Alzheimer's disease (AD) is a systemic neurodegenerative disorder, the incidence of which increases with the age growth [1]. Nowadays, AD has become a severe threat to the elderly health and global medical resource. The course of AD is slow, insidious, and irreversible. As the disease progresses, patients might experience cognitive impairment, memory decline, emotional disorders, personality changes, even culminating in death [2]. However, AD pathological courses are complex and varied, involving multiple systems and links. Generally, several hypotheses have been put forward: β-amyloid (Aβ) deposits, tau hyperphosphorylation, synaptic dysfunction, oxidative stress, neuroinflammation, central cholinergic system dysfunction, etc. [[3], [4], [5], [6]]. Drug development based on the cholinergic neuron hypothesis is a significant direction of AD therapy, and most commercially available drugs (Donepezil, Galantamine, Rivastigmine, etc.) fall into this category.

This hypothesis regarded that acetylcholine (ACh) dysfunction is closely related to typical AD pathological features: cognitive dysfunction, learning ability decline and memory loss [7]. Meanwhile, ACh could be hydrolyzed by cholinesterases (ChEs), mainly composed of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Most current drugs, including Rivastigmine and Donepezil, could improve the learning and memory ability of AD patients through inhibiting ChEs activity and increasing ACh level. As reported, AChE and BChE share 65% homological amino acid sequences and both contain a catalytic anionic subsite (CAS), a peripheral anionic site (PAS), an acyl-binding pocket, a choline-binding pocket and an oxyanion hole [8]. Even though, some subtle residue differences in the acyl pocket are pivotal for designing selective potent BChE inhibitors (Supplementary Fig. 1; Supplementary Table 1) [[9], [10], [11]]. Under normal physiological conditions, AChE is responsible for ACh degradation, while BChE is usually considered as the redundant “pseudocholinesterase”. However, in the late-stage of AD, AChE decreases heavily and almost loses its hydrolytic function. On the contrary, the level of BChE enhances slightly, and replaces AChE to function as the major hydrolase of ACh [12]. Besides, several AChE inhibitors, like Donepezil, have been clinically reported to cause gastrointestinal side effects and affect adherence to continuous therapy [13]. Since BChE is not a physiologically essential enzyme, specific inhibition exerts no obvious side effects on the peripheral system, which is more advantaged than selective AChE inhibitors from the safety perspective [14]. Additionally, the positive relationship between BChE deposition and Aβ aggregation in senile plaques has been also proved through histochemical localization [15,16]. Therefore, BChE inhibition is a promising and safe method to increase the level of ACh and improve cognition in progressed AD.

Herein, we conducted a virtual screening based on pharmacophore model and obtained a novel BChE inhibitor S21–1001 (eqBChE IC50 = 3.06 ± 1.79 μM, hBChE IC50 = 1.68 ± 1.15 μM). Guided by structural modification and structure-activity relationship (SAR), we identified S21–1011 (eqBChE IC50 = 0.059 ± 0.006 μM, hBChE IC50 = 0.162 ± 0.069 μM) as the optimized molecule. This potent BChE inhibitor showed excellent pharmacokinetic (PK) properties, especially the high oral-bioavailability and the capability of crossing blood-brain barrier (BBB). In pharmacological investigation, S21–1011 was observed to keep the viability of nerve cells from oxidative stress and toxic damages. It also efficiently alleviated cognitive disorder and inflammatory reactions in various AD pathology-like mice models (Fig. 1). These studies uncovered a novel potent BChE inhibitor S21–1011, as a multi-functional agent, could improve cognitive symptoms and protect the neural microenvironment, providing a promising candidate for AD therapy.