Gold(I)-Mediated Radioiododecarboxylation of Arenes.

A novel radioiodination method is developed using carboxylic acids as radiolabeling precursors. This method involves decarboxylation and organogold(I) intermediate formation, enabling efficient radioiodination of (hetero)arenes and cinnamic and phenylpropiolic acids. Additionally, we demonstrated the prolonged stability of crude gold(I) organometallic compounds, showcasing their enduring radiolabeling capabilities.

Reactive astrocytes mediate TSPO overexpression in response to sustained CNTF exposure in the rat striatum.

The 18 kDa translocator protein (TSPO) is a classical marker of neuroinflammation targeted for in vivo molecular imaging. Microglial cells were originally thought to be the only source of TSPO overexpression but astrocytes, neurons and endothelial cells can also up-regulate TSPO depending on the pathological context. This study aims to determine the cellular origin of TSPO overexpression in a simplified model of neuroinflammation and to identify the molecular pathways involved. This is essential to better interpret TSPO molecular imaging in preclinical and clinical settings. We used lentiviral vectors (LV) to overexpress the ciliary neurotrophic factor (CNTF) in the right striatum of 2-month-old Sprague Dawley rats. A LV encoding for ß-Galactosidase (LV-LacZ) was used as control. One month later, TSPO expression was measured by single-photon emission computed tomography (SPECT) imaging using [125I]CLINDE. The fluorescence-activated cell sorting to radioligand-treated tissue (FACS-RTT) method was used to quantify TSPO levels in acutely sorted astrocytes, microglia, neurons and endothelial cells. A second cohort was injected with LV-CNTF and a LV encoding suppressor of cytokine signaling 3 (SOCS3), to inhibit the JAK-STAT3 pathway specifically in astrocytes. GFAP and TSPO expressions were quantified by immunofluorescence. We measured a significant increase in TSPO signal in response to CNTF by SPECT imaging. Using FACS-RTT, we observed TSPO overexpression in reactive astrocytes (+ 153 ± 62%) but also in microglia (+ 2088 ± 500%) and neurons (+ 369 ± 117%), accompanied by an increase in TSPO binding sites per cell in those three cell populations. Endothelial cells did not contribute to TSPO signal increase. Importantly, LV-SOCS3 reduced CNTF-induced astrocyte reactivity and decreased global TSPO immunoreactivity (-71% ± 30%), suggesting that TSPO overexpression is primarily mediated by reactive astrocytes. Overall, this study reveals that CNTF induces TSPO in multiple cell types in the rat striatum, through the JAK2-STAT3 pathway in astrocytes, identifying this cell type as the primary mediator of CNTF effects neuroinflammatory processes. Our results highlight the difficulty to interpret TSPO imaging in term of cellular origin without addition cellular analysis by FACS-RTT or quantitative immunostainings. Consequently, TSPO should only be used as a global marker of neuroinflammation.

Base-Mediated Radio-Iodination of Arenes by Using Organosilane and Organogermane as Radiolabelling Precursors.

The radio-iodination of arenes is investigated from organosilane and organogermane precursors using ipso-electrophilic halogenation (IEH). Discovery of a mild base mediated process allows radio-iodination in HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) of either aryl silane or germane, with germanes being more reactive. Clinical potential of arylgermanes as radio-iodination precursors is demonstrated through the labelling of [125 I]IMTO (iodometomidate) and [125 I]MIBG (meta-iodobenzylguanidine) thus offering an alternative to radio-iododestannylation processes using non-toxic precursors.

Transferability of a two-strip method for the quality control of technetium-99m mercaptoacetyltriglycine ([99mTc]Tc-MAG3).

