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Huntington’s disease (HD) is caused by a CAG trinucleotide repeat expansion in the first exon of the huntingtin (HTT) gene coding for the huntingtin (HTT) protein. The misfolding and consequential aggregation of CAG-expanded mutant HTT (mHTT) underpin HD pathology. Our interest in the life cycle of HTT led us to consider the development of high-affinity small-molecule binders of HTT oligomerized/amyloid-containing species that could serve as either cellular and in vivo imaging tools or potential therapeutic agents. We recently reported the development of PET tracers CHDI-180 and CHDI-626 as suitable for imaging mHTT aggregates, and here we present an in-depth pharmacological investigation of their binding characteristics. We have implemented an array of in vitro and ex vivo radiometric binding assays using recombinant HTT, brain homogenate-derived HTT aggregates, and brain sections from mouse HD models and humans post-mortem to investigate binding affinities and selectivity against other pathological proteins from indications such as Alzheimer’s disease and spinocerebellar ataxia 1. Radioligand binding assays and autoradiography studies using brain homogenates and tissue sections from HD mouse models showed that CHDI-180 and CHDI-626 specifically bind mHTT aggregates that accumulate with age and disease progression. Finally, we characterized CHDI-180 and CHDI-626 regarding their off-target selectivity and binding affinity to beta amyloid plaques in brain sections and homogenates from Alzheimer’s disease patients.

Induced pluripotent stem cell (iPSC) technology enabled the production of pluripotent stem cell lines from somatic cells from a range of known genetic backgrounds. Their ability to differentiate and generate a wide variety of cell types has resulted in their use for various biomedical applications, including toxicity testing. Many of these iPSC lines are now registered in databases and stored in biobanks such as the European Bank for induced pluripotent Stem Cells (EBiSC), which can streamline the quality control and distribution of these individual lines. To generate the quantities of cells for banking and applications like high-throughput toxicity screening, scalable and robust methods need to be developed to enable the large-scale production of iPSCs. 3D suspension culture platforms are increasingly being used by stem cell researchers, owing to a higher cell output in a smaller footprint, as well as simpler scaling by increasing culture volume. Here we describe our strategies for successful scalable production of iPSCs using a benchtop bioreactor and incubator for 3D suspension cultures, while maintaining quality attributes expected of high-quality iPSC lines. Additionally, to meet the increasing demand for "ready-to-use" cell types, we report recent work to establish robust, scalable differentiation protocols to cardiac, neural, and hepatic fate to enable EBiSC to increase available research tools. ispartof: REPRODUCTIVE TOXICOLOGY vol:112 pages:23-35 ispartof: location:United States status: published

O-GlcNAcylation is a post-translational modification of tau understood to lower the speed and yield of its aggregation, a pathological hallmark of Alzheimer's disease (AD). O-GlcNAcase (OGA) is the only enzyme that removes O-linked N-acetyl-d-glucosamine (O-GlcNAc) from target proteins. Therefore, inhibition of OGA represents a potential approach for the treatment of AD by preserving the O-GlcNAcylated tau protein. Herein, we report the multifactorial optimization of high-throughput screening hit 8 to a potent, metabolically stable, and orally bioavailable diazaspirononane OGA inhibitor (+)-56. The human OGA X-ray crystal structure has been recently solved, but bacterial hydrolases are still widely used as structural homologues. For the first time, we reveal how a nonsaccharide series of inhibitors binds bacterial OGA and discuss the suitability of two different bacterial orthologues as surrogates for human OGA. These breakthroughs enabled structure-activity relationships to be understood and provided context and boundaries for the optimization of druglike properties.

