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Cholesterol homeostasis is impaired in Alzheimer's disease; however, attempts to modulate brain cholesterol biology have not translated into tangible clinical benefits for patients to date. Several recent milestone developments have substantially improved our understanding of how excess neuronal cholesterol contributes to the pathophysiology of Alzheimer's disease. Indeed, neuronal cholesterol was linked to the formation of amyloid-ß and neurofibrillary tangles through molecular pathways that were recently delineated in mechanistic studies. Furthermore, remarkable advances in translational molecular imaging have now made it possible to probe cholesterol metabolism in the living human brain with PET, which is an important prerequisite for future clinical trials that target the brain cholesterol machinery in Alzheimer's disease patients-with the ultimate aim being to develop disease-modifying treatments. This work summarizes current concepts of how the biosynthesis, transport and clearance of brain cholesterol are affected in Alzheimer's disease. Further, current strategies to reverse these alterations by pharmacotherapy are critically discussed in the wake of emerging translational research tools that support the assessment of brain cholesterol biology not only in animal models but also in patients with Alzheimer's disease.
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Doença de Alzheimer , Encéfalo , Colesterol , Desenvolvimento de Medicamentos , Doença de Alzheimer/metabolismo , Doença de Alzheimer/tratamento farmacológico , Humanos , Colesterol/metabolismo , Encéfalo/metabolismo , Animais , Desenvolvimento de Medicamentos/métodosRESUMO
The hydrofluorination of alkenes represents an attractive strategy for the synthesis of aliphatic fluorides. This approach provides a direct means to form C(sp3)-F bonds selectively from readily available alkenes. Nonetheless, conducting hydrofluorination using nucleophilic fluorine sources poses significant challenges due to the low acidity and high toxicity associated with HF and the poor nucleophilicity of fluoride. In this study, we present a new Co(salen)-catalyzed hydrofluorination of simple alkenes utilizing Et3N·3HF as the sole source of both hydrogen and fluorine. This process operates via a photoredox-mediated polar-radical-polar crossover mechanism. We also demonstrated the versatility of this method by effectively converting a diverse array of simple and activated alkenes with varying degrees of substitution into hydrofluorinated products. Furthermore, we successfully applied this methodology to 18F-hydrofluorination reactions, enabling the introduction of 18F into potential radiopharmaceuticals. Our mechanistic investigations, conducted using rotating disk electrode voltammetry and DFT calculations, unveiled the involvement of both carbocation and CoIV-alkyl species as viable intermediates during the fluorination step, and the contribution of each pathway depends on the structure of the starting alkene.
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Aggregated α-synuclein (α-syn) protein is a pathological hallmark of Parkinson's disease (PD) and Lewy body dementia (LBD). Development of positron emission tomography (PET) radiotracers to image α-syn aggregates has been a longstanding goal. This work explores the suitability of a pyridothiophene scaffold for α-syn PET radiotracers, where 47 derivatives of a potent pyridothiophene (asyn-44; Kd=1.85â nM) were synthesized and screened against [3H]asyn-44 in competitive binding assays using post-mortem PD brain homogenates. Equilibrium inhibition constant (Ki) values of the most potent compounds were determined, of which three had Ki's in the lower nanomolar range (12-15â nM). An autoradiography study confirmed that [3H]asyn-44 is promising for imaging brain sections from multiple system atrophy and PD donors. Fluorine-18 labelled asyn-44 was synthesized in 6±2 % radiochemical yield (decay-corrected, n=5) with a molar activity of 263±121 GBq/µmol. Preliminary PET imaging of [18F]asyn-44 in rats showed high initial brain uptake (>1.5 standardized uptake value (SUV)), moderate washout (~0.4 SUV at 60â min), and low variability. Radiometabolite analysis showed 60-80 % parent tracer in the brain after 30 and 60â mins. While [18F]asyn-44 displayed good inâ vitro properties and acceptable brain uptake, troublesome radiometabolites precluded further PET imaging studies. The synthesis and inâ vitro evaluation of additional pyridothiophene derivatives are underway, with the goal of attaining improved affinity and metabolic stability.
