Decreased Growth of Neurogenic Sarcomas Vascular Endothelial Growth Factor Receptor 2 Leads to Inhibition of Angiogenesis by Blocking Activation of the

ABSTRACT Neurogenic sarcomas are incurable, common malignant human periph-eral nerve tumors subject to local recurrence and systemic metastasis. Inthis study, the vascularity, vascular endothelial growth factor (VEGF)expression, and effects of inhibiting VEGF receptor on growth of neuro-genic sarcomas were examined. Vascularization and VEGF expressionwere 6.4- and 15-fold higher in tumors than in normal nerves. The smallmolecule inhibitor (SU5416) of VEGF receptor 2 had no effect on neuro-genic sarcoma cell lines in vitro, but the growth of a human tumor explantxenograft model was reduced by 54.8% compared to vehicle. Reduction intumor growth was due to decreased tumor angiogenesis, leading to reduc-tion of tumor cell proliferation and increased apoptosis. Inhibiting VEGFfunction may therefore be a useful adjuvant therapy for neurogenicsarcomas. INTRODUCTIONNF-1 3 is the most common human cancer-predisposing familialsyndrome, with an incidence of 1 in 3500 live births (1). NF-1 ischaracterized by a plethora of clinical manifestations including der-matological, vascular, musculoskeletal, and neurological disorders.The most common malignant tumors are neurogenic sarcomas, whichoccur in 3–5% of NF-1 patients and arise from plexiform neurofibro-mas of the large peripheral nerves. The overall prognosis for patientswith neurogenic sarcomas is poor, with only 30% of the patientsremaining disease free 5 years after radical local surgery. Systemicmetastasis, especially to the lungs, is often the ultimate cause of deathin these patients (2). Angiogenesis is a crucial process in solid tumor growth and me-tastasis (3–8). The entire process of neoangiogenesis can be inducedby VEGF acting as an endothelial cell mitogen and a survival factorby activating its receptors, which are specifically expressed by theendothelial cells (5, 9, 10). VEGF also contributes to metastasis andperitumoral edema by inducing endothelial cell fenestrations in bloodvessels (10–13). VEGF is regulated by several tumor mitogens in-cluding Ras (14–21); cytokines such as interleukin 1 and interleukin6 (22, 23); growth factors such as fibroblast growth factor 4, platelet-derived growth factor, tumor necrosis factor a, transforming growthfactor b, insulin-like growth factor I, and KGF (24–29); and theinactivation of the p53 tumor suppressor gene (30). In addition, VEGFis stimulated by several physiological factors, of which hypoxia andhypoglycemia are the most important and pertinent in the growth ofsolid tumors (31–35). There are several VEGFRs, including VEGFR-1 and VEGFR-2,that are expressed mainly by endothelial cells (36–40). Among theVEGFRs, activation of VEGFR-2 is the most biologically relevant,leading to changes in endothelial cell morphology, actin reorganiza-tion, membrane ruffling, chemotaxis, and proliferation (41, 42). Inhi-bition of VEGFR-2 activation by several different strategies includingusing the VEGFR-2 dominant negative mutant (6, 43), neutralizingantibodies directed at VEGFR-2 or VEGF (5, 44), ribozymes againstVEGFR-2 or antisense strategies against VEGF (45, 46) all lead todecreased tumor angiogenesis and overall tumor growth. Pharmaco-logical strategies, such as the use of SU5416 (SUGEN Inc.), a smallmolecule that specifically inhibits VEGFR-2, are currently the mostfeasible clinical strategies. In this study, we demonstrate that SU5416inhibits tumor angiogenesis and the overall growth of NF-1 neuro-genic sarcomas. This mode of antiangiogenic therapy may be useful asan adjunct to surgery in controlling the local recurrence and theterminal metastasis of disease in patients with NF-1 neurogenic sar-comas and other soft tissue sarcomas.MATERIALS AND METHODS