M1 Muscarinic Agonists Target Major Hallmarks of Alzheimers Disease – an Update

Abraham      Fisher

Abstract

The M1 muscarinic receptor (M1 mAChR), preserved in Alzheimers disease (AD), is a pivotal target that links major hallmarks of AD, e.g. cholinergic deficiency, cognitive dysfunctions, β-amyloid (Aβ) and tau pathologies. Some muscarinic agonists, while effective in AD, had limited clinical value due to adverse effects and lack of M1 selectivity. The M1 selective muscarinic agonists AF102B [Cevimeline], AF150(S) and AF267B – i) elevated αAPPs, decreased Aβ levels and tau hyperphosphorylation, and blocked Aβ-induced neurotoxicity, in vitro, via M1 mAChR-modulation of kinases (e.g. PKC, MAPK and GSK3β); ii) restored cognitive deficits, cholinergic markers, and decreased tau hyperphosphorylation in relevant models with a wide safety margin. AF267B decreased brain Aβ levels in hypercholesterolemic rabbits and decreased CSF Aβ42 in rabbits and removed vascular Aβ42 deposition from cortex in cholinotoxin-treated rabbits. In 3x transgenic-AD mice that recapitulate the major pathologies and cognitive deficits of AD, chronic AF267B treatment rescued cognitive deficits and decreased Aβ42 and tau pathologies in the cortex and hippocampus (not amygdala), via M1 mAChR-activation of ADAM17/TACE and decreased BACE1 steady state levels and inhibition of GSK3β, extending findings from above. Conclusions: A comprehensive therapy should target all AD hallmarks, regardless of the culprit(s) responsible for the disease. In this context, AF267B is the 1st reported low MW CNS-penetrable mono-therapy that meets this challenge. Clinical trials will determine if AF267B may become an important therapy in AD.

Keywords: Alzheimers disease, mAChR, PKC levels, BACE1 inhibitors, M1 agonists

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