99mTc(CO)3(NTA) and 131I-OIH: comparable plasma clearances in patients with chronic kidney disease

A novel objective method for discriminating pathological and physiological colorectal uptake in the lower abdominal region using whole-body dynamic 18F-FDG-PET

OBJECTIVES

To investigate whether the center-of-mass shift distance (CMSD) analysis on whole-body dynamic positron emission tomography (WBD-PET) with continuous bed motion is an objective index for discriminating pathological and physiological uptake in the lower abdominal colon.

METHODS

We retrospectively analyzed the CMSD in 39 patients who underwent delayed imaging to detect incidental focal uptake that was difficult to determine as pathological and physiological on a conventional early-PET (early) image reconstructed by 5-phase WBD-PET images. The CMSD between each phase of WBD-PET images and between conventional early and delayed (two-phase) PET images were classified into pathological and physiological uptake groups based on endoscopic histology or other imaging diagnostics. The diagnostic performance of CMSD analysis on WBD-PET images was evaluated by receiver operator characteristic (ROC) analysis and compared to that of two-phase PET images.

RESULTS

A total of 66 incidental focal uptake detected early image were classified into 19 and 47 pathological and physiological uptake groups, respectively. The CMSD on WBD-PET and two-phase PET images in the pathological uptake group was significantly lower than that in the physiological uptake group (p < 0.01), respectively. The sensitivity, specificity, and accuracy in CMSD analysis on WBD-PET images at the optimal cutoff of 5.2 mm estimated by the Youden index were 94.7%, 89.4%, and 89.4%, respectively, which were not significantly different (p = 0.74) from those of two-phase PET images.

CONCLUSIONS

The CMSD analysis on WBD-PET was useful in discriminating pathological and physiological colorectal uptake in the lower abdominal region, and its diagnostic performance was comparable to that of two-phase PET images. We suggested that CMSD analysis on WBD-PET images would be a novel objective method to omit unnecessary additional delayed imaging.

Non-invasive molecular imaging of kidney diseases

In nephrology, differential diagnosis or assessment of disease activity largely relies on the analysis of glomerular filtration rate, urinary sediment, proteinuria and tissue obtained through invasive kidney biopsies. However, currently available non-invasive functional parameters, and most serum and urine biomarkers, cannot capture intrarenal molecular disease processes specifically. Moreover, although histopathological analyses of kidney biopsy samples enable the visualization of pathological morphological and molecular alterations, they only provide information about a small part of the kidney and do not allow longitudinal monitoring. These limitations not only hinder understanding of the dynamics of specific disease processes in the kidney, but also limit the targeting of treatments to active phases of disease and the development of novel targeted therapies. Molecular imaging enables non-invasive and quantitative assessment of physiological or pathological processes by combining imaging technologies with specific molecular probes. Here, we discuss current preclinical and clinical molecular imaging approaches in nephrology. Non-invasive visualization of the kidneys through molecular imaging can be used to detect and longitudinally monitor disease activity and can therefore provide companion diagnostics to guide clinical trials, as well as the safe and effective use of drugs.

Head to head comparison of [99mTc]Tc(CO)3(NTA) and [99mTc]Tc-MAG3 in patients with suspected obstruction

PURPOSE

^99mTc-tricarbonyl-nitrilotriacetic acid, [^99mTc]Tc(CO)₃(NTA), is a new ^99mTc-renal radiopharmaceutical with a clearance equal to that of ¹³¹I-ortho-iodohippuran, [¹³¹I]I-OIH. Our purpose was to compare the performance of [^99mTc]Tc(CO)₃(NTA) and [^99mTc]Tc-MAG3 in patients with suspected obstruction.

METHODS

[^99mTc]Tc(CO)₃(NTA) was prepared with commercially available NTA ligand and CRS Isolink kit, and isolated by HPLC. Eighteen adult patients referred for diuretic renography received an intravenous injection of approximately 40 mg of furosemide 15 min prior to either [^99mTc]Tc(CO)₃(NTA) or [^99mTc]Tc-MAG3 (mean activity of 47 ± 4.4 MBq). Data were acquired for 24 min followed by an anterior image of the liver and gall bladder and a measure of voided volume. Patients received a second furosemide injection equal to one third of the original dose followed fifteen minutes later by administration of the alternate tracer, mean activity of 320 ± 34 MBq. Clearances were measured using a camera-based technique.

