|
Advertisement |
|
|
||
 |
|
|||||
|
|||||
|
 |
||||||
|
||||||
|
||||||
|
© 2002 American Society for Clinical Oncology
Vascular Permeability Factor/Vascular Endothelial Growth Factor: A Critical Cytokine in Tumor Angiogenesis and a Potential Target for Diagnosis and TherapyByFrom the Department of Pathology, Beth Israel Deaconess Medical Center, and Department of Pathology, Harvard Medical School, Boston, MA. Address reprint requests to Harold F. Dvorak, MD, Department of Pathology, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215; email: hdvorak{at}caregroup.harvard.edu
ABSTRACT: Vascular endothelial growth factor A (VEGF-A), the founding member of the vascular permeability factor (VPF)/VEGF family of proteins, is an important angiogenic cytokine with critical roles in tumor angiogenesis. This article reviews the literature with regard to VEGF-A’s multiple functions, the mechanisms by which it induces angiogenesis, and its current and projected roles in clinical oncology. VEGF-A is a multifunctional cytokine that is widely expressed by tumor cells and that acts through receptors (VEGFR-1, VEGFR-2, and neuropilin) that are expressed on vascular endothelium and on some other cells. It increases microvascular permeability, induces endothelial cell migration and division, reprograms gene expression, promotes endothelial cell survival, prevents senescence, and induces angiogenesis. Recently, VEGF-A has also been shown to induce lymphangiogenesis. Measurements of circulating levels of VEGF-A may have value in estimating prognosis, and VEGF-A and its receptors are potential targets for therapy. Recognized as the single most important angiogenic cytokine, VEGF-A has a central role in tumor biology and will likely have an important role in future approaches designed to evaluate patient prognosis. It may also become an important target for cancer therapy.
VASCULAR PERMEABILITY factor (VPF)/vascular endothelial growth factor A (VEGF-A) is the founding member of a family of closely related cytokines that exert critical functions in vasculogenesis and in both pathologic and physiologic angiogenesis and lymphangiogenesis. Discovered in the late 1970s as a tumor-secreted protein that potently increased microvascular permeability to plasma proteins,1 VEGF-A is a multifunctional cytokine that exerts a variety of effects on vascular endothelial cells that together promote the formation of new blood vessels. Thus, in addition to rendering microvessels hyperpermeable, VEGF-A stimulates endothelial cells to migrate and divide, profoundly alters their pattern of gene expression, and protects them from apoptosis and senescence.2-5 Of course, there are many angiogenic factors, and the current interest in VEGF-A is attributable to several of its unique properties:
As noted above, VEGF-A is a member of a family of dimeric glycoproteins that belong to the platelet-derived growth factor (PDGF) superfamily of growth factors. Other members of the VEGF family include VEGF-B, VEGF-C, VEGF-D, and VEGF-E and placenta growth factor (PlGF). These have thus far been less well studied than VEGF-A, and the interested reader is referred to several recent articles for additional information.11,15-18 Only a few relevant facts concerning other members of the VEGF family are mentioned here. Receptors to which the several members of the VEGF family bind are summarized in Fig 1. PlGF is, as its name implies, strongly expressed in placenta and is thought to have an accessory role in pathologic angiogenesis, serving to potentiate the activity of VEGF-A.16 Mice lacking PlGF are apparently otherwise normal. VEGF-B knockout mice are viable but have small hearts, suggesting that this cytokine has a role in coronary artery development.19 VEGF-C binds to VEGFR-3 (Fig 1), expressed on lymphatic endothelium, and has been implicated in lymphangiogenesis. Like VEGF-C, to which it is structurally related, VEGF-D is an endothelial cell mitogen and interacts with VEGRFR-2 and VEGFR-3. VEGF-E, encoded by the ORF virus, induces angiogenesis through an interaction with VEGFR-2.20
VEGF-A is overexpressed by the vast majority of important solid human cancers (reviewed in2-4) and, increasingly, has been found to be of importance in lymphomas and a variety of hematologic malignancies.21-27 VEGF-A is overexpressed not only by invasive cancer cells but also by at least some premalignant lesions (eg, precursor lesions of breast, cervix, and colon cancers); furthermore, expression levels increased in parallel with malignant progression.28-30 An association between VEGF-A expression and benign tumors is less well established, in part because benign tumors have been less carefully studied in this regard. Pituitary adenomas31 and benign hemangiomas rarely overexpress VEGF-A, whereas more malignant vascular tumors and leiomyomas of the uterus do so.32,33 Finally, although the malignant cells themselves are primarily responsible for VEGF-A expression in tumors, stromal cells and even vascular endothelium may also express VEGF-A, although in lesser amounts, especially at sites of hypoxia.28,34-37
VEGF-A is a highly conserved, disulfide-bonded dimeric glycoprotein of 34 to 45 kd.2-5 It shares low but significant sequence homology with PDGF and, as with PDGF, cysteines form interchain and intrachain bonds that are integral to structure. The two chains that constitute VEGF-A are arranged in antiparallel fashion and the crystal structure and identification of receptor-binding sites (two per molecule) have recently been solved.37 On reduction, VEGF-A separates into major bands of approximately 17 to 23 kd and loses all of its biologic activity. The VEGF-A gene is located on the short arm of chromosome 6 and is differentially spliced to yield several different isoforms, the three most prominent of which encode polypeptides of 189, 165, and 121 amino acids in human cells (corresponding murine proteins are one amino acid shorter).2,5,38,39 The coding region of VEGF-A is composed of eight exons, the first of which encodes a hydrophobic leader sequence, typical of secreted proteins. The 189–amino acid VEGF-A isomer is encoded by all eight exons. The shorter isoforms include the first five exons as well as exon 8. VEGF-A165, most often the predominant isoform, lacks the residues encoded by exon 6 and VEGF-A121 lacks those encoded by both exons 6 and 7. Very recently, an additional form of VEGF-A has been described that acts selectively on endocrine vascular endothelium.40 The several VEGF-A isoforms encoded by alternative splicing have distinct physical properties. VEGF-A121 is freely soluble and does not bind heparin. By contrast, isoforms 165 and 189 have increasing basic charge and bind heparin with increasing affinity; in fact, VEGF-A165 was originally purified on the basis of its affinity for heparin.9,41 Heparin, heparan sulfate, and heparinase all displace the larger VEGF-A isoforms from proteoglycan-binding sites; plasmin cleavage also activates these isoforms by freeing them from cells or matrix.42 Despite these physical differences, the several VEGF-A isoforms apparently have identical biologic activities when free in solution. Evidence supporting the activation of VEGF-A by freeing it from the bound state comes from recent studies of pancreatic islet cell tumors that develop under the control of the SV40 T antigen (so-called RIP-tag tumors). Invasive tumor cells and normal islet cells made roughly equivalent amounts of VEGF-A; however, angiogenesis was initiated only at a stage when islet cells expressed metalloproteases that liberated VEGF-A from matrix.43 Therefore, in this and likely other instances, proteases are required to "pull the angiogenic switch."
VEGF-A mediates its effects by interacting with two high-affinity transmembrane tyrosine kinase receptors that are selectively though not exclusively expressed by vascular endothelium (Fig 1). Both VEGFR-1 (Flt-1) and VEGFR-2 (KDR, flk-1) are overexpressed in the vasculature of tumors that express VEGF-A (Fig 2C and 2D) 44 and have seven immunoglobulin-like extracellular domains and a kinase insert sequence.45,46 In various cultured endothelial cells, VEGFR-1 has a Kd of 1 to 20 pmol/L and a frequency of approximately 3,000 copies per cell; VEGFR-2 binds with a Kd of 50 to 770 pmol/L with approximately 40,000 copies per cell. Receptor frequency may vary in different tissues in vivo. A truncated soluble form of VEGFR-1 that results from alternative splicing is found in serum and retains VEGF-A–binding activity.47,48 Mice null for either VEGFR-1 or VEGFR-2 are embryonic lethals.49,50 Unlike VEGF-C and VEGF-D, VEGF-A does not bind to VEGFR-3 (Fig 1).
