Microfluidic approach for fast labeling optimization and dose-on-demand implementation

Introduction: The diffusion of PET as a pivotal molecular imaging modality has emphasized the need for new positron-emitting radiotracers to be used in diagnostic applications and research. Microfluidic represents an innovative approach, owing to its potential to increase radiochemical productivity in terms of yields, time reduction, precursor consumption and flexible experimental planning. Methods: We focused on fluorine-18 labeling and used a microfluidic platform to perform sequential reactions, by using the same batch of 18F-labeling solution on one or more substrates, during the same experimental session. A solid-phase extraction (SPE) workup procedure was also implemented in the system to provide a repeatable purification step. Results: We were able to quickly optimize the conditions for labeling of ethyl and propyl ditosylate and of a new cannabinoid type 2 (CB2) receptor agonist, CB41. In all substrates, we obtained good incorporation yields (60% to 85%) in short (b90 s) reaction times. Single dosages of the CB2 ligand were sequentially prepared, upon request, in satisfactory quantities and purity for small animal PET scanning. Conclusion: This work demonstrates the usefulness of a microfluidic-based system for a rapid optimization of temperature, flow rate of reactants and their relative ratio in the labeling of different precursors by using the same 18F-fluoride batch. This approach was used to obtain in sequence several injectable doses of a novel CB2 ligand, thus providing the proof of principle that microfluidic systems permit a dose-ondemand production of new radiotracers.