Imaging of dopamine transporter with [18F]LBT-999: initial evaluation in healthy volunteers.

BACKGROUND: The aim of this study was to evaluate in healthy human brain the distribution, uptake, and kinetics of [18F]LBT-999, a PET ligand targeting the dopamine transporter, to assess its ability to explore dopaminergic innervation, using a shorter protocol, more convenient for patients than currently with [123I]ioflupane. METHODS: After intravenous injection of [18F]LBT-999, 8 healthy subjects (53-80y) underwent a dynamic PET-scan. Venous samples were concomitantly obtained for metabolites analysis. Time activity curves (TACs) were generated for several ROIs (caudate, putamen, occipital cortex, substantia nigra and cerebellum). Cerebellum was used as reference region to calculate binding potentials (BPND). RESULTS: No adverse events or detectable pharmacological effects were reported. [18F]LBT-999 PET revealed a good cerebral distribution, with an intense and symmetric uptake in both putamen and caudate (BPND of 6.75±1.17 and 6.30±1.17, respectively), without other brain abnormal tracer accumulation. Regional TACs showed a plateau from the maximal uptake, 20min pi, to the end of the acquisition for both caudate and putamen, whereas uptake in substantia nigra decreased progressively. A faster clearance and lowest BPND values were observed in both cortex and cerebellum. Ratios to the cerebellum exhibit value of about 3 in substantia nigra, close to 10 for both caudate and putamen, and remained around the value of 1 in cortex. The parent fraction of [18F]LBT-999 in plasma was 80%, 60% and 45% at 15, 30 and 45 min pi, respectively. CONCLUSIONS: These findings support the usefulness of [18F]LBT-999 for a quantitative clinical evaluation of presynaptic dopaminergic innervation.

Design of selective COX-2 inhibitors in the (aza)indazole series. Chemistry, in vitro studies, radiochemistry and evaluations in rats of a [18F] PET tracer.

A series of novel derivatives exhibiting high affinity and selectivity towards the COX-2 enzyme in the (aza) indazole series was developed. A short synthetic route involving a bromination/arylation sequence under microwave irradiation and direct C-H activation were established in the indazole and azaindazole series respectively. In vitro assays were conducted and structural modifications were carried out on these scaffolds to furnish compound 16 which exhibited effective COX-2 inhibitory activity, with IC50 values of 0.409 µM and an excellent selectivity versus COX-1. Radiolabeling of this most potent derivative [18F]16 was achieved after boron ester release and the tracer was evaluated in vivo in a rat model of neuroinflammation. All chemistry, radiochemistry and biological experimental data are discussed.

Subjective cognitive decline in cognitively normal elders from the community or from a memory clinic: Differential affective and imaging correlates.

INTRODUCTION: Subjective cognitive decline (SCD) could indicate preclinical Alzheimer's disease, but the existing literature is confounded by heterogeneous approaches to studying SCD. We assessed the differential cognitive, affective, and neuroimaging correlates of two aspects of SCD: reporting high cognitive difficulties on a self-rated questionnaire versus consulting at a memory clinic. METHODS: We compared 28 patients from a memory clinic with isolated SCD, 35 community-recruited elders with similarly high levels of self-reported cognitive difficulties, and 35 community-recruited controls with low self-reported cognitive difficulties. RESULTS: Increased anxiety and amyloid ß deposition were observed in both groups with high self-reported difficulties, whereas subclinical depression and (hippocampal) atrophy were specifically associated with medical help seeking. Cognitive tests showed no group differences. DISCUSSION: These results further validate the concept of SCD in both community- and clinic-based groups. Yet, recruitment methods influence associated biomarkers and affective symptomatology, highlighting the heterogeneous nature of SCD depending on study characteristics.

Molecular Targets for PET Imaging of Activated Microglia: The Current Situation and Future Expectations.

