A Novel Delta Opioid Receptor Antagonist, SoRI-9409, Produces a Selective and Long-Lasting Decrease in Ethanol Consumption in Heavy-Drinking Rats

Background Naltrexone, a compound with high affinity for the μ opioid receptor (MOP-R) reduces alcohol consumption. SoRI-9409 is a derivative of naltrexone that has highest affinity at δ opioid receptors (DOP-Rs). We have investigated the effects of SoRI-9409 on ethanol consumption to determine the consequences of altering the naltrexone compound to a form with increased efficacy at DOP-Rs. Methods Effects of the opioid receptor antagonists, SoRI-9409 (0–30 mg/kg, IP), naltrexone (0–30 mg/kg, IP), or naltrindole (0–10 mg/kg, IP) on ethanol consumption was measured in high- and low-ethanol–consuming rats with two different drinking paradigms. SoRI-9409-, naltrexone-, and naltrindole-mediated inhibition of DOP-R–stimulated [35S]GTPγS binding was measured in brain membranes prepared from high-ethanol–consuming rats. The effects of SoRI-9409 on morphine-mediated analgesia, conditioned place preference, and anxiety were also examined. Results In high- but not low-ethanol–consuming animals, SoRI-9409 is threefold more effective and selective at reducing ethanol consumption when compared with naltrexone or naltrindole for up to 24 hours. SoRI-9409 administered daily for 28 days continuously reduced ethanol consumption, and when the administration of SoRI-9409 was terminated, the amount of ethanol consumed remained lower compared with vehicle-treated animals. Furthermore, SoRI-9409 inhibits DOP-R–stimulated [35S]GTPγS binding in brain membranes of high-ethanol–consuming rats. Conclusions SoRI-9409 causes selective and long-lasting reductions of ethanol consumption. This suggests that compounds that have high affinity for DOP-Rs such as SoRI-9409 might be promising candidates for development as a novel therapeutic for the treatment of alcoholism.