Recently, a nonkinase receptor, neuropilin (NRP-1), has been found to potentiate VEGF-A’s binding to VEGFR-2; previously, neuropilin had been shown to mediate guidance of neurite growth cones.14 Neuropilin is less selectively expressed on vascular endothelium than VEGFR-1 and VEGFR-2, and its role in tumor angiogenesis is only now being investigated.51,52
On binding to its receptors, VEGF-A initiates a cascade of signaling events that begins with autophosphorylation of both receptor tyrosine kinases, followed by activation of numerous downstream proteins including phospholipase C
Earliest Activity In Vivo: Increased Microvascular Permeability VEGF-A was originally discovered because of its ability to increase the permeability of microvessels, primarily postcapillary venules and small veins, to circulating macromolecules. The ability to enhance microvascular permeability remains one of VEGF-A’s most important properties, and the nearly universal hyperpermeability of tumor blood vessels to plasma proteins is largely attributable to tumor cell expression of VEGF-A (Fig 3a). In fact, VEGF-A is one of the most potent vascular permeabilizing agents known, acting at concentrations below 1 nmol/L, and with a potency some 50,000 times that of histamine.1,9,57 VEGF-C, also expressed by some tumors, does enhance microvascular permeability, but less potently than VEGF-A.58,59
Increased microvascular permeability is VEGF-A’s first and most distinctive biologic activity in vivo, becoming evident within 1 minute of injection. Induction of vascular permeability is likely an essential first step in angiogenesis, as all examples of angiogenesis thus far studied, both physiologic and pathologic, are characterized by increased microvascular permeability.2-4,57,60 Increased microvascular permeability results in leakage of plasma proteins, including fibrinogen and other clotting proteins. The clotting system is rapidly activated by means of the tissue factor pathway61,62 and results in deposition of extravascular fibrin in tumor stroma (Fig 3b). Fibrin is a water-retaining gel whose deposition in tissues has at least two consequences: (1) fibrin transforms the normally antiangiogenic stroma of normal tissues into provisional stroma that is strongly proangiogenic8,60,62,63; and (2) coupled with the apparent lack of lymphatics in tumors, fibrin retards clearance of edema fluid, resulting in increased interstitial pressure, a characteristic feature of most solid tumors.64 Although relatively innocuous in some locations, increased intracranial pressure may be disastrous, leading to brain herniation and death.65,66 Tumor-secreted VEGF-A causes microvascular permeability and plasma leakage in the peritoneal and other body cavities, leading to ascites accumulation that can reach massive proportions (many liters). Such accumulations of fluid are not uncommon in patients with primary ovarian carcinoma or metastatic breast cancer; consequences such as impaired breathing and electrolyte imbalance are well known. Immunoreactive and bioactive VEGF-A protein is commonly found in these malignant fluid accumulations, sometimes in high concentrations.67,68 Although there is now general agreement as to VEGF-A’s potency in enhancing microvascular permeability, there is debate as to the pathways that plasma proteins and other circulating macromolecules follow in extravasating from vessels. Work from our laboratory has consistently indicated that, in response to VEGF-A, macromolecules cross the endothelium predominantly by means of a transendothelial cell pathway that involves vesiculovacuolar organelles (VVOs); this is true both in tumor vessels and in the venules of several normal tissues.57,69-71 VVOs are interconnected chains of uncoated cytoplasmic vesicles and vacuoles that are abundant in the endothelial cells of normal venules and of many tumor vessels and that span the entire thickness of endothelial cell cytoplasm from lumen to ablumen (Fig 4a).72 The individual vesicles and vacuoles that constitute VVOs interconnect with each other and with the endothelial cell plasma membrane by stomata that are normally closed by thin diaphragms. In normal adult tissues, extravasation of circulating macromolecules from venules and small veins is quite limited but, to the extent that it occurs, takes place by way of VVOs. In tumor vessels, or in normal skin following local injection of VEGF-A, the stomata open to allow macromolecular tracers to pass through interconnecting vesicles and vacuoles and thereby cross the endothelial cell cytoplasm from the vascular lumen to the ablumen; thus, VVOs provide a pathway whereby plasma and plasma proteins may exit the circulation and enter the tissues. When the interconnections between VVO vesicles and vacuoles are fully opened, these structures form transendothelial cell pores.73-75 VEGF-A also induces endothelial fenestrations that provide an additional transcellular pathway for solute extravasation (Fig 4c).57,76 In contrast, not everyone accepts this formulation, arguing instead that macromolecules extravasate predominantly through an interendothelial cell pathway (ie, by an opening of the junctions between adjacent endothelial cells).77
Subsequent Biologic Activities on Vascular Endothelium VEGF-A is a multifunctional cytokine that exerts many effects on vascular endothelium that only become apparent over the course of hours to days and that critically influence the angiogenic response. These include striking changes in cell morphology and cytoskeleton accompanied by stimulation of endothelial cell migration and division. At a molecular level, VEGF-A reprograms endothelial cell gene expression, leading to increased expression of a number of different proteins, including the procoagulant tissue factor, proteins associated with the fibrinolytic pathway (urokinase, tissue-type plasminogen activator, type 1 plasminogen activator inhibitor, urokinase receptor), matrix metalloproteases, the GLUT-1 glucose transporter, nitric oxide synthase, numerous mitogens, and a number of antiapoptotic factors (eg, bcl-2, A1, survivin, XIAP).2-5,78 VEGF-A also serves as an endothelial cell survival factor, protecting endothelial cells against apoptosis,79 and it delays and may reverse endothelial cell senescence.80 Of considerable interest, tumors that overexpress VEGF-A are, so far without exception, supplied by microvessels whose lining endothelial cells overexpress both VEGFR-1 and VEGFR-2 (Fig 1C and 1D). 2,4,28,29,81-87 The mechanisms relating VEGF receptor overexpression to that of their ligand are largely unknown. However, there is evidence that chronic exposure to high levels of VEGF-A enhances the expression of both VEGF-A receptors on microvascular endothelial cells in vivo, as demonstrated in transgenic mice that overexpress VEGF-A in the skin under the control of a keratin promoter88 and also in mice injected in several different tissues with an adenovirus engineered to overexpress VEGF-A (see below).72
Effects of VEGF-A on Cells Other Than Vascular Endothelium VEGF-A protein is readily detected in tumors by immunohistochemistry.2,3,97 Of interest, antibodies to VEGF-A often stain not only tumor cells but also tumor-associated blood vessels, even though the latter do not themselves express VEGF-A.2,97,98 Indeed, tumor microvessel-associated VEGF-A has been localized to the endothelial cell plasma membrane and to intraendothelial cell VVOs by electron microscopic immunocytochemistry.99 Although these observations make sense in that tumor blood vessels are thought to be the primary target of tumor-secreted VEGF-A, it is nonetheless a surprising finding in that immunohistochemistry is a relatively insensitive detection method and indicates the presence of much larger amounts of VEGF-A than would be required to activate microvascular endothelium. The large VEGF-A accumulations found in tumor vessels likely indicate that these vessels provide a "sink" for binding and retaining VEGF-A locally, preventing the toxic side effects that would result if it were to disseminate widely.
Although constitutively expressed by many tumor cells and transformed cell lines, VEGF-A expression is subject to a number of control mechanisms.
Oxygen Concentration The importance of hypoxic regulation of VEGF-A expression for tumor malignancy and tumor angiogenesis is subject to debate. Many tumors express VEGF-A at high levels even under normoxic conditions.2-4 Also, although it is true that many tumors express large amounts of VEGF-A immediately adjacent to zones of necrosis, the significance of such local expression is uncertain. Zones of tumor necrosis are generally distant from the nearest functioning blood vessels and therefore from potential sites of VEGF-A action; to exert an effect, VEGF-A would have to traverse significant distances, an unlikely possibility given the slow diffusion kinetics of macromolecules in solid tissues.106
Oncogenes and Tumor Suppressor Genes
Cytokines and Other Mediators
Hormones
Other Agents
Because tumors are complex entities that express many different growth factors and cytokines, it has been difficult to determine definitively which are specifically responsible for the growth of tumor blood vessels and, conversely, to determine the types of blood vessels that a single cytokine such as VEGF-A might induce on its own. Recent progress has been made with regard to the second of these questions in studies that made use of a nonreplicating adenoviral vector engineered to express VEGF-A.72 When injected into mouse tissues, the virus infected host cells and these expressed VEGF-A at steady-state levels for approximately 2 weeks. Secreted VEGF-A induced a highly reproducible, time-ordered sequence of events that was qualitatively similar in all tissues studied (Fig 5). Within hours of vector injection, local microvessels became hyperpermeable to plasma proteins, resulting in tissue edema and deposition of an extravascular fibrin gel. By 18 hours, enlarged, thin-walled, pericyte-poor, strongly VEGF receptor–positive "mother" vessels had formed within this gel. Mother vessels are a characteristic type of blood vessel that is found in many human and animal tumors (Fig 6). They form according to a three-step process: (1) proteolytic degradation of the noncompliant (nonelastic) vascular basement membrane, a step necessary to permit vessel enlargement; (2) detachment of pericytes from basement membrane; and (3) spreading and thinning of preexisting vascular endothelium over the expanded surface area that was generated by basement membrane degradation (Fig 4b). The resulting increased endothelial cell surface area is made possible by rapid incorporation of VVO membranes into the plasma membrane.
Mother vessels are transitional structures that generally persist as such for only a few days or weeks. As in tumors, mother vessels divided into smaller channels by a process that involved the projection of endothelial cell cytoplasmic bridges into and across mother vessel lumens; these transluminal "bridges" divided blood flow into smaller channels that over time became separated from each other, forming individual smaller caliber "daughter" capillaries.72,138 Mother vessels also evolved to form glomeruloid bodies, poorly organized conglomerates of endothelial cells and pericytes that, like mother vessels, are found in human tumors, particularly glioblastoma multiforme.139 Taken together, it is clear that VEGF-A can by itself, or through accessory molecules that it induces, generate the formation of at least two types of blood vessels that are characteristic of tumors, mother vessels, and glomeruloid bodies. There is every reason to think, therefore, that tumors induce these same vessel types by secreting VEGF-A and that VEGF-A is sufficient for their generation.
