Automated radiosynthesis and preclinical in vivo evaluation of [18F]Fluoroethylpuromycin as a potential radiotracer for imaging protein synthesis with PET.

ABSTRACT

PURPOSE: From a series of fluorinated analogues of puromycin, we recently identified [18F]fluoroethylpuromycin (FEPURO) as a potential candidate for imaging the rate of protein synthesis in vivo. Herein, we describe the automation of the radiosynthesis, and evaluation of [18F]FEPURO in vivo. PROCEDURES [18F]FEPURO was radiosynthesised in an automated module. PET imaging was conducted in Wistar rats under control and blocking conditions using the protein synthesis inhibitor cycloheximide. Biodistribution and metabolite studies at 30, 60 and 120 min were conducted in healthy rats. RESULTS: Automation of the radiosynthesis resulted in reduction of the synthesis time by half from the manual method. A steady increase in the SUV was observed in the time-activity curves for the whole brain as expected for a protein synthesis marker. However, rapid in vivo metabolism of [18F]FEPURO within 15 min in plasma as well as the brain (4 % of parent 30 min p.i.) indicated formation of the [18F]FET radio-metabolite in >90 % thus suggesting that observed increase in the brain uptake was due to the radiometabolite. CONCLUSIONS: [18F]FEPURO is not a suitable PET radiotracer for imaging protein synthesis rates in brain in vivo due to its rapid metabolism. Further structural modifications to prevent in vivo metabolism are underway.