title: Emergence of polyclonal FLT3 tyrosine kinase domain mutations during sequential therapy with sorafenib and sunitinib in FLT3-ITD-positive acute myeloid leukemia.
abstract: OBJECTIVE
  To evaluate the clinical activity of sequential therapy with sorafenib and sunitinib in FMS-like tyrosine kinase 3 (FLT3)-internal tandem duplication (ITD)-positive acute myelogenous leukemia (AML) and monitor the emergence of secondary FLT3 tyrosine kinase domain (TKD) mutations during treatment.
  
  
  METHODS
  Six children with relapsed/refractory AML were treated with sorafenib in combination with clofarabine and cytarabine, followed by single-agent sorafenib if not a candidate for transplantation. Sunitinib was initiated after sorafenib relapse. Bone marrow samples were obtained for assessment of FLT3 TKD mutations by deep amplicon sequencing. The phase of secondary mutations with ITD alleles was assessed by cloning and sequencing of FLT3 exons 14 through 20. Identified mutations were modeled in Ba/F3 cells, and the effect of kinase inhibitors on FLT3 signaling and cell viability was assessed.
  
  
  RESULTS
  Four patients achieved complete remission, but 3 receiving maintenance therapy with sorafenib relapsed after 14 to 37 weeks. Sunitinib reduced circulating blasts in two patients and marrow blasts in one. Two patients did not respond to sorafenib combination therapy or sunitinib. FLT3 mutations at residues D835 and F691 were observed in sorafenib resistance samples on both ITD-positive and -negative alleles. Deep sequencing revealed low-level mutations and their evolution during sorafenib treatment. Sunitinib suppressed leukemic clones with D835H and F691L mutations, but not D835Y. Cells expressing sorafenib-resistant FLT3 mutations were sensitive to sunitinib in vitro.
  
  
  CONCLUSIONS
  Sunitinib has activity in patients that are resistant to sorafenib and harbor secondary FLT3 TKD mutations. The use of sensitive methods to monitor FLT3 mutations during therapy may allow individualized treatment with the currently available kinase inhibitors.
authors: Authors' Affiliations: Departments of Pharmaceutical Sciences, Structural Biology, Pathology, and Oncology, Hartwell Center for Bioinformatics and Biotechnology, St. Jude Children's Research Hospital; and Department of Pediatrics, University of Tennessee, Memphis, Tennessee.
authors: Sharyn D
authors: SD
authors: Baker
authors: Eric I
authors: EI
authors: Zimmerman
authors: Yong-Dong
authors: YD
authors: Wang
authors: Shelley
authors: S
authors: Orwick
authors: Douglas S
authors: DS
authors: Zatechka
authors: Jassada
authors: J
authors: Buaboonnam
authors: Geoffrey A
authors: GA
authors: Neale
authors: Scott R
authors: SR
authors: Olsen
authors: Eric J
authors: EJ
authors: Enemark
authors: Sheila
authors: S
authors: Shurtleff
authors: Jeffrey E
authors: JE
authors: Rubnitz
authors: Charles G
authors: CG
authors: Mullighan
authors: Hiroto
authors: H
authors: Inaba
mesh_terms: D000293:Adolescent; D000483:Alleles; D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry / Q000627:therapeutic use; D045744:Cell Line, Tumor; D002648:Child; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005260:Female; D006801:Humans; D007211:Indoles / Q000737:chemistry / Q000627:therapeutic use*; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy* / Q000235:genetics*; D008297:Male; D051379:Mice; D008958:Models, Molecular; D008968:Molecular Conformation; D009154:Mutation; D009536:Niacinamide / Q000031:analogs & derivatives* / Q000737:chemistry / Q000627:therapeutic use; D010671:Phenylurea Compounds / Q000737:chemistry / Q000627:therapeutic use*; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs / Q000235:genetics*; D047428:Protein Kinase Inhibitors / Q000737:chemistry / Q000627:therapeutic use; D011758:Pyrroles / Q000737:chemistry / Q000627:therapeutic use*; D000077157:Sorafenib; D000077210:Sunitinib; D016896:Treatment Outcome; D051941:fms-Like Tyrosine Kinase 3 / Q000737:chemistry / Q000235:genetics*
chemical_list: D000970:Antineoplastic Agents; D007211:Indoles; D010671:Phenylurea Compounds; D047428:Protein Kinase Inhibitors; D011758:Pyrroles; D009536:Niacinamide; D000077157:Sorafenib; C497970:FLT3 protein, human; D051941:fms-Like Tyrosine Kinase 3; D000077210:Sunitinib
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