title: Effects of the tyrosine-kinase inhibitor geldanamycin on ligand-induced Her-2/neu activation, receptor expression and proliferation of Her-2-positive malignant cell lines.
abstract: Geldanamycin belongs to the family of benzoquinoid ansamycin tyrosine-kinase inhibitors. We have examined its effects on Her-2/neu kinase activity, protein expression level, and proliferation of Her-2+ malignant cells. In SK-BR-3 breast-cancer cells, short-time treatment with geldanamycin completely abrogated gp30-ligand-induced activation of Her-2 without a change of receptor-expression level. Longer treatment of intact cells with geldanamycin induced decreased steady-state Her-2 autophosphorylation activity, which correlated with reduction of Her-2 protein expression and phosphotyrosine content of several proteins. The decrease was time- and dose-dependent, starting after 1 hr at 100 nM concentration and reaching completion by 24 hr. The reduction of the Her-2 protein level probably resulted from increased degradation, since the Her-2 mRNA level remained constant. Geldanamycin effects were not specific for Her-2, since the non-receptor tyrosine-kinase fyn was inhibited equally. In contrast to these results, protein-kinase-C activity was not affected. In 3 other malignant cell lines expressing different amounts of Her-2 (SK-BR-3 > SK-OV-3 > OVCAR3 > MCF7), geldanamycin also effectively reduced Her-2-kinase activity proportionally to the decrease of protein expression. In contrast, in a [3H]-thymidine-uptake assay, cell growth was meaningfully inhibited by geldanamycin at nanomolar concentrations only in SK-BR-3 (IC50 2 nM) and MCF7 (IC50 20 nM), while OVCAR3 was only moderately sensitive (IC50 2 microM) and SK-OV-3 was clearly resistant to geldanamycin. In direct comparison with herbimycin A, another benzoquinoid ansamycin that has been more thoroughly characterized, the biologic effects of geldanamycin were more pronounced.
authors.affiliation: Metabolism Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: F
authors.initials: F
authors.lastname: Hartmann
authors.forename: E M
authors.initials: EM
authors.lastname: Horak
authors.forename: C
authors.initials: C
authors.lastname: Cho
authors.forename: R
authors.initials: R
authors.lastname: Lupu
authors.forename: J B
authors.initials: JB
authors.lastname: Bolen
authors.forename: M A
authors.initials: MA
authors.lastname: Stetler-Stevenson
authors.forename: M
authors.initials: M
authors.lastname: Pfreundschuh
authors.forename: T A
authors.initials: TA
authors.lastname: Waldmann
authors.forename: I D
authors.initials: ID
authors.lastname: Horak
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology; D016227:Benzoquinones; D001943:Breast Neoplasms / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D047029:Lactams, Macrocyclic; D008024:Ligands; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors*; D010051:Ovarian Neoplasms / Q000473:pathology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011809:Quinones / Q000494:pharmacology*; D012333:RNA, Messenger / Q000096:biosynthesis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors*; D017828:Rifabutin / Q000031:analogs & derivatives; D014407:Tumor Cells, Cultured
chemical_list: D016227:Benzoquinones; D004791:Enzyme Inhibitors; D047029:Lactams, Macrocyclic; D008024:Ligands; D009363:Neoplasm Proteins; D011505:Protein-Tyrosine Kinases; D011809:Quinones; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D018719:Erb-b2 Receptor Tyrosine Kinases; D017828:Rifabutin; C020754:herbimycin; C001277:geldanamycin