The P2X7 receptor tracer [11C]SMW139 as an in vivo marker of neuroinflammation in multiple sclerosis: a first-in man study

Abstract Purpose The novel PET tracer [11C]SMW139 binds with high affinity to the P2X7 receptor, which is expressed on pro-inflammatory microglia. The purposes of this first in-man study were to characterise pharmacokinetics of [11C]SMW139 in patients with active relapsing remitting multiple sclerosis (RRMS) and healthy controls (HC) and to evaluate its potential to identify in vivo neuroinflammation in RRMS. Methods Five RRMS patients and 5 age-matched HC underwent 90-min dynamic [11C]SMW139 PET scans, with online continuous and manual arterial sampling to generate a metabolite-corrected arterial plasma input function. Tissue time activity curves were fitted to single- and two-tissue compartment models, and the model that provided the best fits was determined using the Akaike information criterion. Results The optimal model for describing [11C]SMW139 kinetics in both RRMS and HC was a reversible two-tissue compartment model with blood volume parameter and with the dissociation rate k4 fixed to the whole-brain value. Exploratory group level comparisons demonstrated an increased volume of distribution (VT) and binding potential (BPND) in RRMS compared with HC in normal appearing brain regions. BPND in MS lesions was decreased compared with non-lesional white matter, and a further decrease was observed in gadolinium-enhancing lesions. In contrast, increased VT was observed in enhancing lesions, possibly resulting from disruption of the blood-brain barrier in active MS lesions. In addition, there was a high correlation between parameters obtained from 60- to 90-min datasets, although analyses using 60-min data led to a slight underestimation in regional VT and BPND values. Conclusions This first in-man study demonstrated that uptake of [11C]SMW139 can be quantified with PET using BPND as a measure for specific binding in healthy controls and RRMS patients. Additional studies are warranted for further clinical evaluation of this novel neuroinflammation tracer.

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Kinetic Analysis of the 5-HT2A Ligand [11C]MDL 100,907

Journal of Cerebral Blood Flow & Metabolism ◽

10.1097/00004647-200006000-00002 ◽

2000 ◽

Vol 20 (6) ◽

pp. 899-909 ◽

Cited By ~ 64

Author(s):

Hiroshi Watabe ◽

Michael A. Channing ◽

Margaret G. Der ◽

H. Richard Adams ◽

Elaine Jagoda ◽

...

Keyword(s):

Kinetic Analysis ◽

Specific Binding ◽

Compartment Model ◽

Input Function ◽

Brain Regions ◽

Time Activity ◽

Tissue Compartment ◽

Arterial Blood ◽

Fixed Parameter ◽

Mdl 100,907

The goal of this study was to develop a suitable kinetic analysis method for quantification of 5-HT2A receptor parameters with [11C]MDL 100,907. Twelve control studies and four preblocking studies (400 nmol/kg unlabeled MDL 100,907) were performed in isoflurane-anesthetized rhesus monkeys. The plasma input function was determined from arterial blood samples with metabolite measurements by extraction in ethyl acetate. The preblocking studies showed that a two-tissue compartment model was necessary to fit the time activity curves of all brain regions including the cerebellum—in other words, the need for two compartments is not proof of specific binding. Therefore, a three-tissue compartment model was used to analyze the control studies, with three parameters fixed based on the preblocking data. Reliable fits of control data could be obtained only if no more than three parameters were allowed to vary. For routine use of [11C]MDL 100,907, several simplified methods were evaluated. A two-tissue (2T‘) compartment with one fixed parameter was the most reliable compartmental approach; a one-compartment model failed to fit the data adequately. The Logan graphical approach was also tested and produced comparable results to the 2T’ model. However, a simulation study showed that Logan analysis produced a larger bias at higher noise levels. Thus, the 2T' model is the best choice for analysis of [11C]MDL 100,907 studies.

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The Pharmacokinetics of [18F]UCB-H Revisited in The Healthy Non-Human Primate Brain

10.21203/rs.3.rs-110220/v1 ◽

2020 ◽

Author(s):

Sébastien Goutal ◽

Martine Guillermier ◽

Guillaume Becker ◽

Mylène Gaudin ◽

Yann Bramoullé ◽

...

