Johnny Vercouillie

Initial evaluation in healthy humans of [18F]DPA-714, a potential PET biomarker for neuroinflammation

INTRODUCTION The translocator protein 18 kDa (TSPO), although minimally expressed in healthy brain, is up-regulated in pathological conditions, coinciding with microglial activation. It is thereby a suitable in vivo biomarker of neuroinflammation for detection, evaluation and therapeutic monitoring of brain diseases. We aimed to estimate the radiation dosimetry of the positron emission tomography (PET) TSPO radioligand [(18)F]DPA-714, and we evaluated in healthy volunteers its whole-body uptake and cerebral kinetics. METHODS Biodistribution data from mice were used for the prediction of radiation dosimetry. In human studies, a 90-min dynamic PET scan was performed in seven healthy volunteers after injection of [(18)F]DPA-714 (245±45 MBq). Arterial and venous samples were collected from two subjects, and two additional subjects were submitted to whole-body acquisition. Regions of interest were defined over cerebral structures to obtain mean time-activity curves and to estimate the distribution volume ratios by Logan graphical analysis, and over peripheral organs to obtain standard uptake values. RESULTS The effective dose estimated from biodistribution in mice was 17.2 μSv/MBq. Modeling of regional brain and plasma data showed good in vivo stability of [(18)F]DPA-714 in humans, with only 20% of blood metabolites 20 min postinjection (p.i.). Maximum cerebral uptake was observed 5 min p.i., followed by two decreasing phases: a rapid washout (5-30 min) followed by a slower phase for the remainder of PET acquisition. Whole-body images demonstrate high activity in the gallbladder, heart, spleen and kidneys. CONCLUSIONS This initial study in humans shows that [(18)F]DPA-714 is a promising PET radioligand with excellent in vivo stability and biodistribution, and acceptable effective dose estimation. Therefore, [(18)F]DPA-714 could provide a sensitive measure of neuroinflammatory changes in subsequent clinical investigations.

Precuneus and Cingulate Cortex Atrophy and Hypometabolism in Patients with Alzheimer’s Disease and Mild Cognitive Impairment: MRI and 18F-FDG PET Quantitative Analysis Using FreeSurfer

Objective. The objective of this study was to compare glucose metabolism and atrophy, in the precuneus and cingulate cortex, in patients with Alzheimers disease (AD) and mild cognitive impairment (MCI), using FreeSurfer. Methods. 47 individuals (17 patients with AD, 17 patients with amnestic MCI, and 13 healthy controls (HC)) were included. MRI and PET images using 18F-FDG (mean injected dose of 185 MBq) were acquired and analyzed using FreeSurfer to define regions of interest in the hippocampus, amygdala, precuneus, and anterior and posterior cingulate cortex. Regional volumes were generated. PET images were registered to the T1-weighted MRI images and regional uptake normalized by cerebellum uptake (SUVr) was measured. Results. Mean posterior cingulate volume was reduced in MCI and AD. SUVr were different between the three groups: mean precuneus SUVr was 1.02 for AD, 1.09 for MCI, and 1.26 for controls (p < 0.05); mean posterior cingulate SUVr was 0.96, 1.06, and 1.22 for AD, MCI, and controls, respectively (p < 0.05). Conclusion. We found graduated hypometabolism in the posterior cingulate cortex and the precuneus in prodromal AD (MCI) and AD, whereas atrophy was not significant. This suggests that the use of 18F-FDG in these two regions could be a neurodegenerative biomarker.

Neuroimaging of the vesicular acetylcholine transporter by a novel 4-[18F]fluoro-benzoyl derivative of 7-hydroxy-6-(4-phenyl-piperidin-1-yl)-octahydro-benzo[1,4]oxazines

Phenylpiperidinyl-octahydro-benzo[1,4]oxazines represent a new class of conformationally restrained vesamicol analogues. Derived from this morpholine-fused vesamicol structure, a new fluorine-18-labeled 4-fluorobenzoyl derivative ([(18)F]FBMV) was synthesized with an average specific activity of 75 GBq/micromol and a radiochemical purity of 99%. The radiolabeling method included an exchange reaction of a 4-nitro group of the precursor by fluorine-18, a reduction procedure to eliminate excess of the nitro compound, followed by a high-performance liquid chromatography purification. [(18)F]FBMV demonstrates (i) a moderate lipophilic character with a logD(pH7.0) 1.8+/-0.10; (ii) a considerable binding affinity to the vesicular acetylcholine transporter (VAChT) (K(i)=27.5 nM), as determined using PC12 cells transfected with a VAChT cDNA, and a low affinity to sigma(1,2) receptors (K(i) >3000 nM); (iii) a good uptake into the rat and pig brains; (iv) a typical accumulation in the VAChT-containing brain regions; and (v) an approximately 20% reduction in cortical tracer binding after a specific cholinergic lesion using 192IgG-saporin. [(18)F]FBMV exhibits another PET marker within the group of vesamicol derivatives that demonstrates potentials in imaging brain cholinergic deficits, while its usefulness in clinical practice must await further investigation.

