title: Retinoic acid synergizes ATO-mediated cytotoxicity by precluding Nrf2 activity in AML cells.
abstract: BACKGROUND
  Standard therapy for acute promyelocytic leukaemia (APL) includes retinoic acid (all-trans retinoic acid (ATRA)), which promotes differentiation of promyelocytic blasts. Although co-administration of arsenic trioxide (ATO) with ATRA has emerged as an effective option to treat APL, the molecular basis of this effect remains unclear.
  
  
  METHODS
  Four leukaemia cancer human models (HL60, THP-1, NBR4 and NBR4-R2 cells) were treated either with ATO alone or ATO plus ATRA. Cancer cell survival was monitored by trypan blue exclusion and DEVDase activity assays. Gene and protein expression changes were assessed by RT-PCR and western blot.
  
  
  RESULTS
  ATO induced an antioxidant response characterised by Nrf2 nuclear translocation and enhanced transcription of downstream target genes (that is, HO-1, NQO1, GCLM, ferritin). In cells exposed to ATO plus ATRA, the Nrf2 nuclear translocation was prevented and cytotoxicity was enhanced. HO-1 overexpression reversed partially the cytotoxicity by ATRA-ATO in HL60 cells. The inhibitory effects of ATRA on ATO-mediated responses were not observed in either the ATRA-resistant NB4-R2 cells or in NB4 cells pre-incubated with the RARα antagonist Ro-41-52-53.
  
  
  CONCLUSIONS
  The augmented cytotoxicity observed in leukaemia cells following combined ATO-ATRA treatment is likely due to inhibition of Nrf2 activity, thus explaining the efficacy of combined ATO-ATRA treatment in the APL therapy.
authors.affiliation: Toxicology and Cancer Biology Research Group (GTOX), Louvain Drug Research Institute, Université catholique de Louvain, Avenue Mounier, 73 bte B1.73.09, Brussels 1200, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Valenzuela
authors.affiliation: Toxicology and Cancer Biology Research Group (GTOX), Louvain Drug Research Institute, Université catholique de Louvain, Avenue Mounier, 73 bte B1.73.09, Brussels 1200, Belgium.
authors.forename: C
authors.initials: C
authors.lastname: Glorieux
authors.affiliation: de Duve Institute, Université catholique de Louvain, Brussels 1200, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Stockis
authors.affiliation: Toxicology and Cancer Biology Research Group (GTOX), Louvain Drug Research Institute, Université catholique de Louvain, Avenue Mounier, 73 bte B1.73.09, Brussels 1200, Belgium.
authors.forename: B
authors.initials: B
authors.lastname: Sid
authors.affiliation: Toxicology and Cancer Biology Research Group (GTOX), Louvain Drug Research Institute, Université catholique de Louvain, Avenue Mounier, 73 bte B1.73.09, Brussels 1200, Belgium.
authors.forename: J M
authors.initials: JM
authors.lastname: Sandoval
authors.affiliation: Toxicology and Cancer Biology Research Group (GTOX), Louvain Drug Research Institute, Université catholique de Louvain, Avenue Mounier, 73 bte B1.73.09, Brussels 1200, Belgium.
authors.forename: K B
authors.initials: KB
authors.lastname: Felipe
authors.affiliation: Toxicology and Cancer Biology Research Group (GTOX), Louvain Drug Research Institute, Université catholique de Louvain, Avenue Mounier, 73 bte B1.73.09, Brussels 1200, Belgium.
authors.forename: M R
authors.initials: MR
authors.lastname: Kviecinski
authors.affiliation: Toxicology and Cancer Biology Research Group (GTOX), Louvain Drug Research Institute, Université catholique de Louvain, Avenue Mounier, 73 bte B1.73.09, Brussels 1200, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Verrax
authors.affiliation: 1] Toxicology and Cancer Biology Research Group (GTOX), Louvain Drug Research Institute, Université catholique de Louvain, Avenue Mounier, 73 bte B1.73.09, Brussels 1200, Belgium [2] Facultad de Ciencias de la Salud, Universidad Arturo Prat, Casilla 121, Iquique, Chile.
authors.forename: P
authors.initials: P
authors.lastname: Buc Calderon
mesh_terms: D000077237:Arsenic Trioxide; D001152:Arsenicals / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D004357:Drug Synergism; D005978:Glutathione / Q000378:metabolism; D018922:HL-60 Cells; D051547:Heme Oxygenase-1 / Q000378:metabolism; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000188:drug therapy* / Q000378:metabolism*; D051267:NF-E2-Related Factor 2 / Q000378:metabolism*; D010087:Oxides / Q000494:pharmacology*; D018168:Receptors, Retinoic Acid / Q000235:genetics; D000072482:Retinoic Acid Receptor alpha; D014212:Tretinoin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D001152:Arsenicals; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D010087:Oxides; C000607071:RARA protein, human; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D014212:Tretinoin; C496541:HMOX1 protein, human; D051547:Heme Oxygenase-1; D005978:Glutathione; D000077237:Arsenic Trioxide