Search for New Anti-angiogenic Agents Targeting on Endothelial Cell Growth or Motility.

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On the guidance of selective growth inhibition against human umbilical vein endothelial cells (HUVECs), we searched for anti-angiogenic substances from extracts of marine organisms.Bastadins, cyclic tetramers of brominated-tyrosine^1, were isolated from the marine sponge Ianthella basta. Among of them, bastadin 6, a major constituent, showed a selective growth inhibition against HUVECs. Bastadin 6 was found to inhibit VEGF- or bFGF-dependent proliferation (IC_<50>=0.052μM) of HUVECs, 20 to 100-fold selectively in comparison with normal fibroblast (3Y1) or several tumor cells (KB3-1, K562, and Neuro2A). Bastadin 6 also inhibited VEGF- or bFGF-induced tubular formation (0.1μM, 6h treatment) and VEGF-induced migration (1μM, 4h treatment) of HUVECs. Moreover, bastadin 6 almost completely blocked VEGF-or bFGF-induced in vivo neovascularization in mice corneal assay and suppressed growth of subcutaneously inoculated A431 solid tumor in nude mice (100mg/kg, i.p.). Bastadin 6 induced cell deat … More h of HUVECs with apoptotic phenotype, whereas it showed no effect on the VEGF-induced auto-phosphorylation of VEGF receptors, Flt1 and KDR/Flk-1. These evidences suggested that the anti-angiogenic effect of bastadin 6 is closely related to selective induction activity of apoptosis against endothelial cells.We studied total synthesis of bastadin 6 in order to establish a practical synthetic method for further biological analysis. According to the reported method., utilizing the enzymatic oxidative coupling of bromophenols as the key reaction, we developed an improved synthetic route by changing starting materials and reaction conditions. We also developed a novel Ce(NH_4)_2(NO_3)_6 (CAN)-mediated oxidative coupling reaction of 2,6-dibromophenols to give the diaryl ether derivatives. Condensation of two segments and subsequent intramolecular macrocyclization gave bastadin 6 in 9 steps, 26% overall yield.In order to analyze the structure-requirement for the anti-angiogenic activity of bastadin, structure-activity relationship of bastadin 6 was studied. Protection of oxime moiety was found to cause a complete loss of the growth inhibitory activity of HUVEC, and non-oxime analog also showed a significantly weak activity. Furthermore, debrominated analog showed a weak activity. Less