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Author Notes:

Corresponding Author: Jessica Raper, Ph.D. Mailing address: Yerkes National Primate Research Center, 954 Gatewood Rd NE, Atlanta, GA 30329. jraper@emory.edu. Phone: 404-727-8334.

Adriana Galvan ORCID: 0000-0001-9939-0130

J.R. and A.G. designed the study, collected and analyze data, and wrote the manuscript.

R.D.M. and J.S.D. assisted in the design of the study, assayed samples, and wrote the manuscript.

L.H., J.B., and T.W. assisted in the writing and editing of the manuscript.

The authors thank Rebecca Richardson, M.A. for her assistance with the data collection.

The authors declare no competing financial interest.


Research Funding:

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).


  • Science & Technology
  • Life Sciences & Biomedicine
  • Biochemistry & Molecular Biology
  • Chemistry, Medicinal
  • Neurosciences
  • Pharmacology & Pharmacy
  • Neurosciences & Neurology
  • Rhesus macaque
  • pharmacokinetics
  • blood-brain barrier
  • clozapine

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


Journal Title:

ACS Chemical Neuroscience


Volume 8, Number 7


, Pages 1570-1576

Type of Work:

Article | Post-print: After Peer Review


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.

Copyright information:

© 2017 American Chemical Society.

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