title: Expression of ABCC-type nucleotide exporters in blasts of adult acute myeloid leukemia: relation to long-term survival.
abstract: OBJECTIVE
  Successful treatment of acute myeloid leukemia (AML) remains a therapeutic challenge, with a high percentage of patients suffering from persistent or relapsed disease. Resistance to drug therapy can develop from increased drug export and/or altered intracellular signaling. Both mechanisms are mediated by the efflux transporters ABCC4 (MRP4), ABCC5 (MRP5), and ABCC11 (MRP8), which are involved in cellular efflux of endogenous signaling molecules (e.g., cyclic adenosine 3', 5'-monophosphate and cyclic guanosine 3',5'-monophosphate) and nucleoside analogues. The nucleoside analogue cytosine arabinoside (AraC) is administered to all patients with AML.
  
  
  METHODS
  Expression of ABCC transporters MRP4, MRP5, and MRP8 in blast samples from 50 AML patients was investigated by real-time reverse transcription-PCR analysis and correlated with clinical outcome measures. Accumulation of radiolabeled AraC, transport of AraC metabolites, and AraC cytotoxicity were analyzed in MRP8-transfected LLC-PK1 cells.
  
  
  RESULTS
  Regression analysis revealed that high expression of MRP8 is associated with a low probability of overall survival assessed over 4 years (P<0.03). MRP8-transfected LLC-PK1 cells accumulated reduced intracellular levels of AraC (63% of the parental vector-transfected LLC-PK1 control cells) as well as AraC metabolites. Furthermore, AraC monophosphate was transported by MRP8-enriched membrane vesicles (116+/-6 versus 65+/-13 pmol/mg/10 minutes by control vesicles), and MRP8-transfected cells were resistant to AraC.
  
  
  CONCLUSIONS
  These data suggest that MRP8 is differentially expressed in AML blasts, that expression of MRP8 serves as a predictive marker for treatment outcome in AML, and that efflux of AraC metabolites by MRP8 is a mechanism that contributes to resistance of AML blasts.
authors.affiliation: Medical Science Division, Fox Chase Cancer Center, Philadelphia, Pennsylvania, USA.
authors.forename: Yanping
authors.initials: Y
authors.lastname: Guo
authors.forename: Kathleen
authors.initials: K
authors.lastname: Köck
authors.forename: Christoph A
authors.initials: CA
authors.lastname: Ritter
authors.forename: Zhe-Sheng
authors.initials: ZS
authors.lastname: Chen
authors.forename: Markus
authors.initials: M
authors.lastname: Grube
authors.forename: Gabriele
authors.initials: G
authors.lastname: Jedlitschky
authors.forename: Thomas
authors.initials: T
authors.lastname: Illmer
authors.forename: Mary
authors.initials: M
authors.lastname: Ayres
authors.forename: James F
authors.initials: JF
authors.lastname: Beck
authors.forename: Werner
authors.initials: W
authors.lastname: Siegmund
authors.forename: Gerhard
authors.initials: G
authors.lastname: Ehninger
authors.forename: Varsha
authors.initials: V
authors.lastname: Gandhi
authors.forename: Heyo K
authors.initials: HK
authors.lastname: Kroemer
authors.forename: Gary D
authors.initials: GD
authors.lastname: Kruh
authors.forename: Markus
authors.initials: M
authors.lastname: Schaich
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000328:Adult; D000368:Aged; D001752:Blast Crisis; D002462:Cell Membrane / Q000378:metabolism; D003561:Cytarabine / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D018374:LLC-PK1 Cells; D015470:Leukemia, Myeloid, Acute / Q000378:metabolism* / Q000401:mortality / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism*; D011379:Prognosis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013234:Stem Cells / Q000378:metabolism / Q000473:pathology; D015996:Survival Rate
chemical_list: D018528:ATP-Binding Cassette Transporters; D003561:Cytarabine; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012333:RNA, Messenger; C435500:ABCC11 protein, human; C073492:ABCC4 protein, human; C120809:ABCC5 protein, human