A Practical Iron-Based Newman-Kwart Rearrangement Under Oxidative Conditions

Herein, we report that iron(II)/ammonium persulfate in aqueous acetonitrile mediates the Newman- Kwart rearrangement of O-aryl carbamothioates. Electron-rich substrates react rapidly under moderate heating to afford the rearranged products in excellent yields. The mild conditions, rapid reaction rates, and suitability for scale up offers immediate practical benefits to access functionalised thiophenols

Ex vivo characterization of neuroinflammatory and neuroreceptor changes during epileptogenesis using candidate positron emission tomography biomarkers

Objective: Identification of patients at risk of developing epilepsy before the first spontaneous seizure may promote the development of preventive treatment providing opportunity to stop or slow down the disease. // Methods: As development of novel radiotracers and on‐site setup of existing radiotracers is highly time‐consuming and expensive, we used dual‐centre in vitro autoradiography as an approach to characterize the potential of innovative radiotracers in the context of epilepsy development. Using brain slices from the same group of rats, we aimed to characterise the evolution of neuroinflammation and expression of inhibitory and excitatory neuroreceptors during epileptogenesis using translational positron emission tomography (PET) tracers; 18F‐flumazenil (18F‐FMZ; GABAA receptor), 18F‐FPEB (metabotropic glutamate receptor 5; mGluR5), 18F‐flutriciclamide (translocator protein; TSPO, microglia activation) and 18F‐deprenyl (monoamine oxidase B, astroglia activation). Autoradiography images from selected time points after pilocarpine‐induced status epilepticus (SE; baseline, 24 and 48 hours, 5, 10 and 15 days and 6 and 12‐14 weeks after SE) were normalized to a calibration curve, co‐registered to an MRI‐based 2D region‐of‐interest atlas, and activity concentration (Bq/mm2) was calculated. // Results: In epileptogenesis‐associated brain regions, 18F‐FMZ and 18F‐FPEB showed an early decrease after SE. 18F‐FMZ decrease was maintained in the latent phase and further reduced in the chronic epileptic animals, while 18F‐FPEB signal recovered from day 10, reaching baseline levels in chronic epilepsy. 18F‐flutriciclamide showed an increase of activated microglia at 24 hours after SE, peaking at 5‐15 days and decreasing during the chronic phase. On the other hand, 18F‐deprenyl autoradiography showed late astrogliosis, peaking in the chronic phase. // Significance: Autoradiography revealed different evolution of the selected targets during epileptogenesis. Our results suggest an advantage of combined imaging of inter‐related targets like glutamate and GABAA receptors, or microglia and astrocyte activation, in order to identify important interactions, especially when using PET imaging for the evaluation of novel treatments

Imaging tau pathology in Alzheimer's disease with positron emission tomography: lessons learned from imaging-neuropathology validation studies

Though the presence of both amyloid-β (Aβ) plaques and tau neurofibrillary tangles is necessary for neuropathologic diagnosis of Alzheimer’s disease (AD), it is now widely recognized that tau burden correlates more strongly with neurodegeneration and cognitive impairment in life than the development of Aβ plaques [1]. Recent developments of tau-sensitive radiotracers for imaging with positron emission tomography (PET) have, for the first time, enabled visualisation, mapping, and quantification of inclusions of aggregated, paired helical filament (PHF) tau associated with AD in the living brain [2]. In-depth characterisation of tau PET tracers, and in particular comparison of antemortem PET readings with postmortem neuropathologic findings, were of paramount importance to understand the clinical potential and limitations of the new imaging tools. In the case of [18F]flortaucipir, the most widely used tau PET ligand, these cross-validation studies, together with autoradiography evaluations, provided information about the specificity of this tracer to PHF-tau in AD but also revealed substantial undesired (off-target) binding and limited ability to detect PHF-tau at the earliest Braak stages [3,4,5,6,7]. The combined data subsequently underpinned the implementation of an effective method for the clinical interpretation of [18F]flortaucipir PET scans [3]. Ultimately, these efforts have led to the approval of [(18)^F]flortaucipir by the US Food and Drug Administration (FDA) as the first PET radiopharmaceutical indicated to ‘estimate the density and distribution of aggregated neurofibrillary tangles in patients with cognitive impairment who are being evaluated for AD (Tauvid prescribing information, https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/212123s000lbl.pdf)

Synthesis and evaluation of a (125)I-labeled iminodihydroquinoline-derived tracer for imaging of voltage-gated sodium channels