OBJECTIVES: Technetium-99m mercapto-acetyl-triglycine ([99mTc]Tc-MAG3) is a radiopharmaceutical diagnostic agent used in nuclear medicine intended for the exploration of nephrological and urological disorders. Patient safety and reliability of this imaging procedure especially depend on the radiochemical purity (RCP) of the [99mTc]Tc-MAG3 preparation. Recently, the Summary of Product Characteristics (SPC) of NephroMAG, a kit dedicated to [99mTc]Tc-MAG3 preparation, proposed a two-strip thin layer chromatography (TLC) based quality control (QC) method. Also, Straub et al recently proposed another TLC based QC method. We sought to evaluate the transferability of these QC methods in our hospital radiopharmacy and compared them to our currently employed TLC method and radio-HPLC (high-pressure liquid chromatography) to select the most appropriate in the context of hospital radiopharmacy. METHODS: Ten consecutive [99mTc]Tc-MAG3 preparations were controlled using: HPLC combined with a radiodetector (radio-HPLC), a single strip TLC method (method 1) in current use in our centre, a two-strip TLC method described in the SPC (method SPC) and a two-strip TLC method (method 2) described by Straub et al. Quantitative results for the four tested QC methods were measured and compared in terms of RCP (%), sodium pertechnetate ([99mTc]TcO4 -) (%) and duration of analysis (min). RESULTS: RCP was significantly different between method SPC and radio-HPLC (p<0.001) and method 2 (p<0.001). Also, the percentage of [99mTc]TcO4 - was statistically different between the radio-HPLC and the method SPC (p<0.001), but not with the method 1 and method 2 group (p>0.05). The duration of analysis (min) was significantly different between the four QC procedures (p<0.001) with method 2 and method SPC being the quickest. CONCLUSIONS: Our study showed it is possible to transfer and select a quick and reliable QC method for the preparation of NephroMAG kits in our centre. We therefore advise the widespread use of the method from Straub et al in hospital radiopharmacies.

Low-dose brain irradiation normalizes TSPO and CLUSTERIN levels and promotes the non-amyloidogenic pathway in pre-symptomatic TgF344-AD rats.

Preclinical studies have recently evaluated the impact of low-dose brain radiation therapy (LD-RT) in animal models of Alzheimer's disease (AD) showing anti-amyloid and anti-inflammatory effects of this treatment. Its effectiveness varied, however, depending on the LD-RT protocol used and the stage when the treatment was applied. In this study, we aimed to evaluate the therapeutic potential of 10 Gy delivered in five daily fractions of 2 Gy (a protocol previously shown to induce an improvement of cognitive performances) in 9-month-old TgF344-AD rats, modeling at a pre-symptomatic stage of the disease. We showed that at an early stage, LD-RT was able to lower levels of the 18-kDa translocator protein (TSPO)-mediated neuroinflammation to normal ranges in addition to the secreted CLUSTERIN, another inflammatory protein also involved in Aß aggregation. In addition, we demonstrated that LD-RT reduces all amyloid forms (~ - 60 to - 80%, P < 0.01; soluble and aggregated forms of Aß40, Aß42, and Aßoligomers). Interestingly, we showed for the first time that sAPPα levels were improved by the treatment, showing a higher activation of the non-amyloidogenic pathway, that could favor neuronal survival. The current evidence confirms the capacity of LD-RT to successfully modulate two pathological hallmarks of AD, namely amyloid and neuroinflammation, when applied before symptoms onset.

Synthesis and Physicochemical Properties of Cryptophazane-A Soluble and Functionalizable C1 -Symmetrical Cryptophane.

The first example of a cryptophazane, a cryptophane functionalized with a nitrogen atom replacing one of the methylene bridges, is obtained with a 28 % overall yield over 8 steps, through the preparation of a C1 -symmetrical aza-cyclotriveratrylene (aza-CTV). Herein, we demonstrate that the introduction of a nitrogen atom on this part of the cryptophane core enhances the solubility in organic media of both the cryptophane and the synthetic intermediates, while presenting the same conformation as known cryptophanes. Cryptophazane was prepared on a multigram scale and easily functionalized. We also investigated its ability to encapsulate xenon atoms using hyperpolarized 129 Xe (HP 129 Xe) NMR spectroscopy. We found that both its affinity and exchange kinetics were in the appropriate range for applications in 129 Xe magnetic resonance imaging (MRI). Combined with the wide range of possible functionalization, this makes cryptophazane an excellent candidate for targeted HP 129 Xe MRI.