Microglia, as cellular mediators of neuroinflammation, are implicated in the pathogenesis of a wide range of neurodegenerative diseases. Positron emission tomography (PET) imaging of microglia has matured over the last 20 years, through the development of radiopharmaceuticals targeting several molecular biomarkers of microglial activation and, among these, mainly the translocator protein-18 kDa (TSPO). Nevertheless, current limitations of TSPO as a PET microglial biomarker exist, such as low brain density, even in a neurodegenerative setting, expression by other cells than the microglia (astrocytes, peripheral macrophages in the case of blood brain barrier breakdown), genetic polymorphism, inducing a variation for most of TSPO PET radiopharmaceuticals' binding affinity, or similar expression in activated microglia regardless of its polarization (pro- or anti-inflammatory state), and these limitations narrow its potential interest. We overview alternative molecular targets, for which dedicated radiopharmaceuticals have been proposed, including receptors (purinergic receptors P2X7, cannabinoid receptors, α7 and α4ß2 nicotinic acetylcholine receptors, adenosine 2A receptor, folate receptor ß) and enzymes (cyclooxygenase, nitric oxide synthase, matrix metalloproteinase, ß-glucuronidase, and enzymes of the kynurenine pathway), with a particular focus on their respective contribution for the understanding of microglial involvement in neurodegenerative diseases. We discuss opportunities for these potential molecular targets for PET imaging regarding their selectivity for microglia expression and polarization, in relation to the mechanisms by which microglia actively participate in both toxic and neuroprotective actions in brain diseases, and then take into account current clinicians' expectations.

Translocator Protein-18 kDa (TSPO) Positron Emission Tomography (PET) Imaging and Its Clinical Impact in Neurodegenerative Diseases.

In vivo exploration of activated microglia in neurodegenerative diseases is achievable by Positron Emission Tomography (PET) imaging, using dedicated radiopharmaceuticals targeting the translocator protein-18 kDa (TSPO). In this review, we emphasized the major advances made over the last 20 years, thanks to TSPO PET imaging, to define the pathophysiological implication of microglia activation and neuroinflammation in neurodegenerative diseases, including Parkinson's disease, Huntington's disease, dementia, amyotrophic lateral sclerosis, multiple sclerosis, and also in psychiatric disorders. The extent and upregulation of TSPO as a molecular biomarker of activated microglia in the human brain is now widely documented in these pathologies, but its significance, and especially its protective or deleterious action regarding the disease's stage, remains under debate. Thus, we exposed new and plausible suggestions to enhance the contribution of TSPO PET imaging for biomedical research by exploring microglia's role and interactions with other cells in brain parenchyma. Multiplex approaches, associating TSPO PET radiopharmaceuticals with other biomarkers (PET imaging of cellular metabolism, neurotransmission or abnormal protein aggregates, but also other imaging modalities, and peripheral cytokine levels measurement and/or metabolomics analysis) was considered. Finally, the actual clinical impact of TSPO PET imaging as a routine biomarker of neuroinflammation was put into perspective regarding the current development of diagnostic and therapeutic strategies for neurodegenerative diseases.

Detection of Neuroinflammation in a Rat Model of Subarachnoid Hemorrhage Using [18F]DPA-714 PET Imaging.

Subarachnoid hemorrhage (SAH) can lead to delayed cerebral ischemia, which increases the rate of morbidity and mortality. The detection of microglial activation may serve as a biomarker for the identification of patients at risk of this deleterious consequence. We assessed this hypothesis in a rat model of SAH in which the exploration of neuroinflammation related to microglial activation was correlated with the degree of bleeding. We used the rat filament model and evaluated (at 48 hours postsurgery) the intensity of neuroinflammation using positron emission tomography (PET) imaging with the 18-kDa translocator protein (TSPO) tracer [(18)F]DPA-714, quantitative autoradiography with [(3)H]PK-11195, and SAH grade by postmortem brain picture. High SAH grades were strongly and positively correlated with in vivo PET imaging of TSPO in the cortex and striatum. In addition, a positive correlation was found in the cortex in TSPO, with densities determined by imaging and autoradiographic approaches. Qualitative immunofluorescence studies indicated that overexpression of TSPO was linked to astrocytic/microglial activation. In this model, PET imaging of TSPO using [(18)F]DPA-714 appeared to be a relevant index of the degree of bleeding, indicating that this imaging method could be used in human patients to improve the management of patients with SAH.