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Idiopathic pulmonary fibrosis (IPF) is a fatal disease characterized by unpredictable progression and limited therapeutic options. Current diagnosis relies on high resolution computed tomography (HRCT), which may not adequately capture early signs of deterioration. The enzyme autotaxin (ATX) emerges as a prominently expressed extracellular secretory enzyme in the lungs of IPF patients. The objective of this study was to evaluate the effectiveness of 18F-labeled ATX-targeted tracer [18F]ATX-1905, in comparison with [18F]FDG, for early fibrosis diagnosis, disease evolution monitoring, and treatment efficacy assessment in bleomycin-induced pulmonary fibrosis (BPF) models. To assess treatment efficacy, mice were treated with two commonly used drugs for IPF, pirfenidone or nintedanib, from Day 9 to Day 23 postbleomycin administration. Lung tissue assessments encompassed inflammation severity via H&E staining, and Ashcroft scoring via Masson staining, alongside quantification of ATX expression through ELISA. Positron emission tomography (PET) imaging employing [18F]FDG and [18F]ATX-1905 tracked disease progression pre- and post-treatment. The extent of pulmonary fibrosis corresponded to changes in ATX expression levels in the BPF mouse model. Notably, [18F]ATX-1905 exhibited elevated uptake in BPF lungs during the progression of the disease, particularly evident at the early stage (Day 9). This uptake was inhibited by an ATX inhibitor, PF-8380, underscoring the specificity of the radiotracer. Conversely, [18F]FDG uptake, peaking at Day 15, decreased subsequently, likely reflective of diminished inflammation. A 2-week treatment regimen using either pirfenidone or nintedanib resulted in notable reductions of ATX expression levels and fibrosis degrees within lung tissues, based on ELISA and Masson staining, as evidenced by PET imaging with [18F]ATX-1905. [18F]FDG uptake also decreased following the treatment period. Additionally, PET/CT imaging extended to a nonhuman primate (NHP) BPF model. The uptake of [18F]ATX-1905 (SUVmax = 2.2) was significantly higher than that of [18F]FDG (SUVmax = 0.7) in fibrotic lung tissue. Using our novel ATX-specific radiotracer [18F]ATX-1905 and PET/CT imaging, we demonstrated excellent ability in early fibrosis detection, disease monitoring, and treatment assessment within lungs of the BPF mouse models. [18F]ATX-1905 displayed remarkable specificity for ATX expression and high sensitivity for ATX alterations, suggesting its potential for monitoring varying ATX expression in lungs of IPF patients.
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Numerous methods have been reported for detecting ROS/RNS in vitro and in vivo; however, detecting methods for the secondary products of the ROS/RNS reactions, particularly quasi-stable oxidized products, have been much less explored. In this report, we observed that half-curcumins could generate chemiluminescence. In contrast to other chemiluminescence scaffolds, the distinguishing feature of a half-curcumin is the formation of a carbanion intermediate of its acetylacetone moiety, opening unique avenues for applications. In this study, we designed a series of half-curcumins CRANAD-Xs and found that CRANAD-164 could be used to detect quasi-stable oxidized proteins (QSOP) in vivo and in patient serum samples. We illustrated that CRANAD-164 could be used to monitor the responses of taurine, an amino acid with newly reported anti-aging capacity, in an inflammatory mouse model. Remarkably, we further demonstrated that the QSOP levels were much higher in the disease serum samples, including Alzheimer's disease, compared to the samples from healthy controls. Moreover, our results revealed that the sera chemiluminescence intensities were higher in aged healthy controls compared to young healthy subjects, suggesting that CRANAD-164 can be used to monitor the increase of QSOP during aging.
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N-methyl-D-aspartate receptors (NMDAR), ionotropic glutamate receptors, mediate a slow component of excitatory synaptic transmission in the central nervous system and play a key role in normal brain function and development. Genetic variations in GRIN genes encoding NMDAR subunits that alter the receptor's functional characteristics are associated with a wide range of neurological and neuropsychiatric conditions. Pathological GRIN variants located in the M2 re-entrant loop lining the channel pore cause significant functional changes, the most consequential alteration being a reduction in voltage-dependent Mg2+ inhibition. Voltage-dependent Mg2+ block is a unique feature of NMDAR biology whereby channel activation requires both ligand binding and postsynaptic membrane depolarization. Thus, loss of NMDAR Mg2+ block will have a profound impact on synaptic function and plasticity. Here, we choose 11 missense variants within the GRIN1, GRIN2A, and GRIN2B genes that alter residues located in the M2 loop and significantly reduce Mg2+ inhibition. Each variant was evaluated for tolerance to genetic variation using the 3-dimensional structure and assessed for functional rescue pharmacology via electrophysiological recordings. Three FDA-approved NMDAR drugs-memantine, dextromethorphan, and ketamine-were chosen based on their ability to bind near the M2 re-entrant loop, potentially rectifying dysregulated NMDAR function by supplementing the reduced voltage-dependent Mg2+ block. These results provide insight of structural determinants of FDA-approved NMDAR drugs at their binding sites in the channel pore and may further define conditions necessary for the use of such agents as potential rescue pharmacology.
