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Gärde M, Matheson GJ, Varnäs K, Svenningsson P, Hedman-Lagerlöf E, Lundberg J, Farde L, Tiger M. Altered Serotonin 1B Receptor Binding After Escitalopram for Depression Is Correlated With Treatment Effect. Int J Neuropsychopharmacol 2024; 27:pyae021. [PMID: 38695786 PMCID: PMC11119883 DOI: 10.1093/ijnp/pyae021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/21/2024] [Accepted: 05/01/2024] [Indexed: 05/25/2024] Open
Abstract
BACKGROUND Major depressive disorder (MDD) is commonly treated with selective serotonin reuptake inhibitors (SSRIs). SSRIs inhibit the serotonin transporter (5-HTT), but the downstream antidepressant mechanism of action of these drugs is poorly understood. The serotonin 1B (5-HT1B) receptor is functionally linked to 5-HTT and 5-HT1B receptor binding and 5-HT1B receptor mRNA is reduced in the raphe nuclei after SSRI administration in primates and rodents, respectively. The effect of SSRI treatment on 5-HT1B receptor binding in patients with MDD has not been examined previously. This positron emission tomography (PET) study aimed to quantify brain 5-HT1B receptor binding changes in vivo after SSRI treatment for MDD in relation to treatment effect. METHODS Eight unmedicated patients with moderate to severe MDD underwent PET with the 5-HT1B receptor radioligand [11C]AZ10419369 before and after 3 to 4 weeks of treatment with the SSRI escitalopram 10 mg daily. Depression severity was assessed at time of PET and after 6 to 7 weeks of treatment with the Montgomery-Åsberg Depression Rating Scale. RESULTS We observed a significant reduction in [11C]AZ10419369 binding in a dorsal brainstem (DBS) region containing the median and dorsal raphe nuclei after escitalopram treatment (P = .036). Change in DBS [11C]AZ10419369 binding correlated with Montgomery-Åsberg Depression Rating Scale reduction after 3-4 (r = 0.78, P = .021) and 6-7 (r = 0.94, P < .001) weeks' treatment. CONCLUSIONS Our findings align with the previously reported reduction of 5-HT1B receptor binding in the raphe nuclei after SSRI administration and support future studies testing change in DBS 5-HT1B receptor binding as an SSRI treatment response marker.
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Mattsson P, Cselényi Z, Forsberg Morén A, Freund-Levi Y, Wahlund LO, Halldin C, Farde L. High Contrast PET Imaging of Subcortical and Allocortical Amyloid-β in Early Alzheimer's Disease Using [11C]AZD2184. J Alzheimers Dis 2024; 98:1391-1401. [PMID: 38552111 DOI: 10.3233/jad-231013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/20/2024]
Abstract
Background Deposits of amyloid-β (Aβ) appear early in Alzheimer's disease (AD). Objective The aim of the present study was to compare the presence of cortical and subcortical Aβ in early AD using positron emission tomography (PET). Methods Eight cognitively unimpaired (CU) subjects, 8 with mild cognitive impairment (MCI) and 8 with mild AD were examined with PET and [11C]AZD2184. A data driven cut-point for Aβ positivity was defined by Gaussian mixture model of isocortex binding potential (BPND) values. Results Sixteen subjects (3 CU, 5 MCI and 8 AD) were Aβ-positive. BPND was lower in subcortical and allocortical regions compared to isocortex. Fifteen of the 16 Aβ-positive subjects displayed Aβ binding in striatum, 14 in thalamus and 10 in allocortical regions. Conclusions Aβ deposits appear to be widespread in early AD. It cannot be excluded that deposits appear simultaneously throughout the whole brain which has implications for improved diagnostics and disease monitoring.
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Varnäs K, Nag S, Halldin C, Farde L. PET Evaluation of the Novel F-18 Labeled Reversible Radioligand [ 18F]GEH200449 for Detection of Monoamine Oxidase-B in the Non-Human Primate Brain. ACS Chem Neurosci 2023; 14:3206-3211. [PMID: 37587571 PMCID: PMC10485887 DOI: 10.1021/acschemneuro.3c00332] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2023] [Accepted: 08/07/2023] [Indexed: 08/18/2023] Open
Abstract
Positron emission tomography (PET) using radioligands for the enzyme monoamine oxidase B (MAO-B) is increasingly applied as a marker for astrogliosis in neurodegenerative disorders. In the present study, a novel reversible fluorine-18 labeled MAO-B compound, [18F]GEH200449, was evaluated as a PET radioligand in non-human primates. PET studies of [18F]GEH200449 at baseline showed brain exposure (maximum concentration: 3.4-5.2 SUV; n = 5) within the range of that for suitable central nervous system radioligands and a regional distribution consistent with the known localization of MAO-B. Based on the quantitative assessment of [18F]GEH200449 data using the metabolite-corrected arterial plasma concentration as input function, the Logan graphical analysis was selected as the preferred method of quantification. The binding of [18F]GEH200449, as calculated based on regional estimates of the total distribution volume, was markedly inhibited (occupancy >80%) by the administration of the selective MAO-B ligands L-deprenyl (0.5 and 1.0 mg/kg) or rasagiline (0.75 mg/kg) prior to radioligand injection. Radioligand binding was displaceable by the administration of L-deprenyl (0.5 mg/kg) at 25 min after radioligand injection, thus supporting reversible binding to MAO-B. These observations support that [18F]GEH200449 is a reversible MAO-B radioligand suitable for applied studies in humans.
