The establishment of a vascular supply is required for organ development and differentiation as well as for tissue repair and reproductive functions in the adult1 Neovascularization (angiogenesis) is also implicated in the pathogenesis of a number of disorders These include: proliferative retinopathies, age-related macular degeneration, tumors, rheumatoid arthritis, and psoriasis1,2 A strong correlation has been noted between density of microvessels in primary breast cancers and their nodal metastases and patient survival3 Similarly, a correlation has been reported between vascularity and invasive behavior in several other tumors4–6

The biology of vascular endothelial growth factor

The development of new blood vessels (angiogenesis) is required for many physiological processes including embryogenesis, wound healing and corpus luteum formation. Blood vessel neoformation is also important in the pathogenesis of many disorders, particularly rapid growth and metastasis of solid tumours. There are several potential mediators of tumour angiogenesis, including basic and acidic fibroblast growth factors, tumour necrosis factor-alpha and transforming factors-alpha and -beta. But it is unclear whether any of these agents actually mediates angiogenesis and tumour growth in vivo. Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen and an angiogenesis inducer released by a variety of tumour cells and expressed in human tumours in situ. To test whether VEGF may be a tumour angiogenesis factor in vivo, we injected human rhabdomyosarcoma, glioblastoma multiforme or leiomyosarcoma cell lines into nude mice. We report here that treatment with a monoclonal antibody specific for VEGF inhibited the growth of the tumours, but had no effect on the growth rate of the tumour cells in vitro. The density of vessels was decreased in the antibody-treated tumours. These findings demonstrate that inhibition of the action of an angiogenic factor spontaneously produced by tumour cells may suppress tumour growth in vivo.

Inhibition of vascular endothelial growth factor-induced angiogenesis suppresses tumour growth in vivo

Purpose To investigate the efficacy and safety of bevacizumab plus carboplatin and paclitaxel in patients with advanced or recurrent non-small-cell lung cancer. Patients and Methods In a phase II trial, 99 patients were randomly assigned to bevacizumab 7.5 (n = 32) or 15 mg/kg (n = 35) plus carboplatin (area under the curve = 6) and paclitaxel (200 mg/m2) every 3 weeks or carboplatin and paclitaxel alone (n = 32). Primary efficacy end points were time to disease progression and best confirmed response rate. On disease progression, patients in the control arm had the option to receive single-agent bevacizumab 15 mg/kg every 3 weeks. Results Compared with the control arm, treatment with carboplatin and paclitaxel plus bevacizumab (15 mg/kg) resulted in a higher response rate (31.5% v 18.8%), longer median time to progression (7.4 v 4.2 months) and a modest increase in survival (17.7 v 14.9 months). Of the 19 control patients that crossed over to single-agent bevacizumab, five experienced stable disease, and...

Randomized Phase II Trial Comparing Bevacizumab Plus Carboplatin and Paclitaxel With Carboplatin and Paclitaxel Alone in Previously Untreated Locally Advanced or Metastatic Non-Small-Cell Lung Cancer

Shaker A. Mousa and Thomas M. Reilly The DuPont Merck Pharmaceutical Company Cardiovascular Diseases Div., Exp. Station, Wilmington, DE 19880-0400 The present investigation was undertaken to compare the effects of different direct thrombin inhibitors including hirudin, DUP 714 (Ac-D-Phe-Pro-boro Arg) and PPACK (Phe-Pro-Arg-chloromethyl ketone) with different platelet GPIIblIIIa antagonists including linear Arginine-Glycine-Aspartate (RGD), cyclic RGD, peptidomimetic and non-peptide inhibitors on various platelet functions including: (a) platelet aggregation, (b) fibrinogen binding, (c) platelet plasminogen activator inhibitor type-l (PAl -1) release, (d) platelet serotonin release, and (e) platelet intracellular Ca++ mobilization. Hirudin, DUP 714 and PPACK were effective in inhibiting all of the responses (a-e) mediated by thrombin, with ICsos ranging from 0.002 to 0.9 uM depending upon the concentration of thrombin used, but not those mediated by other platelet agonists including collagen, ADP, and arachidonic acid. In contrast, linear RGD, constrained cyclic RGD (XM648), an RGD peptidomimetic (YY751), a non-peptide GPIIb/IIIa antagonist were effective in blocking fibrinogen binding and platelet aggregation mediated by any of the agonists. The potency of XL 111, XM648 and YY751 in inhibiting thrombin-mediated platelet aggregation (a) and fibrinogen binding (b) ranged from ICso of 0.05 to 1.0 uM in (a) and IC50 of 0.01 to 0.005 uM in (b). However, all platelet GPIIb/IIIa antagonists tested were ineffective in blocking either (c), (d) or (e). Flow cytometric analysis using dual fluorescence markers for the platelet GPIIblIIIa membrane receptors (FIrC-Iabeled cyclic RGD analog, XL086) and for the alpha granule (PE-monoclonal antibody for P-selectin) demonstrated a dissociation between the platelet GPIIb/IIIa receptors by inhibitors and platelet granular secretion. These data suggest that GPIIb/IIIa receptor blockade as compared with direct inhibition of thrombin, does not inhibit intracellular CaH mobilization signal transduction. These data also show that GPIIb/IIIa antagonists, in contrast to thrombin inhibitors, inhibit platelet aggregation mediated by different agonists. The universal anti-aggregatory efficacy of the GPIIb/IIIa antagonists and efficacy of the thrombin inhibitors against Cardiovascular Disease 2 Edited by L.L. Gallo, Plenum Press, New York, 1995 255 thrombin-induced platelet secretion suggest potential benefits of their combinations in various thrombotic disorders.

Cardiovascular Disease 2

The ability of tumours to induce new blood-vessel formation has been a major focus of cancer research over the past few decades, and vascular endothelial growth factor (VEGF) is now known to be central to this process. The quest for VEGF and other factors that promote tumour angiogenesis was initiated many decades ago, and a long and complicated path has led to the development of inhibitors of these molecules as anticancer agents. How did this field begin, and how have we arrived at our present understanding of the role of VEGF in tumour progression.

VEGF and the quest for tumour angiogenesis factors.

Vascular endothelial growth factor (VEGF) is a mitogen with a specificity for endothelial cells in vitro and an angiogenic inducer in vivo. We tested the hypothesis that VEGF may confer on expressing cells a growth advantage in vivo. Dihydrofolatereductase--Chinese hamster ovary cells were transfected with expression vectors which direct the constitutive synthesis of VEGF. Neither the expression nor the exogenous administration of VEGF stimulated anchorage-dependent or anchorage-independent growth of Chinese hamster ovary cells in vitro. However, VEGF-expressing clones, unlike control cells, demonstrated an ability to proliferate in nude mice. Histologic examination revealed that the proliferative lesions were compact, well vascularized, and nonedematous. Ultrastructural analysis revealed that capillaries within the lesions were of the continuous type. These findings indicate that the expression of VEGF may confer on cells the ability to grow in vivo in the absence of transformation by purely paracrine mechanisms. Since VEGF is a widely distributed protein, this property may have relevance for a variety of physiological and pathological proliferative processes.

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Expression of vascular endothelial growth factor does not promote transformation but confers a growth advantage in vivo to Chinese hamster ovary cells.

T Terrell

Papers

Expression of vascular endothelial growth factor does not promote transformation but confers a growth advantage in vivo to Chinese hamster ovary cells.