A 804598

The impact of the P2X7 receptor antagonist A-804598 on neuroimmune and behavioral consequences of stress.[Pubmed:25083574]

Behav Pharmacol. 2014 Sep;25(5-6):582-98.

Stress leads to neuroinflammatory and behavioral consequences through upregulation of inflammatory-related cytokines within the central nervous system such as interleukin-1beta (IL-1beta), which may be indicative of microglial priming/activation. Evidence suggests that the P2X7 receptor (P2X7R) may play an important role in the synthesis and conversion of IL-1beta. In a series of six experiments, adult male rats were intubated with a highly selective P2X7R antagonist (A-804598) before footshock exposure. As expected, footshock increased IL-1beta and CD14 mRNA in the paraventricular nucleus, and A-804598 (25 mg/kg) partially attenuated these effects. Footshock also increased hypothalamic IL-1 protein in whole hypothalamic blocks, but no effect was observed on the formation of pro-IL-1beta or IL-1beta in the paraventricular nucleus as assessed using western blotting. A-804598 also did not reverse the suppression in exploration produced by stress exposure. The present findings support the use of the footshock paradigm as a method for inducing stress-related neuroimmune and behavioral changes, but the evidence to support the role of A-804598 as a potential tool to reverse such changes remains modest. This study is the first to examine the role of P2X7R in vivo following footshock exposure. Further characterization of P2X7R may have implications for understanding the relationship between stress and inflammation.

[3H]A-804598 ([3H]2-cyano-1-[(1S)-1-phenylethyl]-3-quinolin-5-ylguanidine) is a novel, potent, and selective antagonist radioligand for P2X7 receptors.[Pubmed:18602931]

Neuropharmacology. 2009 Jan;56(1):223-9.

ATP-sensitive P2X7 receptors are localized on cells of immunological origin including peripheral macrophages and glial cells in the CNS. Activation of P2X7 receptors leads to rapid changes in intracellular calcium concentrations, release of the pro-inflammatory cytokine IL-1beta, and following prolonged agonist exposure, the formation of cytolytic pores in plasma membranes. Data from gene knockout studies and recently described selective antagonists indicate a role for P2X7 receptor activation in inflammation and pain. While several species selective P2X7 antagonists exist, A-804598 represents a structurally novel, competitive, and selective antagonist that has equivalent high affinity at rat (IC50 = 10 nM), mouse (IC50 = 9 nM) and human (IC50 = 11 nM) P2X7 receptors. A-804598 also potently blocked agonist stimulated release of IL-1beta and Yo-Pro uptake from differentiated THP-1 cells that natively express human P2X7 receptors. A-804598 was tritiated ([3H]A-804598; 8.1Ci/mmol) and utilized to study recombinant rat P2X7 receptors expressed in 1321N1 cells. [3H]A-804598 labeled a single class of high affinity binding sites (Kd=2.4 nM and apparent Bmax=0.56 pmol/mg). No specific binding was observed in untransfected 1321N1 cells. The pharmacological profile for P2X antagonists to inhibit [3H]A-804598 binding correlated with their ability to block functional activation of P2X7 receptors (r=0.95, P<0.05). These data demonstrate that A-804598 is one of the most potent and selective antagonists for mammalian P2X7 receptors described to date and [3H]A-804598 is a high affinity antagonist radioligand that specifically labels rat P2X7 receptors.

Receptor localization, native tissue binding and ex vivo occupancy for centrally penetrant P2X7 antagonists in the rat.[Pubmed:20840537]

Br J Pharmacol. 2011 Jan;162(2):405-14.

BACKGROUND AND PURPOSE: The P2X7 receptor is implicated in inflammation and pain and is therefore a potential target for therapeutic intervention. Here, the development of a native tissue radioligand binding, localization and ex vivo occupancy assay for centrally penetrant P2X7 receptor antagonists is described. EXPERIMENTAL APPROACH: Autoradiography studies using the P2X7 antagonist radioligand [(3)H]-A-804598 were carried out in rat brain and spinal cord. Subsequent in vitro binding and ex vivo occupancy assays were performed using rat cortex homogenate. KEY RESULTS: P2X7 expression was shown to be widespread throughout the rat brain, and in the grey matter of the spinal cord. In binding assays in rat cortex homogenate, approximately 60% specific binding was achieved at equilibrium. In kinetic binding assays, k(on) and k(off) values of 0.0021.min(-)(1).nM(-)(1) and 0.0070.min(-)(1) were determined, and the K(d) derived from kinetic measurements was consistent with that derived from saturation analysis. Novel P2X7 antagonists inhibited the binding of [(3)H]-A-804598 to rat cortex P2X7 receptors with K(i) values of <40 nM. In an ex vivo occupancy assay, a P2X7 antagonist dosed orally to rats caused a concentration-dependent inhibition of the specific binding of [(3)H]-A-804598 to rat cortex. CONCLUSIONS AND IMPLICATIONS: The present study describes the development of an assay that allows localization of P2X7 receptors, the measurement of the binding affinity of P2X7 receptor antagonists in native tissue, and provides a means of determining central P2X7 receptor occupancy. These assays could form an important part of a P2X7 drug discovery programme.

A-804598 is a CNS penetrant, competitive and selective P2X7 receptor antagonist with IC50s of 9 nM, 10 nM and 11 nM for mouse, rat and human P2X7 receptors, respectively.

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