title: Non-competitive steroid inhibition of oestrogen receptor functions.
abstract: Currently available antioestrogens, such as tamoxifen, are competitive inhibitors that bind to the ligand binding sites of oestrogen receptors, ERalpha and ERbeta. The search for alternative anti-hormone therapies is prompted by the need for drugs that are effective when tumours become tamoxifen resistant. The existence of different receptor isoforms also raise the possibility of improving selectivity. Earlier use of the 3beta-hydroxysteroid dehydrogenase inhibitor, trilostane (4alpha,5- epoxy-17beta-hydroxy-3-oxo-5alpha-androstane-2alpha-carbonitrile), suggested that it had beneficial actions in breast cancer that were only partially attributable to inhibition of steroidogenesis. The present studies on the interactions of trilostane with oestrogen receptors show that it (i) inhibits oestrogen-stimulated proliferation in MCF-7 breast cancer cells, (ii) enhances the affinity of oestradiol binding to ER in rat uteri and specifically increases oestradiol binding to an ERbeta-like isoform, (iii) inhibits ERalpha and ERbeta binding to the classical vitellogenin gene oestrogen response element (ERE) and (iv) inhibits oestrogen-stimulated gene transcription in ERE-linked reporter systems in MCF-7 cells. The results demonstrate a novel, presumably allosteric, mode of antioestrogen action. The beneficial actions of trilostane in breast cancer may be attributed to the combination of this antioestrogen effect with its well documented suppression of steroidogenesis.
authors.affiliation: School of Biological Sciences, Queen Mary, University of London, United Kingdom.
authors.forename: John R
authors.initials: JR
authors.lastname: Puddefoot
authors.forename: Stewart
authors.initials: S
authors.lastname: Barker
authors.forename: Hilary R
authors.initials: HR
authors.lastname: Glover
authors.forename: Sylvanie D M
authors.initials: SD
authors.lastname: Malouitre
authors.forename: Gavin P
authors.initials: GP
authors.lastname: Vinson
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism; D013196:Dihydrotestosterone / Q000031:analogs & derivatives / Q000494:pharmacology*; D024202:Electrophoretic Mobility Shift Assay; D004958:Estradiol / Q000378:metabolism / Q000494:pharmacology; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D007700:Kinetics; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011960:Receptors, Estrogen / Q000037:antagonists & inhibitors* / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D020033:Protein Isoforms; D011960:Receptors, Estrogen; D013196:Dihydrotestosterone; D004958:Estradiol; C009954:trilostane