Alleviation of Cocaine Withdrawal and Pertinent Interactions between Salvinorin-based Antagonists and Kappa Opioid Receptor

Abstract

The kappa opioid receptor (KOR) is involved in the regulation of both reward and mood processes. Recent reports find that the use of drugs of abuse increases the production of dynorphin and overall activation of KOR. Long-acting KOR antagonists, such as norbinaltorphimine (nor-BNI), JDTic, and 5'-guanidinonaltrindole (GNTI), are shown to halt depressive and anxiety-related disorders, which are the common side effects of withdrawal that can lead to the relapse of drug use. Unfortunately, these prototypical KOR antagonists are known to induce selective KOR antagonism that is delayed by hours and extremely prolonged, and their use in humans comes with serious safety concerns because they possess a large window for potential drug-drug interactions. Additionally, their persisted pharmacodynamic activities can hinder the ability to reverse unanticipated side effects instantly. Herein we report our studies on the lead selective, salvinorin-based KOR antagonist (1) as well as nor-BNI on C57BL/6N mice for spontaneous cocaine withdrawal. Assessment of pharmacokinetics showed 1 to be a short-acting compound with an average half-life of 3.75 h across different compartments (brain, spinal cord, liver, and plasma). Both 1 (5 mg/kg) and nor-BNI (5 mg/kg) were shown to reduce spontaneous withdrawal behavior in mice, with 1 producing additional anti-anxiety-like behavior in a light-dark transition test (however, no mood-related effects of 1 or nor-BNI were observed at the current dosing in an elevated plus maze or a tail suspension test). Our results support the study of selective, short-acting KOR antagonists for the treatment of psychostimulant withdrawal and the associated negative mood states that contribute to relapse. Additionally, we identified pertinent interactions between 1 and KOR via computational studies, including induced-fit docking, mutagenesis, and molecular dynamics simulations, to gain insights into the design of future selective, potent, and short-acting salvinorin-based antagonists.