RESULTS

The clearance of NTA was greater than that of MAG3, 331 ± 146 versus 271 ± 105 mL/min/1.73 m², respectively, p < 0.0001. The kidney to background ratio for NTA was greater than that of MAG3 for both left and right kidneys, p < 0.001; the 20 min/maximum count ratio was significantly less, p < 0.0001. There was no significant difference in the voiding volumes following NTA and MAG3 administration, 598 ± 237 mL versus 498 ± 170 mL, respectively, p = 0.07. Gall bladder activity was not observed with NTA but was present in 6/17 MAG3 studies. Images and renogram curves were comparable except for two patients where the NTA study excluded obstruction but the MAG3 study suggested an indeterminate or obstructed kidney.

CONCLUSIONS

Unlike MAG3, NTA is not eliminated via the hepatobiliary track. Moreover, NTA has a higher kidney to background ratio and more rapid clearance than MAG3. These advantages should allow more robust camera-based clearance measurements and may lead to better discrimination between obstructed and non-obstructed kidneys.

fac-99mTc/Re-tricarbonyl complexes with tridentate aminocarboxyphosphonate ligands: suitability of the phosphonate group in chelate ligand design of new imaging agents

Ligands that coordinate via dianionic phosphonate groups have not been widely utilized in radiopharmaceuticals. N-(phosphonomethyl)iminodiacetic acid (1, PMIDA) and N-(phosphonomethyl)glycine (2, PMG) were investigated as new chelators for the 99mTc/Re-tricarbonyl "core" (fac-M(CO)3, M = 99mTc, Re) present in a major class of radiopharmaceuticals. fac-M(CO)3(PMIDA) and fac-M(CO)3(PMG) complexes were studied by HPLC and 1H/13C/31P NMR methods for M = Re (Re-1 and Re-2) and by HPLC for M = 99mTc ( 99m Tc-1 and 99m Tc-2). Re-1 and 99m Tc-1 complexes exhibit a similar pH-dependent equilibrium between geometric linkage isomers (M-1a and M-1b). However, only one isomer exists for M-2 under all conditions. Structural characterization by X-ray crystallography reveals the presence of a bond between a phosphonate oxygen and the Re(I) center in fac-Re(CO)3(PMG) (Re-2). Detailed comparisons of NMR data for Re-2 conclusively demonstrate that the phosphonate group is coordinated in Re-1b (isomer favored at high pH) but not in Re-1a, which has a dangling N-(phosphonomethyl) group. To our knowledge, Re-1b and Re-2 and their 99mTc analogs are the first well-documented examples of complexes with these metal-tricarbonyl cores having a dianionic phosphonate group directly coordinated in a fac-M(CO)3-O-P grouping. Pharmacokinetic studies using Sprague-Dawley rats reveal that 99m Tc-2 is a robust tracer. Hence, phosphonate groups should be considered in designing 99mTc and 186/188Re radiopharmaceuticals, including agents with bioactive moieties attached to dangling carboxylate or phosphonate groups.

Multifunctional Cyclopentadienes as a Scaffold for Combinatorial Bioorganometallics in [(η5 -C5 H2 R1 R2 R3 )M(CO)3 ] (M=Re, 99m Tc) Piano-Stool Complexes

Multifunctional cyclopentadiene (Cp) ligands and their rhenium and ^99m Tc complexes were prepared by a versatile synthetic route. The properties of these Cp ligands can be tuned on demand, either during their synthesis (variation of R₁ ) or through post-synthetic functionalization with two equal or different vectors (V₁ and V₂ ). Variation of these groups enables a combinatorial approach in the synthesis of bioorganometallic complexes. This is demonstrated by the preparation of Cp ligands containing both electron-donating and electron-withdrawing groups at the R₁ position and their subsequent homo- or heterofunctionalization with biovector models (benzylamine and phenylalanine) under standard amide bond-formation conditions. All ligands can be coordinated to the fac-[Re(CO)₃ ]⁺ and fac-[^99m Tc(CO)₃ ]⁺ cores to give tetrafunctional complexes in straightforward and functional-group-tolerant procedures. The ^99m Tc complexes were prepared in one step, in 30 min, and under aqueous conditions from generator-eluted [^99m TcO₄ ]^- .

