Ian A. Cliffe

A pharmacological profile of the selective silent 5-HT1A receptor antagonist, WAY-100635

WAY-100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2- pyridinyl)cyclohexanecarboxamide trihydrochloride) is an achiral phenylpiperazine derivative that binds with high affinity and selectivity to the 5-HT1A receptor. WAY-100635 displaced specific binding of the 5-HT1A radioligand, [3H]8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin), to rat hippocampal membranes with a pIC50 of 8.87. This represented a greater than 100-fold selectivity relative to binding at other 5-HT receptor subtypes and major neurotransmitter receptor, reuptake and ion channel sites. In functional assays, WAY-100635 was a potent 5-HT1A receptor antagonist, with no evidence of any 5-HT1A receptor agonist or partial agonist activity. In the isolated guinea-pig ileum WAY-100635 was a potent and, at high concentrations, an insurmountable antagonist of the 5-HT1A receptor agonist action of 5-carboxamidotryptamine, with an apparent pA2 value (at 0.3 nM) of 9.71. WAY-100635 blocked the inhibitory action of 8-OH-DPAT on dorsal raphe neuronal firing in the anaesthetised rat at doses which had no inhibitory action per se. In behavioural models, WAY-100635 itself induced no overt behavioural changes but potently antagonised the behavioural syndrome induced by 8-OH-DPAT in the rat and guinea-pig (minimum effective dose = 0.003 mg/kg s.c. and ID50 = 0.01 mg/kg s.c., respectively). WAY-100635 also blocked the hypothermia induced by 8-OH-DPAT in the mouse and rat with ID50 values of 0.01 mg/kg s.c. These data indicate that WAY-100635 will be used as a standard antagonist in further studies of 5-HT1A receptor function.

WAY100135: a novel, selective antagonist at presynaptic and postsynaptic 5-HT1A receptors

The novel phenylpiperazine derivative, (+/-)-WAY100135 (N-tert-butyl-3-(4-(2-methoxyphenyl)piperazin-1-yl)-2-phenylpro pionamide dihydrochloride), is a selective antagonist at both somatodendritic and postsynaptic 5-HT1A receptors. The IC50 of (+/-)-WAY100135 at the rat hippocampal 5-HT1A receptor was 34 nM, whereas its IC50 at a range of other receptor sites was > 2 microM. Up to a dose of 2.5 mg/kg i.v. (+/-)-WAY100135 induced a maximum 30% inhibition of raphe neuronal firing and (at 0.5 mg/kg i.v.) antagonised the inhibition of firing induced by 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin) in anaesthetised rats. (+/-)-WAY100135 antagonised the action of 5-carboxamidoiodotryptamine in the guinea-pig ileum, with a pA2 of 7.2. (+/-)-WAY100135 had no agonist-like behavioural effects but antagonised the behavioural syndrome and hypothermia induced by 8-OH-DPAT in the rat and mouse, respectively. The interaction of (+/-)-WAY100135 with the 5-HT1A receptor was stereoselective; the (+)-enantiomer being markedly more active in binding, functional and behavioural studies. These data indicate that (+/-)-WAY100135 is the first highly selective antagonist at both somatodendritic and postsynaptic 5-HT1A receptors.

Exquisite delineation of 5-HT1A receptors in human brain with PET and [carbonyl-11C]WAY-100635

The 5-HT1A receptor antagonist, WAY-100635 [N-(2-(4-(2-methoxyphenyl)- 1-piperazinyl)ethyl)-N-(2-pyridyl) cyclohexanecarboxamide], was labelled in its carbonyl group with carbon-11 (t1/2 = 20.4 min), injected intravenously into healthy male volunteers and studied with positron emission tomography (PET). The acquired data provide exquisite delineation of 5-HT1A receptors in brain, with the ratio of radioactivity uptake in receptor-rich regions, such as medial temporal cortex, to that in receptor-devoid cerebellum reaching 25 by 60 min after radioligand injection. Application of biomathematical modelling to the data revealed high values (7.8) for binding potential, a measure of Bmax/Kp, in receptor-rich regions. Only very polar radioactive metabolites were present in plasma, a finding consistent with the low level of nonspecific binding seen in cerebellum. [carbonyl-11C]WAY-100635 is concluded to be far superior to the previously reported [0-methyl-11C]WAY-100635 as a radioligand for PET studies of 5-HT1A receptors in human brain.

First delineation of 5-HT1A receptors in human brain with PET and [11C]WAY-100635

The selective 5-HT1A receptor radioligand, [11C]WAY-100635 ([11C]N-2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-2- pyridyl)cyclohexanecarboxamide), has been injected intravenously into healthy male volunteers and studied by PET (positron emission tomography). The results provide the first delineation of 5-HT1A receptors in living human brain and demonstrate the potential to use [11C]WAY-100635 for the study of central 5-HT1A receptors in patients with psychiatric and neurological disorders and for the investigation of the pharmacology of drugs acting on the central nervous system.