A new (68)Ga anionic concentration and purification method for automated synthesis of [(68)Ga]-DOTA or NODAGA conjugated peptides in high radiochemical purity.

The (68)Ge/(68)Ga generator is of increasing interest for clinical PET. For successful labelling, the eluate has to be purified. The aim of our approach is to improve the existing anionic methods which have a number of advantages compared to other methods but which use high concentrated HCl, and require an additional anionizing step. A new (68)Ga-eluate anionic purification method that enables rapid and high efficiency labelling of DOTA and NODAGA conjugated peptides in high radiochemical purity is described. The new method uses NaCl as an alternative Cl(-) source to the corrosive HCl and combines the three standard steps in a single step. The recovery yield was ≥90%, and the (68)Ge breakthrough was in conformity with the European Pharmacopeia limit. An automated labelling of DOTA and NODAGA-conjugated peptides was performed with the new method, using acetate sodium buffer, with a total duration of 13 min and a radiochemical yield >85%. The labelled peptides have a radiochemical purity exceeding 99% and can be used directly without any further purification step and without the quality control by gas chromatography. Furthermore, the new method has an economic advantage: it offers the possibility to use generator until 20 months after the calibration date.

Translocator protein (18 kDa) mapping with [125I]-CLINDE in the quinolinic acid rat model of excitotoxicity: a longitudinal comparison with microglial activation, astrogliosis, and neuronal death.

Excitotoxicity leads to an inflammatory reaction involving an overexpression of: translocator protein 18 kDa (TSPO) in cerebral microglia and astrocytes. Therefore, we performed ex vivo explorations with [125]-CLINDE, a TSPO-specific radioligand, to follow the time course of TSPO expression, in parallel with lesion progression, over 90 days after induction of cerebral excitotoxicity in rats intrastriatally injected with quinolinic acid. Biodistribution data showed a significant increase in CLINDE uptake on the injured side from 1 days postlesion (dpl); the maximal striatal binding values evidenced a plateau between 7 and 30 dpl. [125I]-CLINDE binding was displaced from the lesion by PK11195, suggesting TSPO specificity. These results were confirmed by ex vivo autoradiography. Combined immunohistochemical studies showed a marked increase in microglial expression in the lesion, peaking at 14 dpl, and astrocytic reactivity enhanced at 7 and 14 dpl, whereas a prominent neuronal cell loss was observed. At 90 dpl, CLINDE binding and immunoreactivity targeting activated microglia, astrogliosis, and neuronal cell density returned to a basal level. These results show that both neuroinflammation and neuronal loss profiles occurred concomitantly and appeared to be transitory processes. These findings provide the possibility of a therapeutic temporal window to compare the differential effects of antiinflammatory treatments in slowing down neurodegeneration in this rodent model, with potential applications to humans.

Region-specific hierarchy between atrophy, hypometabolism, and ß-amyloid (Aß) load in Alzheimer's disease dementia.

Gray matter atrophy, glucose hypometabolism, and ß-amyloid Aß deposition are well-described hallmarks of Alzheimer's disease, but their relationships are poorly understood. The present study aims to compare the local levels of these three alterations in humans with Alzheimer's disease. Structural magnetic resonance imaging, (18)F-fluorodeoxyglucose positron emission tomography (PET), and (18)F-florbetapir PET data from 34 amyloid-negative healthy controls and 20 demented patients with a high probability of Alzheimer's disease etiology (attested using neuroimaging biomarkers as recently recommended) were analyzed. For each patient and imaging modality, age-adjusted Z-score maps were computed, and direct between-modality voxelwise comparison and correlation analyses were performed. Significant differences in the levels of atrophy, hypometabolism, and Aß deposition were found in most brain areas, but the hierarchy differed across regions. A cluster analysis revealed distinct subsets of regions: (1) in the hippocampus, atrophy exceeded hypometabolism, whereas Aß load was minimal; (2) in posterior association areas, Aß deposition was predominant, together with high hypometabolism and lower but still significant atrophy; and (3) in frontal regions, Aß deposition was maximal, whereas structural and metabolic alterations were low. Atrophy and hypometabolism significantly correlated in the hippocampus and temporo-parietal cortex, whereas Aß load was not significantly related to either atrophy or hypometabolism. These findings provide direct evidence for regional variations in the hierarchy and relationships between Aß load, hypometabolism, and atrophy. Altogether, these variations probably reflect the differential involvement of region-specific pathological or protective mechanisms, such as the presence of neurofibrillary tangles, disconnection, as well as compensation processes.

