title: Biodistribution and dosimetry of [123I]iodo-PK 11195: a potential agent for SPET imaging of the peripheral benzodiazepine receptor.
abstract: The highest concentrations of the peripheral benzodiazepine receptor (PBR) are found in the kidneys and heart. In addition, the PBR has been reported to reflect neuro-inflammatory damage by co-localisation with activated microglia. PK 11195 is a high-affinity ligand for the PBR. The aim of this study was to investigate in humans the biodistribution and dosimetry of [123I]iodoPK 11195, a potential single-photon emission tomography tracer for the PBR. Five healthy volunteers were injected with 112 MBq of [123I]iodo-PK 11195. Sequential whole-body scans were performed up to 72 h post injection. Multiple blood samples were taken, and urine was collected to measure the fraction voided by the renal system. Decay-corrected regions of interest of the whole-body images were analysed, and geometric mean count rates were used to determine organ activity. Organ absorbed doses and effective dose were calculated using the MIRD method. [123I]iodo-PK 11195 was rapidly cleared from the blood, mainly by the hepatobiliary system. Approximately 22% was voided in urine after 48 h. Average organ residence times were 0.74, 0.44 and 0.29 h for the liver, upper large intestine and lower large intestine, respectively. The testes received the highest dose, 109.4 microGy/MBq. All other organs investigated received doses of less than 50 microGy/MBq. The effective dose was 40.3 microSv/MBq. In conclusion, [123I]iodo-PK 11195 is a suitable agent for the visualisation of the PBR and indirectly for the imaging of neuro-inflammatory lesions. Taking into account the radiation burden of 7.46 mSv following an administration of 185 MBq, a [123I]iodo-PK 11195 investigation has to be considered an ICRP risk category IIb investigation.
authors.affiliation: Department of Biological Psychiatry, Groningen University Hospital, The Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Versijpt
authors.forename: F
authors.initials: F
authors.lastname: Dumont
authors.forename: H
authors.initials: H
authors.lastname: Thierens
authors.forename: H
authors.initials: H
authors.lastname: Jansen
authors.forename: F
authors.initials: F
authors.lastname: De Vos
authors.forename: G
authors.initials: G
authors.lastname: Slegers
authors.forename: P
authors.initials: P
authors.lastname: Santens
authors.forename: R A
authors.initials: RA
authors.lastname: Dierckx
authors.forename: J
authors.initials: J
authors.lastname: Korf
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D007546:Isoquinolines / Q000493:pharmacokinetics*; D008297:Male; D008875:Middle Aged; D011874:Radiometry; D011963:Receptors, GABA-A / Q000032:analysis*; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D007457:Iodine Radioisotopes; D007546:Isoquinolines; D011963:Receptors, GABA-A; C037850:PK 11195