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

• Published in: Molecular imaging and biology Vol. 10; no. 2; pp. 82 - 91
• Main Authors: Chin, Frederick T., Namavari, Mohammed, Levi, Jelena, Subbarayan, Murugesan, Ray, Pritha, Chen, Xiaoyuan, Gambhir, Sanjiv S.
• Format: Journal Article
• Language: English
• Published: New York Springer-Verlag 01.03.2008; Springer Nature B.V
• Subjects: Animals; Arabinofuranosyluracil - analogs & derivatives; Arabinofuranosyluracil - chemical synthesis; Cell Line, Tumor; Chromatography, High Pressure Liquid; Cyclotrons; Fluorine Radioisotopes; Gene Expression; Genes, Reporter; Herpes simplex virus 1; Herpesvirus 1, Human - enzymology; Imaging; Medicine; Medicine & Public Health; Mice; Mice, Nude; Mutant Proteins - genetics; Neoplasm Transplantation; Positron-Emission Tomography - methods; Radiology; Rats; Research Article; Spectrophotometry, Ultraviolet; Thymidine Kinase - genetics; Transfection; Molecular imaging; Semiautomated; Thymidine kinase; F]FEAU; Reporter genes; [; Gene therapy
• ISSN: 1536-1632; 1860-2002
• DOI: 10.1007/s11307-007-0122-3

2′-Deoxy-2′-[ 18 F]fluoro-5-ethyl-1-β- 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 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, [ 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 β-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.