The biologic activity of selenoestrogens

For differential imaging of mammary tumors with estrogen receptors and without estrogen receptors we required gamma-emitting estrogen analogues. In this paper we report on the binding properties of 7 alpha-, 16 alpha-, and 17 alpha-methylselenoestrogens and 17 alpha-phenylselenoestrogens relative to the binding properties of estradiol. The selenium-containing estrogens retained the ability to displace [3H]estradiol from the estrogen receptor of rabbit uterine cytosol, although in most instances the displacement was small (3-7% compared to estradiol). The most active compounds were 16 alpha-phenylselenoestrone, 16 alpha-methylselenoestradiol, and 17 alpha-methylselenomethyl-estradiol which had relative binding of 23, 27, and 31%, respectively, compared with that of estradiol. 16 alpha-Methylselenoestradiol was able to translocate the estrogen cytosol receptor to the nucleus, in vitro, but was not able to increase the uterine weight when administered to mice in vivo.