Tumor Diagnosis, Staging, and Prognosis The amount of VEGF-A expressed by cancer cells has been found to correlate with poor prognosis in many types of tumors, including carcinomas of the breast, kidney, colon, brain, ovary, cervix, thyroid, bladder, esophagus, and prostate, and in osteoid and soft tissue sarcomas and pediatric tumors.122,126,140-157 In all of these reports, the amount of VEGF-A (measured in different studies by immunohistochemistry, in situ hybridization, quantitative immunoassays, Western blotting, or reverse-transcriptase polymerase chain reaction) correlated with one or more of the following prognostic measures: tumor size, metastasis, and shorter tumor-free and overall survival. Also, VEGF-A mRNA levels have been found to correlate with vascular density in some (eg, carcinomas of the cervix, breast) but not all cancers.156,157 Although not as yet exhaustively investigated, it is clear that tumor metastases also overexpress VEGF-A much as do the primary tumors from which they arose.2,4,153 From the above, it is clear that the amount of VEGF-A expressed by tumors affects clinical outcome; however, none of the techniques used to quantitate tumor VEGF-A expression levels in solid tumors is routine and it is uncertain at present whether, if such studies were widely undertaken, they would be clinically useful or cost-effective for predicting outcomes in individual patients. VEGF-A levels can be more conveniently measured in body fluids than in tumor homogenates, and it is well documented that patients with large tumor burdens and widespread metastatic disease have increased levels of circulating VEGF-A as measured by enzyme-linked immunosorbent assay or other assays.68,126,158-166 In these and other studies, high serum VEGF-A levels in cancer patients, often multiples of those found in normal individuals, were generally associated with unfavorable clinical parameters such as disease progression, poor response to chemotherapy, and poor survival. Increasing serum VEGF-A levels may therefore be clinically useful in signifying increased growth, recurrence, or metastatic spread in individual patients. In contrast, VEGF-A serum measurements cannot be expected to be helpful in patients with minimal disease and therefore have no role as a screening tool. Unfortunately, measurements of VEGF-A in blood are not as straightforward as might be expected. Serum VEGF-A levels are difficult to interpret because platelets sequester this cytokine and because plasma alpha-2 macroglobulin binds it and makes it unavailable to at least some antibodies.126,163,166-169 Also, both megakaryocytes and leukocytes synthesize VEGF-A.166,167,170-173 Therefore, serum levels reflect not only VEGF-A of tumor origin but also that released from platelets and leukocytes during the course of blood clotting, making it difficult to establish a range of normal values. In one study,126 the mean VEGF-A plasma level in control subjects was 27 pg/mL, whereas in serum from the same individuals after blood clotting it was 172 pg/mL. Because of this complication, some authors have recommended that VEGF-A be measured in plasma.126,167 This also may not be entirely satisfactory because plasma VEGF-A levels represent equilibrium between free VEGF-A and that sequestered within platelets. Also, as the result of therapy or for other reasons, the blood cells of cancer patients may synthesize increased amounts of VEGF-A, and platelet activation is common in cancer and in other systemic disease states, potentially leading to increased levels of plasma VEGF-A unrelated to that synthesized by tumors. An additional factor to be considered is whether circulating VEGF-A is elevated in other diseases associated with angiogenesis and local overproduction of VEGF-A (eg, inflammatory diseases such as rheumatoid arthritis and psoriasis)2-4 (for a more complete discussion of VEGF-A measurements and their significance, see174). For the present, we must agree with George et al,163 who state that "definitive proof of the relationship of circulating VEGF levels to tumor angiogenesis, malignant potential, surgical cure, or responses to therapy has yet to be established in any study." Nonetheless, further work may demonstrate that circulating VEGF-A levels are of value in monitoring individual cancer patients who have undergone treatment or who are being considered for additional therapy. As noted above, VEGF-A has also been measured in other body fluids. VEGF-A levels are markedly elevated in malignant pleural effusions caused by ovarian, gastric, and colon cancers67,68,175,176 and in malignant as opposed to benign ovarian cysts.177 The sensitivity and specificity of urinary levels of VEGF-A for diagnosing primary or recurrent bladder cancer have been claimed to be superior to cytology.178
Potential Therapeutic Applications Related to VPF/VEGF VEGF-A’s importance in initiating tumor angiogenesis has made it a target of therapies designed to diminish the tumor vasculature. Human and animal tumors express and secrete large amounts of VEGF-A, and these accumulate on tumor blood vessels in amounts that apparently far exceed those needed for endothelial cell signaling.97,98,188 Moreover, systemically administered antibodies to VEGF-A accumulate selectively in tumor vessels in much higher concentrations than in normal tissues.189 There is strong evidence that neutralizing antibodies against VEGF-A, and antibodies that block VEGF-A receptors, effectively retard tumor growth and may reduce tumor size in mice, effects that are clearly mediated through inhibition of angiogenesis.184,190-198 More recently, antibodies have been developed that selectively recognize the complex that VEGF-A forms with one of its receptors (VEGFR-2) on vascular endothelium.199,200 These antibodies could be especially useful because they selectively target tumor vessels in which VEGF-A is receptor-bound and avoid side effects that might result from inactivation of free VEGF-A.201,202 Other approaches for inhibiting VEGF-A activity provide further proof of principle. These include withdrawal of androgen from mice bearing tumors that are dependent on this hormone for stimulating VEGF-A production and downregulation of VEGF-A transcription by administration of tetracycline to mice whose tumors have been engineered to repress VEGF-A transcription when this antibiotic is present.79,203,204 An approach that may ultimately be of great clinical importance is that afforded by small, orally available molecules that selectively block or prevent activation of VEGF-A’s receptor tyrosine kinases. Several of these with activity against VEGFR-2 have been found to inhibit the growth of murine tumors.205-207 Other types of small molecules may also have value in inhibiting VEGF-A–mediated tumor angiogenesis. Recently, it was found, quite unexpectedly, that dopamine and other related catecholamine neurotransmitters that interact with the dopamine D2 receptor selectively inhibit VEGF-A–induced angiogenesis and inhibit the growth of tumors that express VEGF-A.208 Dopamine is best known clinically for its use in the treatment of Parkinson’s disease, but recently dopamine receptors, including the D2 receptor, have been found on vascular endothelium. At nontoxic doses, dopamine inhibited all VEGF-A activities tested including stimulation of microvascular permeability and endothelial cell proliferation and migration. These results are of interest for a second reason in that they reveal a new link between the nervous system and angiogenesis. Despite the current wave of enthusiasm for therapies designed to inhibit tumor angiogenesis or to destroy existing tumor blood vessels, there are a number of reasons for caution. First, even if therapies directed against VEGF-A are effective initially, tumors may escape from inhibition after a time as they mutate to express other angiogenic growth factors.204 Second, strategies directed against the tumor vasculature, although successful in reducing tumor bulk, typically leave behind a viable rim of tumor cells at the tumor-host interface, a zone that is supplied by the normal host vasculature.209 This rim of viable tumor must be dealt with to prevent regrowth. Third, recent evidence suggests that p53-deficient tumors may be less responsive to antiangiogenic therapy than tumors in which p53 is functioning because the former are less dependent on the generation of a new vasculature than their genetically normal counterparts.210 p53 is of course mutated in a large fraction of human cancers. Finally, the goal is not to cure mouse cancer but human cancer. Despite the spectacular successes reported in the treatment of mouse tumors, clinical trials to date have for the most part been discouragingly negative. This is disappointing but perhaps not surprising in that most of the patients treated thus far have had advanced disease and had already failed conventional treatments. Also, antiangiogenesis therapy differs fundamentally from chemotherapy, and it may be some time before physicians learn how best to implement it optimally. On a more hopeful note, phase I and II studies with the humanized Genentech (South San Francisco, CA) monoclonal antibody against VEGF-A have shown promise in the treatment of several human cancers.211 However, this encouraging news must be tempered by side effects that occur in some patients, including hypertension, thrombosis, proteinuria, and fatal hemorrhage.212 Taken together, antiangiogenesis, antitumor vasculature and, more specifically, anti–VEGF-A therapies are in their infancy and it is too early to assess their ultimate potential for treating human cancer. Although it seems at present unlikely that these therapies will be effective as standalone therapies, they may well have great value as adjuvant therapies, allowing reduced dosage of toxic conventional treatments such as radiation and chemotherapy.186,187,196,213,214 Further results with antibodies, tyrosine kinase inhibitors, and other small molecules now in development or in early stages of testing are awaited with considerable interest.
Supported by United States Public Health Service, National Institutes of Health grant nos. CA-50453, CA-58845, and HL-54519; by the BIH Pathology Foundation, Inc; and under terms of a contract from the National Foundation for Cancer Research.