Radiotracers for the Central Serotoninergic System.

This review lists the most important radiotracers described so far for imaging the central serotoninergic system. Single-photon emission computed tomography and positron emission tomography radiotracers are reviewed and critically discussed for each receptor.

Alterations in dopamine system and in its connectivity with serotonin in a rat model of Alzheimer's disease.

Dopamine pathways alterations are reported in Alzheimer's disease. However, it is difficult in humans to establish when these deficits appear and their impact in the course of Alzheimer's disease. In the TgF344-Alzheimer's disease rat model at the age of 6 months, we showed a reduction in in vivo release of striatal dopamine due to serotonin 5HT2A-receptor blockade, in the absence of alterations in 5HT2A-receptor binding, suggesting a reduction in 5HT2A-receptor-dopamine system connectivity. In addition, a functional hypersensitivity of postsynaptic dopamine D2-receptors and D2-autoreceptors was also reported without any change in D2-receptor density and in the absence of amyloid plaques or overexpression of the 18 kDa translocator protein (an inflammatory marker) in areas of the dopamine system. Citalopram, a selective serotonin reuptake inhibitor, induced functional 5HT2A-receptor-D2-receptor connectivity changes but had no effect on D2-autoreceptor hypersensitivity. In older rats, dopamine cell bodies overexpressed translocator protein and dopamine projection sites accumulated amyloid. Interestingly, the 5HT2A-receptor density is decreased in the accumbens subdivisions and the substantia nigra pars compacta. This reduction in the striatum is related to the astrocytic expression of 5HT2A-receptor. Our results indicate that both serotonin/dopamine connectivity and dopamine signalling pathways are dysregulated and potentially represent novel early diagnostic and therapeutic avenues.

Investigation by mass spectrometry and 32P post-labelling of DNA adducts formation from 1,2-naphthoquinone, an oxydated metabolite of naphthalene.

Naphthalene is the simplest representative of polycyclic aromatic hydrocarbons (PAHs). It is detected as major pollutant in the different compartments of the environment. This compound is considered by the international agency for research on cancer (IARC), the specialized cancer agency of the World Health Organisation (WHO), as a possible carcinogenic (group 2B) since 2002, mainly based on studies on chronic inhalation in rodent by the national toxicology program of the U.S. department of health and human services. In humans, its main metabolites correspond to derivatives substituted in position and 1 and 2 as 1,2-naphthoquinone (1,2-NphQ). Based on previous studies, 1,2-NphQ is supposed to react with DNA to form mostly depurinating adducts, a possible initiating step of carcinogenicity. To confirm this potentiality, adducts were synthetized by the reaction of 1,2-NphQ with 2'-deoxyguanosine (2'-dG) in N,N-dimethylformamide (DMF), water and calf thymus DNA. 2'-dG adducts were analyzed by 32P post-labelling, HPLC with ultra-violet detection and ultra-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). We found stable DNA adducts detected in DNA. We proposed a formation mechanism by a 1,4-Michael addition with 2'-dG. Adducts with 2'-deoxyxanthosine are formed after a spontaneous deamination of 2'-dG. These adducts are good candidates as biomarkers allowing evaluation of exposure to naphthalene and its derivatives in the development of pathologies such as cancer.

Recent Advances in Synthetic Methods for Radioiodination.

Organic compounds bearing radioisotopes of iodine are widely used for biological research, diagnostic imaging, and radiotherapy. Early reported synthetic methods for the incorporation of radioiodine have generally involved high temperature reactions or strongly oxidizing conditions. To overcome these limitations and to cope with the demand for novel radioiodinated probes, there has been a surge in the development of new synthetic methodology for radioiodination. This synopsis describes the key transformations developed recently.

