title: A preclinical model for noninvasive imaging of hypoxia-induced gene expression; comparison with an exogenous marker of tumor hypoxia.
abstract: OBJECTIVE
  Hypoxia is associated with tumor aggressiveness and is an important cause of resistance to radiation therapy and chemotherapy. Assays of tumor hypoxia could provide selection tools for hypoxia-modifying treatments. The purpose of this study was to develop and characterize a rodent tumor model with a reporter gene construct that would be transactivated by the hypoxia-inducible molecular switch, i.e., the upregulation of HIF-1.
  
  
  METHODS
  The reporter gene construct is the herpes simplex virus 1-thymidine kinase (HSV1-tk) fused with the enhanced green fluorescent protein (eGFP) under the regulation of an artificial hypoxia-responsive enhancer/promoter. In this model, tumor hypoxia would up-regulate HIF-1, and through the hypoxia-responsive promoter transactivate the HSV1-tkeGFP fusion gene. The expression of this reporter gene can be assessed with the 124I-labeled reporter substrate 2'-fluoro-2'-deoxy-1-beta-D-arabinofuranosyl-5-iodouracil (124I-FIAU), which is phosphorylated by the HSV1-tk enzyme and trapped in the hypoxic cells. Animal positron emission tomography (microPET) and phosphor plate imaging (PPI) were used in this study to visualize the trapped 124I-FIAU, providing a distribution of the hypoxia-induced molecular events. The distribution of 124I-FIAU was also compared with that of an exogenous hypoxic cell marker, 18F-fluoromisonidazole (FMISO).
  
  
  RESULTS
  Our results showed that 124I-FIAU microPET imaging of the hypoxia-induced reporter gene expression is feasible, and that the intratumoral distributions of 124I-FIAU and 18F-FMISO are similar. In tumor sections, detailed radioactivity distributions were obtained with PPI which also showed similarity between 124I-FIAU and 18F-FMISO.
  
  
  CONCLUSIONS
  This reporter system is sufficiently sensitive to detect hypoxia-induced transcriptional activation by noninvasive imaging and might provide a valuable tool in studying tumor hypoxia and in validating existing and future exogenous markers for tumor hypoxia.
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, NY, New York 10021, USA.
authors.forename: Bixiu
authors.initials: B
authors.lastname: Wen
authors.forename: Paul
authors.initials: P
authors.lastname: Burgman
authors.forename: Pat
authors.initials: P
authors.lastname: Zanzonico
authors.forename: Joseph
authors.initials: J
authors.lastname: O'donoghue
authors.forename: Shangde
authors.initials: S
authors.lastname: Cai
authors.forename: Ron
authors.initials: R
authors.lastname: Finn
authors.forename: Inna
authors.initials: I
authors.lastname: Serganova
authors.forename: Ronald
authors.initials: R
authors.lastname: Blasberg
authors.forename: Juri
authors.initials: J
authors.lastname: Gelovani
authors.forename: Gloria C
authors.initials: GC
authors.lastname: Li
authors.forename: C Clifton
authors.initials: CC
authors.lastname: Ling
mesh_terms: D000230:Adenocarcinoma / Q000000981:diagnostic imaging* / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001086:Arabinofuranosyluracil / Q000031:analogs & derivatives* / Q000493:pharmacokinetics*; D014408:Biomarkers, Tumor / Q000378:metabolism*; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004195:Disease Models, Animal; D004353:Drug Evaluation, Preclinical; D005240:Feasibility Studies; D005462:Fluorine Radioisotopes / Q000493:pharmacokinetics; D020869:Gene Expression Profiling / Q000379:methods*; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics; D008920:Misonidazole / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D009687:Nuclear Proteins / Q000378:metabolism*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D051381:Rats; D013937:Thymidine Kinase / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D014408:Biomarkers, Tumor; D004268:DNA-Binding Proteins; D005462:Fluorine Radioisotopes; C497444:Hif1a protein, rat; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007457:Iodine Radioisotopes; D009687:Nuclear Proteins; D019275:Radiopharmaceuticals; D014157:Transcription Factors; D014764:Viral Proteins; C031843:fluoromisonidazole; D001086:Arabinofuranosyluracil; C043457:fialuridine; D008920:Misonidazole; C099241:thymidine kinase, Canid herpesvirus 1; D013937:Thymidine Kinase