Characterization of the radioactive metabolites of the 5-HT1A receptor radioligand, [O-methl-11C]WAY-100635, in monkey and human plasma by HPLC: Comparison of the behaviour of an identified radioactive metabolite with parent radioligand in monkey using PET

N-(2-(4-(2-Methoxy-phenyl)-1-piperazin-1-yl)ethyl)-N-(2-pyridyl) cyclohexanecarboxamide (WAY-100635), labelled in the O-methyl group with carbon-11 (t1/2 = 20.4 min), is a promising radioligand for application with positron emission tomography (PET) to the study of 5-HT1A receptors in living human brain. An understanding of the metabolism of this new radioligand is crucial to the development of a biomathematical model for the interpretation of the kinetics of radioactivity uptake in brain in terms of receptor-binding parameters. After intravenous injection of [O-methyl-11C]WAY-100635 into humans, radioactivity was found to clear rapidly from blood and plasma. By using established methods for the analysis of radioactivity in plasma, it was found that intravenously injected [O-methyl-11C]WAY-100635 is rapidly metabolised to more polar radioactive compounds in a cynomolgus monkey and in humans. Thus, at 60 min postinjection, parent radioligand represented 40% and 5% of the radioactivity in monkey and human plasma, respectively. In monkey and human, one of the radioactive metabolites was identified as the descyclohexanecarbonyl analogue of the parent radioligand, namely [O-methyl-11C]WAY-100634. This compound is known to have high affinity for 5-HT1A receptors and alpha 1-adrenoceptors. In a PET experiment it was demonstrated that, after IV injection of [O-methyl-11C]WAY-100634 into a cynomolgus monkey, radioactivity was avidly taken up by brain. Uptake of radioactivity was higher in 5-HT1A receptor-rich frontal cortex than in cerebellum, which is devoid of 5-HT1A receptors. Polar radioactive metabolites appeared in plasma. The results suggest that the use of WAY-100635 labelled with carbon-11 in its cyclohexanecarbonyl moiety may provide enhanced signal contrast in PET studies and a possibility to develop a simple biomathematical model for regional brain radioactivity uptake.

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.

Antagonists of the human adenosine A2A receptor. Part 3 Design and synthesis of pyrazolo[3,4-d]pyrimidines, pyrrolo[2,3-d]pyrimidines and 6-arylpurines

A series of pyrazolo[3,4-d]pyrimidine, pyrrolo[2,3-d]pyrimidine and 6-arylpurine adenosine A(2A) antagonists is described. Many examples were highly selective against the human A(1) receptor sub-type and were active in an in vivo model of Parkinsons disease.

A retrospect on the discovery of way-100635 and the prospect for improved 5-HT1A receptor PET radioligands

Abstract. An outline is given of the developments that led to the identification of [O-methyl-(11)C]WAY-100635 (4) as the first useful PET ligand for imaging serotonin(1A) (5-HT(1A)) receptors in the living human brain. Recent attempts to develop 5-HT(1A) receptor radioligands superior to 4 are reviewed, and [carbonyl-(11)C]WAY-100635 (6) has been shown to be the best currently available radioligand for human studies. Of other (11)C-radiolabelled compounds, [O-methyl-(11)C](R,S)-CPC-222 (9), DWAY (8), and [(11)C]NAD-299 (14) all demonstrate specific binding to 5-HT(1A) receptors in animals and warrant further expedited studies in humans. The trans-fluorocyclohexane, 12, and fluorobenzene, [(18)F]p-MPPF 13, are highlighted as examples of promising (18)F-labelled ligands.

Antagonists of the human adenosine A2A receptor. Part 2: Design and synthesis of 4-arylthieno[3,2-d]pyrimidine derivatives

We describe herein the discovery and development of a series of 4-arylthieno[3,2-d]pyrimidines which are potent adenosine A(2A) receptor antagonists. These novel compounds show high degrees of selectivity against the human A(1), A(2B) and A(3) receptor sub-types. Moreover, a number of these compounds show promising activity in vivo, suggesting potential utility in the treatment of Parkinsons disease.

Progress in the development of small molecule inhibitors of insulin-like growth factor-1 receptor kinase

Insulin-like growth factor-1 receptor (IGF-1R) is a receptor tyrosine kinase that plays a key role in tumor cell proliferation and in the inhibition of apoptosis, and therefore is a potential target for the treatment of cancer. The blockade of IGF-1R kinase activity by small molecule binding to the catalytic domain of the receptor offers promise for the future and this review summarizes the patent literature from 2000 to early 2006.