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Phosphorothioates (PS) have proven their effectiveness in the area of therapeutic oligonucleotides with applications spanning from cancer treatment to neurodegenerative disorders. Initially, PS substitution was introduced for the antisense oligonucleotides (PS ASOs) because it confers an increased nuclease resistance meanwhile ameliorates cellular uptake and in-vivo bioavailability. Thus, PS oligonucleotides have been elevated to a fundamental asset in the realm of gene silencing therapeutic methodologies. But, despite their wide use, little is known on the possibly different structural changes PS-substitutions may provoke in DNA·RNA hybrids. Additionally, scarce information and significant controversy exists on the role of phosphorothioate chirality in modulating PS properties. Here, through comprehensive computational investigations and experimental measurements, we shed light on the impact of PS chirality in DNA-based antisense oligonucleotides; how the different phosphorothioate diastereomers impact DNA topology, stability and flexibility to ultimately disclose pro-Sp S and pro-Rp S roles at the catalytic core of DNA Exonuclease and Human Ribonuclease H; two major obstacles in ASOs-based therapies. Altogether, our results provide full-atom and mechanistic insights on the structural aberrations PS-substitutions provoke and explain the origin of nuclease resistance PS-linkages confer to DNA·RNA hybrids; crucial information to improve current ASOs-based therapies.
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Oligonucleótidos Antisentido , Oligonucleótidos Fosforotioatos , Humanos , Oligonucleótidos Fosforotioatos/química , Oligonucleótidos Antisentido/química , ADN , Transporte Biológico , AzufreRESUMEN
PURPOSE: Beta-secretase 1 (BACE1) enzyme is implicated in the pathophysiology of Alzheimer's disease. [18F]PF-06684511 is a positron emission tomography (PET) radioligand for imaging BACE1. Despite favorable brain kinetic properties, the effective dose (ED) of [18F]PF-06684511 estimated in non-human primates was relatively high. This study was therefore designed to evaluate the whole-body distribution, dosimetry, quantification, and test-retest reliability of imaging brain BACE1 with [18F]PF-06684511 in healthy volunteers. METHODS: Five subjects were studied for the dosimetry study. Whole-body PET was performed for 366 min with 4 PET-CT sessions. Estimates of the absorbed radiation dose were calculated using the male adult model. Eight subjects participated in the test-retest study. Brain PET measurements were conducted for 123 min with an interval of 5 to 19 days between test and retest conditions. The total distribution volume (VT) was estimated with one-tissue (1T), two-tissue (2T), compartment model (CM), and graphical analysis. Test-retest variability (TRV) and intraclass correlation coefficient (ICC) of VT were calculated as reliability measures. RESULTS: In the dosimetry study, the highest uptake was found in the liver (25.2 ± 2.3 %ID at 0.5 h) and the largest dose was observed in the pancreas (92.9 ± 52.2 µSv/MBq). The calculated ED was 24.7 ± 0.8 µSv/MBq. In the test-retest study, 2TCM described the time-activity curves well. VT (2TCM) was the highest in the anterior cingulate cortex (6.28 ± 1.09 and 6.85 ± 0.81) and the lowest in the cerebellum (4.23 ± 0.88 and 4.20 ± 0.75). Mean TRV and ICC of VT (2TCM) were 16.5% (12.4-20.5%) and 0.496 (0.291-0.644). CONCLUSION: The ED of [18F]PF-06684511 was similar to other 18F radioligands, allowing repeated PET measurements. 2TCM was the most appropriate quantification method. TRV of VT was similar to other radioligands without a reference region, albeit with lower ICC. These data indicated that [18F]PF-06684511 is a suitable radioligand to measure BACE1 level in the human brain. TRIAL REGISTRATION: EudraCT 2016-001110-19 (registered 2016-08-08).
