Browsing by Author "Peyronneau, MA"

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    Metabolism of CLINDE, a peripheral benzodiazepine receptor SPECT ligand
    (Springer, 2010-10-11) Peyronneau, MA; Mattner, F; Howell, NR; Jiang, C; Pelegrini, P; Greguric, I; Loc'h, C; Katsifis, A
    Aim: The iodinated imidazopyridine, N′, N′-diethyl-6-Chloro-(4′-[123I]iodophenyl)imidazo[1,2-a]pyridine-3-acetamide ([123I]CLINDE) has been characterized as a high affinity and selectivity ligand for SPECT imaging the peripheral benzodiazepine receptor (TSPO)1. As part of the development of this probe and for future investigations in humans, the metabolism of CLINDE was investigated in different species. The aim of this study was to identify the main metabolic pathways and the form(s) of cytochrome P450 (CYP) responsible for the biotransformation of this ligand. Materials and Methods: The in vitro metabolism of CLINDE and [123I]-CLINDE was carried out using rat and human liver microsomes as well as human recombinant CYP. Similar studies were performed in rat hepatocytes. Microsomalor hepatocyte incubations were analyzed by LC/MS and the structure of the metabolites characterized by MS-MS experiments. Results: In rat and human liver microsomes, CLINDE was converted to two main polar metabolites identified by LC/MS asN-dealkylated (m/z440)and hydroxylated metabolites (m/z484). In rat liver microsomes, the main metabolite resulted from hydroxylation of the ligand. In human liver microsomes, the metabolism of CLINDE was slower with major formation of anN-dealkyl metabolite. Microsomes from baculovirus-infected insect cells expressing human P450s isoforms (CYP1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C18,2C19, 2D6, 2E1, 3A4, 3A5, SF9 control) were used to test their ability to catalyse the oxidation of CLINDE. CYP3A4 and CYP3A5 exhibited the highest catalytic activity for N-dealkylation, (3.3 and 3.8 nmol/nmolP450/min), followed byCYP2C19 (0.67 nmol/nmolP450/min) and CYP2D6 0.09 nmol/nmolP450/min). The other CYP isoforms did not form any detectable metabolites. For the hydroxylase activity relative to the formation of the molecular ion at m/z 484, CYP1A1 (4.05nmol/nmolP450/min), CYP1A2 (1.85 nmol/nmolP450/min) appeared to be the morecatalytically active, followed by CYP3A4 (0.95 nmol/nmolP450/min) and CYP2C19(0.42 nmol/nmolP450/min). The iodine atom was conserved in all the identified metabolites during the process of biotransformation. In rat hepatocytes, [123-I]-CLINDE was extensively and rapidly converted to at least five radiometabolites, the major metabolite being issued from methyl-hydroxylation. Conclusion: Cytochrome P450 catalysed in vitro studies of CLINDE, demonstrated the formation of N-dealkylated and hydroxylated metabolites. Species differences were observed in the rate of formation of rat and human metabolites. The above results suggest that CYP3A4 and CYP3A5 most markedly catalysed N-dealkylation of CLINDE while the hydroxylation was likely to depend more strongly on CYP1A isoforms (extrahepatic CYP1A1 and hepaticCYP1A2).
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    Preclinical in vivo and in vitro comparison of the translocator protein PET ligands [18F]PBR102 and [18F]PBR111
    (Springer Link, 2016-10-04) Eberl, S; Katsifis, A; Peyronneau, MA; Wen, LF; Henderson, D; Loc’h, C; Greguric, I; Verschuer, J; Pham, TQ; Lam, P; Mattner, F; Mohamed, A; Fulham, MJ
    Purpose To determine the metabolic profiles of the translocator protein ligands PBR102 and PBR111 in rat and human microsomes and compare their in vivo binding and metabolite uptake in the brain of non-human primates (Papio hamadryas) using PET-CT. Methods In vitro metabolic profiles of PBR102 and PBR111 in rat and human liver microsomes were assessed by liquid chromatography–tandem mass spectrometry. [18F]PBR102 and [18F]PBR111 were prepared by nucleophilic substitution of their corresponding p-toluenesulfonyl precursors with [18F]fluoride. List mode PET-CT brain imaging with arterial blood sampling was performed in non-human primates. Blood plasma measurements and metabolite analysis, using solid-phase extraction, provided the metabolite profile and metabolite-corrected input functions for kinetic model fitting. Blocking and displacement PET-CT scans, using PK11195, were performed. Results Microsomal analyses identified the O-de-alkylated, hydroxylated and N-de-ethyl derivatives of PBR102 and PBR111 as the main metabolites. The O-de-alkylated compounds were the major metabolites in both species; human liver microsomes were less active than those from rat. Metabolic profiles in vivo in non-human primates and previously published rat experiments were consistent with the microsomal results. PET-CT studies showed that K1 was similar for baseline and blocking studies for both radiotracers; VT was reduced during the blocking study, suggesting low non-specific binding and lack of appreciable metabolite uptake in the brain. Conclusions [18F]PBR102 and [18F]PBR111 have distinct metabolic profiles in rat and non-human primates. Radiometabolites contributed to non-specific binding and confounded in vivo brain analysis of [18F]PBR102 in rodents; the impact in primates was less pronounced. Both [18F]PBR102 and [18F]PBR111 are suitable for PET imaging of TSPO in vivo. In vitro metabolite studies can be used to predict in vivo radioligand metabolism and can assist in the design and development of better radioligands. © 2016 Springer-Verlag