REVIEW Vascular endothelial growth factor and its receptors ... - Nature

Leukemia (2003) 17, 1961–1966 & 2003 Nature Publishing Group All rights reserved 0887-6924/03 $25.00 www.nature.com/leu

REVIEW Vascular endothelial growth factor and its receptors in multiple myeloma R Ria1, AM Roccaro1, F Merchionne1, A Vacca1, F Dammacco1 and D Ribatti2 1 Department of Biomedical Sciences and Human Oncology, Bari, Italy; and 2Department of Human Anatomy and Histology, University of Bari Medical School, Bari, Italy

Multiple myeloma (MM) progresses from an avascular to a vascular phase (active MM) accompanied by a significant increase in microvessel density in the bone marrow. This article summarizes the literature concerning the specific role played by vascular endothelial growth factor (VEGF) in this process. Recent applications of antiangiogenic agents that interfere with VEGF signaling and block MM progression are also described. Leukemia (2003) 17, 1961–1966. doi:10.1038/sj.leu.2403076 Keywords: angiogenesis; endothelial cells; multiple myeloma; tumor growth; vascular endothelial growth factor

Angiogenesis and tumor angiogenesis Angiogenesis, the formation of new blood vessels from preexisting ones, takes place in various physiological and pathological conditions, such as embryonic development, wound healing, the menstrual cycle and chronic inflammation and tumors.1,2 The angiogenic cascade is a multistep process that includes sequential basement membrane degradation, endothelial cell migration and invasion of the surrounding extracellular matrix (ECM), endothelial cell proliferation and capillary lumen formation, while investment of the vessel wall with pericytes and subsequent inhibition of endothelial proliferation, basement membrane reconstitution and junctional complex formation stabilize the newly formed microvasculature. Angiogenesis and the production of angiogenic factors are fundamental for tumor progression in the form of growth, invasion and metastasis.1 Tumor angiogenesis is linked to a switch in the equilibrium between positive and negative regulators3 and mainly depend on the release by neoplastic cells of growth factors specific for endothelial cells and able to stimulate growth of the host’s blood vessels.

Vascular endothelial growth factor/vascular permeability factor Vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) is a major regulator of tumor-associated angiogenesis and promotes tumor growth, invasion and metastasis.4 The VEGF family includes VEGF-A, VEGF-B, VEGF-C, VEGF-D, VEGF-E and placenta growth factor. VEGF gene encodes for VEGF-A isoforms (VEGF-A121–206) by alternative splicing that differently encodes exons 6 and 7 (Figure 1a), where the peptides responsible for the heparin-binding capacity are Correspondence: Professor Dr D Ribatti, Department of Human Anatomy and Histology, Policlinico, Piazza Giulio Cesare, 11, I-70124 Bari, Italy; Fax: þ 39 080 5478 310 Email: [email protected] Received 28 April 2003; accepted 12 June 2003

located.5 The heparin-binding domains help VEGF-A to anchor to the ECM and are involved in binding to heparin sulfate and presentation to VEGF receptors (VEGFR).6 VEGF isoforms with higher heparin affinity are rapidly sequestrated by the heparansulfate proteoglycans located at the endothelial cell surface and in the ECM. Moreover, these proteoglycans are an extracellular storage of VEGF isoforms and enhance the interactions with their own receptors.7 Several factors regulate VEGF expression, including interleukin (IL)-1b,8 IL-6,9 IL-10 and IL-13,10 fibroblast growth factor4 (FGF-4),11 platelet-derived growth factor (PDGF),12 transforming growth factor (TGF)-b,13 insulin-like growth factor-1,14 tumor necrosis factor (TNF)-a,15 gonadotropins,16 hypoxia and nitric oxide.17,18 VEGF expression may also be regulated by the von Hippel Landau and the p53 genes. Mutations of these two genes are associated with an increased angiogenesis and an increased VEGF expression.19,20

VEGF receptors All the VEGF isoforms share common tyrosine kinase receptors (VEGFR-1 or Flt-1, VEGFR-2 or KDR/Flk-1, VEGFR-3 or Flt-4) (Figure 1b).21 VEGF-A binds with high-affinity VEGFR-1 and VEGFR-2 with high affinity and plays an essential role in vasculogenesis and angiogenesis.22 It has also been shown to induce lymphangiogenesis through VEGFR-2. VEGF-B overlaps VEGF-A activities by activating VEGFR-1.23 VEGF-C and VEGFD are both angiogenic via VEGFR-2 and VEGFR-3 and lymphangiogenic (primarily VEGF-D) via VEGFR-3.24,25 VEGFR have seven immunoglobulin-like loops in their extracellular domain and display tyrosine kinase activity in their intracellular domains.26 VEGFR-1 and VEGFR-2 are expressed on the surface of endothelial cells as well as trophoblast and placenta cells,27 monocytes,28,29 mesangial cells30 (VEGFR-1), hematopoietic stem cells31,32 and retinal progenitor cells33 (VEGFR-2), while VEGFR-3 is expressed on the surface of lymphatic endothelial cells.34 A nonkinase receptor, neuropilin-1, initially shown to mediate guidance of neurite growth, acts as a high-affinity coreceptor and enhances the binding of VEGF-A to VEGFR-2 and is expressed on the surface of endothelial and tumor cells.35

