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Mol Imaging Biol. 2019 Dec 2. doi: 10.1007/s11307-019-01435-1. [Epub ahead of print]

In vitro and In vivo Assessment of Suitable Reference Region and Kinetic Modelling for the mGluR1 Radioligand [11C]ITDM in Mice.

Author information

1
Molecular Imaging Center Antwerp (MICA), Faculty of Medicine and Health Sciences, University of Antwerp, Universiteitsplein 1, Wilrijk, Belgium.
2
Department of Nuclear Medicine, Antwerp University Hospital, Edegem, Belgium.
3
CHDI Management/CHDI Foundation, Los Angeles, CA, USA.
4
Molecular Imaging Center Antwerp (MICA), Faculty of Medicine and Health Sciences, University of Antwerp, Universiteitsplein 1, Wilrijk, Belgium. steven.staelens@uantwerpen.be.

Abstract

PURPOSE:

This study aimed at investigating binding specificity, suitability of reference region-based kinetic modelling, and pharmacokinetics of the metabotropic glutamate receptor 1 (mGluR1) radioligand [11C]ITDM in mice.

PROCEDURES:

We performed in vivo blocking as well as displacement of [11C]ITDM during positron emission tomography (PET) imaging using the specific mGluR1 antagonist YM-202074. Additionally, we assessed in vitro blocking of [3H]ITDM at two different doses of YM-202074. As an alternative to reference region models, we validated the use of a noninvasive image-derived input function (IDIF) compared to an arterial input function measured with an invasive arteriovenous (AV) shunt using a population-based curve for radiometabolite correction and characterized the pharmacokinetic modelling of [11C]ITDM in the mouse brain. Finally, we also assessed semi-quantitative approaches.

RESULTS:

In vivo blocking with YM-202074 resulted in a decreased [11C]ITDM binding, ranging from - 35.8 ± 8.0 % in pons to - 65.8 ± 3.0 % in thalamus. Displacement was also markedly observed in all tested regions. In addition, in vitro [3H]ITDM binding could be blocked in a dose-dependent manner. The volume of distribution (VT) based on the noninvasive IDIF (VT (IDIF)) showed excellent agreement with the VT values based on the metabolite-corrected plasma input function regardless of the metabolite correction (r2 > 0.943, p < 0.0001). Two-tissue compartmental model (2TCM) was found to be the preferred model and showed optimal agreement with Logan plot (r2 > 0.960, p < 0.0001). A minimum scan duration of 80 min was required for proper parameter estimation. SUV was not reliable (r2 = 0.379, p = 0.0011), unlike the SUV ratio to the SUV of the input function, which showed to be a valid approach.

CONCLUSIONS:

No suitable reference region could be identified for [11C]ITDM as strongly supported by in vivo and in vitro evidence of specific binding in all brain regions. However, by applying appropriate kinetic models, [11C]ITDM PET imaging represents a promising tool to visualize mGluR1 in the mouse brain.

KEYWORDS:

Arteriovenous shunt; Kinetic modelling; Mouse; PET; Preclinical imaging; Reference region; [11C]ITDM; mGluR1

PMID:
31792838
DOI:
10.1007/s11307-019-01435-1

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