1. Dvorak HF, Orenstein NS, Carvalho AC, et al: Induction of a fibrin-gel investment: An early event in line 10 hepatocarcinoma growth mediated by tumor-secreted products. J Immunol 122: 166-174, 1979 2. Brown LF, Detmar M, Claffey K, et al: Vascular permeability factor/vascular endothelial growth factor: A multifunctional angiogenic cytokine. EXS 79: 233-269, 1997[Medline] 3. Dvorak HF, Brown LF, Detmar M, et al: Vascular permeability factor/vascular endothelial growth factor, microvascular hyperpermeability, and angiogenesis. Am J Pathol 146: 1029-1039, 1995[Abstract] 4. Stiver S, Dvorak H: Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF). J Clin Ligand Assay 23: 193-205, 2000 5. Ferrara N: Molecular and biological properties of vascular endothelial growth factor. J Mol Med 77: 527-543, 1999[CrossRef][Medline] 6. Carmeliet P, Ferreira V, Breier G, et al: Abnormal blood vessel development and lethality in embryos lacking a single VEGF allele. Nature 380: 435-439, 1996[CrossRef][Medline] 7. Ferrara N, Carver-Moore K, Chen H, et al: Heterozygous embryonic lethality induced by targeted inactivation of the VEGF gene. Nature 380: 439-442, 1996[CrossRef][Medline] 8. Dvorak HF, Dvorak AM, Manseau EJ, et al: Fibrin gel investment associated with line 1 and line 10 solid tumor growth, angiogenesis, and fibroplasia in guinea pigs: Role of cellular immunity, myofibroblasts, microvascular damage, and infarction in line 1 tumor regression. J Natl Cancer Inst 62: 1459-1472, 1979[Medline]
9. Senger DR, Galli SJ, Dvorak AM, et al: Tumor cells secrete a vascular permeability factor that promotes accumulation of ascites fluid. Science 219: 983-985, 1983 10. Dvorak HF, Nagy JA, Dvorak AM: Structure of solid tumors and their vasculature: Implications for therapy with monoclonal antibodies. Cancer Cells 3: 77-85, 1991[Medline] 11. Joukov V, Pajusola K, Kaipainen A, et al: A novel vascular endothelial growth factor, VEGF-C, is a ligand for the Flt4 (VEGFR-3) and KDR (VEGFR-2) receptor tyrosine kinases. EMBO J 15: 290-298, 1996[Medline]
12. Valtola R, Salven P, Heikkila P, et al: VEGFR-3 and its ligand VEGF-C are associated with angiogenesis in breast cancer. Am J Pathol 154: 1381-1390, 1999
13. Jeltsch M, Kaipainen A, Joukov V, et al: Hyperplasia of lymphatic vessels in VEGF-C transgenic mice. Science 276: 1423-1425, 1997 14. Soker S, Takashima S, Miao HQ, et al: Neuropilin-1 is expressed by endothelial and tumor cells as an isoform-specific receptor for vascular endothelial growth factor. Cell 92: 735-745, 1998[CrossRef][Medline] 15. Matsumoto T, Claesson-Welsh L: VEGF receptor signal transduction. Sci STKE 112: RE21, 2001 16. Carmeliet P, Moons L, Luttun A, et al: Synergism between vascular endothelial growth factor and placental growth factor contributes to angiogenesis and plasma extravasation in pathological conditions. Nat Med 7: 575-583, 2001[CrossRef][Medline]
17. DiSalvo J, Bayne ML, Conn G, et al: Purification and characterization of a naturally occurring vascular endothelial growth factor: Placenta growth factor heterodimer. J Biol Chem 270: 7717-7723, 1995
18. Olofsson B, Pajusola K, Kaipainen A, et al: Vascular endothelial growth factor B, a novel growth factor for endothelial cells. Proc Natl Acad Sci U S A 93: 2576-2581, 1996 19. Joukov V, Kaipainen A, Jeltsch M, et al: Vascular endothelial growth factors VEGF-B and VEGF-C. J Cell Physiol 173: 211-215, 1997[CrossRef][Medline] 20. Meyer M, Clauss M, Lepple-Wienhues A, et al: A novel vascular endothelial growth factor encoded by Orf virus, VEGF-E, mediates angiogenesis via signaling through VEGFR-2 (KDR) but not VEGFR-1 (Flt-1) receptor tyrosine kinases. EMBO J 18: 363-374, 1999[CrossRef][Medline] 21. Anderson KC: Multiple myeloma: Advances in disease biology—Therapeutic implications. Semin Hematol 38: 6-10, 2001[Medline] 22. Aoki Y, Tosato G: Vascular endothelial growth factor/vascular permeability factor in the pathogenesis of primary effusion lymphomas. Leuk Lymphoma 41: 229-237, 2001[Medline]
23. Bellamy WT, Richter L, Frutiger Y, et al: Expression of vascular endothelial growth factor and its receptors in hematopoietic malignancies. Cancer Res 59: 728-733, 1999
24. Chen H, Treweeke AT, West DC, et al: In vitro and in vivo production of vascular endothelial growth factor by chronic lymphocytic leukemia cells. Blood 96: 3181-3187, 2000 25. Foss HD, Araujo I, Demel G, et al: Expression of vascular endothelial growth factor in lymphomas and Castleman’s disease. J Pathol 183: 44-50, 1997[CrossRef][Medline]
26. Hussong JW, Rodgers GM, Shami PJ: Evidence of increased angiogenesis in patients with acute myeloid leukemia. Blood 95: 309-313, 2000
27. Kini AR, Peterson LA, Tallman MS, et al: Angiogenesis in acute promyelocytic leukemia: Induction by vascular endothelial growth factor and inhibition by all-trans retinoic acid. Blood 97: 3919-3924, 2001 28. Brown LF, Berse B, Jackman RW, et al: Expression of vascular permeability factor (vascular endothelial growth factor) and its receptors in breast cancer. Hum Pathol 26: 86-91, 1995[CrossRef][Medline]
29. Guidi AJ, Abu-Jawdeh G, Berse B, et al: Vascular permeability factor (vascular endothelial growth factor) expression and angiogenesis in cervical neoplasia. J Natl Cancer Inst 87: 1237-1245, 1995 30. Wong MP, Cheung N, Yuen ST, et al: Vascular endothelial growth factor is up-regulated in the early pre-malignant stage of colorectal tumour progression. Int J Cancer 81: 845-850, 1999[CrossRef][Medline] 31. Berkman RA, Merrill MJ, Reinhold WC, et al: Expression of the vascular permeability factor/vascular endothelial growth factor gene in central nervous system neoplasms. J Clin Invest 91: 153-159, 1993[Medline] 32. Brown LF, Tognazzi K, Dvorak HF, et al: Strong expression of kinase insert domain-containing receptor, a vascular permeability factor/vascular endothelial growth factor receptor in AIDS-associated Kaposi’s sarcoma and cutaneous angiosarcoma. Am J Pathol 148: 1065-1074, 1996[Abstract] 33. Harrison-Woolrych ML, Sharkey AM, Charnock-Jones DS, et al: Localization and quantification of vascular endothelial growth factor messenger ribonucleic acid in human myometrium and leiomyomata. J Clin Endocrinol Metab 80: 1853-1858, 1995[Abstract]
34. Hlatky L, Tsionou C, Hahnfeldt P, et al: Mammary fibroblasts may influence breast tumor angiogenesis via hypoxia-induced vascular endothelial growth factor up-regulation and protein expression. Cancer Res 54: 6083-6086, 1994 35. Detmar M, Brown LF, Berse B, et al: Hypoxia regulates the expression of vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) and its receptors in human skin. J Invest Dermatol 108: 263-268, 1997[CrossRef][Medline] 36. Fukumura D, Xavier R, Sugiura T, et al: Tumor induction of VEGF promoter activity in stromal cells. Cell 94: 715-725, 1998[CrossRef][Medline]
37. Muller YA, Li B, Christinger HW, et al: Vascular endothelial growth factor: Crystal structure and functional mapping of the kinase domain receptor binding site. Proc Natl Acad Sci U S A 94: 7192-7197, 1997 38. Claffey KP, Senger DR, Spiegelman BM: Structural requirements for dimerization, glycosylation, secretion, and biological function of VPF/VEGF. Biochim Biophys Acta 1246: 1-9, 1995[CrossRef][Medline]
39. Tischer E, Mitchell R, Hartman T, et al: The human gene for vascular endothelial growth factor: Multiple protein forms are encoded through alternative exon splicing. J Biol Chem 266: 11947-11954, 1991
40. Lin R, LeCouter J, Kowalski J, et al: Characterization of endocrine gland-derived vascular endothelial growth factor signaling in adrenal cortex capillary endothelial cells. J Biol Chem 277: 8724-8729, 2002
41. Senger DR, Connolly DT, Van De Water L, et al: Purification and NH2-terminal amino acid sequence of guinea pig tumor-secreted vascular permeability factor. Cancer Res 50: 1774-1778, 1990
42. Houck KA, Leung DW, Rowland AM, et al: Dual regulation of vascular endothelial growth factor bioavailability by genetic and proteolytic mechanisms. J Biol Chem 267: 26031-26037, 1992 43. Bergers G, Brekken R, McMahon G, et al: Matrix metalloproteinase-9 triggers the angiogenic switch during carcinogenesis. Nat Cell Biol 2: 737-744, 2000[CrossRef][Medline] 44. Senger D, Van De Water L, Brown L, et al: Vascular permeability factor (VPF, VEGF) in tumor biology. Cancer Metastasis Rev 12: 303-324, 1993[CrossRef][Medline]
45. de Vries C, Escobedo JA, Ueno H, et al: The fms-like tyrosine kinase, a receptor for vascular endothelial growth factor. Science 255: 989-991, 1992 46. Terman BI, Carrion ME, Kovacs E, et al: Identification of a new endothelial cell growth factor receptor tyrosine kinase. Oncogene 6: 1677-1683, 1991[Medline]
