Comparison of a new ¹⁸F renal tracer, Al¹⁸F-NODA-butyric acid, with ¹³¹I-OIH in normal rats

Objectives Al¹⁸F-NODA-butyric acid complex was recently identified as a potential renal tracer (JNM 2011, 52, Suppl.1,170P). The goal of this work was to evaluate the pharmacokinetic properties of the ¹⁸F agent using dynamic microPET/CT and by comparison with those of ¹³¹I-OIH, the clinical radioactive standard for the measurement of effective renal plasma flow.

Methods Radiolabeling of the NODA-butyric acid (NODA-BA) ligand was performed using Al¹⁸F method; the labeled compound was isolated by HPLC. Biodistribution studies were performed in rats (n = 5) at 10 and 60 min post-injection, using ¹³¹I-OIH as an internal control. Urine, blood samples and vital organs were collected, counted and %ID/organ determined. Urine was also analyzed for metabolites by HPLC. Dynamic microPET/CT studies were conducted in rats.

Results An aqueous, one step Al¹⁸F labeling of NODA-BA produced the Al¹⁸F-NODA-BA complex with high radiochemical purity (> 98%). The labeled complex was stable at pH 7.4 for 5h at 25 °C. The percent injected dose in the urine at 10 and 60 min was 58 ± 4% and 92 ± 3% that of ¹³¹I-OIH, respectively. The hepatic/gastrointestinal activity was less for the ¹⁸F tracer than for the ¹³¹I tracer both at 10 and 60 min; however, Al¹⁸F-NODA-BA was better retained in blood at 10 min (8.5 ± 0.8%) than was ¹³¹I-OIH (5.1 ± 0.5%). The kidney activity was comparable at 10 min (~ 5 %) but was higher for Al¹⁸F-NODA-BA at 60 min (1.9 ± 0.4% for ¹⁸F tracer vs. 0.7 ± 0.4% for ¹³¹I tracer). The ¹⁸F tracer was excreted intact in the urine, with no metabolic products. Dynamic PET showed a rapid transit of the ¹⁸F tracer through the kidneys into the bladder.

Conclusions These encouraging results warrant further investigation of Al¹⁸F-based compounds as PET radiotracers for the evaluation of renal function.

Research Support NIH Grant R37 DK38842