title: Breakdown of the FLT3-ITD/STAT5 axis and synergistic apoptosis induction by the histone deacetylase inhibitor panobinostat and FLT3-specific inhibitors.
abstract: Activating mutations of the class III receptor tyrosine kinase FLT3 are the most frequent molecular aberration in acute myeloid leukemia (AML). Mutant FLT3 accelerates proliferation, suppresses apoptosis, and correlates with poor prognosis. Therefore, it is a promising therapeutic target. Here, we show that RNA interference against FLT3 with an internal tandem duplication (FLT3-ITD) potentiates the efficacy of the histone deacetylase inhibitor (HDACi) panobinostat (LBH589) against AML cells expressing FLT3-ITD. Similar to RNA interference, tyrosine kinase inhibitors (TKI; AC220/cpd.102/PKC412) in combination with LBH589 exhibit superior activity against AML cells. Median dose-effect analyses of drug-induced apoptosis rates of AML cells (MV4-11 and MOLM-13) revealed combination index (CI) values indicating strong synergism. AC220, the most potent and FLT3-specific TKI, shows highest synergism with LBH589 in the low nanomolar range. A 4-hour exposure to LBH589 + AC220 already generates more than 50% apoptosis after 24 hours. Different cell lines lacking FLT3-ITD as well as normal peripheral blood mononuclear cells are not significantly affected by LBH589 + TKI, showing the specificity of this treatment regimen. Immunoblot analyses show that LBH589 + TKI induce apoptosis via degradation of FLT3-ITD and its prosurvival target STAT5. Previously, we showed the LBH589-induced proteasomal degradation of FLT3-ITD. Here, we show that activated caspase-3 also contributes to the degradation of FLT3-ITD and that STAT5 is a direct target of this protease. Our data strongly emphasize HDACi/TKI drug combinations as promising modality for the treatment of FLT3-ITD-positive AMLs.
authors.affiliation: Institute of Biochemistry and Biophysics, Center for Molecular Biomedicine, Friedrich-Schiller University, Hans-Knöll-Str. 2, Jena 07745, Germany.
authors.forename: Kristin
authors.initials: K
authors.lastname: Pietschmann
authors.forename: Hella Anna
authors.initials: HA
authors.lastname: Bolck
authors.forename: Marc
authors.initials: M
authors.lastname: Buchwald
authors.forename: Steffi
authors.initials: S
authors.lastname: Spielberg
authors.forename: Harald
authors.initials: H
authors.lastname: Polzer
authors.forename: Karsten
authors.initials: K
authors.lastname: Spiekermann
authors.forename: Gesine
authors.initials: G
authors.lastname: Bug
authors.forename: Thorsten
authors.initials: T
authors.lastname: Heinzel
authors.forename: Frank-Dietmar
authors.initials: FD
authors.lastname: Böhmer
authors.forename: Oliver H
authors.initials: OH
authors.lastname: Krämer
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D052160:Benzothiazoles / Q000737:chemistry / Q000494:pharmacology; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D004357:Drug Synergism; D020440:Gene Duplication; D055785:Gene Knockdown Techniques; D056572:Histone Deacetylase Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D006877:Hydroxamic Acids / Q000737:chemistry / Q000494:pharmacology*; D007211:Indoles / Q000737:chemistry / Q000494:pharmacology*; D015470:Leukemia, Myeloid, Acute / Q000473:pathology; D000077767:Panobinostat; D010671:Phenylurea Compounds / Q000737:chemistry / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000737:chemistry / Q000494:pharmacology; D055550:Protein Stability / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects; D050799:STAT5 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D019311:Staurosporine / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology; D051941:fms-Like Tyrosine Kinase 3 / Q000037:antagonists & inhibitors* / Q000235:genetics* / Q000378:metabolism
chemical_list: D052160:Benzothiazoles; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; D007211:Indoles; D010671:Phenylurea Compounds; D047428:Protein Kinase Inhibitors; D050799:STAT5 Transcription Factor; C544967:quizartinib; D000077767:Panobinostat; C497970:FLT3 protein, human; D051941:fms-Like Tyrosine Kinase 3; D020169:Caspases; D019311:Staurosporine; C059539:midostaurin