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Secretasas de la Proteína Precursora del Amiloide , Tomografía Computarizada por Tomografía de Emisión de Positrones , Adulto , Ácido Aspártico Endopeptidasas , Encéfalo/diagnóstico por imagen , Humanos , Masculino , Tomografía de Emisión de Positrones , Radiometría , Radiofármacos , Reproducibilidad de los Resultados , Distribución Tisular , Tomografía Computarizada por Rayos XRESUMEN
Macrocycles pose challenges for computer-aided drug design due to their conformational complexity. One fundamental challenge is identifying all low-energy conformations of the macrocyclic ring, which is important for modeling target binding, passive membrane permeation, and other conformation-dependent properties. Macrocyclic polyketides are medically and biologically important natural products characterized by structural and functional diversity. Advances in synthetic biology and semisynthetic methods may enable creation of an even more diverse set of non-natural product polyketides for drug discovery and other applications. However, the conformational sampling of these flexible compounds remains demanding. We developed and optimized a dihedral angle-based macrocycle conformational sampling method for macrocycles of arbitrary structure, and here we apply it to diverse polyketide natural products. First, we evaluated its performance using a data set of 37 polyketides with available crystal structures, with 9-22 rotatable bonds in the macrocyclic ring. Our optimized protocol was able to reproduce the crystal structure of polyketides' aglycone backbone within 0.50 Å RMSD for 31 out of 37 polyketides. Consistent with prior structural studies, our analysis suggests that polyketides tend to have multiple distinct low-energy structures, including the bioactive (target-bound) conformation as well as others of unknown significance. For this reason, we also introduce a strategy to improve both efficiency and accuracy of the conformational search by utilizing torsional restraints derived from NMR vicinal proton couplings to restrict the conformational search. Finally, as a first application of the method, we made blinded predictions of the passive membrane permeability of a diverse set of polyketides, based on their predicted structures in low- and high-dielectric media.
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Productos Biológicos/química , Productos Biológicos/metabolismo , Biología Computacional/métodos , Policétidos/química , Policétidos/metabolismo , Bases de Datos de Proteínas , Modelos Moleculares , Conformación Molecular , PermeabilidadRESUMEN
Herein we report the identification of (+)-N-(2-((1H-pyrazol-1-yl)methyl)-3-((1R,3r,5S)-6'-fluoro-8-azaspiro[bicyclo[3.2.1]octane-3,1'-isochroman]-8-yl)propyl)-N-[(3)H]-methylacetamide {[(3)H]PF-7191 [(+)-11]} as a promising radiotracer for the nociceptin opioid peptide (NOP) receptor. (+)-11 demonstrated high NOP binding affinity (Ki = 0.1 nM), excellent selectivity over other opioid receptors (>1000×) and good brain permeability in rats (C(b,u)/C(p,u) = 0.29). Subsequent characterization of [(3)H](+)-11 showed a high level of specific binding and a brain bio-distribution pattern consistent with known NOP receptor expression. Furthermore, the in vivo brain binding of [(3)H](+)-11 in rats was inhibited by a selective NOP receptor antagonist in a dose-responsive manner. This overall favorable profile indicated that [(3)H](+)-11 is a robust radiotracer for pre-clinical in vivo receptor occupancy (RO) measurements and a possible substrate for carbon-11 labeling for positron emission tomography (PET) imaging in higher species.
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Encéfalo/metabolismo , Diseño de Fármacos , Péptidos Opioides/metabolismo , Receptores Opioides/metabolismo , Tritio/metabolismo , Animales , Relación Dosis-Respuesta a Droga , Evaluación Preclínica de Medicamentos/métodos , Péptidos Opioides/química , Unión Proteica/fisiología , Ratas , Tritio/química , Receptor de NociceptinaRESUMEN
Borrelidin (1) is a nitrile-containing bacterially derived polyketide that is a potent inhibitor of bacterial and eukaryotic threonyl-tRNA synthetases. We now report the discovery of borrelidin B (2), a tetrahydro-borrelidin derivative containing an aminomethyl group in place of the nitrile functionality in borrelidin. The discovery of this new metabolite has implications for both the biosynthesis of the nitrile group and the bioactivity of the borrelidin compound class. Screening in the SToPS assay for tRNA synthetase inhibition revealed that the nitrile moiety is essential for activity, while profiling using our in-house image-based cytological profiling assay demonstrated that 2 retains biological activity by causing a mitotic stall, even in the absence of the nitrile motif.