Amyloid load and translocator protein 18 kDa in APPswePS1-dE9 mice: a longitudinal study.

We studied concomitantly the level of neuroinflammation and β-amyloid (Aβ) load in the APPswePS1dE9 transgenic mouse model of Alzheimers disease using positron emission tomography. The translocator protein 18 kDa (TSPO) tracer [(18)F]DPA-714 was used to measure neuroinflammation and [(18)F]AV-45 for Aβ load in mice at 6, 9, 12, 15, and 19 months of age. At 19 months, we also analyzed the neuroinflammatory and neuroanatomic status of mice brains. The main affected brain areas were the cortex and hippocampus, with a concomitant progression of neuroinflammation with increased amyloid burden. At 19 months, no increase in TSPO binding was observed in the cerebellum; immunostaining revealed W0-2-positive plaques, indicating that the amyloid deposits seemed not stimulate inflammation. This finding was in agreement with the observed level of microglia and astrocytes staining. Our findings provide a better understanding of the relationships between neuroinflammation and plaque accumulation in the course of the disease in this mouse model. The monitoring of both processes should be of value to validate potential therapeutic approaches.

EANM guideline for the preparation of an Investigational Medicinal Product Dossier (IMPD)

The preparation of an Investigational Medicinal Product Dossier (IMPD) for a radiopharmaceutical to be used in a clinical trial is a challenging proposition for radiopharmaceutical scientists working in small-scale radiopharmacies. In addition to the vast quantity of information to be assembled, the structure of a standard IMPD is not well suited to the special characteristics of radiopharmaceuticals. This guideline aims to take radiopharmaceutical scientists through the practicalities of preparing an IMPD, in particular giving advice where the standard format is not suitable. Examples of generic IMPDs for three classes of radiopharmaceuticals are given: a small molecule, a kit-based diagnostic test and a therapeutic radiopharmaceutical.

Brain [18F]FDDNP binding and glucose metabolism in advanced elderly healthy subjects and Alzheimer's disease patients.

BACKGROUND Positron emission tomography (PET) imaging of brain amyloid (Aβ) and neurofibrillary tangle (NFT) load is a candidate biomarker of Alzheimers disease (AD). OBJECTIVES To compare brain Aβ and NFT load and glucose metabolism in advanced elderly (70 years and older) patients with AD and healthy controls (HCs) by PET with [18F]FDDNP and [18F]FDG. METHODS Seven AD patients (mean ± SD age 79.3 ± 3.6 y, Mini-Mental State Examination (MMSE) score 22.1 ± 2.5) and eight HCs (mean age ± SD, 75.7 ± 3.9 y; MMSE score 29.0 ± 1.2) underwent PET with [18F]FDDNP and [18F]FDG. RESULTS Global [18F]FDDNP uptake was significantly higher (p < 0.05) in AD patients (1.15 ± 0.04) than in HCs (1.10 ± 0.06), while global brain metabolism was lower in AD patients than in HCs (AD patients 0.96 ± 0.09; HCs 1.13 ± 0.11; p < 0.05). In HCs, brain glucose metabolism was correlated with age for both the global [18F]FDG SUVr and in the parietal and posterior cingulate regions, while no correlation was found between age and [18F]FDDNP uptake. In AD patients, global [18F]FDDNP uptake and uptake in the frontal and anterior cingulate regions of interest were correlated with MMSE score, while no correlation was observed with brain glucose metabolism. CONCLUSION Imaging Aβ load and NFT with [18F]FDDNP can distinguish AD patients from HCs in an advanced elderly population. It seems to be less sensitive than [18F]FDG to the brain changes observed with normal aging, but more sensitive to cognitive decline in advanced elderly AD patients.

