Comparison of [18F]FHBG and [14C]FIAU for imaging of HSV1-tk reporter gene expression: adenoviral infection vs stable transfection.
Earlier studies involving comparison of different reporter probes have shown conflicting results between pyrimidine nucleosides [e.g., 2'-fluoro-2'-deoxy-1-beta- d-arabinofuranosyl-5-iodouracil (FIAU)] and acycloguanosine derivatives [e.g., penciclovir (PCV), 9-(4-fluoro-3-hydroxymethylbutyl)guanine (FHBG)]. We hypothesized that this reported discrepancy may be related to how the reporter gene is delivered to the cells-stably transfected vs adenoviral infection. We directly compared the uptake characteristics of [(18)F]FHBG, [(3)H]PCV, and [(14)C]FIAU in cell culture and in vivo using an adenoviral mediated gene transfer model and stably transfected cells. We further compared the uptake of three reporter probes using both HSV1-tk and a mutant HSV1-sr39tk expressing cells to assess the optimal reporter probe/reporter gene combination. [(14)C]FIAU accumulation was greater than that of [(3)H]PCV and [(18)F]FHBG in control cells and in HSV1-tk stably transfected cells ( P<0.001). After infection of C6 cells with AdCMV- HSV1-tk (1.5x10(8) pfu), [(18)F]FHBG and [(3)H]PCV accumulation was significantly greater than that of [(14)C]FIAU ( P<0.01). [(18)F]FHBG and [(3)H]PCV accumulated to a significantly greater extent than [(14)C]FIAU in C6-stb-sr39tk+ and AdCMV- HSV1-sr39tk infected C6 cells ( P<0.001). Results from the nude mice supported the results in cell culture. [(14)C]FIAU led to significantly higher %ID/g in C6-stb-tk+ xenografts than [(18)F]FHBG ( P<0.05); however, compared with [(14)C]FIAU, [(18)F]FHBG led to as high %ID/g in HSV1-tk expressing hepatocytes and to significantly greater %ID/g in C6-stb-sr39tk+ xenografts and HSV1-sr39tk expressing hepatocytes. Dynamic sequential images showed that [(18)F]FHBG was well retained in HSV1-sr39tk expressing cells (C6-stb-sr39tk+) for at least 4 h after injection, while it was rapidly cleared from HSV1-tk expressing cells (MH3924A-stb-tk+). [(14)C]FIAU accumulated in HSV1-tk stably expressing cells to a greater extent than either [(3)H]PCV or [(18)F]FHBG. However, the accumulation of [(3)H]PCV and [(18)F]FHBG in adenoviral infected C6 cells or hepatocytes was equivalent to or greater than that of [(14)C]FIAU. These results may be due to intracellular biochemical changes (e.g., thymidine) when cells are infected with adenovirus. For adenoviral studies, the [(18)F]FHBG/ HSV1-sr39tk combination was shown to be more sensitive than the [(14)C]FIAU/ HSV1-tk combination HSV1-tk.
The Crump Institute for Molecular Imaging, Department of Molecular and Medical Pharmacology, UCLA School of Medicine, Los Angeles, CA 90095-1770, USA.
Jung-Jun
JJ
Min
Meera
M
Iyer
Sanjiv S
SS
Gambhir
D000257:Adenoviridae Infections / Q000000981:diagnostic imaging / Q000276:immunology / Q000378:metabolism; D000818:Animals; D001086:Arabinofuranosyluracil / Q000031:analogs & derivatives* / Q000493:pharmacokinetics*; D045744:Cell Line, Tumor; D017930:Genes, Reporter / Q000235:genetics; D005910:Glioma / Q000000981:diagnostic imaging* / Q000378:metabolism*; D006147:Guanine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics*; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D008657:Metabolic Clearance Rate; D051379:Mice; D009928:Organ Specificity; D011506:Proteins / Q000378:metabolism*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D051381:Rats; D014018:Tissue Distribution; D014055:Tomography, Emission-Computed / Q000379:methods; D014162:Transfection / Q000379:methods*
C113308:9-(4-fluoro-3-hydroxymethylbutyl)guanine; D047908:Intracellular Signaling Peptides and Proteins; C477373:MON1B protein, human; D011506:Proteins; D019275:Radiopharmaceuticals; D001086:Arabinofuranosyluracil; C043457:fialuridine; D006147:Guanine