Identification and pharmacological profile of SPP1, a potent, functionally selective and brain penetrant agonist at muscarinic M₁ receptors

Abstract

Background and Purpose We aimed to identify and develop novel, selective muscarinic M1 receptor agonists as potential therapeutic agents for the symptomatic treatment of Alzheimer's disease. Experimental Approach We developed and utilized a novel M1 receptor occupancy assay to drive a structure activity relationship in a relevant brain region while simultaneously tracking drug levels in plasma and brain to optimize for central penetration. Functional activity was tracked in relevant native in vitro assays allowing translational (rat–human) benchmarking of structure–activity relationship molecules to clinical comparators. Key Results Using this paradigm, we identified a series of M1 receptor selective molecules displaying desirable in vitro and in vivo properties and optimized key features, such as central penetration while maintaining selectivity and a partial agonist profile. From these compounds, we selected spiropiperidine 1 (SPP1). In vitro, SPP1 is a potent, partial agonist of cortical and hippocampal M1 receptors with activity conserved across species. SPP1 displays high functional selectivity for M1 receptors over native M2 and M3 receptor anti‐targets and over a panel of other targets. Assessment of central target engagement by receptor occupancy reveals SPP1 significantly and dose‐dependently occupies rodent cortical M1 receptors. Conclusions and Implications We report the discovery of SPP1, a novel, functionally selective, brain penetrant partial orthosteric agonist at M1 receptors, identified by a novel receptor occupancy assay. SPP1 is amenable to in vitro and in vivo study and provides a valuable research tool to further probe the role of M1 receptors in physiology and disease.

Molecular Characterization and Expression of SPP1, LAP3 and LCORL and Their Association with Growth Traits in Sheep

“…The SPP1 is a highly phosphorylated protein containing a polyaspartic acid sequence and a conserved RGD motif, and plays important roles in physiological processes such as inflammatory responses, calcification, organ development, immune cell function and carcinogenesis [20]. In vitro, SPP1 is a potent, partial agonist of cortical and hippocampal M1 receptors with activity conserved across species [21]. The region between −112 and −62 bp of the SPP1 promoter is highly conserved in the rat, mouse and human promoters and contains a number of consensus regions, including an E-box and a GC-rich region [22].…”

Drug Design Targeting the Muscarinic Receptors and the Implications in Central Nervous System Disorders

“…The essential feature appears to be the delicate balance between brain penetration and partial-agonist-like efficacy profile to minimize peripheral AEs and M 1 mediated adverse effects. While not yet applied in clinical trials, the most recent advancement has come from Eli Lilly in late 2018 in the form of SPP1 ( Figure 1 ), a selective M 1 partial agonist based on a spiro-piperidine core (similar to AZD-6088), which showed >100-fold functional selectivity versus M 2 /M 3 (a clear improvement over HTL-9936) [ 71 , 72 ]. Significantly, these successful efforts demonstrate that high sequence homology need not preclude the development of orthosteric compounds and indicate that the field remains open for continued exploration.…”

Multitargeting nature of muscarinic orthosteric agonists and antagonists

“…In general, mAChR agonists (and partial agonists, see Table 1 ) are not subtype-selective. Concretely, pilocarpine, bethanechol, oxotremorine, arecoline, oxotremorine-M, xanomeline, cevimeline, methacholine, iperoxo, methylfurmetide, pentylthio-TZTP, sabcomeline, arecaidine propargyl ester, milameline, furtrethonium (furmethid), aceclidine and relatively newly synthesized compounds, such as SPP1, NNC 11-1585, NNC 11-1607, and NNC 11-1314, are nonselective with respect to a single mAChR subtype ( Alexander S. P. et al, 2017 ; Broad et al, 2019 ), although they can express higher selectivity for some subtypes, as is the case for NNC 11-1585, which is more selective for M 1 and M 2 mAChRs than for other mAChR subtypes. Some of them, although declared as subtype-selective, do not reveal specific subtype selectivity.…”