title: Sorafenib inhibits imatinib-resistant KIT and platelet-derived growth factor receptor beta gatekeeper mutants.
abstract: OBJECTIVE
  Targeting of KIT and platelet-derived growth factor receptor (PDGFR) tyrosine kinases by imatinib is an effective anticancer strategy. However, mutations of the gatekeeper residue (T670 in KIT and T681 in PDGFRbeta) render the two kinases resistant to imatinib. The aim of this study was to evaluate whether sorafenib (BAY 43-9006), a multitargeted ATP-competitive inhibitor of KIT and PDGFR, was active against imatinib-resistant KIT and PDGFRbeta kinases.
  
  
  METHODS
  We used in vitro kinase assays and immunoblot with phosphospecific antibodies to determine the activity of sorafenib on KIT and PDGFRbeta kinases. We also exploited reporter luciferase assays to measure the effects of sorafenib on KIT and PDGFRbeta downstream signaling events. The activity of sorafenib on interleukin-3-independent proliferation of Ba/F3 cells expressing oncogenic KIT or its imatinib-resistant T670I mutant was also tested.
  
  
  RESULTS
  Sorafenib efficiently inhibited gatekeeper mutants of KIT and PDGFRbeta (IC(50) for KIT T670I, 60 nmol/L; IC(50) for PDGFRbeta T681I, 110 nmol/L). Instead, it was less active against activation loop mutants of the two receptors (IC(50) for KIT D816V, 3.8 micromol/L; IC(50) for PDGFRbeta D850V, 1.17 micromol/L) that are also imatinib-resistant. Sorafenib blocked receptor autophosphorylation and signaling of KIT and PDGFRbeta gatekeeper mutants in intact cells as well as activation of AP1-responsive and cyclin D1 gene promoters, respectively. Finally, the compound inhibited KIT-dependent proliferation of Ba/F3 cells expressing the oncogenic KIT mutant carrying the T670I mutation.
  
  
  CONCLUSIONS
  Sorafenib might be a promising anticancer agent for patients carrying KIT and PDGFRbeta gatekeeper mutations.
authors.affiliation: Istituto di Endocrinologia ed Oncologia Sperimentale del CNR, Dipartimento di Biologia e Patologia Cellulare e Molecolare, Università di Napoli Federico II, Naples, Italy.
authors.forename: Teresa
authors.initials: T
authors.lastname: Guida
authors.forename: Suresh
authors.initials: S
authors.lastname: Anaganti
authors.forename: Livia
authors.initials: L
authors.lastname: Provitera
authors.forename: Richard
authors.initials: R
authors.lastname: Gedrich
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Sullivan
authors.forename: Scott M
authors.initials: SM
authors.lastname: Wilhelm
authors.forename: Massimo
authors.initials: M
authors.lastname: Santoro
authors.forename: Francesca
authors.initials: F
authors.lastname: Carlomagno
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001549:Benzamides; D001557:Benzenesulfonates / Q000494:pharmacology*; D001667:Binding, Competitive; D049109:Cell Proliferation; D006801:Humans; D000068877:Imatinib Mesylate; D020128:Inhibitory Concentration 50; D007377:Interleukin-3 / Q000378:metabolism; D051379:Mice; D009154:Mutation; D009536:Niacinamide / Q000031:analogs & derivatives; D010671:Phenylurea Compounds; D010879:Piperazines / Q000494:pharmacology*; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism*; D020574:Proto-Oncogene Proteins c-sis / Q000235:genetics* / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology*; D000077157:Sorafenib
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D001557:Benzenesulfonates; D007377:Interleukin-3; D010671:Phenylurea Compounds; D010879:Piperazines; D020574:Proto-Oncogene Proteins c-sis; D011725:Pyridines; D011743:Pyrimidines; D009536:Niacinamide; D000068877:Imatinib Mesylate; D000255:Adenosine Triphosphate; D000077157:Sorafenib; D019009:Proto-Oncogene Proteins c-kit