Parkinson's disease is one of the fastest-growing neurodegenerative disorders, with no effective treatments to modify its progression. Microglial-driven neuroinflammation, mediated by NOD-leucine rich repeat and pyrin containing protein 3 (NLRP3) inflammasome activation, plays a key role in disease onset and progression. The NLRP3 inflammasome is upregulated in microglia from Parkinson's disease patients and activated by oxidative stress and α-synuclein aggregates, triggering the release of pro-inflammatory mediators that contribute to neuroinflammation and neuronal death. MCC950, the first described specific NLRP3 inhibitor, has shown promise in Parkinson's disease models but is limited by suboptimal pharmacokinetics and safety, hindering its clinical development. Here, we developed a novel NLRP3 inflammasome inhibitor, MCC7840 (also known as Inzomelid or Emlenoflast), and utilized clinically relevant PET-MRI imaging biomarkers to assess its therapeutic efficacy in preclinical models of Parkinson's disease. MCC7840 inhibited NLRP3 in human and mouse microglia with nanomolar potency, while demonstrating improved systemic exposure, half-life, brain permeability and bioavailability compared with MCC950. In a murine NLRP3 gain-of-function model of Muckle-Wells syndrome, MCC7840 effectively inhibited mortality and demonstrated superior potency compared with MCC950. Chronic oral administration of MCC7840 protected against neuroinflammation, motor deficits and dopamine loss in both 6-hydroxydopamine and preformed α-synuclein fibril mouse models of Parkinson's disease. Radiotracer imaging of multiple PET markers in the same mouse revealed that MCC7840 attenuated neuroinflammation (translocator protein ligand; 18F-DPA-714), preserved dopamine uptake (fluorodopa; 18F-FDOPA), mitigated dopamine transporter (DAT) loss (DAT ligand; 18F-FBCTT) and reduced blood-brain barrier leakage (gadolinium contrast MRI). Notably, MCC7840 was effective in a slowly progressing 12-month α-synuclein model, even when administered after symptom onset, 4 months post-α-synuclein injection. These findings highlight the utility of PET/MRI as a non-invasive tool to evaluate drug efficacy and support MCC7840, and other brain-penetrant NLRP3 inhibitors, as promising disease-modifying therapies for Parkinson's disease, warranting future clinical investigation.

Protein phosphatase 2A (PP2A), a member of the phosphoprotein phosphatase (PPP) family, plays a pivotal role in regulating tau dephosphorylation, thereby maintaining the functional integrity of this brain-specific protein in microtubule assembly. Progressive downregulation of PP2A has been implicated in the pathogenesis of Alzheimer’s disease (AD). The identification of high-affinity PP2A ligands presents a promising avenue for monitoring early-stage dementia progression through alternative molecular mechanisms. Utilizing the catalytic binding pocket model of PP1 as a structural surrogate for PPPs, three distinct fragments derived from various natural PP2A inhibitors were found to exhibit equivalent binding functionality. Building upon this framework in small-molecule design, a synthetic spiroketal compound was developed based on the C1–C14 acidic fragment of okadaic acid (OA), a PP2A-selective inhibitor. This compound emerges as a promising candidate for further therapeutic and diagnostic investigation.

