title: Imaging of viral thymidine kinase gene expression by replicating oncolytic adenovirus and prediction of therapeutic efficacy.
abstract: OBJECTIVE
  We have used a genetically attenuated adenoviral vector which expresses HSVtk to assess the possible additive role of suicidal gene therapy for enhanced oncolytic effect of the virus. Expression of TK was measured using a radiotracer-based molecular counting and imaging system.
  
  
  METHODS
  Replication-competent recombinant adenoviral vector (Ad-DeltaE1B19/55) was used in this study, whereas replication-incompetent adenovirus (Ad-DeltaE1A) was generated as a control. Both Ad-DeltaE1B19/55-TK and Ad-DeltaE1A-TK comprise the HSVtk gene inserted into the E3 region of the viruses. YCC-2 cells were infected with the viruses and incubated with 2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl-5-iodouracil (I-131 FIAU) to measure amount of radioactivity. The cytotoxicity of the viruses was determined, and gamma ray imaging of HSVtk gene was performed. MTT assay was also performed after GCV treatment.
  
  
  RESULTS
  On gamma counter-analyses, counts/ minute (cpm)/microg of protein showed MOIs dependency with DeltaE1B19/55-TK infection. On MTT assay, Ad-DeltaE1B19/55-TK led to more efficient cell killing than Ad-DeltaE1A-TK. On plate imaging by gamma camera, both Ad-DeltaE1B19/55-TK and Ad-DeltaE1A-TK infected cells showed increased I-131 FIAU uptake in a MOI dependent pattern, and with GCV treatment, cell viability of DeltaE1B19/55-TK infection was remarkably reduced compared to that of Ad-DeltaE1A-TK infection.
  
  
  CONCLUSIONS
  Replicating Ad-DeltaE1B19/55-TK showed more efficient TK expression even in the presence of higher-cancer cell killing effects compared to non-replicating Ad-DeltaE1A-TK. Therefore, GCV treatment still possessed an additive role to oncolytic effect of Ad-DeltaE1B19/55-TK. The expression of TK by oncolytic viruses could rapidly be screened using a radiotracer-based counting and imaging technique.
authors.affiliation: Division of Nuclear Medicine, Department of Radiology, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Eun-Jung
authors.initials: EJ
authors.lastname: Kim
authors.forename: Ji Young
authors.initials: JY
authors.lastname: Yoo
authors.forename: Young-Hwan
authors.initials: YH
authors.lastname: Choi
authors.forename: Keun-Jae
authors.initials: KJ
authors.lastname: Ahn
authors.forename: Jong-Doo
authors.initials: JD
authors.lastname: Lee
authors.forename: Chae-Ok
authors.initials: CO
authors.lastname: Yun
authors.forename: Mijin
authors.initials: M
authors.lastname: Yun
mesh_terms: D000256:Adenoviridae / Q000235:genetics* / Q000502:physiology; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D015774:Ganciclovir / Q000494:pharmacology; D015870:Gene Expression; D015316:Genetic Therapy / Q000379:methods; D005822:Genetic Vectors; D006801:Humans; D050130:Oncolytic Virotherapy; D050504:Oncolytic Viruses / Q000235:genetics* / Q000502:physiology; D018139:Simplexvirus / Q000235:genetics; D013778:Tetrazolium Salts / Q000032:analysis; D013844:Thiazoles / Q000032:analysis; D013937:Thymidine Kinase / Q000235:genetics* / Q000378:metabolism; D019076:Transgenes; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism; D014779:Virus Replication
chemical_list: D013778:Tetrazolium Salts; D013844:Thiazoles; D014764:Viral Proteins; D013937:Thymidine Kinase; C022616:thiazolyl blue; D015774:Ganciclovir