VEGFR signaling pathway VEGFR via phosphotyrosine residues located in the carboxyterminal region (Figure 2) may activate a tyrosine kinase cascade involving various intracellular proteins, particularly phosphatidyl-inositol-30 kinase.36 Mice expressing only the extracellular domain of VEGFR-1 develop normally,37 suggesting that

VEGF in multiple myeloma R Ria et al

1962

a

Exon 1-

6

6’

8

7

21

VEGF206 VEGF189 VEGF165 VEGF145 VEGF121

b

S S

adhesion plaques and the reorganization of actin fibers.38 Other different transduction pathways are also involved, such as the proteins Fyn and Yes of the Src family, Nck and SHP-1 and SHP2 phosphatases for VEGFR-1,39,40 and Shc and Grb2 for VEGFR2 and VEGFR-3.41,42 MAP kinases (MAPK) are the final effectors of the signal to the nucleus, where they modulate the expression of genes involved in several biological activities of endothelial cells, such as proliferation, migration and survival.43 The three best-characterized families of MAPK are the extracellular signal regulated kinase (ERK1/2), stress-activated protein kinase-1 (SAPK1) and SAPK2/p38 kinases. Treating endothelial cells with VEGF activates both ERK1/2 and SAPK2/p38 MAPK and increases cell migration and incorporation of thymidine into DNA.44 This increased migration and cell proliferation is completely dependent on activation of VEGFR-2, since it is totally inhibited by a VEGFR-2 blocking antibody.45 These results are consistent with the concept that VEGFR-2 is a positive regulator of angiogenesis and that VEGFR-1 is involved in the downregulation of the VEGFR-2-mediated events.

Neuropilin-1 Neuropilin-2 Heparan-sulphate proteoglycane

VEGFR-1 VEGFR-2 VEGFR-3 (Flt-1) (KDR/Flk-1) (Flt-4)

Figure 1 (a) Alternative splicing of the mRNA for VEGF-A. (b) VEGF receptors. All the VEGF receptors, neuropilin-1 and -2 and heparin sulfate proteoglycans cooperate on the surface of endothelial cells in the VEGF signaling pathway responsible for the angiogenesis process.

VEGF

Focal adhesion

Cytoskeletal Organization

P

P

P

P

PI3K

FAK SHC PKB

Ras Cell survival MAP

Gene expression

Proliferation Migration

Angiogenesis

Figure 2

Angiogenesis in multiple myeloma In multiple myeloma (MM), bone marrow angiogenesis measured as microvessel density (MVD) increases with progression from gammopathy of undetermined significance (MGUS) to nonactive MM and the active MM, and is related with the plasma cell labeling index.46,47 MVD is five- to six-fold larger in active MM compared to nonactive MM or MGUS.47 Assuming that MVD depends on angiogenesis, these results are consistent with the notion that angiogenesis favors expansion of the MM mass by promoting plasma cell proliferation. Increased MVD and high bone marrow angiogenesis are an adverse prognostic factor in MM.48,49 CD34-positive microvessel areas in the bone marrow of patients with newly diagnosed MM correlate in a multivariate analysis with bone marrow plasma cell infiltration and b2-microglobulin.50 Moreover, after chemotherapy, MVD decreases significantly in patients in complete or partial remission.50 Myeloma plasma cells produce and release angiogenic factors such as FGF-2 and VEGF in their conditioned medium (CM)47,51 and also induce angiogenesis in vivo in the chick chorioallantoic membrane assay.47 They secrete matrix metalloproteinase-2 and -9 (MMP-2 and MMP-9) and urokinase-type plasminogen activator47 and cytokines recruiting inflammatory cells, such as mast cells that then induce angiogenesis through secretion of angiogenic factors in their granules.52 All these findings indicate that myeloma plasma cells induce angiogenesis directly via the secretion of angiogenic cytokines and indirectly by induction of host inflammatory cell infiltration, and degrade the ECM with their matrix-degrading enzymes. This, in association with their interaction with the ECM proteins through the expression of adhesion molecules,53,54 explains their proliferation and diffusion in intra- and extramedullary sites.

VEGF receptors signaling pathway.

