Project Summary America is currently facing a dire opioid epidemic, which affects two million people and causes more than 130 overdose deaths per day on average. Heroin is one primary culprit. Current treatments for heroin addiction—for instance methadone—directly target the opioid system; this approach is limited by high abuse potential, relatively high cost, and strict regulation of clinical use. These challenges highlight an urgent need to develop a non-opioid pharmacological intervention for heroin addiction, particularly one that does not target the opioid receptors. Based on associations between legalized use of medical marijuana and a reduction in opioid prescription rates and deaths, preclinical studies showing that cannabinoids affect addictive-like behavior, and our own preliminary results in rodent models of heroin addiction, we aim to develop and test the efficacy of a selective cannabinoid 2 receptor (CB2R) agonist in treating heroin use disorder. This drug would be a non-psychoactive analog of tetrahydrocannabinol (THC), which would not activate the cannabinoid 1 receptor (CB1R) believed to be responsible for the psychoactive effects of THC. Both CB1R and CB2R are G-protein-coupled receptors that are part of the endocannabinoid system and are expressed in the brain. CB2R’s location in the brain (mesolimbic dopamine (DA) system) and prior evidence that altering the mesolimbic DA system promotes or prevents drug reward, dependence, and addiction, support the investigation of CB2R as a therapeutic target for modulating heroin drug-seeking behavior. In rodent models, selective CB2R agonists have been shown to reduce cocaine self-administration (SA) or block cocaine-induced conditioned place preference (CPP). Our preliminary studies demonstrate that cannabis extract and THC (but not cannabidiol (CBD)) can reduce several heroin-addictive behaviors in rats and that both acute and chronic dosing of THC mitigates the negative effects of naloxone-precipitated withdrawal in heroin-addicted mice. The goal of this project is to repurpose CB2-C48, a highly selective CB2R agonist developed in a drug discovery program for pain, as a potential therapeutic for heroin addiction. We have used the following target profile for selection of the CB2R agonist : 1) Potent agonist of CB2R; 2) High receptor selectivity (>100-fold over CB1R); 3) Good in vitro and in vivo stability properties; and 4) High CNS penetration. SA1 will characterize CB2-C48 as a candidate tool compound, with the target profile outlined above, for species selectivity, pharmacokinetic (PK), and preliminary safety studies, while SA2 will assess the efficacy of CB2-C48 as a selective CB2R agonist in proof of concept efficacy studies in in vivo rodent models of heroin addiction.