5--amino-5--deoxyadenosine and 5-iodotubercidin

Adenosine levels increase at seizure foci as part of a postulated endogenous negative feedback mechanism that controls seizure activity through activation of A1 adenosine receptors. Agents that amplify this site- and event-specific surge of adenosine could provide antiseizure activity similar to that of adenosine receptor agonists but with fewer dose-limiting side effects. Inhibitors of adenosine kinase (AK) were examined because AK is normally the primary route of adenosine metabolism. The AK inhibitors 5'-amino-5'-deoxyadenosine, 5-iodotubercidin, and 5'-deoxy-5-iodotubercidin inhibited maximal electroshock (MES) seizures in rats. Several structural classes of novel AK inhibitors were identified and shown to exhibit similar activity, including a prototype inhibitor, 4-(N-phenylamino)-5-phenyl-7-(5'-deoxyribofuranosyl)pyrrolo[2, 3-d]pyrimidine (GP683; MES ED50 = 1.1 mg/kg). AK inhibitors also reduced epileptiform discharges induced by removal of Mg2+ in a rat neocortical preparation. Overall, inhibitors of adenosine deaminase or of adenosine transport were less effective. The antiseizure activities of GP683 in the in vivo and in vitro preparations were reversed by the adenosine receptor antagonists theophylline and 8-(p-sulfophenyl)theophylline. GP683 showed little or no hypotension or bradycardia and minimal hypothermic effect at anticonvulsant doses. This improved side effect profile contrasts markedly with the profound hypotension, bradycardia, and hypothermia and greater inhibition of motor function observed with the adenosine receptor agonist N6-cyclopentyladenosine and opens the way to clinical evaluation of AK inhibitors as a novel, adenosine-based approach to anticonvulsant therapy.

Topics: Adenosine; Adenosine Kinase; Animals; Anticonvulsants; Cattle; Cells, Cultured; Deoxyadenosines; Electroshock; Endothelium, Vascular; Enzyme Inhibitors; Male; Microcirculation; Motor Activity; Neocortex; Pyrimidines; Radioligand Assay; Rats; Rats, Inbred Strains; Recombinant Proteins; Seizures; Structure-Activity Relationship; Tubercidin

The present study examined the spinal antinociceptive effects of adenosine analogs and inhibitors of adenosine kinase and adenosine deaminase in the carrageenan-induced thermal hyperalgesia model in the rat. The possible enhancement of the antinociceptive effects of adenosine kinase inhibitors by an adenosine deaminase inhibitor also was investigated. Unilateral hindpaw inflammation was induced by an intraplantar injection of lambda carrageenan (2 mg/100 microl), which consistently produced significant paw swelling and thermal hyperalgesia. Drugs were administered intrathecally, either by acute percutaneous lumbar puncture (individual agents and combinations) or via an intrathecal catheter surgically implanted 7-10 days prior to drug testing (antagonist experiments). N6-cyclohexyladenosine (CHA; adenosine A1 receptor agonist; 0.01-1 nmol), 2-[p-(2-carboxyethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenos ine (CGS21680; adenosine A2A receptor agonist; 0.1-10 nmol), 5'-amino-5'-deoxyadenosine (NH2dAdo; adenosine kinase inhibitor: 10-300 nmol), and 5-iodotubercidin (ITU; adenosine kinase inhibitor; 0.1-100 nmol) produced, to varying extents, dose-dependent antinociception. No analgesia was seen following injection of 2'-deoxycoformycin (dCF; an adenosine deaminase inhibitor; 100-300 nmol). Reversal of drug effects by caffeine (non-selective adenosine A1/A2 receptor antagonist; 515 nmol) confirmed the involvement of the adenosine receptor, while antagonism by 8-cyclopentyl-1,3-dimethylxanthine (CPT; adenosine A1 receptor antagonist; 242 nmol), but not 3,7-dimethyl-1-propargylxanthine (DMPX; adenosine A2A receptor antagonist; 242 nmol), evidenced an adenosine A1 receptor mediated spinal antinociception by NH2dAdo. dCF (100 nmol), which was inactive by itself, enhanced the effects of 10 nmol and 30 nmol NH2dAdo. Enhancement of the antinociceptive effect of ITU by dCF was less pronounced. None of the antinociceptive drug regimens had any effect on paw swelling. These results demonstrate that both directly and indirectly acting adenosine agents, when administered spinally, produce antinociception through activation of spinal adenosine A1 receptors in an inflammatory model of thermal hyperalgesia. The spinal antinociceptive effects of selected adenosine kinase inhibitors can be significantly augmented when administered simultaneously with an adenosine deaminase inhibitor.

