N-{4-Chloro-2-[(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)methyl]phenyl}-2-hydroxybenzamide (CPPHA) acts through a novel site as a positive allosteric modulator of group 1 metabotropic glutamate receptors.
Recent studies suggest that a novel positive allosteric modulator (PAM) of the metabotropic glutamate receptor (mGluRs), mGluR5, termed 4-nitro-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (VU-29), potentiates mGluR5 responses by actions at a site that is overlapping with the binding site of 2-methyl-6-(phenylethynyl)pyridine (MPEP), a previously identified negative allosteric modulator of this receptor. It is interesting that a structurally distinct PAM, N-{4-Chloro-2-[(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)methyl]phenyl}-2-hydroxybenzamide (CPPHA), does not to bind to the MPEP site. We now report that CPPHA potentiates mGluR5 responses by a mechanism that is distinct from that of VU-29. VU-29- and CPPHA-induced potentiation of mGluR5 responses are blocked by a neutral ligand at the MPEP allosteric site termed 5-methyl-2-(phenylethynyl)pyridine (5MPEP). However, increasing concentrations of 5MPEP induce parallel rightward shifts in the VU-29 concentration-response curve, whereas 5MPEP inhibits CPPHA potentiation in a noncompetitive manner. Consistent with this, a mutation (A809V/mGluR5) that reduces binding of ligands to the MPEP site eliminates the effect of VU-29 but has no effect on the response to CPPHA. On the other hand, a mutation (F585I/mGluRs) that eliminates the effect of CPPHA does not alter the response to VU-29. CPPHA is also a PAM at mGluR1. It is interesting that the corresponding mutation of F585I/mGluR5 in mGluR1 (F599I/mGluR1) eliminates CPPHA's effect without altering the potentiation of a known PAM of mGluR1, (S)-2-(4-fluorophenyl)-1-(toluene-4-sulfonyl)pyrrolidine (Ro 67-7476). Likewise, another mutation (V757L/mGluR1) that abolishes potentiation of Ro 67-7476 has no effect on CPPHA. Finally, CPPHA does not displace binding of a radioligand for the mGluR1 allosteric antagonist characterized previously. Together, these data suggest that CPPHA acts at a novel allosteric site on both mGluR1 and -5 to potentiate responses to activation of these receptors.
Chen
Yelin
Y
Department of Pharmacology, Vanderbilt University Medical Center, 23rd Avenue South at Pierce, 417-D Preston Research Building, Nashville, TN 37232-6600, USA.
Goudet
Cyril
C
Pin
Jean-Philippe
JP
Conn
P Jeffrey
PJ
D000494:Allosteric Regulation; D000495:Allosteric Site / Q000187:drug effects*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001253:Astrocytes / Q000187:drug effects; D001549:Benzamides / Q000737:chemistry / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D018929:Cell Culture Techniques; D002460:Cell Line; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007668:Kidney / Q000166:cytology; D008024:Ligands; D008969:Molecular Sequence Data; D015394:Molecular Structure; D017434:Protein Structure, Tertiary; D011869:Radioligand Assay; D051381:Rats; D018094:Receptors, Metabotropic Glutamate / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D014633:Valine / Q000378:metabolism
D001549:Benzamides; D008024:Ligands; D018094:Receptors, Metabotropic Glutamate; C104077:metabotropic glutamate receptor type 1; D014633:Valine; D002118:Calcium