Colchicine and 2-methoxyestradiol Inhibit Human Angiogenesis.

BACKGROUND: Angiogenesis is a critical determinant of tumor growth and the development of metastases. Tubulin inhibitors have been shown to be effective inhibitors of angiogenesis. We hypothesized that colchicine, a well-know tubulin inhibitor and 2-methoxyestradiol (2 MeOH), a novel tubulin inhibitor, would limit the initiation of a human angiogenic response and would limit subsequent neovessel growth in a dose-dependent manner.
METHODS: To test this hypothesis, we cultured full-thickness human placental vein discs from three placentas in a fibrin-thrombin clot model. Both colchicine and 2 MeOH were tested over a wide range of concentrations (10(-6) to 10(-12) M) to determine their effect on the percent of wells that initiated an angiogenic response (%I) and the subsequent growth (Angiogenic Index, 0-16 range) of vein-derived neovessels.
RESULTS: Colchicine at doses of 10(-6) and 10(-8) M completely inhibited the angiogenic response (CI: 95%, P < 0.0001) but lower (10(-10) to 10(-12) M) doses did not significantly inhibit angiogenesis (P = NS). Effective in vitro colchicine levels far exceed achievable non-toxic human plasma levels. In contrast, 2-methoxyestradiol decreased initiation and angiogenic growth significantly at 10(-6) M (CI: 95%, P < 0.0001), but did not significantly decrease angiogenesis at doses of 10(-8), 10(-10), or 10(-12) M. In contrast to colchicine, human plasma levels of 10(-6) M 2 MeOH are achievable clinically with little or no associated toxicity.
CONCLUSIONS: Effective in vitro drug levels of 2 MeOH can be achieved in vivo, suggesting that 2 MeOH may have a role in the clinical treatment of angiogenesis-dependent diseases.