Keyword(s):

Slow Component ◽

Specific Binding ◽

Compartment Model ◽

Brain Regions ◽

Volume Of Distribution ◽

Binding Potential ◽

Pharmacokinetic Data ◽

Limited Information ◽

Human Primate

Abstract Background Positron Emission Tomography (PET) imaging of the Synaptic Vesicle glycoprotein (SV) 2A is a new tool to quantify synaptic density. [18F]UCB-H was one of the first promising SV2A-ligands to be labelled and used in vivo in rodent and human, while limited information on its pharmacokinetic properties is available in the non-human primate. Here, we aimed to characterize [18F]UCB-H in the non-human cynomolgus primate and to discuss the obtained results in the light of the current state of SV2A PET ligands.Results [18F]UCB-H pharmacokinetic data was optimally fitted with a two-compartment model (2TCM), even though a slow component led to instability for the estimation of k3 and k4, and hence the total volume of distribution. 2TCM with coupled fit K1/k2 across brain regions stabilized the quantification, and confirmed a lower non-displaceable binding potential, BPND (estimated by k3/k4), of [18F]UCB-H compared to the newest SV2A-ligands. However, the non-displaceable distribution volume (VND) and the influx parameter (K1) is similar to what has been reported for other SV2A ligands. These data were reinforced by displacement studies using [19F]UCB-H, demonstrating only 50 % displacement of the total [18F]UCB-H signal at maximal occupancy of SV2A. Conclusions Modeling issues with a 2TCM due to a slow component have previously been reported for other SV2A ligands with low specific binding, or after blocking of specific binding. As all SV2A ligands share chemical structural similarities, we hypothesize that this slow binding component is common for all SV2A ligands, but only hampers quantification when specific binding is low.

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The pharmacokinetics of [18F]UCB-H revisited in the healthy non-human primate brain

EJNMMI Research ◽

10.1186/s13550-021-00777-8 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Sébastien Goutal ◽

Martine Guillermier ◽

Guillaume Becker ◽

Mylène Gaudin ◽

Yann Bramoullé ◽

...

Keyword(s):

Slow Component ◽

Specific Binding ◽

Compartment Model ◽

Brain Regions ◽

Volume Of Distribution ◽

Pharmacokinetic Data ◽

Limited Information ◽

Positron Emission ◽

Human Primate

Abstract Background Positron Emission Tomography (PET) imaging of the Synaptic Vesicle glycoprotein (SV) 2A is a new tool to quantify synaptic density. [18F]UCB-H was one of the first promising SV2A-ligands to be labelled and used in vivo in rodent and human, while limited information on its pharmacokinetic properties is available in the non-human primate. Here, we evaluate the reliability of the three most commonly used modelling approaches for [18F]UCB-H in the non-human cynomolgus primate, adding the coupled fit of the non-displaceable distribution volume (VND) as an alternative approach to improve unstable fit. The results are discussed in the light of the current state of SV2A PET ligands. Results [18F]UCB-H pharmacokinetic data was optimally fitted with a two-compartment model (2TCM), although the model did not always converge (large total volume of distribution (VT) or large uncertainty of the estimate). 2TCM with coupled fit K1/k2 across brain regions stabilized the quantification, and confirmed a lower specific signal of [18F]UCB-H compared to the newest SV2A-ligands. However, the measures of VND and the influx parameter (K1) are similar to what has been reported for other SV2A ligands. These data were reinforced by displacement studies using [19F]UCB-H, demonstrating only 50% displacement of the total [18F]UCB-H signal at maximal occupancy of SV2A. As previously demonstrated in clinical studies, the graphical method of Logan provided a more robust estimate of VT with only a small bias compared to 2TCM. Conclusions Modeling issues with a 2TCM due to a slow component have previously been reported for other SV2A ligands with low specific binding, or after blocking of specific binding. As all SV2A ligands share chemical structural similarities, we hypothesize that this slow binding component is common for all SV2A ligands, but only hampers quantification when specific binding is low.

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A metabolically stable PET tracer for imaging synaptic vesicle protein 2A: Synthesis and preclinical characterization of [18F]SDM-16

10.1101/2021.06.25.449978 ◽

2021 ◽

Author(s):

Chao Zheng ◽

Daniel Holden ◽

Ming-Qiang Zheng ◽

Richard Pracitto ◽

Kyle C. Wilcox ◽

...