Progressive supranuclear palsy: in vivo SPECT imaging of presynaptic vesicular acetylcholine transporter with [123I]-iodobenzovesamicol.

PURPOSE: To evaluate the integrity of brain cholinergic pathways in vivo in patients with progressive supranuclear palsy (PSP) by measuring the vesicular acetylcholine transporter expression at single photon emission computed tomography (SPECT) with [123I]-iodobenzovesamicol. MATERIALS AND METHODS: All participants provided informed written consent according to institutional human ethics committee guidelines. Ten patients with PSP and 12 healthy volunteers underwent dynamic [123I]-iodobenzovesamicol SPECT and magnetic resonance (MR) imaging. CT and MR images were used to register the dynamic SPECT image to the Montreal Neurologic Institute brain template, which includes the regions of interest of the striatum and the septo-hippocampal, innominato-cortical, and ponto-thalamic cholinergic pathways. For each region of interest, pharmacokinetic modeling of regional time activity curves was used to calculate [123I]-iodobenzovesamicol to vesicular acetylcholine transporter binding potential value, proportional to vesicular acetylcholine transporter expression. RESULTS: When compared with control participants, patients with PSP had binding potential values that were unchanged in the striatum and septohippocampal pathway, significantly lower in the anterior cingulate cortex (P=.017) in the innominatocortical pathway, and significantly decreased in the thalamus (P=.014) in the pontothalamic cholinergic pathway. In addition, binding potential values in the thalamus were positively correlated with those in the pedunculopontine nucleus (ρ=0.81, P<.004) and binding potential values in both the thalamus (ρ=-0.88, P<.001) and pedunculopontine nucleus (ρ=-0.80, P<.010) were inversely correlated with disease duration. CONCLUSION: Cholinergic pathways were differentially affected in the PSP group, with a significant alteration of pontothalamic pathways that increased with disease progression at both cell body and terminal levels, while the innominatocortical pathway was only mildly affected, and the septohippocampal pathway and the striatum were both preserved.

Longitudinal and parallel monitoring of neuroinflammation and neurodegeneration in a 6-hydroxydopamine rat model of Parkinson's disease.

As neuroinflammatory processes are involved in the pathogenesis of Parkinson's disease (PD), we achieved the longitudinal evaluation of them in parallel with the modifications of dopaminergic function at several time-points after 6-hydroxydopamine (6-OHDA) lesion in the rat mimicking an early stage of PD. After unilateral intrastriatal 6-OHDA administration, we quantified the temporal evolution of the 18 kDa translocator protein (TSPO), TH-immunoreactivity and dopamine transporters in the striatum and substantia nigra pars compacta (SNc) from 3- to 56-days postlesion (dpl). Increased binding of TSPO ligands used, i.e., [(3)H]PK11195 and [(125)I]CLINDE, was observed in the lesioned striatum at 3, 7, and 14 dpl, followed by a progressive return to the basal level at 56 dpl. The binding profile in the SNc showed progressive binding beginning at 3 dpl, peaking at 14 dpl, and progressively decreasing until 56 dpl. In this model, the neuroinflammatory and neurodegenerative processes occurred concomitantly. The transitory occurrence of microglial activation could be involved in the lasting installation of dopaminergic neuron loss.

QSAR study and synthesis of new phenyltropanes as ligands of the dopamine transporter (DAT).

