Thiolutin, an inhibitor of HUVEC adhesion to vitronectin, reduces paxillinin HUVECS and suppresses tumor cell-induced angiogenesis

Recent studies have shown that integrin alphav beta3, a receptor for vitron ectin, plays an important role in tumor-induced angiogenesis and tumor grow th and that antagonists of alphav beta3 inhibit angiogenic processes includ ing endothelial cell adhesion and migration. On the other hand, most inhibi tors of integrin alphav beta3 are peptide antagonists that include the ArgG ly-Asp (RGD) motif We therefore reasoned that non-peptide inhibitors of end othelial cell adhesion to vitronectin might be useful for inhibition of tum or angiogenesis in vivo. We screened for low-molecular-weight natural produ cts able to inhibit adhesion of human umbilical vein endothelial cells (HUV ECs) to vitronectin, and pyrrothine group compounds including aureothricin, thioaurin and thiolutin were isolated from microbial culture broths, Of th ese compounds, thiolutin inhibited adhesion of HUVECs to vitronectin the mo st effectively (IC50, 0.83 muM) In vivo experiments showed that thiolutin s ignificantly suppressed angiogenesis induced by tumor cells (S-180), a path ological form of neovascularization, in a mouse dorsal air sac assay system , To explore the mechanism of inhibition of HUVEC adhesion to vitronectin b y thiolutin, we examined the effect of this agent on intracellular cell adh esion signaling. We found that the amount of paxillin in HUVECs war signifi cantly reduced by thiolutin treatment, while those of other focal adhesion proteins including vinculin and focal adhesion kinase (FAK) were not. were Metabolic labeling experiments showed that thiolutin enhanced degradation o f paxillin in HUVECs. Protease inhibitors (MG 1 1 5 and E64-D) decreased th e rate of degradation of the paxillin induced by thiolutin and partially re stored thiolutin-induced inhibition of HUVEC adhesion to vitronectin, Based on these findings, we concluded that thiolutin, an inhibitor of HUVEC adhe sion to vitronectin, reduces the paxillin level in HUVECs and suppresses tu mor cell-induced angiogenesis in vivo. (C) 2001 Wiley-Liss, Inc.