Parkinson's disease (PD) is one of the fastest-growing neurological disorders, characterized by the progressive loss of dopaminergic neurons in the substantia nigra and the presence of α-synuclein (Syn) aggregates. Immune-mediated neuroinflammation driven by microglia contributes to PD pathology. We previously showed that inhibiting the microglial NLRP3 inflammasomes prevents Syn pathology in mice, but the role of the complement system remains unexplored. Using transcriptomic and proteomic data, we identified widespread upregulation of complement in PD patient brains at sites of dopaminergic neuron loss and in peripheral blood. We demonstrated that fibrillar Syn activates complement in human plasma, with proteomic studies supporting C5a as a key factor upregulated in PD patient serum, along with markedly increased C5aR1 expression in human and mouse microglia.In three distinct preclinical PD models, complement and microglial C5aR1 were upregulated following dopaminergic degeneration in the nigrostriatal pathway. Genetic deletion of key complement effectors at the C3, C5, and MAC levels in a neurotoxin-based PD model highlighted a critical role for C5aR1 in neurodegeneration. To test the therapeutic potential of this pathway, we first examined the efficacy of the C5aR1 inhibitor, PMX205, in reducing neuropathology and motor dysfunction in the 6-OHDA model. We correlated behaviour, microglial activation, and dopamine spatial distribution using mass spectrometry imaging (MALDI-MSI), showing neuroprotection in 6-OHDA-injected human C5aR1 knock-in mice and in wild-type mice orally dosed with PMX205. Next, we tested PMX205 in a 12-month Syn fibril model of PD. In parallel, we utilized F18-DPA-714 PET/CT imaging to visualize microglial activation in living mice. We identified that prophylactic (0-12 months) and therapeutic (4-12 months) oral administration of PMX205 ameliorated motor deficits, dopaminergic neurodegeneration, and F18-DPA-714 signals in this model.Mechanistically, we show that Syn triggered cell intrinsic microglial C5a-C5aR1 engagement, leading to NLRP3 inflammasome activation via potassium efflux. This process was impaired in the absence or inhibition of C5aR1 in human and mouse microglia, suggesting that persistent complement activation by fibrillar Syn exacerbates disease pathology. Our findings indicate that targeting complement and C5aR1 with pharmacological inhibitors could mitigate microglial-driven neuroinflammation, offering a potential strategy to slow or halt disease progression in PD.

Alzheimer's disease (AD) is the most common type of human dementia and is responsible for over 60% of diagnosed dementia cases worldwide. Abnormal deposition of β-amyloid and the accumulation of neurofibrillary tangles have been recognised as the two pathological hallmarks targeted by AD diagnostic imaging as well as therapeutics. With the progression of pathological studies, the two hallmarks and their related pathways have remained the focus of researchers who seek for AD diagnostic and therapeutic strategies in the past decades. In this work, we reviewed the development of the AD biomarkers and their corresponding target-specific small molecule drugs for both diagnostic and therapeutic applications, underlining their success, failure, and future possibilities.

Multimodal imaging provides rich biological information, which can be exploited to study drug activity, disease associated phenotypes, and pharmacological responses. Here we show discovery and validation of a new probe targeting the endocannabinoid α/β-hydrolase domain 6 (ABHD6) enzyme by utilizing positron emission tomography (PET) and matrix-assisted laser desorption/ionization (MALDI) imaging. [18F]JZP-MA-11 as the first PET ligand for in vivo imaging of the ABHD6 is reported and specific uptake in ABHD6-rich peripheral tissues and major brain regions was demonstrated using PET. A proof-of-concept study in nonhuman primate confirmed brain uptake. In vivo pharmacological response upon ABHD6 inhibition was observed by MALDI imaging. These synergistic imaging efforts used to identify biological information cannot be obtained by a single imaging modality and hold promise for improving the understanding of ABHD6-mediated endocannabinoid metabolism in peripheral and central nervous system disorders.

This work investigates the preparation of 1,7-dioxaspiro [5.5]undecane derivatives via the application of the template compound 2,8-bis(bromomethyl)-1,7-dioxaspiro [5.5]undecane and a series of catalysed carbonyl-ene reactions introducing aromatic and non-aromatic linkers to the heterocyclic system, providing an alternative approach to various marine toxin fragments.

