Synthesis and evaluation of N-¹⁸F-fluorodeoxyglycosyl aminohippuric as a novel PET renal agent

Objectives: Positron emission tomography (PET) is capable of providing more excellent spatial resolution and absolute quantitative measurements than gamma imaging. The objective of this study was to synthesis a new fluorine-18 labeled hippurate, N-¹⁸F-fluorodeoxyglycosyl aminohippuric ([¹⁸F]FDG-AHP), using [¹⁸F]FDG as a building block, and investigate its suitability as a PET renal agent.

Methods: [¹⁸F]FDG-AHP was synthesized by a directly condensation of 2-deoxy-2-¹⁸F-fluoro-D-glucose ([¹⁸F]FDG) with aminohippuric at 80 °C for 30 min in an acidic condition. After reaction, 10 mL sterile water was added, and the solution was filtered through an QMA Sep-Pak cartridge which had been converted to the OH^- form by treatment with 10 mL of 1N NaOH and 10 mL of H₂O. [¹⁸F]FDG-AHP was trapped on the QMA cartridge and then eluted with 3mL saline. Dynamic micro-PET/CT studies were carried out for 3600 s (total 21 frames: 10 frames × 30 sec, 11 frames × 300 sec) in normal rats injected with [¹⁸F]FDG-AHP. The obtained PET images were analyzed with the PMOD imaging software (version 3.8) to assess in vivo kinetics for each rat. Results: [¹⁸F]FDG-AHP was obtained in 21.4±5.6 % radiochemical yield (based upon [¹⁸F]FDG, n=6) within a total synthesis time of 50 min. Dynamic micro-PET/CT revealed a significant kidneys uptake and a rapid clearance of [¹⁸F]FDG-AHP through the kidneys into the bladder without other tissue uptakes. The time-activity curves (renograms) of kidneys revealed that the time of maximal (T_max) and half-maximal concentration (T_1/2max) were 2.75±0.50 min and 12.50±0.50 min, respectively. Biodistribution study showed that the heart (blood) clearance was rapid and the activity of most of organs (such as hepatic, spleen, gastrointestinal and bone) was low during the whole 1 h of examing time.

Conclusions: A novel [¹⁸F]fluorine labeled hippurate derivative [¹⁸F]FDG-AHP was synthesized using [¹⁸F]FDG as a building block. These preliminary results suggest that [¹⁸F]FDG-AHP, as a novel radiopharmaceutical, performed the potential of assessing renal function by PET. Key Words: [¹⁸F]FDG-AHP; Renal radiopharmaceutical; PET; Aminohippuric; [¹⁸F]FDG

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