Role of VEGF in progression of MM signaling through the kinase domain is dispensable for endothelial cell differentiation and angiogenesis. The signal transduction pathway involving VEGFR is mediated by focal adhesion proteins such as FAK, paxillin and cortactin, which are responsible for the stabilization of focal Leukemia

It is likely that VEGF-A exerts autocrine effects, for example, by stimulating motility and survival on tumor cells that express VEGFR.55,56 VEGFR are predominant in endothelial cells surrounding or penetrating malignant tissue, but absent from vascular cells in the surrounding normal tissue.57


1963 This finding suggests that VEGFR expression is induced in endothelial cells during tumor angiogenesis by VEGF secreted by tumor cells. The paracrine role of VEGF in MM was first proposed by Dankbar et al,58 who found that IL-6 stimulation of plasma cells purified from the marrow of MM patients resulted in an increase in VEGF secretion. Similarly, stimulation of endothelial cells and bone marrow stromal cells with VEGF induced a significant and dose-dependent increase in IL-6 secretion. IL-6 is a potent growth factor for myeloma cells and an inhibitor of plasma cell apoptosis. Elevated serum IL-6 receptor concentrations are associated with a poor prognosis in MM and used as an indicator of disease activity.59 Other cytokines, including TNFa, have been reported to be involved in the control of VEGF production by myeloma cells.60 Moreover, VEGF directly, or indirectly through its stimulatory activity on TNF-a and Il-b1 stimulates the activation of osteoclasts and thus contributes to the lytic lesions in MM.61 Bellamy et al 62 and Podak et al 63,64 reported expression of VEGFR-1 by myeloma cells by immunohistochemical and RT-PCR studies and Kumar et al 65 have revealed expression of VEGFR-1 and VEGFR-2 by both myeloma cell lines and primary myeloma cells. Elevated serum VEGF in MM patients51 is correlated with both increased angiogenesis in MM bone marrow and a higher plasma cell labeling index.47,66 Binding of MM cells to bone marrow stromal cells markedly upregulates VEGF secretion.67 We have demonstrated that VEGF is secreted by myeloma cells and stimulates proliferation and chemotaxis in both endothelial cells (VEGFR-2 signaling) and stromal cells (VEGFR-1 signaling).68 Stromal cells, in turn, secrete VEGF-C and VEGF-D, which interact with plasma cells (VEGFR-3 signaling). We also noted higher VEGF expression in MM than in MGUS and showed that the increased proliferation and chemotaxis displayed by endothelial and stromal cells in response to plasma cells CM is not fully abolished by addition of VEGF antibody.68 The secretion of other angiogenic cytokines may thus be presumed. The data also show that VEGF also plays an important role in both autocrine and paracrine growth of MM cells.

VEGF as a potential target for antiangiogenic treatment Ongoing studies on antiangiogenic treatment are reviewed by the National Cancer Institute (http://www.cancer.gov). There are many clinical studies on the use of antiangiogenic drugs in hematological malignancies. The VEGF signaling pathway can be inhibited at various levels, that is, by blocking the activity of VEGF with monoclonal antibodies,69 blocking the VEGFR with specific inhibitors70 or interfering with the tyrosine kinases activated by the VEGF/VEGFR interaction.71 Systemically administered antibodies to VEGF-A accumulate selectively in tumor vessels in much higher concentrations than in normal tissue.72 These antibodies and those that block VEGF-A-R retard tumor growth and reduce tumor size in mice.73-75 The latest antibodies selectively recognize the complex that VEGF-A forms with VEGFR-2 on vascular endothelium.76 Preclinical studies with VEGF-neutralizing antibodies had shown that inhibition of VEGF inhibits MMP production and induction of apoptosis in cells expressing VEGFR,77 suppresses the production of TNF-a and IL-1b in bone marrow stromal cells and inhibits leukemia colony formation in cultures of cells from patients with chronic

myelomonocytic leukemia and refractory anemia with blast excess.78 A humanized murine anti-VEGF monoclonal antibody, Bevacizumab, that recognizes all VEGF isoforms without crossreactivity with other growth factors has displayed potent antitumor activity in experimental models.77 Some phase I and II studies with Bevacizumab alone or in association with other agents are under way in sarcomas, renal, breast and lung cancer and chronic myeloid leukemia.79,80 Another antiangiogenic target is the blockade of VEGFR or the tyrosine kinase proteins involved in signal transduction. Small selective nonimmunogenic synthetic molecules have shown specific activity associated with an acceptable toxicity profile and good resistance to enzyme lysis.81 These compounds show good inhibition of VEGFR and may inhibit tumor cells expressing these targets. Inhibition of VEGFR signaling pathway can downregulate angiogenesis and its associated features in bone marrow of patients with MM. Thalidomide and its immunomodulatory derivatives,82 the proteasome inhibitor PS 34183 and arsenic trioxide,84,85 directly induce apoptosis or G1 growth arrest in drug-resistant MM cell lines and MM patient cells. They also inhibit the transcription, secretion and actions of cytokines, such as IL-6, VEGF and TNF-a. Gupta et al 67 found that both thalidomide and its analog ImiD1 (cc 4047) reduce VEGF and IL-6 secretion in cocultures of bone marrow stromal cells and MM cells. Finally, the postulated mechanism of action of 2-methoxyestradiol in MM includes downregulation of VEGF expression. Lin et al 86 investigated the effect of PTK 787, a tyrosine kinase inhibitor, initially designed to inhibit VEGF signal transduction by binding directly to the ATP-binding sites of VEGFR, both directly on MM cells and in the bone marrow. They found that PTK 787 directly inhibits proliferation and migration of MM cell lines and patient MM cells that express VEGFR-1. It enhances the anti-MM activity of dexamethasone, overcomes the protective effect of IL-6 against dexamethasone-induced MM cell apoptosis and inhibits the secretion of IL-6 induced by binding of MM cells to bone marrow stromal cells as the resultant proliferation of adherent MM cells. The compound SU6668, an inhibitor of thyrosine kinase of VEGFR, is currently being investigated in a phase II MM study.87

