title: Analogs of GnRH-I and GnRH-II inhibit epidermal growth factor-induced signal transduction and resensitize resistant human breast cancer cells to 4OH-tamoxifen.
abstract: About 50-64% of human breast cancers express receptors for GnRH-I. Direct antiproliferative effects of analogs of GnRH-I on human breast cancer cell lines have been shown. They are at least in part mediated by antagonizing growth promoting effects of estradiol, epidermal growth factor (EGF) or insulin-like growth factor. Recently, expression of a putative receptor for GnRH-II in human tissues was demonstrated. Antiproliferative effects of GnRH-II in human endometrial and ovarian cancer cells were shown not to be mediated through the GnRH-I receptor. Now we demonstrate direct anti-proliferative effects of the GnRH-I analog Triptorelin and the GnRH-II analog [d-Lys(6)]GnRH-II in MCF-7 and T47D human breast cancer cells expressing GnRH-I receptors and putative GnRH-II receptors. Pretreatment with Triptorelin or [d-Lys(6)]GnRH-II blocked EGF-induced autophosphoryla-tion of EGF receptor and activation of mitogen-activated protein kinase (extracellular-signal-regulated kinase 1/2 (ERK1/2)) in these cells. In sublines of MCF-7 and T47D cells, which were developed to be resistant to 4OH-tamoxifen, HER-2/p185 was overexpressed. Pretreatment of these cell lines with Triptorelin or [d-Lys(6)]GnRH-II completely abolished resistance to 4OH-tamoxifen, assessed by 4OH-tamoxifen-induced apoptosis. Analogs of GnRH-I and GnRH-II counteract EGF-dependent signal transduction in human breast cancer cells with expression of receptors for GnRH-I and GnRH-II. Through this mechanism, they probably reverse acquired resistance to 4OH-tamoxifen mediated through overexpression or activation of receptors of the c-erbB family.
authors.affiliation: Department of Gynecology and Obstetrics, Georg-August-University, Robert-Koch-Street 40, D-37075 Göttingen, Germany.
authors.forename: Andreas R
authors.initials: AR
authors.lastname: Günthert
authors.forename: Carsten
authors.initials: C
authors.lastname: Gründker
authors.forename: Agnes
authors.initials: A
authors.lastname: Olota
authors.forename: Julia
authors.initials: J
authors.lastname: Läsche
authors.forename: Nicola
authors.initials: N
authors.lastname: Eicke
authors.forename: Günter
authors.initials: G
authors.lastname: Emons
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000473:pathology / Q000503:physiopathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000378:metabolism; D004965:Estrogen Antagonists / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D000077156:Gefitinib; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D010766:Phosphorylation / Q000187:drug effects; D011799:Quinazolines / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects*; D013629:Tamoxifen / Q000031:analogs & derivatives* / Q000494:pharmacology; D017329:Triptorelin Pamoate / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D004965:Estrogen Antagonists; C505959:GnRH-II, Lys(6)-; D011799:Quinazolines; D017329:Triptorelin Pamoate; D013629:Tamoxifen; C016601:afimoxifene; D007987:Gonadotropin-Releasing Hormone; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D048049:Extracellular Signal-Regulated MAP Kinases; D000077156:Gefitinib