47. Kendall RL, Thomas KA: Inhibition of vascular endothelial cell growth factor activity by an endogenously encoded soluble receptor. Proc Natl Acad Sci U S A 90: 10705-10709, 1993 48. Kendall RL, Wang G, Thomas KA: Identification of a natural soluble form of the vascular endothelial growth factor receptor, FLT-1, and its heterodimerization with KDR. Biochem Biophys Res Commun 226: 324-328, 1996[CrossRef][Medline] 49. Fong GH, Rossant J, Gertsenstein M, et al: Role of the Flt-1 receptor tyrosine kinase in regulating the assembly of vascular endothelium. Nature 376: 66-70, 1995[CrossRef][Medline] 50. Shalaby F, Rossant J, Yamaguchi TP, et al: Failure of blood-island formation and vasculogenesis in Flk-1-deficient mice. Nature 376: 62-66, 1995[CrossRef][Medline] 51. Miao HQ, Klagsbrun M: Neuropilin is a mediator of angiogenesis. Cancer Metastasis Rev 19: 29-37, 2000[CrossRef][Medline]
52. Miao HQ, Lee P, Lin H, et al: Neuropilin-1 expression by tumor cells promotes tumor angiogenesis and progression. FASEB J 14: 2532-2539, 2000
53. Zeng H, Dvorak HF, Mukhopadhyay D: Vascular permeability factor (VPF)/vascular endothelial growth factor (VEGF) receptor-1 down-modulates VPF/VEGF receptor-2-mediated endothelial cell proliferation, but not migration, through phosphatidylinositol 3-kinase-dependent pathways. J Biol Chem 276: 26969-26979, 2001
54. Clauss M, Weich H, Breier G, et al: The vascular endothelial growth factor receptor Flt-1 mediates biological activities: Implications for a functional role of placenta growth factor in monocyte activation and chemotaxis. J Biol Chem 271: 17629-17634, 1996
55. Gille H, Kowalski J, Li B, et al: Analysis of biological effects and signaling properties of Flt-1 (VEGFR-1) and KDR (VEGFR-2): A reassessment using novel receptor-specific vascular endothelial growth factor mutants. J Biol Chem 276: 3222-3230, 2001
56. Bussolati B, Dunk C, Grohman M, et al: Vascular endothelial growth factor receptor-1 modulates vascular endothelial growth factor-mediated angiogenesis via nitric oxide. Am J Pathol 159: 993-1008, 2001 57. Dvorak HF, Nagy JA, Feng D, et al: Vascular permeability factor/vascular endothelial growth factor and the significance of microvascular hyperpermeability in angiogenesis. Curr Top Microbiol Immunol 237: 97-132, 1999[Medline]
58. Joukov V, Kumar V, Sorsa T, et al: A recombinant mutant vascular endothelial growth factor-C that has lost vascular endothelial growth factor receptor-2 binding, activation, and vascular permeability activities. J Biol Chem 273: 6599-6602, 1998
59. Kadambi A, Carreira CM, Yun CO, et al: Vascular endothelial growth factor (VEGF)-C differentially affects tumor vascular function and leukocyte recruitment: Role of VEGF-receptor 2 and host VEGF-A. Cancer Res 61: 2404-2408, 2001 60. Dvorak HF: Tumors: Wounds that do not heal—Similarities between tumor stroma generation and wound healing. N Engl J Med 315: 1650-1655, 1986[Medline]
61. Dvorak HF, Van DeWater L, Bitzer AM, et al: Procoagulant activity associated with plasma membrane vesicles shed by cultured tumor cells. Cancer Res 43: 4434-4442, 1983
62. Dvorak HF, Senger DS, Dvorak AM, et al: Regulation of extravascular coagulation by microvascular permeability. Science 227: 1059-1061, 1985 63. Dvorak HF, Harvey VS, Estrella P, et al: Fibrin containing gels induce angiogenesis: Implications for tumor stroma generation and wound healing. Lab Invest 57: 673-686, 1987[Medline]
64. Boucher Y, Jain RK: Microvascular pressure is the principal driving force for interstitial hypertension in solid tumors: Implications for vascular collapse. Cancer Res 52: 5110-5114, 1992 65. Boucher Y, Salehi H, Witwer B, et al: Interstitial fluid pressure in intracranial tumours in patients and in rodents. Br J Cancer 75: 829-836, 1997[Medline] 66. Criscuolo GR: The genesis of peritumoral vasogenic brain edema and tumor cysts: A hypothetical role for tumor-derived vascular permeability factor. Yale J Biol Med 66: 277-314, 1993[Medline]
67. Olson TA, Mohanraj D, Carson LF, et al: Vascular permeability factor gene expression in normal and neoplastic human ovaries. Cancer Res 54: 276-280, 1994
68. Yeo KT, Wang HH, Nagy JA, et al: Vascular permeability factor (vascular endothelial growth factor) in guinea pig and human tumor and inflammatory effusions. Cancer Res 53: 2912-2918, 1993 69. Kohn S, Nagy JA, Dvorak HF, et al: Pathways of macromolecular tracer transport across venules and small veins: Structural basis for the hyperpermeability of tumor blood vessels. Lab Invest 67: 596-607, 1992[Medline] 70. Dvorak AM, Kohn S, Morgan ES, et al: The vesiculo-vacuolar organelle (VVO): A distinct endothelial cell structure that provides a transcellular pathway for macromolecular extravasation. J Leukoc Biol 59: 100-115, 1996[Abstract]
71. Feng D, Nagy J, Hipp J, et al: Vesiculo-vacuolar organelles and the regulation of venule permeability to macromolecules by vascular permeability factor, histamine, and serotonin. J Exp Med 183: 1981-1986, 1996 72. Pettersson A, Nagy JA, Brown LF, et al: Heterogeneity of the angiogenic response induced in different normal adult tissues by vascular permeability factor/vascular endothelial growth factor. Lab Invest 80: 99-115, 2000[Medline]
73. Feng D, Nagy JA, Hipp J, et al: Reinterpretation of endothelial cell gaps induced by vasoactive mediators in guinea-pig, mouse and rat: Many are transcellular pores. J Physiol 504: 747-761, 1997 74. Feng D, Nagy JA, Pyne K, et al: Pathways of macromolecular extravasation across microvascular endothelium in response to VPF/VEGF and other vasoactive mediators. Microcirculation 6: 23-44, 1999[CrossRef][Medline] 75. Feng D, Nagy JA, Dvorak AM, et al: Different pathways of macromolecule extravasation from hyperpermeable tumor vessels. Microvasc Res 59: 24-37, 2000[CrossRef][Medline] 76. Roberts WG, Palade GE: Increased microvascular permeability and endothelial fenestration induced by vascular endothelial growth factor. J Cell Sci 108: 2369-2379, 1995[Abstract] 77. McDonald DM, Thurston G, Baluk P: Endothelial gaps as sites for plasma leakage in inflammation. Microcirculation 6: 7-22, 1999[CrossRef][Medline]
78. Garcia-Cardena G, Folkman J: Is there a role for nitric oxide in tumor angiogenesis? J Natl Cancer Inst 90: 560-561, 1998 79. Benjamin LE, Golijanin D, Itin A, et al: Selective ablation of immature blood vessels in established human tumors follows vascular endothelial growth factor withdrawal. J Clin Invest 103: 159-165, 1999[Medline] 80. Watanabe Y, Lee SW, Detmar M, et al: Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) delays and induces escape from senescence in human dermal microvascular endothelial cells. Oncogene 14: 2025-2032, 1997[CrossRef][Medline] 81. Brown LF, Berse B, Jackman RW, et al: Increased expression of vascular permeability factor (vascular endothelial growth factor) and its receptors in kidney and bladder carcinomas. Am J Pathol 143: 1255-1262, 1993[Abstract]
82. Brown LF, Berse B, Jackman RW, et al: Expression of vascular permeability factor (vascular endothelial growth factor) and its receptors in adenocarcinomas of the gastrointestinal tract. Cancer Res 53: 4727-4735, 1993 83. Hatva E, Kaipainen A, Mentula P, et al: Expression of endothelial cell-specific receptor tyrosine kinases and growth factors in human brain tumors. Am J Pathol 146: 368-378, 1995[Abstract] 84. Hatva E, Bohling T, Jaaskelainen J, et al: Vascular growth factors and receptors in capillary hemangioblastomas and hemangiopericytomas. Am J Pathol 148: 763-775, 1996[Abstract]
85. Plate KH, Breier G, Millauer B, et al: Up-regulation of vascular endothelial growth factor and its cognate receptors in a rat glioma model of tumor angiogenesis. Cancer Res 53: 5822-5827, 1993 86. Plate KH, Risau W: Angiogenesis in malignant gliomas. Glia 15: 339-347, 1995[CrossRef][Medline]
87. Wizigmann-Voos S, Breier G, Risau W, et al: Up-regulation of vascular endothelial growth factor and its receptors in von Hippel-Lindau disease-associated and sporadic hemangioblastomas. Cancer Res 55: 1358-1364, 1995 88. Detmar M, Brown LF, Schon MP, et al: Increased microvascular density and enhanced leukocyte rolling and adhesion in the skin of VEGF transgenic mice. J Invest Dermatol 111: 1-6, 1998[CrossRef][Medline]
