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.

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.

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.

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.

Bis(het)aryl-1,2,3-triazole quinuclidines as α7 nicotinic acetylcholine receptor ligands: Synthesis, structure affinity relationships, agonism activity, [18F]-radiolabeling and PET study in rats.

In this paper we describe the design and synthesis of bis(Het)Aryl-1,2,3-triazole quinuclidine α7R ligands using an efficient three-step sequence including a Suzuki-Miyaura cross coupling reaction with commercially available and home-made boron derivatives. The exploration of SAR required the preparation of uncommon boron derivatives. Forty final drugs were tested for their ability to bind the target and nine of them exhibited Ki values below nanomolar concentrations. The best scores were always obtained when the 5-phenyl-2-thiophenyl core was attached to the triazole. The selectivity of these compounds towards the nicotinic α4ß2 and serotoninergic 5HT3 receptors was assessed and their brain penetration was quantified by the preparation and in vivo evaluation of two [18F] radiolabelled derivatives. It can be expected from our results that some of these compounds will be suitable for further developments and will have effects on cognitive disorders.

The Story of the Dopamine Transporter PET Tracer LBT-999: From Conception to Clinical Use.

The membrane dopamine transporter (DAT) is involved in a number of brain disorders and its exploration by positron emission tomography (PET) imaging is highly relevant for the early and differential diagnosis, follow-up and treatment assessment of these diseases. A number of carbon-11 and fluor-18 labeled tracers are to date available for this aim, the majority of them being derived from the chemical structure of cocaine. The development of such a tracer, from its conception to its use, is a long process, the expected result being to obtain the best radiopharmaceutical adapted for clinical protocols. In this context, the cocaine derivative (E)-N-(4-fluorobut-2-enyl)2ß-carbomethoxy-3ß-(4'-tolyl)nortropane, or LBT-999, has passed all the required stages of the development that makes it now a highly relevant imaging tool, particularly in the context of Parkinson's disease. This review describes the different steps of the development of LBT-999 which initially came from its non-fluorinated derivative (E)-N-(3-iodoprop-2-enyl)-2-carbomethoxy-3-(4-methylphenyl) nortropane, or PE2I, because of its high promising properties. [18F]LBT-999 has been extensively characterized in rodent and non-human primate models, in which it demonstrated its capability to explore in vivo the DAT localized at the dopaminergic nerve endings as well as at the mesencephalic cell bodies, in physiological conditions. In lesion-induced rat models of Parkinson's disease, [18F]LBT-999 was able to precisely quantify in vivo the dopaminergic neuron loss, and to assess the beneficial effects of therapeutic approaches such as pharmacological treatment and cell transplantation. Finally recent clinical data demonstrated the efficiency of [18F]LBT-999 in the diagnosis of Parkinson's disease.

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.

The Place of PET to Assess New Therapeutic Effectiveness in Neurodegenerative Diseases.

In vivo exploration of neurodegenerative diseases by positron emission tomography (PET) imaging has matured over the last 20 years, using dedicated radiopharmaceuticals targeting cellular metabolism, neurotransmission, neuroinflammation, or abnormal protein aggregates (beta-amyloid and intracellular microtubule inclusions containing hyperphosphorylated tau). The ability of PET to characterize biological processes at the cellular and molecular levels enables early detection and identification of molecular mechanisms associated with disease progression, by providing accurate, reliable, and longitudinally reproducible quantitative biomarkers. Thus, PET imaging has become a relevant imaging method for monitoring response to therapy, approved as an outcome measure in bioclinical trials. The aim of this paper is to review and discuss the current inputs of PET in the assessment of therapeutic effectiveness in neurodegenerative diseases connected by common pathophysiological mechanisms, including Parkinson's disease, Huntington's disease, dementia, amyotrophic lateral sclerosis, multiple sclerosis, and also in psychiatric disorders. We also discuss opportunities for PET imaging to drive more personalized neuroprotective and therapeutic strategies, taking into account individual variability, within the growing framework of precision medicine.

Amyloid PET Positivity in Different Primary Progressive Aphasia Phenotypes.

