Lieven Declercq

Neuroinflammation is important in Amyotrophic Lateral Sclerosis (ALS). The P2X7 receptor (P2X7R) is a promising target for neuroinflammation. The objective was to compare 18F-DPA714, a second generation translocator protein tracer, with 11C-JNJ717, a novel P2X7R tracer, in vitro and in vivo in ALS. Methods: In vitro : Autoradiography with 18F-DPA714 and 11C-JNJ717 was performed on human ALS brain sections in comparison to immunofluorescence with Iba1 and GFAP. In vivo : Three early stage ALS… Show more

Neuroinflammation is important in Amyotrophic Lateral Sclerosis (ALS). The P2X7 receptor (P2X7R) is a promising target for neuroinflammation. The objective was to compare 18F-DPA714, a second generation translocator protein tracer, with 11C-JNJ717, a novel P2X7R tracer, in vitro and in vivo in ALS. Methods: In vitro : Autoradiography with 18F-DPA714 and 11C-JNJ717 was performed on human ALS brain sections in comparison to immunofluorescence with Iba1 and GFAP. In vivo : Three early stage ALS patients (59.3±7.2y,3M) and 6 HV (48.2±16.5,2M) underwent dynamic PET-MR scanning with 18F-DPA714 and 11C-JNJ717. VT images were calculated using Logan plot and analysed on VOI basis. Results: Autoradiography showed no difference in 11C-JNJ717 binding, but increased 18F-DPA714 binding in motor cortex correlating with Iba1 expression (glial cells). Similar findings were observed in vivo with a 13% increased 18F-DPA714 binding in motor cortex. Conclusion: In symptomatic ALS patients, 18F-DPA714 showed increased signal while 11C-JNJ717 was not elevated. Show less

In Alzheimer’s disease, the density and spread of aggregated tau protein tracks well with neurodegeneration and cognitive decline, making the imaging of aggregated tau a compelling biomarker. A SAR exploration around an isoquinoline hit, followed by an exploration of tolerated fluorination positions allowed us to identify 9 (JNJ-64326067), a potent and selective binder to aggregated tau with a favorable PK profile and no apparent off-target binding. This was confirmed in rat and monkey PET… Show more

In Alzheimer’s disease, the density and spread of aggregated tau protein tracks well with neurodegeneration and cognitive decline, making the imaging of aggregated tau a compelling biomarker. A SAR exploration around an isoquinoline hit, followed by an exploration of tolerated fluorination positions allowed us to identify 9 (JNJ-64326067), a potent and selective binder to aggregated tau with a favorable PK profile and no apparent off-target binding. This was confirmed in rat and monkey PET studies using [18F]9. Show less

To assess the binding of the PET tracer [18F]THK5351 in patients with different primary progressive aphasia (PPA) variants and its correlation with clinical deficits. The majority of patients with nonfluent variant (NFV) and logopenic variant (LV) PPA have underlying tauopathy of the frontotemporal lobar or Alzheimer disease type, respectively, while patients with the semantic variant (SV) have predominantly transactive response DNA binding protein 43-kDa pathology.

MAGL is a potential therapeutic target for oncological and psychiatric diseases. Our objective was to develop a PET tracer for in vivo quantification of MAGL. We report [¹¹C]MA-PB-1 as an irreversible MAGL inhibitor PET tracer. The in vitro inhibitory activity, ex vivo distribution, brain kinetics and specificity of [¹¹C]MA-PB-1 binding were studied. Ex vivo biodistribution and microPET showed good brain uptake which could be blocked by pretreatment with both MA-PB-1 and a structurally… Show more

MAGL is a potential therapeutic target for oncological and psychiatric diseases. Our objective was to develop a PET tracer for in vivo quantification of MAGL. We report [¹¹C]MA-PB-1 as an irreversible MAGL inhibitor PET tracer. The in vitro inhibitory activity, ex vivo distribution, brain kinetics and specificity of [¹¹C]MA-PB-1 binding were studied. Ex vivo biodistribution and microPET showed good brain uptake which could be blocked by pretreatment with both MA-PB-1 and a structurally non-related MAGL inhibitor MJN110. These initial results suggest that [¹¹C]MA-PB-1 is a suitable tracer for in vivo imaging of MAGL. Show less

Purpose:
Activation of the innate immune system plays a significant role in pathologies of the central nervous system (CNS). In order to follow disease progression and evaluate effectiveness of potential treatments involved in neuroinflammation, it is important to track neuroinflammatory markers in vivo longitudinally. The translocator protein (TSPO) is used as a target to image neuroinflammation as its expression is upregulated in reactive glial cells during CNS pathologies. However, it… Show more

Purpose:
Activation of the innate immune system plays a significant role in pathologies of the central nervous system (CNS). In order to follow disease progression and evaluate effectiveness of potential treatments involved in neuroinflammation, it is important to track neuroinflammatory markers in vivo longitudinally. The translocator protein (TSPO) is used as a target to image neuroinflammation as its expression is upregulated in reactive glial cells during CNS pathologies. However, it remains unclear in which microglial phenotypes TSPO levels are upregulated, as microglia can display a plethora of activation states that can be protective or detrimental to the CNS.

