Translocator Protein (18 kDa) Polymorphism (rs6971) Explains in-vivo Brain Binding Affinity of the PET Radioligand [18F]-FEPPA

[18F]-FEPPA binds to the 18-kDa translocator protein (TSPO) and is used in positron emission tomography (PET) to detect microglial activation. However, quantitative interpretations of the PET signal with new generation TSPO PET radioligands are confounded by large interindividual variability in binding affinity. This presents as a trimodal distribution, reflecting high-affinity binders (HABs), low-affinity binder (LAB), and mixed-affinity binders (MABs). Here, we show that one polymorphism (rs6971) located in exon 4 of the TSPO gene, which results in a nonconservative amino-acid substitution from alanine to threonine (Ala147Thr) in the TSPO protein, predicts [18F]-FEPPA total distribution volume in human brains. In addition, [18F]-FEPPA exhibits clearly different features in the shape of the time activity curves between genetic groups. Testing for the rs6971 polymorphism may allow quantitative interpretation of TSPO PET studies with new generation of TSPO PET radioligands.

Download Full-text

Optimised GMP-compliant production of [18F]DPA-714 on the Trasis AllinOne module

EJNMMI Radiopharmacy and Chemistry ◽

10.1186/s41181-021-00133-0 ◽

2021 ◽

Vol 6 (1) ◽

Author(s):

Klaudia A. Cybulska ◽

Vera Bloemers ◽

Lars R. Perk ◽

Peter Laverman

Keyword(s):

Significant Degree ◽

Translocator Protein ◽

Positron Emission ◽

Leaving Group ◽

Inflammatory Processes ◽

Single Production ◽

Translocator Protein 18 Kda ◽

Radiochemical Yields ◽

Specific Ligand

Abstract Background The translocator protein 18 kDa is recognised as an important biomarker for neuroinflammation due to its soaring expression in microglia. This process is common for various neurological disorders. DPA-714 is a potent TSPO-specific ligand which found its use in Positron Emission Tomography following substitution of fluorine-19 with fluorine-18, a positron-emitting radionuclide. [18F]DPA-714 enables visualisation of inflammatory processes in vivo non-invasively. Radiolabelling of this tracer is well described in literature, including validation for clinical use. Here, we report significant enhancements to the process which resulted in the design of a fully GMP-compliant robust synthesis of [18F]DPA-714 on a popular cassette-based system, Trasis AllinOne, boosting reliability, throughput, and introducing a significant degree of simplicity. Results [18F]DPA-714 was synthesised using the classic nucleophilic aliphatic substitution on a good leaving group, tosylate, with [18F]fluoride using tetraethylammonium bicarbonate in acetonitrile at 100∘C. The process was fully automated on a Trasis AllinOne synthesiser using an in-house designed cassette and sequence. With a relatively small precursor load of 4 mg, [18F]DPA-714 was obtained with consistently high radiochemical yields of 55-71% (n=6) and molar activities of 117-350 GBq/µmol at end of synthesis. With a single production batch, starting with 31-42 GBq of [18F]fluoride, between 13-20 GBq of the tracer can be produced, enabling multi-centre studies. Conclusion To the best of our knowledge, the process presented herein is the most efficient [18F]DPA-714 synthesis, with advantageous GMP compliance. The use of a Trasis AllinOne synthesiser increases reliability and allows rapid training of production staff.

Download Full-text

[18f]Feppa Pet Imaging For Monitoring Neuroinflammation In Nonhuman Primates

10.21203/rs.3.rs-17421/v1 ◽

2020 ◽

Author(s):

Matthew Zammit ◽

Yunlong Tao ◽

Miles Olsen ◽

Jeanette Metzger ◽

Scott Vermilyea ◽

...

Keyword(s):