Design of iodinated radioligands for SPECT imaging of central human 5-HT4R using a ligand lipophilicity efficiency approach.

A series of iodinated ligands for the SPECT imaging of 5-HT4 receptors was designed starting from the previously reported hit MR-26132. We focused on the modulation of the piperidine-containing lateral chain by introducing hydrophilic groups in order to decrease the liphophilicity of the new ligands. All the synthesized compounds were tested for their binding affinities on 5-HT4Rs and based on the Ligand Lipophilicity Efficiency approach, compound 13 was further selected for radioiodination with iodine-125 and imaging experiments. Compound 13 showed its ability to displace the specific signal of the reference compound [125I]SB-207710 but no significant detection of [125I]13 was observed in vivo in SPECT experiments.

TSPO and amyloid deposits in sub-regions of the hippocampus in the 3xTgAD mouse model of Alzheimer's disease.

The involvement of the 18kDa translocator protein (TSPO), a marker of neuroinflammation, in Alzheimer's disease (AD) remains controversial. In the present report, we used [125I]-CLINDE, a SPECT TSPO radiotracer never before used in AD, and we investigated the relationship between TSPO and amyloid plaque density (using [125I]-DRM106) in a triple transgenic mouse model of AD (3xTgAD, APPSWE, PS1M146V and TauP301L). Our results show that TSPO increases appear before those of amyloid deposits. Moreover, the different parts of the hippocampus are differentially affected. Indeed, for both TSPO and amyloid, the subiculum is affected earlier and the ventral hippocampus later than the dorsal hippocampus. In the subiculum and the dorsal hippocampus of 3xTgAD mice, a positive correlation between TSPO and of amyloid deposit levels is observed. This data supports the hypothesis that TSPO could be used as a predictive marker of amyloid pathology. In addition, our immunohistochemical data shows a segregation of TSPO in the hippocampus and immunofluorescence imaging revealed a mainly microglial origin of the TSPO expression. Thus, imaging TSPO with CLINDE may be a good alternative to PET radiotracers.

Palladium-Mediated Site-Selective C-H Radio-iodination.

The palladium-mediated C-H radio-iodination of arenes using sodium iodide as the primary isotopic source is reported and performed without chemical know-how in 30 min and applied to the synthesis of complex radio-iodinated compounds of biological interest.

Boron reagents for divergent radiochemistry.

Radiolabelled (bio)molecules have advanced many areas of science from fundamental biology to human health including applications in molecular imaging and more generally nuclear medicine. Today, the field of radiochemistry is rapidly expanding, a trend resulting from the increasing demand for labelled molecules necessary for diagnosis and to accelerate pharmaceutical drug development. More often, the synthesis of labelled (bio)molecules employs a pre-functionalised precursor to allow for the chemoselective installation of a particular radioisotope-containing substituent. Among the array of precursors available, boron reagents occupy a prominent place because they are easy to handle, numerous possibilities exist for their preparation, and their reactivity has been well studied especially in cross-coupling chemistry. In this review, we discuss the value of boron-based precursors for the radiolabelling of (bio)molecules with the radionuclides carbon-11, fluorine-18, iodine-123, iodine-125 and iodine-131, and we illustrate how these radiosynthetic advances have opened the radiochemical space available for areas such as PET and SPECT imaging.

Radiosynthesis of SPECT tracers via a copper mediated 123I iodination of (hetero)aryl boron reagents.

A general method for the copper mediated nucleophilic 123I-iodination of (hetero)aryl boronic esters and acids has been developed. The broad substrate scope of this radiosynthetic approach allows access to [123I]DPA-713, [123I]IMPY, [123I]MIBG and [123I]IPEB that are four commonly used SPECT radiotracers. Our results infer that aryl boronic reagents can now be employed as common precursors for both fluorine-18 and iodine-123 radiolabelling.