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Jangard S, Jayaram-Lindström N, Isacsson NH, Matheson GJ, Plavén-Sigray P, Franck J, Borg J, Farde L, Cervenka S. Striatal dopamine D2 receptor availability as a predictor of subsequent alcohol use in social drinkers. Addiction 2023; 118:1053-1061. [PMID: 36710462 DOI: 10.1111/add.16144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2022] [Accepted: 01/11/2023] [Indexed: 01/31/2023]
Abstract
BACKGROUND AND AIMS Whereas striatal dopamine D2 receptor (D2R) availability has shown to be altered in individuals with alcohol use disorder (AUD) and in healthy individuals with a family history of AUD, the role of D2R in the development of AUD is unknown. In this positron emission tomography (PET) study, we measured whether D2R availability is associated with subsequent alcohol use and alcohol-related factors, at a follow-up 8 to 16 years post-PET scan, in social drinkers. DESIGN Longitudinal study investigating the association between PET data and later self-report measures in healthy individuals. SETTING Academic research imaging centre in Stockholm, Sweden. PARTICIPANTS There were 71 individuals (68 of whom had evaluable PET data, 5 females, 42.0 years mean age) from a series of previous PET studies. MEASUREMENTS One PET examination with the D2R antagonist radioligand [11 C]raclopride at baseline and self-report measures assessing alcohol use, drug use, impulsivity, reward sensitivity and family history of alcohol or substance use disorder at follow-up. FINDINGS We found no evidence for an association between D2R availability and later alcohol use (B = -0.019, B 95% CI = -0.043 to -0.006, P = 0.147) nor for the majority of the alcohol-related factors (B 95% CI = -0.034 to 0.004, P = 0.273-0.288). A negative association with a small effect size was found between D2R availability and later impulsivity (B = -0.017, B 95% CI = -0.034 to -0.001, P = 0.046). CONCLUSIONS Low striatal dopamine D2 receptor availability may not be a strong predictor in the development of alcohol use disorder.
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Orhan F, Goiny M, Becklén M, Mathé L, Piehl F, Schwieler L, Fatouros-Bergman H, Farde L, Cervenka S, Sellgren CM, Engberg G, Erhardt S. CSF dopamine is elevated in first-episode psychosis and associates to symptom severity and cognitive performance. Schizophr Res 2023; 257:34-40. [PMID: 37271040 DOI: 10.1016/j.schres.2023.05.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Revised: 01/13/2023] [Accepted: 05/11/2023] [Indexed: 06/06/2023]
Abstract
BACKGROUND The hypothesis of dopamine dysfunction in psychosis has evolved since the mid-twentieth century. However, clinical support from biochemical analysis of the transmitter in patients is still missing. The present study assessed dopamine and related metabolites in the cerebrospinal fluid (CSF) of first-episode psychosis (FEP) subjects. METHODS Forty first-episode psychosis subjects and twenty healthy age-matched volunteers were recruited via the Karolinska Schizophrenia Project, a multidisciplinary research consortium that investigates the pathophysiology of schizophrenia. Psychopathology, disease severity, and cognitive performance were rated as well as cerebrospinal fluid concentrations of dopamine and related metabolites were measured using a sensitive high-pressure liquid chromatography assay. RESULTS CSF dopamine was reliably detected in 50 % of healthy controls and in 65 % of first-episode psychosis subjects and significantly higher in first-episode psychosis subjects compared to age-matched healthy controls. No difference in CSF dopamine levels was observed between drug-naive subjects and subjects with short exposure to antipsychotics. The dopamine concentrations were positively associated with illness severity and deficits in executive functioning. CONCLUSIONS Dopamine dysfunction has long been considered a cornerstone of the pathophysiology of schizophrenia, although biochemical support for elevated brain dopamine levels has been lacking. The results of the present study, showing that FEP subjects have increased CSF dopamine levels that correlate to disease symptoms, should fill the knowledge gap in this regard.
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Cselényi Z, Wallin J, Tjerkoski J, Bloth B, Svensson S, Nennesmo I, Sunnemark D, Jelic V, Farde L, Svenningsson P. [C]PBB3 binding in Aβ(-) or Aβ(+) Corticobasal syndrome. Synapse 2023; 77:e22269. [PMID: 36951466 DOI: 10.1002/syn.22269] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 02/25/2023] [Accepted: 03/15/2023] [Indexed: 03/24/2023]
Abstract
BACKGROUND Corticobasal syndrome (CBS) is associated with 4-repeat tauopathy and/or Alzheimer's disease pathologies. OBJECTIVES To examine tau and amyloid-β (Aβ) deposits in CBS patients using positron emission tomography (PET). METHODS Eight CBS patients and three healthy individuals lacking amyloid pathology underwent PET with [C]PBB3 for tau imaging, and [C]AZD2184 for Aβ. Subcortical and cortical binding of [C]PBB3 was compared between Aβ(-) and Aβ(+) CBS patients and reference group. Postmortem analysis was done in one CBS patient. RESULTS Three CBS patients were considered Aβ(+). Total binding was higher in all patients compared to the reference group. Similar regional binding profiles of [C]PBB3 in Aβ(+) and Aβ(-) CBS patients were found. Elevated [C]PBB3 binding in pallidum was observed in all CBS patients. Cortical [C]PBB3 binding was higher in Aβ(+) compared to Aβ(-) patients. Postmortem analysis of a CBS patient revealed corticobasal degeneration neuropathology and [C]PBB3 autofluorescence in some tau-positive structures. CONCLUSIONS [C]PBB3 is elevated in CBS patients with binding in relevant areas capturing some, but not all, 4-repeat tauopathy in CBS. This article is protected by copyright. All rights reserved.
