Multitarget Biological Profiling of New Naphthoquinone and Anthraquinone-Based Derivatives for the Treatment of Alzheimer’s Disease

Abstract

Two series of naphthoquinone and anthraquinone derivatives decorated with an aromatic/heteroaromatic chain have been synthesized and evaluated as potential promiscuous agents capable of targeting different factors playing a key role in Alzheimer's disease (AD) pathogenesis. On the basis of the <i>in vitro</i> biological profiling, most of them exhibited a significant ability to inhibit amyloid aggregation, PHF6 tau sequence aggregation, acetylcholinesterase (AChE), and monoamine oxidase (MAO) B. In particular, naphthoquinone <b>2</b> resulted as one of the best performing multitarget-directed ligand (MTDL) experiencing a high potency profile in inhibiting β-amyloid (Aβ₄₀) aggregation (IC₅₀ = 3.2 μM), PHF6 tau fragment (91% at 10 μM), AChE enzyme (IC₅₀ = 9.2 μM) jointly with a remarkable inhibitory activity against MAO B (IC₅₀ = 7.7 nM). Molecular modeling studies explained the structure-activity relationship (SAR) around the binding modes of representative compound <b>2</b> in complex with hMAO B and hAChE enzymes, revealing inhibitor/protein key contacts and the likely molecular rationale for enzyme selectivity. Compound <b>2</b> was also demonstrated to be a strong inhibitor of Aβ₄₂ aggregation, with potency comparable to quercetin. Accordingly, atomic force microscopy (AFM) revealed that the most promising naphthoquinones <b>2</b> and <b>5</b> and anthraquinones <b>11</b> and <b>12</b> were able to impair Aβ₄₂ fibrillation, deconstructing the morphologies of its fibrillar aggregates. Moreover, the same compounds exerted a moderate neuroprotective effect against Aβ₄₂ toxicity in primary cultures of cerebellar granule cells. Therefore, our findings demonstrate that these molecules may represent valuable chemotypes toward the development of promising candidates for AD therapy.