PURPOSE: Primary progressive aphasia (PPA) is a neurological syndrome in which language functions become progressively impaired with relative sparing of memory and other instrumental functions. The pathologic causes of PPA are heterogeneous, but studies suggest that logopenic PPA (LPA) is underpinned by Alzheimer disease (AD) pathology in a high proportion of cases. The purposes of this descriptive and retrospective study were to characterize F-florbetapir PET imaging in a group of patients with a clinical syndrome of PPA, to determine the value of clinical characterization based on language phenotype in predicting the underlying pathology of PPA with F-florbetapir, and to quantify amyloid load in PPA subjects classified as "positive" F-florbetapir scans. Then, we compare the quantification and distribution of F-florbetapir uptake with those of typical, predominantly amnestic AD patients. METHODS: We conducted a PET study with F-florbetapir in a cohort of 12 right-handed patients diagnosed with PPA: 3 patients with semantic-variant PPA, 5 with nonfluent PPA, 1 with LPA, and 3 unclassifiable patients. We evaluated amyloid deposition between APP groups and 11 patients with typical amnestic AD. RESULTS: Among the 12 patients with PPA syndrome, 8 (66.7%) were considered as amyloid positive. One of the 3 patients with semantic-variant PPA was F-florbetapir positive. In contrast, 4 of the 5 nonfluent-variant PPA, 2 of the 3 unclassifiable cases and the single patient with LPA were F-florbetapir positive. A significantly higher F-florbetapir uptake was observed in PPA F-florbetapir-positive patients compared with typical AD patients. This difference was observed in all regions of interest, except in posterior cingulate and temporal cortex. CONCLUSIONS: These results suggest that F-florbetapir PET may be useful in a routine clinical procedure to improve the reliability of identifying AD pathology in patients with PPA syndrome, with different clinical subtypes of the PPA syndrome.

TSPO PET Imaging: From Microglial Activation to Peripheral Sterile Inflammatory Diseases?

Peripheral sterile inflammatory diseases (PSIDs) are a heterogeneous group of disorders that gathers several chronic insults involving the cardiovascular, respiratory, gastrointestinal, or musculoskeletal system and wherein inflammation is the cornerstone of the pathophysiology. In PSID, timely characterization and localization of inflammatory foci are crucial for an adequate care for patients. In brain diseases, in vivo positron emission tomography (PET) exploration of inflammation has matured over the last 20 years, through the development of radiopharmaceuticals targeting the translocator protein-18 kDa (TSPO) as molecular biomarkers of activated microglia. Recently, TSPO has been introduced as a possible molecular target for PSIDs PET imaging, making this protein a potential biomarker to address disease heterogeneity, to assist in patient stratification, and to contribute to predicting treatment response. In this review, we summarized the major research advances recently made in the field of TSPO PET imaging in PSIDs. Promising preliminary results have been reported in bowel, cardiovascular, and rheumatic inflammatory diseases, consolidated by preclinical studies. Limitations of TSPO PET imaging in PSIDs, regarding both its large expression in healthy peripheral tissues, unlike in central nervous system, and the production of peripheral radiolabeled metabolites, are also discussed, regarding their possible consequences on TSPO PET signal's quantification.

The Variability of Translocator Protein Signal in Brain and Blood of Genotyped Healthy Humans Using In Vivo 123I-CLINDE SPECT Imaging: A Test-Retest Study.

123I-CLINDE is a radiotracer developed for SPECT and targets the 18-kDa translocator protein (TSPO). TSPO is upregulated in glial cells and used as a measure of neuroinflammation in a variety of central nervous system diseases. The aim of this study was to examine the test-retest variability of 123I-CLINDE binding in healthy subjects. Methods: SPECT scans were acquired over 90 min in 16 healthy controls (9 women, 8 mixed-affinity binders [MABs] and 8 high-affinity binders [HABs] twice with an interval of 35 ± 15 d). Arterial input functions were based on individual blood measurements in 8 subjects and a population-based approach in combination with individual whole-blood time-activity curves in the other 8 subjects. Seven brain volumes of interest were extracted and quantified by SUVs and by 2-tissue-compartment modeling for calculation of distribution volumes (VT). Test-retest variability was measured by percentage difference (PD), the absolute PD, intraclass correlation coefficient (ICC), and coefficient of variation. Results: The absolute PD of brain SUV and the VT had similar values. The ICC values were higher for VTs than for brain SUVs, which were both moderate to high; however, lower ICC values were observed when calculated separately for HABs and MABs. Test-retest reproducibility was higher in subjects with immediate centrifugation of blood samples. The population-based method efficiently recovered data with delayed centrifugation. The VT of a 49-y-old male HAB was 7.5 ± 1.4 mL/cm3 compared with 4.6 ± 1.4 mL/cm3 of a sex- and age-matched MAB. The SUVs of a 49-y-old male HAB and MAB were 1.03 ± 0.14 and 0.88 ± 0.15 g/mL, respectively. Conclusion: The test-retest reproducibility of 123I-CLINDE is comparable or better than that reported for commonly used PET TSPO tracers. Because of the binding of 123I-CLINDE to blood cells and peripheral tissues, SUV is not a sufficient surrogate of VT from 2-tissue-compartment modeling. The population-adjusted method has the potential to reduce the complexity of blood analyses of TSPO tracers.