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Ekman S, Cselényi Z, Varrone A, Jucaite A, Martin H, Schou M, Johnström P, Laus G, Lewensohn R, Brown AP, van der Aart J, Vishwanathan K, Farde L. Brain exposure of osimertinib in patients with epidermal growth factor receptor mutation non-small cell lung cancer and brain metastases: A positron emission tomography and magnetic resonance imaging study. Clin Transl Sci 2023. [PMID: 36808835 DOI: 10.1111/cts.13500] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Revised: 02/01/2023] [Accepted: 02/07/2023] [Indexed: 02/22/2023] Open
Abstract
Brain metastases (BMs) are associated with poor prognosis in epidermal growth factor receptor mutation-positive (EGFRm) non-small cell lung cancer (NSCLC). Osimertinib is a third-generation, irreversible, EGFR-tyrosine kinase inhibitor that potently and selectively inhibits EGFR-sensitizing and T790M resistance mutations with efficacy in EGFRm NSCLC including central nervous system (CNS) metastases. The open-label phase I positron emission tomography (PET) and magnetic resonance imaging (MRI) study (ODIN-BM) assessed [11 C]osimertinib brain exposure and distribution in patients with EGFRm NSCLC and BMs. Three dynamic 90-min [11 C]osimertinib PET examinations were acquired together with metabolite-corrected arterial plasma input functions at: baseline, after first oral osimertinib 80 mg dose, and after greater than or equal to 21 days of osimertinib 80 mg q.d. treatment. Contrast-enhanced MRI was performed at screening and after 25-35 days of osimertinib 80 mg q.d.; treatment effect was assessed per CNS Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 and per volumetric changes in total BM using a novel analysis approach. Four patients (aged 51-77 years) completed the study. At baseline, ~1.5% injected radioactivity reached the brain (IDmax[brain] ) 22 min (median, Tmax[brain] ) after injection. Total volume of distribution (VT ) in whole brain was numerically higher compared with the BM regions. After a single oral osimertinib 80 mg dose, there was no consistent decrease in VT in whole brain or BMs. After greater than or equal to 21 days' daily treatment, VT in whole brain and BMs were numerically higher versus baseline. MRI revealed 56%-95% reduction in total BMs volume after 25-35 days of osimertinib 80 mg q.d. treatment. The [11 C]osimertinib crossed the blood-brain and brain-tumor barriers and had a high, homogeneous brain distribution in patients with EGFRm NSCLC and BMs.
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Dahl K, Johnström P, Forsberg-Morén A, Gustafsson B, Miranda-Azpiazu P, Khani Y, Halldin C, Farde L, Elmore CS, Schou M. Synthesis and Preclinical Evaluation of [ 11C]AZ11895530 for PET Imaging of the Serotonin 1A Receptor. ACS Chem Neurosci 2022; 13:2078-2083. [PMID: 35802379 DOI: 10.1021/acschemneuro.2c00205] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
The serotonin 1A (5-HT1A) receptor is a G-protein-coupled receptor implicated in the pathophysiology of several neuropsychiatric and neurodegenerative disorders. We here report the preparation of two candidate 5-HT1A radioligands, [11C]AZ11132132 ([11C]3) and [11C]AZ11895530 ([11C]4), and their subsequent evaluation in vitro using autoradiography and in vivo using positron emission tomography (PET). Compounds 3 and 4 were radiolabeled at high radiochemical purity (>99%) and high molar activity (>38 GBq/μmol) by heteroatom methylation with [11C]methyl iodide. Autoradiography on whole hemispheres from post-mortem human brain revealed substantial nonspecific binding of [11C]3, while the binding of [11C]4 to brain tissue was consistent with the distribution of 5-HT1A receptors and sensitive to co-incubation with the reference 5-HT1A antagonist WAY-100635 (10 μM). Following intravenous injection of [11C]4 into a cynomolgus monkey, brain radioactivity concentration (Cmax ∼ 2.2 SUV) was high whereafter it decreased rapidly. The regional binding potential (BPND) values were calculated using the simplified reference tissue model with cerebellum as reference region. The values varied between 0.2 and 1.0 for temporal cortex, raphe nuclei, frontal cortex, and hippocampus which is consistent with the known 5-HT1A expression pattern. After pretreatment with WAY100635 (0.5 mg/kg), a homogeneous distribution of radioactivity was observed in non-human primate (NHP) brain. Although [11C]4 fulfilled important criteria for successful in vivo neuroimaging, including good blood-brain-barrier permeability and high specific binding in vitro to human brain tissue, the regional BPND values for [11C]4 in NHP brain were low when compared to those obtained with existing radioligands and thus do not merit further investigation of [11C]4. Evaluation of structurally related analogues is underway in our laboratory to identify improved candidates for clinical imaging.
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Rinne JO, Jucaite A, Cselényi Z, Farde L. Glia Imaging Shows Clinical Utility in Differentiating Parkinson's Disease from Multiple System Atrophy. Mov Disord 2022; 37:1776-1778. [PMID: 35666059 PMCID: PMC9541833 DOI: 10.1002/mds.29078] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2022] [Revised: 05/07/2022] [Accepted: 05/10/2022] [Indexed: 11/10/2022] Open
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Mattsson P, Cselényi Z, Andrée B, Borg J, Nag S, Halldin C, Farde L. Decreased 5-HT 1A binding in mild Alzheimer's disease - a PET study. Synapse 2022; 76:e22235. [PMID: 35587913 PMCID: PMC9285435 DOI: 10.1002/syn.22235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 05/05/2022] [Accepted: 05/10/2022] [Indexed: 11/06/2022]
Abstract
INTRODUCTION Decreased 5-HT1A receptor binding has been associated with Alzheimer's disease (AD) and interpreted as a consequence of neuron loss. The purpose of the present study was to compare [11 C]WAY100635 binding to the 5-HT1A receptor in hippocampus, entorhinal cortex, amygdala and pericalcarine cortex in mild AD patients and elderly controls. METHODS AD patients (n = 7) and elderly control subjects (n = 8) were examined with positron emission tomography (PET) and [11 C]WAY100635. PET data acquisition was performed with an ECAT EXACT HR system. Wavelet-aided parametric images of non-displaceable binding potential (BPND ) were generated using Logan's graphical analysis with cerebellum as reference region. Correction for partial volume effects (PVE) was performed with the Müller-Gärtner method (MG). Regions of interest (ROIs) were applied to the individual parametric images and the regional BPND was calculated as the average parametric voxel value within each ROI. Besides comparison between subject groups, correlations between BPND values and scores on Mini Mental State Examination (MMSE), Disability Assessment for Dementia (DAD), and Neuropsychiatric Inventory (NPI) were expressed by Pearson correlation coefficients. RESULTS Mean regional BPND was lower in AD patients compared to control subjects and the difference was statistically significant for hippocampus, entorhinal cortex and amygdala. A statistically significant correlation was obtained between hippocampal BPND values and DAD scores. CONCLUSION The results of the present study corroborate and extend previous findings of decreased 5-HT1A binding in AD and strengthen the support for 5-HT1A receptor PET as a tool for assessment of neurodegenerative changes in mild AD. This article is protected by copyright. All rights reserved.
