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Ups J Med Sci. 2011 May;116(2):100-6. doi: 10.3109/03009734.2011.563878. Epub 2011 Mar 28.

Assessment of receptor occupancy-over-time of two dopamine transporter inhibitors by [(11)C]CIT and target controlled infusion.

Author information

  • 1Department of Radiology, Oncology and Radiation Sciences, Division of Radiology, Uppsala University, Uppsala, Sweden. olof.eriksson@radiol.uu.se

Abstract

INTRODUCTION:

Occupancy-over-time was determined for two dopamine transporter (DAT) inhibitors through modeling of their ability to displace the PET ligand [(11)C]CIT. The tracer was held at a pseudo steady state in a reference tissue by target controlled infusion.

METHODS:

Rhesus monkeys (n = 5) were given [(11)C]CIT and studied with a PET scanner. Tracer uptake in the reference tissue cerebellum was held at a pseudo steady state by use of target controlled infusion. The pharmacokinetics/pharmacodynamics(PK/PD) of [(11)C]CIT was assessed through the simplified reference tissue model (SRTM). Bupropion (n = 2) and GBR-12909 (n = 2) receptor occupancies were estimated through modeling of their effects on [(11)C]CIT displacement.

RESULTS:

There was a high uptake of [(11)C]CIT in striatum, which contains a high DAT density. The reference tissue cerebellum had a comparatively low uptake. The modeling of [(11)C]CIT PK/PD properties in striatum showed high binding potential (BP = 5.34 ± 0.78). Both DAT inhibitors caused immediate displacement of [(11)C]CIT after administration. The occupancy-over-time was modeled as a mono-exponential function, describing initial maximal occupancy (Occ(0)) and rate of ligand-receptor dissociation (k(off)). GBR-12909 showed irreversible binding (k(off) = 0) after an initial occupancy of 76.1%. Bupropion had a higher initial occupancy (84.5%) followed by a release half-life of 33 minutes (k(off) = 0.021).

CONCLUSIONS:

The proposed model can be used for assessment of in-vivo occupancy-over-time of DAT ligands by use of target controlled infusion of [(11)C]CIT. The concept of assessing drug-receptor interactions by studying perturbations of a PET tracer from a pseudo steady state can be transferred to other CNS systems.

PMID:
21443419
[PubMed - indexed for MEDLINE]
PMCID:
PMC3078538
Free PMC Article
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