Keyword(s):

Synaptic Vesicle ◽

Nonhuman Primate ◽

Specific Binding ◽

Volume Of Distribution ◽

Binding Potential ◽

Time Activity ◽

Peripheral Tissues ◽

High Affinity ◽

Arterial Blood ◽

Pet Tracer

Purpose: To investigate the synaptic vesicle glycoprotein 2A (SV2A) expression in the whole central nervous system and peripheral tissues, a metabolically stable SV2A radiotracer is desirable to minimize a potential confounding effect of radiometabolites. The aim of this study was to develop and evaluate a metabolically stable SV2A radiotracer, [18F]SDM-16, in nonhuman primate brains. Methods: The racemic SDM-16 (4-(3,5-difluorophenyl)-1-((2-methyl-1H-imidazol-1-yl)methyl)pyrrolidin-2-one ) was synthesized and assayed for in vitro SV2A binding affinity. We synthesized the enantiopure [18F]SDM-16 using the corresponding arylstannane precursor. Nonhuman primate brain PET was performed on a FOCUS 220 system. Arterial blood was drawn for metabolite analysis and construction of plasma input function. Regional time-activity curves (TACs) were evaluated with the one-tissue compartment (1TC) model to obtain the volume of distribution (VT). Binding potential (BPND) was calculated using either the nondisplaceable volume of distribution (VND) or the centrum semiovale (CS) as the reference region. Results: Racemic SDM-16 was synthesized in 3 steps with 44% overall yield and has high affinity (Ki = 3.7 nM) to human SV2A. [18F]SDM-16 was prepared in greater than 99% radiochemical and enantiomeric purity. This radiotracer displayed high specific binding in brain and was metabolically more stable than other SV2A PET tracers. The plasma free fraction (fP) of [18F]SDM-16 was 69%, which was higher than those of [11C]UCB-J (46%), [18F]SynVesT-1 (43%), [18F]SynVesT-2 (41%), and [18F]UCB-H (43%). The TACs were well described with the 1TC. The averaged test-retest variability (TRV) was -9%, and averaged absolute TRV (aTRV) was 10% for all analyzed brain regions. Conclusion: We have successfully synthesized a metabolically stable and high affinity SV2A PET tracer, [18F]SDM-16, which showed high specific and reversible binding in the NHP brain. [18F]SDM-16 may have potential application in the visualization and quantification of SV2A beyond the brain.

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A metabolically stable PET tracer for imaging synaptic vesicle protein 2A: Synthesis and preclinical characterization of [18F]SDM-16

10.21203/rs.3.rs-672703/v1 ◽

2021 ◽

Author(s):

Chao Zheng ◽

Daniel Holden ◽

Ming-Qiang Zheng ◽

Richard Pracitto ◽

Kyle C. Wilcox ◽

...

Keyword(s):

Synaptic Vesicle ◽

Nonhuman Primate ◽

Specific Binding ◽

Volume Of Distribution ◽

Binding Potential ◽

Time Activity ◽

Peripheral Tissues ◽

High Affinity ◽

Arterial Blood ◽

Pet Tracer

Abstract PurposeTo investigate the synaptic vesicle glycoprotein 2A (SV2A) expression in the whole central nervous system and peripheral tissues, a metabolically stable SV2A radiotracer is desirable to minimize a potential confounding effect of radiometabolites. The aim of this study was to develop and evaluate a metabolically stable SV2A radiotracer, [18 F]SDM-16, in nonhuman primate brains. MethodsThe racemic SDM-16 (4-(3,5-difluorophenyl)-1-((2-methyl-1H-imidazol-1yl)methyl)pyrrolidin-2-one) was synthesized and assayed for in vitro SV2A binding affinity. We synthesized the enantiopure [18F]SDM-16 using the corresponding arylstannane precursor. Nonhuman primate brain PET was performed on a FOCUS 220 system. Arterial blood was drawn for metabolite analysis and construction of plasma input function. Regional time-activity curves (TACs) were evaluated with the one-tissue compartment (1TC) model to obtain the volume of distribution (VT). Binding potential (BPND) was calculated using either the nondisplaceable volume of distribution (VND) or the centrum semiovale (CS) as the reference region. ResultsRacemic SDM-16 was synthesized in 3 steps with 44% overall yield and has high affinity (K i = 3.7 nM) to human SV2A. [18F]SDM-16 was prepared in greater than 99% radiochemical and enantiomeric purity. This radiotracer displayed high specific binding in brain and was metabolically more stable than other SV2A PET tracers. The plasma free fraction (fP) of [ 18 F]SDM-16 was 69%, which was higher than those of [11C]UCB-J (46%), [18F]SynVesT-1 (43%), [18F]SynVesT-2 (41%), and [18F]UCB-H (43%). The TACs were well described with the 1TC. The averaged test-retest variability (TRV) was -9±8%, and averaged absolute TRV (aTRV) was 10±7% for all analyzed brain regions. ConclusionWe have successfully synthesized a metabolically stable and high affinity SV2A PET tracer, [18F]SDM-16, which showed high specific and reversible binding in the NHP brain. [18F]SDM-16 may have potential application in the visualization and quantification of SV2A beyond the brain.