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Jucaite A, Cselényi Z, Kreisl WC, Rabiner EA, Varrone A, Carson RE, Rinne JO, Savage A, Schou M, Johnström P, Svenningsson P, Rascol O, Meissner WG, Barone P, Seppi K, Kaufmann H, Wenning GK, Poewe W, Farde L. Glia Imaging Differentiates Multiple System Atrophy from Parkinson's Disease: A Positron Emission Tomography Study with [ 11 C]PBR28 and Machine Learning Analysis. Mov Disord 2021; 37:119-129. [PMID: 34609758 DOI: 10.1002/mds.28814] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 09/06/2021] [Accepted: 09/10/2021] [Indexed: 11/07/2022] Open
Abstract
BACKGROUND The clinical diagnosis of multiple system atrophy (MSA) is challenged by overlapping features with Parkinson's disease (PD) and late-onset ataxias. Additional biomarkers are needed to confirm MSA and to advance the understanding of pathophysiology. Positron emission tomography (PET) imaging of the translocator protein (TSPO), expressed by glia cells, has shown elevations in MSA. OBJECTIVE In this multicenter PET study, we assess the performance of TSPO imaging as a diagnostic marker for MSA. METHODS We analyzed [11 C]PBR28 binding to TSPO using imaging data of 66 patients with MSA and 24 patients with PD. Group comparisons were based on regional analysis of parametric images. The diagnostic readout included visual reading of PET images against clinical diagnosis and machine learning analyses. Sensitivity, specificity, and receiver operating curves were used to discriminate MSA from PD and cerebellar from parkinsonian variant MSA. RESULTS We observed a conspicuous pattern of elevated regional [11 C]PBR28 binding to TSPO in MSA as compared with PD, with "hotspots" in the lentiform nucleus and cerebellar white matter. Visual reading discriminated MSA from PD with 100% specificity and 83% sensitivity. The machine learning approach improved sensitivity to 96%. We identified MSA subtype-specific TSPO binding patterns. CONCLUSIONS We found a pattern of significantly increased regional glial TSPO binding in patients with MSA. Intriguingly, our data are in line with severe neuroinflammation in MSA. Glia imaging may have potential to support clinical MSA diagnosis and patient stratification in clinical trials on novel drug therapies for an α-synucleinopathy that remains strikingly incurable. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.
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Jucaite A, Stenkrona P, Cselényi Z, De Vita S, Buil-Bruna N, Varnäs K, Savage A, Varrone A, Johnström P, Schou M, Davison C, Sykes A, Pilla Reddy V, Hoch M, Vazquez-Romero A, Moein MM, Halldin C, Merchant MS, Pass M, Farde L. Brain exposure of the ATM inhibitor AZD1390 in humans-a positron emission tomography study. Neuro Oncol 2021; 23:687-696. [PMID: 33123736 DOI: 10.1093/neuonc/noaa238] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND The protein kinase ataxia telangiectasia mutated (ATM) mediates cellular response to DNA damage induced by radiation. ATM inhibition decreases DNA damage repair in tumor cells and affects tumor growth. AZD1390 is a novel, highly potent, selective ATM inhibitor designed to cross the blood-brain barrier (BBB) and currently evaluated with radiotherapy in a phase I study in patients with brain malignancies. In the present study, PET was used to measure brain exposure of 11C-labeled AZD1390 after intravenous (i.v.) bolus administration in healthy subjects with an intact BBB. METHODS AZD1390 was radiolabeled with carbon-11 and a microdose (mean injected mass 1.21 µg) was injected in 8 male subjects (21-65 y). The radioactivity concentration of [11C]AZD1390 in brain was measured using a high-resolution PET system. Radioactivity in arterial blood was measured to obtain a metabolite corrected arterial input function for quantitative image analysis. Participants were monitored by laboratory examinations, vital signs, electrocardiogram, adverse events. RESULTS The brain radioactivity concentration of [11C]AZD1390 was 0.64 SUV (standard uptake value) and reached maximum 1.00% of injected dose at Tmax[brain] of 21 min (time of maximum brain radioactivity concentration) after i.v. injection. The whole brain total distribution volume was 5.20 mL*cm-3. No adverse events related to [11C]AZD1390 were reported. CONCLUSIONS This study demonstrates that [11C]AZD1390 crosses the intact BBB and supports development of AZD1390 for the treatment of glioblastoma multiforme or other brain malignancies. Moreover, it illustrates the potential of PET microdosing in predicting and guiding dose range and schedule for subsequent clinical studies.
