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Effect of (Z)-isomer content on [11C]ABP688 binding potential in humans.

Eur J Nucl Med Mol Imaging. 2019 May;46(5):1175-1178

Authors: Smart K, Cox SML, Kostikov A, Shalai A, Scala SG, Tippler M, Jaworska N, Boivin M, Séguin JR, Benkelfat C, Leyton M

Abstract

PURPOSE: To determine how the low-affinity (Z)-isomer of the radiotracer [11C]ABP688 affects binding potential values in vivo in humans.

METHODS: High-resolution [11C]ABP688 PET scans were acquired on 74 healthy volunteers (25 male, 49 female, mean age 20?±?3.0). The relative contents of (E)- and (Z)-isomers were determined prior to injection using analytical high-performance liquid chromatography [rt(E)?=?10 min, rt(Z)?=?8.5 min]. Mean binding potential [BPND?=?fND * (Bavail/KD)] values were calculated in the striatum, limbic regions, and prefrontal cortex using the simplified reference tissue model with cerebellar grey matter as reference.

RESULTS: Mean?±?SD (E)-isomer content in [11C]ABP688 production was 92?±?3.8% (range 78-97%). Percent (E)-isomer was positively correlated with BPND in the striatum (??=?0.28, p?=?0.015) and limbic regions (??=?0.25, p?=?0.036). In multiple regression analysis, sex (ß?=?0.39, p?=?0.001) and (E)-isomer content (ß?=?0.23, p?=?0.040) were significant predictors of BPND.

CONCLUSIONS: Even modest levels of (Z)-[11C]ABP688 can reduce estimates of tracer binding in vivo. Future studies should use production methods that enrich levels of (E)-[11C]ABP688, report tracer isomer ratios, and account for this factor in their analyses.

PMID: 30607444 [PubMed - in process]