A first-in-man PET study of 2-amino-[3-¹¹C] isobutyric acid for the amino acid transport System A: biodistribution and dosimetry in healthy volunteers

Purpose: This first-in-human study aimed to assess the biodistribution, radiation dosimetry, and safety of the novel PET tracer [3-¹¹C]AIB, a putative System A amino acid transport probe, in healthy volunteers. Methods: Six healthy male participants underwent whole-body PET/CT scans following a rapid intravenous bolus of [3-¹¹C]AIB (injected dose: 366.9 ± 17.9 MBq). Dynamic imaging of the upper abdomen was performed for 4 min post-injection, followed by static whole-body scans up to 90 min. The volumes of interest were drawn on major organs to derive time activity curves for dosimetry calculations. Safety was assessed through vital signs and laboratory tests before and after imaging. Results: High tracer uptake was observed in the salivary glands, pancreas, kidneys, and liver, whereas uptake in the brain and skeletal muscles remained low. The principal route of excretion was via the urinary tract. The effective dose was 5.1 µSv/MBq, corresponding to 1.9 mSv for 370 MBq injection comparable to other 11C-labeled amino acid tracers. No adverse events or significant changes in clinical assessments were noted. Conclusions: This first-in-man evaluation of [3-¹¹C]AIB demonstrated its safety and acceptable radiation dosimetry profile comparable to other ¹¹C-labeled amino acid tracers. The distinct biodistribution pattern with minimal uptake in the brain and skeletal muscles creates high contrast conditions for potential tumor imaging in these regions. The rapid kinetics suggest imaging protocols could be optimized for shorter acquisition times. These characteristics position [3-¹¹C]AIB as a promising radiotracer warranting investigations in cancer types with altered System A amino acid transport and metabolism.