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Kinetic Modeling of [11C]Raclopride: Combined PET-Microdialysis Studies

Journal of Cerebral Blood Flow & Metabolism ◽

10.1097/00004647-199709000-00002 ◽

1997 ◽

Vol 17 (9) ◽

pp. 932-942 ◽

Cited By ~ 133

Author(s):

Christopher J. Endres ◽

Bhaskar S. Kolachana ◽

Richard C. Saunders ◽

Tom Su ◽

Daniel Weinberger ◽

...

Keyword(s):

Positron Emission Tomography ◽

Specific Binding ◽

Compartment Model ◽

Emission Tomography ◽

Extended Model ◽

Simulation Studies ◽

Time Activity ◽

Endogenous Dopamine ◽

Positron Emission

The in vivo binding of D2 receptor ligands can be affected by agents that alter the concentration of endogenous dopamine. To define a more explicit relation between dopamine and D2 receptor binding, the conventional compartment model for reversible ligands has been extended to account for a time-varying dopamine pulse. This model was tested with [11C]raclopride positron emission tomography and dopamine microdialysis data that were acquired simultaneously in rhesus monkeys. The microdialysis data were incorporated into the model assuming a proportional relation to synaptic dopamine. Positron emission tomography studies used a bolus-plus-infusion tracer delivery with amphetamine given at 40 minutes to induce dopamine release. The extended model described the entire striatal time–activity curve, including the decrease in radioactivity concentration after an amphetamine-induced dopamine pulse. Based on these results, simulation studies were performed using the extended model. The simulation studies showed that the percent decrease in specific binding after amphetamine measured with the bolus-plus-infusion protocol correlates well with the integral of the postamphetamine dopamine pulse. This suggests that changes in specific binding observed in studies in humans can be interpreted as being linearly proportional to the integral of the amphetamine-induced dopamine pulse.

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Adenosine A2A receptor in schizophrenia: an in vivo brain PET imaging study

Psychopharmacology ◽

10.1007/s00213-021-05900-0 ◽

2021 ◽

Author(s):

Tiago Reis Marques ◽

Sridhar Natesan ◽

Eugenii A. Rabiner ◽

Graham E. Searle ◽

Roger Gunn ◽

...

Keyword(s):

Healthy Subjects ◽

Tracer Uptake ◽

Psychotic Symptoms ◽

Binding Potential ◽

Primary Role ◽

Healthy Controls ◽

Pet Tracer ◽

A2a Receptor ◽

Globus Pallidum

AbstractAdenosine A2A receptors are highly enriched in the basal ganglia system, a region that is functionally implicated in schizophrenia. Preclinical evidence suggests a cross-regulation between adenosine A2A and dopamine D2 receptors in this region and that it is linked to the sensitization of the dopamine system. However, the relationship between A2A receptor availability and schizophrenia has not been directly examined in vivo in patients with this disorder. To investigate, using positron emission tomography (PET), the availability of A2A receptors in patients diagnosed with schizophrenia in comparison to matched healthy controls. A2A receptor availability was measured using the PET tracer [11C]SCH442416. Twelve male patients with chronic schizophrenia were compared to 13 matched healthy subjects. All patients were medicated with antipsychotics and none presented with any motor or extrapyramidal symptoms. Binding potential (BPND), a ratio measure between specific and non-specific tracer uptake, were compared between the groups for the caudate, putamen, accumbens and globus pallidum. There was no differences between A2A receptor binding potential (BPND) of schizophrenia patients in the caudate (p = 0.16), putamen (p = 0.86), accumbens (p = 0.44) and globus pallidum (p = 0.09) to that of matched healthy subjects. There was also no significant correlation between [11C]SCH442416 binding and severity of psychotic symptoms (p = 0.2 to 0.82) or antipsychotic dosage (p = 0.13 to 0.34). By showing that A2A receptor availability in medicated patients with chronic male schizophrenia is not different than in healthy controls, this study does not support the primary role of this receptor in the pathogenesis of schizophrenia.

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Characterization in Non-human Primates of (R)-[18F]OF-Me-NB1 and (S)-[18F]OF-Me-NB1 for Imaging the GluN2B Subunits of the NMDA Receptor

10.21203/rs.3.rs-1068936/v1 ◽

2021 ◽

Author(s):

Ming-Qiang Zheng ◽

Hazem Ahmed ◽

Kelly Smart ◽

Yuping Xu ◽

Daniel Holden ◽

...

