title: Systemic blockade of P2X3 and P2X2/3 receptors attenuates bone cancer pain behaviour in rats.
abstract: Pain remains an area of considerable unmet clinical need, and this is particularly true of pain associated with bone metastases, in part because existing analgesic drugs show only limited efficacy in many patients and in part because of the adverse side effects associated with these agents. An important issue is that the nature and roles of the algogens produced in bone that drive pain-signalling systems remain unknown. Here, we tested the hypothesis that adenosine triphosphate is one such key mediator through actions on P2X3 and P2X2/3 receptors, which are expressed selectively on primary afferent nocioceptors, including those innervating the bone. Using a well-established rat model of bone cancer pain, AF-353, a recently described potent and selective P2X3 and P2X2/3 receptor antagonist, was administered orally to rats and found to produce highly significant prevention and reversal of bone cancer pain behaviour. This attenuation occurred without apparent modification of the disease, since bone destruction induced by rat MRMT-1 carcinoma cells was not significantly altered by AF-353. Using in vivo electrophysiology, evidence for a central site of action was provided by dose-dependent reductions in electrical, mechanical and thermal stimuli-evoked dorsal horn neuronal hyperexcitability following direct AF-353 administration onto the spinal cord of bone cancer animals. A peripheral site of action was also suggested by studies on the extracellular release of adenosine triphosphate from MRMT-1 carcinoma cells. Moreover, elevated phosphorylated-extracellular signal-regulated kinase expression in dorsal root ganglion neurons, induced by co-cultured MRMT-1 carcinoma cells, was significantly reduced in the presence of AF-353. These data suggest that blockade of P2X3 and P2X2/3 receptors on both the peripheral and central terminals of nocioceptors contributes to analgesic efficacy in a model of bone cancer pain. Thus, systemic P2X3 and P2X2/3 receptor antagonists with central nervous system penetration may offer a promising therapeutic tool in treating bone cancer pain.
authors.affiliation: Neurorestoration Group, Wolfson Centre for Age-Related Diseases, King’s College London, London, UK. timothy.kaan@alumni.ubc.ca
authors.forename: Timothy K Y
authors.initials: TK
authors.lastname: Kaan
authors.forename: Ping K
authors.initials: PK
authors.lastname: Yip
authors.forename: Sital
authors.initials: S
authors.lastname: Patel
authors.forename: Meirion
authors.initials: M
authors.lastname: Davies
authors.forename: Fabien
authors.initials: F
authors.lastname: Marchand
authors.forename: Debra A
authors.initials: DA
authors.lastname: Cockayne
authors.forename: Philip A
authors.initials: PA
authors.lastname: Nunn
authors.forename: Anthony H
authors.initials: AH
authors.lastname: Dickenson
authors.forename: Anthony P D W
authors.initials: AP
authors.lastname: Ford
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhong
authors.forename: Marzia
authors.initials: M
authors.lastname: Malcangio
authors.forename: Stephen B
authors.initials: SB
authors.lastname: McMahon
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000284:Administration, Oral; D000578:Amidines; D000818:Animals; D001859:Bone Neoplasms / Q000150:complications / Q000473:pathology; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D002277:Carcinoma / Q000150:complications / Q000473:pathology; D002478:Cells, Cultured; D018920:Coculture Techniques / Q000379:methods; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005727:Ganglia, Spinal / Q000166:cytology; D006930:Hyperalgesia / Q000188:drug therapy; D010146:Pain / Q000000981:diagnostic imaging / Q000188:drug therapy* / Q000209:etiology / Q000523:psychology*; D010147:Pain Measurement; D058919:Purinergic P2 Receptor Antagonists; D011743:Pyrimidines / Q000627:therapeutic use*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D058476:Receptors, Purinergic P2X2; D058477:Receptors, Purinergic P2X3; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000502:physiology; D055114:X-Ray Microtomography / Q000379:methods
chemical_list: D000578:Amidines; C546403:P2rx2 protein, rat; C546410:P2rx3 protein, rat; D058919:Purinergic P2 Receptor Antagonists; D011743:Pyrimidines; C542959:RO-4 compound; D018048:Receptors, Purinergic P2; D058476:Receptors, Purinergic P2X2; D058477:Receptors, Purinergic P2X3; C031455:diamidino compound 253-50; D000255:Adenosine Triphosphate; D048049:Extracellular Signal-Regulated MAP Kinases; D015740:Calcitonin Gene-Related Peptide