Procedures:
We assessed the levels of TSPO transcripts in cultured microglia that were polarized into pro- and anti-inflammatory states in vitro and in the brain of mice in which an anti-inflammatory environment was induced in vivo. In addition, we used a mouse model of peroxisomal multifunctional protein-2 (MFP2) deficiency that exhibits widespread neuroinflammation despite no neuronal loss and monitored TSPO expression by immunohistochemistry and by imaging using the TSPO radiotracer [18F]DPA-714.

Results:
TSPO expression was selectively increased in so-called classically activated or M1 microglia but not in alternatively activated or M2 microglia in vitro. In agreement, TSPO transcript levels were not induced in an anti-inflammatory brain environment. We found that both transcript and protein levels of TSPO are significantly increased in the brain of Mfp2−/− compared to those of the control mice and TSPO immunoreactivity colocalized predominantly with microglia in Mfp2−/− brain. In vitro and ex vivo autoradiography in Mfp2−/− mice using the TSPO radiotracer [18F]DPA-714 confirmed increased expression of TSPO. These data demonstrate that TSPO imaging reveals microgliosis in non-neurodegenerative brain pathologies. Show less

In this study we have synthesized and evaluated 18F-JNJ64349311, a tracer with high affinity for aggregated tau and high in vitro selectivity for tau over β-amyloid, in comparison with the benchmark compound 18F-AV1451 in mice, rats and a rhesus monkey. Methods: Using autoradiography studies in vitro binding characteristics were determined on Alzheimer’s disease (AD), Progressive supranuclear palsy (PSP) and Corticobasal degeneration (CBD) patient brain tissue slices. Ex vivo biodistribution… Show more

In this study we have synthesized and evaluated 18F-JNJ64349311, a tracer with high affinity for aggregated tau and high in vitro selectivity for tau over β-amyloid, in comparison with the benchmark compound 18F-AV1451 in mice, rats and a rhesus monkey. Methods: Using autoradiography studies in vitro binding characteristics were determined on Alzheimer’s disease (AD), Progressive supranuclear palsy (PSP) and Corticobasal degeneration (CBD) patient brain tissue slices. Ex vivo biodistribution studies were performed in mice. Radiometabolites were quantified in brain and plasma of mice and in plasma of a rhesus monkey using high performance liquid chromatography. Dynamic micro positron-emission tomography (µPET) studies were performed in rats and in a rhesus monkey to evaluate tracer pharmacokinetics in brain. Results: Mouse biodistribution studies showed moderate initial brain uptake and rapid brain wash-out. Radiometabolite analyses after injection of 18F-JNJ64349311 in mice showed the presence of a polar radiometabolite in plasma, but not in brain. Semi-quantitative autoradiography studies on post-mortem tissue sections of human AD brains showed highly displaceable binding to tau-rich regions. No specific binding was, however, found on human PSP and CBD brain slices. µPET-scans on Wistar rats revealed moderate initial brain uptake (standardized uptake value, SUV of ~ 1.5 at 1 min p.i.) and rapid brain wash-out. Gradual bone uptake was, however, also observed. Blocking and displacement did not affect brain time-activity curves, suggesting no off-target specific binding of the tracer in healthy rat brain. A µPET scan on a rhesus monkey revealed moderate initial brain uptake (SUV of 1.9 at 1 min p.i.) with a rapid wash-out. In monkey, no bone uptake was detected during the 120-min scan. Conclusion: This biological evaluation suggests that 18F-JNJ64349311 is a promising tau PET tracer candidate, with a favourable pharmacokinetic profile as compared to 18F-AV1451. Show less

Clinical trials aiming to develop disease-altering drugs for Alzheimer’s disease (AD), a neurodegenerative disorder with devastating consequences, are failing at an alarming rate. Poorly defined inclusion-and outcome criteria, due to a limited amount of objective biomarkers, is one of the major concerns. Non-invasive molecular imaging techniques, positron emission tomography and single photon emission (computed) tomography (PET and SPE(C)T), allow visualization and quantification of a wide… Show more