Pet Imaging ◽

Microglial Activation ◽

Nonhuman Primates ◽

Rhesus Macaques ◽

Induced Pluripotent Stem Cell ◽

Asymmetry Index ◽

Translocator Protein ◽

Imaging Data ◽

Positron Emission

Abstract Purpose The aim of this study was to examine whether the translocator protein 18-kDa (TSPO) PET ligand [ 18 F]FEPPA has the sensitivity for detecting changes in microglial activation in hemiparkinsonian rhesus macaques treated with allogeneic grafts of induced pluripotent stem cell-derived midbrain dopaminergic neurons (iPSC-mDA). Methods In vivo positron emission tomography (PET) imaging with [ 18 F]FEPPA was used in conjunction with postmortem CD68 immunostaining to evaluate neuroinflammation in the brains of hemiparkinsonian rhesus macaques (n = 6) that received allogeneic iPSC-mDA grafts in the putamen ipsilateral to MPTP administration. Results Based on visual inspection of the imaging data and assessment of radiotracer uptake, nonhuman primates with allogeneic grafts showed increased [ 18 F]FEPPA binding at the graft sites relative to the contralateral putamen. From PET asymmetry analysis of the images, the mean asymmetry index of the monkeys was AI = -0.110 ± 0.025. Evaluation and scoring of CD68 immunoreactivity by an investigator blind to the treatment identified significantly more neuroinflammation in the grafted areas of the putamen compared to the contralateral nucleus (p = 0.0004). [ 18 F]FEPPA PET standard uptake values normalized to the contralateral putamen (SUV norm ) showed a positive correlation with CD68 immunoreactivity ratings in the monkeys (Pearson’s r = 0.83; p = 0.0008). Conclusion These findings reveal that [ 18 F]FEPPA PET is an effective marker for detecting increased microglial activation and demonstrate sufficient sensitivity to detect small changes in neuroinflammation in vivo following allogeneic cell engraftment.

Download Full-text

PET Imaging of Neuroinflammation in Alzheimer’s Disease

Frontiers in Immunology ◽

10.3389/fimmu.2021.739130 ◽

2021 ◽

Vol 12 ◽

Author(s):

Rong Zhou ◽

Bin Ji ◽

Yanyan Kong ◽

Limei Qin ◽

Wuwei Ren ◽

...

Keyword(s):

Alzheimer’S Disease ◽

Alzheimer's Disease ◽

Time Course ◽

Rapid Development ◽

Translocator Protein ◽

Positron Emission ◽

Protein Tracers ◽

Improved Performance ◽

New Generation

Neuroinflammation play an important role in Alzheimer’s disease pathogenesis. Advances in molecular imaging using positron emission tomography have provided insights into the time course of neuroinflammation and its relation with Alzheimer’s disease central pathologies in patients and in animal disease models. Recent single-cell sequencing and transcriptomics indicate dynamic disease-associated microglia and astrocyte profiles in Alzheimer’s disease. Mitochondrial 18-kDa translocator protein is the most widely investigated target for neuroinflammation imaging. New generation of translocator protein tracers with improved performance have been developed and evaluated along with tau and amyloid imaging for assessing the disease progression in Alzheimer’s disease continuum. Given that translocator protein is not exclusively expressed in glia, alternative targets are under rapid development, such as monoamine oxidase B, matrix metalloproteinases, colony-stimulating factor 1 receptor, imidazoline-2 binding sites, cyclooxygenase, cannabinoid-2 receptor, purinergic P2X7 receptor, P2Y12 receptor, the fractalkine receptor, triggering receptor expressed on myeloid cells 2, and receptor for advanced glycation end products. Promising targets should demonstrate a higher specificity for cellular locations with exclusive expression in microglia or astrocyte and activation status (pro- or anti-inflammatory) with highly specific ligand to enable in vivo brain imaging. In this review, we summarised recent advances in the development of neuroinflammation imaging tracers and provided an outlook for promising targets in the future.

Download Full-text

Cellular sources of TSPO expression in healthy and diseased brain

European Journal of Nuclear Medicine and Molecular Imaging ◽

10.1007/s00259-020-05166-2 ◽

2021 ◽

Author(s):

Erik Nutma ◽

Kelly Ceyzériat ◽

Sandra Amor ◽

Stergios Tsartsalis ◽

Philippe Millet ◽

...

Keyword(s):

Cell Activity ◽

Brain Regions ◽

Cellular Level ◽

Translocator Protein ◽

Disease Stage ◽

Animal Models Of Disease ◽

Positron Emission ◽

Neuropsychiatric Diseases ◽

Tspo Expression

AbstractThe 18 kDa translocator protein (TSPO) is a highly conserved protein located in the outer mitochondrial membrane. TSPO binding, as measured with positron emission tomography (PET), is considered an in vivo marker of neuroinflammation. Indeed, TSPO expression is altered in neurodegenerative, neuroinflammatory, and neuropsychiatric diseases. In PET studies, the TSPO signal is often viewed as a marker of microglial cell activity. However, there is little evidence in support of a microglia-specific TSPO expression. This review describes the cellular sources and functions of TSPO in animal models of disease and human studies, in health, and in central nervous system diseases. A discussion of methods of analysis and of quantification of TSPO is also presented. Overall, it appears that the alterations of TSPO binding, their cellular underpinnings, and the functional significance of such alterations depend on many factors, notably the pathology or the animal model under study, the disease stage, and the involved brain regions. Thus, further studies are needed to fully determine how changes in TSPO binding occur at the cellular level with the ultimate goal of revealing potential therapeutic pathways.

