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Hjorth S, Karlsson C, Jucaite A, Varnäs K, Wählby Hamrén U, Johnström P, Gulyás B, Donohue SR, Pike VW, Halldin C, Farde L. A PET study comparing receptor occupancy by five selective cannabinoid 1 receptor antagonists in non-human primates. Neuropharmacology 2015; 101:519-30. [PMID: 25791528 DOI: 10.1016/j.neuropharm.2015.03.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Revised: 02/05/2015] [Accepted: 03/07/2015] [Indexed: 01/14/2023]
Abstract
There is a medical need for safe and efficacious anti-obesity drugs with acceptable side effect profiles. To mitigate the challenge posed by translating target interaction across species and balancing beneficial vs. adverse effects, a positron emission tomography (PET) approach could help guide clinical dose optimization. Thus, as part of a compound differentiation effort, three novel selective CB1 receptor (CB1R) antagonists, developed by AstraZeneca (AZ) for the treatment of obesity, were compared with two clinically tested reference compounds, rimonabant and taranabant, with regard to receptor occupancy relative to dose and exposure. A total of 42 PET measurements were performed in 6 non-human primates using the novel CB1R antagonist radioligand [(11)C]SD5024. The AZ CB1R antagonists bound in a saturable manner to brain CB1R with in vivo affinities similar to that of rimonabant and taranabant, compounds with proven weight loss efficacy in clinical trials. Interestingly, it was found that exposures corresponding to those needed for optimal clinical efficacy of rimonabant and taranabant resulted in a CB1R occupancy typically around ∼20-30%, thus much lower than what would be expected for classical G-protein coupled receptor (GPCR) antagonists in other therapeutic contexts. These findings are also discussed in relation to emerging literature on the potential usefulness of 'neutral' vs. 'classical' CB1R (inverse agonist) antagonists. The study additionally highlighted the usefulness of the radioligand [(11)C]SD5024 as a specific tracer for CB1R in the primate brain, though an arterial input function would ideally be required in future studies to further assure accurate quantitative analysis of specific binding.
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Affiliation(s)
- Stephan Hjorth
- Biosciences, CVMD Innovative Medicines, AstraZeneca R&D, Mölndal, Sweden
| | - Cecilia Karlsson
- CVMD Translational Medicine Unit, Early Clinical Development, Innovative Medicines, AstraZeneca R&D, Mölndal, Sweden.
| | - Aurelija Jucaite
- AstraZeneca Translational Science Centre and Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Katarina Varnäs
- Centre for Psychiatric Research, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Ulrika Wählby Hamrén
- Quantitative Clinical Pharmacology, Early Clinical Development, Innovative Medicines, AstraZeneca R&D, Mölndal, Sweden
| | - Peter Johnström
- AstraZeneca Translational Science Centre and Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Balázs Gulyás
- Centre for Psychiatric Research, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Sean R Donohue
- Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA
| | - Victor W Pike
- Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA
| | - Christer Halldin
- Centre for Psychiatric Research, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Lars Farde
- AstraZeneca Translational Science Centre and Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden
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Decrease of mGluR5 receptor density goes parallel with changes in enkephalin and substance P immunoreactivity in Huntington's disease: a preliminary investigation in the postmortem human brain. Brain Struct Funct 2014; 220:3043-51. [PMID: 24969128 DOI: 10.1007/s00429-014-0812-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Accepted: 05/26/2014] [Indexed: 12/24/2022]
Abstract
Group 1 metabotropic glutamate subtype 5 receptors (mGluR5) contribute to the control of motor behavior by regulating the balance between excitation and inhibition of outputs in the basal ganglia. The density of these receptors is increased in patients with Parkinson's disease and motor complications. We hypothesized that similar changes may occur in Huntington's disease (HD) and aimed at testing this hypothesis in a preliminary experimental series in postmortem human brain material obtained from HD patients. Using autoradiography, we analyzed mGluR5 density in the putamen, caudate nucleus and cerebellum (control region) in postmortem tissue samples from three patients with HD and three controls with two mGluR5-specific radioligands ([(3)H]ABP688 and [(11)C]ABP688). The density of enkephalin (Enk)- or substance P (SP)-containing neurons was assessed using immunohistochemical and cell-counting methods. [(3)H]ABP688 binding in HD was reduced in the caudate (-70.4 %, P < 0.001), in the putamen (-33.3 %, P = 0.053), and in the cerebellum (-8.79 %, P = 0.930) vs controls. Results with [(11)C]ABP688 were similar; there was good correlation between [(11)C]ABP688 and [(3)H]ABP688 binding ratios. Total cell density was similar in all three brain regions in HD patients and controls. Neuronal density was 69 % lower in the caudate (P = 0.002) and 64 % lower in the putamen (P < 0.001) of HD patients vs controls. Both direct and indirect pathways were affected, with ≥ 90 % decrease in the density of Enk- and SP-containing neurons in the caudate and putamen of HD patients vs controls (P < 0.001). In contrast to earlier observations in PD, in HD, compared to controls, the mGluR5 density was significantly lower in the caudate nucleus. The decrease in neuronal density suggests that neuronal loss was largely responsible for the observed decrease in mGluR5.