89. Clauss M, Gerlach M, Gerlach H, et al: Vascular permeability factor: A tumor-derived polypeptide that induces endothelial cell and monocyte procoagulant activity, and promotes monocyte migration. J Exp Med 172: 1535-1545, 1990 90. Brown LF, Detmar M, Tognazzi K, et al: Uterine smooth muscle cells express functional receptors (flt-1 and KDR) for vascular permeability factor/vascular endothelial growth factor. Lab Invest 76: 245-255, 1997[Medline] 91. Herold-Mende C, Steiner HH, Andl T, et al: Expression and functional significance of vascular endothelial growth factor receptors in human tumor cells. Lab Invest 79: 1573-1582, 1999[Medline]
92. Robinson GS, Ju M, Shih SC, et al: Nonvascular role for VEGF: VEGFR-1, 2 activity is critical for neural retinal development. FASEB J 15: 1215-1217, 2001
93. Feng D, Nagy JA, Brekken RA, et al: Ultrastructural localization of the vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) receptor-2 (FLK-1, KDR) in normal mouse kidney and in the hyperpermeable vessels induced by VPF/VEGF-expressing tumors and adenoviral vectors. J Histochem Cytochem 48: 545-556, 2000 94. Nagy J, Vasile E, Brown L, et al: Vascular permeability factor/vascular endothelial growth factor-A (VPF/VEGF, VEGF-A) induces lymphangiogenesis as well as angiogenesis. FASEB J 16: A367, 2002 (abstr)
95. Soker S, Kaefer M, Johnson M, et al: Vascular endothelial growth factor-mediated autocrine stimulation of prostate tumor cells coincides with progression to a malignant phenotype. Am J Pathol 159: 651-659, 2001
96. Bachelder RE, Crago A, Chung J, et al: Vascular endothelial growth factor is an autocrine survival factor for neuropilin-expressing breast carcinoma cells. Cancer Res 61: 5736-5740, 2001
97. Dvorak HF, Sioussat TM, Brown LF, et al: Distribution of vascular permeability factor (vascular endothelial growth factor) in tumors: Concentration in tumor blood vessels. J Exp Med 174: 1275-1278, 1991 98. Plate KH, Breier G, Weich HA, et al: Vascular endothelial growth factor is a potential tumour angiogenesis factor in human gliomas in vivo. Nature 359: 845-848, 1992[CrossRef][Medline] 99. Qu H, Nagy JA, Senger DR, et al: Ultrastructural localization of vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) to the abluminal plasma membrane and vesiculovacuolar organelles of tumor microvascular endothelium. J Histochem Cytochem 43: 381-389, 1995[Abstract] 100. Eriksson U, Alitalo K: Structure, expression and receptor-binding properties of novel vascular endothelial growth factors. Curr Top Microbiol Immunol 237: 41-57, 1999[Medline] 101. Claffey KP, Robinson GS: Regulation of VEGF/VPF expression in tumor cells: Consequences for tumor growth and metastasis. Cancer Metastasis Rev 15: 165-176, 1996[CrossRef][Medline] 102. Shih SC, Claffey KP: Hypoxia-mediated regulation of gene expression in mammalian cells. Int J Exp Pathol 79: 347-357, 1998[CrossRef][Medline]
103. Levy AP, Levy NS, Wegner S, et al: Transcriptional regulation of the rat vascular endothelial growth factor gene by hypoxia. J Biol Chem 270: 13333-13340, 1995 104. Forsythe JA, Jiang BH, Iyer NV, et al: Activation of vascular endothelial growth factor gene transcription by hypoxia-inducible factor 1. Mol Cell Biol 16: 4604-4613, 1996[Abstract]
105. Gerber HP, Condorelli F, Park J, et al: Differential transcriptional regulation of the two vascular endothelial growth factor receptor genes: Flt-1, but not Flk-1/KDR, is up-regulated by hypoxia. J Biol Chem 272: 23659-23667, 1997
106. Jain RK: Transport of molecules in the tumor interstitium: A review. Cancer Res 47: 3039-3051, 1987 107. Mukhopadhyay D, Tsiokas L, Zhou XM, et al: Hypoxic induction of human vascular endothelial growth factor expression through c-Src activation. Nature 375: 577-581, 1995[CrossRef][Medline]
108. Rak J, Mitsuhashi Y, Bayko L, et al: Mutant ras oncogenes upregulate VEGF/VPF expression: Implications for induction and inhibition of tumor angiogenesis. Cancer Res 55: 4575-4580, 1995 109. Rak J, Filmus J, Finkenzeller G, et al: Oncogenes as inducers of tumor angiogenesis. Cancer Metastasis Rev 14: 263-277, 1995[CrossRef][Medline] 110. Rak J, Kerbel RS: Ras regulation of vascular endothelial growth factor and angiogenesis. Methods Enzymol 333: 267-283, 2001[Medline] 111. Ohh M, Kaelin WG Jr: The von Hippel-Lindau tumour suppressor protein: New perspectives. Mol Med Today 5: 257-263, 1999[CrossRef][Medline] 112. Clifford SC, Maher ER: Von Hippel-Lindau disease: Clinical and molecular perspectives. Adv Cancer Res 82: 85-105, 2001[Medline]
113. Pal S, Claffey KP, Dvorak HF, et al: The von Hippel-Lindau gene product inhibits vascular permeability factor/vascular endothelial growth factor expression in renal cell carcinoma by blocking protein kinase C pathways. J Biol Chem 272: 27509-27512, 1997
114. Siemeister G, Weindel K, Mohrs K, et al: Reversion of deregulated expression of vascular endothelial growth factor in human renal carcinoma cells by von Hippel-Lindau tumor suppressor protein. Cancer Res 56: 2299-2301, 1996
115. Mukhopadhyay D, Tsiokas L, Sukhatme VP: Wild-type p53 and v-Src exert opposing influences on human vascular endothelial growth factor gene expression. Cancer Res 55: 6161-6165, 1995
116. Pal S, Datta K, Mukhopadhyay D: Central role of p53 on regulation of vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) expression in mammary carcinoma. Cancer Res 61: 6952-6957, 2001
117. Zhang L, Yu D, Hu M, et al: Wild-type p53 suppresses angiogenesis in human leiomyosarcoma and synovial sarcoma by transcriptional suppression of vascular endothelial growth factor expression. Cancer Res 60: 3655-3661, 2000 118. Claffey KP, Abrams K, Shih SC, et al: Fibroblast growth factor 2 activation of stromal cell vascular endothelial growth factor expression and angiogenesis. Lab Invest 81: 61-75, 2001[Medline] 119. Wojta J, Kaun C, Breuss JM, et al: Hepatocyte growth factor increases expression of vascular endothelial growth factor and plasminogen activator inhibitor-1 in human keratinocytes and the vascular endothelial growth factor receptor flk-1 in human endothelial cells. Lab Invest 79: 427-438, 1999[Medline]
120. Stavri GT, Zachary IC, Baskerville PA, et al: Basic fibroblast growth factor upregulates the expression of vascular endothelial growth factor in vascular smooth muscle cells: Synergistic interaction with hypoxia. Circulation 92: 11-14, 1995
121. Derynck R, Goeddel DV, Ullrich A, et al: Synthesis of messenger RNAs for transforming growth factors alpha and beta and the epidermal growth factor receptor by human tumors. Cancer Res 47: 707-712, 1987
122. Slaton JW, Inoue K, Perrotte P, et al: Expression levels of genes that regulate metastasis and angiogenesis correlate with advanced pathological stage of renal cell carcinoma. Am J Pathol 158: 735-743, 2001 123. Berse B, Brown LF, Van de Water L, et al: Vascular permeability factor (vascular endothelial growth factor) gene is expressed differentially in normal tissues, macrophages, and tumors. Mol Biol Cell 3: 211-220, 1992[Abstract]
124. Cullinan-Bove K, Koos RD: Vascular endothelial growth factor/vascular permeability factor expression in the rat uterus: Rapid stimulation by estrogen correlates with estrogen-induced increases in uterine capillary permeability and growth. Endocrinology 133: 829-837, 1993 125. Garrido C, Saule S, Gospodarowicz D: Transcriptional regulation of vascular endothelial growth factor gene expression in ovarian bovine granulosa cells. Growth Factors 8: 109-117, 1993[Medline]
126. Adams J, Carder PJ, Downey S, et al: Vascular endothelial growth factor (VEGF) in breast cancer: Comparison of plasma, serum, and tissue VEGF and microvessel density and effects of tamoxifen. Cancer Res 60: 2898-2905, 2000 127. Sato K, Yamazaki K, Shizume K, et al: Stimulation by thyroid-stimulating hormone and Grave’s immunoglobulin G of vascular endothelial growth factor mRNA expression in human thyroid follicles in vitro and flt mRNA expression in the rat thyroid in vivo. J Clin Invest 96: 1295-1302, 1995[Medline] 128. Soh EY, Sobhi SA, Wong MG, et al: Thyroid-stimulating hormone promotes the secretion of vascular endothelial growth factor in thyroid cancer cell lines. Surgery 120: 944-947, 1996[CrossRef][Medline] 129. Tsopanoglou NE, Maragoudakis ME: On the mechanism of thrombin-induced angiogenesis. J Biol Chem 34: 23969-23976, 1999
130. Kronemann N, Bouloumi A, Bassus S, et al: Aggregating human platelets stimulate expression of vascular endothelial growth factor in cultured vascular smooth muscle cells through a synergistic effect of transforming growth factor-beta(1) and platelet-derived growth factor(AB). Circulation 100: 855-860, 1999 131. Li J, Hampton T, Morgan JP, et al: Stretch-induced VEGF expression in the heart. J Clin Invest 100: 18-24, 1997[Medline]
