title: The cystine/cysteine cycle and GSH are independent and crucial antioxidant systems in malignant melanoma cells and represent druggable targets.
abstract: OBJECTIVE
  Cancer chemoresistance is often due to upregulation of antioxidant systems. Therapeutic targeting of these systems is however hampered by their redundancy. Here, we have performed a functional dissection of the antioxidant systems in different melanoma cases aimed at the identification of the most effective redox active drug.
  
  
  RESULTS
  We have identified two crucial antioxidant mechanisms: glutathione (GSH), the major intracellular redox buffer, and the cystine/cysteine cycle, which switches the extracellular redox state from an oxidized to a reduced state. The two mechanisms are independent in melanoma cells and may be substitutes for each other, but targeting both of them is lethal. Exposure to the pro-oxidant compound As(2)O(3) induces an antioxidant response. However, while in these cells the intracellular redox balance remains almost unaffected, a reduced environment is generated extracellularly. GSH depletion by buthioninesulfoximine (BSO), or cystine/cysteine cycle inhibition by (S)-4-carboxyphenylglycine (sCPG), enhanced the sensitivity to As(2)O(3). Remarkably, sCPG also prevented the remodeling of the microenvironment redox state.
  
  
  METHODS
  We propose that the definition of the prevalent antioxidant system(s) in tumors is crucial for the design of tailored therapies involving redox-directed drugs in association with pro-oxidant drugs.
  
  
  CONCLUSIONS
  In melanoma cells, BSO is the best enhancer of As(2)O(3) sensitivity. However, since the strong remodeling of the microenvironmental redox state caused by As(2)O(3) may promote tumor progression, the concomitant use of cystine/cysteine cycle blockers is recommended.
authors.affiliation: Cell Biology Unit, National Cancer Research Institute, Genova, Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Venè
authors.forename: Patrizia
authors.initials: P
authors.lastname: Castellani
authors.forename: Laura
authors.initials: L
authors.lastname: Delfino
authors.forename: Maria
authors.initials: M
authors.lastname: Lucibello
authors.forename: Maria Rosa
authors.initials: MR
authors.lastname: Ciriolo
authors.forename: Anna
authors.initials: A
authors.lastname: Rubartelli
mesh_terms: D000975:Antioxidants / Q000378:metabolism*; D000077237:Arsenic Trioxide; D001152:Arsenicals / Q000494:pharmacology; D015153:Blotting, Western; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D003545:Cysteine / Q000378:metabolism*; D003553:Cystine / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism*; D005998:Glycine / Q000031:analogs & derivatives / Q000494:pharmacology; D024243:HMGB1 Protein / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D008545:Melanoma / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D010087:Oxides / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
chemical_list: D000975:Antioxidants; D001152:Arsenicals; D024243:HMGB1 Protein; D010087:Oxides; D017382:Reactive Oxygen Species; C453101:carboxyphenylglycine; D003553:Cystine; D019328:Buthionine Sulfoximine; D005978:Glutathione; D003545:Cysteine; D000077237:Arsenic Trioxide; D005998:Glycine