title: Estrogen induces death of tamoxifen-resistant MCF-7 cells: contrasting effect of the estrogen receptor downregulator fulvestrant.
abstract: A common problem in breast cancer therapy is resistance to the antiestrogen tamoxifen. However, tamoxifen-resistant breast tumors can still respond to other hormonal therapies. In animal models of tamoxifen-resistant breast cancer cells, physiological levels of estrogen can induce tumor regression. Recently, the estrogen receptor downregulator fulvestrant was shown to promote tumor growth of tamoxifen-resistant cells when added in combination with physiological levels of estrogen. Here, we show, using a cell culture model, that continuous exposure of tamoxifen-resistant cells to physiological levels of estrogen leads to cell death. Addition of the estrogen receptor downregulator fulvestrant prevents estrogen-induced death in a dose-dependent manner. Our data indicate that endogenous levels of estrogen affect the response of tamoxifen-resistant cells to fulvestrant. These results suggest that failure of fulvestrant to inhibit tumor growth in some tamoxifen-resistant patients may be due to endogenous estrogen levels. Moreover, these studies support short-term treatment with estrogen as a second-line hormonal therapy for tamoxifen-resistant breast cancer.
authors.affiliation: Department of Pharmacology, Penn State College of Medicine, Hershey, PA 17033, USA. mcplanas@psu.edu
authors.forename: Maricarmen D
authors.initials: MD
authors.lastname: Planas-Silva
authors.forename: Paul K
authors.initials: PK
authors.lastname: Waltz
authors.forename: Robin L
authors.initials: RL
authors.lastname: Kilker
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D049109:Cell Proliferation / Q000187:drug effects; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D000077267:Fulvestrant; D006801:Humans; D009376:Neoplasms, Hormone-Dependent / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D011960:Receptors, Estrogen / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D004965:Estrogen Antagonists; D020847:Estrogen Receptor Modulators; D004967:Estrogens; D011960:Receptors, Estrogen; D013629:Tamoxifen; D000077267:Fulvestrant; D004958:Estradiol