Concluding remarks The expression levels of VEGF, as well as MVD, as indicators of angiogenesis are accepted parameters in hematological tumors and correlated with the clinical outcome. The importance of angiogenesis in MM is unquestionable, as well as the central role played by VEGF in survival, proliferation and diffusion of plasma cells with paracrine and autocrine mechanisms. Employment of an antibody against VEGF and small molecule tyrosine kinase inhibitors to interfere with its signaling illustrates the potential of antiangiogenic approaches in the treatment of MM. Nevertheless, several questions are still unsolved. Treatment directed against VEGF-A for example is effective, but only initially. Tumors eventually escape from inhibition by muting to express other angiogenic growth factors.88

Acknowledgements This work is supported in part by Associazione Italiana per la Ricerca sul Cancro (AIRC, Milan) and Ministry for Education, the Universities and Research (MIUR, ‘Molecular Engineering – C03’ Leukemia


1964 funds, Interuniversity Funds for Basic Research (FIRB), Rome, Italy). RR is the recipient of a fellowship from the European Union x94/342/CE.

References 1 Folkman J. Angiogenesis in cancer, vascular, rheumatoid and other disease. Nat Med 1995; 1: 27–31. 2 Risau W. Mechanisms of angiogenesis. Nature 1997; 386: 671–674. 3 Hanahan D, Folkman J. Patterns and emerging mechanisms of the angiogenic switch during tumorigenesis. Cell 1996; 86: 353–364. 4 Dvorak HF. Vascular permeability factor/vascular endothelial growth factor: a critical cytokine in tumor angiogenesis and a potential target for diagnosis and therapy. J Clin Oncol 2002; 20: 4368–4380. 5 Robinson CJ, Stringer SE. The splice variants of vascular endothelial growth factor (VEGF) and their receptors. J Cell Sci 2001; 114: 853–865. 6 Poltorak Z, Cohen T, Sivan R et al. VEGF 145, a secreted vascular endothelial growth factor isoform that binds to extracellular matrix. J Biol Chem 1997; 272: 7151–7158. 7 Plouet J, Moro F, Bertagnolli S, Coldeboeuf N, Mazarguil H, Clamens S et al. Extracellular cleavage of the vascular endothelial growth factor 189-amino acid form by urokinase is required for its mitogenic effect. J Biol Chem 1997; 272: 13390–13396. 8 Li J, Perrella MA, Tsai JC, Yet SF, Hsieh CM, Yoshizumi M et al. Induction of vascular endothelial growth factor gene expression by interleukin-1 beta in rat aortic smooth muscle cells. J Biol Chem 1995; 270: 308–312. 9 Cohen T, Nahari D, Cerem LW, Neufeld G, Levi BZ. Interleukin 6 induces the expression of vascular endothelial growth factor. J Biol Chem 1996; 271: 736–741. 10 Matsumoto K, Ohi H, Kanmatsuse K. Interleukin 10 and interleukin 13 synergize to inhibit vascular permeability factor release by peripheral blood mononuclear cells from patients with lipoid nephrosis. Nephron 1997; 77: 212–218. 11 Deroanne CF, Hajitou A, Calberg-Bacq CM, Nusgens BV, Lapiere CM. Angiogenesis by fibroblast growth factor 4 is mediated through an autocrine up-regulation of vascular endothelial growth factor expression. Cancer Res 1997; 57: 5590–5597. 12 Finkenzeller G, Sparacio A, Technau A, Marme D, Siemeister G. Sp1 recognition sites in the proximal promoter of the human vascular endothelial growth factor gene are essential for plateletderived growth factor-induced gene expression. Oncogene 1997; 15: 669–676. 13 Pertovaara L, Kaipainen A, Mustonen T, Orpana A, Ferrara N, Saksela O et al. Vascular endothelial growth factor is induced in response to transforming growth factor-beta in fibroblastic and epithelial cells. J Biol Chem 1994; 269: 6271–6274. 14 Goad DL, Rubin J, Wang H, Tashjian Jr AH, Patterson C. Enhanced expression of vascular endothelial growth factor in human SaOS-2 osteoblast-like cells and murine osteoblasts induced by insulin-like growth factor I. Endocrinology 1996; 137: 2262–2268. 15 Ryuto M, Ono M, Izumi H, Yoshida S, Weich HA, Kohno K et al. Induction of vascular endothelial growth factor by tumor necrosis factor alpha in human glioma cells. Possible roles of SP-1. J Biol Chem 1996; 271: 28220–28228. 16 Wang TH, Horng SG, Chang CL, Wu HM, Tsai YJ, Wang HS et al. Human chorionic gonadotropin-induced ovarian hyperstimulation syndrome is associated with up-regulation of vascular endothelial growth factor. J Clin Endocrinol Metab 2002; 87: 3300–3308. 17 Dembinska-Kiec A, Dulak J, Partyka L, Krzesz R, Dudek D, Bartus S et al. Induction of nitric oxide synthase (NOS) and vascular endothelial growth factor (VEGF) in experimental model of angioplasty and heart ischemia. Adv Exp Med Biol 1997; 433: 163–167. 18 Dembinska-Kiec A, Dulak J, Partyka L, Huk I, Mailnski T. VEGFnitric oxide reciprocal regulation. Nat Med 1997; 3: 1177. 19 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 1995; 55: 6161–6165. 20 Mukhopadhyay D, Knebelmann B, Cohen HT, Ananth S, Sukhatme VP. The von Hippel–Lindau tumor suppressor Leukemia

