Landscape of brain myeloid cell transcriptome along the spatiotemporal progression of Alzheimer's disease reveals distinct sequential responses to Aß and tau.

Human microglia are critically involved in Alzheimer's disease (AD) progression, as shown by genetic and molecular studies. However, their role in tau pathology progression in human brain has not been well described. Here, we characterized 32 human donors along progression of AD pathology, both in time-from early to late pathology-and in space-from entorhinal cortex (EC), inferior temporal gyrus (ITG), prefrontal cortex (PFC) to visual cortex (V2 and V1)-with biochemistry, immunohistochemistry, and single nuclei-RNA-sequencing, profiling a total of 337,512 brain myeloid cells, including microglia. While the majority of microglia are similar across brain regions, we identified a specific subset unique to EC which may contribute to the early tau pathology present in this region. We calculated conversion of microglia subtypes to diseased states and compared conversion patterns to those from AD animal models. Targeting genes implicated in this conversion, or their upstream/downstream pathways, could halt gene programs initiated by early tau progression. We used expression patterns of early tau progression to identify genes whose expression is reversed along spreading of spatial tau pathology (EC > ITG > PFC > V2 > V1) and identified their potential involvement in microglia subtype conversion to a diseased state. This study provides a data resource that builds on our knowledge of myeloid cell contribution to AD by defining the heterogeneity of microglia and brain macrophages during both temporal and regional pathology aspects of AD progression at an unprecedented resolution.

Common mouse models of tauopathy reflect early but not late human disease.

BACKGROUND: Mouse models that overexpress human mutant Tau (P301S and P301L) are commonly used in preclinical studies of Alzheimer's Disease (AD) and while several drugs showed therapeutic effects in these mice, they were ineffective in humans. This leads to the question to which extent the murine models reflect human Tau pathology on the molecular level. METHODS: We isolated insoluble, aggregated Tau species from two common AD mouse models during different stages of disease and characterized the modification landscape of the aggregated Tau using targeted and untargeted mass spectrometry-based proteomics. The results were compared to human AD and to human patients that suffered from early onset dementia and that carry the P301L Tau mutation. RESULTS: Both mouse models accumulate insoluble Tau species during disease. The Tau aggregation is driven by progressive phosphorylation within the proline rich domain and the C-terminus of the protein. This is reflective of early disease stages of human AD and of the pathology of dementia patients carrying the P301L Tau mutation. However, Tau ubiquitination and acetylation, which are important to late-stage human AD are not represented in the mouse models. CONCLUSION: AD mouse models that overexpress human Tau using risk mutations are a suitable tool for testing drug candidates that aim to intervene in the early formation of insoluble Tau species promoted by increased phosphorylation of Tau.

Uncovering specificity of endogenous TAU aggregation in a human iPSC-neuron TAU seeding model.

Tau pathobiology has emerged as a key component underlying Alzheimer's disease (AD) progression; however, human neuronal in vitro models have struggled to recapitulate tau phenomena observed in vivo. Here, we aimed to define the minimal requirements to achieve endogenous tau aggregation in functional neurons utilizing human induced pluripotent stem cell (hiPSC) technology. Optimized hiPSC-derived cortical neurons seeded with AD brain-derived competent tau species or recombinant tau fibrils displayed increases in insoluble, endogenous tau aggregates. Importantly, MAPT-wild type and MAPT-mutant hiPSC-neurons exhibited unique propensities for aggregation dependent on the seed strain rather than the repeat domain identity, suggesting that successful templating of the recipient tau may be driven by the unique conformation of the seed. The in vitro model presented here represents the first successful demonstration of combining human neurons, endogenous tau expression, and AD brain-derived competent tau species, offering a more physiologically relevant platform to study tau pathobiology.

Evaluation of Small-Animal PET Outcome Measures to Detect Disease Modification Induced by BACE Inhibition in a Transgenic Mouse Model of Alzheimer Disease.