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Positron emission tomography (PET) is a powerful imaging tool for drug discovery, clinical diagnosis, and monitoring of disease progression. Fluorine-18 is the most common radionuclide used for PET, but advances in radiotracer development have been limited by the historical lack of methodologies and precursors amenable to radiolabeling with fluorine-18. Radiolabeling of electron-rich (hetero)aromatic rings remains a long-standing challenge in the production of PET radiopharmaceuticals. In this personal account, we discuss the history of spirocyclic iodonium ylide precursors, from inception to applications in clinical research, for the incorporation of fluorine-18 into complex non-activated (hetero)aromatic rings.
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Radioisótopos de Flúor , Compostos Radiofarmacêuticos , Tomografia por Emissão de Pósitrons/métodos , Descoberta de DrogasRESUMO
OBJECTIVES: Translocator protein 18 kDa (TSPO) positron emission tomography (PET) can be harnessed for the non-invasive detection of macrophage-driven inflammation. [18F]LW223, a newly reported TSPO PET tracer which was insensitive to rs6971 polymorphism, showed favorable performance characteristics in a recent imaging study involving a rat myocardial infarction model. To enable quantitative neuroimaging with [18F]LW223, we conducted kinetic analysis in the non-human primate (NHP) brain. Further, we sought to assess the utility of [18F]LW223-based TSPO imaging in a first-in-human study. METHODS: Radiosynthesis of [18F]LW223 was accomplished on an automated module, whereas molar activities, stability in formulation, lipophilicity and unbound free fraction (fu) of the probe were measured. Brain penetration and target specificity of [18F]LW223 in NHPs were corroborated by PET-MR imaging under baseline and pre-blocking conditions using the validated TSPO inhibitor, (R)-PK11195, at doses ranging from 5 to 10 mg/kg. Kinetic modeling was performed using one-tissue compartment model (1TCM), two-tissue compartment model (2TCM) and Logan graphical analyses, using dynamic PET data acquisition, arterial blood collection and metabolic stability testing. Clinical PET scans were performed in two healthy volunteers (HVs). Regional brain standard uptake value ratio (SUVr) was assessed for different time intervals. RESULTS: [18F]LW223 was synthesized in non-decay corrected radiochemical yields (n.d.c. RCYs) of 33.3 ± 6.5% with molar activities ranging from 1.8 ± 0.7 Ci/µmol (n = 11). [18F]LW223 was stable in formulation for up to 4 h and LogD7.4 of 2.31 ± 0.13 (n = 6) and fu of 5.80 ± 1.42% (n = 6) were determined. [18F]LW223 exhibited good brain penetration in NHPs, with a peak SUV value of ca. 1.79 in the whole brain. Pre-treatment with (R)-PK11195 substantially accelerated the washout and attenuated the area under the time-activity curve, indicating in vivo specificity of [18F]LW223 towards TSPO. Kinetic modeling demonstrated that 2TCM was the most suitable model for [18F]LW223-based neuroimaging. Global transfer rate constants (K1) and total volumes of distribution (VT) were found to be 0.10 ± 0.01 mL/cm3/min and 2.30 ± 0.17 mL/cm3, respectively. Dynamic PET data analyses across distinct time windows revealed that the VT values were relatively stable after 60 min post-injection. In a preliminary clinical study with two healthy volunteers, [18F]LW223 exhibited good brain uptake and considerable tracer retention across all analyzed brain regions. Of note, an excellent correlation between SUVr with VT was obtained when assessing the time interval from 20 to 40 min post tracer injection (SUVr(20-40 min), R2 = 0.94, p < 0.0001), suggesting this time window may be suitable to estimate specific binding to TSPO in human brain. CONCLUSION: Our findings indicate that [18F]LW223 is suitable for quantitative TSPO-targeted PET imaging in higher species. Employing state-of-the-art kinetic modeling, we found that [18F]LW223 was effective in mapping TSPO throughout the NHP brain, with best model fits obtained from 2TCM and Logan graphical analyses. Overall, our results indicate that [18F]LW223 exhibits favorable tracer performance characteristics in higher species, and this novel imaging tool may hold promise to provide effective neuroinflammation imaging in patients with neurological disease.