Summary Polymorphism in the microglial receptor CD33 gene has been linked to late-onset Alzheimer disease (AD), and reduced expression of the CD33 sialic acid-binding domain confers protection. Thus, CD33 inhibition might be an effective therapy against disease progression. Progress toward discovery of selective CD33 inhibitors has been hampered by the absence of an atomic resolution structure. We report here the crystal structures of CD33 alone and bound to a subtype-selective sialic acid mimetic called P22 and use them to identify key binding residues by site-directed mutagenesis and binding assays to reveal the molecular basis for its selectivity toward sialylated glycoproteins and glycolipids. We show that P22, when presented on microparticles, increases uptake of the toxic AD peptide, amyloid-β (Aβ), into microglial cells. Thus, the sialic acid-binding site on CD33 is a promising pharmacophore for developing therapeutics that promote clearance of the Aβ peptide that is thought to cause AD., Graphical Abstract, Highlights • A sialic acid mimetic increases the uptake of Alzheimer peptide into microglia • Crystal structure of cell surface receptor CD33 bound to the sialic acid mimetic • Crystal structure of unliganded CD33 and mutagenesis studies revealed key residues • CD33 carbohydrate-binding site is a pharmacophore for Alzheimer drug development, Molecular Structure; Neuroscience; Molecular Neuroscience; Components of the Immune System; Protein Structure Aspects

Astrocytes, the main supportive cell type of the brain, show functional impairments upon ageing and in a broad spectrum of neurological disorders. Limited access to human astroglia for pre-clinical studies has been a major bottleneck delaying our understanding of their role in brain health and disease. We demonstrate here that functionally mature human astrocytes can be generated by SOX9 overexpression for 6 days in pluripotent stem cell (PSC)-derived neural progenitor cells. Inducible (i)SOX9-astrocytes display functional properties comparable to primary human astrocytes comprising glutamate uptake, induced calcium responses and cytokine/growth factor secretion. Importantly, electrophysiological properties of iNGN2-neurons co-cultured with iSOX9-astrocytes are indistinguishable from gold-standard murine primary cultures. The high yield, fast timing and the possibility to cryopreserve iSOX9-astrocytes without losing functional properties makes them suitable for scaled-up production for high-throughput analyses. Our findings represent a step forward to an all-human iPSC-derived neural model for drug development in neuroscience and towards the reduction of animal use in biomedical research. Graphical Abstract

APOE genotype is the strongest genetic risk factor for Alzheimer’s Disease (AD). The low degree of homology between mouse and human APOE is a concerning issue in preclinical models currently used to study the role of this gene in AD pathophysiology. A key objective of ADAPTED (Alzheimer’s Disease Apolipoprotein Pathology for Treatment Elucidation and Development) project was to generate in vitro models that better recapitulate human APOE biology. We describe a new set of induced pluripotent stem cells (iPSC) lines carrying common APOE variants (Ɛ2, Ɛ3, and Ɛ3/Ɛ4) and a knock-out isogenic to the parental APOE Ɛ4/Ɛ4 line (UKBi011-A)., This study was funded by the ADAPTED (Alzheimer’s Disease Apolipoprotein Pathology for Treatment Elucidation and Development) consortium which has received funding from the Innovative Medicines Initiative 2 Joint Undertaking under Grant Agreement No 115975. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme and the European Federation of Pharmaceutical Industries and Associations.

Neurog2 is the gene encoding the neuronal transcription factor NGN2, which can convert stem cells into functional neurons in a fast and efficient way. Here we report the generation of two iPS cell lines, where DOX inducible constructs of neurog2 either without or with T2A-eGFP were inserted into the safe-site locus AAVS1. These iPS cell lines, BIONi010-C-13 and BIONi010-C-15, respectively, stay pluripotent without DOX but differentiate to (GFP positive) neurons when DOX is added without the need of differentiation factors.