In this study, we investigated the effects of chronic administration of an inhibitor of the ß-site amyloid precursor protein-cleaving enzyme 1 (BACE1) on Alzheimer-related pathology by multitracer PET imaging in transgenic APPPS1-21 (TG) mice. Methods: Wild-type (WT) and TG mice received vehicle or BACE inhibitor (60 mg/kg) starting at 7 wk of age. Outcome measures of brain metabolism, neuroinflammation, and amyloid-ß pathology were obtained through small-animal PET imaging with 18F-FDG, 18F-peripheral benzodiazepine receptor (18F-PBR), and 18F-florbetapir (18F-AV45), respectively. Baseline scans were acquired at 6-7 wk of age and follow-up scans at 4, 7, and 12 mo. 18F-AV45 uptake was measured at 8 and 13 mo of age. After the final scans, histologic measures of amyloid-ß (4G8), microglia (ionized calcium binding adaptor molecule 1), astrocytes (glial fibrillary acidic protein), and neuronal nuclei were performed. Results: TG mice demonstrated significant age-associated increases in 18F-AV45 uptake. An effect of treatment was observed in the cortex (P = 0.0014), hippocampus (P = 0.0005), and thalamus (P < 0.0001). Histology confirmed reduction of amyloid-ß pathology in TG-BACE mice. Regardless of treatment, TG mice demonstrated significantly lower 18F-FDG uptake than WT mice in the thalamus (P = 0.0004) and hippocampus (P = 0.0332). Neuronal nucleus staining was lower in both TG groups in the thalamus and cortex. 18F-PBR111 detected a significant age-related increase in TG mice (P < 0.0001) but did not detect the treatment-induced reduction in activated microglia as demonstrated by histology. Conclusion: Although 18F-FDG, 18F-PBR111, and 18F-AV45 all detected pathologic alterations between TG and WT mice, only 18F-AV45 could detect an effect of BACE inhibitor treatment. However, changes in WT binding of 18F-AV45 undermine the specificity of this effect.

Preclinical Evaluation of 18F-JNJ64349311, a Novel PET Tracer for Tau Imaging.

In this study, we have synthesized and evaluated 18F-JNJ64349311, a tracer with high affinity for aggregated tau (inhibition constant value, 8 nM) and high (≥500×) in vitro selectivity for tau over ß-amyloid, in comparison with the benchmark compound 18F-AV1451 (18F-T807) in mice, rats, and a rhesus monkey. Methods: In vitro binding characteristics were determined for Alzheimer's disease, progressive supranuclear palsy, and corticobasal degeneration patient brain tissue slices using autoradiography studies. Ex vivo biodistribution studies were performed in mice. Radiometabolites were quantified in the brain and plasma of mice and in the plasma of a rhesus monkey using high-performance liquid chromatography. Dynamic small-animal PET studies were performed in rats and a rhesus monkey to evaluate tracer pharmacokinetics in the brain. Results: Mouse biodistribution studies showed moderate initial brain uptake and rapid brain washout. Radiometabolite analyses after injection of 18F-JNJ64349311 in mice showed the presence of a polar radiometabolite in plasma, but not in the brain. Semiquantitative autoradiography studies on postmortem tissue sections of human Alzheimer's disease brains showed highly displaceable binding to tau-rich regions. No specific binding was, however, found on human progressive supranuclear palsy and corticobasal degeneration brain slices. Small-animal PET scans of Wistar rats revealed moderate initial brain uptake (SUV, ∼1.5 at 1 min after injection) and rapid brain washout. 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 the healthy rat brain. A small-animal PET scan of a rhesus monkey revealed moderate initial brain uptake (SUV, 1.9 at 1 min after injection) with a rapid washout. In the monkey, no bone uptake was detected during the 120-min scan. Conclusion: This biologic evaluation suggests that 18F-JNJ64349311 is a promising tau PET tracer candidate, with a favorable pharmacokinetic profile, as compared with 18F-AV1451.

Discovery of N-(Pyridin-4-yl)-1,5-naphthyridin-2-amines as Potential Tau Pathology PET Tracers for Alzheimer's Disease.