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Encéfalo , Tomografia por Emissão de Pósitrons , Animais , Humanos , Encéfalo/metabolismo , Proteínas de Transporte/metabolismo , Cinética , Tomografia por Emissão de Pósitrons/métodos , Primatas/metabolismo , Compostos Radiofarmacêuticos , Receptores de GABA/metabolismo , Receptores de GABA-A/metabolismoRESUMO
BACKGROUND: Myocardial perfusion imaging by positron emission tomography (PET-MPI) is the current gold standard for quantification of myocardial blood flow. 18F-flurpiridaz was recently introduced as a valid alternative to currently used PET-MPI probes. Nonetheless, optimum scan duration and time interval for image analysis are currently unknown. Further, it is unclear whether rest/stress PET-MPI with 18F-flurpiridaz is feasible in mice. METHODS: Rest/stress PET-MPI was performed with 18F-flurpiridaz (0.6-3.0 MBq) in 27 mice aged 7-8 months. Regadenoson (0.1 µg/g) was used for induction of vasodilator stress. Kinetic modeling was performed using a metabolite-corrected arterial input function. Image-derived myocardial 18F-flurpiridaz uptake was assessed for different time intervals by placing a volume of interest in the left ventricular myocardium. RESULTS: Tracer kinetics were best described by a two-tissue compartment model. K1 ranged from 6.7 to 20.0 mL·cm-3·min-1, while myocardial volumes of distribution (VT) were between 34.6 and 83.6 mL·cm-3. Of note, myocardial 18F-flurpiridaz uptake (%ID/g) was significantly correlated with K1 at rest and following pharmacological vasodilation for all time intervals assessed. However, while Spearman's coefficients (rs) ranged between 0.478 and 0.681, R2 values were generally low. In contrast, an excellent correlation of myocardial 18F-flurpiridaz uptake with VT was obtained, particularly when employing the averaged myocardial uptake from 20 to 40 min post tracer injection (R2 ≥ 0.98). Notably, K1 and VT were similarly sensitive to pharmacological vasodilation induction. Further, mean stress-to-rest ratios of K1, VT, and %ID/g 18F-flurpiridaz were virtually identical, suggesting that %ID/g 18F-flurpiridaz can be used to estimate coronary flow reserve (CFR) in mice. CONCLUSION: Our findings suggest that a simplified assessment of relative myocardial perfusion and CFR, based on image-derived tracer uptake, is feasible with 18F-flurpiridaz in mice, enabling high-throughput mechanistic CFR studies in rodents.
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Imagem de Perfusão do Miocárdio , Camundongos , Animais , Imagem de Perfusão do Miocárdio/métodos , Estudos de Viabilidade , Tomografia por Emissão de Pósitrons/métodos , Miocárdio , Processamento de Imagem Assistida por ComputadorRESUMO
Hepatocellular carcinoma (HCC) is a prevalent liver malignancy, which ranks third in the cancer-related cause of deaths in worldwide and ninth in the United States. Currently, HCC is typically diagnosed by ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI) scan at its late stage and the survival of HCC patients after diagnosis is usually very poor. Therefore, the development of novel and effective tool for early diagnosis, characterization and staging of HCC patients is of critical importance. Recent studies have demonstrated correlation of HCC with MAGL. In HCC cells, upregulation of MAGL activity enhanced cell invasiveness ability, while pharmacological blockade of MAGL led to significant inhibition of this trend. In this study, we aim to visualize the expression and activity of hepatic MAGL in different HCC cells and HCC patients' samples by taking advantage of positron emission tomography (PET) imaging with our previously developed MAGL radioligand [11C]MAGL-0519. As a result, [11C]MAGL-0519 exhibited higher radioactivity accumulation in HepaG2 and Hepa 1-6 cell lines compared with that of normal liver cells (AML-12 and LX-2), indicating higher MAGL expression levels in these HCC cells. This rationale was then validated by Western blot and immunofluorescent staining analysis. Furthermore, HCC patients' liver sections exhibited significantly increased uptake of [11C]MAGL-0519, which was consistent with the results in cell uptake assays. Taking together, these results provided a biological rationale and built a foundation to use [11C]MAGL-0519 as a potential and effective PET ligand for the diagnosis of HCC.