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Ekman S, Cselényi Z, Varrone A, Jucaite A, Martin H, Schou M, Johnström P, Laus G, Lewensohn R, Brown A, Van Der Aart J, Vishwanathan K, Farde L. P76.72 A PET and MRI Study Exploring Osimertinib Brain Exposure and Efficacy in EGFRm NSCLC CNS Metastases. J Thorac Oncol 2021. [DOI: 10.1016/j.jtho.2021.01.1129] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Nag S, Jia Z, Svedberg M, Jackson A, Ahmad R, Luthra S, Varnäs K, Farde L, Halldin C. Synthesis and Autoradiography of Novel F-18 Labeled Reversible Radioligands for Detection of Monoamine Oxidase B. ACS Chem Neurosci 2020; 11:4398-4404. [PMID: 33284012 PMCID: PMC7747220 DOI: 10.1021/acschemneuro.0c00631] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
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Monoamine oxidase B (MAO-B) is an
important enzyme regulating the
levels of monoaminergic neurotransmitters. Selective MAO-B inhibitors
have been labeled with carbon-11 or fluorine-18 to visualize the localization
of MAO-B in vivo by positron emission tomography
(PET) and thereby have been useful for studying neurodegenerative
diseases. The aim of this study was to develop promising fluorine-18
labeled reversible MAO-B PET radioligands and their biological evaluation in vitro by autoradiography. Radiolabeling was achieved
by classical one-step fluorine-18 nucleophilic substitution reaction.
The stability and radiochemical yield was analyzed with HPLC. All
five fluorine-18 labeled compounds were tested in human whole hemisphere
autoradiography experiments. Five compounds (GEH200439, GEH200448,
GEH200449, GEH200431A, and GEH200431B) were successfully radiolabeled
with fluorine-18, and the incorporation yield of the fluorination
reactions varied from 10 to 45% depending on the compound. The radiochemical
purity was higher than 99% for all at the end of synthesis. Radioligands
were found to be stable, with a radiochemical purity of >99% in
a
sterile phosphate buffered saline (pH = 7.4) over the duration of
the study. The ARG binding density of only 18F-GEH200449
was consistent with known MAO-B expression in the human brain. Radiolabeling
of five new fluorine-18 MAO-B reversible inhibitors was successfully
accomplished. Compound 18F-GEH200449 binds specifically
to MAO-B in vitro postmortem brain and could be a
potential candidate for in vivo PET investigation.
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Freiburghaus T, Svensson JE, Matheson GJ, Plavén-Sigray P, Lundberg J, Farde L, Cervenka S. Low convergent validity of [ 11C]raclopride binding in extrastriatal brain regions: A PET study of within-subject correlations with [ 11C]FLB 457. Neuroimage 2020; 226:117523. [PMID: 33144221 DOI: 10.1016/j.neuroimage.2020.117523] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Revised: 10/24/2020] [Accepted: 10/26/2020] [Indexed: 11/16/2022] Open
Abstract
Dopamine D2 receptors (D2-R) in extrastriatal brain regions are of high interest for research in a wide range of psychiatric and neurologic disorders. Pharmacological competition studies and test-retest experiments have shown high validity and reliability of the positron emission tomography (PET) radioligand [11C]FLB 457 for D2-R quantification in extrastriatal brain regions. However, this radioligand is not available at most research centers. Instead, the medium affinity radioligand [11C]raclopride, which has been extensively validated for quantification of D2-R in the high-density region striatum, has been applied also in studies on extrastriatal D2-R. Recently, the validity of this approach has been questioned by observations of low occupancy of [11C]raclopride in extrastriatal regions in a pharmacological competition study with quetiapine. Here, we utilise a data set of 16 healthy control subjects examined with both [11C]raclopride and [11C]FLB 457 to assess the correlation in binding potential (BPND) in extrastriatal brain regions. BPND was quantified using the simplified reference tissue model with cerebellum as reference region. The rank order of mean regional BPND values were similar for both radioligands, and corresponded to previously reported data, both post-mortem and using PET. Nevertheless, weak to moderate within-subject correlations were observed between [11C]raclopride and [11C]FLB 457 BPND extrastriatally (Pearson's R: 0.30-0.56), in contrast to very strong correlations between repeated [11C]FLB 457 measurements (Pearson's R: 0.82-0.98). In comparison, correlations between repeated [11C]raclopride measurements were low to moderate (Pearson's R: 0.28-0.75). These results are likely related to low signal to noise ratio of [11C]raclopride in extrastriatal brain regions, and further strengthen the recommendation that extrastriatal D2-R measures obtained with [11C]raclopride should be interpreted with caution.
