Nuclear uptake of a 17 beta-estradiol-fluorescein derivative as a marker of estrogen dependence.

17-Fluorescein-labeled estradiol was prepared by linkage of fluorescein-isothiocyanate through a succinamide-ethyl-amine chain to the 17 position of 17 beta-estradiol. This compound, N-fluoresceino-N'[17 beta-(estradiol-hemisuccinamido)-ethyl]-thiourea, displaced tritiated estradiol from purified estrogen-receptor protein and readily crossed intact cellular membranes. In female rats, in-vivo injection was followed by nuclear labeling of endometrium, whereas nuclear labeling of non-target tissue was absent. Temperature-dependent nuclear transfer could be visualized directly by fluorescent microscopy when human estradiol target tissue (mammary and proliferative endometrium) was incubated in vitro with the compound. Temperature-dependent nuclear labeling was not present in human non-target tissue, including skeletal muscle, skin, stomach, colon, appendix, and lung, after in-vitro incubation. Temperature-dependent nuclear labeling with the compound was inhibited by estradiol and mixtures of natural and synthetic estrogens. A significant positive correlation of the presence of nuclear labeling in human mammary cancer was obtained with standard dextran-coated charcoal radioligand assay for estradiol receptor. Unlike radiologand assay and cytochemical assays, nuclear uptake of the fluorescein-labeled estradiol appears to require an intact estradiol-receptor mechanism.