Antidotes for Acute Cannabinoid Intoxication

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PROJECT SUMMARY/ABSTRACT - In response to PAR-16-384, the goal of this NIDA/NIH Chemical Discovery (CHEM) Award (R21/R33) proposal is to discover antidotes for treating “Acute Marijuana Intoxication” produced by Δ9-tetrahydrocannabinol (THC) and the next generation synthetic psychoactive cannabinoids (SPCs) such as JWH-018. The cannabis constituent THC exerts its psychotropic effects (marijuana “high”) mainly via CB1R activation. SPCs mimic the effects of THC with higher potency and are illegally sold as “designer drugs”. Although acute toxicity is benign in the average adult, patients who consume high doses of THC (herbal and synthetic) present themselves with recurrent episodes of nausea and vomiting (Hyperemesis Syndrome), injected conjunctiva, and experience impaired cognition, motor skills and psychotic symptoms in the ER. In comparison, the neurotoxicity associated with SPCs is more severe wherein patients are admitted into the ER for altered mental status, somnolence, cardiotoxicity, stroke, kidney damage and acute psychosis. There are no antidotes available for treating acute cannabinoid poisoning, highlighting the need to address this critical public-health issue. The goal of this project is to discover antidotes to counteract the intoxicating effects of excessive CB1R activation and be therapeutically useful in an emergency setting. In this regard, the R21 phase will focus on use of in silico analysis, synthesis and characterization of compounds with favorable drug-like safety profiles. The synthesized ligands will be tested for their affinity and selectivity for CB1R and for their functional in vitro efficacy using the cAMP assay. Subsequently, ligands will be evaluated for their stability in plasma, whole blood and towards liver microsomes. Accordingly, their biochemical half-lives and interspecies variations will be determined. The R33 phase will focus on lead optimization, scale-up and re-synthesis along with in vivo evaluation of compounds in mice (both genders). Ligands will be first studied using a physiologically effective dose i.v. to quantify relative brain penetration using LC/MS/MS. Compounds exhibiting good brain penetration, when administered i.v., will be screened for their ability to rapidly normalize an on-going hypothermic effect induced by an acute dose of an agonist. Ligands with minimal intrinsic activity will be assayed i.v. using the functional observation battery (FOB) for their ability to normalize the neurological effects produced by “suprapharmacological” doses of the CB1 agonist. Given that the patients’ drug histories may not be known at admission, a key desired characteristic of short-acting antagonists as compared to the CB1 inverse-agonist, rimonabant (SR), is that they not elicit a physical withdrawal syndrome in cannabis-dependent subjects. To test this hypothesis, lead compounds will be administered to mice treated repeatedly with THC or JWH-018, to investigate whether they precipitate withdrawal. Results will be compared to rimonabant. Data will be used in an iterative manner to establish proof- of-concept and ultimately identify compounds for treating acute cannabinoid intoxication.