Mutant huntingtin (mHTT) protein carrying the elongated N-terminal polyglutamine (polyQ) tract misfolds and forms protein aggregates characteristic of Huntington's disease (HD) pathology. A high-affinity ligand specific for mHTT aggregates could serve as a positron emission tomography (PET) imaging biomarker for HD therapeutic development and disease progression. To identify such compounds with binding affinity for polyQ aggregates, we embarked on systematic structural activity studies; lead optimization of aggregate-binding affinity, unbound fractions in brain, permeability, and low efflux culminated in the discovery of compound 1, which exhibited target engagement in autoradiography (ARG) studies in brain slices from HD mouse models and postmortem human HD samples. PET imaging studies with 11C-labeled 1 in both HD mice and WT nonhuman primates (NHPs) demonstrated that the right-hand-side labeled ligand [11C]-1R (CHDI-180R) is a suitable PET tracer for imaging of mHTT aggregates. [11C]-1R is now being advanced to human trials as a first-in-class HD PET radiotracer.

INTRODUCTION: Tauopathies are neurodegenerative diseases characterized by TAU protein-related pathology, including frontotemporal dementia and Alzheimer's disease among others. Mutant TAU animal models are available, but none of them faithfully recapitulates human pathology and are not suitable for drug screening. METHODS: To create a new in vitro tauopathy model, we generated a footprint-free triple MAPT-mutant human induced pluripotent stem cell line (N279K, P301L, and E10+16 mutations) using clustered regularly interspaced short palindromic repeats-FokI and piggyBac transposase technology. RESULTS: Mutant neurons expressed pathogenic 4R and phosphorylated TAU, endogenously triggered TAU aggregation, and had increased electrophysiological activity. TAU-mutant cells presented deficiencies in neurite outgrowth, aberrant sequence of differentiation to cortical neurons, and a significant activation of stress response pathways. RNA sequencing confirmed stress activation, demonstrated a shift toward GABAergic identity, and an upregulation of neurodegenerative pathways. DISCUSSION: In summary, we generated a novel in vitro human induced pluripotent stem cell TAU-mutant model displaying neurodegenerative disease phenotypes that could be used for disease modeling and drug screening. ispartof: ALZHEIMERS & DEMENTIA vol:14 issue:10 pages:1261-1280 ispartof: location:United States status: published

Neurogenin 2 encodes a neural-specific transcription factor (NGN2) able to drive neuronal fate on somatic and stem cells. NGN2 is expressed in neural progenitors within the developing central and peripheral nervous systems. Overexpression of NGN2 in human induced pluripotent stem cells (hiPSCs) or human embryonic stem cells has been shown to efficiently trigger conversion to neurons. Here we describe two gene-edited hiPSC lines harbouring a doxycycline (DOX)-inducible cassette in the AAVS1 locus driving expression of NGN2 (BIONi010-C-13) or NGN2-T2A-GFP (BIONi010-C-15). By introducing NGN2-expressing cassette, we reduce variability associated with conventional over-expression methods such as viral transduction, making these lines amenable for scale-up production and screening processes. DOX-treated hiPSCs convert to neural phenotype within one week and display the expression of structural neuronal markers such as Beta-III tubulin and tau. We performed functional characterization of NGN2-neurons co-cultured with hiPSC-derived astrocytes in a "fully-humanized" set up. Passive properties of NGN2-neurons were indistinguishable from mouse primary cells while displaying variable activity in extracellular recordings performed in multi-electrode arrays (MEAs). We demonstrate that hiPSC-derived astrocytes and neurons can be co-cultured and display functional properties comparable to the gold standard used in electrophysiology. Both lines are globally available via EBiSC repository at https://cells.ebisc.org/. ispartof: STEM CELL RESEARCH vol:54 ispartof: location:England status: published