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Nitrilos/síntesis química , Treonina-ARNt Ligasa/antagonistas & inhibidores , Aminoacil-ARNt Sintetasas/metabolismo , Alcoholes Grasos/química , Alcoholes Grasos/aislamiento & purificación , Alcoholes Grasos/farmacología , Estructura Molecular , Nitrilos/metabolismoRESUMEN
Non-catechol-based high-affinity selective dopamine D1 receptor (D1R) agonists were recently described, and candidate PET ligands were selected on the basis of favorable properties. The objective of this study was to characterize in vivo in nonhuman primates 2 novel D1R agonist PET radiotracers, racemic 18F-MNI-800 and its more active atropisomeric (-)-enantiomer, 18F-MNI-968. Methods: Ten brain PET experiments were conducted with 18F-MNI-800 on 2 adult rhesus macaques and 2 adult cynomolgus macaques, and 8 brain PET experiments were conducted with 18F-MNI-968 on 2 adult rhesus macaques and 2 adult cynomolgus macaques. PET data were analyzed with both plasma-input-based methods and reference-region-based methods. Whole-body PET images were acquired with 18F-MNI-800 from 2 adult rhesus macaques for radiation dosimetry estimates. Results:18F-MNI-800 and 18F-MNI-968 exhibited regional uptake consistent with D1R distribution. Specificity and selectivity were demonstrated by dose-dependent blocking with the D1 antagonist SCH-23390. 18F-MNI-968 showed a 30% higher specific signal than 18F-MNI-800, with a nondisplaceable binding potential of approximately 0.3 in the cortex and approximately 1.1 in the striatum. Dosimetry radiation exposure was favorable, with an effective dose of about 0.023 mSv/MBq. Conclusion:18F-MNI-968 has significant potential as a D1R agonist PET radiotracer, and further characterization in human subjects is warranted.
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Dopamina , Tomografía de Emisión de Positrones , Animales , Macaca mulatta , Imagen de Cuerpo EnteroRESUMEN
ß-secretase 1 (BACE1) is a key enzyme in the generation of ß-amyloid, which is accumulated in the brain of Alzheimer disease patients. PF-06684511 was identified as a candidate PET ligand for imaging BACE1 in the brain and showed high specific binding in an initial assessment in a nonhuman primate (NHP) PET study using 18F-PF-06684511. In this effort, we aimed to quantitatively evaluate the regional brain distribution of 18F-PF-06684511 in NHPs under baseline and blocking conditions and to assess the target occupancy of BACE1 inhibitors. In addition, NHP whole-body PET measurements were performed to estimate the effective radiation dose. Methods: Initial brain PET measurements were performed at baseline and after oral administration of 5 mg/kg of LY2886721, a BACE1 inhibitor, in 2 cynomolgus monkeys. Kinetic analysis was performed with the radiometabolite-corrected plasma input function. In addition, a wide dose range of another BACE1 inhibitor, PF-06663195, was examined to investigate the relationship between the brain target occupancy and plasma concentration of the drug. Finally, the effective radiation dose of 18F-PF-06684511 was estimated on the basis of the whole-body PET measurements in NHPs. Results: Radiolabeling was accomplished successfully with an incorporation radiochemical yield of 4%-12% (decay-corrected) from 18F ion. The radiochemical purity was greater than 99%. The whole-brain uptake of 18F-PF-06684511 peaked (â¼220% SUV) at approximately 20 min and decreased thereafter (â¼100% SUV at 180 min). A 2-tissue-compartment model described the time-activity curves well. Pretreatment with LY2886721 reduced the total distribution volume of 18F-PF-06684511 by 48%-80% depending on the brain region, confirming its in vivo specificity. BACE1 occupancy of PF-06663195, estimated using the Lassen occupancy plot, showed a dose-dependent increase. The effective dose of 18F-PF-06684511 was 0.043 mSv/MBq for humans. Conclusion: 18F-PF-06684511 is the first successful PET radioligand for BACE1 brain imaging that demonstrates favorable in vivo binding and brain kinetics in NHPs.
