A fluorescent probe for rapid detection of estrogen receptors

Fluorescein conjugates to estradiol-17 beta by the sixth carbon (6-FE) and to estrone by the 17th carbon (17-FE) were used to detect estrogen receptors (ERs) in breast cancer tissue sections and in cultured cell lines (human mammary carcinoma MCF-7 and Copenhagen rat prostatic tumor R3327-AT). 17-FE was found to interact with ERs better than 6-FE by biochemical and histochemical techniques. Thin layer chromatography analysis of ethanolic extracts of 17-FE incorporated in tissues and cultured cells showed that over 95% of 17-FE was not metabolized. We concluded that the fluorescence observed in tissue sections and cultured cells was due to 17-FE and not to fluorescein dissociated from the conjugate. Analysis of 65 human breast cancer showed that 74% of the cases were positive for specific 17-FE uptake and 26% were negative. The fluorescence was consistently brighter in the ductal and glandular epithelial cells than in the stroma. specific 17-FE uptake in the nucleoli was observed in MCF-7 and in R3327-AT tumor cells in in vitro cultures, suggesting that these nucleolar estrogen receptors may play a key role in the mechanism of estrogen action. Problems of fluorescence quantitation in tissue sections and cells are discussed.