title: Imaging expression of cytosine deaminase-herpes virus thymidine kinase fusion gene (CD/TK) expression with [124I]FIAU and PET.
abstract: Double prodrug activation gene therapy using the Escherichia coli cytosine deaminase (CD)-herpes simplex virus type 1 thymidine kinase (HSV1-tk) fusion gene (CD/TK) with 5-fluorocytosine (5FC), ganciclovir (GCV), and radiotherapy is currently under evaluation for treatment of different tumors. We assessed the efficacy of noninvasive imaging with [124I]FIAU (2'-fluoro-2'-deoxy-1-beta-D-arabinofuranosyl-5-iodo-uracil) and positron emission tomography (PET) for monitoring expression of the CD/TK fusion gene. Walker-256 tumor cells were transduced with a retroviral vector bearing the CD/TK gene (W256CD/TK cells). The activity of HSV1-TK and CD subunits of the CD/TK gene product was assessed in different single cell-derived clones of W256CD/TK cells using the FIAU radiotracer accumulation assay in cells and a CD enzyme assay in cell homogenates, respectively. A linear relationship was observed between the levels of CD and HSV1-tk subunit expression in corresponding clones in vitro over a wide range of CD/TK expression levels. Several clones of W256CD/TK cells with significantly different levels of CD/TK expression were selected and used to produce multiple subcutaneous tumors in rats. PET imaging of HSV1-TK subunit activity with [124I]FIAU was performed on these animals and demonstrated that different levels of CD/TK expression in subcutaneous W256CD/TK tumors can be imaged quantitatively. CD expression in subcutaneous tumor sample homogenates was measured using a CD enzyme assay. A comparison of CD and HSV1-TK subunit enzymatic activity of the CD/TK fusion protein in vivo showed a significant correlation. Knowing this relationship, the parametric images of CD subunit activity were generated. Imaging with [124I]FIAU and PET could provide pre- and posttreatment assessments of CD/TK-based double prodrug activation in clinical gene therapy trials.
authors.affiliation: Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, NY 10021, USA.
authors.forename: Trevor
authors.initials: T
authors.lastname: Hackman
authors.forename: Michail
authors.initials: M
authors.lastname: Doubrovin
authors.forename: Julius
authors.initials: J
authors.lastname: Balatoni
authors.forename: Tatiana
authors.initials: T
authors.lastname: Beresten
authors.forename: Vladimir
authors.initials: V
authors.lastname: Ponomarev
authors.forename: Bradly
authors.initials: B
authors.lastname: Beattie
authors.forename: Ronald
authors.initials: R
authors.lastname: Finn
authors.forename: William
authors.initials: W
authors.lastname: Bornmann
authors.forename: Ronald
authors.initials: R
authors.lastname: Blasberg
authors.forename: Juri Gelovani
authors.initials: JG
authors.lastname: Tjuvajev
mesh_terms: D001086:Arabinofuranosyluracil / Q000031:analogs & derivatives* / Q000493:pharmacokinetics*; D043525:Cytosine Deaminase; D015971:Gene Expression Regulation, Enzymologic; D015967:Gene Expression Regulation, Viral; D005822:Genetic Vectors; D018259:Herpesvirus 1, Human / Q000201:enzymology / Q000235:genetics*; D006801:Humans; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics*; D009700:Nucleoside Deaminases / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000235:genetics; D013937:Thymidine Kinase / Q000235:genetics*; D014055:Tomography, Emission-Computed; D014407:Tumor Cells, Cultured
chemical_list: D007457:Iodine Radioisotopes; D011993:Recombinant Fusion Proteins; D001086:Arabinofuranosyluracil; C043457:fialuridine; D013937:Thymidine Kinase; D009700:Nucleoside Deaminases; D043525:Cytosine Deaminase