A novel selective metabotropic glutamate receptor 4 agonist reveals new possibilities for developing subtype selective ligands with therapeutic potential

Abstract

Metabotropic glutamate (mGlu) receptors are promising targets to treat numerous brain disorders. So far, allosteric modulators are the only subtype selective ligands, but pure agonists still have strong therapeutic potential. Here, we aimed at investigating the possibility of developing subtype-selective agonists by extending the glutamate-like structure to hit a nonconsensus binding area. We report the properties of the first mGlu4-selective orthosteric agonist, derived from a virtual screening hit, LSP4-2022 using cell-based assays with recombinant mGlu receptors [EC(50): 0.11 ± 0.02, 11.6 ± 1.9, 29.2 ± 4.2 μM (n>19) in calcium assays on mGlu4, mGlu7, and mGlu8 receptors, respectively, with no activity at the group I and -II mGlu receptors at 100 μM]. LSP4-2022 inhibits neurotransmission in cerebellar slices from wild-type but not mGlu4 receptor-knockout mice. In vivo, it possesses antiparkinsonian properties after central or systemic administration in a haloperidol-induced catalepsy test, revealing its ability to cross the blood-brain barrier. Site-directed mutagenesis and molecular modeling was used to identify the LSP4-2022 binding site, revealing interaction with both the glutamate binding site and a variable pocket responsible for selectivity. These data reveal new approaches for developing selective, hydrophilic, and brain-penetrant mGlu receptor agonists, offering new possibilities to design original bioactive compounds with therapeutic potential.

Allosteric Binding Site and Activation Mechanism of Class C G-Protein Coupled Receptors: Metabotropic Glutamate Receptor Family

“…5a to c, the three PAMs are located closely to the hydroxyl in Ser760 5.47 and Ser825 7.35 . So the hydrogen acceptor groups in the PAMs formed two hydrogen bonds with Ser760 5.47 and , respectively, indicating the importance of these two residues, which was consistent with former reports (18,26,64). Other residues also contributed to the binding and selectivity due to their hydrophobic nature, including (selective residues).…”

“…This indicated that potential selectivity can be found in group III. Goudent et al (18) recently reported an orthosteric bitopic mGluR4 agonist with more than 30-fold selectivity over other group III mGluRs.…”

Overlapping binding sites drive allosteric agonism and positive cooperativity in type 4 metabotropic glutamate receptors

“…All types of mGlu 4 activators, agonists, ago-PAMs, and PAMs exhibiting high degree of cooperativity have been shown to be active in vivo (8,11,33,43,44,(48)(49)(50)(51). It can be speculated that pure mGlu 4 PAMs may be devoid of side effects but, to date, no clear adverse effect has been observed (8,50,51). Thus, for medicinal chemists to find the best therapeutic profile of mGlu 4 allosteric ligands, further experiments will be necessary to elucidate this point.…”

“…All 4 PAMs induced mobilization of intracellular calcium, suggesting that they all possess agonist activity, albeit very low for MPEP. The EC 50 values measured for VU0415374, VU0155041, PHCCC, and MPEP are 0.32 6 0.23 (n = 4), 11 6 2.9 (n = 4), 28 6 17 (n = 4), and 110 6 30 mM (n = 4), respectively. Agonist potencies, defined as 1/EC 50 , are in the same rank order as those given by the operational efficacies (t) provided by the operational model (Table 1).…”

Chloride is an Agonist of Group II and III Metabotropic Glutamate Receptors

“…While targeting this region has already been proposed as a strategy for the design of subtype-selective group III mGlu receptor agonists (Acher et al, 2011;Goudet et al, 2012), mGlu4, mGlu6, and mGlu8 receptors all contain functional chloride sites. In contrast to the claim that all mGlu receptors share the putative chloride binding site (Acher et al, 2011), our results demonstrate that this site is not conserved at mGlu2 receptors.…”