Human biodistribution and radiation dosimetry of the demyelination tracer [F]3F4AP.

Purpose: [F]3F4AP is a novel PET radiotracer that targets voltage-gated potassium (K) channels and has shown promise for imaging demyelinated lesions in animal models of neurological diseases. This study aimed to evaluate the biodistribution, safety, and radiation dosimetry of [F]3F4AP in healthy human volunteers.

Methods: Four healthy volunteers (2 females) underwent a 4-h dynamic PET scan from the cranial vertex to mid-thigh using multiple bed positions after administration of 368 ± 17.9 MBq (9.94 ± 0.48 mCi) of [F]3F4AP. Volumes of interest for relevant organs were manually drawn guided by the CT, and PET images and time-activity curves (TACs) were extracted. Radiation dosimetry was estimated from the integrated TACs using OLINDA software. Safety assessments included measuring vital signs immediately before and after the scan, monitoring for adverse events, and obtaining a comprehensive metabolic panel and electrocardiogram within 30 days before and after the scan.

Results: [F]3F4AP distributed throughout the body with the highest levels of activity in the kidneys, urinary bladder, stomach, liver, spleen, and brain and with low accumulation in muscle and fat. The tracer cleared quickly from circulation and from most organs. The clearance of the tracer was noticeably faster than previously reported in nonhuman primates (NHPs). The average effective dose (ED) across all subjects was 12.1 ± 2.2 μSv/MBq, which is lower than the estimated ED from the NHP studies (21.6 ± 0.6 μSv/MBq) as well as the ED of other fluorine-18 radiotracers such as [F]FDG (~ 20 μSv/MBq). No differences in ED between males and females were observed. No substantial changes in safety assessments or adverse events were recorded.

Conclusion: The biodistribution and radiation dosimetry of [F]3F4AP in humans are reported for the first time. The average total ED across four subjects was lower than most F-labeled PET tracers. The tracer and study procedures were well tolerated, and no adverse events occurred.