Chronic inflammation represents a central component in the pathogenesis of Alzheimer's disease (AD). Recent work suggests that breaking immune tolerance by Programmed cell Death-1 (PD1) checkpoint inhibition produces an IFN-γ-dependent systemic immune response, with infiltration of the brain by peripheral myeloid cells and neuropathological as well as functional improvements even in mice with advanced amyloid pathology (Baruch et al., (2016): Nature Medicine, 22:135–137). Immune checkpoint inhibition was therefore suggested as potential treatment for neurodegenerative disorders when activation of the immune system is appropriate. Because a xenogeneic rat antibody (mAb) was used in the study, whether the effect was specific to PD1 target engagement was uncertain. In the present study we examined whether PD1 immunotherapy can lower amyloid-β pathology in a range of different amyloid transgenic models performed at three pharmaceutical companies with the exact same anti-PD1 isotype and two mouse chimeric variants. Although PD1 immunotherapy stimulated systemic activation of the peripheral immune system, monocyte-derived macrophage infiltration into the brain was not detected, and progression of brain amyloid pathology was not altered. Similar negative results of the effect of PD1 immunotherapy on amyloid brain pathology were obtained in two additional models in two separate institutions. These results show that inhibition of PD1 checkpoint signaling by itself is not sufficient to reduce amyloid pathology and that additional factors might have contributed to previously published results (Baruch et al., (2016): Nature Medicine, 22:135–137). Until such factors are elucidated, animal model data do not support further evaluation of PD1 checkpoint inhibition as a therapeutic modality for Alzheimer's disease.

A fast track “Hot Start” process was implemented to launch the European Bank for Induced Pluripotent Stem Cells (EBiSC) to provide early release of a range of established control and disease linked human induced pluripotent stem cell (hiPSC) lines. Established practice amongst consortium members was surveyed to arrive at harmonised and publically accessible Standard Operations Procedures (SOPs) for tissue procurement, bio-sample tracking, iPSC expansion, cryopreservation, qualification and distribution to the research community. These were implemented to create a quality managed foundational collection of lines and associated data made available for distribution. Here we report on the successful outcome of this experience and work flow for banking and facilitating access to an otherwise disparate European resource, with lessons to benefit the international research community.eTOCThe report focuses on the EBiSC experience of rapidly establishing an operational capacity to procure, bank and distribute a foundational collection of established hiPSC lines. It validates the feasibility and defines the challenges of harnessing and integrating the capability and productivity of centres across Europe using commonly available resources currently in the field.

Tau aggregation is the pathological hallmark that best correlates with the progression of Alzheimer's disease (AD). The presence of neurofibrillary tangles (NFTs), formed of hyperphosphorylated tau, leads to neuronal dysfunction and loss, and is directly associated with the cognitive decline observed in AD patients. The limited success in targeting β-amyloid pathologies has reinforced the hypothesis of blocking tau phosphorylation, aggregation, and/or spreading as alternative therapeutic entry points to treat AD. Identification of novel therapies requires disease-relevant and scalable assays capable of reproducing key features of the pathology in an in vitro setting. Here we use induced pluripotent stem cells (iPSCs) as a virtually unlimited source of human cortical neurons to develop a robust and scalable tau aggregation model compatible with high-throughput screening (HTS). We downscaled cell culture conditions to 384-well plate format and used Matrigel to introduce an extra physical protection against cell detachment that reduces shearing stress and better recapitulates pathological conditions. We complemented the assay with AlphaLISA technology for the detection of tau aggregates in a high-throughput-compatible format. The assay is reproducible across users and works with different commercially available iPSC lines, representing a highly translational tool for the identification of novel treatments against tauopathies, including AD.