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Secretasas de la Proteína Precursora del Amiloide/metabolismo , Encéfalo/diagnóstico por imagen , Encéfalo/metabolismo , Radioisótopos de Flúor/metabolismo , Tomografía de Emisión de Positrones , Pirazinas/metabolismo , Tiazinas/metabolismo , Animales , Femenino , Cinética , Ligandos , Macaca fascicularis , Masculino , Modelos Biológicos , Radioquímica , Imagen de Cuerpo EnteroRESUMEN
A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.
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Monoacylglycerol lipase (MAGL), a serine hydrolase extensively expressed throughout the brain, serves as a key gatekeeper regulating the tone of endocannabinoid signaling. Preclinically, inhibition of MAGL is known to provide therapeutic benefits for a number of neurological disorders. The availability of a MAGL-specific positron emission tomography (PET) ligand would considerably facilitate the development and clinical characterization of MAGL inhibitors via noninvasive and quantitative PET imaging. Herein, we report the identification of the potent and selective irreversible MAGL inhibitor 7 (PF-06809247) as a suitable radioligand lead, which upon radiolabeling was found to exhibit a high level of MAGL specificity; this enabled cross-species measurement of MAGL brain expression (Bmax), assessment of in vivo binding in the rat, and nonhuman primate PET imaging.
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Encéfalo/diagnóstico por imagen , Monoacilglicerol Lipasas/química , Tomografía de Emisión de Positrones , Animales , Sitios de Unión , Encéfalo/enzimología , Carbamatos/farmacología , Perros , Diseño de Fármacos , Endocannabinoides/metabolismo , Inhibidores Enzimáticos/farmacología , Humanos , Ligandos , Células de Riñón Canino Madin Darby , Imagen por Resonancia Magnética , Ratas , Ratas Sprague-Dawley , SolventesRESUMEN
The recent increase in the number of X-ray crystal structures of G-protein coupled receptors (GPCRs) has been enabling for structure-based drug design (SBDD) efforts. These structures have revealed that GPCRs are highly dynamic macromolecules whose function is dependent on their intrinsic flexibility. Unfortunately, the use of static structures to understand ligand binding can potentially be misleading, especially in systems with an inherently high degree of conformational flexibility. Here, we show that docking a set of dopamine D3 receptor compounds into the existing eticlopride-bound dopamine D3 receptor (D3R) X-ray crystal structure resulted in poses that were not consistent with results obtained from site-directed mutagenesis experiments. We overcame the limitations of static docking by using large-scale high-throughput molecular dynamics (MD) simulations and Markov state models (MSMs) to determine an alternative pose consistent with the mutation data. The new pose maintains critical interactions observed in the D3R/eticlopride X-ray crystal structure and suggests that a cryptic pocket forms due to the shift of a highly conserved residue, F6.52. Our study highlights the importance of GPCR dynamics to understand ligand binding and provides new opportunities for drug discovery.
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Receptores de Dopamina D3/antagonistas & inhibidores , Receptores Acoplados a Proteínas G/química , Receptores Acoplados a Proteínas G/metabolismo , Animales , Sitios de Unión/fisiología , Línea Celular , Cristalografía por Rayos X/métodos , Humanos , Ligandos , Simulación del Acoplamiento Molecular/métodos , Simulación de Dinámica Molecular , Mutagénesis Sitio-Dirigida/métodos , Unión Proteica/fisiología , Salicilamidas/química , Salicilamidas/metabolismo , Células Sf9RESUMEN
Alzheimer's disease (AD) is characterized by accumulation of ß-amyloid (Aß) plaques and neurofibrillary tau tangles in the brain. ß-Site amyloid precursor protein cleaving enzyme 1 (BACE1) plays a key role in the generation of Aß fragments via extracellular cleavage of the amyloid precursor protein (APP). We became interested in developing a BACE1 PET ligand to facilitate clinical assessment of BACE1 inhibitors and explore its potential in the profiling and selection of patients for AD trials. Using a set of PET ligand design parameters, compound 3 (PF-06684511) was rapidly identified as a lead with favorable in vitro attributes and structural handles for PET radiolabeling. Further evaluation in an LC-MS/MS "cold tracer" study in rodents revealed high specific binding to BACE1 in brain. Upon radiolabeling, [18F]3 demonstrated favorable brain uptake and high in vivo specificity in nonhuman primate (NHP), suggesting its potential for imaging BACE1 in humans.