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Carcinoma Hepatocelular , Neoplasias Hepáticas , Carcinoma Hepatocelular/diagnóstico por imagem , Carcinoma Hepatocelular/patologia , Humanos , Ligantes , Neoplasias Hepáticas/diagnóstico por imagem , Neoplasias Hepáticas/patologia , Tomografia por Emissão de PósitronsRESUMO
Monoacylglycerol lipase (MAGL) constitutes a serine hydrolase that orchestrates endocannabinoid homeostasis and exerts its function by catalyzing the degradation of 2-arachidonoylglycerol (2-AG) to arachidonic acid (AA). As such, selective inhibition of MAGL represents a potential therapeutic and diagnostic approach to various pathologies including neurodegenerative disorders, metabolic diseases and cancers. Based on a unique 4-piperidinyl azetidine diamide scaffold, we developed a reversible and peripheral-specific radiofluorinated MAGL PET ligand [18F]FEPAD. Pharmacokinetics and binding studies on [18F]FEPAD revealed its outstanding specificity and selectivity towards MAGL in brown adipose tissue (BAT) - a tissue that is known to be metabolically active. We employed [18F]FEPAD in PET studies to assess the abundancy of MAGL in BAT deposits of mice and found a remarkable degree of specific tracer binding in the BAT, which was confirmed by post-mortem tissue analysis. Given the negative regulation of endocannabinoids on the metabolic BAT activity, our study supports the concept that dysregulation of MAGL is likely linked to metabolic disorders. Further, we now provide a suitable imaging tool that allows non-invasive assessment of MAGL in BAT deposits, thereby paving the way for detailed mechanistic studies on the role of BAT in endocannabinoid system (ECS)-related pathologies.
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Endocanabinoides , Monoacilglicerol Lipases , Endocanabinoides/metabolismo , Tecido Adiposo Marrom/diagnóstico por imagem , Tecido Adiposo Marrom/metabolismo , Tomografia por Emissão de Pósitrons/métodos , Ligantes , Inibidores Enzimáticos/farmacologiaRESUMO
OBJECTIVES: To enable non-invasive real-time quantification of vasopressin 1A (V1A) receptors in peripheral organs, we sought to develop a suitable PET probe that would allow specific and selective V1A receptor imaging in vitro and in vivo. METHODS: We synthesized a high-affinity and -selectivity ligand, designated compound 17. The target structure was labeled with carbon-11 and tested for its utility as a V1A-targeted PET tracer by cell uptake studies, autoradiography, in vivo PET imaging and ex vivo biodistribution experiments. RESULTS: Compound 17 (PF-184563) and the respective precursor for radiolabeling were synthesized in an overall yield of 49% (over 7 steps) and 40% (over 8 steps), respectively. An inhibitory constant of 0.9 nM towards the V1A receptors was measured, while excellent selectivity over the related V1B, V2 and OT receptor (IC50 >10,000 nM) were obtained. Cell uptake studies revealed considerable V1A binding, which was significantly reduced in the presence of V1A antagonists. Conversely, there was no significant blockade in the presence of V1B and V2 antagonists. In vitro autoradiography and PET imaging studies in rodents indicated specific tracer binding mainly in the liver. Further, the pancreas, spleen and the heart exhibited specific binding of [11C]17 ([11C]PF-184563) by ex vivo biodistribution experiments. CONCLUSION: We have developed the first V1A-targeted PET ligand that is suitable for subtype-selective receptor imaging in peripheral organs including the liver, heart, pancreas and spleen. Our findings suggest that [11C]PF-184563 can be a valuable tool to study the role of V1A receptors in liver diseases, as well as in cardiovascular pathologies.
