Inhibition of Angiogenesis by Rhizoxin, a Microbial Metabolite Containing Two Epoxide Groups

Previous studies by our and other groups have shown that microbial products containing more than one epoxide group, including eponemycin, radicicol, depudecin and AGM‐1470, exhibit anti‐angio‐genic activity in an in vivo assay system involving chorioallantoic membranes (CAMs) of growing chick embryos. Based on these findings, rhizoxin, a microbial metabolite that contains two epoxide groups and exhibits anti‐tubulin activity, was tested for anti‐angiogenic activity in a CAM assay system. Rhizoxin caused dose‐dependent inhibition of embryonic angiogenesis, the ID(S(1) value being 2 ng (3.2 pmol) per egg. In addition, this compound (2 nig/kg i.p.) significantly suppressed neovascnlarizatlou induced by M5076 mouse tumor cells in a mouse dorsal air sac assay system, compared to the vehicle alone (P<0.05). These results indicate that rhizoxin is a novel inhibitor of angiogenesis, and that it has potential as a new therapeutic agent for cancer.