The dopamine transporter (DAT) plays a pivotal role in the regulation of dopamine neurotransmission, and is involved in a number of physiological functions and brain disorders. Furthermore the DAT analysis by molecular imaging techniques is a useful tool for the diagnosis and follow up treatment of diseases involving the DAT. In order to predict the affinity of new derivatives for the DAT, different QSAR molecular modeling models based on cocaine were compared. We have evaluated in these models tropane derivatives synthesized with original synthons which coupled properties of both fluorine and iodine atoms. One compound showed a high in vitro affinity and selectivity for the DAT (K(i)=0.87±0.04 nM). This compound should be radiolabeled with radioiodine for further investigations by SPECT.

Development and preclinical evaluation of [18F]FBVM as a new potent PET tracer for vesicular acetylcholine transporter.

Age-related neurodegenerative diseases have in common the occurrence of cognitive impairment, a highly incapacitating process that involves the cholinergic neurotransmission system. The vesicular acetylcholine transporter (VAChT) positron emission tomography (PET) tracer [18F]fluoroethoxybenzovesamicol ((-)-[18F]FEOBV) has recently demonstrated its high value to detect alterations of the cholinergic system in Alzheimer's disease, Parkinson's disease and dementia with Lewy body. We present here the development of the new vesamicol derivative tracer (-)-(R,R)-5-[18F]fluorobenzovesamicol ((-)[18F]FBVM) that we compared to (-)[18F]FEOBV in the same experimental conditions. We show that: i) in vitro affinity for the VAChT was 50-fold higher for (-)FBVM (Ki = 0.9 ± 0.3 nM) than for (-)FEOBV (Ki = 61 ± 2.8 nM); ii) in vivo in rats, a higher signal-to-noise specific brain uptake and a lower binding to plasma proteins and peripheral defluorination were obtained for (-)[18F]FBVM compared to (-)[18F]FEOBV. Our findings demonstrate that (-)[18F]FBVM is a highly promising PET imaging tracer which could be sufficiently sensitive to detect in humans the cholinergic denervation that occurs in brain areas having a low density of VAChT such as the cortex and hippocampus.

Evaluation of a 3D local multiresolution algorithm for the correction of partial volume effects in positron emission tomography.

PURPOSE: Partial volume effects (PVEs) are consequences of the limited spatial resolution in emission tomography leading to underestimation of uptake in tissues of size similar to the point spread function (PSF) of the scanner as well as activity spillover between adjacent structures. Among PVE correction methodologies, a voxel-wise mutual multiresolution analysis (MMA) was recently introduced. MMA is based on the extraction and transformation of high resolution details from an anatomical image (MR/CT) and their subsequent incorporation into a low-resolution PET image using wavelet decompositions. Although this method allows creating PVE corrected images, it is based on a 2D global correlation model, which may introduce artifacts in regions where no significant correlation exists between anatomical and functional details. METHODS: A new model was designed to overcome these two issues (2D only and global correlation) using a 3D wavelet decomposition process combined with a local analysis. The algorithm was evaluated on synthetic, simulated and patient images, and its performance was compared to the original approach as well as the geometric transfer matrix (GTM) method. RESULTS: Quantitative performance was similar to the 2D global model and GTM in correlated cases. In cases where mismatches between anatomical and functional information were present, the new model outperformed the 2D global approach, avoiding artifacts and significantly improving quality of the corrected images and their quantitative accuracy. CONCLUSIONS: A new 3D local model was proposed for a voxel-wise PVE correction based on the original mutual multiresolution analysis approach. Its evaluation demonstrated an improved and more robust qualitative and quantitative accuracy compared to the original MMA methodology, particularly in the absence of full correlation between anatomical and functional information.

Detection and quantification of remote microglial activation in rodent models of focal ischaemia using the TSPO radioligand CLINDE.

