title: A human-derived reporter gene for noninvasive imaging in humans: mitochondrial thymidine kinase type 2.
abstract: A human-derived intrinsically nonimmunogenic reporter gene was tested for PET imaging of different molecular-genetic processes for potential clinical use.
  
  
  METHODS
  The human mitochondrial thymidine kinase type 2 (hTK2) reporter gene truncated at the N terminus (DeltahTK2), alone or fused with green fluorescent protein (GFP), was used for preclinical evaluation in a mouse model. The levels of enzymatic activity of DeltahTK2 and DeltahTK2 GFP proteins were assessed using radiotracer accumulation and prodrug activation assays in vitro and in subcutaneous tumors grown from the corresponding cell lines in nude mice. Kinetic analyses of (124)I-2'-fluoro-2'-deoxy-1-beta-D-beta-arabinofuranosyl-5-iodouracil (FIAU), (18)F-2'-fluoro-2'-deoxy-1-beta-D-beta-arabinofuranosyl-5-ethyluracil (FEAU), or (18)F-9-(4-(18)F-fluoro-3-hydroxymethylbutyl)guanine (FHBG) uptake in tumors and biodistribution studies were performed.
  
  
  RESULTS
  DeltahTK2 was successfully expressed in the cytoplasm of transduced cells. A new anti-hTK2 monoclonal antibody 8G2 was developed. The levels of FIAU and FEAU accumulation in cells expressing DeltahTK2 and DeltahTK2 GFP were at least 10-fold higher than in wild-type cells in vitro and about 6 times higher in vivo. We determined that FEAU is a more specific reporter substrate for DeltahTK2 than FIAU, whereas FHBG is not phosphorylated by this enzyme. In addition, we showed that DeltahTK2 transduced cells can be eliminated by treatment with d-arabinofuranosyl-cytosine.
  
  
  CONCLUSIONS
  We have tested a human-derived reporter gene that is likely to be nonimmunogenic and potentially allows for long-term monitoring of different molecular-genetic processes by nuclear imaging techniques in humans. Using (124)I-FIAU, (18)F-FIAU, or (18)F-FEAU, it should be possible to image DeltahTK2 reporter gene expression with PET in preclinical and clinical studies.
authors.affiliation: Department of Radiology, Memorial Sloan-Kettering Cancer Center, New York, NY, USA.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Ponomarev
authors.forename: Michael
authors.initials: M
authors.lastname: Doubrovin
authors.forename: Aleksander
authors.initials: A
authors.lastname: Shavrin
authors.forename: Inna
authors.initials: I
authors.lastname: Serganova
authors.forename: Tatiana
authors.initials: T
authors.lastname: Beresten
authors.forename: Ludmila
authors.initials: L
authors.lastname: Ageyeva
authors.forename: Changde
authors.initials: C
authors.lastname: Cai
authors.forename: Julius
authors.initials: J
authors.lastname: Balatoni
authors.forename: Mian
authors.initials: M
authors.lastname: Alauddin
authors.forename: Juri
authors.initials: J
authors.lastname: Gelovani
mesh_terms: D045744:Cell Line, Tumor; D017930:Genes, Reporter / Q000235:genetics; D005910:Glioma / Q000000981:diagnostic imaging* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008928:Mitochondria / Q000201:enzymology*; D011877:Radionuclide Imaging; D013937:Thymidine Kinase / Q000235:genetics / Q000378:metabolism*
chemical_list: C105339:thymidine kinase 2; D013937:Thymidine Kinase