title: Androgen receptor overexpression induces tamoxifen resistance in human breast cancer cells.
abstract: Although the androgen receptor (AR) is a known clinical target in prostate cancer, little is known about its possible role in breast cancer. We have investigated the role of AR expression in human breast cancer in response to treatment with the antiestrogen tamoxifen. Resistance to tamoxifen is a major problem in treating women with breast cancer. By gene expression profiling, we found elevated AR and reduced estrogen receptor (ER) alpha mRNA in tamoxifen-resistant tumors. Exogenous overexpression of AR rendered ERalpha-positive MCF-7 breast cancer cells resistant to the growth-inhibitory effects of tamoxifen in anchorage-independent growth assays and in xenograft studies in athymic nude mice. AR-overexpressing cells remained sensitive to growth stimulation with dihydrotestosterone. Treatment with the AR antagonist Casodex (bicalutamide) reversed this resistance, demonstrating the involvement of AR signaling in tamoxifen resistance. In AR-overexpressing cells, tamoxifen induced transcriptional activation by ERalpha that could be blocked by Casodex, suggesting that AR overexpression enhances tamoxifen's agonistic properties. Our data suggest a role for AR overexpression as a novel mechanism of hormone resistance, so that AR may offer a new clinical therapeutic target in human breast cancers.
authors.affiliation: Breast Center, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: Francesca
authors.initials: F
authors.lastname: De Amicis
authors.forename: Janagi
authors.initials: J
authors.lastname: Thirugnansampanthan
authors.forename: Yukun
authors.initials: Y
authors.lastname: Cui
authors.forename: Jennifer
authors.initials: J
authors.lastname: Selever
authors.forename: Amanda
authors.initials: A
authors.lastname: Beyer
authors.forename: Irma
authors.initials: I
authors.lastname: Parra
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Weigel
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Herynk
authors.forename: Anna
authors.initials: A
authors.lastname: Tsimelzon
authors.forename: Michael T
authors.initials: MT
authors.lastname: Lewis
authors.forename: Gary C
authors.initials: GC
authors.lastname: Chamness
authors.forename: Susan G
authors.initials: SG
authors.lastname: Hilsenbeck
authors.forename: Sebastiano
authors.initials: S
authors.lastname: Andò
authors.forename: Suzanne A W
authors.initials: SA
authors.lastname: Fuqua
mesh_terms: D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005260:Female; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D020411:Oligonucleotide Array Sequence Analysis; D011944:Receptors, Androgen / Q000096:biosynthesis* / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013629:Tamoxifen / Q000494:pharmacology*; D014162:Transfection; D023041:Xenograft Model Antitumor Assays
chemical_list: D018931:Antineoplastic Agents, Hormonal; D011944:Receptors, Androgen; D013629:Tamoxifen