NEUTRALIZING ANTIBODIES AGAINST EPIDERMAL GROWTH-FACTOR AND ERBB-2 NEU RECEPTOR TYROSINE KINASES DOWN-REGULATE VASCULAR ENDOTHELIAL GROWTH-FACTOR PRODUCTION BY TUMOR-CELLS IN-VITRO AND IN-VIVO - ANGIOGENIC IMPLICATIONS FOR SIGNAL-TRANSDUCTION THERAPY OF SOLID TUMORS/

The overexpression in tumor cells of (proto)-oncogenic receptor tyrosi ne kinases such as epidermal growth factor receptor (EGFR) or ErbB2/ne u (also known as HER-2) is generally thought to contribute to the deve lopment of solid tumors primarily through their effects on promoting u ncontrolled cell proliferation, However, agents that antagonize the fu nction of the protein products encoded by these (proto)oncogenes are k nown to behave in vivo in a cytotoxic-like manner, This implies that s uch oncogenes may regulate critical cell survival functions, including angiogenesis, The latter could occur as a consequence of regulation o f relevant growth factors by such oncogenes, We therefore sought to de termine whether EGFR or ErbB2/neu may contribute to tumor angiogenesis by examining their effects on the expression of vascular endothelial cell growth factor (VEGF)/vascular permeability factor (VPF), one of t he most important of all known inducers of tumor angiogenesis. We foun d that in vitro treatment of EGFR-positive A431 human epidermoid carci noma cells, which are known to be heavily dependent on VEGF/VPF in viv o as an angiogenesis growth factor, with the C225 anti-EGFR neutralizi ng antibody caused a dose-dependent inhibition of VEGF protein express ion, Prominent suppression of VEGF/VPF expression in vivo, as web as a significant reduction in tumor blood vessel counts, were also observe d in established A431 tumors shortly after injection of the antibody a s few as four times into nude mice. Transformation of NIH 3T3 fibrobla sts with mutant ErbB2/neu, another EGFR-like oncogenic tyrosine kinase , resulted in a significant induction of VEGF/VPF, and the magnitude o f this effect was further elevated by hypoxia, Moreover, treatment of ErbB2/neu-positive SKBR-3 human breast cancer cells in vitro with a sp ecific neutralizing anti-ErbB2/neu monoclonal antibody (4D5) resulted in a dose-dependent reduction of VEGF/VPF protein expression, Taken to gether, the results suggest that oncogenic properties of EGFR and ErbB 2/neu may, at least in part, be mediated by stimulation of tumor angio genesis by up-regulating potent angiogenesis growth factors such as VE GF/VPF, These genetic changes may cooperate with epigenetic/environmen tal effects such as hypoxia to maximally stimulate VEGF/VPF expression , Therapeutic disruption of EGFR or ErbB2/neu protein function in vivo may therefore result in partial suppression of angiogenesis, a featur e that could enhance the therapeutic index of such agents in vivo and endow them with anti-tumor effects, the magnitude of which may be out of proportion with their observed cytostatic effects in monolayer tiss ue culture.