Spectroelectrochemical studies of TDMQ20: A potential drug against Alzheimer's disease

Alzheimer's Disease (AD), reported for the first time in 1906, is a common disease that remains incurable to this day. In the past, a family of treatments using Cu(II) chelators failed during clinical trials, evidencing the importance of pre-clinical studies. In this work, we performed electrochemical characterisation of TDMQ20, a new potential drug against AD, using electrochemistry and spectroelectrochemistry. On the basis of voltammetry, we determined that TDMQ20 undergoes a two-step irreversible oxidation process and a one-step irreversible reduction process. Both oxidation and reduction reactions are pH-sensitive. Bidimensional UV-Vis spectroelectrochemistry (UV-Vis-SEC) allowed us to confirm that oxidation of TDMQ20 can occur both on the aliphatic chain and on the aromatic ring. The results expand the knowledge of the TDMQ20 redox activity in the human body which is important from the point of view of the toxicity of the proposed therapy.

The Specific Copper(II) Chelator TDMQ20 Is Efficient for the Treatment of Wilson's Disease in Mice

(1) Background: In patients with Wilson's disease, the deficiency of the copper carrier ATP7B causes the accumulation of copper in the liver, brain and various other organs. Lifelong treatment is therefore mandatory, using copper chelators to increase the excretion of copper and to avoid life-threatening damage. The clinically used reference drug, D-penicillamine, exhibit numerous adverse effects, especially a frequent severe and irreversible neurological worsening, mainly due to its lack of metal selectivity; (2) Methods: A new tetradentate ligand based on an 8-aminoquinoline entity, named TDMQ20, which is highly selective for copper compared with other metal ions, is evaluated in "toxic milk" TX mice as an oral treatment of this Wilson's disease murine model; (3) Results: The concentration of copper in the liver of "toxic milk" TX mice decreased and the fecal excretion of copper increased upon oral treatment with TDMQ20. Both effects are dose-dependent, and more pronounced than those of D-penicillamine; (4) Conclusions: The TDMQ20 copper chelator is more efficient than the reference drug D-penicillamine for the treatment of a Wilson's disease murine model. Pharmacological data obtained with TDMQ20 on the TX mouse model strongly support the selection of this ligand as a drug candidate for this genetic disease.

Distribution in Rat Blood and Brain of TDMQ20, a Copper Chelator Designed as a Drug-Candidate for Alzheimer's Disease

(1) Background: TDMQ20 is a specific regulator of copper homeostasis in the brain, able to inhibit cognitive impairment in the early stages of Alzheimer's disease (AD) in mouse models of AD. To promote the further development of this drug-candidate, preliminary data on the pharmacokinetics of TDMQ20 in a mammal model have been collected. Since TDMQ20 should be administered orally, its absorption by the gastrointestinal tract was evaluated by comparison of blood concentrations after administration by oral and IV routes, and its ability to reach its target (the brain) was confirmed by comparison between blood and brain concentrations after oral administration. (2) Methods: plasmatic and brain concentrations of the drug after oral or intravenous treatment of rats at pharmacologically relevant doses were determined as a function of time. (3) Results: oral absorption of TDMQ20 was rapid and bioavailability was high (66% and 86% for males and females, respectively). The drug accumulated in the brain for several hours (brain-plasma ratio 3 h after oral administration = 2.6), and was then efficiently cleared. (4) Conclusions: these data confirm that TDMQ20 efficiently crosses the brain-blood barrier and is a relevant drug-candidate to treat AD.

TDMQ20, a Specific Copper Chelator, Reduces Memory Impairments in Alzheimer's Disease Mouse Models

Besides targeting amyloid or tau metabolisms, regulation of redox metal ions is a recognized therapeutic target for Alzheimer's disease (AD). Based on the bioinorganic chemistry of copper, we designed specific chelators of copper(II) (TDMQs) insight to regulate copper homeostasis in the brain and to inhibit the deleterious oxidative stress catalyzed by copper-amyloid complexes. An oral treatment by TDMQ20 was able to fully reverse the cognitive and behavioral impairment in three different murine models, two nontransgenic models mimicking the early stage of AD and a transgenic model representing a more advanced stage of AD. To our knowledge, such a comparative study using the same molecule has never been performed. Regular C57BL/6 mice received a single injection of human Cu-Aβ_1-42 in the lateral ventricles (icv-CuAβ) or in the hippocampus (hippo-CuAβ). In both cases, mice developed a cognitive impairment similar to that of transgenic 5XFAD mice. Oral administration of TDMQ20 to icv-CuAβ or hippo-CuAβ mice within a 16-day period resulted in a significant improvement of the cognitive status. The 3-month treatment of transgenic 5XFAD mice with TDMQ20 also resulted in behavioral improvements. The consistent positive pharmacological results obtained using these different AD models correlate well with previously obtained physicochemical data of TDMQ20. The short-term novel object recognition (NOR) test was found particularly relevant to evaluate the rescue of declarative memory impairment. TDMQ20 was also able to reduce the oxidative stress in the mouse cortex. Due to its reliability and facile use, the hippo-CuAβ model can be considered as a robust nontransgenic model to evaluate the activity of potential drugs on the early stages of memory deficits.

Metal Ions in Alzheimer's Disease: A Key Role or Not?

Despite tremendous research efforts in universities and pharmaceutical companies, effective drugs are still lacking for the treatment of Alzheimer's disease (AD). The biochemical mechanisms of this devastating neurodegenerative disease have not yet been clearly understood. Besides a small percentage of cases with early onset disease having a genetic origin (<5%, familial AD), most cases develop in the elderly as a sporadic form due to multiple and complex parameters of aging. Consequently, AD is spreading in all countries with a long life expectancy. AD is characterized by deposition of senile plaques made of β-amyloid proteins (Aβ) and by hyperphosphorylation of tau proteins, which have been considered as the main drug targets up to now. However, antibodies targeting amyloid aggregates, as well as enzyme inhibitors aiming to modify the amyloid precursor protein processing, have failed to improve cognition in clinical trials. Thus, to set up effective drugs, it is urgent to enlarge the panel of drug targets. Evidence of the link between AD and redox metal dysregulation has also been supported by post-mortem analyses of amyloid plaques, which revealed accumulation of copper, iron, and zinc by 5.7, 2.8, and 3.1 times, respectively, the levels observed in normal brains. Copper-amyloid complexes, in the presence of endogenous reductants, are able to catalyze the reduction of dioxygen and to produce reduced, reactive oxygen species (ROS), leading to neuron death. The possibility of using metal chelators to regenerate normal trafficking of metal ions has been considered as a promising strategy in order to reduce the redox stress lethal for neurons. However, most attempts to use metal chelators as therapeutic agents have been limited to existing molecules available from the shelves. Very few chelators have resulted from a rational design aiming to create drugs with a safety profile and able to cross the blood-brain barrier after an oral administration. In the human body, metals are handled by a sophisticated protein network to strictly control their transport and reactivity. Abnormal concentrations of certain metals may lead to pathological events due to misaccumulation and irregular reactivity. Consequently, therapeutic attempts to restore metal homeostasis should carefully take into account the coordination chemistry specificities of the concerned redox-active metal ions. This Account is focused on the role of the main biologically redox-active transition metals, iron and copper. For iron, the recent debate on the possible role of magnetite in AD pathogenesis is presented. The section devoted to copper is focused on the design of specific copper chelators as drug candidates able to regulate copper homeostasis and to reduce the oxidative damage responsible for the neuron death observed in AD brains. A short survey on non-redox-active metal ions is also included at the beginning, such as aluminum and its controversial role in AD and zinc which is a key metal ion in the brain.