title: Differential mRNA expression of Ara-C-metabolizing enzymes explains Ara-C sensitivity in MLL gene-rearranged infant acute lymphoblastic leukemia.
abstract: Infant acute lymphoblastic leukemia (ALL) is characterized by a high incidence of mixed lineage leukemia (MLL) gene rearrangements, a poor outcome, and resistance to chemotherapeutic drugs. One exception is cytosine arabinoside (Ara-C), to which infant ALL cells are highly sensitive. To investigate the mechanism underlying Ara-C sensitivity in infants with ALL, mRNA levels of Ara-C-metabolizing enzymes were measured in infants (n = 18) and older children (noninfants) with ALL (n = 24). In the present study, infant ALL cells were 3.3-fold more sensitive to Ara-C (P =.007) and accumulated 2.3-fold more Ara-CTP (P =.011) upon exposure to Ara-C, compared with older children with ALL. Real-time quantitative reverse trancriptase-polymerase chain reaction (RT-PCR) (TaqMan) revealed that infants express 2-fold less of the Ara-C phosphorylating enzyme deoxycytidine kinase (dCK) mRNA (P =.026) but 2.5-fold more mRNA of the equilibrative nucleoside transporter 1 (hENT1), responsible for Ara-C membrane transport (P =.001). The mRNA expression of pyrimidine nucleotidase I (PN-I), cytidine deaminase (CDA), and deoxycytidylate deaminase (dCMPD) did not differ significantly between both groups. hENT1 mRNA expression inversely correlated with in vitro resistance to Ara-C (r(s) = -0.58, P =.006). The same differences concerning dCK and hENT1 mRNA expression were observed between MLL gene-rearranged (n = 14) and germ line MLL cases (n = 25). An oligonucleotide microarray screen (Affymetrix) comparing patients with MLL gene-rearranged ALL with those with nonrearranged ALL also showed a 1.9-fold lower dCK (P =.001) and a 2.7-fold higher hENT1 (P =.046) mRNA expression in patients with MLL gene-rearranged ALL. We conclude that an elevated expression of hENT1, which transports Ara-C across the cell membrane, contributes to Ara-C sensitivity in MLL gene-rearranged infant ALL.
authors.affiliation: University Hospital Rotterdam/Sophia Children's Hospital, Department of Pediatric Oncology/Hematology, Erasmus Medical Center, The Netherlands. stam@kgk.fgg.eur.nl
authors.forename: Ronald W
authors.initials: RW
authors.lastname: Stam
authors.forename: Monique L
authors.initials: ML
authors.lastname: den Boer
authors.forename: Jules P P
authors.initials: JP
authors.lastname: Meijerink
authors.forename: Marli E G
authors.initials: ME
authors.lastname: Ebus
authors.forename: Godefridus J
authors.initials: GJ
authors.lastname: Peters
authors.forename: Paul
authors.initials: P
authors.lastname: Noordhuis
authors.forename: Gritta E
authors.initials: GE
authors.lastname: Janka-Schaub
authors.forename: Scott A
authors.initials: SA
authors.lastname: Armstrong
authors.forename: Stanley J
authors.initials: SJ
authors.lastname: Korsmeyer
authors.forename: Rob
authors.initials: R
authors.lastname: Pieters
mesh_terms: D001085:Arabinofuranosylcytosine Triphosphate / Q000378:metabolism; D002470:Cell Survival; D002648:Child; D002675:Child, Preschool; D003561:Cytarabine / Q000378:metabolism* / Q000627:therapeutic use*; D003844:DCMP Deaminase / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D003842:Deoxycytidine Kinase / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D033721:Equilibrative Nucleoside Transporter 1 / Q000235:genetics; D005260:Female; D015870:Gene Expression; D015321:Gene Rearrangement; D011495:Histone-Lysine N-Methyltransferase; D006801:Humans; D007223:Infant; D008297:Male; D051788:Myeloid-Lymphoid Leukemia Protein; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy* / Q000201:enzymology*; D011519:Proto-Oncogenes; D011742:Pyrimidine Nucleotides / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D014157:Transcription Factors; D014407:Tumor Cells, Cultured
chemical_list: D004268:DNA-Binding Proteins; D033721:Equilibrative Nucleoside Transporter 1; C497422:KMT2A protein, human; D011742:Pyrimidine Nucleotides; D012333:RNA, Messenger; C438649:SLC29A1 protein, human; D014157:Transcription Factors; D003561:Cytarabine; D001085:Arabinofuranosylcytosine Triphosphate; D051788:Myeloid-Lymphoid Leukemia Protein; D011495:Histone-Lysine N-Methyltransferase; D003842:Deoxycytidine Kinase; D003844:DCMP Deaminase