title: The cytotoxicity of garlic-related disulphides and thiosulfonates in WHCO1 oesophageal cancer cells is dependent on S-thiolation and not production of ROS.
abstract: BACKGROUND
  Garlic has been used for centuries in folk medicine for its health promoting and cancer preventative properties. The bioactive principles in crushed garlic are allyl sulphur compounds which are proposed to chemically react through (i) protein S-thiolation and (ii) production of ROS.
  
  
  METHODS
  A collection of R-propyl disulphide and R-thiosulfonate compounds were synthesised to probe the importance of thiolysis and ROS generation in the cytotoxicity of garlic-related compounds in WHCO1 oesophageal cancer cells.
  
  
  RESULTS
  A significant correlation (R(2)=0.78, Fcrit (7,1) α=0.005) was found between the cytotoxicity IC(50) and the leaving group pK(a) of the R-propyl disulphides and thiosulfonates, supporting a mechanism that relies on the thermodynamics of a mixed disulphide exchange reaction. Disulphide (1) and thiosulfonate (11) were further evaluated mechanistically and found to induce G(2)/M cell-cycle arrest and apoptosis, inhibit cell proliferation, and generate ROS. When the ROS produced by 1 and 11 were quenched with Trolox, ascorbic acid or N-acetyl cysteine (NAC), only NAC was found to counter the cytotoxicity of both compounds. However, NAC was found to chemically react with 11 through mixed disulphide formation, providing an explanation for this apparent inhibitory result.
  
  
  CONCLUSIONS
  Cellular S-thiolation by garlic related disulphides appears to be the cause of cytotoxicity in WHCO1 cells. Generation of ROS appears to only play a secondary role.
  
  
  CONCLUSIONS
  Our findings do not support ROS production causing the cytotoxicity of garlic-related disulphides in WHCO1 cells. Importantly, it was found that the popular ROS inhibitor NAC interferes with the assay.
authors.affiliation: Department of Integrative Biomedical Sciences, Division of Medical Biochemistry, University of Cape Town, Anzio Road, Observatory,7925 Cape Town, South Africa.
authors.forename: Muneerah
authors.initials: M
authors.lastname: Smith
authors.affiliation: Department of Chemistry, University of Cape Town, Rondebosch, 7701 Cape Town, South Africa.
authors.forename: Roger
authors.initials: R
authors.lastname: Hunter
authors.affiliation: Department of Chemistry, University of Cape Town, Rondebosch, 7701 Cape Town, South Africa.
authors.forename: Nashia
authors.initials: N
authors.lastname: Stellenboom
authors.affiliation: Department of Chemistry, University of Cape Town, Rondebosch, 7701 Cape Town, South Africa.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Kusza
authors.affiliation: Department of Integrative Biomedical Sciences, Division of Medical Biochemistry, University of Cape Town, Anzio Road, Observatory,7925 Cape Town, South Africa; International Centre for Genetic Engineering and Biotechnology, Anzio Road, Observatory, 7925 Cape Town, South Africa.
authors.forename: M Iqbal
authors.initials: MI
authors.lastname: Parker
authors.affiliation: Department of Chemistry, University of Cape Town, Rondebosch, 7701 Cape Town, South Africa.
authors.forename: Ahmed N H
authors.initials: AN
authors.lastname: Hammouda
authors.affiliation: Department of Chemistry, University of Cape Town, Rondebosch, 7701 Cape Town, South Africa.
authors.forename: Graham
authors.initials: G
authors.lastname: Jackson
authors.affiliation: Department of Chemistry, University of Cape Town, Rondebosch, 7701 Cape Town, South Africa.
authors.forename: Catherine H
authors.initials: CH
authors.lastname: Kaschula
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000138:chemical synthesis / Q000494:pharmacology*; D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004220:Disulfides / Q000138:chemical synthesis / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004938:Esophageal Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D000077277:Esophageal Squamous Cell Carcinoma; D059565:G2 Phase Cell Cycle Checkpoints / Q000187:drug effects; D005737:Garlic; D006801:Humans; D015394:Molecular Structure; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013329:Structure-Activity Relationship; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D013886:Thiosulfonic Acids / Q000138:chemical synthesis / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D000975:Antioxidants; D004220:Disulfides; D017382:Reactive Oxygen Species; D013438:Sulfhydryl Compounds; D013886:Thiosulfonic Acids