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Secretasas de la Proteína Precursora del Amiloide/metabolismo , Ácido Aspártico Endopeptidasas/metabolismo , Encéfalo/metabolismo , Inhibidores de Proteasas/farmacología , Pirazinas/farmacología , Radiofármacos/farmacología , Tiazinas/farmacología , Secretasas de la Proteína Precursora del Amiloide/antagonistas & inhibidores , Animales , Ácido Aspártico Endopeptidasas/antagonistas & inhibidores , Radioisótopos de Flúor , Ligandos , Masculino , Ratones , Tomografía de Emisión de Positrones , Inhibidores de Proteasas/síntesis química , Inhibidores de Proteasas/química , Inhibidores de Proteasas/farmacocinética , Pirazinas/síntesis química , Pirazinas/química , Pirazinas/farmacocinética , Radiofármacos/síntesis química , Radiofármacos/química , Radiofármacos/farmacocinética , Tiazinas/síntesis química , Tiazinas/química , Tiazinas/farmacocinéticaRESUMEN
A major challenge in the development of ß-site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitors for the treatment of Alzheimer's disease is the alignment of potency, drug-like properties, and selectivity over related aspartyl proteases such as Cathepsin D (CatD) and BACE2. The potential liabilities of inhibiting BACE2 chronically have only recently begun to emerge as BACE2 impacts the processing of the premelanosome protein (PMEL17) and disrupts melanosome morphology resulting in a depigmentation phenotype. Herein, we describe the identification of clinical candidate PF-06751979 (64), which displays excellent brain penetration, potent in vivo efficacy, and broad selectivity over related aspartyl proteases including BACE2. Chronic dosing of 64 for up to 9 months in dog did not reveal any observation of hair coat color (pigmentation) changes and suggests a key differentiator over current BACE1 inhibitors that are nonselective against BACE2 in later stage clinical development.
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Secretasas de la Proteína Precursora del Amiloide/antagonistas & inhibidores , Ácido Aspártico Endopeptidasas/antagonistas & inhibidores , Encéfalo/metabolismo , Diseño de Fármacos , Hipopigmentación , Inhibidores de Proteasas , Piranos , Pigmentación de la Piel/efectos de los fármacos , Tiazinas , Tiazoles , Precursor de Proteína beta-Amiloide/metabolismo , Animales , Encéfalo/efectos de los fármacos , Células Cultivadas , Perros , Humanos , Hipopigmentación/inducido químicamente , Masculino , Melanocitos/efectos de los fármacos , Ratones , Ratones Endogámicos C57BL , Modelos Moleculares , Estructura Molecular , Inhibidores de Proteasas/administración & dosificación , Inhibidores de Proteasas/efectos adversos , Inhibidores de Proteasas/química , Conformación Proteica , Piranos/administración & dosificación , Piranos/efectos adversos , Piranos/química , Tiazinas/administración & dosificación , Tiazinas/efectos adversos , Tiazinas/química , Tiazoles/administración & dosificación , Tiazoles/efectos adversos , Tiazoles/químicaRESUMEN
Positron Emission Tomography (PET), as a non-invasive translatable imaging technology, can be incorporated into various stages of the CNS drug discovery process to provide valuable information for key preclinical and clinical decision-making. Novel CNS PET ligand discovery efforts in the industry setting, however, are facing unique challenges associated with lead design and prioritization, and budget constraints. In this review, three strategies aiming toward improving the central nervous system (CNS) PET ligand discovery process are described: first, early determination of receptor density (Bmax) and bio-distribution to inform PET viability and resource allocation; second, rational design and design prioritization guided by CNS PET design parameters; finally, a cost-effective in vivo specific binding assessment using a liquid chromatography-mass spectrometry (LC-MS/MS) "cold tracer" method. Implementation of these strategies allowed a more focused and rational CNS PET ligand discovery effort to identify high quality PET ligands for neuroimaging.
