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Evaluation in vitro and in animals of a new 11C-labeled PET radioligand for metabotropic glutamate receptors 1 in brain

  • Paolo Zanotti-Fregonara
  • Vanessa N. Barth
  • Jeih-San Liow
  • Sami S. Zoghbi
  • David T. Clark
  • Emily Rhoads
  • Edward Siuda
  • Beverly A. Heinz
  • Eric Nisenbaum
  • Bruce Dressman
  • Elizabeth Joshi
  • Debra Luffer-Atlas
  • Matthew J. Fisher
  • John J. Masters
  • Nancy Goebl
  • Steven L. Kuklish
  • Cheryl Morse
  • Johannes Tauscher
  • Victor W. Pike
  • Robert B. InnisEmail author
Original Article

Abstract

Purpose

Two allosteric modulators of the group I metabotropic glutamate receptors (mGluR1 and mGluR5) were evaluated as positron emission tomography (PET) radioligands for mGluR1.

Methods

LY2428703, a full mGluR1 antagonist (IC50 8.9 nM) and partial mGluR5 antagonist (IC50 118 nM), and LSN2606428, a full mGluR1 and mGluR5 antagonist (IC50 35.3 nM and 10.2 nM, respectively) were successfully labeled with 11C and evaluated as radioligands for mGluR1. The pharmacology of LY2428703 was comprehensively assessed in vitro and in vivo, and its biodistribution was investigated by liquid chromatography-mass spectrometry/mass spectrometry, and by PET imaging in the rat. In contrast, LSN2606428 was only evaluated in vitro; further evaluation was stopped due to its unfavorable pharmacological properties and binding affinity.

Results

11C-LY2428703 showed promising characteristics, including: (1) high potency for binding to human mGluR1 (IC50 8.9 nM) with no significant affinity for other human mGlu receptors (mGluR2 through mGluR8); (2) binding to brain displaceable by administration of an mGluR1 antagonist; (3) only one major radiometabolite in both plasma and brain, with a negligible brain concentration (with 3.5 % of the total radioactivity in cerebellum) and no receptor affinity; (4) a large specific and displaceable signal in the mGluR1-rich cerebellum with no significant in vivo affinity for mGluR5, as shown by PET studies in rats; and (5) lack of substrate behavior for efflux transporters at the blood–brain barrier, as shown by PET studies conducted in wild-type and knockout mice.

Conclusion

11C-LY2428703, a new PET radioligand for mGluR1 quantification, displayed promising characteristics both in vitro and in vivo in rodents.

Keywords

mGlu1 receptors PET Brain 

Notes

Acknowledgments

The authors are grateful to the NIH Clinical PET Center (Chief, Dr. P. Herscovitch) for cyclotron production of carbon-11. Ioline Henter provided excellent editorial assistance.

Disclosure

This work was supported in part by the Intramural Research Program of the National Institute of Mental Health, National Institutes of Health (IRP-NIMH-NIH).

Supplementary material

259_2012_2269_MOESM1_ESM.docx (65 kb)
ESM 1 (DOCX 65.0 KB)

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Copyright information

© Springer-Verlag Berlin Heidelberg (outside the USA) 2012

Authors and Affiliations

  • Paolo Zanotti-Fregonara
    • 1
  • Vanessa N. Barth
    • 2
  • Jeih-San Liow
    • 1
  • Sami S. Zoghbi
    • 1
  • David T. Clark
    • 1
  • Emily Rhoads
    • 2
  • Edward Siuda
    • 2
  • Beverly A. Heinz
    • 2
  • Eric Nisenbaum
    • 2
  • Bruce Dressman
    • 2
  • Elizabeth Joshi
    • 2
  • Debra Luffer-Atlas
    • 2
  • Matthew J. Fisher
    • 2
  • John J. Masters
    • 2
  • Nancy Goebl
    • 2
  • Steven L. Kuklish
    • 2
  • Cheryl Morse
    • 1
  • Johannes Tauscher
    • 2
  • Victor W. Pike
    • 1
  • Robert B. Innis
    • 1
    • 3
    Email author
  1. 1.Molecular Imaging BranchNational Institute of Mental Health, National Institutes of HealthBethesdaUSA
  2. 2.Eli Lilly & Co.IndianapolisUSA
  3. 3.Molecular Imaging BranchNational Institute of Mental HealthBethesdaUSA

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