21 22

23 24

25

26 27

28

29

30

31

32

33

34

35

36 37

38 39

40

gene product interacts with Sp1 to repress vascular endothelial growth factor promoter activity. Mol Cell Biol 1997; 17: 5629–5639. Klagsbrun M, D’Amore PA. Vascular endothelial growth factor and its receptors. Cytokine Growth Factor Rev 1996; 7: 259–270. Larcher F, Murillas R, Bolontrade M, Conti CJ, Jorcano JL. VEGF/VPF overexpression in skin of transgenic mice induces angiogenesis, vascular hyperpermeability and accelerated tumor development. Oncogene 1998; 17: 303–311. Olofsson B, Jeltsch M, Eriksson U, Alitalo K. Current biology of VEGF-B and VEGF-C. Curr Opin Biotechnol 1999; 10: 528–535. Hamada K, Oike Y, Takakura N, Ito Y, Jussila L, Dumont DJ et al. VEGF-C signaling pathways through VEGFR-2 and VEGFR-3 in vasculoangiogenesis and hematopoiesis. Blood 2000; 96: 3793–3800. Achen MG, Williams RA, Baldwin ME, Lai P, Roufail S, Alitalo K et al. The angiogenic and lymphangiogenic factor vascular endothelial growth factor-D exhibits a paracrine mode of action in cancer. Growth Factors 2002; 20: 99–107. Shibuya M, Ito N, Claesson-Welsh L. Structure and function of vascular endothelial growth factor receptor-1 and -2. Curr Top Microbiol Immunol 1999; 237: 59–83. Shore VH, Wang TH, Wang CL, Torry RJ, Caudle MR, Torry DS. Vascular endothelial growth factor, placenta growth factor and their receptors in isolated human trophoblast. Placenta 1997; 18: 657–665. Barleon B, Sozzani S, Zhou D, Weich HA, Mantovani A, Marme D. Migration of human monocytes in response to vascular endothelial growth factor (VEGF) is mediated via the VEGF receptor flt-1. Blood 1996; 87: 3336–3343. Sawano A, Iwai S, Sakurai Y, Ito M, Shitara K, Nakahata T et al. Flt-1, vascular endothelial growth factor receptor 1, is a novel cell surface marker for the lineage of monocyte–macrophages in humans. Blood 2001; 97: 785–791. Thomas S, Vanuystel J, Gruden G, Rodriguez V, Burt D, Gnudi L et al. Vascular endothelial growth factor receptors in human mesangium in vitro and in glomerular disease. J Am Soc Nephrol 2000; 11: 1236–1243. Peichev M, Naiyer AJ, Pereira D, Zhu Z, Lane WJ, Williams M et al. Expression of VEGFR-2 and AC133 by circulating human CD34(+) cells identifies a population of functional endothelial precursors. Blood 2000; 95: 952–958. Gerber HP, Malik AK, Solar GP, Sherman D, Liang XH, Meng G et al. VEGF regulates haematopoietic stem cell survival by an internal autocrine loop mechanism. Nature 2002; 417: 954–958. Suzuma K, Takagi H, Otani A, Suzuma I, Honda Y. Increased expression of KDR/Flk-1 (VEGFR-2) in murine model of ischemiainduced retinal neovascularization. Microvasc Res 1998; 56: 183–191. Kukk E, Lymboussaki A, Taira S, Kaipainen A, Jeltsch M, Joukov V et al. VEGF-C receptor binding and pattern of expression with VEGFR-3 suggests a role in lymphatic vascular development. Development 1996; 122: 3829–3837. Soker S, Takashima S, Miao HQ, Neufeld G, Klagsbrun M. Neuropilin-1 is expressed by endothelial and tumor cells as an isoform-specific receptor for vascular endothelial growth factor. Cell 1998; 92: 735–745. Qi JH, Claesson-Welsh L. VEGF-induced activation of phosphoinositide 3-kinase is dependent on focal adhesion kinase. Exp Cell Res 2001; 263: 173–182. Hiratsuka S, Minowa O, Kuno J, Noda T, Shibuya M. Flt-1 lacking the tyrosine kinase domain is sufficient for normal development and angiogenesis in mice. Proc Natl Acad Sci USA 1998; 95: 9349–9354. Gingras D, Lamy S, Beliveau R. Tyrosine phosphorylation of the vascular endothelial-growth-factor receptor-2 (VEGFR-2) is modulated by Rho proteins. Biochem J 2000; 348: 273–280. Waltenberger J, Claesson-Welsh L, Siegbahn A, Shibuya M, Heldin CH. Different signal transduction properties of KDR and Flt1, two receptors for vascular endothelial growth factor. J Biol Chem 1994; 269: 26988–26995. Kroll J, Waltenberger J. The vascular endothelial growth factor receptor KDR activates multiple signal transduction pathways


