Abstract
INTRODUCTION: Our previous work demonstrated that the (99m)Tc renal tracer, (99m)Tc(CO)(3)(FEDA) ((99m)Tc-1), has a rapid clearance comparable in rats to that of (131)I-OIH, the radioactive gold standard for the measurement of effective renal plasma flow. The uncharged fluoroethyl pendant group of (99m)Tc-1 provides a route to the synthesis of a structurally analogous rhenium-tricarbonyl (18)F renal imaging agent, Re(CO)(3)([(18)F]FEDA) ((18)F-1). Our goal was to develop an efficient one-step method for the preparation of (18)F-1 and to compare its pharmacokinetic properties with those of (131)I-OIH in rats. METHODS: (18)F-1 was prepared by the nucleophilic (18)F-fluorination of its tosyl precursor. The labeled compound was isolated by HPLC and subsequently evaluated in Sprague-Dawley rats using (131)I-OIH as an internal control and by dynamic PET/CT imaging. Plasma protein binding (PPB) and erythrocyte uptake (RCB) were determined and the urine was analyzed for metabolites. RESULTS: (18)F-1 was efficiently prepared as a single species with high radiochemical purity (>99%) and it displayed high radiochemical stability in vitro and in vivo. PPB was 87% and RCB was 21%. Biodistribution studies confirmed rapid renal extraction and high specificity for renal excretion, comparable to that of (131)I-OIH, with minimal hepatic/gastrointestinal elimination. The activity in the urine, as a percentage of (131)I-OIH, was 92% and 95% at 10 and 60 min, respectively. All other organs (heart, spleen, lungs) showed a negligible tracer uptake (<0.4% ID). Dynamic microPET/CT imaging demonstrated rapid transit of (18)F-1 through the kidneys and into the bladder; there was no demonstrable activity in bone verifying the absence of free [(18)F]fluoride. CONCLUSIONS: (18)F-1 exhibited a high specificity for the kidney, rapid renal excretion comparable to that of (131)I-OIH and high in vivo radiochemical stability. Not only is (18)F-1 a promising PET renal tracer, but it provides a route to the development of a pair of analogous (18)F/(99m)Tc renal imaging agents with almost identical structures and comparable pharmacokinetic properties. These promising in vivo results warrant subsequent evaluation in humans.