¹¹C-PABA as a Novel PET Radiotracer for Functional Renal Imaging: Preclinical and First-in-Human Studies

Abstract

para-Aminobenzoic acid (PABA) has been previously used as an exogenous marker to verify completion of 24-hour urine sampling. Therefore, we hypothesized that radiolabeled PABA with ¹¹C could allow high-quality dynamic PET of the kidneys while reducing the radiation exposure due to its short biological and physical half-lives. We evaluated if ¹¹C-PABA could visualize renal anatomy and quantify function in healthy rats, rabbits, and first-in-human studies in healthy volunteers. Methods: Healthy rats and rabbits were injected with ¹¹C-PABA intravenously. Subsequently, a dynamic PET was performed, followed by post-mortem tissue biodistribution studies. 11C-PABA PET was directly compared with the current standard, ^99mTc-MAG3 in rats. Three healthy human subjects also underwent dynamic PET after intravenous injection of ¹¹C-PABA. Results: In healthy rats and rabbits, dynamic PET demonstrated a rapid accumulation of ¹¹C-PABA in the renal cortex, followed by rapid excretion through the pelvicalyceal system. In humans, ¹¹C-PABA PET was safe and well tolerated. There were no adverse or clinically detectable pharmacologic effects in any subject. The cortex was delineated on PET, and the activity gradually transited to the medulla and then renal pelvis with high spatiotemporal resolution. Conclusion: ¹¹C-PABA demonstrated fast renal excretion with very low background signal in animals and humans. These results suggest that ¹¹C-PABA could be used as a novel radiotracer for functional renal imaging, providing high-quality spatiotemporal images with low radiation exposure.