2-Methoxyestradiol, an Endogenous Mammalian Metabolite, Inhibits Tubulin Polymerization by Interacting at the Colchicine Site

• Published in: Proceedings of the National Academy of Sciences - PNAS 1994-04, Vol.91 (9), p.3964-3968
• Main Authors: D'Amato, Robert J., Lin, Chii M., Flynn, Evelyn, Folkman, Judah, Hamel, Ernest
• Format: Article
• Language: English
• Subjects: 2-Methoxyestradiol; Animals; Antimitotics; Binding, Competitive; Biochemistry; Cattle; Colchicine - metabolism; Drug interactions; Estradiol - analogs & derivatives; Estradiol - chemistry; Estradiol - pharmacology; Estrogens; Glutamates - pharmacology; In Vitro Techniques; Inhibitory concentration 50; Metabolites; Microscopy, Electron; Microtubules; Microtubules - drug effects; Molecules; Polymerization; Polymers; Poultry; Steroids; Structure-Activity Relationship; Tubulin - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.91.9.3964

A metabolite of estradiol, 2-methoxyestradiol (2ME), inhibits angiogenesis in the chicken embryo chorioallantoic membrane assay. Since 2ME causes mitotic perturbations, we examined its interactions with tubulin. In our standard 1.0 M glutamate system (plus 1.0 mM MgCl2at 37⚬C), superstoichiometric concentrations (relative to tubulin) of 2ME inhibited the nucleation and propagation phases of tubulin assembly but did not affect the reaction extent. Although polymer formed in the presence of 2ME was more cold-stable than control polymer, morphology was little changed. Under suboptimal reaction conditions (0.8 M glutamate/no MgCl2at 26⚬C), substoichiometric 2ME totally inhibited polymerization. No other estrogenic compound was as effective as 2ME as an inhibitor of polymerization or of the binding of colchicine to tubulin. Inhibition of colchicine binding was competitive (Ki, 22 μM). Thus, a mammalian metabolite of estradiol binds to the colchicine site of tubulin and, depending on reaction conditions, either inhibits assembly or seems to be incorporated into a polymer with altered stability properties.