1965 41

42

43

44

45

46 47

48

49

50

51

52

53

54

55

56

57

in porcine aortic endothelial cells. J Biol Chem 1997; 272: 32521–32527. Fournier E, Blaikie P, Rosnet O, Margolis B, Birnbaum D, Borg JP. Role of tyrosine residues and protein interaction domains of SHC adaptor in VEGF receptor 3 signaling. Oncogene 1999; 18: 507–514. Zanetti A, Lampugnani MG, Balconi G, Breviario F, Corada M, Lanfrancone L et al. Vascular endothelial growth factor induces SHC association with vascular endothelial cadherin: a potential feedback mechanism to control vascular endothelial growth factor receptor-2 signaling. Arterioscler Thromb Vasc Biol 2002; 22: 617–622. Meyer RD, Dayanir V, Majnoun F, Rahimi N. The presence of a single tyrosine residue at the carboxyl domain of vascular endothelial growth factor receptor-2/FLK-1 regulates its autophosphorylation and activation of signaling molecules. J Biol Chem 2002; 277: 27081–27087. Rousseau S, Houle F, Landry J, Huot J. P38 MAP kinase activation by vascular endothelial growth factor mediates actin reorganization and cell migration in human endothelial cells. Oncogene 1997; 15: 2169–2177. Rousseau S, Houle F, Kotanides H, Witte L, Waltenberger J, Landry J et al. Vascular endothelial growth factor (VEGF)-driven actinbased motility is mediated by VEGFR2 and requires concerted activation of stress-activated protein kinase-2 (SAPK2/p38) and geldanamycin-sensitive phosphorylation of focal adhesion kinase. J Biol Chem 2000; 275: 10661–10672. Vacca A, Ribatti D, Roncali L, Ranieri G, Serio G, Silvestris F et al. Bone marrow angiogenesis and progression in multiple myeloma. Br J Haematol 1994; 87: 503–508. Vacca A, Iurlaro M, Ribatti D, Minischetti M, Nico B, Ria R et al. Bone marrow neovascularization, plasma cell angiogenic potential and matrix metalloproteinase-2 secretion parallel progression of human multiple myeloma. Blood 1999; 93: 3064–3073. Sezer O, Eucker J, Bauhuis C, Schweigert M, Luftner D, Kalus U et al. Bone marrow microvessel density is a prognostic factor for survival in patients with multiple myeloma. Ann Hematol 2000; 79: 574–577. Iwasaki T, Hamano T, Ogata A, Hashimoto N, Kitano M, Kakishita E. Clinical significance of vascular endothelial growth factor and hepatocyte growth factor in multiple myeloma. Br J Haematol 2002; 116: 796–802. Sezer O, Niemoller K, Jakob C, Zavrski I, Heider U, Eucker J et al. Relationship between bone marrow angiogenesis and plasma cell infiltration and serum beta2-microglobulin levels in patients with multiple myeloma. Ann Hematol 2001; 80: 598–601. Di Raimondo F, Azzaro MP, Palumbo G, Bagnato S, Giustolisi G, Floridia P et al. Angiogenic factors in multiple myeloma: higher levels in bone marrow than in peripheral blood. Haematologica 2000; 85: 800–805. Ribatti D, Vacca A, Nico B, Quondamatteo F, Ria R, Minischetti M et al. Bone marrow angiogenesis and mast cell density increase simultaneously with progression of human multiple myeloma. Br J Cancer 1999; 79: 451–455. Rawstron AC, Barrans SL, Blythe D, English A, Richards SJ, Fenton JA et al. In multiple myeloma, only a single stage of neoplastic plasma cell differentiation can be identified by VLA-5 and CD45 expression. Br J Haematol 2001; 113: 794–802. Ria R, Vacca A, Ribatti D, Di Raimondo F, Merchionne F, Dammacco F. aVb3 integrin engagement enhances cell invasiveness in human multiple myeloma. Haematologica 2002; 87: 836–845. Bachelder RE, Crago A, Chung J, Wendt MA, Shaw LM, Robinson G et al. Vascular endothelial growth factor is an autocrine survival factor for neuropilin-expressing breast carcinoma cells. Cancer Res 2001; 61: 5736–5740. Soker S, Kaefer M, Johnson M, Klagsbrun M, Atala A, Freeman MR. Vascular endothelial growth factor-mediated autocrine stimulation of prostate tumor cells coincides with progression to a malignant phenotype. Am J Pathol 2001; 159: 651–659. Nicosia RF. What is the role of vascular endothelial growth factorrelated molecules in tumor angiogenesis? Am J Pathol 1998; 153: 11–16.

