Robust and Facile Automated Radiosynthesis of [(18)F]FSPG on the GE FASTlab

PURPOSE: (S)-4-(3-(18)F-Fluoropropyl)-ʟ-Glutamic Acid ([(18)F]FSPG) is a radiolabeled non-natural amino acid that is used for positron emission tomography (PET) imaging of the glutamate/cystine antiporter, system x(C)(-), whose expression is upregulated in many cancer types. To increase the clinical adoption of this radiotracer, reliable and facile automated procedures for [(18)F]FSPG production are required. Here, we report a cassette-based method to produce [(18)F]FSPG at high radioactivity concentrations from low amounts of starting activity. PROCEDURES: An automated synthesis and purification of [(18)F]FSPG was developed using the GE FASTlab. Optimization of the reaction conditions and automated manipulations were performed by measuring the isolated radiochemical yield of [(18)F]FSPG and by assessing radiochemical purity using radio-HPLC. Purification of [(18)F]FSPG was conducted by trapping and washing of the radiotracer on Oasis MCX SPE cartridges, followed by a reverse elution of [(18)F]FSPG in phosphate-buffered saline. Subsequently, the [(18)F]FSPG obtained from the optimized process was used to image an animal model of non-small cell lung cancer. RESULTS: The optimized protocol produced [(18)F]FSPG in 38.4 ± 2.6 % radiochemical yield and >96 % radiochemical purity with a molar activity of 11.1 ± 7.7 GBq/μmol. Small alterations, including the implementation of a reverse elution and an altered Hypercarb cartridge, led to significant improvements in radiotracer concentration from <10 MBq/ml to >100 MBq/ml. The improved radiotracer concentration allowed for the imaging of up to 20 mice, starting with just 1.5 GBq of [(18)F]Fluoride. CONCLUSIONS: We have developed a robust and facile method for [(18)F]FSPG radiosynthesis in high radiotracer concentration, radiochemical yield, and radiochemical purity. This cassette-based method enabled the production of [(18)F]FSPG at radioactive concentrations sufficient to facilitate large-scale preclinical experiments with a single prep of starting activity. The use of a cassette-based radiosynthesis on an automated synthesis module routinely used for clinical production makes the method amenable to rapid and widespread clinical translation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11307-021-01609-w.