Synthesis and evaluation of 2'-deoxy-2'-18F-fluoro-5-fluoro-1-beta-D-arabinofuranosyluracil as a potential PET imaging agent for suicide gene expression.
2'-deoxy-2'-(18)F-fluoro-5-fluoro-1-beta-D-arabinofuranosyluracil ((18)F-FFAU) has been synthesized and evaluated in HT-29 cells as a potential PET agent for herpes simplex virus type 1 thymidine kinase (HSV1-tk) gene expression.


METHODS
2-Deoxy-2-(18)F-fluoro-1,3,5-tri-O-benzoyl-alpha-D-arabinofuranose was prepared by the reaction of the respective 2-triflate with tetrabutylammonium (18)F-fluoride. The fluorosugar was converted to its 1-bromo derivative and coupled with protected 5-fluorouracil. The crude product was hydrolyzed in base and purified by high-performance liquid chromatography to obtain the (18)F-FFAU. In vitro studies were performed in HT-29 cells by incubation at various time points. In vivo studies including biodistribution and microPET were performed in tumor-bearing nude mice.


RESULTS
The radiochemical yield was 20%-30% decay corrected with an average of 25% in 4 runs. Radiochemical purity was >99% and average specific activity was 85 GBq/micromol (2,300 mCi/micromol) (end of synthesis). In vitro accumulation of (3)H-FFAU in HSV1-tk-expressing cells was approximately 180-fold (P < 0.001) higher than that in the wild-type cells between 30 and 120 min. In vivo uptake of (3)H-FFAU in HSV1-tk-positive tumors at 2 h was approximately 8-fold (P < 0.001) higher than that in the control tumors. Tumor uptake (percentage injected dose per gram of tissue) and the uptake ratio (tk-positive to wild type) of (3)H-FFAU in tk-positive cells was higher compared with those of our earlier studies using 2'-(14)C-deoxy-2'-fluoro-5-methyl-1-beta-D-arabinofuranosyluracil ((14)C-FMAU) and 9-(4-(18)F-fluoro-3-hydroxymethylbutyl)guanine ((18)F-FHBG) in the same cell lines. microPET on tumor-bearing nude mice also demonstrated a very high uptake of (18)F-FFAU in tk-positive tumors compared with that of the control tumor without significant accumulation in other organs.


CONCLUSIONS
These results demonstrate that (18)F-FFAU has superior biodistribution characteristics and significantly higher in vivo uptake in HSV1-tk-expressing tumor compared with previously studied agents.
Alauddin
Mian M
MM
PET Imaging Science Center, Department of Radiology, University of Southern California, Los Angeles, California, USA.
Shahinian
Antranic
A
Park
Ryan
R
Tohme
Michel
M
Fissekis
John D
JD
Conti
Peter S
PS
D000818:Animals; D001086:Arabinofuranosyluracil / Q000031:analogs & derivatives* / Q000138:chemical synthesis; D005462:Fluorine Radioisotopes / Q000493:pharmacokinetics*; D005472:Fluorouracil / Q000031:analogs & derivatives* / Q000138:chemical synthesis; D015870:Gene Expression; D019073:HT29 Cells; D018259:Herpesvirus 1, Human / Q000201:enzymology*; D006801:Humans; D051379:Mice; D049268:Positron-Emission Tomography / Q000379:methods*; D013937:Thymidine Kinase / Q000378:metabolism*
C496306:2'-deoxy-2'-18F-fluoro-5-fluoro-1-beta-D-arabinofuranosyluracil; D005462:Fluorine Radioisotopes; D001086:Arabinofuranosyluracil; D013937:Thymidine Kinase; D005472:Fluorouracil