title: 6-Mercaptopurine transport in human lymphocytes: correlation with drug-induced cytotoxicity.
abstract: OBJECTIVE
  6-mercaptopurine (6-MP) is efficacious in the treatment of inflammatory bowel disease (IBD). However, about one-third of patients respond poorly to therapy. This study aimed to characterize the inherent differences in 6-MP transport that may cotribute to the differences in treatment responses.
  
  
  METHODS
  Intracellular 6-MP accumulation was assayed in Epstein-Barr virus (EBV)-transformed lymphocytes from IBD patients, using (14) C-radiolabeled 6-MP. Cell proliferation was determined by methyl thiazolyl tetrazolium (MTT) assay. Apoptosis was assayed based on the activation of caspase 3. The expressions of 15 potential 6-MP transporters were evaluated by reverse transcription-polymerase chain reaction (RT-PCR).
  
  
  RESULTS
  Intracellular 6-MP accumulation, varying significantly among patients, was carrier-dependent and partially sodium-dependent. 6-MP cytotoxicity was, at least in part, due to apoptosis and correlated with intracellular drug accumulation. The efflux transporters did not appear to contribute to the variability of intracellular drug accumulation between patients, since none correlated with drug accumulation or cytotoxicity. Rather, differential expression of five influx/uptake transporters might be a key contributor to the difference in the accumulation of and susceptibility to the drug.
  
  
  CONCLUSIONS
  The heterogeneity of the drug transporters may be the reason for the therapeutic sensitivity of 6-MP in IBD patients. As the 6-MP uptake is a carrier-mediated and partially sodium-dependent process, future studies are necessary to evaluate the role of the putative transporters and their correlation with drug sensitivity in patients.
authors.affiliation: Division of Pediatric Gastroenterology and Nutrition, Department of Pediatrics Division of Gastroenterology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Laurie S
authors.initials: LS
authors.lastname: Conklin
authors.forename: Carmen
authors.initials: C
authors.lastname: Cuffari
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Okazaki
authors.forename: Yinglei
authors.initials: Y
authors.lastname: Miao
authors.forename: Bahman
authors.initials: B
authors.lastname: Saatian
authors.forename: Tian-E
authors.initials: TE
authors.lastname: Chen
authors.forename: Ming
authors.initials: M
authors.lastname: Tse
authors.forename: Steven R
authors.initials: SR
authors.lastname: Brant
authors.forename: Xuhang
authors.initials: X
authors.lastname: Li
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D017209:Apoptosis / Q000187:drug effects; D001667:Binding, Competitive / Q000502:physiology; D002250:Carbon Radioisotopes; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D002461:Cell Line, Transformed; D002470:Cell Survival / Q000187:drug effects; D003603:Cytotoxins / Q000493:pharmacokinetics; D004351:Drug Resistance / Q000502:physiology; D005260:Female; D015870:Gene Expression / Q000502:physiology; D024601:Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+) / Q000378:metabolism; D006801:Humans; D007166:Immunosuppressive Agents / Q000009:adverse effects / Q000493:pharmacokinetics; D015212:Inflammatory Bowel Diseases / Q000188:drug therapy* / Q000378:metabolism; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D015122:Mercaptopurine / Q000009:adverse effects* / Q000493:pharmacokinetics*; D008875:Middle Aged; D012964:Sodium / Q000494:pharmacology; D055815:Young Adult
chemical_list: D002250:Carbon Radioisotopes; D002352:Carrier Proteins; D003603:Cytotoxins; D007166:Immunosuppressive Agents; D012964:Sodium; D015122:Mercaptopurine; D024601:Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+); C505407:CASP3 protein, human; D053148:Caspase 3