Keyword(s):

Rhesus Monkeys ◽

Dynamic Range ◽

Arterial Input Function ◽

Specific Binding ◽

Parent Compound ◽

Brain Regions ◽

Binding Potential ◽

Fast Kinetics ◽

Sigma 1 Receptor

Abstract PurposeGluN2B containing N-methyl-D-aspartate receptors (NMDARs) play an essential role in neurotransmission and are a potential treatment target for multiple neurological and neurodegenerative diseases, including stroke, Alzheimer’s disease, and Parkinson’s disease. In a previous report (R)-[18F]OF-Me-NB1 was reported to be more specific and selective for targeting the GluN2B subunits of the NMDAR. Here we report a comprehensive evaluation of (R)-[18F]OF-Me-NB1 and (S)-[18F]OF-Me-NB1 in non-human primates.MethodsThe radiosynthesis of (R)-[18F]OF-Me-NB1 and (S)-[18F]OF-Me-NB1 was accomplished as reported previously with minor modifications. PET scans in two rhesus monkeys were conducted on the Focus 220 scanner. Blocking studies were performed after treatment of the animals with the GluN2B antagonist Co101,244 or the sigma-1 receptor antagonist FTC-146. One-tissue (1T) compartment model and multilinear analysis-1 (MA1) method with arterial input function were used to obtain regional volume of distribution (VT, mL/cm3). Occupancy values by the two blockers were obtained by the Lassen plot. Regional non-displaceable binding potential (BPND) was calculated from the corresponding baseline VT and the VND derived from the occupancy plot of the Co101,244 blocking scans. Results(R)- and (S)-[18F]OF-Me-NB1 were produced in >99% radiochemical and enantiomeric purity, with molar activity of 224.22 ± 161.69 MBq/nmol at the end of synthesis (n=10). Metabolism was moderate, with ~30% parent compound remaining for (R)-[18F]OF-Me-NB1 and 20% for (S)-[18F]OF-Me-NB1 at 30 min post injection. Plasma free fraction was 1-2%. In brain regions both (R)- and (S)-[18F]OF-Me-NB1 displayed fast uptake with slower clearance for the (R)- than (S)-enantiomer. For (R)-[18F]OF-Me-NB1, both the 1T model and MA1 method gave reliable estimates of regional VT values, with MA1 VT (mL/cm3) ranging from 8.9 in the cerebellum to 12.8 in the cingulate cortex. Blocking with 0.25 mg/kg of Co101,244 greatly reduced the uptake of (R)-[18F]OF-Me-NB1 across all brain regions, resulting in an occupancy of 77% and VND of 6.36, while 0.027 mg/kg of FTC-146 reduced specific binding by 30%. Regional BPND, as a measure of specific binding signals, ranged from 0.40 in the cerebellum to 1.01 in the cingulate cortex.ConclusionsIn rhesus monkeys, (R)-[18F]OF-Me-NB1 exhibited fast kinetics and heterogeneous uptake across brain regions, while the (S)-enantiomer displayed a narrower dynamic range of uptake across regions. Blocking study with a GluN2B antagonist indicated binding specificity. Value of BPND were >0.5 in most brain regions, suggesting good in vivo specific binding signals. Taken together, results from the current study demonstrated the potential of (R)-[18F]OF-Me-NB1 as a useful radiotracer for imaging the GluN2B receptor.

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Parametric methods for [18F]flortaucipir PET

Journal of Cerebral Blood Flow & Metabolism ◽

10.1177/0271678x18820765 ◽

2018 ◽

Vol 40 (2) ◽

pp. 365-373 ◽

Cited By ~ 3

Author(s):

Sandeep SV Golla ◽

Emma E Wolters ◽

Tessa Timmers ◽

Rik Ossenkoppele ◽

Chris WJ van der Weijden ◽

...