A mini-HTS on 4000 compounds selected using 2D fragment-based similarity and 3D pharmacophoric and shape similarity to known selective tau aggregate binders identified N-(6-methylpyridin-2-yl)quinolin-2-amine 10 as a novel potent binder to human AD aggregated tau with modest selectivity versus aggregated ß-amyloid (Aß). Initial medicinal chemistry efforts identified key elements for potency and selectivity, as well as suitable positions for radiofluorination, leading to a first generation of fluoroalkyl-substituted quinoline tau binding ligands with suboptimal physicochemical properties. Further optimization toward a more optimal pharmacokinetic profile led to the discovery of 1,5-naphthyridine 75, a potent and selective tau aggregate binder with potential as a tau PET tracer.

Striatal phosphodiesterase 10A availability is altered secondary to chronic changes in dopamine neurotransmission.

BACKGROUND: Phosphodiesterase 10A (PDE10A) is an important regulator of nigrostriatal dopamine (DA) neurotransmission. However, little is known on the effect of alterations in DA neurotransmission on PDE10A availability. Here, we used [18F]JNJ42259152 PET to measure changes in PDE10A availability, secondary to pharmacological alterations in DA release and to investigate whether these are D1- or D2-receptor driven. RESULTS: Acute treatment of rats using D-amphetamine (5 mg, s.c. and 1 mg/kg i.v.) did not result in a significant change in PDE10A BPND compared to baseline conditions. 5-day D-amphetamine treatment (5 mg/kg, s.c.) increased striatal PDE10A BPND compared to the baseline (+24 %, p = 0.03). Treatment with the selective D2 antagonist SCH23390 (1 mg/kg) and D-amphetamine decreased PDE10A binding (-22 %, p = 0.03). Treatment with only SCH23390 further decreased PDE10A binding (-26 %, p = 0.03). No significant alterations in PDE10A mRNA levels were observed. CONCLUSIONS: Repeated D-amphetamine treatment significantly increased PDE10A binding, which is not observed upon selective D1 receptor blocking. This study suggests a potential pharmacological interaction between PDE10A enzymes and drugs modifying DA neurotransmission. Therefore, PDE10A binding in patients with neuropsychiatric disorders might be modulated by chronic DA-related treatment.

What We Observe In Vivo Is Not Always What We See In Vitro: Development and Validation of 11C-JNJ-42491293, A Novel Radioligand for mGluR2.

Positive allosteric modulators (PAM) of metabotropic glutamate receptor 2 (mGluR2) are a potential therapy for anxiety, schizophrenia, and addiction. Aside from pathophysiologic imaging studies, an mGluR2 PET tracer would enable confirmation of sufficient central target engagement and assist dose selection for proof-of-concept studies of PAM compounds. 11C-JNJ-42491293, a novel high-affinity radioligand (human 50% inhibitory concentration = 9.6 nM) for the PAM site of mGluR2, was evaluated as a selective mGluR2 PAM PET tracer. METHODS: In vitro and ex vivo autoradiography binding experiments in Wistar and in mGluR2 knockout and wildtype rats as well as in vivo biodistribution and brain PET imaging studies in wildtype and mGluR2 knockout rats in a primate and in humans were performed. RESULTS: In vitro binding studies and in vivo imaging studies in Wistar rats showed moderate brain uptake, with a distribution pattern fully consistent with the reported intracerebral distribution of mGluR2. Given these promising findings, biodistribution, dosimetry, and brain kinetic modeling of 11C-JNJ-42491293 were determined in humans. Because of an unexpected high myocardial retention, additional 11C-JNJ-42491293 imaging studies were performed in recently available mGluR2 knockout and wildtype rats and in a monkey using a structurally distinct mGluR2 PAM ligand with affinity for the same site, demonstrating off-target binding in vivo that could not have been anticipated from previous in vitro experiments. To date, the target of this non-mGluR2 tracer binding remains unknown. CONCLUSION: On the basis of in vivo selectivity issues suggested by human distribution and demonstrated in knockout rat models, 11C-JNJ-42491293 was considered unsuitable as a specific PET ligand for in vivo imaging of mGluR2. These results emphasize the importance of elaborated in vitro/in vivo comparative studies and, when available, validation with knockout animal models or structurally distinct ligands with affinity for the same site, in radiotracer development.

