title: Dexamethasone inhibits the HSV-tk/ ganciclovir bystander effect in malignant glioma cells.
abstract: BACKGROUND
  HSV-tk/ ganciclovir (GCV) gene therapy has been extensively studied in the setting of brain tumors and largely relies on the bystander effect. Large studies have however failed to demonstrate any significant benefit of this strategy in the treatment of human brain tumors. Since dexamethasone is a frequently used symptomatic treatment for malignant gliomas, its interaction with the bystander effect and the overall efficacy of HSV-TK gene therapy ought to be assessed.
  
  
  METHODS
  Stable clones of TK-expressing U87, C6 and LN18 cells were generated and their bystander effect on wild type cells was assessed. The effects of dexamethasone on cell proliferation and sensitivity to ganciclovir were assessed with a thymidine incorporation assay and a MTT test. Gap junction mediated intercellular communication was assessed with microinjections and FACS analysis of calcein transfer. The effect of dexamethasone treatment on the sensitivity of TK-expressing to FAS-dependent apoptosis in the presence or absence of ganciclovir was assessed with an MTT test. Western blot was used to evidence the effect of dexamethasone on the expression of Cx43, CD95, CIAP2 and BclXL.
  
  
  RESULTS
  Dexamethasone significantly reduced the bystander effect in TK-expressing C6, LN18 and U87 cells. This inhibition results from a reduction of the gap junction mediated intercellular communication of these cells (GJIC), from an inhibition of their growth and thymidine incorporation and from a modulation of the apoptotic cascade.
  
  
  CONCLUSIONS
  The overall efficacy of HSV-TK gene therapy is adversely affected by dexamethasone co-treatment in vitro. Future HSV-tk/ GCV gene therapy clinical protocols for gliomas should address this interference of corticosteroid treatment.
authors.affiliation: Department of Neurosurgery, University of Liège, Liège, Belgium. pierre.robe@ulg.ac.be
authors.forename: Pierre A
authors.initials: PA
authors.lastname: Robe
authors.forename: Minh
authors.initials: M
authors.lastname: Nguyen-Khac
authors.forename: Olivier
authors.initials: O
authors.lastname: Jolois
authors.forename: Bernard
authors.initials: B
authors.lastname: Rogister
authors.forename: Marie-Paule
authors.initials: MP
authors.lastname: Merville
authors.forename: Vincent
authors.initials: V
authors.lastname: Bours
mesh_terms: D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D000998:Antiviral Agents / Q000494:pharmacology*; D017209:Apoptosis; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000188:drug therapy / Q000628:therapy*; D024201:Bystander Effect; D002450:Cell Communication; D045744:Cell Line, Tumor; D002469:Cell Separation; D002470:Cell Survival; D004396:Coloring Agents / Q000494:pharmacology; D018031:Connexin 43 / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D053222:Fas Ligand Protein; D005434:Flow Cytometry; D015774:Ganciclovir / Q000494:pharmacology*; D017629:Gap Junctions; D015316:Genetic Therapy / Q000379:methods*; D005910:Glioma / Q000235:genetics* / Q000628:therapy*; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D015233:Models, Statistical; D018139:Simplexvirus / Q000235:genetics*; D013778:Tetrazolium Salts / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D013937:Thymidine Kinase / Q000378:metabolism; D048069:Tumor Necrosis Factors / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism; D019014:fas Receptor / Q000096:biosynthesis
chemical_list: D000893:Anti-Inflammatory Agents; D000998:Antiviral Agents; D004396:Coloring Agents; D018031:Connexin 43; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D051034:Inhibitor of Apoptosis Proteins; D008562:Membrane Glycoproteins; D013778:Tetrazolium Salts; D013844:Thiazoles; D048069:Tumor Necrosis Factors; D051020:bcl-X Protein; D019014:fas Receptor; D003907:Dexamethasone; D013937:Thymidine Kinase; C022616:thiazolyl blue; D015774:Ganciclovir