Role of protein kinase C-dependent signaling pathways in the antiangiogenic properties of nafoxidine.

We analyzed the effect of nafoxidine on the earlier biological processes of angiogenesis and explored the role of different signaling pathways involved in the in vitro response of endothelial cells (HUVEC). Nafoxidine significantly inhibited adhesion, spreading, migration and invasion of HUVEC at concentrations ranging from 1 to 2.5 microM. Endothelial cord formation on Matrigel was inhibited by nafoxidine and cotreatment with phorbol-12-myristate-13-acetate (PMA) clearly prevented the antiangiogenic effect of the antiestrogen. On the contrary, cotreatment with the PKC inhibitor bisindolylmaleimide potentiated inhibition of cord formation. PMA also inhibited the nafoxidine-induced secretion of metalloproteinase-2 and tissue inhibitor of metalloproteinases-1 in HUVEC monolayers. Cotreatment with the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine and the cAMP analog N6,2'-o-dibutyryladenosine 3',5'-cyclic monophosphate prevented the inhibition of endothelial cord formation induced by nafoxidine. Our work presents evidence about the signaling pathways involved in the antiangiogenic effect of nafoxidine, suggesting that PKC-dependent signaling pathways are essential in angiogenesis during endothelial cord formation.

Altered tumor angiogenesis and metastasis of B16 melanoma in transgenic mice overexpressing tissue inhibitor of metalloproteinases-1.

Tissue inhibitor of metalloproteinases-1 (TIMP-1) has emerged as a multifunctional protein that plays contrasting roles during angiogenesis and cancer spread. We have investigated the growth, vascularization and metastasis of B16 melanoma cells in a transgenic mouse model with elevated TIMP-1 levels in the systemic circulation. Transgenic C57BL/6j-CBA mice overexpressing human TIMP-1 in the liver under the control of the mouse albumin promoter/enhancer were employed. An early subcutaneous growth advantage and an increased tumor angiogenic response were observed in transgenic animals with respect to wild-type hybrid mice. On the contrary, there was a dramatic decrease in the lung colonizing ability of B16 melanoma cells in TIMP-1 transgenic mice. No significant effect on metastasis formation was observed in another transgenic mouse model with increased TIMP-1 expression in lungs but low plasma levels, where the transgene was placed under the control of the murine mammary tumor virus promoter. These results support the notion that TIMP-1 displays paradoxical effects on tumor progression and suggest that circulating TIMP-1 is efficient in suppressing lung colonization of melanoma cells.