Initial preclinical evaluation of ¹⁸F-fluorodeoxysorbitol PET as a novel functional renal imaging agent

Accurate assessment of kidney function plays an essential role for optimal clinical decision making in a variety of diseases. The major intrinsic advantages of PET are superior spatial and temporal resolutions for quantitative tomographic renal imaging. 2-deoxy-2-¹⁸F-fluorodeoxysorbitol (¹⁸F-FDS) is an analog of sorbitol that is reported to be freely filtered at the renal glomerulus without reabsorption at the tubule. Furthermore, it can be synthesized via simple reduction of widely available ¹⁸F-FDG. We tested the feasibility of ¹⁸F-FDS renal PET imaging in rats. Methods: The systemic and renal distribution of ¹⁸F-FDS were determined by dynamic 35-min PET imaging (15 frames x 8 s, 26 frames x 30 s, 20 frames x 60 s) with a dedicated small-animal PET system and postmortem tissue counting in healthy rats. Distribution of coinjected ^99mTc-diethylenetriaminepentaacetic acid (DTPA) was also estimated as a reference. Plasma binding and in vivo stability of ¹⁸F-FDS were determined. Results: In vivo PET imaging visualized rapid excretion of the administrated ¹⁸F-FDS from both kidneys, with minimal tracer accumulation in other organs. Initial cortical tracer uptake followed by visualization of the collecting system could be observed with high contrast. Split-function renography curves were successfully obtained in healthy rats (the time of maximal concentration [T_max] right [R] = 2.8 ± 1.2 min, T_max left [L] = 2.9 ± 1.5 min, the time of half maximal concentration [T_1/2max] R = 8.8 ± 3.7 min, T_1/2max L = 11.1 ± 4.9 min). Postmortem tissue counting of ¹⁸F-FDS confirmed the high kidney extraction (kidney activities at 10, 30, and 60 min after tracer injection [percentage injected dose per gram]: 1.8 ± 0.7, 1.2 ± 0.1, and 0.5 ± 0.2, respectively) in a degree comparable to ^99mTc-DTPA (2.5 ± 1.0, 1.5 ± 0.2, and 0.8 ± 0.3, respectively). Plasma protein binding of ¹⁸F-FDS was low (<0.1%), and metabolic transformation was not detected in serum and urine. Conclusion: In rat experiments, ¹⁸F-FDS demonstrated high kidney extraction and excretion, low plasma protein binding, and high metabolic stability as preferable properties for renal imaging. These preliminary results warrant further confirmatory studies in large animal models and clinical studies as a novel functional renal imaging agent, given the advantages of PET technology and broad tracer availability.