58 Dankbar B, Padro T, Leo R, Feldmann B, Kropff M, Mesters RM et al. Vascular endothelial growth factor and interleukin-6 in paracrine tumor-stromal cell interactions in multiple myeloma. Blood 2000; 95: 2630–2636. 59 Pulkki K, Pelliniemi TT, Kajamaki A, Tienhaara A, Laakso M, Lahtinen R. Soluble interleukin-6 receptor as a prognostic factor in multiple myeloma. Br J Haematol 1996; 92: 370–374. 60 Neufeld G, Cohen T, Gengrinovitch S, Poltorak Z. Vascular endothelial growth factor (VEGF) and its receptors. FASEB J 1999; 13: 9–22. 61 Nakagawa M, Kaneda T, Arakawa T, Morita S, Sato T, Yomada T et al. Vascular endothelial growth factor (VEGF) directly enhances osteoclastic bone resorption and survival of mature osteoclasts. FEBS Lett 2000; 473: 161–164. 62 Bellamy WT, Richter L, Frutiger Y, Grogan TM. Expression of vascular endothelial growth factor and its receptors in hematopoietic malignancies. Cancer Res 1999; 59: 728–733. 63 Podar K, Tai YT, Davies FE, Lentzsch S, Sattler M, Hideshima T et al. Vascular endothelial growth factor triggers signaling cascades mediating multiple myeloma cell growth and migration. Blood 2001; 98: 428–435. 64 Podar K, Tai YT, Lin BK, Narsimhan RP, Sattler M, Kijima T et al. Vascular endothelial growth factor (VEGF)-induced migration of multiple myeloma cells is associated with b1-integrin and PI3-kinase-dependent PKCa activation. J Biol Chem 2002; 277: 7875–7881. 65 Kumar S, Witzig TE, Thompson MA. Expression of angiogenic cytokines by plasma cells: a comparison of MGUS, smoldering myeloma and newly diagnosed symptomatic myeloma. Blood 2002; 100: 807a (abstract). 66 Rajkumar SV, Leong T, Roche PC, Fonseca R, Dispenzieri A, Lacy MQ et al. Prognostic value of bone marrow angiogenesis in multiple myeloma. Clin Cancer Res 2000; 6: 3111–3116. 67 Gupta D, Treon SP, Shima Y, Hideshima T, Podar K, Tai YT et al. Adherence of multiple myeloma cells to bone marrow stromal cells upregulates vascular endothelial growth factor secretion: therapeutic applications. Leukemia 2001; 15: 1950–1961. 68 Vacca A, Ria R, Ribatti D, Semeraro F, Djonov V, Di Raimondo F et al. A paracrine loop in the vascular endothelial growth factor pathway triggers tumor angiogenesis and growth in multiple myeloma. Haematologica 2003; 88: 176–185. 69 Jung YD, Mansfield PF, Akagi M, Takeda A, Liu W, Bucana CD et al. Effects of combination anti-vascular endothelial growth factor receptor and anti-epidermal growth factor receptor therapies on the growth of gastric cancer in a nude mouse model. Eur J Cancer 2002; 38: 1133–1140. 70 Kim ES, Serur A, Huang J, Manley CA, McCrudden KW, Frischer JS et al. Potent VEGF blockade causes regression of coopted vessels in a model of neuroblastoma. Proc Natl Acad Sci USA 2002; 99: 11399–11404. 71 Wedge SR, Ogilvie DJ, Dukes M, Kendrew J, Chester R, Jackson JA et al. ZD6474 inhibits vascular endothelial growth factor signaling, angiogenesis, and tumor growth following oral administration. Cancer Res 2002; 62: 4645–4655. 72 Ke-Lin J, Qu-Hong A, Nagy JA, Eckelhoefer IA, Masse EM, Dvorak AM et al. Vascular targeting of solid ascites tumours with antibodies to vascular endothelial growth factor. Eur J Cancer 1996; 32A: 2467–2473. 73 Kim KJ, Li B, Winer J, Armanini M, Gillett N, Phillips HS et al. Inhibition of vascular endothelial growth factor-induced angiogenesis suppresses tumor growth in vivo. Nature 1993; 362: 841–844. 74 Millauer B, Shawver LK, Plate KH, Risau W, Ullrich A. Glioblastoma growth inhibited in vivo by a dominant-negative Flk-1 mutant. Nature 1994; 367: 576–579. 75 Martiny-Baron G, Marme D. VEGF-mediated tumour angiogenesis: a new target for cancer therapy. Curr Opin Biotechnol 1995; 6: 675–680. 76 Brekken RA, Overholser JP, Stastny VA, Waltenberger J, Minna JD, Thorpe PE. 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 2000; 60: 5117–5124.

