title: Reversal of acquired drug resistance in FLT3-mutated acute myeloid leukemia cells via distinct drug combination strategies.
abstract: OBJECTIVE
  FMS-like tyrosine kinase-3 (FLT3) internal tandem duplication (FLT3-ITD) mutations are common in patients with acute myeloid leukemia (AML). These patients regularly develop resistance to FLT3 inhibitors suggesting that targeted combination drug strategies are needed to enhance AML therapy efficacy.
  
  
  METHODS
  Acquired point mutations of FLT3-ITD gene were screened using cDNA-based sequencing approach in vitro sorafenib-resistant cells, which were developed by long-term exposure of Ba/F3-ITD to increasing doses of sorafenib, and in FLT3-ITD mutated AML patients, who developed relapse following sorafenib therapy. Drug effects (e.g., proliferation inhibition, apoptosis induction, and changes in signal transduction protein expression) were assessed in AML cells harboring the point mutations in vitro and in FLT3-ITD-mutated AML patient samples.
  
  
  RESULTS
  We identified several acquired point mutations in the tyrosine kinase domains (TKD) of the FLT3 gene in sorafenib-resistant murine leukemia cell line carrying human FLT3-ITD mutations, which were also detected in two of four sorafenib-resistant patient samples. Engineering these point mutations into Ba/F3-ITD cells generated sublines that demonstrated varying degrees of sorafenib [a type II tyrosine kinase inhibitor (TKI)] resistance. A similar pattern of resistance could be observed by exposing these sublines to the other type II TKIs AC220 and MLN518. However, these sublines retained sensitivity to the type I TKIs PKC412 or crenolanib. The combination of crenolanib with sorafenib demonstrated marked cytotoxic effects in all of the sorafenib-resistant sublines.
  
  
  CONCLUSIONS
  These combination strategies could be clinically important in reversing acquired resistance to FLT3 inhibition in AML.
authors.affiliation: Authors' Affiliations: Section of Molecular Hematology and Therapy, Department of Leukemia, Department of Stem Cell Transplantation and Cellular Therapy, The University of Texas M.D. Anderson Cancer Center, Houston; and AROG Pharmaceuticals LLC, Dallas, Texas.
authors.forename: Weiguo
authors.initials: W
authors.lastname: Zhang
authors.forename: Chen
authors.initials: C
authors.lastname: Gao
authors.forename: Marina
authors.initials: M
authors.lastname: Konopleva
authors.forename: Ye
authors.initials: Y
authors.lastname: Chen
authors.forename: Rodrigo O
authors.initials: RO
authors.lastname: Jacamo
authors.forename: Gautam
authors.initials: G
authors.lastname: Borthakur
authors.forename: Jorge E
authors.initials: JE
authors.lastname: Cortes
authors.forename: Farhad
authors.initials: F
authors.lastname: Ravandi
authors.forename: Abhijit
authors.initials: A
authors.lastname: Ramachandran
authors.forename: Michael
authors.initials: M
authors.lastname: Andreeff
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D004252:DNA Mutational Analysis; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D004357:Drug Synergism; D020440:Gene Duplication; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D009154:Mutation; D009536:Niacinamide / Q000031:analogs & derivatives / Q000494:pharmacology; D010671:Phenylurea Compounds / Q000494:pharmacology; D017354:Point Mutation; D054730:Protein Interaction Domains and Motifs / Q000235:genetics; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D000077157:Sorafenib; D020080:Tandem Repeat Sequences; D051941:fms-Like Tyrosine Kinase 3 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D008565:Membrane Proteins; D010671:Phenylurea Compounds; D047428:Protein Kinase Inhibitors; C084881:flt3 ligand protein; D009536:Niacinamide; D000077157:Sorafenib; D051941:fms-Like Tyrosine Kinase 3