Synthesis and initial preclinical evaluation of the P2X₇ receptor antagonist [¹¹C]A‐740003 as a novel tracer of neuroinflammation

Abstract

Neuroinflammation, in particular activation of microglia, is thought to play an important role in the progression of neurodegenerative diseases. In activated microglia, the purinergic P2X7 receptor is upregulated. A-740003, a highly affine and selective P2X7 receptor antagonist, is a promising candidate for the development of a radiotracer for imaging of neuroinflammation by positron emission tomography. For this purpose, [(11)C]A-740003 was synthesised and evaluated in vivo with respect to both tracer metabolism and biodistribution. In plasma, a moderate metabolic rate was seen. In healthy rat brain, only marginal uptake of [(11)C]A-740003 was observed and, therefore, metabolites in brain could not be determined. Whether the minimal brain uptake is due to the low expression levels of the P2X7 receptor in healthy brain or to limited transport across the blood-brain barrier has yet to be elucidated.

Preclinical Evaluation of a P2X7 Receptor–Selective Radiotracer: PET Studies in a Rat Model with Local Overexpression of the Human P2X7 Receptor and in Nonhuman Primates

“…Unlike 11 C-A-740003, a P2X7R-selective tracer developed by Janssen et al (24), 11 C-JNJ-54173717 was able to cross the FIGURE 3. In vitro autoradiography binding studies on slices of rat brain injected with hP2X7R vector using 11 C-JNJ-54173717 (n 5 4).…”

P2X ion channel receptors and inflammation

“…Ectonucleotidases control P2X7 receptor function, including the resolution as well as the initial phases of inflammation (see [71]). [ 11 C]-A-740003, a P2X7 receptor antagonist, has been used as a novel tracer of neuroinflammation [72].…”

Synthesis of [11C]GSK1482160 as a new PET agent for targeting P2X7 receptor

“…However, an ideal PET radiopharmaceutical is still missing. 11,12 Like others, we have used [ 11 C]PBR28-PET (Figure 1) to image neuroinflammation, targeting the 18-kDa translocator protein (TSPO) formerly named the peripheral benzodiazepine receptor (PBR). 13,14 However, the limitations 15,16 of [ 11 C]PBR28-PET such as low receptor binding, high inter-subject variability in binding affinity, and nonspecific binding in the human brain, due to TSPO polymorphism, have motivated us to search for new molecular targets and PET radioligands.…”

“…12,17 Recently the synthesis and initial preclinical evaluation of a P2X 7 receptor radioligand [ 11 C]A-740003 (racemic compounds, Figure 1) have been reported, but it showed little uptake in brain in healthy male Wistar rats. 12 We have instead initially focused on GSK1482160 (a chiral compound, (S)-N-(2-chloro-3-(trifluoromethyl)benzyl)-1-methyl-5-oxopyrrolidine-2-carboxamide, 3). Originally developed by GlaxoSmithKline, GSK1482160 is a potent P2X 7 antagonist with excellent biological activity {PIC 50 8.5 (IC 50 3 nM) for human P2X 7 , and PIC 50 6.6 for rat P2X 7 }.…”