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As part of our effort in identifying phosphodiesterase (PDE) 4B-preferring inhibitors for the treatment of central nervous system (CNS) disorders, we sought to identify a positron emission tomography (PET) ligand to enable target occupancy measurement in vivo. Through a systematic and cost-effective PET discovery process, involving expression level (Bmax) and biodistribution determination, a PET-specific structure-activity relationship (SAR) effort, and specific binding assessment using a LC-MS/MS "cold tracer" method, we have identified 8 (PF-06445974) as a promising PET lead. Compound 8 has exquisite potency at PDE4B, good selectivity over PDE4D, excellent brain permeability, and a high level of specific binding in the "cold tracer" study. In subsequent non-human primate (NHP) PET imaging studies, [18F]8 showed rapid brain uptake and high target specificity, indicating that [18F]8 is a promising PDE4B-preferring radioligand for clinical PET imaging.
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Fosfodiesterasas de Nucleótidos Cíclicos Tipo 4/metabolismo , Inhibidores de Fosfodiesterasa/metabolismo , Tomografía de Emisión de Positrones/métodos , Animales , Corteza Cerebral/metabolismo , Cromatografía Liquida , Descubrimiento de Drogas , Macaca fascicularis , Ensayo de Unión Radioligante , Relación Estructura-Actividad , Espectrometría de Masas en TándemRESUMEN
Significant progress has been made in prospectively designing molecules using the central nervous system multiparameter optimization (CNS MPO) desirability tool, as evidenced by the analysis reported herein of a second wave of drug candidates that originated after the development and implementation of this tool. This simple-to-use design algorithm has expanded design space for CNS candidates and has further demonstrated the advantages of utilizing a flexible, multiparameter approach in drug discovery rather than individual parameters and hard cutoffs of physicochemical properties. The CNS MPO tool has helped to increase the percentage of compounds nominated for clinical development that exhibit alignment of ADME attributes, cross the blood-brain barrier, and reside in lower-risk safety space (low ClogP and high TPSA). The use of this tool has played a role in reducing the number of compounds submitted to exploratory toxicity studies and increasing the survival of our drug candidates through regulatory toxicology into First in Human studies. Overall, the CNS MPO algorithm has helped to improve the prioritization of design ideas and the quality of the compounds nominated for clinical development.
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Sistema Nervioso Central/efectos de los fármacos , Sistema Nervioso Central/metabolismo , Diseño de Fármacos , Miembro 1 de la Subfamilia B de Casetes de Unión a ATP/metabolismo , Algoritmos , Animales , Transporte Biológico , Barrera Hematoencefálica/efectos de los fármacos , Barrera Hematoencefálica/metabolismo , Humanos , Permeabilidad/efectos de los fármacosRESUMEN
UNLABELLED: The enzyme phosphodiesterase 2A (PF-05270430) is a potential target for development of novel therapeutic agents for the treatment of cognitive impairments. The goal of the present study was to evaluate the PDE2A ligand (18)F-PF-05270430, 4-(3-fluoroazetidin-1-yl)-7-methyl-5-(1-methyl-5-(4-(trifluoromethyl)phenyl)-1H-pyrazol-4-yl)imidazo[1,5-f][1,2,4]triazine, in nonhuman primates. METHODS: (18)F-PF-05270430 was radiolabeled by 2 methods via nucleophilic substitution of its tosylate precursor. Tissue metabolite analysis in rodents and PET imaging in nonhuman primates under baseline and blocking conditions were performed to determine the pharmacokinetic and binding characteristics of the new radioligand. Various kinetic modeling approaches were assessed to select the optimal method for analysis of imaging data. RESULTS: (18)F-PF-05270430 was synthesized in greater than 98% radiochemical purity and high specific activity. In the nonhuman primate brain, uptake of (18)F-PF-05270430 was fast, with peak concentration (SUVs of 1.5-1.8 in rhesus monkeys) achieved within 7 min after injection. The rank order of uptake was striatum > neocortical regions > cerebellum. Regional time-activity curves were well fitted by the 2-tissue-compartment model and the multilinear analysis-1 (MA1) method to arrive at reliable estimates of regional distribution volume (VT) and binding potential (BPND) with 120 min of scan data. Regional VT values (MA1) ranged from 1.28 mL/cm(3) in the cerebellum to 3.71 mL/cm(3) in the putamen, with a BPND of 0.25 in the temporal cortex and 1.92 in the putamen. Regional BPND values estimated by the simplified reference tissue model (SRTM) were similar to those from MA1. Test-retest variability in high-binding regions (striatum) was 4% ± 6% for MA1 VT, 13% ± 6% for MA1 BPND, and 13% ± 7% SRTM BPND, respectively. Pretreatment of animals with the PDE2A inhibitor PF-05180999 resulted in a dose-dependent reduction of (18)F-PF-05270430 specific binding, with a half maximal effective concentration of 69.4 ng/mL in plasma PF-05180999 concentration. CONCLUSION: (18)F-PF-05270430 displayed fast and reversible kinetics in nonhuman primates, as well as specific binding blockable by a PDE2A inhibitor. This is the first PET tracer with desirable imaging properties and demonstrated ability to image and quantify PDE2A in vivo.