Enhanced copper-mediated (18)F-fluorination of aryl boronic esters provides eight radiotracers for PET applications.

[(18)F]FMTEB, [(18)F]FPEB, [(18)F]flumazenil, [(18)F]DAA1106, [(18)F]MFBG, [(18)F]FDOPA, [(18)F]FMT and [(18)F]FDA are prepared from the corresponding arylboronic esters and [(18)F]KF/K222 in the presence of Cu(OTf)2py4. The method was successfully applied using three radiosynthetic platforms, and up to 26 GBq of non-carrier added starting activity of (18)F-fluoride.

Synthesis and evaluation of novel serotonin 4 receptor radiotracers for single photon emission computed tomography.

Despite its implication in several physiological and pathological processes the serotonin subtype-4 receptor (5-HT4R) has seen limited effort for the development of radiolabeling agent especially concerning single photon emission computed tomography (SPECT). Bearing an ester function, the available ligands are rapidly susceptible to hydrolysis which limits their use in vivo. In this study the synthesis of iodinated benzamide and ketone analogs were described. Their affinity for the 5-HT4R and their lipophilicity were evaluated and the most promising derivatives were evaluated ex vivo for their binding to the receptor and for their ability to displace the reference ligand [(125)I]-SB207710.

Iodoindazoles with Selective Magnesiation at Position 3: A Route to Highly Functionalized Indazoles.

A unique route to highly functionalized indazoles is described. A regioselective magnesiation at position 3 of 4-, 5-, 6- and 7-iodo-2-THP-indazoles (THP=tetrahydropyranyl) has been developed using TMPMgCl⋅LiCl (TMP=2,2,6,6-tetramethylpiperidyl). The obtained magnesiate can be trapped by different electrophiles to introduce a wide range of functional groups including halogens, thioalkyls, alcohols, aldehydes, ketones, amides, or esters at position 3. Once this position is functionalized, the iodine atoms can be further reacted through metal-halogen exchange or cross-coupling strategies. Finally, N-substitution reactions allow the synthesis of a variety of highly functionalized indazoles giving access to these valuable scaffolds through a simple and unique route.

Design of a serotonin 4 receptor radiotracer with decreased lipophilicity for single photon emission computed tomography.

With the aim to develop a suitable radiotracer for the brain imaging of the serotonin 4 receptor subtype (5-HT4R) using single photon emission computed tomography (SPECT), we synthesized and evaluated a library of di- and triazaphenanthridines with lipophilicity values which were in the range expected to favour brain penetration, and which demonstrated specific binding to the target of interest. Adding additional nitrogen atoms to previously described phenanthridine ligands exhibiting a high unspecific binding, we were able to design a radioiodinated compound [(125)I]14. This compound exhibited a binding affinity value of 0.094 nM toward human 5-HT4R and a high selectivity over other serotonin receptor subtypes (5-HTR). In vivo SPECT imaging studies and competition experiments demonstrated that the decreased lipophilicity (in comparison with our previously reported compounds 4 and 5) allowed a more specific labelling of the 5-HT4R brain-containing regions.

Room-temperature ortho-alkoxylation and -halogenation of N-tosylbenzamides by using palladium(II)-catalyzed C-H activation.

The N-tosylcarboxamide group can direct the room-temperature palladium-catalyzed C-H alkoxylation and halogenation of substituted arenes in a simple and mild procedure. The room-temperature stoichiometric cyclopalladation of N-tosylbenzamide was first studied, and the ability of the palladacycle to react with oxidants to form C-X and C-O bonds under mild conditions was demonstrated. The reaction conditions were then adapted to promote room-temperature ortho-alkoxylations and ortho-halogenations of N-tosylbenzamides using palladium as catalyst. The scope and limitation of both alkoxylations and halogenations was studied and the subsequent functional transformation of the N-tosylcarboxamide group through nucleophilic additions was evaluated. This methodology offers a simple and mild route to diversely functionalized arenes.