Automated radiosynthesis of 5-[ 11 C]l-glutamine, an important tracer for glutamine utilization.

INTRODUCTION: The natural amino acid l-Glutamine (Gln) is essential for both cell growth and proliferation. In addition to glucose, cancer cells utilize Gln as a carbon source for ATP production, biosynthesis, and as a defense against reactive oxygen species. The utilization of [11 C]Gln has been previously reported as a biomarker for tissues with an elevated demand for Gln, however, the previous reports for the preparation of [11 C]Gln were found to be lacking several crucial aspects necessary for transition to human production. Namely, the presence of unreacted precursor and the use of non-commercialized, custom built, reaction platforms. Herein, we report the development and utilization of methodology for the automated production of [11 C]Gln that meets institutional criteria for human use.

METHODS: The preparation of [11 C]Gln was carried out on the GE FX2 N platform. Briefly, after trapping of [11 C]HCN with a solution of CsHCO3 in DMF, the [11 C]CsCN was reacted with a commercially available precursor. This intermediate was then purified by HPLC and deprotected/hydrolyzed under acidic conditions. Following pH adjustment, the product was filtered to give the desired [11 C]Gln as a sterile injectable. The resulting product was then analyzed for quality assurance.

RESULTS: Automated production by this method reliably provides over 3.7 GBq (100 mCi) of [11 C]Gln. The resulting final drug product was found to have a >99% radiochemical purity, <5% of D-Gln present, no detectable impurities, and the total preparation time was roughly 45 min from the end-of-bombardment.

CONCLUSIONS: A fast, reliable and efficient automated radiosynthesis was developed using a commercially available module. Purifications used throughout allow for both a radiochemically and chemically pure final product solution of [11 C]Gln.