title: Glutathione content but not gamma glutamyl cysteine synthetase mRNA expression predicts cisplatin resistance in head and neck cancer cell lines.
abstract: OBJECTIVE
  To correlate cellular glutathione content and gamma-glutamyl cysteine synthetase (gamma GCS) mRNA expression with cisplatin sensitivity in a panel of seven head and neck squamous cancer cell lines.
  
  
  METHODS
  Cisplatin IC50 was determined for each cell line using a sodium tetreazolium (XTT) assay. Cellular glutathione content was measured by using a previously reported enzymic method. gamma GCS mRNA expression was measured using an RNase protection assay.
  
  
  RESULTS
  Total cellular glutathione was an excellent predictor of cisplatin sensitivity in this series of cell lines. The IC50 for cisplatin in the cell line with the highest glutathione concentration was approximately 90 times higher than in the cell line with the lowest glutathione concentration. Regression analysis showed a highly statistically significant positive correlation between cisplatin IC50 and cellular glutathione (coefficient of determination R2 = 0.81, P = 0.0012). Some-what surprisingly, in contrast to previous studies in ovarian cancer, gamma GCS mRNA expression in these cell lines was not significantly predictive of either total cellular glutathione or cisplatin sensitivity (R2 = 0.005, P = 0.84). As expected, treatment of resistant cell lines with buthionine sulfoximine resulted in decreased cellular glutathione and enhanced cisplatin sensitivity.
  
  
  CONCLUSIONS
  Our results suggest that glutathione may be an important determinant of cisplatin sensitivity in clinical head and neck cancer. Since cisplatin is the most active chemotherapy drug for the treatment of this disease, this correlation may have important clinical relevance. The lack of correlation between glutathione level and gamma GCS expression suggests that salvage or alternate synthetic pathways may be critical in these cells.
authors.affiliation: Department of Otolaryngology/Head and Neck Surgery, Georgetown University, Washington DC 20007, USA.
authors.forename: K
authors.initials: K
authors.lastname: Newkirk
authors.forename: J
authors.initials: J
authors.lastname: Heffern
authors.forename: E
authors.initials: E
authors.lastname: Sloman-Moll
authors.forename: R B
authors.initials: RB
authors.lastname: Sessions
authors.forename: A A
authors.initials: AA
authors.lastname: Rasmussen
authors.forename: P A
authors.initials: PA
authors.lastname: Andrews
authors.forename: K J
authors.initials: KJ
authors.lastname: Cullen
mesh_terms: D019328:Buthionine Sulfoximine / Q000494:pharmacology; D004351:Drug Resistance; D005721:Glutamate-Cysteine Ligase / Q000235:genetics*; D005978:Glutathione / Q000032:analysis*; D006258:Head and Neck Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D006801:Humans; D012333:RNA, Messenger / Q000032:analysis*; D014407:Tumor Cells, Cultured
chemical_list: D012333:RNA, Messenger; D019328:Buthionine Sulfoximine; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione