Radiosynthesis and initial characterization of a PDE10A specific PET tracer [18F]AMG 580 in non-human primates.
BACKGROUND
Phosphodiesterase 10A (PDE10A) is an intracellular enzyme responsible for the breakdown of cyclic nucleotides which are important second messengers for neurotransmission. Inhibition of PDE10A has been identified as a potential target for treatment of various neuropsychiatric disorders. To assist drug development, we have identified a selective PDE10A positron emission tomography (PET) tracer, AMG 580. We describe here the radiosynthesis of [(18)F]AMG 580 and in vitro and in vivo characterization results.


METHODS
The potency and selectivity were determined by in vitro assay using [(3)H]AMG 580 and baboon brain tissues. [(18)F]AMG 580 was prepared by a 1-step [(18)F]fluorination procedure. Dynamic brain PET scans were performed in non-human primates. Regions-of-interest were defined on individuals' MRIs and transferred to the co-registered PET images. Data were analyzed using two tissue compartment analysis (2TC), Logan graphical (Logan) analysis with metabolite-corrected input function and the simplified reference tissue model (SRTM) method. A PDE10A inhibitor and unlabeled AMG 580 were used to demonstrate the PDE10A specificity. KD was estimated by Scatchard analysis of high and low affinity PET scans.


RESULTS
AMG 580 has an in vitro KD of 71.9 pM. Autoradiography showed specific uptake in striatum. Mean activity of 121 ± 18 MBq was used in PET studies. In Rhesus, the baseline BPND for putamen and caudate was 3.38 and 2.34, respectively, via 2TC, and 3.16, 2.34 via Logan, and 2.92, and 2.01 via SRTM. A dose dependent decrease of BPND was observed by the pre-treatment with a PDE10A inhibitor. In baboons, 0.24 mg/kg dose of AMG 580 resulted in about 70% decrease of BPND. The in vivo KD of [(18)F]AMG 580 was estimated to be around 0.44 nM in baboons.


CONCLUSIONS
[(18)F]AMG 580 is a selective and potent PDE10A PET tracer with excellent specific striatal binding in non-human primates. It warrants further evaluation in humans.
Medical Sciences, 271 Running Water Ct, Ambler, PA 19002. Electronic address: peachhillca@yahoo.com.
Dah-Ren
DR
Hwang
Small Molecule Chemistry, Amgen Inc., Thousand Oaks, CA, USA.
Essa
E
Hu
Small Molecule Chemistry, Amgen Inc., Thousand Oaks, CA, USA.
Jennifer R
JR
Allen
Pharmacokinetics and Drug Metabolism, Amgen Inc., Thousand Oaks, CA, USA.
Carl
C
Davis
Neuroscience, Amgen Inc., Thousand Oaks, CA, USA.
James
J
Treanor
Neuroscience, Amgen Inc., Thousand Oaks, CA, USA.
Silke
S
Miller
Neuroscience, Amgen Inc., South San Francisco, USA.
Hang
H
Chen
Department of Nuclear Medicine, Kettering Medical Center, Kettering, OH, USA.
Bingzhi
B
Shi
Department of Nuclear Medicine, Kettering Medical Center, Kettering, OH, USA.
Tanjorie K
TK
Narayanan
Molecular NeuroImaging Inc, New Haven, CT, USA.
Olivier
O
Barret
Molecular NeuroImaging Inc, New Haven, CT, USA.
David
D
Alagille
Medical Sciences, 271 Running Water Ct, Ambler, PA 19002. Electronic address: zhigangy@amgen.com.
Zhigang
Z
Yu
Department of Psychiatry, Columbia University, New York, NY, USA; New York State Psychiatric Institute, NY, USA.
Mark
M
Slifstein
D000631:Aminopyridines / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D000818:Animals; D001345:Autoradiography; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism*; D005260:Female; D005462:Fluorine Radioisotopes / Q000493:pharmacokinetics*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007553:Isotope Labeling; D007700:Kinetics; D008253:Macaca mulatta; D008297:Male; D008657:Metabolic Clearance Rate; D010215:Papio; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D049268:Positron-Emission Tomography / Q000379:methods*; D011854:Radiochemistry; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D014018:Tissue Distribution
D000631:Aminopyridines; D005462:Fluorine Radioisotopes; D019275:Radiopharmaceuticals; D010727:Phosphoric Diester Hydrolases
(18)F; AMG 580; PDE10A; PET