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Benzodiazepinas/farmacologia , Compostos Radiofarmacêuticos/farmacologia , Receptores de Vasopressinas/metabolismo , Triazóis/farmacologia , Animais , Autorradiografia , Benzodiazepinas/farmacocinética , Células CHO , Radioisótopos de Carbono , Cricetulus , Feminino , Ligantes , Fígado/metabolismo , Masculino , Camundongos , Miocárdio/metabolismo , Pâncreas/metabolismo , Tomografia por Emissão de Pósitrons , Compostos Radiofarmacêuticos/farmacocinética , Ratos Wistar , Baço/metabolismo , Triazóis/farmacocinéticaRESUMO
N-methyl-D-aspartate receptors (NMDARs) play critical roles in the physiological function of the mammalian central nervous system (CNS), including learning, memory, and synaptic plasticity, through modulating excitatory neurotransmission. Attributed to etiopathology of various CNS disorders and neurodegenerative diseases, GluN2B is one of the most well-studied subtypes in preclinical and clinical studies on NMDARs. Herein, we report the synthesis and preclinical evaluation of two 11C-labeled GluN2B-selective negative allosteric modulators (NAMs) containing N,N-dimethyl-2-(1H-pyrrolo[3,2-b]pyridin-1-yl)acetamides for positron emission tomography (PET) imaging. Two PET ligands, namely [11C]31 and [11C]37 (also called N2B-1810 and N2B-1903, respectively) were labeled with [11C]CH3I in good radiochemical yields (decay-corrected 28% and 32% relative to starting [11C]CO2, respectively), high radiochemical purity (>99%) and high molar activity (>74 GBq/µmol). In particular, PET ligand [11C]31 demonstrated moderate specific binding to GluN2B subtype by in vitro autoradiography studies. However, because in vivo PET imaging studies showed limited brain uptake of [11C]31 (up to 0.5 SUV), further medicinal chemistry and ADME optimization are necessary for this chemotype attributed to low binding specificity and rapid metabolism in vivo.
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Acetamidas/metabolismo , Pirimidinas/metabolismo , Pirróis/metabolismo , Compostos Radiofarmacêuticos/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Acetamidas/síntese química , Acetamidas/farmacocinética , Animais , Encéfalo/metabolismo , Radioisótopos de Carbono/química , Feminino , Ligantes , Masculino , Metilação , Camundongos Endogâmicos ICR , Tomografia por Emissão de Pósitrons , Pirimidinas/síntese química , Pirimidinas/farmacocinética , Pirróis/síntese química , Pirróis/farmacocinética , Compostos Radiofarmacêuticos/síntese química , Compostos Radiofarmacêuticos/farmacocinética , Ratos Sprague-Dawley , Receptores de N-Metil-D-Aspartato/antagonistas & inibidoresRESUMO
BACKGROUND & AIMS: The vitronectin receptor integrin αvß3 drives fibrogenic activation of hepatic stellate cells (HSCs). Molecular imaging targeting the integrin αvß3 could provide a non-invasive method for evaluating the expression and the function of the integrin αvß3 on activated HSCs (aHSCs) in the injured liver. In this study, we sought to compare differences in the uptake of [18F]-Alfatide between normal and injured liver to evaluate its utility for assessment of hepatic fibrogenesis. METHODS: PET with [18F]-Alfatide, non-enhanced CT, histopathology, immunofluorescence staining, immunoblotting and gene analysis were performed to evaluate and quantify hepatic integrin αvß3 levels and liver fibrosis progression in mouse models of fibrosis (carbon tetrachloride [CCl4] and bile duct ligation [BDL]). The liver AUC divided by the blood AUC over 30 min was used as an integrin αvß3-PET index to quantify fibrosis progression. Ex vivo analysis of frozen liver tissue from patients with fibrosis and cirrhosis verified the animal findings. RESULTS: Fibrotic mouse livers showed enhanced [18F]-Alfatide uptake and retention compared to control livers. The radiotracer was demonstrated to bind specifically with integrin αvß3, which is mainly expressed on aHSCs. Autoradiography and histopathology confirmed the PET imaging results. Further, the mRNA and protein level of integrin αvß3 and its signaling complex were higher in CCl4 and BDL models than controls. The results obtained from analyses on human fibrotic liver sections supported the animal findings. CONCLUSIONS: Imaging hepatic integrin αvß3 with PET and [18F]-Alfatide offers a potential non-invasive method for monitoring the progression of liver fibrosis. LAY SUMMARY: Integrin αvß3 expression on activated hepatic stellate cells (aHSCs) is associated with HSC proliferation during hepatic fibrogenesis. Herein, we show that a radioactive tracer, [18F]-Alfatide, binds to integrin αvß3 with high affinity and specificity. [18F]-Alfatide could thus be used as a non-invasive imaging biomarker to track hepatic fibrosis progression.
