title: Molecular insight into thiopurine resistance: transcriptomic signature in lymphoblastoid cell lines.
abstract: BACKGROUND
  There has been considerable progress in the management of acute lymphoblastic leukemia (ALL) but further improvement is needed to increase long-term survival. The thiopurine agent 6-mercaptopurine (6-MP) used for ALL maintenance therapy has a key influence on clinical outcomes and relapse prevention. Genetic inheritance in thiopurine metabolism plays a major role in interindividual clinical response variability to thiopurines; however, most cases of thiopurine resistance remain unexplained.
  
  
  METHODS
  We used lymphoblastoid cell lines (LCLs) from healthy donors, selected for their extreme thiopurine susceptibility. Thiopurine metabolism was characterized by the determination of TPMT and HPRT activity. We performed genome-wide expression profiling in resistant and sensitive cell lines with the goal of elucidating the mechanisms of thiopurine resistance.
  
  
  RESULTS
  We determined a higher TPMT activity (+44%; P = 0.024) in resistant compared to sensitive cell lines, although there was no difference in HPRT activity. We identified a 32-gene transcriptomic signature that predicts thiopurine resistance. This signature includes the GTPBP4 gene coding for a GTP-binding protein that interacts with p53. A comprehensive pathway analysis of the genes differentially expressed between resistant and sensitive cell lines indicated a role for cell cycle and DNA mismatch repair system in thiopurine resistance. It also revealed overexpression of the ATM/p53/p21 pathway, which is activated in response to DNA damage and induces cell cycle arrest in thiopurine resistant LCLs. Furthermore, overexpression of the p53 target gene TNFRSF10D or the negative cell cycle regulator CCNG2 induces cell cycle arrest and may also contribute to thiopurine resistance. ARHGDIA under-expression in resistant cell lines may constitute a novel molecular mechanism contributing to thiopurine resistance based on Rac1 inhibition induced apoptosis and in relation with thiopurine pharmacodynamics.
  
  
  CONCLUSIONS
  Our study provides new insights into the molecular mechanisms underlying thiopurine resistance and suggests a potential research focus for developing tailored medicine.
authors.affiliation: INSERM UMR-S 1147, 45 rue des Saints-Pères, Paris, 75006 France ; Université Paris Descartes, Sorbonne Paris Cité, 45 rue des Saints-Pères, Paris, 75006 France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Chouchana
authors.affiliation: INSERM UMR-S 1147, 45 rue des Saints-Pères, Paris, 75006 France ; Université Paris Descartes, Sorbonne Paris Cité, 45 rue des Saints-Pères, Paris, 75006 France.
authors.forename: Ana Aurora
authors.initials: AA
authors.lastname: Fernández-Ramos
authors.affiliation: Université Paris Descartes, Sorbonne Paris Cité, 45 rue des Saints-Pères, Paris, 75006 France ; INSERM U1016, Institut Cochin, 22 Rue Mechain, Paris, 75014 France.
authors.forename: Florent
authors.initials: F
authors.lastname: Dumont
authors.affiliation: INSERM UMR-S 1147, 45 rue des Saints-Pères, Paris, 75006 France ; Université Paris Descartes, Sorbonne Paris Cité, 45 rue des Saints-Pères, Paris, 75006 France.
authors.forename: Catherine
authors.initials: C
authors.lastname: Marchetti
authors.affiliation: Université Paris Descartes, Sorbonne Paris Cité, 45 rue des Saints-Pères, Paris, 75006 France ; Assistance Publique-Hôpitaux de Paris, Hôpital Necker-Enfants Malades, Biochimie Métabolique, 149 Rue de Sèvres, Paris, 75015 France.
authors.forename: Irène
authors.initials: I
authors.lastname: Ceballos-Picot
authors.affiliation: INSERM UMR-S 1147, 45 rue des Saints-Pères, Paris, 75006 France ; Université Paris Descartes, Sorbonne Paris Cité, 45 rue des Saints-Pères, Paris, 75006 France ; Assistance Publique-Hôpitaux de Paris, Hôpital Européen Georges Pompidou, Biochimie Pharmacogénétique et Oncologie Moléculaire, 20 rue Leblanc, Paris, 75015 France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Beaune
authors.affiliation: Department of Human Molecular Genetics and Biochemistry, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, Israel.
authors.forename: David
authors.initials: D
authors.lastname: Gurwitz
authors.affiliation: INSERM UMR-S 1147, 45 rue des Saints-Pères, Paris, 75006 France ; Université Paris Descartes, Sorbonne Paris Cité, 45 rue des Saints-Pères, Paris, 75006 France ; Assistance Publique-Hôpitaux de Paris, Hôpital Européen Georges Pompidou, Biochimie Pharmacogénétique et Oncologie Moléculaire, 20 rue Leblanc, Paris, 75015 France.
authors.forename: Marie-Anne
authors.initials: MA
authors.lastname: Loriot