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.

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.

68Ga 'vacuum elution approach' for direct radiolabelling of DOTA-conjugated and NODAGA-conjugated peptides.

BACKGROUND/OBJECTIVES: The Ge/Ga generator is of increasing interest for clinical PET. The arrival on the market of the pharmaceutical-grade generator, which provides an eluate with chemical and radiochemical purities in conformity with the European Pharmacopeia specifications, makes the direct labelling of vectors possible. The kit formulation strategies using single vial productions can improve the access of hospitals and imaging centres that are not equipped with costly automated synthesis modules to the Ga-radiopharmaceutical production. The manual radiosynthesis of Ga requires handling of a relatively high amount of radioactivity, resulting in a high radiation dose to the hand. Moreover, the elution of the Ga/Ge generator with 5 ml of HCl as recommended by the manufacturer leads to a low Ga concentration, which can decrease the efficiency of the labelling procedure. The aim of our approach is to circumvent these disadvantages and to offer an alternative to the hand elution and labelling for a routine production of Ga-radiopharmaceuticals. METHODS: A mixture of buffer and peptide was first transferred to an evacuated collection vial. Fixed volume of HCl was adapted to the inlet line of the generator. The elution was then performed by the action of vacuum and the labeling occurs at RT or 95°C. RESULTS AND CONCLUSION: The 'vacuum elution approach' developed in this work enables the elution of 95% of the available generator activity with 2.5 ml of eluent, the direct labelling of DOTA-conjugated and NODAGA-conjugated peptides with high radiochemical (>97% for all cases) and radionuclidic (100%) purities without exposure of the hand to radiation during the preparation steps.

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.

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 α4ß2 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.

[11C]MADAM Used as a Model for Understanding the Radiometabolism of Diphenyl Sulfide Radioligands for Positron Emission Tomography (PET).

In quantitative PET measurements, the analysis of radiometabolites in plasma is essential for determining the exact arterial input function. Diphenyl sulfide compounds are promising PET and SPECT radioligands for in vivo quantification of the serotonin transporter (SERT) and it is therefore important to investigate their radiometabolism. We have chosen to explore the radiometabolic profile of [11C]MADAM, one of these radioligands widely used for in vivo PET-SERT studies. The metabolism of [11C]MADAM/MADAM was investigated using rat and human liver microsomes (RLM and HLM) in combination with radio-HPLC or UHPLC/Q-ToF-MS for their identification. The effect of carrier on the radiometabolic rate of the radioligand [11C]MADAM in vitro and in vivo was examined by radio-HPLC. RLM and HLM incubations were carried out at two different carrier concentrations of 1 and 10 µM. Urine samples after perfusion of [11C]MADAM/MADAM in rats were also analysed by radio-HPLC. Analysis by UHPLC/Q-ToF-MS identified the metabolites produced in vitro to be results of N-demethylation, S-oxidation and benzylic hydroxylation. The presence of carrier greatly affected the radiometabolism rate of [11C]MADAM in both RLM/HLM experiments and in vivo rat studies. The good concordance between the results predicted by RLM and HLM experiments and the in vivo data obtained in rat studies indicate that the kinetics of the radiometabolism of the radioligand [11C]MADAM is dose-dependent. This issue needs to be addressed when the diarylsulfide class of compounds are used in PET quantifications of SERT.

Precuneus and Cingulate Cortex Atrophy and Hypometabolism in Patients with Alzheimer's Disease and Mild Cognitive Impairment: MRI and (18)F-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 Alzheimer's 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 (18)F-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 (18)F-FDG in these two regions could be a neurodegenerative biomarker.