132. Gruden G, Thomas S, Burt D, et al: Mechanical stretch induces vascular permeability factor in human mesangial cells: Mechanisms of signal transduction. Proc Natl Acad Sci U S A 94: 12112-12116, 1997
133. Chen KD, Li YS, Kim M, et al: Mechanotransduction in response to shear stress: Roles of receptor tryosine kinases, integrins, and Shc. J Biol Chem 274: 18393-18400, 1999
134. Fukumura D, Xu L, Chen Y, et al: Hypoxia and acidosis independently up-regulate vascular endothelial growth factor transcription in brain tumors in vivo. Cancer Res 61: 6020-6024, 2001
135. Hu YL, Tee MK, Goetzl EJ, et al: Lysophosphatidic acid induction of vascular endothelial growth factor expression in human ovarian cancer cells. J Natl Cancer Inst 93: 762-768, 2001
136. Gu JW, Brady AL, Anand V, et al: Adenosine upregulates VEGF expression in cultured myocardial vascular smooth muscle cells. Am J Physiol 277: H595-H602, 1999 137. Nauck M, Karakiulakis G, Perruchoud AP, et al: Corticosteroids inhibit the expression of the vascular endothelial growth factor gene in human vascular smooth muscle cells. Eur J Pharmacol 341: 309-315, 1998[CrossRef][Medline]
138. Nagy JA, Morgan ES, Herzberg KT, et al: Pathogenesis of ascites tumor growth: Angiogenesis, vascular remodeling, and stroma formation in the peritoneal lining. Cancer Res 55: 376-385, 1995
139. Sundberg C, Nagy JA, Brown LF, et al: Glomeruloid microvascular proliferation follows adenoviral vascular permeability factor/vascular endothelial growth factor-164 gene delivery. Am J Pathol 158: 1145-1160, 2001
140. Tabone MD, Landman-Parker J, Arcil B, et al: Are basic fibroblast growth factor and vascular endothelial growth factor prognostic indicators in pediatric patients with malignant solid tumors? Clin Cancer Res 7: 538-543, 2001 141. Mineta H, Miura K, Ogino T, et al: Prognostic value of vascular endothelial growth factor (VEGF) in head and neck squamous cell carcinomas. Br J Cancer 83: 775-781, 2000[CrossRef][Medline]
142. Inoue K, Slaton JW, Karashima T, et al: The prognostic value of angiogenesis factor expression for predicting recurrence and metastasis of bladder cancer after neoadjuvant chemotherapy and radical cystectomy. Clin Cancer Res 6: 4866-4873, 2000
143. Shih CH, Ozawa S, Ando N, et al: Vascular endothelial growth factor expression predicts outcome and lymph node metastasis in squamous cell carcinoma of the esophagus. Clin Cancer Res 6: 1161-1168, 2000
144. Kaya M, Wada T, Akatsuka T, et al: Vascular endothelial growth factor expression in untreated osteosarcoma is predictive of pulmonary metastasis and poor prognosis. Clin Cancer Res 6: 572-577, 2000
145. Heffelfinger SC, Miller MA, Yassin R, et al: Angiogenic growth factors in preinvasive breast disease. Clin Cancer Res 5: 2867-2876, 1999
146. Borre M, Nerstrom B, Overgaard J: Association between immunohistochemical expression of vascular endothelial growth factor (VEGF), VEGF-expressing neuroendocrine-differentiated tumor cells, and outcome in prostate cancer patients subjected to watchful waiting. Clin Cancer Res 6: 1882-1890, 2000
147. Kuniyasu H, Troncoso P, Johnston D, et al: Relative expression of type IV collagenase, E-cadherin, and vascular endothelial growth factor/vascular permeability factor in prostatectomy specimens distinguishes organ-confined from pathologically advanced prostate cancers. Clin Cancer Res 6: 2295-2308, 2000 148. Linderholm B, Tavelin B, Grankvist K, et al: Does vascular endothelial growth factor (VEGF) predict local relapse and survival in radiotherapy-treated node-negative breast cancer? Br J Cancer 81: 727-732, 1999[CrossRef][Medline]
149. Foekens JA, Peters HA, Grebenchtchikov N, et al: High tumor levels of vascular endothelial growth factor predict poor response to systemic therapy in advanced breast cancer. Cancer Res 61: 5407-5414, 2001
150. Cascinu S, Staccioli MP, Gasparini G, et al: Expression of vascular endothelial growth factor can predict event-free survival in stage II colon cancer. Clin Cancer Res 6: 2803-2807, 2000 151. Callagy G, Dimitriadis E, Harmey J, et al: Immunohistochemical measurement of tumor vascular endothelial growth factor in breast cancer: A more reliable predictor of tumor stage than microvessel density or serum vascular endothelial growth factor. Appl Immunohistochem Molecul Morphol 8: 104-109, 2000[CrossRef] 152. Shen GH, Ghazizadeh M, Kawanami O, et al: Prognostic significance of vascular endothelial growth factor expression in human ovarian carcinoma. Br J Cancer 83: 196-203, 2000[CrossRef][Medline] 153. Sato F, Shimada Y, Watanabe G, et al: Expression of vascular endothelial growth factor, matrix metalloproteinase-9 and E-cadherin in the process of lymph node metastasis in oesophageal cancer. Br J Cancer 80: 1366-1372, 1999[CrossRef][Medline] 154. Loncaster JA, Cooper RA, Logue JP, et al: Vascular endothelial growth factor (VEGF) expression is a prognostic factor for radiotherapy outcome in advanced carcinoma of the cervix. Br J Cancer 83: 620-625, 2000[CrossRef][Medline] 155. Yudoh K, Kanamori M, Ohmori K, et al: Concentration of vascular endothelial growth factor in the tumour tissue as a prognostic factor of soft tissue sarcomas. Br J Cancer 84: 1610-1615, 2001[CrossRef][Medline] 156. Abdulrauf SI, Edvardsen K, Ho KL, et al: Vascular endothelial growth factor expression and vascular density as prognostic markers of survival in patients with low-grade astrocytoma. J Neurosurg 88: 513-520, 1998[Medline] 157. Toi M, Hoshina S, Takayanagi T, et al: Association of vascular endothelial growth factor expression with tumor angiogenesis and with early relapse in primary breast cancer. Jpn J Cancer Res 85: 1045-1049, 1994[CrossRef][Medline] 158. Fuhrmann-Benzakein E, Ma MN, Rubbia-Brandt L, et al: Elevated levels of angiogenic cytokines in the plasma of cancer patients. Int J Cancer 85: 40-45, 2000[CrossRef][Medline] 159. Kraft A, Weindel K, Ochs A, et al: Vascular endothelial growth factor in the sera and effusions of patients with malignant and nonmalignant disease. Cancer 85: 178-187, 1999[CrossRef][Medline] 160. Salven P, Manpaa H, Orpana A, et al: Serum vascular endothelial growth factor is often elevated in disseminated cancer. Clin Cancer Res 3: 647-651, 1997[Abstract] 161. Chin KF, Greenman J, Gardiner E, et al: Pre-operative serum vascular endothelial growth factor can select patients for adjuvant treatment after curative resection in colorectal cancer. Br J Cancer 83: 1425-1431, 2000[CrossRef][Medline] 162. Davies MM, Jonas SK, Kaur S, et al: Plasma vascular endothelial but not fibroblast growth factor levels correlate with colorectal liver metastasis vascularity and volume. Br J Cancer 82: 1004-1008, 2000[CrossRef][Medline]
163. George ML, Eccles SA, Tutton MG, et al: Correlation of plasma and serum vascular endothelial growth factor levels with platelet count in colorectal cancer: Clinical evidence of platelet scavenging? Clin Cancer Res 6: 3147-3152, 2000
164. Hefler L, Tempfer C, Obermair A, et al: Serum concentrations of vascular endothelial growth factor in vulvar cancer. Clin Cancer Res 5: 2806-2809, 1999
165. Salven P, Teerenhovi L, Joensuu H: A high pretreatment serum vascular endothelial growth factor concentration is associated with poor outcome in non-Hodgkin’s lymphoma. Blood 90: 3167-3172, 1997
166. Salven P, Orpana A, Joensuu H: Leukocytes and platelets of patients with cancer contain high levels of vascular endothelial growth factor. Clin Cancer Res 5: 487-491, 1999 167. Banks RE, Forbes MA, Kinsey SE, et al: Release of the angiogenic cytokine vascular endothelial growth factor (VEGF) from platelets: Significance for VEGF measurements and cancer biology. Br J Cancer 77: 956-964, 1998[Medline] 168. Gunsilius E, Petzer AL, Gastl G: Correspondence re: P. Salven et al: Leukocytes and platelets of patients with cancer contain high levels of vascular endothelial growth factor—Clin Cancer Res 5:487-91, 1999. Clin Cancer Res 5:2978-2979, 1999 (letter) 169. Kondo S, Asano M, Matsuo K, et al: Vascular endothelial growth factor/vascular permeability factor is detectable in the sera of tumor-bearing mice and cancer patients. Biochim Biophys Acta 1221: 211-214, 1994[Medline] 170. Brown LF, Olbricht SM, Berse B, et al: Overexpression of vascular permeability factor (VPF/VEGF) and its endothelial cell receptors in delayed hypersensitivity skin reactions. J Immunol 154: 2801-2807, 1995[Abstract] 171. Wartiovaara U, Salven P, Mikkola H, et al: Peripheral blood platelets express VEGF-C and VEGF which are released during platelet activation. Thromb Haemost 80: 171-175, 1998[Medline]
