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European Journal of Nuclear Medicine and Molecular Imaging

Published in:

01-02-2017 | Original Article

Preclinical in vivo and in vitro comparison of the translocator protein PET ligands [¹⁸F]PBR102 and [¹⁸F]PBR111

Authors: S. Eberl, A. Katsifis, M. A. Peyronneau, L. Wen, D. Henderson, C. Loc’h, I. Greguric, J. Verschuer, T. Pham, P. Lam, F. Mattner, A. Mohamed, M. J. Fulham

Published in: European Journal of Nuclear Medicine and Molecular Imaging | Issue 2/2017

Abstract

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; V_T 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.

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Title: Preclinical in vivo and in vitro comparison of the translocator protein PET ligands [18F]PBR102 and [18F]PBR111
Authors: S. Eberl
A. Katsifis
M. A. Peyronneau
L. Wen
D. Henderson
C. Loc’h
I. Greguric
J. Verschuer
T. Pham
P. Lam
F. Mattner
A. Mohamed
M. J. Fulham
Publication date: 01-02-2017
Publisher: Springer Berlin Heidelberg
Published in: European Journal of Nuclear Medicine and Molecular Imaging / Issue 2/2017
Print ISSN: 1619-7070
Electronic ISSN: 1619-7089
DOI: https://doi.org/10.1007/s00259-016-3517-z

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Preclinical in vivo and in vitro comparison of the translocator protein PET ligands [¹⁸F]PBR102 and [¹⁸F]PBR111

Abstract

Purpose

Methods

Results

Conclusions

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Abstract

Purpose

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