Metabolism and Distribution of Clozapine-N-oxide: Implications for Nonhuman Primate Chemogenetics

• Type of Material: Article
• Authors: Jessica Raper, Yerkes National Primate Research Center; Ryan D. Morrison, Sano Informed Prescribing Inc; J. Scott Daniels, Sano Informed Prescribing Inc; Leonard Howell, Emory University; Jocelyne Bachevalier, Emory University; Thomas Wichmann, Emory University; Adriana Galvan, Emory University
• Language: English
• Date: 2017-07-01
• Publisher: American Chemical Society
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2017 American Chemical Society.
• Final Published Version (URL): http://dx.doi.org/10.1021/acschemneuro.7b00079
• Title of Journal or Parent Work: ACS Chemical Neuroscience
• ISSN: 1948-7193
• Volume: 8
• Issue: 7
• Start Page: 1570
• End Page: 1576
• Grant/Funding Information: This work was supported through grants from National Institutes of Health (NIH) Office of Research Infrastructure Programs (ORIP; P51-OD011132) and the National Institute of Neurological Disorders and Stroke (NINDS; P50-NS098685, Udall Center of Excellence in Parkinson’s disease).
• Keywords: IN-VITRO; PHARMACOLOGY; Pharmacology & Pharmacy; DREADDS; Science & Technology; Neurosciences & Neurology; Rhesus macaque; clozapine; Life Sciences & Biomedicine; PROTEIN; Biochemistry & Molecular Biology; blood-brain barrier; Neurosciences; DREADDs; Chemistry, Medicinal; TRANSPORT; DESIGNER RECEPTORS; pharmacokinetics; DRUGS; P-GLYCOPROTEIN; NEONATAL AMYGDALA LESIONS
• Research Categories: Psychology, Physiological; Biology, Neuroscience; Psychology, Behavioral

Abstract

The use of Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) in neuroscience has rapidly expanded in rodent studies but has lagged behind in nonhuman primate (NHP) experiments, slowing the development of this method for therapeutic use in humans. One reason for the slow adoption of DREADD technology in primates is that the pharmacokinetic properties and bioavailability of clozapine-n-oxide (CNO), the most commonly used ligand for human muscarinic (hM) DREADDs, are not fully described in primates. We report an extensive pharmacokinetic study using subcutaneous (SC) administration of CNO in five adult rhesus monkeys. CNO reached maximal plasma and cerebrospinal fluid (CSF) concentrations within 2 h after injection, with an observed dose-dependent increase in levels following a 3 and 10 mg/kg SC dose. Since CSF concentrations were below values predicted from unbound plasma concentrations, we investigated whether CNO was restricted from the CNS through active transport at the blood-brain barrier. In vitro assessment demonstrated that CNO is a substrate for P-glycoprotein (Pgp; efflux ratio, 20), thus providing a likely mechanism limiting CNO levels in the CNS. Furthermore, CNO is metabolized to the psychoactive compounds clozapine and n-desmethylclozapine in monkeys. The concentrations of clozapine detected in the CSF are sufficient to activate several types of receptor (including the hM-DREADDs). Our results suggest that CNO metabolism and distribution may interfere with reproducibility and interpretation of DREADD-related experiments in NHPs and calls for a re-evaluation of the use of CNO in DREADD-related experiments in NHPs along with the need to test alternative compounds.