Substituent Effects of N-(1,3-Diphenyl-1H-pyrazol-5-yl)benzamides on Positive Allosteric Modulation of the Metabotropic Glutamate-5 Receptor in Rat Cortical Astrocytes

Abstract

CDPPB [3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide] was recently described as the first centrally active, positive allosteric modulator of rat and human metabotropic glutamate receptor (mGluR) mGluR5 subtype. We explored the structural requirements for potentiation of glutamate-induced calcium release in naturally expressed mGluR5 in cultured rat astrocytes and increasing affinity for the allosteric antagonist binding site by evaluating 50 analogues of CDPPB. In the fluorometric calcium assay, CDPPB exhibited an EC50 value of 77 +/- 15 nM in potentiating mGluR5-mediated responses in cortical astrocytes and a Ki value of 3760 +/- 430 nM in displacing [3H]methoxyPEPy binding in membranes of cultured HEK-293 cells expressing rat mGluR5. The structure-activity relationships showed that electronegative aromatic substituents in the para-position of the benzamide moiety of CDPPB increase potency. Both binding and functional activities were further increased with a halogen atom in the ortho-position of the 1-phenyl ring. These effects of substitution do not match those of either aromatic ring of MPEP [2-methyl-6-(phenylethynyl)pyridine] for the antagonist allosteric binding site. Combination of the optimal substituents and aromatic positions resulted in 4-nitro-N-(1-(2-fluorophenyl)-3-phenyl-1H-pyrazol-5-yl)benzamide (VU-1545) showing Ki = 156 +/- 29 nM and EC50 = 9.6 +/- 1.9 nM in the binding and functional assays, respectively.

Discovery of Novel Allosteric Modulators of Metabotropic Glutamate Receptor Subtype 5 Reveals Chemical and Functional Diversity and In Vivo Activity in Rat Behavioral Models of Anxiolytic and Antipsychotic Activity

“…A significant drawback of available mGluR5 PAMs is a lack of physiochemical and PK properties suitable for optimal in vivo dosing. Extensive medicinal chemistry efforts based on the CDPPB, ADX-47273, and CPPHA scaffolds de Paulis et al, 2006;Zhao et al, 2007;Engers et al, 2009) have failed to produce compounds with the aqueous solubility and PK profiles required for optimal in vivo studies. Although limited in vivo studies have been performed with these earlier compounds, they have required dosing in DMSO, which can compromise the interpretation of in vivo data.…”

ADX47273 [S-(4-Fluoro-phenyl)-{3-[3-(4-fluoro-phenyl)-[1,2,4]-oxadiazol-5-yl]-piperidin-1-yl}-methanone]: A Novel Metabotropic Glutamate Receptor 5-Selective Positive Allosteric Modulator with Preclinical Antipsychotic-Like and Procognitive Activities

“…Recently, ADX47273 (de Paulis et al, 2006) was identified as a novel selective mGlu5 PAM at the 5th International Metabotropic Glutamate Receptors Meeting . Up to 60 M ADX47273 showed no agonist, antagonist, or allosteric modulator activity at other rat and/or human family III GPCRs (mGlu1-8 and GABA-B).…”

Neuroimaging - Clinical Applications

“…(Kinney et al, 2005;Lindsley et al, 2004), respectively. Subsequent structure-activity relationship study on CDPPB identified several nanomolar potent pyrazole ligands (De Paulis et al, 2006). Although these compounds are potent with an EC 50 value of less than 20 nM, their poor binding affinity (K i ) and high lipophilicity The discoveries of noncompetitive allosteric modulators with high binding affinity and subtype-selectivity entitle the exploration of the physiological functions of mGluR5 in normal and pathological states.…”

“…To date, more than 15 mGluR5-selective PET ligands labeled with 18 F or 11 C have been reported (Fig. 6) (Ametamey et al, 2006;De Paulis et al, 2006;Hamill et al, 2005;Honer et al, 2007;Krause et al, 2003;Musachio et al, 2003;Patel et al, 2005;Sanchez-Pernaute et al, 2008;Sime´on et al, 2007;Wang et al, 2007a;Zhu et al, 2007). In 2005, Hamill and colleagues from Merck demonstrated the first successful PET imaging of mGluR5 in rhesus monkeys using [ 18 F]F-MTEB (61) Patel et al, 2005).…”