drug delivery.
Abstract: Solid tumors require blood vessels for growth, and many new cancer therapies are directed against the tumor vasculature. The widely held view is that these antiangiogenic therapies should destroy the tumor vasculature, thereby depriving the tumor of oxygen and nutrients. Here, I review emerging evidence supporting an alternative hypothesis-that certain antiangiogenic agents can also transiently "normalize" the abnormal structure and function of tumor vasculature to make it more efficient for oxygen and drug delivery. Drugs that induce vascular normalization can alleviate hypoxia and increase the efficacy of conventional therapies if both are carefully scheduled. A better understanding of the molecular and cellular underpinnings of vascular normalization may ultimately lead to more effective therapies not only for cancer but also for diseases with abnormal vasculature, as well as regenerative medicine, in which the goal is to create and maintain a functionally normal vasculature.
4,952 citations
TL;DR: Preclinical and clinical studies have shown new molecular targets and principles, which may provide avenues for improving the therapeutic benefit from anti-angiogenic strategies.
Abstract: Blood vessels deliver oxygen and nutrients to every part of the body, but also nourish diseases such as cancer. Over the past decade, our understanding of the molecular mechanisms of angiogenesis (blood vessel growth) has increased at an explosive rate and has led to the approval of anti-angiogenic drugs for cancer and eye diseases. So far, hundreds of thousands of patients have benefited from blockers of the angiogenic protein vascular endothelial growth factor, but limited efficacy and resistance remain outstanding problems. Recent preclinical and clinical studies have shown new molecular targets and principles, which may provide avenues for improving the therapeutic benefit from anti-angiogenic strategies.
4,441 citations
Cites background from "Angiogenesis in health and disease...."
...To name just a few, insufficient vessel growth or maintenance can lead to stroke, myocardial infarction, ulcerative disorders and neurodegeneration, and abnormal vessel growth or remodelling fuels cancer, inflammatory disorders, pulmonary hypertension and blinding eye disease...
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TL;DR: Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen in vitro and an angiogenic inducer in a variety of in vivo models and is implicated in intraocular neovascularization associated with diabetic retinopathy and age-related macular degeneration.
Abstract: Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen in vitro and an angiogenic inducer in a variety of in vivo models. Hypoxia has been shown to be a major inducer of VEGF gene transcription. The tyrosine kinases Flt-1 (VEGFR-1) and Flk-1/KDR (VEGFR-2) are high-affinity VEGF receptors. The role of VEGF in developmental angiogenesis is emphasized by the finding that loss of a single VEGF allele results in defective vascularization and early embryonic lethality. VEGF is critical also for reproductive and bone angiogenesis. Substantial evidence also implicates VEGF as a mediator of pathological angiogenesis. In situ hybridization studies demonstrate expression of VEGF mRNA in the majority of human tumors. Anti-VEGF monoclonal antibodies and other VEGF inhibitors block the growth of several tumor cell lines in nude mice. Clinical trials with various VEGF inhibitors in a variety of malignancies are ongoing. Very recently, an anti-VEGF monoclonal antibody (bevacizumab; Avastin) has been approved by the Food and Drug Administration as a first-line treatment for metastatic colorectal cancer in combination with chemotherapy. Furthermore, VEGF is implicated in intraocular neovascularization associated with diabetic retinopathy and age-related macular degeneration.
3,414 citations
TL;DR: Angiogenesis research will probably change the face of medicine in the next decades, with more than 500 million people worldwide predicted to benefit from pro- or anti-angiogenesis treatments.
Abstract: The growth of blood vessels (a process known as angiogenesis) is essential for organ growth and repair. An imbalance in this process contributes to numerous malignant, inflammatory, ischaemic, infectious and immune disorders. Recently, the first anti-angiogenic agents have been approved for the treatment of cancer and blindness. Angiogenesis research will probably change the face of medicine in the next decades, with more than 500 million people worldwide predicted to benefit from pro- or anti-angiogenesis treatments.
3,300 citations
Cites background from "Angiogenesis in health and disease...."