Summary Tauopathies such as frontotemporal dementia (FTD) remain incurable to date, partially due to the lack of translational in vitro disease models. The MAPT gene, encoding the microtubule-associated protein tau, has been shown to play an important role in FTD pathogenesis. Therefore, we used zinc finger nucleases to introduce two MAPT mutations into healthy donor induced pluripotent stem cells (iPSCs). The IVS10+16 mutation increases the expression of 4R tau, while the P301S mutation is pro-aggregant. Whole-transcriptome analysis of MAPT IVS10+16 neurons reveals neuronal subtype differences, reduced neural progenitor proliferation potential, and aberrant WNT/SHH signaling. Notably, these neurodevelopmental phenotypes could be recapitulated in neurons from patients carrying the MAPT IVS10+16 mutation. Moreover, the additional pro-aggregant P301S mutation revealed additional phenotypes, such as an increased calcium burst frequency, reduced lysosomal acidity, tau oligomerization, and neurodegeneration. This series of iPSCs could serve as a platform to unravel a potential link between pathogenic 4R tau and FTD., Highlights • Analysis of ZFN-engineered MAPT IVS10+16 with or without additional P301S mutation • Neurodevelopmental phenotypes in ZFN and patient-derived MAPT IVS10+16 neurons • Neurodegenerative phenotypes in MAPT IVS10+16/P301S double-mutant neurons, In this article, Verheyen and colleagues introduced 2 MAPT mutations (IVS10+16/P301S) into healthy donor iPSCs. Characterization of MAPT IVS10+16 neurons revealed neurodevelopmental neuron subtype differences, reduced neural progenitor proliferation, and aberrant WNT/SHH signaling, while the additional pro-aggregant P301S mutation revealed phenotypes more related to neurodegeneration. These iPSCs could help to unravel a potential link between pathogenic 4R tau and FTD.

Alzheimer's disease (AD) is the most frequent neurodegenerative disease amongst the elderly. The SNPs rs429358 and rs7412 in the APOE gene are the most common risk factor for sporadic AD, and there are three different alleles commonly referred to as APOE-epsilon 2, APOE-epsilon 3 and APOE-epsilon 4. Induced pluripotent stem cells (iPSCs) hold great promise to model AD as such cells can be differentiated in vitro to the required cell type. Here we report the use of CRISPR/Cas9 technology employed on iPSCs from a healthy individual with an APOE-epsilon 3/epsilon 4 genotype to obtain isogenic APOE-epsilon 2/epsilon 2, APOE-epsilon 3/epsilon 3, APOE-epsilon 4/epsilon 4 lines as well as an APOE-knock-out line.

Tissue transglutaminase 2 (TG2) is a multifunctional protein primarily known for its calcium-dependent enzymatic protein cross-linking activity via isopeptide bond formation between glutamine and lysine residues. TG2 overexpression and activity have been found to be associated with Huntington's disease (HD); specifically, TG2 is up-regulated in the brains of HD patients and in animal models of the disease. Interestingly, genetic deletion of TG2 in two different HD mouse models, R6/1 and R6/2, results in improved phenotypes including a reduction in neuronal death and prolonged survival. Starting with phenylacrylamide screening hit 7d, we describe the SAR of this series leading to potent and selective TG2 inhibitors. The suitability of the compounds as in vitro tools to elucidate the biology of TG2 was demonstrated through mode of inhibition studies, characterization of druglike properties, and inhibition profiles in a cell lysate assay.

The histamine H3 receptor (H3R) plays a regulatory role in the presynaptic release of histamine and several other neurotransmitters, and thus, it is an attractive target for central nervous system indications including cognitive disorders, narcolepsy, attention-deficit hyperactivity disorder, and pain. The development of H3R antagonists was complicated by the similarities between the pharmacophores of H3R and human Ether-a-go-go related gene (hERG) channel blockers, a fact that probably prevented promising compounds from being progressed into the clinic. Using a three-dimensional in silico modeling approach complemented with automated and manual patch clamping, we were able to separate these two pharmacophores and to develop highly potent H3R antagonists with reduced risk of hERG liabilities from initial hit series with low selectivity identified in a high-throughput screening campaign.