Keyword(s):

Specific Binding ◽

Volume Ratio ◽

Compartment Model ◽

Volume Of Distribution ◽

Distribution Volume ◽

Binding Potential ◽

Parametric Images ◽

Distribution Volume Ratio ◽

Pet Scans

[18F]Flortaucipir is a PET tau tracer used to visualize tau binding in Alzheimer’s disease (AD) in vivo. The present study evaluated the performance of several methods to obtain parametric images of [18F]flortaucipir. One hundred and thirty minutes dynamic PET scans were performed in 10 AD patients and 10 controls. Parametric images were generated using different linearization and basis function approaches. Regional binding potential (BPND) and volume of distribution (VT) values obtained from the parametric images were compared with corresponding values derived using the reversible two-tissue compartment model (2T4k_VB). Performance of SUVr parametric images was assessed by comparing values with distribution volume ratio (DVR) and SRTM-derived BPND estimates obtained using non-linear regression (NLR). Spectral analysis (SA) ( r2 = 0.92; slope = 0.99) derived VT correlated well with NLR-derived VT. RPM ( r2 = 0.95; slope = 0.98) derived BPND correlated well with NLR-derived DVR. Although SUVr80–100 min correlated well with NLR-derived DVR ( r2 = 0.91; slope = 1.09), bias in SUVr appeared to depend on uptake time and underlying level of specific binding. In conclusion, RPM and SA provide parametric images comparable to the NLR estimates. Individual SUVr values are biased compared with DVR and this bias requires further study in a larger dataset in order to understand its consequences.

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A metabolically stable PET tracer for imaging synaptic vesicle protein 2A: synthesis and preclinical characterization of [18F]SDM-16

European Journal of Nuclear Medicine and Molecular Imaging ◽

10.1007/s00259-021-05597-5 ◽

2021 ◽

Author(s):

Chao Zheng ◽

Daniel Holden ◽

Ming-Qiang Zheng ◽

Richard Pracitto ◽

Kyle C. Wilcox ◽

...

Keyword(s):

Synaptic Vesicle ◽

Nonhuman Primate ◽

Specific Binding ◽

Volume Of Distribution ◽

Time Activity ◽

Pet Tracers ◽

Arterial Blood ◽

Brain Pet ◽

Pet Tracer

Abstract Purpose To quantify the synaptic vesicle glycoprotein 2A (SV2A) changes in the whole central nervous system (CNS) under pathophysiological conditions, a high affinity SV2A PET radiotracer with improved in vivo stability is desirable to minimize the potential confounding effect of radiometabolites. The aim of this study was to develop such a PET tracer based on the molecular scaffold of UCB-A, and evaluate its pharmacokinetics, in vivo stability, specific binding, and nonspecific binding signals in nonhuman primate brains, in comparison with [11C]UCB-A, [11C]UCB-J, and [18F]SynVesT-1. Methods The racemic SDM-16 (4-(3,5-difluorophenyl)-1-((2-methyl-1H-imidazol-1-yl)methyl)pyrrolidin-2-one) and its two enantiomers were synthesized and assayed for in vitro binding affinities to human SV2A. We synthesized the enantiopure [18F]SDM-16 using the corresponding enantiopure arylstannane precursor. Nonhuman primate brain PET scans were performed on FOCUS 220 scanners. Arterial blood was drawn for the measurement of plasma free fraction (fP), radiometabolite analysis, and construction of the plasma input function. Regional time-activity curves (TACs) were fitted with the one-tissue compartment (1TC) model to obtain the volume of distribution (VT). Nondisplaceable binding potential (BPND) was calculated using either the nondisplaceable volume of distribution (VND) or the centrum semiovale (CS) as the reference region. Results SDM-16 was synthesized in 3 steps with 44% overall yield and has the highest affinity (Ki = 0.9 nM) to human SV2A among all reported SV2A ligands. [18F]SDM-16 was prepared in about 20% decay-corrected radiochemical yield within 90 min, with greater than 99% radiochemical and enantiomeric purity. This radiotracer displayed high specific binding in monkey brains and was metabolically more stable than the other SV2A PET tracers. The fP of [18F]SDM-16 was 69%, which was higher than those of [11C]UCB-J (46%), [18F]SynVesT-1 (43%), [18F]SynVesT-2 (41%), and [18F]UCB-H (43%). The TACs were well described with the 1TC. The averaged test–retest variability (TRV) was 7 ± 3%, and averaged absolute TRV (aTRV) was 14 ± 7% for the analyzed brain regions. Conclusion We have successfully synthesized a novel SV2A PET tracer [18F]SDM-16, which has the highest SV2A binding affinity and metabolical stability among published SV2A PET tracers. The [18F]SDM-16 brain PET images showed superb contrast between gray matter and white matter. Moreover, [18F]SDM-16 showed high specific and reversible binding in the NHP brains, allowing for the reliable and sensitive quantification of SV2A, and has potential applications in the visualization and quantification of SV2A beyond the brain.

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