Modulation of in vivo growth of thyroid tumor-derived cell lines by sense and antisense vascular endothelial growth factor gene

Vascular endothelial growth factor A (VEGF) is a potent mitogen for endothe lial cells in vitro and promotes neo-angiogenesis in vivo, VEGF overexpress ion occurs in most human malignancies including thyroid carcinomas in which elevated VEGF expression is associated with a high tumorigenic potential. To investigate the role of VEGF in angiogenesis associated with development of thyroid carcinomas, we constitutively expressed VEGF(121) into a poorly tumorigenic cell line (NPA) expressing minimal levels of endogenous VEGF. Here we report that VEGF overexpressing NPA cells showed the same growth po tential as untransfected NPA in vitro but formed well-vascularized tumors w hen injected subcutaneously into nude mice with markedly reduced latency co mpared to parental cells. A complementary approach was to suppress VEGF exp ression in a highly tumorigenic anaplastic cell line (ARO) by the transfect ion of an antisense construct. Antisense-transfected ARO cells expressed re duced constitutive levels of VEGF, shelved the same growth potential as unt ransfected ARO cells in vitro and formed small tumors characterized by mini mal vascularization, extensive necrosis and longer latency compared to pare ntal or vector-transfected ARO cells in vivo. Finally, we investigated the expression of both VEGF tyrosine kinase receptors (Flt-1 and Flk-1/KDR) in tumor specimens by RT-PCR, Expression of (Flt-1 and Flk-1/KDR) was low in t issue specimens derived from NPA tumors, but was found enhanced in NPA VEGF tumors; conversely, the expression of VEGF receptors was high in tissue sp ecimens derived from ARO tumors but was decreased in tumors derived from VE GF depleted ARO cells. These results clearly demonstrate that VEGF indirect ly promotes the growth of thyroid tumors by stimulating angiogenesis.