Regioselective Glycosylation of Fluorine-18-Labeled Sorbitol for Enhanced Bacterial Detection In Vivo Using PET

Precise and rapid detection of bacterial infection in vivo remains a significant challenge in clinical practice. In response to this challenge, several pathogen-specific positron emission tomography (PET) tracers have been developed, including the fluorine-18-labeled sorbitol derivative [¹⁸F]-FDS, which shows great promise in detecting bacterial infections in patients. In this study, we tested the hypothesis that the diagnostic performance of [¹⁸F]-FDS could be modulated via regioselective glycosylation to improve radiotracer stability, broaden organism sensitivity, and tune pharmacodynamics. A synthetic sequence was developed, whereby the common radiotracer [¹⁸F]-FDG was converted chemoenzymatically to α- and β-linked disaccharides via reverse phosphorolysis and subsequently reduced to the corresponding glycosylated [¹⁸F]-FDS derivatives. This strategy allowed the syntheses of glucopyranosyl-d-sorbitol analogs [¹⁸F]-FNT (α-1,3 linked), [¹⁸F]-FMT (α-1,4 linked), [¹⁸F]-FLT (β-1,3 linked), and [¹⁸F]-FCT (β-1,4 linked). Among these tracers, the α-linked analogs [¹⁸F]-FNT and [¹⁸F]-FMT showed greater uptake in both Gram-positive and Gram-negative pathogens compared to the β-linked analogs [¹⁸F]-FLT and [¹⁸F]-FCT. In vivo time-course PET imaging of [¹⁸F]-FNT and [¹⁸F]-FMT in uninfected mice revealed favorable pharmacokinetics, including rapid urinary excretion, minimal hepatobiliary retention, and low off-target signals. PET imaging using [¹⁸F]-FNT and [¹⁸F]-FMT detected Klebsiella pneumoniae pulmonary infections in mice with high infected/uninfected tissue ratios (∼6-fold). [¹⁸F]-FNT also showed high infected/uninfected tissue ratios (∼28-fold) in Staphylococcus aureus myositis, whereas the parent [¹⁸F]-FDS tracer was not taken up by the Gram-positive organisms tested. Our findings highlight the potential for PET tracer glycosylation as a tool to modulate target specificity and improve imaging sensitivity. These results also establish [¹⁸F]-FNT as a highly promising PET tracer with a high translational potential for detecting bacterial infection in vivo.