Semiautomated Radiosynthesis and Biological Evaluation of [18F]FEAU: A Novel PET Imaging Agent for HSV1-tk/sr39tk Reporter Gene Expression

2′-Deoxy-2′-[18F]fluoro-5-ethyl-1-β-d-arabinofuranosyluracil ([18F]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 [18F]FEAU routinely. We have developed a routine method using a commercial GE TRACERlab FX-FN radiosynthesis module with customized equipment to provide [18F]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 [18F]FEAU β-anomer in 5 ± 1% overall yield (n = 3 runs) after ~5.5 h and a β/α-anomer ratio of 7.4. Radiochemical/chemical purities and specific activity exceeded 99% and 1.3 Ci/μmol (48 GBq/μmol), respectively. In cell culture, [18F]FEAU showed significantly (P < 0.05) higher accumulation in C6 cells expressing HSV1-tk/sr39tk as compared to wild-type C6 cells. Furthermore, [18F]FEAU showed slightly higher accumulation than 9-[4-[18F]fluoro-3-(hydroxymethyl)butylguanine ([18F]FHBG) in cells expressing HSV1-tk (P < 0.05), whereas [18F]FHBG showed significantly higher (P < 0.05) accumulation than [18F]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 [18F]FEAU mouse images also showed very low gastrointestinal signal with predominant renal clearance as compared to [18F]FHBG. The routine radiosynthesis of [18F]FEAU was successfully semiautomated using a commercial module along with customized equipment to provide the β-anomer in modest yields. Although further studies are needed, early results also suggest [18F]FEAU is a promising PET radiotracer for monitoring HSV1-tk reporter gene expression.