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Células Estreladas do Fígado/metabolismo , Integrina alfaVbeta3/metabolismo , Cirrose Hepática , Peptídeos Cíclicos/farmacologia , Tomografia por Emissão de Pósitrons/métodos , Animais , Progressão da Doença , Imunofluorescência/métodos , Radioisótopos de Flúor/farmacologia , Perfilação da Expressão Gênica/métodos , Cirrose Hepática/diagnóstico por imagem , Cirrose Hepática/metabolismo , Cirrose Hepática/patologia , Camundongos , Imagem Molecular/métodos , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
Cholesterol 24-hydroxylase, also known as CYP46A1 (EC 1.14.13.98), is a monooxygenase and a member of the cytochrome P450 family. CYP46A1 is specifically expressed in the brain where it controls cholesterol elimination by producing 24S-hydroxylcholesterol (24-HC) as the major metabolite. Modulation of CYP46A1 activity may affect Aß deposition and p-tau accumulation by changing 24-HC formation, which thereafter serves as potential therapeutic pathway for Alzheimer's disease. In this work, we showcase the efficient synthesis and preliminary pharmacokinetic evaluation of a novel cholesterol 24-hydroxylase inhibitor 1 for use in positron emission tomography.
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Dióxido de Carbono/química , Isótopos de Carbono , Colesterol 24-Hidroxilase/antagonistas & inibidores , Inibidores Enzimáticos/síntese química , Compostos Radiofarmacêuticos/síntese química , Animais , Inibidores Enzimáticos/química , Inibidores Enzimáticos/farmacocinética , Camundongos , Estrutura Molecular , Neuroimagem , Tomografia por Emissão de Pósitrons , Compostos Radiofarmacêuticos/química , Compostos Radiofarmacêuticos/farmacocinética , Distribuição TecidualRESUMO
Fatty acid amide hydrolase (FAAH) exerts its main function in the catabolism of the endogenous chemical messenger anandamide (AEA), thus modulating the endocannabinoid (eCB) pathway. Inhibition of FAAH may serve as an effective strategy to relieve anxiety and possibly other central nervous system (CNS)-related disorders. Positron emission tomography (PET) would facilitate us to better understand the relationship between FAAH in certain disease conditions, and accelerate clinical translation of FAAH inhibitors by providing in vivo quantitative information. So far, most PET tracers show irreversible binding patterns with FAAH, which would result in complicated quantitative processes. Herein, we have identified a new FAAH inhibitor (1-((1-methyl-1H-indol-2-yl)methyl)piperidin-4-yl)(oxazol-2-yl)methanone (8) which inhibits the hydrolysis of AEA in the brain with high potency (IC50 value 11 nM at a substrate concentration of 0.5 µM), and without showing time-dependency. The PET tracer [11C]8 (also called [11C]FAAH-1906) was successfully radiolabeled with [11C]MeI in 17 ± 6% decay-corrected radiochemical yield (n = 7) with >74.0 GBq/µmol (2 Ci/µmol) molar activity and >99% radiochemical purity. Ex vivo biodistribution and blocking studies of [11C]8 in normal mice were also conducted, indicating good brain penetration, high brain target selectivity, and modest to excellent target selectivity in peripheral tissues. Thus, [11C]8 is a potentially useful PET ligand with enzyme inhibitory and target binding properties consistent with a reversible mode of action.
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Amidoidrolases/antagonistas & inibidores , Encéfalo/efeitos dos fármacos , Compostos Heterocíclicos/farmacologia , Tomografia por Emissão de Pósitrons , Amidoidrolases/análise , Amidoidrolases/metabolismo , Animais , Encéfalo/enzimologia , Relação Dose-Resposta a Droga , Compostos Heterocíclicos/síntese química , Compostos Heterocíclicos/química , Hidrólise , Ligantes , Estrutura Molecular , Ratos , Relação Estrutura-AtividadeRESUMO
Transmembrane AMPA receptor regulatory proteins (TARPs) are a recently discovered family of proteins that modulate AMPA receptors activity. Based on a potent and selective TARP subtype γ-8 antagonist, 6-(methyl(4-(pyridin-2-yl)thiazol-2-yl)amino)benzo[d]thiazol-2(3H)-one (compound 9), we perform the radiosynthesis of its 11C-isotopologue 1 and conduct preliminary PET evaluation to test the feasibility of imaging TARP γ-8 dependent receptors in vivo.