Download Full-text

Effects of Translocator Protein (18 kDa) Ligands on Microglial Activation and Neuronal Death in the Quinolinic-Acid-Injected Rat Striatum

ACS Chemical Neuroscience ◽

10.1021/cn200099e ◽

2012 ◽

Vol 3 (2) ◽

pp. 114-119 ◽

Cited By ~ 29

Author(s):

Katherine R. Leaver ◽

Aaron Reynolds ◽

Sylvie Bodard ◽

Denis Guilloteau ◽

Sylvie Chalon ◽

...

Keyword(s):

Quinolinic Acid ◽

Neuronal Death ◽

Microglial Activation ◽

Translocator Protein ◽

Rat Striatum ◽

Translocator Protein 18 Kda

Download Full-text

Development of a 18F-Labeled Radiotracer with Improved Brain Kinetics for Positron Emission Tomography Imaging of Translocator Protein (18 kDa) in Ischemic Brain and Glioma

Journal of Medicinal Chemistry ◽

10.1021/acs.jmedchem.7b00374 ◽

2017 ◽

Vol 60 (9) ◽

pp. 4047-4061 ◽

Cited By ~ 13

Author(s):

Masayuki Fujinaga ◽

Rui Luo ◽

Katsushi Kumata ◽

Yiding Zhang ◽

Akiko Hatori ◽

...

Keyword(s):

Positron Emission Tomography ◽

Positron Emission Tomography Imaging ◽

Translocator Protein ◽

Emission Tomography ◽

Ischemic Brain ◽

Tomography Imaging ◽

Positron Emission ◽

Translocator Protein 18 Kda

Download Full-text

Synthesis and Evaluation of [18F]FEtLos and [18F]AMBF3Los as Novel 18F-Labelled Losartan Derivatives for Molecular Imaging of Angiotensin II Type 1 Receptors

Molecules ◽

10.3390/molecules25081872 ◽

2020 ◽

Vol 25 (8) ◽

pp. 1872

Author(s):

Martha Sahylí Ortega Pijeira ◽

Paulo Sérgio Gonçalves Nunes ◽

Sofia Nascimento dos Santos ◽

Zhengxing Zhang ◽

Arian Pérez Nario ◽

...

Keyword(s):

Angiotensin Ii ◽

Binding Affinity ◽

Renin Angiotensin System ◽

Prosthetic Group ◽

Positron Emission ◽

One Step ◽

Group 2

Losartan is widely used in clinics to treat cardiovascular related diseases by selectively blocking the angiotensin II type 1 receptors (AT1Rs), which regulate the renin-angiotensin system (RAS). Therefore, monitoring the physiological and pathological biodistribution of AT1R using positron emission tomography (PET) might be a valuable tool to assess the functionality of RAS. Herein, we describe the synthesis and characterization of two novel losartan derivatives PET tracers, [18F]fluoroethyl-losartan ([18F]FEtLos) and [18F]ammoniomethyltrifluoroborate-losartan ([18F]AMBF3Los). [18F]FEtLos was radiolabeled by 18F-fluoroalkylation of losartan potassium using the prosthetic group 2-[18F]fluoroethyl tosylate; whereas [18F]AMBF3Los was prepared following an one-step 18F-19F isotopic exchange reaction, in an overall yield of 2.7 ± 0.9% and 11 ± 4%, respectively, with high radiochemical purity (>95%). Binding competition assays in AT1R-expressing membranes showed that AMBF3Los presented an almost equivalent binding affinity (Ki 7.9 nM) as the cold reference Losartan (Ki 1.5 nM), unlike FEtLos (Ki 2000 nM). In vitro and in vivo assays showed that [18F]AMBF3Los displayed a good binding affinity for AT1R-overexpressing CHO cells and was able to specifically bind to renal AT1R. Hence, our data demonstrate [18F]AMBF3Los as a new tool for PET imaging of AT1R with possible applications for the diagnosis of cardiovascular, inflammatory and cancer diseases.

Download Full-text

PET Imaging of [11C]MPC-6827, a Microtubule-Based Radiotracer in Non-Human Primate Brains

Molecules ◽

10.3390/molecules25102289 ◽

2020 ◽

Vol 25 (10) ◽

pp. 2289

Author(s):

Naresh Damuka ◽

Paul Czoty ◽

Ashley Davis ◽

Michael Nader ◽

Susan Nader ◽

...

