Targeting positive modulation and inhibition of ethanol-induced GABAA receptor potentiation as a novel mechanism for alcohol use disorder

Alcohol use disorder (AUD) is the most common substance use disorder (SUD) giving rise to major socioeconomic and health consequences, with an estimated 208 million people affected worldwide. Current pharmacotherapies are minimally ineffective, and none target the direct neurological effects of ethanol. To identify promising pharmacological approaches for the treatment of AUD, understanding of the complex psychophysiological influences of SUD is necessary. Thus, we first review psychophysiological aspects of SUD, including a brief review of the brain disease model of addiction and the psychophysiological overlap between SUD and obsessive-compulsive disorder (OCD). We expand on the preoccupation stage of the addiction, proposing a hypothesis where substance use can become the obsessive focus in those with underlying obsessive-compulsive pathology, leading to development of SUD. Utilizing this hypothesis, and drawing upon efficacy of OUD treatments, we then provide insight and suggestions for future directions for AUD treatments and pharmacological interventions. In agreement with the suggested AUD pharmacotherapy approaches, we have identified dihydromyricetin (DHM), a natural flavonoid, to be a promising starting point towards the development of a novel and effective pharmacological mechanism for AUD treatment, that is more in line with those currently available for OUD. DHM has been shown to counteract major neurological effects of ethanol, reduce voluntary ethanol intake, and provide anxiolytic effects through mutually exclusive binding with flumazenil, a GABAAR allosteric modulator. Despite this promising activity, DHM lacks druglike properties, leading to poor CNS exposure and thus limiting clinical utility. Thus, medicinal chemistry efforts are necessary to address the structural limitations of DHM. Further, as flavonoids are known to have non-specific bioactivities, towards which bioactive metabolites often contribute, exploring the specificity, and druggable potential of DHM bioactivity is necessary. First, we investigated the serum and brain exposure to DHM and metabolites associated with acute anti-intoxicating effects in mice. We found intraperitoneal (IP) administration of DHM 50 mg/kg to be effective at reducing acute ethanol-induced loss of righting reflex (LORR), with these effects limited by rapid serum and brain clearance. Next, we synthesized multiple dihydromyricetin derivatives and assessed intrinsic GABAAR activity, with the aim of determining structure activity relationship (SAR) and enhancing druglike properties. This enabled us to identify 4H-1-Benzopyran-4-one, 2-(3,4-dihydroxy-5-methoxyphenyl)-2,3-dihydro-3,5,7-trihydroxy and 4H-1-Benzopyran-4-one, and 2-(3,4-dihydroxy-5-methoxyphenyl)-2,3-dihydro-3,5,7-trihydroxy, respectively) to be GABAAR active metabolites. Notably, this work enabled us to discover a novel druglike, dihydromyricetin derivative (RU-EC2-52) that is a GABAAR positive allosteric modulator (PAM). Molecular modeling studies (MOE® software) in the benzodiazepine binding site of human GABAAR Cryo-EM structure provided insight into key DHM GABAAR interactions, largely correlating with SAR findings. Combined, these results support the potential of DHM’s mechanism at counteracting neurological effects of high doses of ethanol, provide insight into potential GABAAR active metabolites, and identify RU-EC2-52 to be a promising, druglike GABAAR PAM.Ph.D.Includes bibliographical reference