PURPOSE: Neuroinflammation is involved in stroke pathophysiology and might be imaged using radioligands targeting the 18 kDa translocator protein (TSPO). METHODS: We studied microglial reaction in brain areas remote from the primary lesion site in two rodent models of focal cerebral ischaemia (permanent or transient) using [125I]-CLINDE, a promising TSPO single photon emission computed tomography radioligand. RESULTS: In a mouse model of permanent middle cerebral artery occlusion (MCAO), ex vivo autoradiographic studies demonstrated, besides in the ischaemic territory, accumulation of [125I]-CLINDE in the ipsilateral thalamus with a binding that progressed up to 3 weeks after MCAO. [125I]-CLINDE binding markedly decreased in animals pre-injected with either unlabelled CLINDE or PK11195, while no change was observed with flumazenil pre-treatment, demonstrating TSPO specificity. In rats subjected to transient MCAO, [125I]-CLINDE binding in the ipsilateral thalamus and substantia nigra pars reticulata (SNr) was significantly higher than that in contralateral tissue. Moreover, [125I]-CLINDE binding in the thalamus and SNr was quantitatively correlated to the ischaemic volume assessed by MRI in the cortex and striatum, respectively. CONCLUSION: Clinical consequences of secondary neuronal degeneration in stroke might be better treated thanks to the discrimination of neuronal processes using in vivo molecular imaging and potent TSPO radioligands like CLINDE to guide therapeutic interventions.

Synthesis and in vitro evaluation of fluorinated diphenyloxide derivatives and sulfur analogs as serotonin transporter ligands.

As the serotonin transporter (SERT) is involved in several neurodegenerative and psychiatric disorders; radiopharmaceuticals to image the SERT by PET would be valuable in studying these diseases. To this end we synthesized diphenyloxide derivatives and sulfide analogs, as new tracers, incorporating a fluorine or oxyalkyl fluorinated group on 4' or 5'-position on phenyl ring B. Three of these exhibited good to high in vitro affinity (7

3D QSAR study, synthesis, and in vitro evaluation of (+)-5-FBVM as potential PET radioligand for the vesicular acetylcholine transporter (VAChT).

Located in presynaptic cholinergic nerve terminals, the vesicular acetylcholine transporter (VAChT) represents a potential target for quantitative visualization of early degeneration of cholinergic neurons in Alzheimer's disease using PET. Benzovesamicol derivatives are proposed as radioligands for this purpose. We report QSAR studies of vesamicol and benzovesamicol derivatives taking into account the stereoselectivity of the VAChT binding site. Use of different data sets and different models in this study revealed that both enantiomers of 5-fluoro-3-(4-phenyl-piperidin-1-yl)-1,2,3,4-tetrahydro-naphthalen-2-ol (5-FBVM) are promising candidates, with predicted VAChT affinities between 6.1 and 0.05 nM. The synthesis of enantiopure (R,R)- and (S,S)-5-FBVM and their corresponding triazene precursors for future radiofluorination is reported. Both enantiomers exhibited high in vitro affinity for VAChT [(+)-5-FBVM: K(i)=6.95 nM and (-)-5-FBVM: K(i)=3.68 nM] and were selective for σ(2) receptors (∼70-fold), only (+)-5-FBVM is selective for σ(1) receptors (∼fivefold). These initial results suggest that (+)-(S,S)-5-FBVM warrants further investigation as a potential radioligand for in vivo PET imaging of cholinergic nerve terminals.

Usefulness of PET With [18F]LBT-999 for the Evaluation of Presynaptic Dopaminergic Neuronal Loss in a Clinical Environment.

Purpose: The density of the neuronal dopamine transporter (DAT) is directly correlated with the presynaptic dopaminergic system injury. In a first study, we evaluated the brain distribution and kinetics of [18F]LBT-999, a DAT PET radioligand, in a group of eight healthy subjects. Taking into account the results obtained in healthy volunteers, we wanted to evaluate whether the loss of presynaptic striatal dopaminergic fibers could be estimated, under routine clinical conditions, using [18F]LBT-999 and a short PET acquisition. Materials and methods: Six patients with Parkinson's disease (PD) were compared with eight controls. Eighty-nine minutes of dynamic PET following an intravenous injection of [18F]LBT-999 were acquired. Using regions of interest for striatal nuclei, substantia nigra (SN), cerebellum, and occipital cortex, defined over each T1 3D MRI, time-activity curves (TACs) were obtained. From TACs, binding potential (BPND) using the simplified reference tissue model and distribution volume ratios (DVRs) using Logan graphical analysis were calculated. Ratios obtained for a 10-min image, acquired between 30 and 40 min post-injection, were also calculated. Cerebellum activity was used as non-specific reference region. Results: In PD patients and as expected, striatal uptake was lower than in controls which is confirmed by BPND, DVR, and ratios calculated for both striatal nuclei and SN, significantly inferior in PD patients compared with controls (p < 0.001). Conclusions: PET with [18F]LBT-999 could be an alternative to assess dopaminergic presynaptic injury in a clinical environment using a single 10 min acquisition.