Several classes of cannabinoid receptor type 2 radioligands have been evaluated for imaging of neuroinflammation, with successful clinical translation yet to take place. Here we describe the synthesis of fluorinated 5-azaindoles and pharmacological characterization and in vivo evaluation of 18F-radiolabeled analogues. [18F]2 (hCB2 Ki = 96.5 nM) and [18F]9 (hCB2 Ki = 7.7 nM) were prepared using Cu-mediated 18F-fluorination with non-decay-corrected radiochemical yields of 15 ± 6% and 18 ± 2% over 85 and 80 min, respectively, with high radiochemical purities (>97%) and molar activities (140-416 GBq/μmol). In PET imaging studies in rats, both [18F]2 and [18F]9 demonstrated specific binding in CB2-rich spleen after pretreatment with CB2-specific GW405833. Moreover, [18F]9 exhibited higher brain uptake at later time points in a murine model of neuroinflammation compared with a healthy control group. The results suggest further evaluation of azaindole based CB2 radioligands is warranted in other neuroinflammation models.

Efficacy of diagnostics and therapeutics for brain tumours can be modulated by vascular delivery and blood brain barrier permeability. Simultaneous dynamic gadolinium MR-PET enables independent assessment of vascular delivery and blood brain barrier integrity in a brain tumour animal model in the presence of a PET tracer.Dual echo dynamic gadolinium enhanced gradient echo imaging allows simultaneous calculation of T2* and T1 images from the TE image pairs. Relaxivity values then enabled determination of independent T2*- and T1-derived gadolinium concentrations simultaneously with measurement of [18F]DPA-714 neuroinflammation radiotracer delivery.Separate T2*- and T1-derived gadolinium concentrations curves were derived in a selection of tumours and normal tissue, reflecting vascular delivery and tissue uptake. Changes in the PET activity curves were seen in tumours and normal tissue, reflecting changes in the MR derived dynamic curves. The dramatic changes in the MR-derived vascular delivery and tissue uptake estimates may improve the understanding of the alteration of delivery and uptake of new theranostic agents.

While the dire cardiometabolic consequences of the hypercaloric modern ‘Western’ diet are well known, there is not much information on the health impact of a high sucrose diet not inducing weight gain. Here, we tested the hypothesis that rats reared with intermittent binge access to sucrose in addition to normal chow would develop an inflammatory response in brain. To test this hypothesis, we undertook serial PET/MRI scans with the TSPO ligand [ 18 F]DPA714 in a group of (n=9) rats at baseline and again after voluntarily consuming 5% sucrose solution three days a week for three months. Compared to a control group fed with normal chow (n=9), the sucrose rats indeed showed widespread increases in the availability of cerebral binding sites for the microglial marker, despite normal weight gain compared to the control diet group. Subsequent immunofluorescence staining of the brains confirmed the PET findings, showing a widespread 20% increase in the abundance of IBA-1-positive microglia with characteristic ‘semi-activated’ morphology in the binge sucrose rats, which had 23% lower density of microglial endpoints and 25% lower mean process length compared to microglia in the control rats with ordinary feeding. GFAP immunofluorescence showed no difference in astroglial coverage in the sucrose rats, except for a slight reduction in hypothalamus. The binge sucrose diet-induced neuroinflammation was associated with a significant elevation of white blood cell counts. Taking these results together, we find that long-term intake of sucrose in a binge paradigm, similar in sucrose content to the contemporary Western diet, triggered a low-grade systemic and central inflammation in non-obese rats. The molecular mechanism of this phenomenon remains to be established.