Re(CO)3([18F]FEDA), a novel 18F PET renal tracer: Radiosynthesis and preclinical evaluation

INTRODUCTION

Our previous work demonstrated that the ^99mTc renal tracer, ^99mTc(CO)₃(FEDA) (^99mTc-1), has a rapid clearance comparable in rats to that of ¹³¹I-OIH, the radioactive gold standard for the measurement of effective renal plasma flow. The uncharged fluoroethyl pendant group of ^99mTc-1 provides a route to the synthesis of a structurally analogous rhenium-tricarbonyl ¹⁸F renal imaging agent, Re(CO)₃([¹⁸F]FEDA) (¹⁸F-1). Our goal was to develop an efficient one-step method for the preparation of ¹⁸F-1 and to compare its pharmacokinetic properties with those of ¹³¹I-OIH in rats.

METHODS

¹⁸F-1 was prepared by the nucleophilic ¹⁸F-fluorination of its tosyl precursor. The labeled compound was isolated by HPLC and subsequently evaluated in Sprague-Dawley rats using ¹³¹I-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

¹⁸F-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 ¹³¹I-OIH, with minimal hepatic/gastrointestinal elimination. The activity in the urine, as a percentage of ¹³¹I-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 ¹⁸F-1 through the kidneys and into the bladder; there was no demonstrable activity in bone verifying the absence of free [¹⁸F]fluoride.

CONCLUSIONS

¹⁸F-1 exhibited a high specificity for the kidney, rapid renal excretion comparable to that of ¹³¹I-OIH and high in vivo radiochemical stability. Not only is ¹⁸F-1 a promising PET renal tracer, but it provides a route to the development of a pair of analogous ¹⁸F/^99mTc renal imaging agents with almost identical structures and comparable pharmacokinetic properties. These promising in vivo results warrant subsequent evaluation in humans.

Monoanionic 99mTc-tricarbonyl-aminopolycarboxylate complexes with uncharged pendant groups: Radiosynthesis and evaluation as potential renal tubular tracers

INTRODUCTION

^99mTc(CO)₃-nitrilotriacetic acid, ^99mTc(CO)₃(NTA), is a new renal tubular agent with pharmacokinetic properties comparable to those of ¹³¹I-OIH but the clearance of ^99mTc(CO)₃(NTA) and ¹³¹I-OIH is still less than the clearance of PAH, the gold standard for the measurement of effective renal plasma flow. At physiological pH, dianionic ^99mTc(CO)₃(NTA) has a mononegative inner metal-coordination sphere and a mononegative uncoordinated carboxyl group. To evaluate alternate synthetic approaches, we assessed the importance of an uncoordinated carboxyl group, long considered essential for tubular transport, by evaluating the pharmacokinetics of three analogs with the ^99mTc(CO)₃(NTA) metal-coordination sphere but with uncharged pendant groups.

METHODS

^99mTc(CO)₃ complexes with N-(2-acetamido)iminodiacetic acid (ADA), N-(2-hydroxyethyl)iminodiacetic acid (HDA) and N-(fluoroethyl)iminodiacetic acid (FEDA) were prepared using a tricarbonyl kit and isolated by HPLC. The pharmacokinetics were evaluated in Sprague-Dawley rats, with ¹³¹I-OIH as an internal control; urine was analyzed for metabolites. Plasma protein binding and erythrocyte uptake were determined from the 10min blood samples. Re(CO)₃(FEDA), the analog of ^99mTc(CO)₃(FEDA), was prepared and characterized.

RESULTS

^99mTc(CO)₃(ADA), ^99mTc(CO)₃(HDA) and ^99mTc(CO)₃(FEDA) were efficiently prepared as a single species with high radiochemical purities (>99%). These new monoanionic ^99mTc(CO)₃ tracers with uncharged dangling groups all showed rapid blood clearance and high specificity for renal excretion. Activity in the urine, as a percent of ¹³¹I-OIH at 10 and 60min, was 96% and 99% for ADA, 96% and 100% for HDA, and 100% and 99% for FEDA, respectively. Each new tracer was excreted unchanged in the urine. The Re(CO)₃(FEDA) structure adds compelling evidence that such ^99mTc(CO)₃(NTA) analogs have metal-coordination spheres identical to that of ^99mTc(CO)₃(NTA).