...The formation of vessels is a complex process, requiring a finely tuned balance between numerous stimulatory and inhibitory signals, such as integrins, angiopoietins, chemokines, junctional molecules, oxygen sensors, endogenous inhibitors and many other...
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TL;DR: The maturation of nascent vasculature, formed by vasculogenesis or angiogenesis, requires recruitment of mural cells, generation of an extracellular matrix and specialization of the vessel wall for structural support and regulation of vessel function.
Abstract: The maturation of nascent vasculature, formed by vasculogenesis or angiogenesis, requires recruitment of mural cells, generation of an extracellular matrix and specialization of the vessel wall for structural support and regulation of vessel function. In addition, the vascular network must be organized so that all the parenchymal cells receive adequate nutrients. All of these processes are orchestrated by physical forces as well as by a constellation of ligands and receptors whose spatio-temporal patterns of expression and concentration are tightly regulated. Inappropriate levels of these physical forces or molecules produce an abnormal vasculature--a hallmark of various pathologies. Normalization of the abnormal vasculature can facilitate drug delivery to tumors and formation of a mature vasculature can help realize the promise of therapeutic angiogenesis and tissue engineering.
2,458 citations
Cites background from "Angiogenesis in health and disease...."
...Abnormal maturation in pathological angiogenesis A large number of human diseases are characterized by abnormal vessels (see accompanying review in this issu...
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References
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TL;DR: Once a neglected cell type, dendritic cells can now be readily obtained in sufficient quantities to allow molecular and cell biological analysis and the realization that these cells are a powerful tool for manipulating the immune system is realized.
Abstract: B and T lymphocytes are the mediators of immunity, but their function is under the control of dendritic cells. Dendritic cells in the periphery capture and process antigens, express lymphocyte co-stimulatory molecules, migrate to lymphoid organs and secrete cytokines to initiate immune responses. They not only activate lymphocytes, they also tolerize T cells to antigens that are innate to the body (self-antigens), thereby minimizing autoimmune reactions. Once a neglected cell type, dendritic cells can now be readily obtained in sufficient quantities to allow molecular and cell biological analysis. With knowledge comes the realization that these cells are a powerful tool for manipulating the immune system.
14,532 citations
"Angiogenesis in health and disease...." refers background in this paper
...Type I dendritic cells help eradicate tumors through immune stimulation and suppression of tumor angiogenesi...
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TL;DR: Vascular endothelial growth factor (VEGF) is a key regulator of physiological angiogenesis during embryogenesis, skeletal growth and reproductive functions and is implicated in pathologicalAngiogenesis associated with tumors, intraocular neovascular disorders and other conditions.
Abstract: Vascular endothelial growth factor (VEGF) is a key regulator of physiological angiogenesis during embryogenesis, skeletal growth and reproductive functions. VEGF has also been implicated in pathological angiogenesis associated with tumors, intraocular neovascular disorders and other conditions. The biological effects of VEGF are mediated by two receptor tyrosine kinases (RTKs), VEGFR-1 and VEGFR-2, which differ considerably in signaling properties. Non-signaling co-receptors also modulate VEGF RTK signaling. Currently, several VEGF inhibitors are undergoing clinical testing in several malignancies. VEGF inhibition is also being tested as a strategy for the prevention of angiogenesis, vascular leakage and visual loss in age-related macular degeneration.
8,942 citations
"Angiogenesis in health and disease...." refers background in this paper
...VEGF stimulates physiological and pathological angiogenesis in a strict dose-dependent manner and is therefore currently being evaluated for pro- and antiangiogenic therapy (see accompanying review in this issu...
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TL;DR: It is reported that formation of blood vessels was abnormal, but not abolished, in heterozygous VEGF-deficient (VEGF+/-) embryos, generated by aggregation of embryonic stem (ES) cells with tetraploid embryos (T-ES)16,17, and even more impaired in homozygous D1-VEGF- deficient (VDGF-/-) T-ES embryos, resulting in death at mid-gestation.
