title: Inhibition of medullary thyroid carcinoma cell proliferation and RET phosphorylation by tyrosine kinase inhibitors.
abstract: BACKGROUND
  Most medullary thyroid carcinomas (MTCs) result from gain-of-function mutations in the RET proto-oncogene, which encodes a transmembrane tyrosine kinase receptor. Systemic therapies have not been effective in treating this disease. We evaluated the effects of 3 tyrosine kinase inhibitors (TKIs) on MTC cell growth and RET tyrosine kinase activity by using an in vitro model.
  
  
  METHODS
  An MTC cell line (TT cells, RETc634 mutant) cultured in RPMI medium was exposed to varying concentrations of STI571, genistein, or allyl-geldanamycin with controls (no TKI) for 3 to 48 hours. Cellular protein was analyzed by immunoprecipitated Western blot analysis probing with a monoclonal antiphosphotyrosine antibody. Cell proliferation was determined by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) and 5-bromo-2'-deoxyuridine (BrdU) assays.
  
  
  RESULTS
  RET phosphorylation was inhibited at 24 hours of exposure to 5 to 20 micromol/L STI571 and 48 hours of exposure to genistein (200 micromol/L) and allyl-geldanamycin (6 micromol/L). RET protein was detected in equal concentrations in all experimental conditions. MTT and BrdU assays demonstrated a dose-dependent decrease in TT cell proliferation with exposure to the 3 TKIs.
  
  
  CONCLUSIONS
  These TKIs selectively inhibit cell growth and RET tyrosine kinase activity of MTC cells in vitro in a dose manner. This study suggests the use of TKIs in human trials as a systemic therapy for MTC.
authors.affiliation: Section of Endocrine and Oncologic Surgery, Washington University School of Medicine, St Louis, MO 63110, USA.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Cohen
authors.forename: Hameda B
authors.initials: HB
authors.lastname: Hussain
authors.forename: Jeffrey F
authors.initials: JF
authors.lastname: Moley
mesh_terms: D001549:Benzamides; D016227:Benzoquinones; D018276:Carcinoma, Medullary; D002455:Cell Division / Q000187:drug effects; D029721:Drosophila Proteins; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D019833:Genistein / Q000494:pharmacology; D006801:Humans; D000068877:Imatinib Mesylate; D047029:Lactams, Macrocyclic; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051096:Proto-Oncogene Proteins c-ret; D011743:Pyrimidines / Q000494:pharmacology*; D011809:Quinones / Q000494:pharmacology; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D013964:Thyroid Neoplasms; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000201:enzymology
chemical_list: D001549:Benzamides; D016227:Benzoquinones; D029721:Drosophila Proteins; D004791:Enzyme Inhibitors; D047029:Lactams, Macrocyclic; C000715470:MAS1 protein, human; D010879:Piperazines; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D011743:Pyrimidines; D011809:Quinones; D000068877:Imatinib Mesylate; D019833:Genistein; D011505:Protein-Tyrosine Kinases; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; C416649:Ret protein, Drosophila; C001277:geldanamycin