Longitudinal Characterization of [18F]-FDG and [18F]-AV45 Uptake in the Double Transgenic TASTPM Mouse Model.

We aimed to monitor the timing of amyloid-ß deposition in relation to changes in brain function using in vivo imaging with [18F]-AV45 and [18F]-FDG in a mouse model of Alzheimer's disease. TASTPM transgenic mice and wild-type controls were scanned longitudinally with [18F]-AV45 and [18F]-FDG before (3 months of age) and at multiple time points after the onset of amyloid deposition (6, 9, 12, and 15 months of age). As expected with increasing amyloidosis, TASTPM mice demonstrated progressive age-dependent increases in [18F]-AV45 uptake that were significantly higher than for WT from 9 months onwards and correlated to ex vivo measures of amyloid burden. The metabolism of [18F]-AV45 produces several brain penetrant radiometabolites and normalization to a reference region helps to negate this non-specific binding and improve the sensitivity of [18F]-AV45. The observed trajectory of [18F]-FDG alterations deviated from our proposed hypothesis of gradual decreases with worsening amyloidosis. While [18F]-FDG uptake in TASTPM mice was significantly lower than that of WT at 9 months, reduced [18F]-FDG was not associated with aging in TASTPM mice. Moreover, [18F]-FDG uptake did not correlate to measures of ex vivo amyloid burden. Our findings suggest that while amyloid-ß is sufficient to induce hypometabolism, these pathologies are not linked in a dose-dependent manner in TASTPM mice.

Metabotropic glutamate receptor 2/3 density and its relation to the hippocampal neuropathology in a model of temporal lobe epilepsy in rats.

Dysregulation in the glutamatergic function is considered a major contributor to hyperexcitatory neuronal networks in mesial temporal lobe epilepsy (MTLE). Studies in animal models of MTLE have shown positive outcomes of augmenting group 2-metabotropic receptor functions that can regulate neuronal excitability from extrasynaptic locations. To assist in efficient translation of these findings to the clinical settings, we aimed to characterise the expression of mGluR2/3 receptors in the brain areas relevant to MTLE. mGluR2/3 density was determined by autoradiographic techniques using [3H]-LY341495 at various cross-sectional timepoints following kainic acid-induced status epilepticus (KASE) covering the acute, latent and chronic phases of epilepsy pathogenesis. We found a significant reduction in the mGluR density in the CA1 and temporal cortex during the acute (2day) timepoint after SE in KASE rats whereas a reduced receptor density was only found in temporal cortex during the latent period (7day). During the late latent phase (14day), a generalised increase in the receptor density was found in widely distributed brain areas of KASE rats. Finally, in the chronic periods (day 42 and 84) a significant decrease was seen in the stratum lacunosum moleculare in the KASE rats. Moreover, mGluR2/3 density in the CA1 regions strongly correlated with the neuronal cell scores in the hippocampal regions. Our findings suggest a time dependent evolving pattern of mGluR2/3 density during the pathogenesis of MTLE and provide insights for utilising this data for in vivo imaging to predict the specific timepoints and responsiveness to the therapy targeting mGluR2/3.

BiDiFuse: a FIJI plugin for fusing bi-directionally recorded microscopic image volumes.

Deep tissue imaging is increasingly used for non-destructive interrogation of intact organs and small model organisms. An intuitive approach to increase the imaging depth by almost a factor of 2 is to record a sample from two sides and fuse both image stacks. However, imperfect three-dimensional alignment of both stacks presents a computational challenge. We have developed a FIJI plugin, called BiDiFuse, which merges bi-directionally recorded image stacks via 3D rigid transformations. The method is broadly applicable, considering it is compatible with all optical sectioning microscopes and it does not rely on fiducial markers for image registration. AVAILABILITY AND IMPLEMENTATION: The method is freely available as a plugin for FIJI from https://github.com/JanDetrez/BiDiFuse/ CONTACT: winnok.devos@uantwerpen.be.

