PF-06827443 Displays Robust Allosteric Agonist and Positive Allosteric Modulator Activity in High Receptor Reserve and Native Systems.

Positive allosteric modulators (PAMs) of the M1 subtype of muscarinic acetylcholine receptor have attracted intense interest as an exciting new approach for improving the cognitive deficits in schizophrenia and Alzheimer's disease. Recent evidence suggests that the presence of intrinsic agonist activity of some M1 PAMs may reduce efficacy and contribute to adverse effect liability. However, the M1 PAM PF-06827443 was reported to have only weak agonist activity at human M1 receptors but produced M1-dependent adverse effects. We now report that PF-06827443 is an allosteric agonist in cell lines expressing rat, dog, and human M1 and use of inducible cell lines shows that agonist activity of PF-06827443 is dependent on receptor reserve. Furthermore, PF-06827443 is an agonist in native tissue preparations and induces behavioral convulsions in mice similar to other ago-PAMs. These findings suggest that PF-06827443 is a robust ago-PAM, independent of species, in cell lines and native systems.