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Compuestos de Azabiciclo/farmacocinética , Azetidinas/farmacocinética , Encéfalo/diagnóstico por imagen , Encéfalo/metabolismo , Fosfodiesterasas de Nucleótidos Cíclicos Tipo 2/metabolismo , Imagen Molecular/métodos , Tomografía de Emisión de Positrones/métodos , Animales , Macaca mulatta , Masculino , Tasa de Depuración Metabólica , Especificidad de Órganos , Radiofármacos , Ratas , Ratas Sprague-Dawley , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , Especificidad de la Especie , Distribución TisularRESUMEN
The synthesis and structure-activity relationships of a series of 6-phenyl-2-aminopyridines that potently and selectively inhibit the neuronal isoform of nitric oxide synthase (nNOS) are described. Compound 14bi from this series exhibits potent in vivo activity in harmaline-induced cGMP formation in rat cerebellum, a functional model of nNOS inhibition, and in the PCP-induced hypermotility model in the rat. These results suggest that 14bi may be a useful reagent for evaluating potential therapeutic applications of nNOS inhibitors in the central nervous system.
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Aminopiridinas/síntesis química , Óxido Nítrico Sintasa/antagonistas & inhibidores , Tetrahidronaftalenos/síntesis química , Aminopiridinas/química , Aminopiridinas/farmacología , Animales , Cerebelo/efectos de los fármacos , Cerebelo/metabolismo , GMP Cíclico/biosíntesis , Masculino , Actividad Motora/efectos de los fármacos , Óxido Nítrico Sintasa/química , Óxido Nítrico Sintasa de Tipo I , Ratas , Ratas Sprague-Dawley , Relación Estructura-Actividad , Tetrahidronaftalenos/química , Tetrahidronaftalenos/farmacologíaRESUMEN
Cholinesterase inhibitors vary in their selectivity for acetylcholinesterase versus butyrylcholinesterase. We examined several cholinesterase inhibitors and assessed the relative role of acetylcholinesterase versus butyrylcholinesterase inhibition in central and peripheral responses to these medications. Donepezil and icopezil are highly selective for acetylcholinesterase, whereas tacrine and heptylphysostigmine demonstrated greater potency for butyrylcholinesterase over acetylcholinesterase. All four compounds increased acetylcholine levels in mouse brains. Dose-response curves for tremor (central effect) and salivation (peripheral effect) showed that donepezil and icopezil possess a more favourable therapeutic index than the nonselective inhibitors, tacrine and heptylphysostigmine. Co-administration of the selective butyrylcholinesterase inhibitor tetraisopropylpyrophosphoramide (iso-OMPA) potentiated peripheral, but not central, effects of the selective acetylcholinesterase inhibitor icopezil. The improved therapeutic index observed in mice with icopezil is due to a high degree of selectivity for acetylcholinesterase versus butyrylcholinesterase, suggesting that high selectivity for acetylcholinesterase may contribute to the clinically favourable tolerability profile of agents such as donepezil in Alzheimer's disease patients.