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Pithia N, Gulati N, Pandey S, Coleman R, Kant R, Mukherjee J. Synthesis and biological evaluation of 18F-Norfallypride in the rodent brain using PET imaging. Nucl Med Biol 2013; 40:697-704. [DOI: 10.1016/j.nucmedbio.2013.02.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2013] [Revised: 02/05/2013] [Accepted: 02/21/2013] [Indexed: 10/27/2022]
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Sromek AW, Si YG, Zhang T, George SR, Seeman P, Neumeyer JL. Synthesis and Evaluation of Fluorinated Aporphines: Potential Positron Emission Tomography Ligands for D2 Receptors. ACS Med Chem Lett 2011; 2:189-194. [PMID: 21666830 DOI: 10.1021/ml1001689] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The 2-fluoroalkoxy substituted catechol-aporphines 6, 8a-f and 11-monohydroxyaporphines 11a-e were synthesized and found to have high in vitro affinity and selectivity for the dopamine D(2) receptors. The catechol aporphines, 8b and 8d, and the monohydroxy aporphines, 11a-d, were identified as candidates for development as potential PET ligands.
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Affiliation(s)
- Anna W. Sromek
- Alcohol & Drug Abuse Research Center, McLean Hospital, Harvard Medical School, 115 Mill Street, Belmont, Massachusetts 02478-9106, United States
| | - Yu-Gui Si
- Alcohol & Drug Abuse Research Center, McLean Hospital, Harvard Medical School, 115 Mill Street, Belmont, Massachusetts 02478-9106, United States
| | - Tangzhi Zhang
- Alcohol & Drug Abuse Research Center, McLean Hospital, Harvard Medical School, 115 Mill Street, Belmont, Massachusetts 02478-9106, United States
| | - Susan R. George
- Department of Pharmacology, University of Toronto, Toronto, Ontario, Canada
| | - Philip Seeman
- Department of Pharmacology, University of Toronto, Toronto, Ontario, Canada
| | - John L. Neumeyer
- Alcohol & Drug Abuse Research Center, McLean Hospital, Harvard Medical School, 115 Mill Street, Belmont, Massachusetts 02478-9106, United States
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Vázquez N, Gómez-Vallejo V, Calvo J, Padro D, Llop J. Synthesis of D2 receptor ligand analogs incorporating one dicarba-closo-dodecaborane unit. Tetrahedron Lett 2011. [DOI: 10.1016/j.tetlet.2010.11.161] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Vandehey NT, Moirano JM, Converse AK, Holden JE, Mukherjee J, Murali D, Nickles RJ, Davidson RJ, Schneider ML, Christian BT. High-affinity dopamine D2/D3 PET radioligands 18F-fallypride and 11C-FLB457: a comparison of kinetics in extrastriatal regions using a multiple-injection protocol. J Cereb Blood Flow Metab 2010; 30:994-1007. [PMID: 20040928 PMCID: PMC2897717 DOI: 10.1038/jcbfm.2009.270] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
(18)F-Fallypride and (11)C-FLB457 are commonly used PET radioligands for imaging extrastriatal dopamine D(2)/D(3) receptors, but differences in their in vivo kinetics may affect the sensitivity for measuring subtle changes in receptor binding. Focusing on regions of low binding, a direct comparison of the kinetics of (18)F-fallypride and (11)C-FLB457 was made using a MI protocol. Injection protocols were designed to estimate K(1), k(2), f(ND)k(on), B(max), and k(off) in the midbrain and cortical regions of the rhesus monkey. (11)C-FLB457 cleared from the arterial plasma faster and yielded a ND space distribution volume (K(1)/k(2)) that is three times higher than (18)F-fallypride, primarily due to a slower k(2) (FAL:FLB; k(2)=0.54 min(-1):0.18 min(-1)). The dissociation rate constant, k(off), was slower for (11)C-FLB457, resulting in a lower K(Dapp) than (18)F-fallypride (FAL:FLB; 0.39 nM:0.13 nM). Specific D(2)/D(3) binding could be detected in the cerebellum for (11)C-FLB457 but not (18)F-fallypride. Both radioligands can be used to image extrastriatal D(2)/D(3) receptors, with (11)C-FLB457 providing greater sensitivity to subtle changes in low-receptor-density cortical regions and (18)F-fallypride being more sensitive to endogenous dopamine displacement in medium-to-high-receptor-density regions. In the presence of specific D(2)/D(3) binding in the cerebellum, reference region analysis methods will give a greater bias in BP(ND) with (11)C-FLB457 than with (18)F-fallypride.
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Affiliation(s)
- Nicholas T Vandehey
- Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin, USA.
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