A first-in-man study of [¹⁸F] FEDAC: a novel PET tracer for the 18-kDa translocator protein

N-benzyl-N-methyl-2-[7, 8-dihydro-7-(2-[¹⁸F] fluoroethyl) -8-oxo-2-phenyl-9H-purin-9-yl] acetamide ([¹⁸F] FEDAC) is a novel positron emission tomography (PET) tracer that targets the translocator protein (TSPO; 18 kDa) in the mitochondrial outer membrane, which is known to be upregulated in various diseases such as malignant tumors, neurodegenerative diseases, and neuroinflammation. This study presents the first attempt to use [¹⁸F]FEDAC PET/CT and evaluate its biodistribution as well as the systemic radiation exposure to the radiotracer in humans.

Seventeen whole-body [¹⁸F]FEDAC PET/CT (injected dose, 209.1 ± 6.2 MBq) scans with a dynamic scan of the upper abdomen were performed in seven participants. Volumes of interest were assigned to each organ, and a time-activity curve was created to evaluate the biodistribution of the radiotracer. The effective dose was calculated using IDAC-Dose 2.1.

Immediately after the intravenous injection, the radiotracer accumulated significantly in the liver and was subsequently excreted into the gastrointestinal tract through the biliary tract. It also showed high levels of accumulation in the kidneys, but showed minimal migration to the urinary bladder. Thus, the liver was the principal organ that eliminated [¹⁸F] FEDAC. Accumulation in the normal brain tissue was minimal. The effective dose estimated from biodistribution in humans was 19.47 ± 1.08 µSv/MBq, and was 3.60 mSV for 185 MBq dose.

[¹⁸F]FEDAC PET/CT provided adequate image quality at an acceptable effective dose with no adverse effects. Therefore, [¹⁸F]FEDAC may be useful in human TSPO-PET imaging.