CONCLUSIONS

New tracers lacking the negatively charged pendant carboxyl group previously thought to be essential for rapid renal extraction, ^99mTc(CO)₃(ADA), ^99mTc(CO)₃(HDA) and ^99mTc(CO)₃(FEDA), exhibit pharmacokinetics in rats comparable to those of ^99mTc(CO)₃(NTA) and ¹³¹I-OIH. Furthermore, these encouraging results in rats warrant evaluation of this new tracer type in humans.

Structure and Properties of fac-[Re(I)(CO)3(NTA)](2-) (NTA(3-) = Trianion of Nitrilotriacetic Acid) and fac-[Re(I)(CO)3(L)](n-) Analogues Useful for Assessing the Excellent Renal Clearance of the fac-[(99m)Tc(I)(CO)3(NTA)](2-) Diagnostic Renal Agent

We previously identified two new agents based on the [(99m)Tc(V)O](3+) core with renal clearances in human volunteers 30% higher than that of the widely used clinical tracer (99m)Tc-MAG3 (MAG3(5-) = penta-anion of mercaptoacetyltriglycine). However, renal agents with even higher clearances are needed. More recently, we changed our focus from the [(99m)Tc(V)O](3+) core to the discovery of superior tracers based on the fac-[(99m)Tc(I)(CO)3](+) core. Compared to (99m)Tc-MAG3, fac-[(99m)Tc(I)(CO)3(NTA)](2-) (NTA(3-) = trianion of nitrilotriacetic acid) holds great promise by virtue of its efficient renal clearance via tubular secretion and the absence of hepatobiliary elimination, even in patients with severely reduced renal function. We report here NMR, molecular (X-ray) structure, and solution data on fac-[Re(I)(CO)3(NTA)](2-) with a -CH2CO2(-) dangling monoanionic chain and on two fac-[Re(I)(CO)3(L)](-) analogues with either a -CH2CONH2 or a -CH2CH2OH dangling neutral chain. In these three fac-[Re(I)(CO)3(L)](n-) complexes, the fac-[Re(I)(CO)3(N(CH2CO2)2)](-) moiety is structurally similar and has similar electronic properties (as assessed by NMR data). In reported and ongoing studies, the two fac-[(99m)Tc(I)(CO)3(L)](-) analogues with these neutral dangling chains were found to have pharmacokinetic properties very similar to those of fac-[(99m)Tc(I)(CO)3(NTA)](2-). Therefore, we reach the unexpected conclusion that in fac-[(99m)Tc(I)(CO)3(L)](n-) agents, renal clearance is affected much more than anticipated by features of the core plus the chelate rings (the [(99m)Tc(I)(CO)3(N(CH2CO2)2)](-) moiety) than by the presence of a negatively charged dangling carboxylate chain.

Clinical problems in renovascular disease and the role of nuclear medicine

Although renovascular disease remains defined as a stenosis of the main renal artery or its proximal branches (renal artery stenosis [RAS]), its clinical overview has changed dramatically over the last 15-20 years and its management is more controversial than ever before. The clinical problems, not only diagnosis and treatment but also the relative contribution of different pathophysiological mechanisms involved in the progression of kidney disease, have shifted dramatically. This presentation aims to emphasize the paradigm change revisiting the (recent) past focused on renovascular hypertension (RVH) to the current context of preservation or recovery of threatened renal function in patients with progressive atherosclerotic renovascular disease until its last stage of irreversible "ischemic nephropathy." In the past, the foreground was occupied by RVH, a very rare disease, where the activation of the renin-angiotensin-aldosterone system (RAAS) was supposed to play the major, if not only, role in RVH issues. The retrospective RVH diagnosis was established either on the improvement or, more rarely, on the cure of hypertension after revascularization by, most often, a percutaneous transluminal renal angioplasty with or without a stent placement. At this time, captoptril radionuclide renography was an efficient diagnostic tool, because it was a functional (angiotensin-converting enzyme inhibition), noninvasive test aiming to evidence both the RAAS activation and the lateralization (or asymmetry) of renin secretion by the kidney affected by a "hemodynamically significant" RAS. At present, even if captoptril radionuclide renography could be looked upon as the most efficient (and cost effective in selected high-risk patients) noninvasive, functional test to predict the improvement of hypertension after RAS correction, its clinical usefulness is questioned as the randomized, prospective trials failed to demonstrate any significant benefits (either on blood pressure control or on renal function protection) of the revascularization over current antihypertensive therapy. Today many patients with RVH remain undetected for years because they are treated successfully and at low expense with these new blockers of RAAS. In addition to its well-known role in hemodynamics, angiotensin II promotes activations of profibrogenic and inflammatory factors and cells and stimulates reactive oxygen species generation. The "atherosclerotic milieu" itself plays a role in the loss of renal microvessels and defective angiogenesis. After an "adaptative" phase, ischemia eventually develops and induces hypoxia, the substratum of ischemic nephropathy. Because blood oxygen level-dependent MRI may provide an index of oxygen content in vivo, it may be useful to predict renal function outcome after percutaneous transluminal renal angioplasty. New PET tracers, dedicated to assess RAAS receptors, inflammatory cell infiltrates, angiogenesis, and apoptose, would be tested in this context of atherosclerotic renovascular disease.

