title: Ponatinib (AP24534) is a novel potent inhibitor of oncogenic RET mutants associated with thyroid cancer.
abstract: BACKGROUND
  The RET tyrosine kinase encoding gene acts as a dominantly transforming oncogene in thyroid carcinoma and other malignancies. Ponatinib (AP24534) is an oral ATP-competitive tyrosine kinase inhibitor that is in advanced clinical experimentation in leukemia.
  
  
  OBJECTIVE
  We tested whether ponatinib inhibited RET kinase and oncogenic activity.
  
  
  METHODS
  Ponatinib activity was studied by an in vitro RET immunocomplex kinase assay and immunoblotting. The effects of ponatinib on proliferation of human TT, MZ-CRC-1, and TPC-1 thyroid carcinoma cells, which harbor endogenous oncogenic RET alleles, and of NIH3T3 fibroblasts transfected with oncogenic RET mutants were determined. Ponatinib activity on TT cell xenografted tumors in athymic mice was measured.
  
  
  RESULTS
  Ponatinib inhibited immunopurified RET kinase at the IC₅₀ of 25.8 nM (95% confidence interval [CI] = 23.15-28.77 nM). It also inhibited (IC₅₀ = 33.9 nM; 95% CI = 26.41-43.58 nM) kinase activity of RET/V804M, a RET mutant displaying resistance to other tyrosine kinase inhibitor. Ponatinib blunted phosphorylation of point-mutant and rearranged RET-derived oncoproteins and inhibited proliferation of RET-transformed fibroblasts and RET mutant thyroid carcinoma cells. Finally, after 3 weeks of treatment with ponatinib (30 mg/kg/d), the volume of TT cell (medullary thyroid carcinoma) xenografts was reduced from 133 mm³ to an unmeasurable size (difference = 133 mm³, 95% CI = -83 to 349 mm³) (P < .001). Ponatinib-treated TT cell tumors displayed a reduction in the mitotic index, RET phosphorylation, and signaling.
  
  
  CONCLUSIONS
  Ponatinib is a potent inhibitor of RET kinase and has promising preclinical activity in models of RET-driven medullary thyroid carcinoma.
authors.affiliation: Istituto di Endocrinologia ed Oncologia Sperimentale del Consiglio Nazionale delle Ricerche, Dipartimento di Medicina Molecolare e Biotecnologie Mediche, Università di Napoli Federico II, 80131 Naples, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: De Falco
authors.forename: Preziosa
authors.initials: P
authors.lastname: Buonocore
authors.forename: Magesh
authors.initials: M
authors.lastname: Muthu
authors.forename: Liborio
authors.initials: L
authors.lastname: Torregrossa
authors.forename: Fulvio
authors.initials: F
authors.lastname: Basolo
authors.forename: Marc
authors.initials: M
authors.lastname: Billaud
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Gozgit
authors.forename: Francesca
authors.initials: F
authors.lastname: Carlomagno
authors.forename: Massimo
authors.initials: M
authors.lastname: Santoro
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D002277:Carcinoma / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D018278:Carcinoma, Neuroendocrine; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology / Q000627:therapeutic use*; D051379:Mice; D008819:Mice, Nude; D050505:Mutant Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use*; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D051096:Proto-Oncogene Proteins c-ret / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D011724:Pyridazines / Q000494:pharmacology / Q000627:therapeutic use*; D011897:Random Allocation; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D047368:Tumor Burden / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D007093:Imidazoles; D050505:Mutant Proteins; D047428:Protein Kinase Inhibitors; D011724:Pyridazines; D011994:Recombinant Proteins; C545373:ponatinib; D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human