Differential Effects of Structural Modifications on the Competition of Chalcones for the PIB Amyloid Imaging Ligand-Binding Site in Alzheimer's Disease Brain and Synthetic Aβ Fibrils

Pre-clinical evaluation of 99mTc-labeled chalcone derivative for amyloid-β imaging post-head trauma

Aβ42 plaque formation is one of the preliminary pathologic events that occur post traumatic brain injury (TBI) which is also among the most noteworthy hallmarks of AD. Their pre symptomatic detection is therefore vital for better disease management. Chalcone-picolinic acid chelator derivative, 6-({[(6-carboxypyridin-2-yl)methyl](2-{4-[(2E)-3-[4-(dimethyl amino)phenyl]prop-2-enoyl]phenoxy}ethyl)amino}methyl)pyridine-2-carboxylic acid, Py-chal was synthesized to selectively identify amyloid plaques formed post head trauma using SPECT imaging by stable complexation to 99mTc with > 97% efficiency without compromising amyloid specificity. The binding potential of the Py-chal ligand to amyloid plaques remained high as confirmed by in vitro binding assay and photophysical spectra. Further, the Py-chal complex stained amyloid aggregates in the brain sections of rmTBI mice model. In vivo scintigraphy in TBI mice model displayed high uptake followed by high retention while the healthy rabbits displayed higher brain uptake followed by a rapid washout attributed to absence of amyloid plaques. Higher uptake in brain of TBI model was also confirmed by ex vivo biodistribution analysis wherein brain uptake of 3.38 ± 0.2% ID/g at 2 min p.i. was observed for TBI mice model. This was followed by prolonged retention and more than twofold higher activity as compared to sham mice brain. This preliminary data suggests the specificity of the radiotracer for amyloid detection post head trauma and applicability of 99mTc labeled Py-chal complex for TBI-induced β-amyloid SPECT imaging.

Combining Chalcones with Donepezil to Inhibit Both Cholinesterases and Aβ Fibril Assembly

The fact that the number of people with Alzheimer's disease is increasing, combined with the limited availability of drugs for its treatment, emphasize the need for the development of novel effective therapeutics for treating this brain disorder. Herein, we focus on generating 12 chalcone-donepezil hybrids, with the goal of simultaneously targeting amyloid-β (Aβ) peptides as well as cholinesterases (i.e., acetylcholinesterase (AChE) and butyrylcholinesterase (BChE)). We present the design, synthesis, and biochemical evaluation of these two series of novel 1,3-chalcone-donepezil (15a-15f) or 1,4-chalcone-donepezil (16a-16f) hybrids. We evaluate the relationship between their structures and their ability to inhibit AChE/BChE activity as well as their ability to bind Aβ peptides. We show that several of these novel chalcone-donepezil hybrids can successfully inhibit AChE/BChE as well as the assembly of N-biotinylated Aβ(1-42) oligomers. We also demonstrate that the Aβ binding site of these hybrids differs from that of Pittsburgh Compound B (PIB).

Multifunctional Donepezil Analogues as Cholinesterase and BACE1 Inhibitors

A series of 22 donepezil analogues were synthesized through alkylation/benzylation and compared to donepezil and its 6-O-desmethyl adduct. All the compounds were found to be potent inhibitors of both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), two enzymes responsible for the hydrolysis of the neurotransmitter acetylcholine in Alzheimer’s disease patient brains. Many of them displayed lower inhibitory concentrations of EeAChE (IC₅₀ = 0.016 ± 0.001 µM to 0.23 ± 0.03 µM) and EfBChE (IC₅₀ = 0.11 ± 0.01 µM to 1.3 ± 0.2 µM) than donepezil. One of the better compounds was tested against HsAChE and was found to be even more active than donepezil and inhibited HsAChE better than EeAChE. The analogues with the aromatic substituents were generally more potent than the ones with aliphatic substituents. Five of the analogues also inhibited the action of β-secretase (BACE1) enzyme.

A direct crossed polymerization of triphenylamines and cyclohexanones via CC bond formation: the method and its bioimaging application

Fluorescent polymers synthesized by ACC reactions with interesting optical performances and the potential cell imaging applications.