Preclinical Evaluation of a P2X7 Receptor-Selective Radiotracer: PET Studies in a Rat Model with Local Overexpression of the Human P2X7 Receptor and in Nonhuman Primates.

UNLABELLED: The P2X7 receptor (P2X7R) orchestrates neuroinflammation, and this is the basis for an increased interest in the development of antagonists inhibiting P2X7R function in the brain. This study provides the preclinical evaluation of (11)C-JNJ-54173717, a PET tracer for P2X7R in both rats and nonhuman primates. METHODS: (11)C-JNJ-54173717 is a high-affinity radiotracer for the human P2X7R (hP2X7R). Biodistribution and radiometabolite studies were performed. Viral vectors encoding either enhanced green fluorescent protein-hP2X7R or 3flag-hP2X7R were engineered and validated in cell culture. hP2X7R was regionally overexpressed in the rat striatum after stereotactic injection of viral vectors. Dynamic small-animal PET studies were performed in vector-injected rats and in healthy monkeys using (11)C-JNJ-54173717. RESULTS: The affinity of JNJ-54173717 was 1.6 ± 0.1 nM in a rat cortex P2X7R membrane binding assay. In a functional assay at the recombinant human and rat P2X7R orthologs, the half maximal inhibitory concentration (IC50) of JNJ-54173717 was 4.2 ± 0.01 nM and 7.6 ± 0.01 nM, respectively. The rat biodistribution study showed that (11)C-JNJ-54173717 crossed the blood-brain barrier and was cleared from plasma mainly via the hepatobiliary pathway. A polar radiometabolite was found in rat plasma. No radiometabolites were detected in rat brain. Dynamic small-animal PET showed binding of (11)C-JNJ-54173717 in the striatum expressing hP2X7R, with rapid washout from the noninjected control striatum and other brain regions. Likewise, (11)C-JNJ-54173717 PET signal was blocked by a chemically distinct P2X7R ligand, indicating specific binding to P2X7R in the monkey brain. CONCLUSION: JNJ-54173717 is a high-affinity P2X7R antagonist. An animal rat model stably expressing hP2X7R was developed and validated, identifying favorable characteristics for (11)C-JNJ-54173717 as a PET radioligand for in vivo visualization of hP2X7R. (11)C-JNJ-54173717 selectively visualized P2X7R in the monkey brain, and this radioligand will be further evaluated in a clinical setting to study P2X7R expression levels in neurodegenerative disorders.

Image Informatics Strategies for Deciphering Neuronal Network Connectivity.

Brain function relies on an intricate network of highly dynamic neuronal connections that rewires dramatically under the impulse of various external cues and pathological conditions. Amongst the neuronal structures that show morphological plasticity are neurites, synapses, dendritic spines and even nuclei. This structural remodelling is directly connected with functional changes such as intercellular communication and the associated calcium bursting behaviour. In vitro cultured neuronal networks are valuable models for studying these morpho-functional changes. Owing to the automation and standardization of both image acquisition and image analysis, it has become possible to extract statistically relevant readouts from such networks. Here, we focus on the current state-of-the-art in image informatics that enables quantitative microscopic interrogation of neuronal networks. We describe the major correlates of neuronal connectivity and present workflows for analysing them. Finally, we provide an outlook on the challenges that remain to be addressed, and discuss how imaging algorithms can be extended beyond in vitro imaging studies.

The Effects of Physiological and Methodological Determinants on 18F-FDG Mouse Brain Imaging Exemplified in a Double Transgenic Alzheimer Model.

