Purpose: We report findings from the first-in-human study of [ 11 C]MDTC, a radiotracer developed to image the cannabinoid receptor type 2 (CB2R) with positron emission tomography (PET).
Methods: Ten healthy adults were imaged according to a 90 min dynamic PET protocol after bolus intravenous injection of [ 11 C]MDTC. Five participants also completed a second [ 11 C]MDTC PET scan to assess test-retest reproducibility of receptor-binding outcomes. The kinetic behavior of [ 11 C]MDTC in human brain was evaluated using a metabolite-corrected arterial plasma input function with compartmental modeling and graphical analysis approaches. Four additional healthy adults completed whole-body [ 11 C]MDTC PET/CT to calculate organ doses and the whole-body effective dose.
Results: [ 11 C]MDTC brain PET and [ 11 C]MDTC whole body PET/CT was well-tolerated. The model of choice for fitting the time activity curves (TACs) across brain regions of interest was a two-tissue compartment model with the blood volume fraction included as a fitting parameter (2TCM-vB). Regional distribution volume (V T ) values computed from Logan graphical analysis correlated well with those estimated using the 2TCM-vB model. Cortical regions and thalamus had higher V T than brainstem, striatum, hippocampus, and corpus callosum. Test-retest reliability of V T demonstrated a mean absolute variability of 7.13%, with an intraclass correlation coefficient 0.91. The measured effective dose of [ 11 C]MDTC was 5.29 µSv/MBq.
Conclusion: These data support use of [ 11 C]MDTC PET for in vivo neuroimaging of CB2R in humans. Future in vivo studies using [ 11 C]MDTC PET in neuroinflammatory conditions are needed to assess the detection of high expression of the CB2R by activated microglia in human brain.