It's a Trap! Aldolase-Prescribed C₄ Deoxyradiofluorination Affords Intracellular Trapping and the Tracing of Fructose Metabolism by PET

Fructose metabolism has been implicated in various diseases, including metabolic disorders, neurodegenerative disorders, cardiac disorders, and cancer. However, the limited availability of a quantitative imaging radiotracer has hindered its exploration in pathology and diagnostic imaging. Methods: We adopted a molecular design strategy based on the catalytic mechanism of aldolase, a key enzyme in fructolysis. We successfully synthesized a radiodeoxyfluorinated fructose analog, [F-18]4-fluoro-4-deoxyfructose ([F-18]4-FDF), in high molar activity. Results: Through heavy isotope tracing by mass spectrometry, we demonstrated that C-4-deoxyfluorination of fructose led to effective trapping as fluorodeoxysorbitol and fluorodeoxyfructose-1-phosphate in vitro, unlike C-1- and C-6-fluorinated analogs that resulted in fluorolactate accumulation. This observation was consistent in vivo, where [F-18]6-fluoro-6-deoxyfructose displayed substantial bone uptake due to metabolic processing whereas [F-18]4-FDF did not. Importantly, [F-18]4-FDF exhibited low uptake in healthy brain and heart tissues, known for their high glycolytic activity and background levels of [F-18]FDG uptake. [F-18]4-FDF PET/CT allowed for sensitive mapping of neuro- and cardioinflammatory responses to systemic lipopolysaccharide administration. Conclusion: Our study highlights the significance of aldolase-guided C-4 radiodeoxyfluorination of fructose in enabling effective radiotracer trapping, overcoming limitations of C-1 and C-6 radioanalogs toward a clinically viable tool for imaging fructolysis in highly glycolytic tissues.