Abstract
Positive allosteric modulators (PAMs) of the M(1) 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 M(1) PAMs may reduce efficacy and contribute to adverse effect liability. However, the M(1) PAM PF-06827443 was reported to have only weak agonist activity at human M(1) receptors but produced M(1)-dependent adverse effects. We now report that PF-06827443 is an allosteric agonist in cell lines expressing rat, dog, and human M(1) 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.