Assessment of the Protection of Dopaminergic Neurons by an α7 Nicotinic Receptor Agonist, PHA 543613 Using [18F]LBT-999 in a Parkinson’s Disease Rat Model

The inverse association between nicotine intake and Parkinson’s disease (PD) is well established and suggests that this molecule could be neuroprotective through anti-inflammatory action mediated by nicotinic receptors, including the α7-subtype (α7R). The objective of this study was to evaluate the effects of an agonist of α7R, PHA 543613, on striatal dopaminergic neurodegeneration and neuroinflammation in a rat model of PD induced by 6-hydroxydopamine (6-OHDA) lesion. Adult male Wistar rats were lesioned in the right striatum and assigned to either the PHA group (n = 7) or the Sham group (n = 5). PHA 543613 hydrochloride at the concentration of 6 mg/kg (PHA group) or vehicle (Sham group) was intra-peritoneally injected 2 h before 6-OHDA lesioning and then at days 2, 4, and 6 post-lesion. Positron emission tomography (PET) imaging was performed at 7 days post-lesion using [18F]LBT-999 to quantify the striatal dopamine transporter (DAT). After PET imaging, neuroinflammation was evaluated in same animals in vitro through the measurement of the microglial activation marker 18 kDa translocator protein (TSPO) by quantitative autoradiography with [3H]PK-11195. The DAT density reflecting the integrity of dopaminergic neurons was significantly decreased while the intensity of neuroinflammation measured by TSPO density was significantly increased in the lesioned compared to intact striatum in both groups. However, these both modifications were partially reversed in the PHA group compared to Sham. In addition, a significant positive correlation between the degree of lesion and the intensity of neuroinflammation was evidenced. These findings indicate that PHA 543613 exerts neuroprotective effects on the striatal dopaminergic neurons associated with a reduction in microglial activation in this model of PD. This reinforces the hypothesis that an α7R agonist could provide beneficial effects for the treatment of PD.

18F-FDG and 18F-florbetapir PET in clinical practice: regional analysis in mild cognitive impairment and Alzheimer disease.

Objective The aim of this study is to compare regional cerebral metabolic rate of glucose metabolism and amyloid-&bgr; density in patients with Alzheimer disease (AD), mild cognitive impairment (MCI), and healthy elderly subjects. Methods Eighteen patients (including 6 AD, 5 amnestic MCI, and 7 controls) were enrolled at the University Hospital of Tours, France, and submitted to clinical, neuropsychological, and MRI examinations. PET images using 18F-florbetapir (266 MBq) and 18F-FDG (185 MBq) were acquired. SUV ratios in specific regions were defined using PMOD3.2 software. Results The mean values of 18F-FDG SUV ratio were significantly lower in frontal, anterior cingulate, and temporal regions in MCI patients than in normal elderly (−15%, −22%, and −11%, respectively). Alzheimer disease patients showed global cerebral metabolic rate of glucose metabolism decrease, especially in parietal and precuneus regions (−15% and −13% compared with healthy control subjects). Only precuneus cortex showed an increased 18F-florbetapir uptake in AD. There was no other significant regional difference in the amyloid-&bgr; density. Conclusions In this study, we observed regional brain metabolic changes between MCI, AD, and controls, whereas only precuneus showed an increased amyloid-&bgr; density in AD. 18F-florbetapir PET analysis needs to be visual and global, whereas 18F-FDG analysis can be regional.

Design of α7 nicotinic acetylcholine receptor ligands in quinuclidine, tropane and quinazoline series. Chemistry, molecular modeling, radiochemistry, in vitro and in rats evaluations of a [ 18 F] quinuclidine derivative

In this report, we describe the synthesis of a novel library of α7 nAChR ligands based on the modulation of the quinuclidine, quinazoline and tropane moieties. Spirane derivatives were newly synthesized under stereo specific 1,3 dipolar cylcoadditions. Only amide derivatives bonded efficiently to the receptor with Ki measured between 14 and 133 nM. The best fluorinated candidate was selected and radiolabeled. The potent [(18)F]4 PET tracer was evaluated in rats and its brain accumulation quantified.

Design of α7 nicotinic acetylcholine receptor ligands using the (het)Aryl-1,2,3-triazole core: Synthesis, in vitro evaluation and SAR studies

We report here the synthesis of a large library of 1,2,3-triazole derivatives which were in vitro tested as α7 nAchR ligands. The SAR study revealed that several crucial factors are involved in the affinity of these compounds for α7 nAchR such as a (R) quinuclidine configuration and a mono C-3 quinuclidine substitution. The triazole ring was substituted by a phenyl ring bearing small OMe/CH2F groups or fluorine atom and by several heterocycles such as thiophenes, furanes, benzothiophenes or benzofuranes. Among the 30 derivatives tested, the two derivatives 10 and 39 with Ki in the nanomolar range were identified (2.3 and 3 nM respectively). They exhibited a strict selectivity toward the α4β2 nicotinic receptor (up to 1 μM) but interacted with the 5HT3 receptors with Ki around 3 nM. Synthesis, SAR studies and a full description of the derivatives are reported.