Estrogen levels in breast tumors of post-menopausal women are at least 10 times higher than estrogen levels in plasma. The high level of estrogen in these tumors is postulated to be due to in situ formation of estrogen, possibly through conversion of estrone sulfate to estrone by the enzyme estrone sulfatase. Thus, inhibitors of estrone sulfatase are potential agents for the treatment of hormone-dependent breast cancers. We designed and synthesized a series of estra-1,3,5(10)triene-17-one, 3-amino and estra-1,3,5(10)triene-17-one, 3-thio derivatives. We have shown previously that several of these compounds substantially inhibit estrone sulfatase, exceeding Danazol in their inhibitory activity. However, little is known about the metabolism of these compounds and the possible effects of their metabolites in vivo. Two probable metabolites of the synthetic estrone analogs are estra-1,3,5(10)triene-17-one, 3-amine (E(1)-NH2), and estra-1,3,5(10)triene-17-one, 3-thiol (E(1)-SH). We tested these two compounds for estrogenicity, antiestrogenicity and inhibition of estrone sulfatase activity using a combination of in vivo and in vitro assays. The ovariectomized rat uterine weight gain assay was used to test for estrogenicity. Neither E(1)-NH2 nor E(1)-SH were estrogenic, as indicated by a lack of uterine weight gain when given at 25 mu g/day for 7 days. The test compounds also were not antiestrogenic, in that they did not block estrone-induced uterine weight gain when given (100 mu g/day) simultaneously with estrone (2 mu g/day). Both compounds showed low affinity for the estrogen receptor. Using rat uterine cytosol as a source of estrogen receptor, the compounds displaced only a small percentage of [H-3]estradiol binding, even when present at 1000-fold excess. Inhibition of estrone sulfatase activity was tested using human placental microsomes as a source of estrone sulfatase. E(1)-NH2 and E(1)SH showed very low levels of estrone sulfatase inhibition (15.1 and 9.8%, respectively) under conditions where Danazol showed more than 60% inhibition. Our results indicate that neither of these two compounds would present significant problems if they were the primary metabolite in a treatment involving estrone sulfatase inhibition of estrogen-dependent breast cancer.
