3,17-Disubstituted 2-Alkylestra-1,3,5(10)-trien-3-ol Derivatives:  Synthesis, In Vitro and In Vivo Anticancer Activity

Estradiol-3,17-O,O-bis-sulfamates inhibit steroid sulfatase (STS), carbonic anhydrase (CA), and, when substituted at C-2, cancer cell proliferation and angiogenesis. C-2 Substitution and 17-sulfamate replacement of the estradiol-3,17-O,O-bis-sulfamates were explored with efficient and practical syntheses developed. Evaluation against human cancer cell lines revealed the 2-methyl derivative 27 (DU145 GI50 = 0.38 μM) as the most active novel bis-sulfamate, while 2-ethyl-17-carbamate derivative 52 (GI50 = 0.22 μM) proved most active of its series (cf. 2-ethylestradiol-3,17-O,O-bis-sulfamate 4 GI50 = 0.21 μM). Larger C-2 substituents were deleterious to activity. 2-Methoxy-17-carbamate 50 was studied by X-ray crystallography and was surprisingly 13-fold weaker as an STS inhibitor compared to parent bis-sulfamate 3. The potential of 4 as an orally dosed anti-tumor agent is confirmed using breast and prostate cancer xenografts. In the MDA-MB-231 model, dramatic reduction in tumor growth or regression was observed, with effects sustained after cessation of treatment. 3-O-Sulfamoylated 2-alkylestradiol-17-O-carbamates and sulfamates have considerable potential as anticancer agents.