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Colclough N, Chen K, Johnström P, Strittmatter N, Yan Y, Wrigley GL, Schou M, Goodwin R, Varnäs K, Adua SJ, Zhao M, Nguyen DX, Maglennon G, Barton P, Atkinson J, Zhang L, Janefeldt A, Wilson J, Smith A, Takano A, Arakawa R, Kondrashov M, Malmquist J, Revunov E, Vazquez-Romero A, Moein MM, Windhorst AD, Karp NA, Finlay MRV, Ward RA, Yates JW, Smith PD, Farde L, Cheng Z, Cross DA. Preclinical Comparison of the Blood–brain barrier Permeability of Osimertinib with Other EGFR TKIs. Clin Cancer Res 2020; 27:189-201. [DOI: 10.1158/1078-0432.ccr-19-1871] [Citation(s) in RCA: 50] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2019] [Revised: 06/18/2020] [Accepted: 09/29/2020] [Indexed: 11/16/2022]
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Varnäs K, Finnema SJ, Johnström P, Arakawa R, Halldin C, Eriksson LI, Farde L. Effects of sevoflurane anaesthesia on radioligand binding to monoamine oxidase-B in vivo. Br J Anaesth 2020; 126:238-244. [PMID: 33036760 PMCID: PMC8258980 DOI: 10.1016/j.bja.2020.08.052] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Revised: 08/24/2020] [Accepted: 08/31/2020] [Indexed: 11/28/2022] Open
Abstract
Background The molecular actions underlying the clinical effects of inhaled anaesthetics such as sevoflurane and isoflurane are not fully understood. Unexpected observations in positron emission tomography (PET) studies with [11C]AZD9272, a metabotropic glutamate receptor 5 (mGluR5) radioligand with possible affinity for monoamine oxidase-B (MAO-B), suggest that its binding is sensitive to anaesthesia with sevoflurane. The objective of the present study was to assess the effects of sevoflurane anaesthesia on the binding of [11C]AZD9272 and of [11C]L-deprenyl-D2, a radioligand selective for MAO-B in non-human primates (NHPs). Methods Altogether, 12 PET measurements were conducted with a high-resolution research tomograph using the ligands [11C]AZD9272 or [11C]L-deprenyl-D2 in six cynomolgus monkeys anaesthetised with sevoflurane or ketamine/xylazine. Results The specific binding of [11C]AZD9272 and [11C]L-deprenyl-D2 was markedly reduced during anaesthesia with sevoflurane compared with ketamine/xylazine. The reduction was 80–90% (n=3) for [11C]AZD9272 and 77–80% (n=3) for [11C]L-deprenyl-D2. Conclusions Sevoflurane anaesthesia inhibited radioligand binding to MAO-B in the primate brain. The observation of lower MAO-B binding at clinically relevant concentrations of sevoflurane warrants further exploration of the potential role of MAO-B related mechanisms in regulation of systemic blood pressure during anaesthesia.
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Fazio P, Ferreira D, Svenningsson P, Halldin C, Farde L, Westman E, Varrone A. High-resolution PET imaging reveals subtle impairment of the serotonin transporter in an early non-depressed Parkinson's disease cohort. Eur J Nucl Med Mol Imaging 2020; 47:2407-2416. [PMID: 32020370 PMCID: PMC7396398 DOI: 10.1007/s00259-020-04683-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Accepted: 01/03/2020] [Indexed: 12/14/2022]
Abstract
PURPOSE The serotonin transporter (SERT) is a biochemical marker for monoaminergic signaling in brain and has been suggested to be involved inthe pathophysiology of Parkinson's disease (PD). The aim of this PET study was to examine SERT availability in relevant brain regions in early stages ofnon-depressed PD patients. METHODS In a cross-sectional study, 18 PD patients (13 M/5F, 64 ± 7 years, range 46-74 years, disease duration 2.9 ± 2.6 years; UPDRS motor 21.9 ± 5.2) and 20 age- and gender-matched healthy control (HC) subjects (15 M/5F, 61 ± 7 years, range 50-72 years) were included. In a subsequent longitudinal phase, ten of the PD patients (7 M/3F, UPDRS motor 20.6 ± 6.9) underwent a second PET measurement after 18-24 months. After a 3-T MRI acquisition, baseline PET measurements were performed with [11C]MADAM using a high-resolution research tomograph. The non-displaceablebinding potential (BPND) was chosen as the outcome measure and was estimated at voxel level on wavelet-aided parametric images, by using the Logan graphical analysis and the cerebellum as reference region. A molecular template was generated to visualize and define different subdivisions of the raphe nuclei in the brainstem. Subortical and cortical regions of interest were segmented using FreeSurfer. Univariate analyses and multivariate network analyses were performed on the PET data. RESULTS The univariate region-based analysis showed no differences in SERT levels when the PD patients were compared with the HC neither at baseline or after 2 years of follow-up. The multivariate network analysis also showed no differences at baseline. However, prominent changes in integration and segregation measures were observed at follow-up, indicating a disconnection of the cortical and subcortical regions from the three nuclei of the raphe. CONCLUSION We conclude that the serotoninergic system in PD patients seems to become involved with a network dysregulation as the disease progresses, suggesting a disturbed serotonergic signaling from raphe nuclei to target subcortical and cortical regions.
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Matheson GJ, Plavén-Sigray P, Louzolo A, Borg J, Farde L, Petrovic P, Cervenka S. Dopamine D1 receptor availability is not associated with delusional ideation measures of psychosis proneness. Schizophr Res 2020; 222:175-184. [PMID: 32616361 DOI: 10.1016/j.schres.2020.06.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Revised: 05/25/2020] [Accepted: 06/01/2020] [Indexed: 10/24/2022]
Abstract
The dopamine D1 receptor (D1R) is thought to play a role in psychosis and schizophrenia, however positron emission tomography studies comparing patients and controls have been inconsistent. To circumvent some of the limitations of clinical studies, such as antipsychotic exposure, an alternative approach is to examine subclinical psychotic symptoms within the general population, i.e. psychosis proneness traits. In this study, we investigated whether D1R availability is associated with delusional ideation in healthy controls, in four experiments, using [11C]SCH23390 PET (n = 76) and psychometric questionnaires (n = 217). We performed exploratory analyses, direct self-replication, and confirmatory analyses using Bayesian statistical modelling. Collectively, we found strong evidence that there is little to no linear association between delusional ideation and D1R. If hypothesised changes in D1R in drug-naive psychosis patients can be confirmed, our results suggest that they may either occur at disease onset, or that they are associated with specific aspects of psychosis other than delusional ideation.
