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In vitro binding of a radio-labeled positive allosteric modulator for metabotropic glutamate receptor subtype 5.
MedLine Citation:
PMID:  23150216     Owner:  NLM     Status:  Publisher    
The positive allosteric modulator (PAM) binding site for metabotropic glutamate receptor subtype 5 (mGlu(5) ) lacks a readily available radio-labeled tracer for detailed structure-activity studies. This communication describes a selective mGlu(5) compound, 7-methyl-2-(4-(pyridin-2-yloxy)benzyl)-5-(pyridin-3-yl)isoindolin-1-one (PBPyl) that binds with high affinity to human mGlu(5) and exhibits functional PAM activity. Analysis of PBPyl by FLIPR revealed an EC(50) of 87 nM with an 89% effect in transfected HEK293 cells and an EC(50) of 81 nM with a 42% effect in rat primary neurons. PBPylexhibited5-fold functional selectivity for mGlu(5) in a full mGlu receptor panel. Unlabeled PBPylwas tested for specific binding using a liquid chromatography mass spectrometry (LC/MS/MS) based filtration binding assay and exhibited 40% specific binding in recombinant membranes, a value higher than any candidate compound tested. In competition binding studies with [(3) H]MPEP, the mGlu(5) receptor negative allosteric modulator (NAM), PBPyl exhibited a k(i) value of 34 nM. PBPyl also displaced[(3) H]ABP688, another mGluR(5) receptor NAM, in tissue sections from mouse and rat brain using autoradiography. Areas of specific binding included the frontal cortex, striatum and nucleus accumbens.PBPyl was radiolabeled to a specific activity of 15 Ci/mmol and tested for specific binding in a filter plate format. In recombinant mGlu(5b) membranes, [(3) H]PBPyl exhibited saturable binding with a K(d) value of 18.6 nM. In competition binding experiments, [(3) H]PBPyl was displaced by high affinity mGlu(5) positive and negative modulators. Further tests showed that PBPyl displays less than optimal characteristics as an in vivotool, including a high volume of distribution and ClogP making it more suitable as an in vitro compound. However, this is the first report of direct binding of an mGlu(5) receptor PAM that may valuablefor SARstudiesin the development of novel PET imaging agents for this important therapeutic target. Synapse, 2012. © 2012 Wiley Periodicals, Inc.
John R Zysk; Nathan Spear; William Fieles; Mark M Stein; Linda S Sygowski; Megan M King; Valerie Hoesch; Richard Hastings; Becky Brockel; Mylinh Do; Peter Ström; Reto Gadient; Vijay Chhajlani; Charles S Elmore; Donna L Maier
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-11-14
Journal Detail:
Title:  Synapse (New York, N.Y.)     Volume:  -     ISSN:  1098-2396     ISO Abbreviation:  Synapse     Publication Date:  2012 Nov 
Date Detail:
Created Date:  2012-11-14     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8806914     Medline TA:  Synapse     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
Copyright © 2012 Wiley Periodicals, Inc.
Department of Neuroscience, AstraZeneca Pharmaceuticals, CNS R&D, Wilmington, DE.
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