In vivo imaging of voltage-gated sodium channels (VGSCs) can potentially provide insights into the activation of neuronal pathways and aid the diagnosis of a number of neurological diseases. The iminodihydroquinoline WIN17317-3 is one of the most potent sodium channel blockers reported to date and binds with high affinity to VGSCs throughout the rat brain. We have synthesized a (125)I-labeled analogue of WIN17317-3 and evaluated the potential of the tracer for imaging of VGSCs with SPECT. Automated patch clamp studies with CHO cells expressing the Nav1.2 isoform and displacement studies with [(3)H]BTX yielded comparable results for the non-radioactive iodinated iminodihydroquinoline and WIN17317-3. However, the (125)I-labeled tracer was rapidly metabolized in vivo, and suffered from low brain uptake and high accumulation of radioactivity in the intestines. The results suggest that iminodihydroquinolines are poorly suited for tracer development

Functional imaging in microfluidic chambers reveal sensory neuron sensitivity is differentially regulated between neuronal regions

Primary afferent sensory neurons are incredibly long cells, often traversing distances of over one metre in humans. Cutaneous sensory stimuli are transduced in the periphery by specialised endorgans or free nerve endings which code the stimulus into electrical action potentials that propagate towards the central nervous system. Despite significant advances in our knowledge of sensory neuron physiology and ion channel expression, many commonly used techniques fail to accurately model the primary afferent neuron in its entirety. In vitro experiments often focus on the cell somata and neglect the fundamental processes of peripheral stimulus transduction and action potential propagation. Despite this, these experiments are commonly used as a model for cellular investigations of the receptive terminals. We demonstrate that ratiometric calcium imaging performed in compartmentalised sensory neuron cultures can be used to directly and accurately compare the sensitivity and functional protein expression of isolated neuronal regions in vitro. Using microfluidic chambers, we demonstrate that the nerve terminals of cultured DRG neurons can be depolarised to induce action potential propagation, which has both TTX-resistant and TTXsensitive components. Furthermore, we show that there is a differential regulation of proton sensitivity between the sensory terminals and somata in cultured sensory neurons. We also demonstrate that capsaicin sensitivity is highly dependent on embryonic dissection age. This approach enables a comprehensive method to study the excitability and regional sensitivity of cultured sensory neurons on a single cell level. Examination of the sensory terminals is crucial to further understand the properties and diversity of DRG sensory neurons

Development of purine-derived (18)F-labeled pro-drug tracers for imaging of MRP1 activity with PET.

Multidrug resistance-associated protein 1 (MRP1) is a drug efflux transporter that has been implicated in the pathology of several neurological diseases, and is associated with development of multidrug resistance. To enable measurement of MRP1 function in the living brain, a series of 6-halopurines decorated with fluorinated side chains have been synthesized and evaluated as putative pro-drug tracers. The tracers were designed to undergo conjugation with glutathione within the brain, and hence form the corresponding MRP1 substrate tracers in situ. 6-Bromo-7-(2-[(18)F]fluoroethyl)purine showed good brain uptake and rapid metabolic conversion. Dynamic PET imaging demonstrated a marked difference in brain clearance rates between wild-type and mrp1 knockout mice, suggesting that the tracer can allow non-invasive assessment of MRP1 activity in vivo

Hyperpolarised 13C MRI: a new horizon for non-invasive diagnosis of aggressive breast cancer

Hyperpolarised 13C MRI (HP-MRI) is a novel imaging technique that allows real-time analysis of metabolic pathways in vivo. 1 The technology to conduct HP-MRI in humans has recently become available and is starting to be clinically applied. As knowledge of molecular biology advances, it is increasingly apparent that cancer cell metabolism is related to disease outcomes, with lactate attracting specific attention. 2 Recent reviews of breast cancer screening programs have raised concerns and increased public awareness of over treatment. The scientific community needs to shift focus from improving cancer detection alone to pursuing novel methods of distinguishing aggressive breast cancers from those which will remain indolent. HP-MRI offers the opportunity to identify aggressive tumour phenotypes and help monitor/predict therapeutic response. Here we report one of the first cases of breast cancer imaged using HP-MRI alongside correlative conventional imaging, including breast MRI

First-in-human in vivo non-invasive assessment of intra-tumoral metabolic heterogeneity in renal cell carcinoma

Intratumoral genetic heterogeneity and the role of metabolic reprogramming in renal cell carcinoma have been extensively documented. However, the distribution of these metabolic changes within the tissue has not been explored. We report on the first-in-human in vivo non-invasive metabolic interrogation of renal cell carcinoma using hyperpolarized carbon-13 (13C) MRI and describe the validation of in vivo lactate metabolic heterogeneity against multi regional ex vivo mass spectrometry. hyperpolarized carbon-13 (13C)-MRI provides an in vivo assessment of metabolism and provides a novel opportunity to safely and non-invasively assess cancer heterogeneity