INTRODUCTION: In this study, the influence of physiological determinants on 18F-fluoro-d-glucose ((18)F-FDG) brain uptake was evaluated in a mouse model of Alzheimer disease. MATERIALS AND METHODS: TASTPM (Tg) and age-matched C57BL/6 J (WT) mice were fasted for 10 hours, while another group was fasted for 20 hours to evaluate the effect of fasting duration. The effect of repeatedly scanning was evaluated by scanning Tg and WT mice at days 1, 4, and 7. Brain (18)F-FDG uptake was evaluated in the thalamus being the most indicative region. Finally, the cerebellum was tested as a reference region for the relative standard uptake value (rSUV). RESULTS: When correcting the brain uptake for glucose, the effect of different fasting durations was attenuated and the anticipated hypometabolism in Tg mice was demonstrated. Also, with repeated scanning, the brain uptake values within a group and the hypometabolism of the Tg mice only remained stable over time when glucose correction was applied. Finally, hypometabolism was also observed in the cerebellum, yielding artificially higher rSUV values for Tg mice. CONCLUSION: Corrections for blood glucose levels have to be applied when semiquantifying (18)F-FDG brain uptake in mouse models for AD. Potential reference regions for normalization should be thoroughly investigated to ensure that they are not pathologically affected also by afferent connections.

In vivo molecular neuroimaging of glucose utilization and its association with fibrillar amyloid-ß load in aged APPPS1-21 mice.

INTRODUCTION: Radioligand imaging is a powerful in vivo method to assess the molecular basis of Alzheimer's Disease. We therefore aimed to visualize the pathological deposition of fibrillar amyloid-ß and neuronal dysfunction in aged double transgenic mice. METHODS: Using non-invasive positron emission tomography (PET) we assessed brain glucose utilization with [(18)F]FDG and fibrillar amyloidosis with [(11)C]PiB and [(18)F]AV45 in 12 month old APPPS1-21 (n = 10) mice and their age-matched wild-type controls (n = 15). PET scans were analyzed with statistical parametric mapping (SPM) to detect significant differences in tracer uptake between genotypes. After imaging, mice were sacrificed and ex vivo measures of amyloid-ß burden with immunohistochemistry as well as glucose utilization with [(14)C]-2DG autoradiography were obtained as gold standards. RESULTS: Voxel-wise SPM analysis revealed significantly decreased [(18)F]FDG uptake in aged APPPS1-21 mice in comparison to WT with the thalamus (96.96 %, maxT = 3.35) and striatum (61.21 %, maxT = 3.29) demonstrating the most widespread reductions at the threshold of p < 0.01. [(11)C]PiB binding was significantly increased in APPPS1-21 mice, most notably in the hippocampus (87.84 %, maxT = 7.15) and cortex (69.08 %, maxT = 7.95), as detected by SPM voxel-wise analysis at the threshold of p < 0.01. Using the same threshold [(18)F]AV45 uptake was comparably lower with less significant differences. Compared to their respective ex vivo equivalents [(18)F]FDG demonstrated significant positive correlation to [(14)C]2-DG autoradiography (r = 0.67, p <0.0001) while [(11)C]PiB and [(18)F]AV45 binding did not correlate to ex vivo immunohistochemistry for amyloid-ß (r = 0.25, p = 0.07 and r = 0.17, p = 0.26 respectively). Lastly no correlation was observed between regions of high amyloid burden and those with decreased glucose utilization (r = 0.001, p = 0.99). CONCLUSIONS: Our findings support that fibrillar amyloid-ß deposition and reduced glucose utilization can be visualized and quantified with in vivo µPET imaging in aged APPPS1-21 mice. Therefore, the combined use of [(18)F]FDG and amyloid µPET imaging can shed light on the underlying relationship between fibrillar amyloid-ß pathology and neuronal dysfunction.

Peripheral Administration of Tumor Necrosis Factor-Alpha Induces Neuroinflammation and Sickness but Not Depressive-Like Behavior in Mice.