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Tjerkaski J, Cervenka S, Farde L, Matheson GJ. Kinfitr - an open-source tool for reproducible PET modelling: validation and evaluation of test-retest reliability. EJNMMI Res 2020; 10:77. [PMID: 32642865 PMCID: PMC7343683 DOI: 10.1186/s13550-020-00664-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2020] [Accepted: 06/25/2020] [Indexed: 01/26/2023] Open
Abstract
BACKGROUND In positron emission tomography (PET) imaging, binding is typically estimated by fitting pharmacokinetic models to the series of measurements of radioactivity in the target tissue following intravenous injection of a radioligand. However, there are multiple different models to choose from and numerous analytical decisions that must be made when modelling PET data. Therefore, it is important that analysis tools be adapted to the specific circumstances, and that analyses be documented in a transparent manner. Kinfitr, written in the open-source programming language R, is a tool developed for flexible and reproducible kinetic modelling of PET data, i.e. performing all steps using code which can be publicly shared in analysis notebooks. In this study, we compared outcomes obtained using kinfitr with those obtained using PMOD: a widely used commercial tool. RESULTS Using previously collected test-retest data obtained with four different radioligands, a total of six different kinetic models were fitted to time-activity curves derived from different brain regions. We observed good correspondence between the two kinetic modelling tools both for binding estimates and for microparameters. Likewise, no substantial differences were observed in the test-retest reliability estimates between the two tools. CONCLUSIONS In summary, we showed excellent agreement between the open-source R package kinfitr, and the widely used commercial application PMOD. We, therefore, conclude that kinfitr is a valid and reliable tool for kinetic modelling of PET data.
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Cselényi Z, Jucaite A, Kristensson C, Stenkrona P, Ewing P, Varrone A, Johnström P, Schou M, Vazquez-Romero A, Moein MM, Bolin M, Siikanen J, Grybäck P, Larsson B, Halldin C, Grime K, Eriksson UG, Farde L. Quantification and reliability of [ 11C]VC - 002 binding to muscarinic acetylcholine receptors in the human lung - a test-retest PET study in control subjects. EJNMMI Res 2020; 10:59. [PMID: 32495011 PMCID: PMC7270393 DOI: 10.1186/s13550-020-00634-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Accepted: 04/22/2020] [Indexed: 01/20/2023] Open
Abstract
BACKGROUND The radioligand [11C]VC-002 was introduced in a small initial study long ago for imaging of muscarinic acetylcholine receptors (mAChRs) in human lungs using positron emission tomography (PET). The objectives of the present study in control subjects were to advance the methodology for quantification of [11C]VC-002 binding in lung and to examine the reliability using a test-retest paradigm. This work constituted a self-standing preparatory step in a larger clinical trial aiming at estimating mAChR occupancy in the human lungs following inhalation of mAChR antagonists. METHODS PET measurements using [11C]VC-002 and the GE Discovery 710 PET/CT system were performed in seven control subjects at two separate occasions, 2-19 days apart. One subject discontinued the study after the first measurement. Radioligand binding to mAChRs in lung was quantified using an image-derived arterial input function. The total distribution volume (VT) values were obtained on a regional and voxel-by-voxel basis. Kinetic one-tissue and two-tissue compartment models (1TCM, 2TCM), analysis based on linearization of the compartment models (multilinear Logan) and image analysis by data-driven estimation of parametric images based on compartmental theory (DEPICT) were applied. The test-retest repeatability of VT estimates was evaluated by absolute variability (VAR) and intraclass correlation coefficients (ICCs). RESULTS The 1TCM was the statistically preferred model for description of [11C]VC-002 binding in the lungs. Low VAR (< 10%) across analysis methods indicated good reliability of the PET measurements. The VT estimates were stable after 60 min. CONCLUSIONS The kinetic behaviour and good repeatability of [11C]VC-002 as well as the novel lung image analysis methodology support its application in applied studies on drug-induced mAChR receptor occupancy and the pathophysiology of pulmonary disorders. TRIAL REGISTRATION ClinicalTrials.gov identifier: NCT03097380, registered: 31 March 2017.
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Nag S, Varnäs K, Arakawa R, Jahan M, Schou M, Farde L, Halldin C. Synthesis, Biodistribution, and Radiation Dosimetry of a Novel mGluR5 Radioligand: 18F-AZD9272. ACS Chem Neurosci 2020; 11:1048-1057. [PMID: 32167745 PMCID: PMC7309225 DOI: 10.1021/acschemneuro.9b00680] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
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The metabotropic
glutamate receptor subtype mGluR5 has been proposed
as a potential drug target for CNS disorders such as anxiety, depression,
Parkinson’s disease, and epilepsy. The AstraZeneca compound
AZD9272 has previously been labeled with carbon-11 and used as a PET
radioligand for mGluR5 receptor binding. The molecular structure of
AZD9272 allows one to label the molecule with fluorine-18 without
altering the structure. The aim of this study was to develop a fluorine-18
analogue of AZD9272 and to examine its binding distribution in the
nonhuman primate brain in vivo as well as to obtain
whole body radiation dosimetry. 18F-AZD9272 was successfully
synthesized from a nitro precursor. The radioligand was stable, with
a radiochemical purity of >99% at 2 h after formulation in a sterile
phosphate buffered solution (pH = 7.4). After injection of 18F-AZD9272 in two cynomolgus monkeys, the maximum whole brain radioactivity
concentration was 4.9–6.7% of the injected dose (n = 2) and PET images showed a pattern of regional radioactivity consistent
with that previously obtained for 11C-AZD9272. The percentage
of parent radioligand in plasma was 59 and 64% (n = 2) at 120 min after injection of 18F-AZD9272, consistent
with high metabolic stability. Two whole body PET scans were performed
in nonhuman primates for a total of 231 min after injection of 18F-AZD9272. Highest uptakes were seen in liver and small intestine,
followed by brain and kidney. The estimated effective dose was around
0.017 mSv/MBq. 18F-AZD9272 shows suitable properties as
a PET radioligand for in vivo imaging of binding
in the primate brain. 18F-labeled AZD9272 offers advantages
over 11C-AZD9272 in terms of higher image resolution, combined
with a longer half-life. Moreover, based on the distribution and the
estimated radiation burden, imaging of 18F-AZD9272 could
be used as an improved tool for quantitative assessment and characterization
of AZD9272 binding sites in the human brain by using PET.