Topics: Adenosine; Adenosine Deaminase; Animals; Antihypertensive Agents; Carrageenan; Deoxyadenosines; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Edema; Enzyme Inhibitors; Excipients; Hot Temperature; Hyperalgesia; Male; Neuritis; Neurons; Nociceptors; Pentostatin; Phenethylamines; Purinergic P1 Receptor Antagonists; Rats; Rats, Sprague-Dawley; Tubercidin

Activation of glutamate receptors triggers the release of adenosine, which exerts important inhibitory actions in the brain. Evoked adenosine release is potentiated when either adenosine kinase or adenosine deaminase are inhibited. We studied the effects of concurrent inhibition of adenosine kinase and adenosine deaminase on N-methyl-D-aspartate (NMDA)-evoked formation of extracellular adenosine in slices of rat parietal cortex, to determine if combinations of inhibitors of adenosine kinase and adenosine deaminase can produce supra-additive potentiation of this adenosine formation. Combinations of low concentrations of the adenosine kinase inhibitors 5'-amino-5'-deoxyadenosine (0.2 microM) or 5'-iodotubercidin (0.01 microM) with a low concentration of the adenosine deaminase inhibitor 2'-deoxycoformycin (0.2 microM) produced additive potentiations of NMDA-evoked adenosine release from slices of rat parietal cortex. However, combinations of low concentrations of 5'-amino-5'-deoxyadenosine (0.2 microM) or 5'-iodotubercidin (0.01 microM) with a maximal concentration of 2'-deoxycoformycin (200 microM) produced supra-additive potentiation of NMDA-evoked adenosine release. These findings suggest that such combinations of adenosine kinase inhibitors with adenosine deaminase inhibitors may provide useful strategies for developing therapies to treat disorders associated with excessive NMDA receptor activation, such as seizures, ischemic damage and neurodegenerative diseases.

Topics: Adenosine; Adenosine Deaminase Inhibitors; Adenosine Kinase; Animals; Cerebral Cortex; Deoxyadenosines; Drug Synergism; Enzyme Inhibitors; Excitatory Amino Acid Agonists; Male; N-Methylaspartate; Pentostatin; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Tubercidin

Inhibitors of adenosine kinase, but not adenosine deaminase, produce antinociception when administered spinally. In this study, we evaluated the relative contribution of adenosine kinase and adenosine deaminase to the regulation of adenosine release into the extracellular space within the spinal cord by determining the effects of the adenosine kinase inhibitors 5'-amino-5'-deoxyadenosine and 5-iodotubercidin, and the adenosine deaminase inhibitor 2'-deoxycoformycin on adenosine release from spinal cord slices in an in vitro perfusion system. Both 5'-amino-5'-deoxyadenosine (5-50 microM) and 5-iodotubercidin (5-50 microM), but not 2'-deoxycoformycin (50 microM), augmented adenosine release. 5-Iodotubercidin was slightly more potent and effective than 5'-amino-5'-deoxyadenosine in augmenting release except at the highest concentration, where it was considerably more effective. Combinations of 2'-deoxycoformycin (50 microM) and minimally active concentrations of 5'-amino-5'-deoxyadenosine and 5-iodotubercidin (5 microM each) produced a synergistic enhancement of release. These results support a predominant involvement of adenosine kinase in regulating extracellular adenosine levels in the spinal cord, but adenosine deaminase also can play a significant role.

Topics: Adenosine; Adenosine Deaminase Inhibitors; Adenosine Kinase; Animals; Deoxyadenosines; Dose-Response Relationship, Drug; Enzyme Inhibitors; In Vitro Techniques; Male; Pentostatin; Rats; Rats, Sprague-Dawley; Spinal Cord; Tubercidin