title: Single agent- and combination treatment with two targeted suicide gene therapy systems is effective in chemoresistant small cell lung cancer cells.
abstract: BACKGROUND
  Transcriptional targeted suicide gene (SG) therapy driven by the insulinoma-associated 1 (INSM1) promoter makes it possible to target suicide toxin production and cytotoxicity exclusively to small cell lung cancer (SCLC) cells and tumors. It remains to be determined whether acquired chemoresistance, as observed in the majority of SCLC patients, desensitizes SCLC cells to INSM1 promoter-driven SG therapy.
  
  
  METHODS
  A panel of SCLC cell lines resistant to clinically relevant chemotherapeutics was characterized regarding the expression of proteins involved in response to chemotherapy and regarding INSM1 promoter activity. Sensitivity towards INSM1 promoter-driven SG therapy was tested using different systems: Yeast cytosine deaminase-uracil phosphoribosyl transferase (YCD-YUPRT) in combination with the prodrug 5-fluorocytosine (5-FC) or Escherichia coli nitroreductase (NTR) together with the bromomustard prodrug SN27686.
  
  
  RESULTS
  The chemoresistant cell lines displayed heterogeneous expression profiles of molecules involved in multidrug resistance, apoptosis and survival pathways. Despite this, the INSM1 promoter activity was found to be unchanged or increased in SCLC chemoresistant cells and xenografts compared to chemosensitive variants. INSM1 promoter-driven SG therapy with YCD-YUPRT/5-FC or NTR/SN27686, was found to induce high levels of cytotoxicity in both chemosensitive and chemoresistant SCLC cells. Moreover, the combination of INSM1 promoter-driven YCD-YUPRT/5-FC therapy and chemotherapy, as well as the combination of INSM1 promoter-driven YCD-YUPRT/5-FC and NTR/SN27686 therapy, was observed to be superior to single agent therapy in chemoresistant SCLC cells.
  
  
  CONCLUSIONS
  Collectively, the present study demonstrates that targeted SG therapy is a potent therapeutic approach for chemoresistant SCLC patients, with the highest efficacy achieved when applied as combination SG therapy or in combination with standard chemotherapy.
authors.affiliation: Department of Radiation Biology, The Finsen Center, National University Hospital, Copenhagen, Denmark.
authors.forename: Signe R
authors.initials: SR
authors.lastname: Michaelsen
authors.forename: Camilla L
authors.initials: CL
authors.lastname: Christensen
authors.forename: Maxwell
authors.initials: M
authors.lastname: Sehested
authors.forename: Frederik
authors.initials: F
authors.lastname: Cramer
authors.forename: Thomas T
authors.initials: TT
authors.lastname: Poulsen
authors.forename: Adam V
authors.initials: AV
authors.lastname: Patterson
authors.forename: Hans S
authors.initials: HS
authors.lastname: Poulsen
mesh_terms: D000818:Animals; D017209:Apoptosis; D045744:Cell Line, Tumor; D002470:Cell Survival; D017024:Chemotherapy, Adjuvant; D043525:Cytosine Deaminase / Q000235:genetics / Q000627:therapeutic use; D019008:Drug Resistance, Neoplasm; D004359:Drug Therapy, Combination; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005437:Flucytosine / Q000627:therapeutic use; D041722:Genes, Transgenic, Suicide / Q000235:genetics*; D015316:Genetic Therapy / Q000379:methods*; D006801:Humans; D008175:Lung Neoplasms / Q000628:therapy*; D008297:Male; D051379:Mice; D009601:Nitroreductases / Q000627:therapeutic use; D010430:Pentosyltransferases / Q000235:genetics / Q000627:therapeutic use; D011401:Promoter Regions, Genetic / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics*; D055752:Small Cell Lung Carcinoma / Q000628:therapy*; D015003:Yeasts / Q000201:enzymology / Q000235:genetics
chemical_list: D012097:Repressor Proteins; C087342:INSM1 protein, human; D005437:Flucytosine; D009601:Nitroreductases; D010430:Pentosyltransferases; C023269:uracil phosphoribosyltransferase; D043525:Cytosine Deaminase