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Tiger M, Svensson J, Liberg B, Saijo T, Schain M, Halldin C, Farde L, Lundberg J. [ 11 C]raclopride positron emission tomography study of dopamine-D 2/3 receptor binding in patients with severe major depressive episodes before and after electroconvulsive therapy and compared to control subjects. Psychiatry Clin Neurosci 2020; 74:263-269. [PMID: 31943514 DOI: 10.1111/pcn.12980] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Revised: 01/03/2020] [Accepted: 01/07/2020] [Indexed: 12/24/2022]
Abstract
AIM The aim of the study was to test: (i) if D2 /D3 binding in three functional subsections of striatum is different in patients with severe major depressive episodes than in controls; and (ii) if this difference is normalized after electroconvulsive therapy (ECT). METHODS Nine inpatients were examined with positron emission tomography (PET) and the radioligand [11 C]raclopride before and after an average of 8.4 ECT sessions. Treatment response was assessed using the Montgomery-Åsberg Depression Rating Scale. Nine age- and sex-matched controls were examined twice with PET and [11 C]raclopride. RESULTS [11 C]raclopride binding was significantly lower in all three subsections of striatum in patients compared to controls (Cohen's dz , 1.14-1.68; P = 0.003-0.027). Montgomery-Åsberg Depression Ratings decreased significantly after ECT (P < 0.001; Cohen's dz , 2.9). ECT had no statistically significant effect on [11 C]raclopride binding, although post-ECT binding estimates were more similar to those obtained in controls in all subsections of striatum. CONCLUSION Using PET and [11 C]raclopride, we found support for the notion that severe major depressive episodes are associated with significantly lower dopamine D2 /D3 binding in all three subsections of striatum compared to controls. We noted no significant effect on D2 /D3 binding in the patient group after response to ECT.
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Varrone A, Varnäs K, Jucaite A, Cselényi Z, Johnström P, Schou M, Vazquez-Romero A, Moein MM, Halldin C, Brown AP, Vishwanathan K, Farde L. A PET study in healthy subjects of brain exposure of 11C-labelled osimertinib - A drug intended for treatment of brain metastases in non-small cell lung cancer. J Cereb Blood Flow Metab 2020; 40:799-807. [PMID: 31006308 PMCID: PMC7168784 DOI: 10.1177/0271678x19843776] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Revised: 03/05/2019] [Accepted: 03/11/2019] [Indexed: 12/19/2022]
Abstract
Osimertinib is a tyrosine kinase inhibitor (TKI) of the mutated epidermal growth factor receptor (EGFRm) with observed efficacy in patients with brain metastases. Brain exposure and drug distribution in tumor regions are important criteria for evaluation and confirmation of CNS efficacy. The aim of this PET study was therefore to determine brain distribution and exposure of 11C-labelled osimertinib administered intravenously in subjects with an intact blood-brain barrier. Eight male healthy subjects (age 52 ± 8 years) underwent one PET measurement with 11C-osimertinib. The pharmacokinetic parameters Cmax(brain) (standardized uptake value), Tmax(brain) and AUC0-90 minbrain/blood ratio were calculated. The outcome measure for 11C-osimertinib brain exposure was the total distribution volume (VT). 11C-osimertinib distributed rapidly to the brain, with higher uptake in grey than in white matter. Mean Cmax, Tmax and AUC0-90 minbrain/blood ratio were 1.5 (range 1-1.8), 13 min (range 5-30 min), and 3.8 (range 3.3-4.1). Whole brain and white matter VT were 14 mL×cm-3 (range 11-18) and 7 mL×cm-3 (range 5-12). This study in healthy volunteers shows that 11C-osimertinib penetrates the intact blood-brain barrier. The approach used further illustrates the role of molecular imaging in facilitating the development of novel drugs for the treatment of malignancies affecting the brain.
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Lindberg A, Arakawa R, Nogami T, Nag S, Schou M, Elmore CS, Farde L, Pike VW, Halldin C. Potential for imaging the high-affinity state of the 5-HT 1B receptor: a comparison of three PET radioligands with differing intrinsic activity. EJNMMI Res 2019; 9:100. [PMID: 31754940 PMCID: PMC6872687 DOI: 10.1186/s13550-019-0570-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Accepted: 11/01/2019] [Indexed: 11/19/2022] Open
Abstract
Background Over the last decade, a few radioligands have been developed for PET imaging of brain 5-HT1B receptors. The 5-HT1B receptor is a G-protein-coupled receptor (GPCR) that exists in two different agonist affinity states. An agonist ligand is expected to be more sensitive towards competition from another agonist, such as endogenous 5-HT, than an antagonist ligand. It is of interest to know whether the intrinsic activity of a PET radioligand for the 5-HT1B receptor impacts on its ability to detect changes in endogenous synaptic 5-HT density. Three high-affinity 11C-labeled 5-HT1B PET radioligands with differing intrinsic activity were applied to PET measurements in cynomolgus monkey to evaluate their sensitivity to be displaced within the brain by endogenous 5-HT. For these experiments, fenfluramine was pre-administered at two different doses (1.0 and 5.0 mg/kg, i.v.) to induce synaptic 5-HT release. Results A dose-dependent response to fenfluramine was detected for all three radioligands. At the highest dose of fenfluramine (5.0 mg/kg, i.v.), reductions in specific binding in the occipital cortex increased with radioligand agonist efficacy, reaching 61% for [11C]3. The most antagonistic radioligand showed the lowest reduction in specific binding. Conclusions Three 5-HT1B PET radioligands were identified with differing intrinsic activity that could be used in imaging high- and low-affinity states of 5-HT1B receptors using PET. From this limited study, radioligand sensitivity to endogenous 5-HT appears to depend on agonist efficacy. More extensive studies are required to substantiate this suggestion.
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