title: A novel FIP1L1-PDGFRA mutant destabilizing the inactive conformation of the kinase domain in chronic eosinophilic leukemia/hypereosinophilic syndrome.
abstract: BACKGROUND
  The Fip1-like-1-platelet-derived growth factor receptor alpha (FIP1L1-PDGFRA) gene fusion is a common cause of chronic eosinophilic leukemia (CEL)/hypereosinophilic syndrome (HES), and patients suffering from this particular subgroup of CEL/HES respond to low-dose imatinib therapy. However, some patients may develop imatinib resistance because of an acquired T674I mutation, which is believed to prevent drug binding through steric hindrance.
  
  
  METHODS
  In an imatinib resistant FIP1L1-PDGFRA positive patient, we analyzed the molecular structure of the fusion gene and analyzed the effect of several kinase inhibitors on FIP1L1-PDGFRA-mediated proliferative responses in vitro.
  
  
  RESULTS
  Sequencing of the FIP1L1-PDGFRA fusion gene revealed the occurrence of a S601P mutation, which is located within the nucleotide binding loop. In agreement with the clinical observations, imatinib did not inhibit the proliferation of S601P mutant FIP1L1-PDGFRA-transduced Ba/F3 cells. Moreover, sorafenib, which has been described to inhibit T674I mutant FIP1L1-PDGFRA, failed to block S601P mutant FIP1L1-PDGFRA. Structural modeling revealed that the newly identified S601P mutated form of PDGFRA destabilizes the inactive conformation of the kinase domain that is necessary to bind imatinib as well as sorafenib.
  
  
  CONCLUSIONS
  We identified a novel mutation in FIP1L1-PDGFRA resulting in both imatinib and sorafenib resistance. The identification of novel drug-resistant FIP1L1-PDGFRA variants may help to develop the next generation of target-directed compounds for CEL/HES and other leukemias.
authors.affiliation: Institute of Pharmacology, University of Bern, Bern, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Salemi
authors.forename: S
authors.initials: S
authors.lastname: Yousefi
authors.forename: D
authors.initials: D
authors.lastname: Simon
authors.forename: I
authors.initials: I
authors.lastname: Schmid
authors.forename: L
authors.initials: L
authors.lastname: Moretti
authors.forename: L
authors.initials: L
authors.lastname: Scapozza
authors.forename: H-U
authors.initials: HU
authors.lastname: Simon
mesh_terms: D000595:Amino Acid Sequence; D001549:Benzamides; D001557:Benzenesulfonates / Q000494:pharmacology; D002908:Chronic Disease; D004351:Drug Resistance; D006801:Humans; D017681:Hypereosinophilic Syndrome / Q000188:drug therapy / Q000235:genetics*; D000068877:Imatinib Mesylate; D008969:Molecular Sequence Data; D009154:Mutation; D009536:Niacinamide / Q000031:analogs & derivatives; D015514:Oncogene Proteins, Fusion / Q000737:chemistry / Q000235:genetics*; D010671:Phenylurea Compounds; D010879:Piperazines / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D011725:Pyridines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D020796:Receptor, Platelet-Derived Growth Factor alpha / Q000737:chemistry / Q000235:genetics*; D000077157:Sorafenib; D039221:mRNA Cleavage and Polyadenylation Factors / Q000737:chemistry / Q000235:genetics*
chemical_list: D001549:Benzamides; D001557:Benzenesulfonates; D015514:Oncogene Proteins, Fusion; D010671:Phenylurea Compounds; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011725:Pyridines; D011743:Pyrimidines; D039221:mRNA Cleavage and Polyadenylation Factors; D009536:Niacinamide; D000068877:Imatinib Mesylate; D000077157:Sorafenib; C479819:FIP1L1-PDGFRA fusion protein, human; D020796:Receptor, Platelet-Derived Growth Factor alpha