Synthesis and biological evaluation of new 2-methoxyestradiol derivatives: Potent inhibitors of angiogenesis and tubulin polymerization

Here, we report the structural optimization of a hit natural compound, 2-ME₂ (2-methoxyestradiol), which exhibited inhibitory activity but low potency on tubulin polymerization, anti- angiogenesis, MCF-7 proliferation and metastasis in vitro and in vivo. A novel series of 3,17-modified and 17-modified analogs of 2-ME₂ were synthesized and investigated for their antiproliferative activity against MCF-7 and another five different human cancer cell lines leading to the discovery of 9i. 9i bind to tubulin colchicine site tightly, inhibited tubulin polymerization and disrupted cellular microtubule networks. Cellular mechanism studies revealed that 9i could induce G2/M phase arrest by down-regulated expression of p-Cdc2, P21 and cell apoptosis by regulating apoptosis-related proteins (Parp, Caspase families) in a dose-dependent manner. Importantly, 9i significantly inhibited HUVEC tube formation, proliferation, migration and invasion. The inhibitory effect against angiogenesis in vivo was confirmed by zebrafish xenograft. Furthermore, 9i could effectively inhibit the proliferation and metastasis of MCF-7 cells in vitro and in zebrafish xenograft. The satisfactory physicochemical property and metabolic stability of 9i further indicated that it can act as a promising and potent anti-angiogenesis, inhibiting proliferation and metastasis of breast cancer agent via targeting tubulin colchicine binding site.

Concise synthesis of 2-methoxyestradiol from 17β-estradiol through the C(sp2)-H hydroxylation

A four-step route for the synthesis of 2-methoxyestradiol (5) starting from 17β-estradiol (1) has been achieved with a 51% overall yield. The key step was the ruthenium-catalyzed ortho-C(sp²)-H bond hydroxylation of aryl carbamates. Using dimethyl carbamate as the directing group, [RuCl₂(p-cymene)]₂ as the catalyst, PhI(OAc)₂ as the oxidant and trifluoroacetate/trifluoroacetic anhydride (1:1) as the co-solvent, the hydroxyl group could be singly installed at the 2-position of 3-dimethylcarbamoyloxyestradiol (2) with 65% yield. Subsequent methylation of hydroxy and removal of dimethyl carbamate afforded 2-methoxyestradiol (5).

Synthesis, molecular modeling and biological evaluation of potent analogs of 2-methoxyestradiol

The endogenous steroid 2-methoxyestradiol (1) has attracted a great interest as a lead compound towards the development of new anti-cancer drugs. Herein, the synthesis, molecular modeling, anti-proliferative and anti-angiogenic effects of ten 2-ethyl and four 2-methoxy analogs of estradiol are reported. The ethyl group was introduced to the steroid A-ring using a novel Friedel-Crafts alkylation protocol. Several analogs displayed potent anti-proliferative activity with IC₅₀-values in the submicromolar range towards the CEM human leukemia cancer cell line. As such, all of these compounds proved to be more active than the lead compound 2-methoxyestradiol (1) in these cells. The six most cytostatic analogs were also tested as anti-angiogenic agents using an in vitro tube formation assay. The IC₅₀-values were determined to be in the range of 0.1 μM ± 0.03 and 1.1 μM ± 0.2. These six compounds were also modest inhibitors against tubulin polymerization with the most potent inhibitor was 14b (IC₅₀ = 2.1 ± 0.1 μM). Binding studies using N,N'-ethylene-bis(iodoacetamide) revealed that neither14a or 14b binds to the colchicine binding site in the tubulin protein, in contrast to 2-methoxyestradiol (1). These observations were supported by molecular modeling studies. Results from a MDA-MB-231 cell cycle assay showed that both 10e and 14b gave accumulation in the G2/M phase resulting in induction of apoptosis. The results presented herein shows that the novel analogs reported exhibit their anticancer effects via several modes of action.