Serine racemase is responsible for the synthesis of D-serine, an endogenous co-agonist for N-methyl-D-aspartate receptor-type glutamate receptors (NMDARs). This pyridoxal 5'-phosphate-dependent enzyme is involved both in the reversible conversion of L- to D-serine and serine catabolism by alpha,beta-elimination of water, thereby regulating D-serine levels. Because D-serine affects NMDAR signaling throughout the brain, serine racemase is a promising target for the treatment of disorders related to NMDAR dysfunction. To provide a molecular basis for rational drug design the x-ray crystal structures of human and rat serine racemase were determined at 1.5- and 2.1-A resolution, respectively, and in the presence and absence of the orthosteric inhibitor malonate. The structures revealed a fold typical of beta-family pyridoxal 5'-phosphate enzymes, with both a large domain and a flexible small domain associated into a symmetric dimer, and indicated a ligand-induced rearrangement of the small domain that organizes the active site for specific turnover of the substrate.

Identification and optimization of two classes of CB2 selective agonists are described. A representative from each class is profiled in a murine model of inflammation and each shows similar efficacy to prednisolone upon oral dosing.

Dysregulation of the kynurenine (Kyn) pathway has been associated with the progression of Huntington's disease (HD). In particular, elevated levels of the kynurenine metabolites 3-hydroxy kynurenine (3-OH-Kyn) and quinolinic acid (Quin), have been reported in the brains of HD patients as well as in rodent models of HD. The production of these metabolites is controlled by the activity of kynurenine mono-oxygenase (KMO), an enzyme which catalyzes the synthesis of 3-OH-Kyn from Kyn. In order to determine the role of KMO in the phenotype of mouse models of HD, we have developed a potent and selective KMO inhibitor termed CHDI-340246. We show that this compound, when administered orally to transgenic mouse models of HD, potently and dose-dependently modulates the Kyn pathway in peripheral tissues and in the central nervous system. The administration of CHDI-340246 leads to an inhibition of the formation of 3-OH-Kyn and Quin, and to an elevation of Kyn and Kynurenic acid (KynA) levels in brain tissues. We show that administration of CHDI-340246 or of Kyn and of KynA can restore several electrophysiological alterations in mouse models of HD, both acutely and after chronic administration. However, using a comprehensive panel of behavioral tests, we demonstrate that the chronic dosing of a selective KMO inhibitor does not significantly modify behavioral phenotypes or natural progression in mouse models of HD.

Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG trinucleotide repeat expansion in the huntingtin gene. Major pathological hallmarks of HD include inclusions of mutant huntingtin (mHTT) protein, loss of neurons predominantly in the caudate nucleus, and atrophy of multiple brain regions. However, the early sequence of histological events that manifest in region- and cell-specific manner has not been well characterized. Here we use a high-content histological approach to precisely monitor changes in HTT expression and characterize deposition dynamics of mHTT protein inclusion bodies in the recently characterized zQ175 knock-in mouse line. We carried out an automated multi-parameter quantitative analysis of individual cortical and striatal cells in tissue slices from mice aged 2–12 months and confirmed biochemical reports of an age-associated increase in mHTT inclusions in this model. We also found distinct regional and subregional dynamics for inclusion number, size and distribution with subcellular resolution. We used viral-mediated suppression of total HTT in the striatum of zQ175 mice as an example of a therapeutically-relevant but heterogeneously transducing strategy to demonstrate successful application of this platform to quantitatively assess target engagement and outcome on a cellular basis.

Human pluripotent stem cells (PSCs) provide a unique entry to study species-specific aspects of human disorders such as Alzheimer's disease (AD). However, in vitro culture of neurons deprives them of their natural environment. Here we transplanted human PSC-derived cortical neuronal precursors into the brain of a murine AD model. Human neurons differentiate and integrate into the brain, express 3R/4R Tau splice forms, show abnormal phosphorylation and conformational Tau changes, and undergo neurodegeneration. Remarkably, cell death was dissociated from tangle formation in this natural 3D model of AD. Using genome-wide expression analysis, we observed upregulation of genes involved in myelination and downregulation of genes related to memory and cognition, synaptic transmission, and neuron projection. This novel chimeric model for AD displays human-specific pathological features and allows the analysis of different genetic backgrounds and mutations during the course of the disease.