Introduction: Prenatal ethanol exposure (PEE) has been shown to alter the level and function of receptors in the brain, one of which is GABA(a) receptors (GABA(a)R), the major inhibitory ligand gated ion channels that mediate neuronal inhibition. High dose PEE in animals resulted in the upregulation of GABA(a)R, but the effects of low and moderate dose PEE at early gestation have not been investigated. This study aimed at examining GABA(a)R density in the adult mouse brain following PEE during a period equivalent to the first 3 to 4 weeks in human gestation. It was hypothesized that early moderate PEE would cause alterations in brain GABA(a)R levels in the adult offspring. Methods: C57BL/6J mice were given 10% v/v ethanol during the first 8 gestational days. Male offspring were studied using in-vivo Positron Emission Tomography (PET)/Magnetic Resonance Imaging (MRI), biodistribution, invitro autoradiography using [F-18]AH114726. a novel flumazenil analogue with a high affinity for the benzodiazepine-binding site, and validated using immunohistochemistry. Results: In vivo PET and biodistribution did not detect alteration in brain tracer uptake. In vitro radiotracer studies detected significantly reduced GABA(a)R in the olfactory bulbs. Immunohistochemistry detected reduced GABA(a)R in the cerebral cortex, cerebellum and hippocampus, while Nissl staining showed that cell density was significantly higher in the striatum following PEE. Conclusion: Early moderate PEE may induce long-term alterations in the GABA(a)R system that persisted into adulthood. (C) 2020 Elsevier Inc. All rights reserved.

Aim: R18D is a poly-arginine peptide that has demonstrated neuroprotection in preclinical models of excitotoxicity, stroke, hypoxic-ischemic encephalopathy and traumatic brain injury. Here, we examined the peptide’s uptake in serum. Materials & methods: Healthy, male Sprague–Dawley rats were intravenously administered either 1000 nmol/kg R18D (D-enantiomer of R18) or approximately 2.5 nmol/kg (36 ± 9 MBq) [18F]R18D, for serum and organ tissue uptake, respectively. Serum samples underwent mass spectrometric analysis to detect unbound R18D peptide. Animals administered [18F]R18D were subjected to positron emission tomography imaging. Results & conclusion: Free R18D was detected at 5 min post-infusion in serum samples. [18F]R18D was rapidly distributed to the kidney (6–7%ID/g), and a small fraction localized to the brain (0.115–0.123%ID/g) over a 60-min acquisition period.

N-(2-chloro-5-(S-2-[F-18]fluoroethyl)thiophenyl)-N'-(3-thiomethylphenyl)-N'-methylguanidine, ([F-18]GE-179), has been identified as a promising positron emission tomography (PET) ligand for the intra-channel phencyclidine (PCP) binding site of the N-methyl-D-aspartate (NMDA) receptor. The radiosynthesis of [F-18]GE-179 has only been performed at low radioactivity levels. However, the manufacture of a GMP compliant product at high radioactivity levels was required for clinical studies. We describe the development of a process using the GE FASTlab (TM) radiosynthesis platform coupled with HPLC purification. The radiosynthesis is a two-step process, involving the nucleophilic fluorination of ethylene ditosylate, 11, followed by alkylation to the deprotonated thiol precursor, N-(2-chloro-5-thiophenol)-N'-(3-thiomethylphenyl)-N'-methyl guanidine, 8. The crude product was purified by semi-preparative HPLC to give the formulated product in an activity yield (AY) of 7 +/- 2% (n = 15) with a total synthesis time of 120 minutes. The radioactive concentration (RAC) and radiochemical purity (RCP) were 328 +/- 77 MBq/mL and 96.5 +/- 1% respectively and the total chemical content was 2 +/- 1 mu g. The final formulation volume was 14 mL. The previously described radiosynthesis of [F-18]GE-179 was successfully modified to deliver an process on the FASTlab (TM) that allows the manufacture of a GMP quality product from high starting radioactivitity (up to 80 GBq) and delivers a product suitable for clinical use.