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Enfermedad de Alzheimer/tratamiento farmacológico , Enfermedad de Alzheimer/enzimología , Inhibidores de la Colinesterasa/farmacología , Fisostigmina/análogos & derivados , Acetilcolina/metabolismo , Animales , Encéfalo/efectos de los fármacos , Encéfalo/metabolismo , Butirilcolinesterasa/sangre , Inhibidores de la Colinesterasa/uso terapéutico , Donepezilo , Relación Dosis-Respuesta a Droga , Humanos , Indanos/farmacología , Masculino , Ratones , Fisostigmina/farmacología , Piperidinas/farmacología , Ratas , Ratas Sprague-Dawley , Tacrina/farmacologíaRESUMEN
To accelerate the discovery of novel small molecule central nervous system (CNS) positron emission tomography (PET) ligands, we aimed to define a property space that would facilitate ligand design and prioritization, thereby providing a higher probability of success for novel PET ligand development. Toward this end, we built a database consisting of 62 PET ligands that have successfully reached the clinic and 15 radioligands that failed in late-stage development as negative controls. A systematic analysis of these ligands identified a set of preferred parameters for physicochemical properties, brain permeability, and nonspecific binding (NSB). These preferred parameters have subsequently been applied to several programs and have led to the successful development of novel PET ligands with reduced resources and timelines. This strategy is illustrated here by the discovery of the novel phosphodiesterase 2A (PDE2A) PET ligand 4-(3-[(18)F]fluoroazetidin-1-yl)-7-methyl-5-{1-methyl-5-[4-(trifluoromethyl)phenyl]-1H-pyrazol-4-yl}imidazo[5,1-f][1,2,4]triazine, [(18)F]PF-05270430 (5).
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Compuestos de Azabiciclo/síntesis química , Azetidinas/síntesis química , Encéfalo/diagnóstico por imagen , Fosfodiesterasas de Nucleótidos Cíclicos Tipo 2/metabolismo , Radiofármacos/síntesis química , Animales , Compuestos de Azabiciclo/química , Compuestos de Azabiciclo/farmacocinética , Azetidinas/química , Azetidinas/farmacocinética , Encéfalo/enzimología , Simulación por Computador , Bases de Datos Factuales , Perros , Diseño de Fármacos , Radioisótopos de Flúor , Humanos , Ligandos , Macaca fascicularis , Masculino , Modelos Biológicos , Permeabilidad , Tomografía de Emisión de Positrones , Unión Proteica , Radiofármacos/química , Radiofármacos/farmacocinética , Ratas , Ratas Wistar , Relación Estructura-ActividadRESUMEN
INTRODUCTION: Fatty acid amide hydrolase (FAAH) is responsible for the enzymatic degradation of the fatty acid amide family of signaling lipids, including the endogenous cannabinoid (endocannabinoid) anandamide. The involvement of the endocannabinoid system in pain and other nervous system disorders has made FAAH an attractive target for drug development. Companion molecular imaging probes are needed, however, to assess FAAH inhibition in the nervous system in vivo. We report here the synthesis and in vivo evaluation of [(18)F]PF-9811, a novel PET ligand for non-invasive imaging of FAAH in the brain. METHODS: The potency and selectivity of unlabeled PF-9811 were determined by activity-based protein profiling (ABPP) both in vitro and in vivo. [(18)F]PF-9811 was synthesized in a 3-step, one-pot reaction sequence, followed by HPLC purification. Biological evaluation was performed by biodistribution and dynamic PET imaging studies in male rats. The specificity of [(18)F]PF-9811 uptake was evaluated by pre-administration of PF-04457845, a potent and selective FAAH inhibitor, 1h prior to radiotracer injection. RESULTS: Biodistribution studies show good uptake (SUV~0.8 at 90 min) of [(18)F]PF-9811 in rat brain, with significant reduction of the radiotracer in all brain regions (37%-73% at 90 min) in blocking experiments. Dynamic PET imaging experiments in rat confirmed the heterogeneous uptake of [(18)F]PF-9811 in brain regions with high FAAH enzymatic activity, as well as statistically significant reductions in signal following pre-administration of the blocking compound PF-04457845. CONCLUSIONS: [(18)F]PF-9811 is a promising PET imaging agent for FAAH. Biodistribution and PET imaging experiments show that the tracer has good uptake in brain, regional heterogeneity, and specific binding as determined by blocking experiments with the highly potent and selective FAAH inhibitor, PF-04457845.