The late detection of cardiotoxic side effects, such as QT prolongation, induced by compounds of pharmacological interest can dramatically impede drug discovery and development projects, and consequently increase their cost. The launch of new drugs with undetected cardiotoxic side effects could have hazardous consequences and could trigger lethal cardiac dysrhythmias in patients. It is desirable, therefore, to test for the potential cardiotoxic side effects of compounds at an early stage of drug development. Electrophysiological test systems and cellular-based fluorometric high-throughput assays are now available for cloned human cardiac ion channels. These test systems are important tools in the preclinical safety evaluation of drugs and newly developed compounds.

MARK phosphorylates the microtubule-associated proteins tau, MAP2, and MAP4 on their microtubule-binding domain, causing their dissociation from microtubules and increased microtubule dynamics. We describe the molecular cloning, distribution, activation mechanism, and overexpression of two MARK proteins from rat that arise from distinct genes. They encode Ser/Thr kinases of 88 and 81 kDa, respectively, and show similarity to the yeast kin1+ and C. elegans par-1 genes that are involved in the establishment of cell polarity. Expression of both isoforms is ubiquitous, and homologous genes are present in humans. Catalytic activity depends on phosphorylation of two residues in subdomain VIII. Overexpression of MARK in cells leads to hyperphosphorylation of MAPs on KXGS motifs and to disruption of the microtubule array, resulting in morphological changes and cell death.

Kynurenine monooxygenase (KMO) catalyzes the conversion of kynurenine to 3-hydroxykynurenine. Modulation of KMO activity has been implicated in several neurodegenerative diseases, including Huntington disease. Our goal is to develop potent and selective small-molecule KMO inhibitors with suitable pharmacokinetic characteristics for in vivo proof-of-concept studies and subsequent clinical development. We developed a comprehensive panel of biochemical and cell-based assays that use liquid chromatography/tandem mass spectrometry to quantify unlabeled kynurenine and 3-hydroxykynurenine. We describe assays to measure KMO inhibition in cell and tissue extracts, as well as cellular assays including heterologous cell lines and primary rat microglia and human peripheral blood mononuclear cells.

Serine racemase is responsible for the synthesis of D-serine, an endogenous co-agonist for N-methyl-D-aspartate receptor-type glutamate receptors (NMDARs). This pyridoxal 5'-phosphate-dependent enzyme is involved both in the reversible conversion of L- to D-serine and serine catabolism by alpha,beta-elimination of water, thereby regulating D-serine levels. Because D-serine affects NMDAR signaling throughout the brain, serine racemase is a promising target for the treatment of disorders related to NMDAR dysfunction. To provide a molecular basis for rational drug design the x-ray crystal structures of human and rat serine racemase were determined at 1.5- and 2.1-A resolution, respectively, and in the presence and absence of the orthosteric inhibitor malonate. The structures revealed a fold typical of beta-family pyridoxal 5'-phosphate enzymes, with both a large domain and a flexible small domain associated into a symmetric dimer, and indicated a ligand-induced rearrangement of the small domain that organizes the active site for specific turnover of the substrate.

A high-throughput screening campaign resulted in the discovery of a highly potent dual cannabinoid receptor 1 (CB1) and 2 (CB2) agonist. Following a thorough SAR exploration, a series of selective CB2 full agonists were identified.