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Benzoxazóis/química , Encéfalo/diagnóstico por imagem , Tomografia por Emissão de Pósitrons , Compostos Radiofarmacêuticos/síntese química , Receptores de AMPA/metabolismo , Animais , Benzoxazóis/síntese química , Radioisótopos de Carbono/química , Estudos de Viabilidade , Marcação por Isótopo , Compostos Radiofarmacêuticos/química , RatosRESUMO
The α-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) belong to the family of ionotropic transmembrane receptors for glutamate (iGluRs) that are implicated in the pathology of neurological disorders and neurodegenerative diseases. Inspired by a recently developed positive allosteric modulator of AMPARs, 4-cyclopropyl-7-(3-methoxyphenoxy)-3,4-dihydro-2H-benzo[ e ][1,2,4]thiadiazine 1,1-dioxide (16; EC50 = 2.0 nM), we designed a new synthetic route for N-protected phenolic precursor 13 and efficiently radiolabeled a PET ligand [11C]AMPA-1905 ([11C]16) using a modified one-pot two-step strategy in high radiochemical yield and high molar activity. Preliminary in vivo evaluation was carried out to investigate the suitability of [11C]16 as a potential PET probe for AMPAR imaging.
RESUMO
Fluorine-18 labeled N,N-diethyl-2-(2-(4-(2-fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)acetamide ([18 F]FDPA) is a potent and selective radiotracer for positron-emission tomography (PET) imaging of the translocator protein 18 kDa (TSPO). Our previous in vitro and in vivo evaluations have proven that this tracer is promising for further human translation. Our study addresses the need to streamline the automatic synthesis of this radiotracer to make it more accessible for widespread clinical evaluation and application. Here, we successfully demonstrate a one-step radiolabeling of [18 F]FDPA based on a novel spirocyclic iodonium ylide (SCIDY) precursor using tetra-n-butyl ammonium methanesulfonate (TBAOMs), which has demonstrated the highest radiochemical yields and molar activity from readily available [18 F]fluoride ion. The nucleophilic radiofluorination was completed on a GE TRACERlab FX2 N synthesis module, and the formulated [18 F]FDPA was obtained in nondecay corrected (n.d.c) radiochemical yields of 15.6 ± 4.2%, with molar activities of 529.2 ± 22.5 GBq/µmol (14.3 ± 0.6 Ci/µmol) at the end of synthesis (60 minutes, n = 3) and validated for human use. This methodology facilitates efficient synthesis of [18 F]FDPA in a commercially available synthesis module, which would be broadly applicable for routine production and widespread clinical PET imaging studies.
Assuntos
Receptores de GABA/metabolismo , Compostos de Espiro/química , Automação , Técnicas de Química Sintética , Humanos , Tomografia por Emissão de Pósitrons , Traçadores Radioativos , RadioquímicaRESUMO
[18F]FPEB is a positron emission tomography (PET) radiopharmaceutical used for imaging the abundance and distribution of mGluR5 in the central nervous system (CNS). Efficient radiolabeling of the aromatic ring of [18F]FPEB has been an ongoing challenge. Herein, five metal-free precursors for the radiofluorination of [18F]FPEB were compared, namely, a chloro-, nitro-, sulfonium salt, and two spirocyclic iodonium ylide (SCIDY) precursors bearing a cyclopentyl (SPI5) and a new adamantyl (SPIAd) auxiliary. The chloro- and nitro-precursors resulted in a low radiochemical yield (<10% RCY), whereas both SCIDY precursors and the sulfonium salt precursor produced [18F]FPEB in the highest RCYs of 25% and 36%, respectively. Preliminary PET/CT imaging studies with [18F]FPEB were conducted in a transgenic model of Alzheimer's Disease (AD) using B6C3-Tg(APPswe,PSEN1dE9)85Dbo/J (APP/PS1) mice, and data were compared with age-matched wild-type (WT) B6C3F1/J control mice. In APP/PS1 mice, whole brain distribution at 5 min post-injection showed a slightly higher uptake (SUV = 4.8 ± 0.4) than in age-matched controls (SUV = 4.0 ± 0.2). Further studies to explore mGluR5 as an early biomarker for AD are underway.