Identifying the active conformation of the mGlu4 receptor positive allosteric modulator VU0155041: Implications for drug discovery

Y Harrak1, X Rovira2, P González-Bulnes1, F Malhaire2, C Goudet2, J-P Pin2, J Giraldo3, A Llebaria1. 1Institut de Química AvanÇada de Catalunya (IQAC-CSIC), Departament de Química Biomèdica, Spain, 2Institut de Génomique Fonctionnelle, Département de Pharmacologie Moléculaire, France, 3Universitat Autònoma de Barcelona, Institut de Neurociències, Spain

Over the last few years, drug research on G protein-coupled receptors (GPCRs) has focused largely on allosteric compounds because of the many pharmacological and therapeutic advantages they have. Regretfully, and particularly for these compounds, ligand-GPCR recognition often involves minor structural features making extremely difficult the analysis of structure-activity data. This problem has been recently exemplified for the interaction between metabotropic glutamate (mGlu) receptors and allosteric ligands for which shallow structure-activity relationships (SAR) and subtle molecular switches regulating pharmacology modes have been reported1.

The mGlu receptors belong to class C GPCRs. There are eight mGlu receptors assembled into three (I, II, III) groups. There is increasing evidence showing that agonists and positive allosteric modulators (PAMs) of mGlu4 receptor, which belongs to group III, have positive therapeutic effects on several neurological diseases amongst them Parkinson’s disease2 and neuropathic pain3. Thus, identification of SAR for the mGlu4 receptor can be a valuable tool in pharmaceutical research.

To provide insight on the structural determinants of the allosteric modulation of the mGlu4 receptor, we focused our attention on the selective mGlu4 PAM cis-2-(3,5-dichlorophenylcarbamoyl)cyclo-hexanecarboxylic acid (VU0155041)4. In a recent study, it was found that the two enantiomers of this chiral compound differ in potency and two conformations were energetically and geometrically characterized by computational methods. However, because the difference in energy was very low (0.8 kcal/mol), the active conformation could not be elucidated5.

To that aim, we restricted the conformational freedom of the cyclohexane moiety by inserting a C=C bond in particular positions of the ring, leading to three compounds ( DB1, DB2 and DB3). The receptor was cotransfected with a chimeric Gq/i-protein, which couples to the phospholipase C pathway, thus allowing monitoring of receptor activity by measurement of Ca2+ release. High-level quantum chemical calculations were performed on ligand compounds to characterize the potential active conformations. The pharmacologic profile of the synthesized compounds (logEC50 (M) mean ± SEM of triplicates -5.86±0.13, not determined (>-4), -5.43±0.16, -4.50±0.10 for VU0155041, DB1, DB2 and DB3, respectively) together with structural comparisons between calculated conformations allowed us to identify the active conformation of the mGlu4 PAM VU0155041 thus providing a pharmacophore for mGlu4 positive allosteric modulation that hopefully will be useful for drug design.

References

1. Wood MR et al. 2011 Biochemistry 50, 2403-2410.

2. Goudet C et al FASEB J. 2012 doi: 10.1096/fj.11-195941.

3. Goudet C et al. Pain. 2008 (1):112-24.

4. M. Niswender, et al Mol.Pharmacol 2008, 74 1345-1358.

5. Christov C et al ChemMedChem. 2011 6(1):131-40.