dx.doi.org/10.1124/molpharm.123.000678Pharmacol104:17-27, July 2023

Metabotropic glutamate receptor 7 (mGlu7) is a G protein cou-pled receptor that has demonstrated promise as a therapeutic target across a number of neurologic and psychiatric diseases. Compounds that modulate the activity of mGlu7, such as posi-tive and negative allosteric modulators, may represent new therapeutic strategies to modulate receptor activity. The en-dogenous neurotransmitter associated with the mGlu receptor family, glutamate, exhibits low efficacy and potency in activat-ing mGlu7, and surrogate agonists, such as the compound L-(+)-2-Amino-4-phosphonobutyric acid (L-AP4), are often used for receptor activation and compound profiling. To under-stand the implications of the use of such agonists in the devel-opment of positive allosteric modulators (PAMs), we performed a systematic evaluation of receptor activation using a system in which mutations can be made in either protomer of the mGlu7 dimer; we employed mutations that prevent interaction with the or-thosteric site as well as the G-protein coupling site of the receptor. We then measured increases in calcium levels downstream of a promiscuous G protein to assess the effects of mutations in one of the two protomers in the presence of two different agonists and three positive allosteric modulators. Our results reveal that distinct PAMs, for example N-[3-Chloro-4-[(5-chloro-2-pyridinyl)oxy]-phenyl]-2-pyridinecarboxamide (VU0422288) and 3-(2,3-Difluoro- 4-methoxyphenyl)-2,5-dimethyl-7-(trifluoromethyl)pyrazolo[1,5-a]pyrimidine (VU6005649), do exhibit different maximal levels of potentiation with L-AP4 versus glutamate, but there appear to be common stable receptor conformations that are shared among all of the compounds examined here.