INTRODUCTION:The increase in expression of tryptophan 2, 3-dioxygenases (TDO) and indoleamine 2,3-dioxygenase (IDO) have been reported as potential tumor biomarkers. TDO and IDO are enzymes that catalyze the first and rate-limiting step of the kynurenine pathway. Positron emitting tomography (PET) tracers investigating the kynurenine pathway may allow for the detection of different disease pathologies in vivo including cancer. However, current PET tracers being developed for TDO and IDO have suffered from either multi-step low yielding syntheses or de-fluorination of the tracer in vivo. RESULTS:TDO inhibitors based on 6-fluoroindole with C3 substituents are a class of small molecules that have been shown to bind to TDO effectively, restore tryptophan concentration and decrease the production of immunosuppressive metabolites. The compound 6-fluoro-3-(pyridine-3-yl)-1H-indole has been reported to have high in vitro affinity for TDO. Herein we report the fully automated radiosynthesis of 6-[18F]fluoro-3-(pyridine-3-yl)-1H-indole [18F]4 using a copper-mediated nucleophilic 18F-fluorination resulting in a non-corrected yield of 5 to 6% of the tracer with a radiochemical purity of >99% after 4 h. Small animal dynamic PET/CT imaging of [18F]4 intravenously injected into normal C57BL/6 mice revealed rapid accumulation in heart and brain, reaching maximum occupancy in heart (10.9% ID/g) and brain (8.1% ID/g) at 1.75 min and 2.25 min, respectively. Furthermore, these in vivo studies revealed no de-fluorination of the tracer, as evidence by the absence of [18F]fluoride accumulation in bone. CONCLUSION:In vitro studies demonstrate that 4 has good affinity for hTDO and the radiolabeled analogue [18F]4 can be synthesized with suitable radiochemical yields. [18F]4 demonstrates good uptake in the brain and the radiolabeled compound shows no de-fluorination in vivo in C57BL/6 mice.

The reaction of [18F]fluoromethyl tosylate with methyl(tert-butoxycarbonyl)-l-tryptophanate results in formation the O-alkylated ester of the tryptophan instead of alkylation of the indole nitrogen of tryptophan as initially anticipated. Treatment of protected tryptophan with NaH in dimethyl formamide (DMF) along with [18F]fluoromethyl tosylate at 130°C results in the formation of [18F]fluoromethyl(tert-butoxycarbonyl)-l-tryptophanate. Preferential formation of the O-alkylated product is postulated to be due to the hydrolysis of the ester. Confirmation of the O-alkylation was obtained by synthesizing the [19F]fluoromethyl(tert-butoxycarbonyl)-l-tryptophanate insitu and examining its NMR characteristics using multiple NMR techniques. Similar results were also obtained when reacting Boc-tryptophan-N-carboxyanhydride precursor with fluoromethyl tosylate.

18F‐radiolabeled diphenyl gallium thiosemicarbazone was prepared by [18F] fluoride exchange of a nitrato anion under mild conditions. The diphenyl gallium thiosemicarbazone chloride is easily prepared in gram quantities and can be used at room temperature in the presence of oxygen. The corresponding nitrate complex is prepared using silver nitrate in methanol solvent and can be stored under nitrogen for weeks before radiolabeling. The biodistribution of this new tracer was studied in mice using positron emission tomography (PET).

Our recent investigations for the radiosynthesis of [18 F]fluoromethyl tosylate have highlighted that choice of quaternary methyl ammonium (QMA) cartridge used during the radiosynthesis can significantly impact the radiochemical yields. Often the details of the QMA cartridge used in fluourine-18 syntheses are not fully described. However, our studies demonstrate that the type, the size and nature (method by which it has been conditioned) of the QMA cartridge used during the radiosynthesis can make a significant impact in the labelling efficiency. This paper investigates the use of three QMA cartridges and demonstrates that radiochemical yield (decay corrected) of [18 F]fluoromethyl tosylate can increase from 46 to 60% by simply changing the QMA cartridge (and leaving all other reagents and labelling conditions exactly the same). These learnings may be applied to improve the radiochemical yields of a number of [18 F]-fluorinated tracers (and synthons) where the labelling step is base-sensitive to increase the radiochemical yield, thereby significantly benefiting the radiochemistry and nuclear medicine community. This paper also highlights the necessity of the radiochemistry community to ensure the details of QMA cartridges used in fluorine-18 chemistry are fully and accurately described, since this will improve the translation of radiochemical methods from one laboratory to another.