Initial Evaluation of (99m)Tc(CO)3(ASMA) as a Renal Tracer in Healthy Human Volunteers

PURPOSE

Preclinical studies in rats showed that two of (99m)Tc(CO)3(ASMA) isomers (rac- and L-ASMA) had pharmacokinetic properties equivalent to that of (131)I-OIH, the radiopharmaceutical standard for the measurement of effective renal plasma flow. The aim of this study was to evaluate the pharmacokinetics of (99m)Tc(CO)3(ASMA) isomers in healthy human subjects.

METHODS

Three ASMA ligands (rac-, L- and D-ASMA) were labeled with (99m)Tc(CO)3 using an IsoLink kit (Covidien), and each formed (99m)Tc(CO)3(ASMA) tracer was co-injected with (131)I-OIH into healthy human subjects followed by sequential imaging, plasma clearance measurements and timed urine collection. Plasma protein binding, red cell uptake and percent injected dose in the urine were determined. Urine from each group of volunteers was analyzed for metabolites by HPLC.

RESULTS

Image quality was excellent with all three agents. Each (99m)Tc(CO)3(ASMA) preparation was excreted unchanged in the urine. The plasma clearance ratio ((99m)Tc(CO)3(ASMA)/(131)I-OIH) was 81 ± 3 % for D-ASMA compared to only 20 ± 4 % for L-ASMA and 37 ± 7 % for rac-ASMA; the 81 % clearance ratio for D-ASMA isomer is still ∼ 30 % higher than the (99m)Tc-MAG3/(131)I-OIH clearance ratio (∼50-60 %). Red cell uptake was similar for all three tracers (6-9 %), and all tracers had a relatively rapid renal excretion; at 3 h, the (99m)Tc(CO)3(ASMA)/(131)I-OIH urine ratio was 100 ± 3 % for D-ASMA, 80 ± 2 % for L-ASMA and 88 ± 1 % for rac-ASMA.

CONCLUSIONS

The renal excretion characteristics of (99m)Tc(CO)3(D-ASMA) in humans are superior to those of the other two (99m)Tc(CO)3(ASMA) isomers studied, but are still inferior to (131)I-OIH, even though there was no difference in the clearance of two of (99m)Tc(CO)3(ASMA) isomers and (131)I-OIH in rats. The work described here demonstrates the sensitivity in in vivo biological behavior of (99m)Tc(CO)3(ASMA) isomers to their subtle structural differences.

Radionuclides in nephrourology, part 1: Radiopharmaceuticals, quality control, and quantitative indices

Radionuclide renal scintigraphy provides important functional data to assist in the diagnosis and management of patients with a variety of suspected genitourinary tract problems, but the procedures are underutilized. Maximizing the utility of the available studies (as well as the perception of utility by referring physicians) requires a clear understanding of the clinical question, attention to quality control, acquisition of the essential elements necessary to produce an informed interpretation, and production of a report that presents a coherent impression that specifically addresses the clinical question and is supported by data contained in the report. To help achieve these goals, part 1 of this review covers information that should be provided to the patient before the scan, describes the advantages and limitations of the available radiopharmaceuticals, discusses quality control elements needed to optimize the study, summarizes approaches to the measurements of renal function, and focuses on recommended quantitative indices and their diagnostic applications. Although the primary focus is the adult patient, aspects of the review also apply to the pediatric population.

