Squalene-Adenosine Nanoparticles: Ligands of Adenosine Receptors or Adenosine Prodrug?

Adenosine receptors (ARs) represent key drug targets in many human pathologies, including cardiovascular, neurologic, and inflammatory diseases. To overcome the very rapid metabolization of adenosine, metabolically stable AR agonists and antagonists were developed. However, few of these molecules have reached the market due to efficacy and safety issues. Conjugation of adenosine to squalene to form squalene-adenosine (SQAd) nanoparticles (NPs) dramatically improved the pharmacological efficacy of adenosine, especially for neuroprotection in stroke and spinal cord injury. However, the mechanism by which SQAd NPs displayed therapeutic activity remained totally unknown. In the present study, two hypotheses were discussed: 1) SQAd bioconjugates, which constitute the NP building blocks, act directly as AR ligands; or 2) adenosine, once released from intracellularly processed SQAd NPs, interacts with these receptors. The first hypothesis was rejected, using radioligand displacement assays, as no binding to human ARs was detected, up to 100 µM SQAd, in the presence of plasma. Hence, the second hypothesis was examined. SQAd NPs uptake by HepG2 cells, which was followed using radioactive and fluorescence tagging, was found to be independent of equilibrative nucleoside transporters but rather mediated by low-density lipoprotein receptors. Interestingly, it was observed that after cell internalization, SQAd NPs operated as an intracellular reservoir of adenosine, followed by a sustained release of the nucleoside in the extracellular medium. This resulted in a final paracrine-like activation of the AR pathway, evidenced by fluctuations of the second messenger cAMP. This deeper understanding of the SQAd NPs mechanism of action provides a strong rational for extending the pharmaceutical use of this nanoformulation.Medicinal Chemistr

Efficient tritiation of the translocator protein (18 kDa) selective ligand DPA‐714

International audienceDPA‐714 ( N , N ‐diethyl‐2‐(2‐(4‐(2‐fluoroethoxy)phenyl)‐5,7‐dimethylpyrazolo[1,5‐a]pyrimidin‐3‐yl)acetamide) is a recently discovered fluorinated ligand of the translocator protein 18 kDa (TSPO). Labelled with the short‐lived positron emitter fluorine‐18, this structure is today the radioligand of reference for in vivo imaging of microglia activation and neuroinflammatory processes with positron emission tomography. In the present work, an isotopically tritium‐labelled version was developed ([ 3 H]DPA‐714), in order to access high resolution in vitro and ex vivo microscopic autoradiography studies, repeated and long‐lasting receptor binding studies and in vivo pharmacokinetic determination at late time points. Briefly, DPA‐714 as reference, and its 3,5‐dibrominated derivative as precursor for labelling, were both prepared from DPA‐713 in nonoptimized 32% (two steps) and 10% (three steps) yields, respectively. Reductive debromination using deuterium gas and Pd/C as catalyst in methanol, performed at the micromolar scale, confirmed the regioselective introduction of two deuterium atoms at the meta positions of the phenyl ring. Tritiodebromination was analogously performed using no‐carrier tritium gas. HPLC purification provided >96% radiochemically pure [ 3 H]DPA‐714 (7 GBq) with a 2.1 TBq/mmol specific radioactivity. Interestingly, additional hydrogen‐for‐tritium exchanges were also observed at the 5‐methyl and 7‐methyl positions of the pyrazolo[1,5‐a]pyrimidine, opening novel perspectives in the labelling of compounds featuring this heterocyclic core

Easy-to-Implement Hydrogen Isotope Exchange for the Labeling of N -Heterocycles, Alkylkamines, Benzylic Scaffolds, and Pharmaceuticals

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Tritium labeling of detonation nanodiamonds

International audienceFor the first time, the radioactive labeling of detonation nanodiamonds was efficiently achieved using a tritium microwave plasma. According to our measurements, the total radioactivity reaches 9120 $\pm$ 120 $\mu$Ci mg−1, with 93% of 3H atoms tightly bonded to the surface and up to 7% embedded into the diamond core. Such 3H doping will ensure highly stable radiolabeled nanodiamonds, on which surface functionalization is still allowed. This breakthrough opens the way to biodistribution and pharmacokinetics studies of nanodiamonds, while this approach can be scalable to easily treat bulk quantities of nanodiamonds at low cost

Using hydrogen isotope incorporation as a tool to unravel the surfaces of hydrogen-treated nanodiamonds

International audienceWe report here on a robust and easy-to-implement method for the labelling of detonation nanodiamonds (DND) with hydrogen isotopes (deuterium and tritium), using thermal annealing performed $in\ a\ closed\ system$. With this method, we have synthesized and fully characterized (FTIR, Raman, DLS, $^3$H/$^2$H/$^1$H and $^{13}$C MAS NMR) deuterium-treated and tritium-treated DND and demonstrated the usefulness of isotope incorporation in investigating the surface chemistry of such nanomaterials. For instance, surface treatment with deuterium coupled to FTIR spectroscopy allowed us to discriminate the origin of C–H terminations at the DND surface after the hydrogenation process. As a complementary, tritium appeared very useful for quantification purposes, while $^{1,2,3}$H NMR confirmed the nature of the C–$^{1,2,3}$H bonds created. This isotopic study provides new insights into the characteristics of hydrogen-treated DND

Circulating Lipoproteins: A Trojan Horse Guiding Squalenoylated Drugs to LDL-Accumulating Cancer Cells.

Selective delivery of anticancer drugs to rapidly growing cancercells can be achieved by taking advantage of their high receptor-mediated uptake of low-density lipoproteins (LDLs). Indeed, wehave recently discovered that nanoparticles made of the squa-lene derivative of the anticancer agent gemcitabine (SQGem)strongly interacted with the LDLs in the human blood. In thepresent study, we showed both in vitro and in vivo that suchinteraction led to the preferential accumulation of SQGem incancer cells (MDA-MB-231) with high LDL receptor expression.As a result, an improved pharmacological activity has beenobserved in MDA-MB-231 tumor-bearing mice, an experi-mental model with a low sensitivity to gemcitabine. Accord-ingly, we proved that the use of squalene moieties not onlyinduced the gemcitabine insertion into lipoproteins, but thatit could also be exploited to indirectly target cancer cells in vivo

Multiple Site Hydrogen Isotope Labelling of Pharmaceuticals

International audienceRadiolabelling is fundamental in drug discovery and development as it is mandatory for preclinical ADME studies and late-stage human clinical trials. Herein, a general, effective, and easy to implement method for the multiple site incorporation of deuterium and tritium atoms using the commercially available and air-stable iridium precatalyst [Ir(COD)(OMe)]2 is described. A large scope of pharmaceutically relevant substructures can be labelled using this method including pyridine, pyrazine, indole, carbazole, aniline, oxa-/thia-zoles, thiophene, but also electron-rich phenyl groups. The high functional group tolerance of the reaction is highlighted by the labelling of a wide range of complex pharmaceuticals, containing notably halogen or sulfur atoms and nitrile groups. The multiple site hydrogen isotope incorporation has been explained by the in situ formation of complementary catalytically active species: monometallic iridium complexes and iridium nanoparticles

Analyse LIBS du tritium dans des échantillons de type film mince

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