Evaluation of inhibitors for 17β-hydroxysteroid dehydrogenase type 1 in vivo in immunodeficient mice inoculated with MCF-7 cells stably expressing the recombinant human enzyme

17β-Hydroxysteroid dehydrogenase (17HSD1) is an enzyme activating estrone (E1) to estradiol (E2). In the present study, a mechanistic animal model was set up for evaluating putative inhibitors for the human enzyme in vivo. Estrogen-dependent MCF-7 human breast carcinoma cells were stably transfected with a plasmid expressing human 17HSD1. These cells formed estrogen-dependent tumors in immunodeficient mice. In the optimized model, tumor sizes were decreased in both ovariectomized and intact vehicle-treated mice, whereas they were maintained or slightly increased in mice supplemented 2 weeks with an appropriate dose of the 17HSD1-substrate E1. Tumor sizes in mice treated with 0.1 μmol/kg/d of E1 were reduced by administering 5 μmol/kg/d of different 17HSD1-inhibitors and a 86% reduction in size was detected with the most potent inhibitor. A dose–response relationship in the inhibitory effect of this compound further confirmed the validity of the model for testing the drug candidates in vivo.