Evaluation of [O-methyl-3H]WAY-100635 as an in vivo radioligand for 5-HT1A receptors in rat brain.
N-(2-(4-(2-Methoxyphenyl)-1-piperazinyl)ethyl)-N-(2- pyridyl)cyclohexanecarboxamide trihydrochloride (WAY-100635) is a new, potent and selective 5-HT1A receptor antagonist. We have evaluated radiolabelled WAY-100635 as a prospective radioligand for positron emission tomography (PET) by studying biodistribution in rat ex vivo. After intravenous injection, [O-methyl-3H]WAY-100635 cleared rapidly from plasma but was retained in brain. Specific binding was quantified from kinetic studies, using a reference-tissue compartment model, fitting for binding potential (k3/k4). The regional variation in binding potential correlated with the known distribution of 5-HT1A receptors. Saturation studies gave Bmax values in vivo that were consistent with those reported in vitro. At 60 min after injection, the ratio of radioactivity in 5-HT1A receptor-rich regions (e.g. septum, entorhinal cortex and hippocampus) to that in cerebellum reached approximately 16. Pre-dosing the rats with WAY-100635 (2 mg/kg) reduced this ratio to one, whereas similar pre-dosing with citalopram (5-HT uptake site inhibitor), prazosin (alpha 1A-adrenoceptor antagonist) or idazoxan (alpha 2-adrenoceptor antagonist) caused little or no reduction. Substantial (77%) blockade of [3H]WAY-100635 binding was achieved with the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), and the partial agonists, ipsapirone and buspirone. Thus, the properties of WAY-100635 are such that, when labelled with carbon-11, it could provide a radioligand suitable for clinical and pharmacological investigations of central 5-HT1A receptors in man using PET.
Hume
S P
SP
MRC Clinical Sciences Centre, Royal Postgraduate Medical School, Hammersmith Hospital, London, UK.
Ashworth
S
S
Opacka-Juffry
J
J
Ahier
R G
RG
Lammertsma
A A
AA
Pike
V W
VW
Cliffe
I A
IA
Fletcher
A
A
White
A C
AC
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology; D000818:Animals; D001923:Brain Chemistry; D008297:Male; D010879:Piperazines / Q000378:metabolism* / Q000493:pharmacokinetics; D011725:Pyridines / Q000378:metabolism* / Q000493:pharmacokinetics; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000032:analysis*; D012702:Serotonin Antagonists / Q000378:metabolism*; D014055:Tomography, Emission-Computed
D010879:Piperazines; D011725:Pyridines; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; C090413:N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin