Fully automated production of ¹¹C-doxepin for PET imaging histamine H1 receptor

Objectives: ¹¹C-Doxepin is an established positron emission tomography (PET) probe for imaging the histamine H1 receptor, which is associated with various neurological disorders and allergic diseases. A fully automated current Good Manufacturing Practices (cGMP)-compliant radiosynthesis is therefore desirable in order to facilitate clinical PET studies. We report here a fully automated production method for ¹¹C-doxepin using a multipurpose PET module for clinical use. Methods: ¹¹C-Doxepin was radiosynthesized by N-[¹¹C]methylation of nordoxepin using [ ¹¹C] methyl iodide in DMF solvent, and then purified by HPLC, and finally reformulated with solid phase extraction (SPE) using a cGMP-compliant automated multipurpose PET module developed in house. The final product was analyzed and subjected to quality control according to current US Pharmacopeia requirements. Results: The radiochemical yield (decay corrected) of ¹¹C-doxepin for clinical use was 47.0±5.2% (n=12) based on [¹¹C]methyl iodide, moreover the radiochemical purity of ¹¹C-doxepin was more than 97.5% with 1,200±500 Ci/mmol specific activity(end of production). The total production time of ¹¹C-doxepin was 37 min from end of bombardment (EOB) with the final product passing all tests under cGMP requirements for clinical use. Conclusions: A simplified and reliable fully automated production of ¹¹C-doxepin for clinical use was developed, allowing the synthesis of the tracer with high yield using a cGMP-compliant module and procedure. The success of this approach could make the PET tracer ¹¹C-doxepin more accessible for clinical studies.