172. Mohle R, Green D, Moore MA, et al: Constitutive production and thrombin-induced release of vascular endothelial growth factor by human megakaryocytes and platelets. Proc Natl Acad Sci U S A 94: 663-668, 1997
173. Freeman MR, Schneck FX, Gagnon ML, et al: Peripheral blood T lymphocytes and lymphocytes infiltrating human cancers express vascular endothelial growth factor: A potential role for T cells in angiogenesis. Cancer Res 55: 4140-4145, 1995
174. Jelkmann W: Pitfalls in the measurement of circulating vascular endothelial growth factor. Clin Chem 47: 617-623, 2001
175. Zebrowski BK, Yano S, Liu W, et al: Vascular endothelial growth factor levels and induction of permeability in malignant pleural effusions. Clin Cancer Res 5: 3364-3368, 1999 176. Zebrowski BK, Liu W, Ramirez K, et al: Markedly elevated levels of vascular endothelial growth factor in malignant ascites. Ann Surg Oncol 6: 373-378, 1999[Abstract]
177. Hazelton D, Nicosia RF, Nicosia SV: Vascular endothelial growth factor levels in ovarian cyst fluid correlate with malignancy. Clin Cancer Res 5: 823-829, 1999 178. Jones A, Crew J: Vascular endothelial growth factor and its correlation with superficial bladder cancer recurrence rates and stage progression. Urol Clin North Am 27: 191-197, 2000[CrossRef][Medline] 179. Folkman J: Tumor angiogenesis: Therapeutic implications. N Engl J Med 285: 1182-1186, 1971[Medline] 180. Kerbel RS: Inhibition of tumor angiogenesis as a strategy to circumvent acquired resistance to anti-cancer therapeutic agents. Bioessays 13: 31-36, 1991[CrossRef][Medline] 181. Folkman J: Angiogenesis and angiogenesis inhibition: An overview. EXS 79: 1-8, 1997[Medline] 182. O’Reilly MS, Holmgren L, Shing Y, et al: Angiostatin: A novel angiogenesis inhibitor that mediates the suppression of metastases by a Lewis lung carcinoma. Cell 79: 315-328, 1994[CrossRef][Medline] 183. O’Reilly MS, Boehm T, Shing Y, et al: Endostatin: An endogenous inhibitor of angiogenesis and tumor growth. Cell 88: 277-285, 1997[CrossRef][Medline] 184. Kim KJ, Li B, Winer J, et al: Inhibition of vascular endothelial growth factor-induced angiogenesis suppresses tumour growth in vivo. Nature 362: 841-844, 1993[CrossRef][Medline] 185. Schlaeppi JM, Wood JM: Targeting vascular endothelial growth factor (VEGF) for anti-tumor therapy, by anti-VEGF neutralizing monoclonal antibodies or by VEGF receptor tyrosine-kinase inhibitors. Cancer Metastasis Rev 18: 473-481, 1999[CrossRef][Medline] 186. Klement G, Baruchel S, Rak J, et al: Continuous low-dose therapy with vinblastine and VEGF receptor-2 antibody induces sustained tumor regression without overt toxicity. J Clin Invest 105: R15-R24, 2000[Medline]
187. Browder T, Butterfield CE, Kraling BM, et al: Antiangiogenic scheduling of chemotherapy improves efficacy against experimental drug-resistant cancer. Cancer Res 60: 1878-1886, 2000
188. Brekken RA, Huang X, King SW, et al: Vascular endothelial growth factor as a marker of tumor endothelium. Cancer Res 58: 1952-1959, 1998 189. Ke L, Qu H, Nagy JA, et al: Vascular targeting of solid and ascites tumours with antibodies to vascular endothelial growth factor. Eur J Cancer 32A: 2467-2473, 1996[Medline] 190. Millauer B, Shawver LK, Plate KH, et al: Glioblastoma growth inhibited in vivo by a dominant-negative Flk-1 mutant. Nature 367: 576-579, 1994[CrossRef][Medline]
191. Gerber HP, Kowalski J, Sherman D, et al: Complete inhibition of rhabdomyosarcoma xenograft growth and neovascularization requires blockade of both tumor and host vascular endothelial growth factor. Cancer Res 60: 6253-6258, 2000 192. Ferrara N: Role of vascular endothelial growth factor in the regulation of angiogenesis. Kidney Int 56: 794-814, 1999[CrossRef][Medline]
193. Mordenti J, Thomsen K, Licko V, et al: Efficacy and concentration-response of murine anti-VEGF monoclonal antibody in tumor-bearing mice and extrapolation to humans. Toxicol Pathol 27: 14-21, 1999
194. Mesiano S, Ferrara N, Jaffe RB: Role of vascular endothelial growth factor in ovarian cancer: Inhibition of ascites formation by immunoneutralization. Am J Pathol 153: 1249-1256, 1998 195. Borgstrom P, Bourdon MA, Hillan KJ, et al: Neutralizing anti-vascular endothelial growth factor antibody completely inhibits angiogenesis and growth of human prostate carcinoma micro tumors in vivo. Prostate 35: 1-10, 1998[CrossRef][Medline]
196. Lee CG, Heijn M, di Tomaso E, et al: Anti-vascular endothelial growth factor treatment augments tumor radiation response under normoxic or hypoxic conditions. Cancer Res 60: 5565-5570, 2000 197. Martiny-Baron G, Marme D: VEGF-mediated tumour angiogenesis: A new target for cancer therapy. Curr Opin Biotechnol 6: 675-680, 1995[CrossRef][Medline] 198. Rowe DH, Huang J, Li J, et al: Suppression of primary tumor growth in a mouse model of human neuroblastoma. J Pediatr Surg 35: 977-981, 2000[CrossRef][Medline] 199. Brekken RA, Thorpe PE: VEGF-VEGF receptor complexes as markers of tumor vascular endothelium. J Control Release 74: 173-181, 2001[CrossRef][Medline]
200. Cooke SP, Boxer GM, Lawrence L, et al: A strategy for antitumor vascular therapy by targeting the vascular endothelial growth factor: Receptor complex. Cancer Res 61: 3653-3659, 2001
201. Brekken RA, Overholser JP, Stastny VA, et al: Selective inhibition of vascular endothelial growth factor (VEGF) receptor 2 (KDR/Flk-1) activity by a monoclonal anti-VEGF antibody blocks tumor growth in mice. Cancer Res 60: 5117-5124, 2000 202. Thorpe PE, Ran S: Tumor infarction by targeting tissue factor to tumor vasculature. Cancer J Sci Am 6: S237-S244, 2000 (suppl 3)
203. Benjamin LE, Keshet E: Conditional switching of vascular endothelial growth factor (VEGF) expression in tumors: Induction of endothelial cell shedding and regression of hemangioblastoma-like vessels by VEGF withdrawal. Proc Natl Acad Sci U S A 94: 8761-8766, 1997
204. Jain RK, Safabakhsh N, Sckell A, et al: Endothelial cell death, angiogenesis, and microvascular function after castration in an androgen-dependent tumor: Role of vascular endothelial growth factor. Proc Natl Acad Sci U S A 95: 10820-10825, 1998
205. Drevs J, Hofmann I, Hugenschmidt H, et al: Effects of PTK787/ZK 222584, a specific inhibitor of vascular endothelial growth factor receptor tyrosine kinases, on primary tumor, metastasis, vessel density, and blood flow in a murine renal cell carcinoma model. Cancer Res 60: 4819-4824, 2000
206. Shaheen RM, Davis DW, Liu W, et al: Antiangiogenic therapy targeting the tyrosine kinase receptor for vascular endothelial growth factor receptor inhibits the growth of colon cancer liver metastasis and induces tumor and endothelial cell apoptosis. Cancer Res 59: 5412-5416, 1999
207. Wedge SR, Ogilvie DJ, Dukes M, et al: ZD4190: An orally active inhibitor of vascular endothelial growth factor signaling with broad-spectrum antitumor efficacy. Cancer Res 60: 970-975, 2000 208. Basu S, Nagy JA, Pal S, et al: The neurotransmitter dopamine inhibits angiogenesis induced by vascular permeability factor/vascular endothelial growth factor. Nat Med 7: 569-574, 2001[CrossRef][Medline]
209. Huang X, Molema G, King S, et al: Tumor infarction in mice by antibody-directed targeting of tissue factor to tumor vasculature. Science 275: 547-550, 1997
210. Yu JL, Rak JW, Coomber BL, et al: Effect of p53 status on tumor response to antiangiogenic therapy. Science 295: 1526-1528, 2002 211. Bevacizumab: Anti-VEGF monoclonal antibody, avastin, rhumab-VEGF. Drugs R D 3:28-30, 2002 212. Chen HX, Gore-Langton RE, Cheson BD: Clinical trials referral resource: Current clinical trials of the anti-VEGF monoclonal antibody bevacizumab. Oncology (Huntingt) 15:1017, 1020, 1023-1026, 2001
213. Gorski DH, Beckett MA, Jaskowiak NT, et al: Blockage of the vascular endothelial growth factor stress response increases the antitumor effects of ionizing radiation. Cancer Res 59: 3374-3378, 1999
214. Bergers G, Javaherian K, Lo KM, et al: Effects of angiogenesis inhibitors on multistage carcinogenesis in mice. Science 284: 808-812, 1999 Submitted October 18, 2001; accepted July 19, 2002.
This article has been cited by other articles:
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|||||||||||
|
|||||||||||
|
|
Copyright © 2002 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
|
TOP
ABSTRACT
INTRODUCTION
, PI3-K, GAP, the Ras GTPase-activating protein, MAPK, and others (reviewed in
), is degraded rapidly under normoxic conditions by the ubiquitin pathway; however, when stabilized by hypoxia, HIF-1
