Automated synthesis of [¹¹C]L-glutamine on Synthra HCN plus synthesis module

Background: L-Glutamine (L-Gln) is the most abundant amino acid present in the human body and is involved in numerous metabolic pathways. Glutaminolysis is the metabolic process deployed by many aggressive cancers such as triple negative breast cancer (TNBC). Imaging the metabolic pathways of L-glutamine could provide more insights into tumor biology. Reliable and reproducible automated synthesis of [¹¹C]L-glutamine PET (Positron Emission Tomography) radiotracer is critical for these studies.

Results: [¹¹C]L-Glutamine ([¹¹C]L-Gln) was reliably and reproducibly synthesized. The automated process involves cleaning and drying of the synthesis module, azeotropic drying of crown ether and cesium bicarbonate, conversion of [¹¹C]CO₂ to [¹¹C] CsCN, incorporation of [¹¹C] CN into the starting material, and hydrolysis and deprotection of the corresponding [¹¹C] nitrile to yield [¹¹C]L-glutamine. Starting with approximately 1 Ci of [¹¹C] cesium cyanide ([¹¹C]CsCN), 47-77 mCi (n = 4) of the final product, [¹¹C]L-Gln, was obtained after sterile filtration. The radiochemical purity of the final product was > 90% with almost exclusively L-glutamine isomer. The yield of [¹¹C]L-Gln was 43-52% (n = 4), decay corrected to end of [¹¹C] CsCN trapping in the reaction vessel.

Conclusions: All the steps including drying of the mixture of base and crown ether, preparation of [¹¹C] cyanide, radiochemical synthesis and formulation were accomplished on a single synthesis unit. [¹¹C]L-Gln has been successfully adapted and optimized on an automated synthesis module, Synthra HCN Plus. This process can be readily adapted for clinical research use.