Received for publication November 10, 2006.
Revised February 12, 2007.
Accepted for publication February 13, 2007.

Interaction of novel positive allosteric modulators of metabotropic glutamate receptor 5 with the negative allosteric antagonist site is required for potentiation of receptor responses

Abstract

Exciting advances have been made in discovery of selective positive allosteric modulators of the metabotropic glutamate receptor (mGluR) mGluR5. These compounds may provide a novel approach that could be useful in treatment of certain CNS disorders. However, because of their low potencies, previously described mGluR5 potentiators are not useful for functional studies in native preparations. Also, binding sites at which these compounds act have not been identified. It has been suggested that two allosteric potentiators, DFB and CDPPB, act by binding to the same allosteric site as the negative allosteric modulators of mGluR5 such as MPEP. However, another mGluR5 potentiator (CPPHA) does not bind to this site, bringing this hypothesis into question. We have now synthesized a series of CDPPB analogs and report that these compounds bind to the MPEP site with affinities that are closely related to their potencies as mGluR5 potentiators. Furthermore, allosteric potentiation is antagonized by a neutral ligand at the MPEP site and reduced by a mutation of mGluR5 that eliminates MPEP binding. Together, these data suggest that interaction with the MPEP site is important for allosteric potentiation of mGluR5 by CDPPB and related compounds. In addition, whole cell patch clamp studies in midbrain slices reveal that a highly potent analog of CDPPB, VU-29, selectively potentiates mGluR5 but not mGluR1-mediated responses in midbrain neurons whereas a previously identified allosteric potentiator of mGluR1 has the opposite effect.

Key words: Metabotropic glutamate, Func. analysis receptor/ion channel mutants, Mutagenesis/Chimeric approaches, Receptor binding studies

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