Complexes possessing rare "tertiary" sulfonamide nitrogen-to-metal bonds of normal length: fac-[Re(CO)3(N(SO2R)dien)]PF6 complexes with hydrophilic sulfonamide ligands

Tertiary sulfonamide nitrogen-to-metal bonds of normal length are very rare. We recently discovered such a bond in one class of fac-[Re(CO)3(N(SO2R)(CH2Z)2)](n) complexes (Z = 2-pyridyl) with N(SO2R)dpa ligands derived from di-(2-picolyl)amine (N(H)dpa). fac-[M(CO)3(N(SO2R)(CH2Z)2)](n) agents (M = (186/188)Re, (99m)Tc) could find use as radiopharmaceutical bioconjugates when R is a targeting moiety. However, the planar, electron-withdrawing 2-pyridyl groups of N(SO2R)dpa destabilize the ligand to base and create relatively rigid chelate rings, raising the possibility that the rare M-N(sulfonamide) bond is an artifact of a restricted geometry. Also, the hydrophobic 2-pyridyl groups could cause undesirable accumulation in the liver, limiting future use in radiopharmaceuticals. Our goal is to identify a robust, hydrophilic, and flexible N(CH2Z)2 chelate framework. New C2-symmetric ligands, N(SO2R)(CH2Z)2 with (Z = CH2NH2; R = Me, dmb, or tol), were prepared by treating N(H)dien(Boc)2, a protected diethylenetriamine (N(H)dien) derivative, with methanesulfonyl chloride (MeSO2Cl), 3,5-dimethylbenzenesulfonyl chloride (dmbSO2Cl), and 4-methylbenzenesulfonyl chloride (tolSO2Cl). Treatment of fac-[Re(CO)3(H2O)3](+) with these ligands, designated as N(SO2R)dien, afforded new fac-[Re(CO)3(N(SO2R)dien)]PF6 complexes. Comparing the fac-[Re(CO)3(N(SO2Me)dien)]PF6 and fac-[Re(CO)3(N(SO2Me)dpa)]PF6 complexes, we find that the Re(I)-N(sulfonamide) bonds are normal in length and statistically identical and that the methyl (13)C NMR signal has an unusually upfield shift compared to that in the free ligand. We attribute this unusual upfield shift to the fact that the sulfonamide N undergoes an sp(2)-to-sp(3) rehybridization upon coordination to Re(I) in both complexes. Thus, the sulfonamide N of N(SO2R)dien ligands is a good donor, even though the chelate rings are conformationally flexible. Addition of the strongly basic and potentially monodentate ligand, 4-dimethylaminopyridine, did not affect the fac-[Re(CO)3(N(SO2tol)dien)]PF6 complex, even after several weeks. This complex is also stable to heat in aqueous solution. These results indicate that N(SO2R)dien ligands form fac-[Re(CO)3(N(SO2R)dien)]PF6 complexes sufficiently robust to be utilized for radiopharmaceutical development.

Al18F-NODA-butyric acid: biological evaluation of a new PET renal radiotracer

INTRODUCTION

Renal scintigraphy is an important imaging modality for the diagnosis and management of a variety of renal diseases including obstruction and renovascular hypertension as well as the evaluation of absolute and relative kidney function. The goal of this work was to evaluate Al(18)F-NODA-butyric acid (Al(18)F-1) as a potential PET tracer to image the kidneys and monitor renal function by comparing its pharmacokinetic properties with those of (131)I-o-iodohippurate ((131)I-OIH), the radioactive standard for the measurement of effective renal plasma flow.

METHODS

Al(18)F-1 was prepared in aqueous conditions using a one-pot Al(18)F-radiofluorination method and its radiochemical purity was determined by HPLC. Biodistribution studies, using (131)I-OIH as an internal control, were performed in normal rats and in rats with renal pedicle ligation. In vitro stability and metabolism of Al(18)F-1 were analyzed by HPLC. Dynamic microPET/CT studies were conducted in normal rats.

RESULTS

Al(18)F-1 showed excellent stability in vitro and in vivo. Biodistribution studies in normal rats and in rats with simulated renal failure confirmed that Al(18)F-1 was exclusively cleared through the renal-urinary pathway and that the hepatic/gastrointestinal activity was less for Al(18)F-1 than for (131)I-OIH both at 10 and 60 min. Dynamic PET showed a rapid transit of Al(18)F-1 through the kidneys into the bladder.

CONCLUSION

These results suggest that the easily labeled Al(18)F-based compounds provide a highly promising approach for the development of a PET renal radiotracer that combines superior imaging qualities with a reliable measure of effective renal plasma flow.