First evaluation of PET-based human biodistribution and radiation dosimetry of C-BU99008, a tracer for imaging the imidazoline binding site.

Background: We measured whole body distribution of C-BU99008, a new PET biomarker for non-invasive identification of the imidazoline binding site. The purpose of this phase I study was to evaluate the biodistribution and radiation dosimetry of C-BU99008 in healthy human subjects.

Methods: A single bolus injection of C-BU99008 (296 ± 10.5 MBq) was administered to four healthy subjects who underwent whole-body PET/CT over 120 min from the cranial vertex to the mid-thigh. Volumes of interest were drawn around visually identifiable source organs to generate time-activity curves (TAC). Residence times were determined from time-activity curves. Absorbed doses to individual organs and the whole body effective dose were calculated using OLINDA/EXM 1.1 for each subject.

Results: The highest measured activity concentration was in the kidney and spleen. The longest residence time was in the muscle at 0.100 ± 0.023 h, followed by the liver at 0.067 ± 0.015 h and lungs at 0.052 ± 0.010 h. The highest mean organ absorbed dose was within the heart wall (0.028 ± 0.002 mGy/MBq), followed by the kidneys (0.026 ± 0.005 mGy/MBq). The critical organ was the heart wall. The total mean effective dose averaged over subjects was estimated to be 0.0056 ± 0.0004 mSv/MBq for an injection of C-BU99008.

Conclusions: The biodistribution of C-BU99008 has been shown here for the first time in humans. Our dosimetry data showed the total mean effective dose over all subjects was 0.0056 ± 0.0004 mSv/MBq, which would result in a total effective dose of 1.96 mSv for a typical injection of 350 MBq of C-BU99008. The effective dose is not appreciably different from those obtained with other C tracers.