The number of projects in drug development that fail in late phases because of cardiac side effects such as QT prolongation can impede drug discovery and development of projects. The molecular target responsible for QT prolongation by a wide range of pharmaceutical agents is the myocardial hERG potassium channel. It is therefore desirable to screen for compound interactions with the hERG channel at an early stage of drug development. Here, the authors report a cell-based fluorescence assay using membrane potential-sensitive fluorescent dyes and stably transfected hERG channels from CHO cells. The assay allows semiautomated screening of compounds for hERG activity on 384-well plates and is sufficiently rapid for testing a large number of compounds. The assay is robust as indicated by a Z' factor larger than 0.6. The throughput is in the range of 10,000 data points per day, which is significantly higher than any other method presently available for hERG. The data obtained with the fluorescence assay were in qualitative agreement with those from patch-clamp electrophysiological analysis. There were no false-positive hits, and the rate of false-negative compounds is currently 12% but might be further reduced by testing compounds at higher concentration. Quantitative differences between fluorescence and electrophysiological methods may be due to the use- or voltage-dependent activity of the antagonists.

The MARK protein kinases were originally identified by their ability to phosphorylate a serine motif in the microtubule-binding domain of tau that is critical for microtubule binding. Here, we report the cloning and expression of a novel human paralog, MARK4, which shares 75% overall homology with MARK1-3 and is predominantly expressed in brain. Homology is most pronounced in the catalytic domain (90%), and MARK4 readily phosphorylates tau and the related microtubule-associated protein 2 (MAP2) and MAP4. In contrast to the three paralogs that all exhibit uniform cytoplasmic localization, MARK4 colocalizes with the centrosome and with microtubules in cultured cells. Overexpression of MARK4 causes thinning out of the microtubule network, concomitant with a reorganization of microtubules into bundles. In line with these findings, we show that a tandem affinity-purified MARK4 protein complex contains alpha-, beta-, and gamma-tubulin. In differentiated neuroblastoma cells, MARK4 is localized prominently at the tips of neurite-like processes. We suggest that although the four MARK/PAR-1 kinases might play multiple cellular roles in concert with different targets, MARK4 is likely to be directly involved in microtubule organization in neuronal cells and may contribute to the pathological phosphorylation of tau in Alzheimer's disease.

Within the past few years, the high-throughput screening (HTS) of compounds targeting cardiac ion channels has been primarily focused on the testing of the HERG channel, which is involved in the termination of cardiac action potential. Interaction of drugs with this channel may induce QT interval prolongation and cardiac arrhythmia. These undesirable side effects have forced several pharmaceutical companies to terminate drug discovery and development projects. The screening of compounds for HERG-mediated activity early in the drug development process may thus help reduce the number of compounds that are withdrawn from late preclinical or early clinical trials due to cardiovascular side effects. However, early screening implies the ability to test large numbers of compounds. Therefore, tests have to be performed rapidly, combining high-throughput and low costs, and allow the use of small amounts of compounds. In this review, the HTS systems currently available to investigate the potential effects of compounds on the activity of the cardiac HERG ion channel will be described and compared.

Long-QT syndrome (LQTS) may cause syncope and sudden death due to cardiac tachyarrhythmia. Chromosome 7-linked LQTS (LQT2) has been correlated with mutations in the human ether-a-go-go-related gene (HERG). HERG forms voltage-gated K channels that may be associated with Mink-related peptide 1 (MiRP1), an auxiliary beta-subunit. The channels mediate currents that resemble native I(Kr). Mutations in the KCNE2 gene encoding MiRP1 may also cause LQTS. In this study, the frequency of mutations in KCNE2 of 150 unrelated LQTS patients without known genotype and of 100 controls was analyzed using single-strand conformation polymorphism analysis and direct sequencing. We identified a novel missense mutation, V65 M, in the KCNE2 gene of a 17-year-old female with syncope and LQTS. Expression studies in Chinese hamster ovary cells revealed that mutant and wild-type MiRP1 co-localized with HERG subunits and formed functional channels. However, mutant HERG/MiRP1(V65M) channels mediated currents with an accelerated inactivation time course compared with wild-type channels. The accelerated inactivation time course of HERG/MiRP1(V65M) channels may decrease I(Kr) current density of myocardial cells, thereby impairing the ability of myocytes to repolarize in response to sudden membrane depolarizations such as extrasystoles.