Abstract: The endothelial cell-specific vascular endothelial growth factor (VEGF) and its cellular receptors Flt-1 and Flk-1 have been implicated in the formation of the embryonic vasculature. This is suggested by their colocalized expression during embryogenesis and the impaired vessel formation in Flk-1 and Flt-1 deficient embryos. However, because Flt-1 also binds placental growth factor, a VEGF homologue, the precise role of VEGF was unknown. Here we report that formation of blood vessels was abnormal, but not abolished, in heterozygous VEGF-deficient (VEGF+/-) embryos, generated by aggregation of embryonic stem (ES) cells with tetraploid embryos (T-ES) and even more impaired in homozygous VEGF-deficient (VEGF-/-) T-ES embryos, resulting in death at mid-gestation. Similar phenotypes were observed in F1-VEGF+/- embryos, generated by germline transmission. We believe that this heterozygous lethal phenotype, which differs from the homozygous lethality in VEGF-receptor-deficient embryos, is unprecedented for a targeted autosomal gene inactivation, and is indicative of a tight dose-dependent regulation of embryonic vessel development by VEGF.
4,216 citations
"Angiogenesis in health and disease...." refers background in this paper
...Loss of a single allele causes embryonic vascular defect...
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TL;DR: The unexpected finding that loss of a single VEGF allele is lethal in the mouse embryo between days 11 and 12 was reported, and angiogenesis and blood-island formation were impaired, resulting in several developmental anomalies.
Abstract: ANGIOGENESIS is required for a wide variety of physiological and pathological processes1. The endothelial cell-specific mitogen vascular endothelial growth factor (VEGF)2,3 is a major mediator of pathological angiogenesis4–6. Also, the expression of VEGF and its two receptors, Flt-1 and Flk-1/KDR, is related to the formation of blood vessels in mouse and rat embryos7–10. Mice homozygous for mutations that inactivate either receptor die in utero between days 8.5 and 9.5 (refs 11,12). However, ligand(s) other than VEGF might activate such receptors13,14. To assess the role of VEGF directly, we disrupted the VEGF gene in embryonic stem cells. Here we report the unexpected finding that loss of a single VEGF allele is lethal in the mouse embryo between days 11 and 12. Angiogenesis and blood-island formation were impaired, resulting in several developmental anomalies. Furthermore, VEGF-null embryonic stem cells exhibit a dramatically reduced ability to form tumours in nude mice.
3,733 citations
"Angiogenesis in health and disease...." refers background in this paper
...Loss of a single allele causes embryonic vascular defect...
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TL;DR: It is confirmed that placental soluble fms-like tyrosine kinase 1 (sFlt1), an antagonist of VEGF and placental growth factor (PlGF), is upregulated in preeclampsia, leading to increased systemic levels of sFlt 1 that fall after delivery, and observations suggest that excess circulating sFelt1 contributes to the pathogenesis of preeClampsia.
Abstract: Preeclampsia, a syndrome affecting 5% of pregnancies, causes substantial maternal and fetal morbidity and mortality. The pathophysiology of preeclampsia remains largely unknown. It has been hypothesized that placental ischemia is an early event, leading to placental production of a soluble factor or factors that cause maternal endothelial dysfunction, resulting in the clinical findings of hypertension, proteinuria, and edema. Here, we confirm that placental soluble fms-like tyrosine kinase 1 (sFlt1), an antagonist of VEGF and placental growth factor (PlGF), is upregulated in preeclampsia, leading to increased systemic levels of sFlt1 that fall after delivery. We demonstrate that increased circulating sFlt1 in patients with preeclampsia is associated with decreased circulating levels of free VEGF and PlGF, resulting in endothelial dysfunction in vitro that can be rescued by exogenous VEGF and PlGF. Additionally, VEGF and PlGF cause microvascular relaxation of rat renal arterioles in vitro that is blocked by sFlt1. Finally, administration of sFlt1 to pregnant rats induces hypertension, proteinuria, and glomerular endotheliosis, the classic lesion of preeclampsia. These observations suggest that excess circulating sFlt1 contributes to the pathogenesis of preeclampsia.
3,613 citations