Biodistribution and radiation dosimetry of a positron emission tomographic ligand, 18F-SP203, to image metabotropic glutamate subtype 5 receptors in humans
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A new PET ligand, 3-fluoro-5-(2-(2-18F-(fluoromethyl)-thiazol-4-yl)ethynyl)benzonitrile (18F-SP203), is a positron emission tomographic radioligand selective for metabotropic glutamate subtype 5 receptors. The purposes of this study were to estimate the radiation-absorbed doses of 18F-SP203 in humans and to determine from the distribution of radioactivity in bone structures with various proportions of bone and red marrow whether 18F-SP203 undergoes defluorination.
Whole-body images were acquired for 5 h after injecting 18F-SP203 in seven healthy humans. Urine was collected at various time points. Radiation-absorbed doses were estimated by the Medical Internal Radiation Dose scheme.
After injecting 18F-SP203, the two organs with highest radiation exposure were urinary bladder wall and gallbladder wall, consistent with both urinary and fecal excretion. In the skeleton, most of the radioactivity was in bone structures that contain red marrow and not in those without red marrow. Although the dose to red marrow (30.9 μSv/MBq) was unusually high, the effective dose (17.8 μSv/MBq) of 18F-SP203 was typical of that of other 18F radiotracers.
18F-SP203 causes an effective dose in humans typical of several other 18F radioligands and undergoes little defluorination.
KeywordsmGluR5 PET Dosimetry Defluorination
This research was supported by the Intramural Program of the National Institute of Mental Health (projects Z01-MH-002795-07 and Z01-MH-002852-04). We thank Leah P. Dickstein, Maria D. Ferraris Araneta, Gerald L. Hodges, Nobuyo Kimura, Barbara Scepura, Cheryl Wallisch, Yi Zhang, Jeih-San Liow, Robert L. Gladding, Amira K. Brown, and the staff of the PET Department for successful completion of the studies; and Dr. Michael G. Stabin for his suggestions concerning the data analysis; and PMOD Technologies (Zurich, Switzerland) for providing its image analysis and modeling software.
Conflict of interest
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