The effect of GP683, an adenosine kinase inhibitor, on the desflurane anesthetic requirement in dogs

Antihyperalgesic activity of nucleoside transport inhibitors in models of inflammatory pain in guinea pigs

Background and methods

The role of the endogenous purine nucleoside, adenosine, in nociception is well established. Inhibition of the equilibrative nucleoside transporter (ENT1) prevents adenosine uptake into cells, and could therefore enhance the antinociceptive properties of adenosine. The effects of ENT1 inhibition were studied in two animal models of inflammatory pain. Analgesic activity was assessed in a complete Freund’s adjuvant (CFA)-induced and carrageenan-induced mechanical and thermal hyperalgesia model in the guinea pig.

Results

Draflazine, dipyridamole, dilazep, lidoflazine, soluflazine, and KF24345 showed efficacy in the CFA thermal hyperalgesia model. Draflazine, the most potent compound in this test, was further characterized in the CFA model of mechanical hyperalgesia and the carrageenan inflammation model of thermal and mechanical hyperalgesia, where it completely reversed the hypersensitivity. The antihyperalgesic effects of draflazine (10 mg/kg, administered subcutaneously) were attenuated by the A1 receptor antagonist, cyclopentyltheophylline (5–40 mg/kg, administered intraperitoneally), by the nonselective adenosine antagonist, caffeine (10–40 mg/kg intraperitoneally), and by the A2 antagonist, DMPX (10 mg/kg administered intraperitoneally).

Conclusion

ENT1 inhibition is an effective way of reversing mechanical and thermal inflammatory hyperalgesia in the guinea pig, and these effects are mediated by enhancement of endogenous adenosine levels. Both A1 and A2 adenosine receptor subtypes are likely to be involved.

Recent developments in the discovery of novel adenosine kinase inhibitors: mechanism of action and therapeutic potential

Adenosine (ADO) is an endogenous inhibitory neuromodulator that limits cellular excitability in response to tissue trauma and inflammation. Adenosine kinase (AK; EC 2.7.1.20) is the primary metabolic enzyme regulating intra- and extracellular concentrations of ADO. AK inhibitors have been shown to significantly increase ADO concentrations at sites of tissue injury and to provide effective antinociceptive, antiinflammatory, and anticonvulsant activity in animal models. Structurally novel nucleoside and non-nucleoside AK inhibitors that demonstrate high specificity for the AK enzyme compared with other ADO metabolic enzymes, transporters, and receptors have recently been synthesized. These compounds have also demonstrated improved cellular and tissue penetration compared with earlier tubercidin analogs. These compounds have been shown to exert beneficial effects in animal models of pain, inflammation and epilepsy with reduced cardiovascular side effects compared with direct acting ADO receptor (P1) agonists, thus supporting the hypothesis that AK inhibitors can enhance the actions of ADO in a site- and event-specific fashion.