Leukemia


1966 77 Presta LG, Chen H, O’Connor SJ, Chisholm V, Meng YG, Krummen L et al. Humanization of an anti-vascular endothelial growth factor monoclonal antibody for the therapy of solid tumors and other disorders. Cancer Res 1997; 57: 4593–5499. 78 Bellamy WT, Richter L, Sirjani D, Roxas C, Glinsmann-Gibson B, Frutiger Y et al. Vascular endothelial cell growth factor is an autocrine promoter of abnormal localized immature myeloid precursors and leukemia progenitor formation in myelodysplastic syndromes. Blood 2001; 97: 1427–1434. 79 Chen HX, Gore-Langton RE, Cheson BD. Clinical trials referral resource: current clinical trials of the anti-VEGF monoclonal antibody bevacizumab. Oncology 2001; 15: 1023–1026. 80 Kabbinavar F, Hurwitz HI, Fehrenbacher L, Meropol NJ, Novotny WF, Lieberman G et al . Phase II, randomized trial comparing bevacizumab plus fluorouracil (FU)/leucovorin (LV) with FU/LV alone in patients with metastatic colorectal cancer. J Clin Oncol 2003; 21: 60–65. 81 Sun L, Tran N, Liang C, Hubbard S, Tang F, Lipson K et al. Identification of substituted 3-[(4,5,6, 7-tetrahydro-1H-indol-2yl)methylene]-1,3-dihydroindol-2-ones as growth factor receptor inhibitors for VEGF-R2 (Flk-1/KDR), FGF-R1, and PDGF-Rbeta tyrosine kinases. J Med Chem 2000; 43: 2655–2663. 82 Hideshima T, Chauhan D, Shima Y, Raje N, Davies FE, Tai YT et al. Thalidomide and its analogs overcome drug resistance of human multiple myeloma cells to conventional therapy. Blood 2000; 96: 2943–2950.

Leukemia

83 Hideshima T, Richardson P, Chauhan D, Palombella VJ, Elliott PJ, Adams J et al. The proteasome inhibitor PS 341 inhibits growth, induces apoptosis, and overcomes drug resistance in human multiple myeloma cells. Cancer Res 2001; 61: 3071–3076. 84 Rousselot P, Labaume S, Marolleau JP, Larghero J, Noguera MH, Brouet JC et al. Arsenic trioxide and melarsoprol induce apoptosis in plasma cell lines and in plasma cells from myeloma patients. Cancer Res 1999; 59: 1041–1048. 85 Park WH, Seol JG, Kim ES, Hyun JM, Jung CW, Lee CC et al. Arsenic trioxide-mediated growth inhibition in MC/CAR myeloma cells cycle arrest in association with induction of cyclin-dependent kinase inhibitor, p21, and apoptosis. Cancer Res 2000; 60: 3065–3071. 86 Lin B, Podar K, Gupta D, Tai YT, Li S, Weller E et al. The vascular endothelial growth factor receptor tyrosine kinase inhibitor PTK787/ZK222584 inhibits growth and migration of multiple myeloma cells in the bone marrow microenvironment. Cancer Res 2002; 62: 5019–5026. 87 Mohler TM, Ho AD, Goldschmidt H, Barlogie B. Angiogenesis in hematologic malignancies. Crit Rev Oncol Hematol 2003; 45: 227–244. 88 Jain RK, Safabakhsh N, Sckell A, Chen Y, Jiang P, Benjamin L 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 USA 1998; 95: 10820–10825.