A Novel in vivo Anti-amnesic Agent, Specially Designed to Express Both Acetylcholinesterase (AChE) Inhibitory, Serotonergic Subtype 4 Receptor (5-HT4R) Agonist and Serotonergic Subtype 6 Receptor (5-HT6R) Inverse Agonist Activities, With a Potential Interest Against Alzheimer's Disease

Abstract

This work describes the conception, synthesis, in vitro and in vivo biological evaluation of novel Multi-Target Directed Ligands (MTDL) able to both activate 5-HT₄ receptors, block 5-HT₆ receptors and inhibit acetylcholinesterase activity (AChE), in order to exert a synergistic anti-amnesic effect, potentially useful in the treatment of Alzheimer's disease (AD). Indeed, both activation of 5-HT₄ and blockage of 5-HT₆ receptors led to an enhanced acetylcholine release, suggesting it could lead to efficiently restoring the cholinergic neurotransmission deficit observed in AD. Furthermore, 5-HT₄ receptor agonists are able to promote the non-amyloidogenic cleavage of the amyloid precursor protein (APP) and to favor the production of the neurotrophic protein sAPPα. Finally, we identified a pleiotropic compound, [1-(4-amino-5-chloro-2-methoxyphenyl)-3-(1-(3-methylbenzyl)piperidin-4-yl)propan-1-one fumaric acid salt (10)], which displayed in vivo an anti-amnesic effect in a model of scopolamine-induced deficit of working memory at a dose of 0.3 mg/kg.

Keywords: 5-HT4 receptors; 5-HT6 receptors; Alzheimer’s disease; MTDL; acetylcholinesterase.

Graphical Abstract

Design of a MTDL able in vitro to both inactivate 5-HT6R and AChE and to activate 5-HT4R and finally displaying in vivo antiamnesiant effect.

Figure 1

Structure of donecopride, idalopirdine and landipirdine.

Figure 2

Structure of compounds 4 and 5a.

Scheme 1

Synthetic pathways for access to compounds 5a–t, 10. Conditions and reagents: (a) CDI, THF; (b) KO₂CCH₂CO₂Et, MgCl₂, THF; (c) N-Boc 4-iodomethylpiperidine, K₂CO₃, DMF; (d) KOH, EtOH/H₂O; (e) TFA, 1,4-dioxan or DCM; (f) R-benzyl bromide, K₂CO₃, 1,4-dioxane or DMF; (g) fumaric acid, iPrOH.

Figure 3

3D representation of (h)5-HT₆R and (h)5-HT₄R affinity and (h)AChE inhibitory activity for compounds 5a–t.

Figure 4

Pharmacological profile of compounds 2, 9 and 10. Representative experiments illustrating agonist activities of 9 and 10 towards (h)5-HT_4(a)R (A) and antagonist activities of SB271046, 2 and 10 towards (h)5-HT₆R stimulated with 5.10⁻⁷M of 5-HT [B; data are means ± standard error of the mean (SEM); n = 2]. (C) Inverse agonist activities of SB271046, 2 and 10 (10⁻⁴M) towards (h)5-HT₆R in absence of 5-HT (means ± SEM of two independent experiments performed in duplicates).

Figure 5

Effect of compound 10 on spontaneous locomotor activity. Data are expressed as the mean ± standard deviation (n = 8). Drugs were administered intraperitoneally (IP) 30 min before the behavioral test. Compound 10: 1–3–10 mg/kg; AMP: amphetamine 2 mg/kg; CPZ: chlorpromazine 3 mg/kg [*p < 0.05 NaCl, Student-Newman-Keuls (SNK) test].

Figure 6

Effect of compound 10 on scopolamine-induced impairment during the spontaneous alternation test. Data are expressed as the mean ± standard deviation (n = 8). Drugs were administered IP 30 min before the test, and scopolamine was administered SC 20 min before the test. Compound 10: 0.3, 1, 3 mg/kg; DPZ: Donepezil; 1 mg/kg; Scopolamine: 0.5 mg/kg (*p < 0.05 vs. 50%; univariate t-test).