A-317491, a novel potent and selective non-nucleotide antagonist of P2X ₃ and P2X _2/3 receptors, reduces chronic inflammatory and neuropathic pain in the rat

Abstract

P2X3 and P2X2/3 receptors are highly localized on peripheral and central processes of sensory afferent nerves, and activation of these channels contributes to the pronociceptive effects of ATP. A-317491 is a novel non-nucleotide antagonist of P2X3 and P2X2/3 receptor activation. A-317491 potently blocked recombinant human and rat P2X3 and P2X2/3 receptor-mediated calcium flux (Ki ‫؍‬ 22-92 nM) and was highly selective (IC50 >10 M) over other P2 receptors and other neurotransmitter receptors, ion channels, and enzymes. A-317491 also blocked native P2X3 and P2X2/3 receptors in rat dorsal root ganglion neurons. Blockade of P2X3 containing channels was stereospecific because the R-enantiomer (A-317344) of A-317491 was significantly less active at P2X3 and P2X2/3 receptors. A-317491 dosedependently (ED50 ‫؍‬ 30 mol͞kg s.c.) reduced complete Freund's adjuvant-induced thermal hyperalgesia in the rat. A-317491 was most potent (ED50 ‫؍‬ 10 -15 mol͞kg s.c.) in attenuating both thermal hyperalgesia and mechanical allodynia after chronic nerve constriction injury. The R-enantiomer, A-317344, was inactive in these chronic pain models. Although active in chronic pain models, A-317491 was ineffective (ED 50 >100 mol͞kg s.c.) in reducing nociception in animal models of acute pain, postoperative pain, and visceral pain. The present data indicate that a potent and selective antagonist of P2X 3 and P2X2/3 receptors effectively reduces both nerve injury and chronic inflammatory nociception, but P2X 3 and P2X2/3 receptor activation may not be a major mediator of acute, acute inflammatory, or visceral pain.T he cloning and characterization of the P2X 3 receptor, a specific ATP-sensitive ligand-gated ion channel that is selectively localized on peripheral and central processes of sensory afferent neurons (1-3), has generated much interest in the role of this receptor in nociceptive signaling (4). The discovery of the P2X 3 receptor has provided a putative mechanism for previous reports that ATP, released from sensory nerves (5), produces fast excitatory potentials in dorsal root ganglion (DRG) neurons (6). These actions appear to be physiologically relevant because iontophoretic application of ATP to human skin elicits pain (7) and exogenously applied ATP enhances pain sensations in a human blister base model (8).The P2X 3 receptor is natively expressed as a functional homomer and as a heteromultimeric combination with the P2X 2 (P2X 2/3 ) receptor (1, 2, 9). Both P2X 3 -containing channels are expressed on a high proportion of isolectin IB4-positive neurons in DRG (3, 10). These receptors share similar pharmacological profiles (11), but differ in their acute desensitization kinetics (10, 12). Immunohistochemical studies have shown that P2X 3 receptor expression is up-regulated in DRG neurons and ipsilateral spinal cord after chronic constriction injury (CCI) of the sciatic nerve (13). Additionally, CCI results in a specific ectopic sensitivity to ATP that is not observed on contralateral (uninjured) nerves (14).Recently, the phenotyp...

P2X receptor antagonists for pain management: examination of binding and physicochemical properties

“…A-317491 has limited CNS penetration following systemic administration. However, systemic administration of high doses or intrathecal administration of this antagonist effectively attenuates tactile allodynia caused by peripheral nerve injury [32,33]. Consistent with these data, ATP-evoked activation of capsaicin-insensitive spinal P2X2/3 receptors underlies an N-methyl-D-aspartate (NMDA)-dependent long lasting allodynic sensitivity in rodents [34].…”

“…A-317491 (compound 7) has nanomolar affinity for blocking both P2X3 and P2X2/3 receptors and is a competitive antagonist [32]. Peripheral and spinal administration of A-317491 attenuates complete Freund's adjuvant (CFA)-induced inflammatory hyperalgesia [33].…”

2′,3′-O-Substituted ATP derivatives as potent antagonists of purinergic P2X3 receptors and potential analgesic agents

“…Further studies led to the discovery of a potent and selective P2X3 receptor antagonist, named A-317491 ( Fig. 1), showing nanomolar activity at both homomeric P2X3 and heteromeric P2X2/3 receptors [46]. The most potent competitive antagonist of P2X3 receptors is the 2′,3′-O-(2,4,6-trinitrophenyl)-ATP (TNP-ATP, Fig.…”

Dor neuropática: aspectos neuroquímicos

“…In experimental models of neuropathic pain P2X 3 receptors are reduced (after axotomy or partial nerve ligature) or increased (chronic constrictive lesion); however, even in the face of reduction those receptors show increased sensitivity. Blockade of P2X 3 receptors attenuates thermal and mechanical allodynia in mice 33 . The expression of P2X 4 receptors is also increased in microglia after nerve damage, and its pharmacological blockade reverses allodynia 34 .…”

“…Em modelos experimentais para dor neuropática, há redução (após axotomia ou ligadura parcial do nervo) ou aumento (lesão constritiva crônica) de receptores P2X 3 ; contudo, mesmo na redução, há aumento da sensibilidade desses receptores. De modo que o bloqueio de receptores P2X 3 atenua a alodinia térmica e mecânica em ratos 33 . Os receptores P2X 4 também aumentam sua expressão na microglia após a lesão de nervo e o bloqueio farmacológico do P2X 4 reverte a alodinia 34 .…”