Semiautomated radiosynthesis and biological evaluation of [18F]FEAU: a novel PET imaging agent for HSV1-tk/sr39tk reporter gene expression.
2'-deoxy-2'-[(18)F]fluoro-5-ethyl-1-beta-D-arabinofuranosyluracil ([(18)F]FEAU) is a promising radiolabeled nucleoside designed to monitor Herpes Simplex Virus Type 1 thymidine kinase (HSV1-tk) reporter gene expression with positron emission tomography (PET). However, the challenging radiosynthesis creates problems for being able to provide [(18)F]FEAU routinely. We have developed a routine method using a commercial GE TRACERlab FX-FN radiosynthesis module with customized equipment to provide [(18)F]FEAU. All radiochemical yields are decay corrected to end-of-bombardment and reported as means +/- SD. Radiofluorination (33 +/- 8%; n = 4), bromination (85 +/- 8%; n = 4), coupling reaction (83 +/- 6%; n = 4), base hydrolysis steps, and subsequent high-performance liquid chromatography purification afforded purified [(18)F]FEAU beta-anomer in 5 +/- 1% overall yield (n = 3 runs) after approximately 5.5 h and a beta/alpha-anomer ratio of 7.4. Radiochemical/chemical purities and specific activity exceeded 99% and 1.3 Ci/micromol (48 GBq/micromol), respectively. In cell culture, [(18)F]FEAU showed significantly (P < 0.05) higher accumulation in C6 cells expressing HSV1-tk/sr39tk as compared to wild-type C6 cells. Furthermore, [(18)F]FEAU showed slightly higher accumulation than 9-[4-[(18)F]fluoro-3-(hydroxymethyl)butylguanine ([(18)F]FHBG) in cells expressing HSV1-tk (P < 0.05), whereas [(18)F]FHBG showed significantly higher (P < 0.05) accumulation than [(18)F]FEAU in HSV1-sr39tk-expressing cells. micro-PET imaging of mice carrying tumor xenografts of C6 cells stably expressing HSV1-tk or HSV1-sr39tk are consistent with the cell uptake results. The [(18)F]FEAU mouse images also showed very low gastrointestinal signal with predominant renal clearance as compared to [(18)F]FHBG. The routine radiosynthesis of [(18)F]FEAU was successfully semiautomated using a commercial module along with customized equipment to provide the beta-anomer in modest yields. Although further studies are needed, early results also suggest [(18)F]FEAU is a promising PET radiotracer for monitoring HSV1-tk reporter gene expression.
D000818:Animals; D001086:Arabinofuranosyluracil / Q000031:analogs & derivatives* / Q000138:chemical synthesis; D045744:Cell Line, Tumor; D002851:Chromatography, High Pressure Liquid; D017357:Cyclotrons; D005462:Fluorine Radioisotopes; D015870:Gene Expression; D017930:Genes, Reporter; D018259:Herpesvirus 1, Human / Q000201:enzymology*; D051379:Mice; D008819:Mice, Nude; D050505:Mutant Proteins / Q000235:genetics*; D009368:Neoplasm Transplantation; D049268:Positron-Emission Tomography / Q000379:methods*; D051381:Rats; D013056:Spectrophotometry, Ultraviolet; D013937:Thymidine Kinase / Q000235:genetics*; D014162:Transfection
D005462:Fluorine Radioisotopes; D050505:Mutant Proteins; D001086:Arabinofuranosyluracil; C054103:2'-fluoro-5-ethylarabinosyluracil; D013937:Thymidine Kinase