title: Resistance developing after long-term ganciclovir prodrug treatment in a preclinical model of NSCLC.
abstract: BACKGROUND
  We recently demonstrated a 100% increase in the survival period with ganciclovir (GCV) therapy in mice hearing orthotopic HSV-TK-positive non-small cell lung cancer (NSCLC) tumors. However, long-term survival was not achieved. The aim of the present study was to evaluate tumor growth during extended GCV therapy and to monitor the herpes simplex virus thymidine kinase (HSV-TK) gene and protein in tumors at different time points.
  
  
  METHODS
  The human NSCLC cell line KNS 62 was retrovirally transduced with the HSV-TK30 gene. Cell suspensions in which 100% or 25% of the cells were TK30-positive were inoculated subcutaneously in SCID bg mice. Tumor growth was evaluated during GCV therapy and HSV-TK DNA, RNA and protein were analyzed at different time points using PCR, RT-PCR and immunoblotting.
  
  
  RESULTS
  HSV-TK DNA, RNA and TK30 protein were demonstrated in the tumors 21 days after subcutaneous tumor inoculation. TK-positive tumors regressed during GCV therapy and tumors in which 25% of the cells were TK-positive grew significantly more slowly than control tumors did. After 4 weeks of GCV therapy, HSV-TK DNA, RNA and TK protein were not detectable in the remaining tumors, which were therefore resistant to further GCV therapy.
  
  
  CONCLUSIONS
  Prodrug therapy of the NSCLC cell line KNS 62, including bystander effects, is sufficient. Nevertheless, GCV-resistant tumors develop after functional loss of the TK gene. In the clinical context, further studies will need to evaluate immunological bystander effects or combinations with other drugs.
authors.affiliation: Department of General and Thoracic Surgery, Molecular Oncology Research Group, University of Schleswig-Holstein, Kiel Campus, Arnold-Heller-Strasse 7, 24105 Kiel, Germany. rkurdow@surgery.uni-kiel.de
authors.forename: Roland
authors.initials: R
authors.lastname: Kurdow
authors.forename: Bodo
authors.initials: B
authors.lastname: Schniewind
authors.forename: Arnd S
authors.initials: AS
authors.lastname: Boehle
authors.forename: Sieglinde
authors.initials: S
authors.lastname: Haye
authors.forename: Lars
authors.initials: L
authors.lastname: Boenicke
authors.forename: Peter
authors.initials: P
authors.lastname: Dohrmann
authors.forename: Holger
authors.initials: H
authors.lastname: Kalthoff
mesh_terms: D000818:Animals; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics / Q000628:therapy*; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D015774:Ganciclovir / Q000493:pharmacokinetics / Q000494:pharmacology*; D015870:Gene Expression; D015316:Genetic Therapy / Q000379:methods; D006801:Humans; D015151:Immunoblotting; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics / Q000628:therapy; D051379:Mice; D016513:Mice, SCID; D011355:Prodrugs / Q000493:pharmacokinetics / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018139:Simplexvirus / Q000201:enzymology / Q000235:genetics; D013937:Thymidine Kinase / Q000235:genetics / Q000378:metabolism; D014161:Transduction, Genetic; D023041:Xenograft Model Antitumor Assays
chemical_list: D011355:Prodrugs; D013937:Thymidine Kinase; D015774:Ganciclovir