Clinical trials aiming to develop disease-altering drugs for Alzheimer’s disease (AD), a neurodegenerative disorder with devastating consequences, are failing at an alarming rate. Poorly defined inclusion-and outcome criteria, due to a limited amount of objective biomarkers, is one of the major concerns. Non-invasive molecular imaging techniques, positron emission tomography and single photon emission (computed) tomography (PET and SPE(C)T), allow visualization and quantification of a wide variety of (patho)physiological processes and allow early (differential) diagnosis in many disorders. PET and SPECT have the ability to provide biomarkers that permit spatial assessment of pathophysiological molecular changes and therefore objectively evaluate and follow up therapeutic response, especially in the brain. A number of specific PET/SPECT biomarkers used in support of emerging clinical therapies in AD are discussed in this review. Show less

Early clinical results of two tau tracers, [18F]T808 and [18F]T807, have recently been reported. In the present study, the biodistribution, radiometabolite quantification, and competition-binding studies were performed in order to acquire comparative preclinical data as well as to establish the value of T808 and T807 as benchmark compounds for assessment of binding affinities of eight new/other tau tracers. Biodistribution studies in mice showed high brain uptake and fast washout. In vivo… Show more

Early clinical results of two tau tracers, [18F]T808 and [18F]T807, have recently been reported. In the present study, the biodistribution, radiometabolite quantification, and competition-binding studies were performed in order to acquire comparative preclinical data as well as to establish the value of T808 and T807 as benchmark compounds for assessment of binding affinities of eight new/other tau tracers. Biodistribution studies in mice showed high brain uptake and fast washout. In vivo radiometabolite analysis using high-performance liquid chromatography showed the presence of polar radiometabolites in plasma and brain. No specific binding of [18F]T808 was found in transgenic mice expressing mutant human P301L tau. In semiquantitative autoradiography studies on human Alzheimer disease slices, we observed more than 50% tau selective blocking of [18F]T808 in the
presence of 1 mmol/L of the novel ligands. This study provides a straightforward comparison of the binding affinity and selectivity for tau of the reported radiolabeled tracers BF-158, BF-170, THK5105, lansoprazole, astemizole, and novel tau positron emission tomography ligands against T807 and T808. Therefore, these data are helpful to identify structural requirements for selective interaction with tau and to compare the performance of new highly selective and specific radiolabeled tau tracers. Show less

As [(18)F]fluoride is a starting reagent in the radiosynthesis of most fluorine-18 labeled positron emission tomography (PET) tracers, its chromatographic behavior on reversed phase (RP) HPLC columns is important for the purification performance and accuracy of RP HPLC quality control methods. We have investigated the chromatographic behavior and recovery of [(18)F]fluoride as a function of the type and brand of RP HPLC column, the pH and the composition of the mobile phase. Elution and elution… Show more

As [(18)F]fluoride is a starting reagent in the radiosynthesis of most fluorine-18 labeled positron emission tomography (PET) tracers, its chromatographic behavior on reversed phase (RP) HPLC columns is important for the purification performance and accuracy of RP HPLC quality control methods. We have investigated the chromatographic behavior and recovery of [(18)F]fluoride as a function of the type and brand of RP HPLC column, the pH and the composition of the mobile phase. Elution and elution profile of [(18)F]fluoride from six RP-HPLC columns (Waters XBridge C18 3 mm × 100 mm 3.5 μm; Grace Platinum EPS C18 4.6 mm × 100 mm, 3 μm; Waters XTerra C18 4.6 mm × 250 mm, 5 μm; Phenomenex C18 4.6 mm × 150 mm, 5 μm; Hamilton PRP-1 column 4.1 mm × 150 mm, 5 μm; Merck KGaA Chromolith Performance C18 3 mm × 100 mm) eluted with mobile phase composed of phosphate or acetate buffers (pH 2, 3, 4, 5, 7.3 and 9) and acetonitrile or ethanol as organic modifier were characterized. The elution profile was determined by on-line radioactivity measurement in the column eluate and recovery was calculated by comparison of radioactivity eluted with the HPLC column present or absent in the chromatographic flow path. Interestingly, [(18)F]fluoride recovery increased with increasing pH. At pH 3 all packed silica-based columns showed significant retention of fluorine-18, whereas almost no retention was observed on a polymeric PRP-1 column. However at pH 5, [(18)F]fluoride recovery was above 90% for each tested column. In addition, small differences were observed when changing the composition of the mobile phase. We therefore recommend to use a mobile phase with pH > 5 for silica based C18 columns for both quality control and semi-preparative HPLC of fluorine-18 labeled PET radiopharmaceuticals. If required a lower pH can be used in combination with a polymer based HPLC column. Show less