Fully automated radiosynthesis of [18F]LBT999 on TRACERlab FXFN and AllinOne modules, a PET radiopharmaceutical for imaging the dopamine transporter in human brain.

BACKGROUND: Fluorine labelled 8-((E)-4-fluoro-but-2-enyl)-3ß-p-tolyl-8-aza-bicyclo[3.2.1]octane-2ß-carboxylic acid methyl ester ([18F]LBT999) is a selective radioligand for the in vivo neuroimaging and quantification of the dopamine transporter by Positron Emission Tomography (PET). [18F]LBT999 was produced on a TRACERlab FXFN for the Phase I study but for Phase III and a potent industrial production transfer, production was also implemented on an AllinOne (AIO) system requiring a single use cassette. Both production methods are reported herein. RESULTS: Automation of [18F]LBT999 radiosynthesis on FXFN was carried out in 35% yield (decay-corrected) in 65 min (n = 16), with a radiochemical purity higher than 99% and a molar activity of 158 GBq/µmol at the end of synthesis. The transfer to the AIO platform followed by optimizations allowed the production of [18F]LBT999 in 32.7% yield (decay-corrected) within 48 min (n = 5), with a radiochemical purity better than 98% and a molar activity above 154 GBq/µmol on average at the end of synthesis. Quality controls of both methods met the specification for clinical application. CONCLUSION: Both modules allow efficient and reproducible radiosynthesis of [18F]LBT999 with good radiochemical yields and a reasonable synthesis time. The developments made on AIO, such as its ability to meet pharmaceutical criteria and to more easily comply with GMP requirements, make it an optimal approach for the potent industrial production of [18F]LBT999 and future wider use.

In vitro autoradiography and in vivo evaluation in cynomolgus monkey of [18F]FE-PE2I, a new dopamine transporter PET radioligand.

This study evaluated the in vitro and in vivo characteristics of a new dopamine transporter (DAT) radioligand, [(18)F]fluoroethyl(FE)PE2I, by autoradiography from postmortem human brain and by positron emission tomography (PET) in three cynomolgus monkeys. In the autoradiography experiments, high [18F]FE-PE2I accumulation was observed in caudate and putamen that was selectively abolished by GBR12909 or beta-CIT but not by maprotiline. High doses of citalopram (>5 microM) also inhibited [18F]FE-PE2I binding in the striatum. In vitro Ki of the radioligand was 12 nM at rodent dopamine transporter. [18F]FE-PE2I brain uptake measured by PET was approximately 4-5% of the injected dose, with highest uptake in striatum followed by midbrain and thalamus, lower uptake in neocortex, and lowest in cerebellum. Peak specific binding in striatum was reached approximately 40 min and in midbrain 20-30 min postinjection. The ratio-to-cerebellum was 7-10 in striatum and 1.5-2.3 in midbrain. BP(ND) measured with simplified reference tissue method using the cerebellum as reference region was 4.5 in striatum and 0.6 in midbrain. No displacement was shown after citalopram or maprotiline administration, while GBR12909 decreased the binding in striatum and midbrain to the level of cerebellum. [18F]FE-PE2I showed relatively fast elimination and metabolism with the presence of two metabolite peaks with similar retention time as the labeled metabolites of [11C]PE2I. [18F]FE-PE2I showed in vivo selectivity for the DAT and compared with [11C]PE2I, it showed faster kinetics and earlier peak equilibrium. The potential influence of the two radiometabolites on PET quantification requires further evaluation.