Functional Impact of Allosteric Agonist Activity of Selective Positive Allosteric Modulators of Metabotropic Glutamate Receptor Subtype 5 in Regulating Central Nervous System Function

   1. Meredith J. Noetzel,
   2. Jerri M. Rook,
   3. Paige N. Vinson,
   4. Hyekyung P. Cho,
   5. Emily Days,
   6. Y. Zhou,
   7. Alice L. Rodriguez,
   8. Hilde Lavreysen,
   9. Shaun R. Stauffer,
  10. Colleen M. Niswender,
  11. Zixiu Xiang,
  12. J. Scott Daniels,
  13. Carrie K. Jones,
  14. Craig W. Lindsley,
  15. C. David Weaver and
  16. P. Jeffrey Conn

   1.
      Department of Pharmacology and Vanderbilt Center for Neuroscience Drug Discovery (M.J.N., J.M.R., P.N.V., H.P.C., E.D., Y.Z., A.L.R., S.R.S., C.M.N., Z.X., J.S.D., C.K.J., C.W.L., C.D.W., P.J.C.), Department of Chemistry (H.P.C., S.R.S., C.W.L.), and Vanderbilt Institute of Chemical Biology (E.D., C.D.W.), Vanderbilt University Medical Center, Nashville, Tennessee; and Neuroscience, Janssen Research and Development, a division of Janssen Pharmaceutica NV, Beerse, Belgium (H.L.)

   1. Address correspondence to:
      Dr. P. Jeffrey Conn, Vanderbilt Center for Neuroscience Drug Discovery, Department of Pharmacology, Vanderbilt University Medical Center, 1215 Light Hall, Nashville, TN 37232-0697. E-mail: jeff.conn{at}vanderbilt.edu

   1.

      This work was previously presented in part in the following publication: Noetzel MJ, Cho HP, Days E, Zhou Y, Rodriguez AL, Steckler T, Lavreysen H, Stauffer SR, Niswender CM, Lindsley CW, Weaver CD, and Conn PJ (2010) Receptor expression level influences the effect of allosteric modulators at metabotropic glutamate receptor 5, in Proceedings of the Neuroscience 2010; 2010 Nov 10–17; San Diego, CA. Society for Neuroscience, Washington, DC.

   1.

      M.N. and J.R. contributed equally to this work.

Abstract

Positive allosteric modulators (PAMs) of metabotropic glutamate receptor subtype 5 (mGlu5) have emerged as an exciting new approach for the treatment of schizophrenia and other central nervous system (CNS) disorders. Of interest, some mGlu5 PAMs act as pure PAMs, only potentiating mGlu5 responses to glutamate whereas others [allosteric agonists coupled with PAM activity (ago-PAMs)] potentiate responses to glutamate and have intrinsic allosteric agonist activity in mGlu5-expressing cell lines. All mGlu5 PAMs previously shown to have efficacy in animal models act as ago-PAMs in cell lines, raising the possibility that allosteric agonist activity is critical for in vivo efficacy. We have now optimized novel mGlu5 pure PAMs that are devoid of detectable agonist activity and structurally related mGlu5 ago-PAMs that activate mGlu5 alone in cell lines. Studies of mGlu5 PAMs in cell lines revealed that ago-PAM activity is dependent on levels of mGlu5 receptor expression in human embryonic kidney 293 cells, whereas PAM potency is relatively unaffected by levels of receptor expression. Furthermore, ago-PAMs have no agonist activity in the native systems tested, including cortical astrocytes and subthalamic nucleus neurons and in measures of long-term depression at the hippocampal Schaffer collateral-CA1 synapse. Finally, studies with pure PAMs and ago-PAMs chemically optimized to provide comparable CNS exposure revealed that both classes of mGlu5 PAMs have similar efficacy in a rodent model predictive of antipsychotic activity. These data suggest that the level of receptor expression influences the ability of mGlu5 PAMs to act as allosteric agonists in vitro and that ago-PAM activity observed in cell-based assays may not be important for in vivo efficacy.
Footnotes

    *

      ↵Graphic The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
    *

      This work was supported by the National Institutes of Health National Institute of Mental Health [Grant 2R01-MH062646-12]; National Institutes of Health National Institute of Neurological Disorders and Stroke [Grants 2R01-NS031373-16A2, F32-NS071746]; and National Institutes of Health National Institute of Mental Health Molecular Libraries Probe Production Centers Network [Grants 5 u54 MH84659-03, 5 u54 MH84659-03S1].
    *

      Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.

      http://dx.doi.org/10.1124/mol.111.075184.
    *

      ABBREVIATIONS:

      mGlu
          metabotropic glutamate receptor
      CNS
          central nervous system
      NMDA
          N-methyl-d-aspartate
      PAM
          positive allosteric modulator
      ago-PAM
          allosteric agonist coupled with PAM activity
      DMEM
          Dulbecco's modified Eagle's medium
      FBS
          fetal bovine serum
      DHPG
          dihydroxyphenylglycine
      VU0360172
          N-cyclobutyl-6-((3-fluorophenyl)ethynyl)nicotinamide
      VU0361747
          (6-((3-fluorophenyl)ethynyl)pyridin-3-yl)(4-hydroxypiperidin-1-yl)methanone
      VU0092273
          (4-hydroxypiperidin-1-yl)(4-phenylethynyl)phenyl)methanone
      VU0240382
          6-(2-phenylethynyl)-1,2,3,4-tetrahydroisoquinolin-1-one
      MTEP
          3-((2-methyl-4-thiazolyl)ethynyl)pyridine
      HEK
          human embryonic kidney
      GIRK
          G protein-coupled inwardly rectifying potassium channels
      DMSO
          dimethyl sulfoxide
      HBSS
          Hanks' balanced salt solution
      CRC
          concentration-response curve
      AGM
          assay growth media
      l-AP4
          l-(+)-2-amino-4-phosphonobutyric acid
      aCSF
          artificial cerebrospinal fluid
      fEPSP
          field excitatory postsynaptic potential
      LTD
          long-term depression
      STN
          subthalamic nucleus
      HPLC
          high-performance liquid chromatography
      SC-CA1
          Schaffer collateral-CA1
      VU29
          N-(1,3-diphenyl-1H-pyrazol-5-yl)-4-nitrobenzamide
      LTP
          long-term potentiation.

    * Received August 8, 2011.
    * Accepted October 20, 2011.

    * Copyright © 2012 The American Society for Pharmacology and Experimental Therapeutics

