Characterization of a CNS penetrant, selective M1muscarinic receptor agonist, 77‐LH‐28‐1

Abstract

Background and purpose: M₁ muscarinic ACh receptors (mAChRs) represent an attractive drug target for the treatment of cognitive deficits associated with diseases such as Alzheimer's disease and schizophrenia. However, the discovery of subtype‐selective mAChR agonists has been hampered by the high degree of conservation of the orthosteric ACh‐binding site among mAChR subtypes. The advent of functional screening assays has enabled the identification of agonists such as AC‐42 (4‐n‐butyl‐1‐[4‐(2‐methylphenyl)‐4‐oxo‐1‐butyl]‐piperidine), which bind to an allosteric site and selectively activate the M₁ mAChR subtype. However, studies with this compound have been limited to recombinantly expressed mAChRs. Experimental approach: In this study, we have compared the pharmacological profile of AC‐42 and a close structural analogue, 77‐LH‐28‐1 (1‐[3‐(4‐butyl‐1‐piperidinyl)propyl]‐3,4‐dihydro‐2(1H)‐quinolinone) at human recombinant, and rat native, mAChRs by calcium mobilization, inositol phosphate accumulation and both in vitro and in vivo electrophysiology. Key results: Calcium mobilization and inositol phosphate accumulation assays revealed that both AC‐42 and 77‐LH‐28‐1 display high selectivity to activate the M₁ mAChR over other mAChR subtypes. Furthermore, 77‐LH‐28‐1, but not AC‐42, acted as an agonist at rat hippocampal M₁ receptors, as demonstrated by its ability to increase cell firing and initiate gamma frequency network oscillations. Finally, 77‐LH‐28‐1 stimulated cell firing in the rat hippocampus in vivo following subcutaneous administration. Conclusions and implications: These data suggest that 77‐LH‐28‐1 is a potent, selective, bioavailable and brain‐penetrant agonist at the M₁ mAChR and therefore that it represents a better tool than AC‐42, with which to study the pharmacology of the M₁ mAChR. British Journal of Pharmacology (2008) 154, 1104–1115; doi:10.1038/bjp.2008.152; published online 5 May 2008