title: Targeting FLT3 in primary MLL-gene-rearranged infant acute lymphoblastic leukemia.
abstract: Acute lymphoblastic leukemia (ALL) in infants is characterized by rearrangements of the mixed lineage leukemia (MLL) gene, drug resistance, and a poor treatment outcome. Therefore, novel therapeutic strategies are needed to improve prognosis. Recently, we showed that FLT3 is highly expressed in MLL rearranged ALL (MLL). Here we demonstrate FLT3 expression in infants with MLL (n = 41) to be significantly higher compared to both infant (n = 8; P < .001) and noninfant patients with ALL (n = 23; P = .001) carrying germline MLL genes. Furthermore, leukemic cells from infants with MLL were significantly more sensitive to the Fms-like tyrosine kinase 3 (FLT3) inhibitor PKC412 (N-benzoyl staurosporine) than noninfant ALL cells, and at least as sensitive as internal tandem duplication-positive (ITD+) AML cells. Surprisingly, activation loop mutations only occurred in about 3% (1 of 36) of the cases and no FLT3/ITDs were observed. However, measuring FLT3 phosphorylation in infants with MLL expressing varying levels of wild-type FLT3 revealed that high-level FLT3 expression is associated with ligand-independent FLT3 activation. This suggests that infant MLL cells displaying activated FLT3 as a result of overexpression can be targeted by FLT3 inhibitors such as PKC412. However, at concentrations of PKC412 minimally required to fully inhibit FLT3 phosphorylation, the cytotoxic effects were only fractional. Thus, PKC412-induced apoptosis in infant MLL cells is unlikely to be a consequence of FLT3 inhibition alone but may involve inhibition of multiple other kinases by this drug.
authors.affiliation: Erasmus Medical Center/Sophia Children's Hospital, Pediatric Oncology/Hematology, Rotterdam, The Netherlands.
authors.forename: Ronald W
authors.initials: RW
authors.lastname: Stam
authors.forename: Monique L
authors.initials: ML
authors.lastname: den Boer
authors.forename: Pauline
authors.initials: P
authors.lastname: Schneider
authors.forename: Peter
authors.initials: P
authors.lastname: Nollau
authors.forename: Martin
authors.initials: M
authors.lastname: Horstmann
authors.forename: H Berna
authors.initials: HB
authors.lastname: Beverloo
authors.forename: Ella
authors.initials: E
authors.lastname: van der Voort
authors.forename: Maria G
authors.initials: MG
authors.lastname: Valsecchi
authors.forename: Paola
authors.initials: P
authors.lastname: de Lorenzo
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Sallan
authors.forename: Scott A
authors.initials: SA
authors.lastname: Armstrong
authors.forename: Rob
authors.initials: R
authors.lastname: Pieters
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis; D001665:Binding Sites; D045744:Cell Line, Tumor; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004252:DNA Mutational Analysis; D017931:DNA Primers / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020440:Gene Duplication; D015321:Gene Rearrangement; D006801:Humans; D047468:Immunoprecipitation; D017404:In Situ Hybridization, Fluorescence; D007223:Infant; D007231:Infant, Newborn; D008024:Ligands; D009154:Mutation; D010766:Phosphorylation; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics*; D011379:Prognosis; D012313:RNA / Q000737:chemistry / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D019311:Staurosporine / Q000031:analogs & derivatives / Q000494:pharmacology; D013778:Tetrazolium Salts / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D017931:DNA Primers; D004791:Enzyme Inhibitors; D008024:Ligands; D013778:Tetrazolium Salts; D013844:Thiazoles; D012313:RNA; D004247:DNA; C022616:thiazolyl blue; D019311:Staurosporine; C059539:midostaurin