title: Reversible resistance induced by FLT3 inhibition: a novel resistance mechanism in mutant FLT3-expressing cells.
abstract: OBJECTIVE
  Clinical responses achieved with FLT3 kinase inhibitors in acute myeloid leukemia (AML) are typically transient and partial. Thus, there is a need for identification of molecular mechanisms of clinical resistance to these drugs. In response, we characterized MOLM13 AML cell lines made resistant to two structurally-independent FLT3 inhibitors.
  
  
  METHODS
  MOLM13 cells were made drug resistant via prolonged exposure to midostaurin and HG-7-85-01, respectively. Cell proliferation was determined by Trypan blue exclusion. Protein expression was assessed by immunoblotting, immunoprecipitation, and flow cytometry. Cycloheximide was used to determine protein half-life. RT-PCR was performed to determine FLT3 mRNA levels, and FISH analysis was performed to determine FLT3 gene expression.
  
  
  CONCLUSIONS
  We found that MOLM13 cells readily developed cross-resistance when exposed to either midostaurin or HG-7-85-01. Resistance in both lines was associated with dramatically elevated levels of cell surface FLT3 and elevated levels of phosphor-MAPK, but not phospho-STAT5. The increase in FLT3-ITD expression was at least in part due to reduced turnover of the receptor, with prolonged half-life. Importantly, the drug-resistant phenotype could be rapidly reversed upon withdrawal of either inhibitor. Consistent with this phenotype, no significant evidence of FLT3 gene amplification, kinase domain mutations, or elevated levels of mRNA was observed, suggesting that protein turnover may be part of an auto-regulatory pathway initiated by FLT3 kinase activity. Interestingly, FLT3 inhibitor resistance also correlated with resistance to cytosine arabinoside. Over-expression of FLT3 protein in response to kinase inhibitors may be part of a novel mechanism that could contribute to clinical resistance.
authors: Department of Medical Oncology/Hematologic Neoplasia, Dana Farber Cancer Institute, Boston, Massachusetts, United States of America. ellen_weisberg@dfci.harvard.edu
authors: Ellen
authors: E
authors: Weisberg
authors: Arghya
authors: A
authors: Ray
authors: Erik
authors: E
authors: Nelson
authors: Sophia
authors: S
authors: Adamia
authors: Rosemary
authors: R
authors: Barrett
authors: Martin
authors: M
authors: Sattler
authors: Chengsheng
authors: C
authors: Zhang
authors: John F
authors: JF
authors: Daley
authors: David
authors: D
authors: Frank
authors: Edward
authors: E
authors: Fox
authors: James D
authors: JD
authors: Griffin
mesh_terms: D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000235:genetics*; D004795:Enzyme Stability / Q000187:drug effects / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects* / Q000235:genetics; D006207:Half-Life; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009154:Mutation; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D010879:Piperazines / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D019311:Staurosporine / Q000031:analogs & derivatives / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects; D051941:fms-Like Tyrosine Kinase 3 / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: C552521:HG-7-85-01 compound; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D013844:Thiazoles; D014443:Tyrosine; C497970:FLT3 protein, human; D051941:fms-Like Tyrosine Kinase 3; D019311:Staurosporine; C059539:midostaurin