Clinical observations indicate that activation of the TNF-α system may contribute to the development of inflammation-associated depression. Here, we tested the hypothesis that systemic upregulation of TNF-α induces neuroinflammation and behavioral changes relevant to depression. We report that a single intraperitoneal injection of TNF-α in mice increased serum and brain levels of the proinflammatory mediators TNF-α, IL-6, and MCP-1, in a dose- and time-dependent manner, but not IL-1ß. Protein levels of the anti-inflammatory cytokine IL-10 increased in serum but not in the brain. The transient release of immune molecules was followed by glial cell activation as indicated by increased astrocyte activation in bioluminescent Gfap-luc mice and elevated immunoreactivity against the microglial marker Iba1 in the dentate gyrus of TNF-α-challenged mice. Additionally, TNF-α-injected mice were evaluated in a panel of behavioral tests commonly used to study sickness and depressive-like behavior in rodents. Our behavioral data imply that systemic administration of TNF-α induces a strong sickness response characterized by reduced locomotor activity, decreased fluid intake, and body weight loss. Depressive-like behavior could not be separated from sickness at any of the time points studied. Together, these results demonstrate that peripheral TNF-α affects the central nervous system at a neuroimmune and behavioral level.

Quantitative µPET Imaging of Cerebral Glucose Metabolism and Amyloidosis in the TASTPM Double Transgenic Mouse Model of Alzheimer's Disease.

Positron emission tomography studies of cerebral glucose utilization and amyloid-ß deposition with fluoro-deoxy-D-glucose ([(18)F]-FDG) and amyloid tracers have shown characteristic pathological changes in Alzheimer's Disease that can be used for disease diagnosis and monitoring. Application of this technology to preclinical research with transgenic animal models would greatly facilitate drug discovery and further understanding of disease processes. The results from preclinical studies with these imaging biomarkers have however been highly inconsistent, causing doubts over whether animal models can truly replicate an AD-like phenotype. In this study we performed in vivo imaging with [(18)F]-FDG and [(18)F]-AV45 in double transgenic TASTPM mice, a transgenic model that been previously demonstrated high levels of fibrillar amyloid-ß and decreases in cerebral glucose utilization with ex vivo techniques. Our results show widespread and significant retention of [(18)F]-AV45 (p < 0.0001) in aged TASTPM mice in addition to significant regional decreases in [(18)F]-FDG uptake (p < 0.05). In vivo quantification of amyloid-ß showed a strong (Pearson's r = 0.7078), but not significant (p = 0.1156), positive correlation with ex vivo measures suggesting some limitations on tracer sensitivity. In the case of [(18)F]-FDG, voxelwise analysis greatly enhanced detection of hypometabolic regions. We further evidenced modest neuronal loss (thalamus p = 0.0318) that could underlie the observed hypometabolism. This research was performed in conjunction with the European Community's Seventh Framework Program (FP7/2007-2013) for the Innovative Medicine Initiative under the PharmaCog Grant Agreement no.115009.

Discovery of VU0409551/JNJ-46778212: An mGlu5 Positive Allosteric Modulator Clinical Candidate Targeting Schizophrenia.

Herein, we report the structure-activity relationship of a novel series of (2(phenoxymethyl)-6,7-dihydrooxazolo[5,4-c]pyridine-5(4H)-yl(aryl)methanones as potent, selective, and orally bioavailable metabotropic glutamate receptor subtype 5 (mGlu5) positive allosteric modulators (PAMs). On the basis of its robust in vitro potency and in vivo efficacy in multiple preclinical models of multiple domains of schizophrenia, coupled with a good DMPK profile and an acceptable therapeutic window, 17a (VU0409551/JNJ-46778212) was selected as a candidate for further development.

Pyrido[4,3-e][1,2,4]triazolo[4,3-a]pyrazines as Selective, Brain Penetrant Phosphodiesterase 2 (PDE2) Inhibitors.

A novel series of pyrido[4,3-e][1,2,4]triazolo[4,3-a]pyrazines is reported as potent PDE2/PDE10 inhibitors with drug-like properties. Selectivity for PDE2 was obtained by introducing a linear, lipophilic moiety on the meta-position of the phenyl ring pending from the triazole. The SAR and protein flexibility were explored with free energy perturbation calculations. Rat pharmacokinetic data and in vivo receptor occupancy data are given for two representative compounds 6 and 12.