Keyword(s):

Pet Imaging ◽

Neurological Disorders ◽

Healthy Male ◽

Time Activity ◽

Positron Emission ◽

Pet Ct ◽

Scan Data ◽

The Brain ◽

Human Primate

Dysregulation of microtubules is commonly associated with several psychiatric and neurological disorders, including addiction and Alzheimer’s disease. Imaging of microtubules in vivo using positron emission tomography (PET) could provide valuable information on their role in the development of disease pathogenesis and aid in improving therapeutic regimens. We developed [11C]MPC-6827, the first brain-penetrating PET radiotracer to image microtubules in vivo in the mouse brain. The aim of the present study was to assess the reproducibility of [11C]MPC-6827 PET imaging in non-human primate brains. Two dynamic 0–120 min PET/CT imaging scans were performed in each of four healthy male cynomolgus monkeys approximately one week apart. Time activity curves (TACs) and standard uptake values (SUVs) were determined for whole brains and specific regions of the brains and compared between the “test” and “retest” data. [11C]MPC-6827 showed excellent brain uptake with good pharmacokinetics in non-human primate brains, with significant correlation between the test and retest scan data (r = 0.77, p = 0.023). These initial evaluations demonstrate the high translational potential of [11C]MPC-6827 to image microtubules in the brain in vivo in monkey models of neurological and psychiatric diseases.

Download Full-text

Noninvasive quantification of macrophagic lung recruitment during experimental ventilation-induced lung injury

Journal of Applied Physiology ◽

10.1152/japplphysiol.00825.2018 ◽

2019 ◽

Vol 127 (2) ◽

pp. 546-558

Author(s):

Laurent Bitker ◽

Nicolas Costes ◽

Didier Le Bars ◽

Franck Lavenne ◽

Maciej Orkisz ◽

...

Keyword(s):

Lung Injury ◽

Protective Ventilation ◽

Lung Recruitment ◽

Translocator Protein ◽

Emission Tomography ◽

Dynamic Strain ◽

Lung Uptake ◽

Positron Emission ◽

Ventilation Induced Lung Injury

Macrophagic lung infiltration is pivotal in the development of lung biotrauma because of ventilation-induced lung injury (VILI). We assessed the performance of [11C](R)-PK11195, a positron emission tomography (PET) radiotracer binding the translocator protein, to quantify macrophage lung recruitment during experimental VILI. Pigs ( n = 6) were mechanically ventilated under general anesthesia, using protective ventilation settings (baseline). Experimental VILI was performed by titrating tidal volume to reach a transpulmonary end-inspiratory pressure (∆PL) of 35–40 cmH2O. We acquired PET/computed tomography (CT) lung images at baseline and after 4 h of VILI. Lung macrophages were quantified in vivo by the standardized uptake value (SUV) of [11C](R)-PK11195 measured in PET on the whole lung and in six lung regions and ex vivo on lung pathology at the end of experiment. Lung mechanics were extracted from CT images to assess their association with the PET signal. ∆PL increased from 9 ± 1 cmH2O under protective ventilation, to 36 ± 6 cmH2O during experimental VILI. Compared with baseline, whole-lung [11C](R)-PK11195 SUV significantly increased from 1.8 ± 0.5 to 2.9 ± 0.5 after experimental VILI. Regional [11C](R)-PK11195 SUV was positively associated with the magnitude of macrophage recruitment in pathology ( P = 0.03). Compared with baseline, whole-lung CT-derived dynamic strain and tidal hyperinflation increased significantly after experimental VILI, from 0.6 ± 0 to 2.0 ± 0.4, and 1 ± 1 to 43 ± 19%, respectively. On multivariate analysis, both were significantly associated with regional [11C](R)-PK11195 SUV. [11C](R)-PK11195 lung uptake (a proxy of lung inflammation) was increased by experimental VILI and was associated with the magnitude of dynamic strain and tidal hyperinflation. NEW & NOTEWORTHY We assessed the performance of [11C](R)-PK11195, a translocator protein-specific positron emission tomography (PET) radiotracer, to quantify macrophage lung recruitment during experimental ventilation-induced lung injury (VILI). In this proof-of-concept study, we showed that the in vivo quantification of [11C](R)-PK11195 lung uptake in PET reflected the magnitude of macrophage lung recruitment after VILI. Furthermore, increased [11C](R)-PK11195 lung uptake was associated with harmful levels of dynamic strain and tidal hyperinflation applied to the lungs.

Download Full-text