title: The RET kinase inhibitor NVP-AST487 blocks growth and calcitonin gene expression through distinct mechanisms in medullary thyroid cancer cells.
abstract: The RET kinase has emerged as a promising target for the therapy of medullary thyroid cancers (MTC) and of a subset of papillary thyroid cancers. NVP-AST487, a N,N'-diphenyl urea with an IC(50) of 0.88 mumol/L on RET kinase, inhibited RET autophosphorylation and activation of downstream effectors, and potently inhibited the growth of human thyroid cancer cell lines with activating mutations of RET but not of lines without RET mutations. NVP-AST487 induced a dose-dependent growth inhibition of xenografts of NIH3T3 cells expressing oncogenic RET, and of the MTC cell line TT in nude mice. MTCs secrete calcitonin, a useful indicator of tumor burden. Human plasma calcitonin levels derived from the TT cell xenografts were inhibited shortly after treatment, when tumor volume was still unchanged, indicating that the effects of RET kinase inhibition on calcitonin secretion were temporally dissociated from its tumor-inhibitory properties. Accordingly, NVP-AST487 inhibited calcitonin gene expression in vitro in TT cells, in part, through decreased gene transcription. These data point to a previously unknown physiologic role of RET signaling on calcitonin gene expression. Indeed, the RET ligands persephin and GDNF robustly stimulated calcitonin mRNA, which was blocked by pretreatment with NVP-AST487. Antagonists of RET kinase activity in patients with MTC may result in effects on plasma calcitonin that are either disproportionate or dissociated from the effects on tumor burden, because RET kinase mediates a physiologic pathway controlling calcitonin secretion. The role of traditional tumor biomarkers may need to be reassessed as targeted therapies designed against oncoproteins with key roles in pathogenesis are implemented.
authors.affiliation: Division of Endocrinology and Metabolism, University of Cincinnati, Cincinnati, Ohio, USA.
authors.forename: Nagako
authors.initials: N
authors.lastname: Akeno-Stuart
authors.forename: Michelle
authors.initials: M
authors.lastname: Croyle
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Knauf
authors.forename: Roberta
authors.initials: R
authors.lastname: Malaguarnera
authors.forename: Donata
authors.initials: D
authors.lastname: Vitagliano
authors.forename: Massimo
authors.initials: M
authors.lastname: Santoro
authors.forename: Christine
authors.initials: C
authors.lastname: Stephan
authors.forename: Konstantina
authors.initials: K
authors.lastname: Grosios
authors.forename: Markus
authors.initials: M
authors.lastname: Wartmann
authors.forename: Robert
authors.initials: R
authors.lastname: Cozens
authors.forename: Giorgio
authors.initials: G
authors.lastname: Caravatti
authors.forename: Doriano
authors.initials: D
authors.lastname: Fabbro
authors.forename: Heidi A
authors.initials: HA
authors.lastname: Lane
authors.forename: James A
authors.initials: JA
authors.lastname: Fagin
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002116:Calcitonin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002224:Carbanilides / Q000494:pharmacology*; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000378:metabolism; D006801:Humans; D020128:Inhibitory Concentration 50; D051379:Mice; D009368:Neoplasm Transplantation; D010766:Phosphorylation; D051096:Proto-Oncogene Proteins c-ret / Q000037:antagonists & inhibitors*; D013964:Thyroid Neoplasms / Q000188:drug therapy* / Q000201:enzymology*; D010671:Phenylurea Compounds; D011743:Pyrimidines
chemical_list: D000970:Antineoplastic Agents; D002116:Calcitonin; D002224:Carbanilides; D004791:Enzyme Inhibitors; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051096:Proto-Oncogene Proteins c-ret; C522130:NVP-AST487; D010671:Phenylurea Compounds; D011743:Pyrimidines