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.