A Novel Metabotropic Glutamate Receptor 5 Positive Allosteric Modulator Acts at a Unique Site and Confers Stimulus Bias to mGlu5 Signaling

Abstract

Metabotropic glutamate receptor 5 (mGlu 5 ) is a target for the treatment of central nervous system (CNS) disorders, such as schizophrenia and Alzheimer's disease. Furthermore, mGlu 5 has been shown to play an important role in hippocampal synaptic plasticity, specifically in long-term depression (LTD) and longterm potentiation (LTP), which is thought to be involved in cognition. Multiple mGlu 5 -positive allosteric modulators (PAMs) have been developed from a variety of different scaffolds. Previous work has extensively characterized a common allosteric site on mGlu 5 , termed the MPEP (2-Methyl-6-(phenylethynyl)pyridine) binding site. However, one mGlu 5 PAM, CPPHA (N-(4-chloro-2-[(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)methyl]phenyl)-2-hydroxybenzamide), interacts with a separate allosteric site on mGlu 5. Using cell-based assays and brain slice preparations, we characterized the interaction of a potent and efficacious mGlu 5 PAM from the CPPHA series termed NCFP (N-(4-chloro-2-((4-fluoro-1,3-dioxoisoindolin-2-yl)methyl)phenyl)picolinamide). NCFP binds to the CPPHA site on mGlu 5 and potentiates mGlu 5 -mediated responses in both recombinant and native systems. However, NCFP provides greater mGlu 5 subtype selectivity than does CPPHA, making it more suitable for studies of effects on mGlu 5 in CNS preparations. Of interest, NCFP does not potentiate responses involved in hippocampal synaptic plasticity (LTD/ LTP), setting it apart from other previously characterized MPEP site PAMs. This suggests that although mGlu 5 PAMs may have similar responses in some systems, they can induce differential effects on mGlu 5 -mediated physiologic responses in the CNS. Such stimulus bias by mGlu 5 PAMs may complicate drug discovery efforts but would also allow for specifically tailored therapies, if pharmacological biases can be attributed to different therapeutic outcomes.

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

“…****P , 0.00001. whereas we find here that it also demonstrates an intrinsic efficacy. In fact, the detection of intrinsic agonist activity of mGlu 5 PAMs has been linked to receptor level expression (45). Similar to what is observed for partial agonists with a low efficacy (46,47), the intrinsic efficacy of PAMs is not detected when the cell surface expression of the receptor is low, whereas it can be observed in high expressing cells.…”

International Union of Basic and Clinical Pharmacology. XC. Multisite Pharmacology: Recommendations for the Nomenclature of Receptor Allosterism and Allosteric Ligands

“…Interestingly, there are also examples of multiple allosteric sites on the same GPCR (Lazareno et al, 2002;de Kruijf et al, 2011;Noetzel et al, 2013;Zweemer et al, 2013), further highlighting the rich potential for allosteric targeting of this receptor family.…”

Molecular Insights into Metabotropic Glutamate Receptor Allosteric Modulation

“…Headless mGlu 1 and mGlu 5 are constitutively active such that negative allosteric modulators behave as inverse agonists (Goudet et al, 2004;Chen et al, 2007;Suzuki et al, 2007). Furthermore, headless mGlu 5 can be stimulated by small molecule positive allosteric modulators that do not necessarily have intrinsic efficacy at the full-length receptor (Chen et al, 2007;Goudet et al, 2004;Noetzel et al, 2013). Interestingly, NCFP had little or no efficacy for stimulating headless mGlu 5 , despite having a similar magnitude of positive cooperativity as VU0092273, which can activate headless mGlu 5 .…”