6-mercaptopurine transport in human lymphocytes: Correlation with drug-induced cytotoxicity

Authors

  • Laurie S. CONKLIN,

    1. Division of Pediatric Gastroenterology and Nutrition, Department of Pediatrics
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    • Current address: Department of Gastroenterology, Children's National Medical Center, Sheikh Zayed Campus for Advanced Children's Medicine, 111 Michigan Avenue NW, Washington, DC 20010, USA

  • Carmen CUFFARI,

    1. Division of Pediatric Gastroenterology and Nutrition, Department of Pediatrics
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  • Toshihiko OKAZAKI,

    1. Division of Gastroenterology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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  • Yinglei MIAO,

    1. Division of Gastroenterology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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  • Bahman SAATIAN,

    1. Division of Gastroenterology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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  • Tian-E. CHEN,

    1. Division of Gastroenterology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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  • Ming TSE,

    1. Division of Gastroenterology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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  • Steven R. BRANT,

    1. Division of Gastroenterology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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  • Xuhang LI

    Corresponding author
    1. Division of Gastroenterology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
      Xuhang LI, Division of Gastroenterology, Department of Medicine, The Johns Hopkins University School of Medicine, 720 Rutland Avenue, 918 Ross Building, Baltimore, MD 21205, USA. Email: xuhang@jhmi.edu
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  • Declaration of personal interests: Carmen CUFFARI has served as a speaker and consultant for Prometheus, Shire, UCB Pharmaceuticals, Nestle, Abbott Laboratories, TAP Pharmaceuticals, Novartis, Roche and Salix Pharmaceuticals. Steven R. BRANT has served as a consultant for UCB Pharmaceuticals and Proctor and Gamble.

  • Declaration of funding interests: Carmen Cuffari has received research funding from Prometheus, Shire, Roche and Glaxo-Wellcome.

Xuhang LI, Division of Gastroenterology, Department of Medicine, The Johns Hopkins University School of Medicine, 720 Rutland Avenue, 918 Ross Building, Baltimore, MD 21205, USA. Email: xuhang@jhmi.edu

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 14C-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.

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