Dihydropyrimidine-Thiones and Clioquinol Synergize To Target β-Amyloid Cellular Pathologies through a Metal-Dependent Mechanism

Abstract

The lack of therapies for neurodegenerative diseases arises from our incomplete understanding of their underlying cellular toxicities and the limited number of predictive model systems. It is critical that we develop approaches to identify novel targets and lead compounds. Here, a phenotypic screen of yeast proteinopathy models identified dihydropyrimidine-thiones (DHPM-thiones) that selectively rescued the toxicity caused by β-amyloid (Aβ), the peptide implicated in Alzheimer’s disease. Rescue of Aβ toxicity by DHPM-thiones occurred through a metal-dependent mechanism of action. The bioactivity was distinct, however, from that of the 8-hydroxyquinoline clioquinol (CQ). These structurally dissimilar compounds strongly synergized at concentrations otherwise not competent to reduce toxicity. Cotreatment ameliorated Aβ toxicity by reducing Aβ levels and restoring functional vesicle trafficking. Notably, these low doses significantly reduced deleterious off-target effects caused by CQ on mitochondria at higher concentrations. Both single and combinatorial treatments also reduced death of neurons expressing Aβ in a nematode, indicating that DHPM-thiones target a conserved protective mechanism. Furthermore, this conserved activity suggests that expression of the Aβ peptide causes similar cellular pathologies from yeast to neurons. Our identification of a new cytoprotective scaffold that requires metal-binding underscores the critical role of metal phenomenology in mediating Aβ toxicity. Additionally, our findings demonstrate the valuable potential of synergistic compounds to enhance on-target activities, while mitigating deleterious off-target effects. The identification and prosecution of synergistic compounds could prove useful for developing AD therapeutics where combination therapies may be required to antagonize diverse pathologies.

Alzheimer’s Disease: Molecular Hallmarks and Yeast Models

“…Despite nearly a billion years of evolutionary divergence, recent estimates showed that a fifth of yeast genes have human disease orthologs lending support to functional discovery investigations using this model [92]. Moreover, thanks to amenability of S. cerevisiae to both classical and advanced molecular genetic techniques, to relatively simple, cheap and quick genetic and environmental manipulations, to the large knowledge base and data collections, high-throughput screening technologies and functional genomics that are not possible in humans [93][94][95], this organism has become a valuable and prevalent eukaryotic model organism to unravel complex and fundamental intracellular mechanisms underlying neurodegeneration [96][97][98][99][100][101][102][103][104].…”

Recent Insights on Alzheimer’s Disease Originating from Yeast Models

“…Finally, a yeast-based screen identified clioquinol and dihydropyrimidine-thiones as compounds being able to ameliorate Aβ toxicity in a synergistic, metal-dependent, way via different mechanisms such as increasing Aβ turnover, restoring vesicle trafficking and oxidative stress protection [ 175 , 176 ] ( Table 1 ). Again, also in transgenic mice models, treatment with clioquinol (analogue) compounds inhibited Aβ accumulation [ 177 ] and resulted in a dramatic improvement in learning and memory, accompanied by marked inhibition of AD-like neuropathology [ 178 ].…”

Tacrines as Therapeutic Agents for Alzheimer's Disease. IV. The Tacripyrines and Related Annulated Tacrines

“…As in the previous attempts, the tacrine scaffold was used as template for ChE inhibition while the 3,4-dihydropyrimidin-2(1H)-thione fragment (Figure 7) was selected on the basis of the well known capacity of 3,4dihydropyrimidin-2(1H)-thiones to act not only as good CCB, [36,37] but also as neuroprotective agents toward Abinduced toxicity, likely by attenuating the metal-mediated toxicity of Ab. [38] Twelve racemic tacripyrimidines, differing from substituents at position 3' and 4' of the aromatic ring, were synthesized by a Friedländer-type reaction [33] from 6-amino-4-phenyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carbonitriles [39] and cyclohexanone (see Figure 7). In vitro and in silico studies showed that the biological activity toward the two selected targets was modulated by the substituent attached to the aromatic ring at position C4.…”

“…The authors designed these new hybrids to achieve compounds with a more balanced activity towards both ChEs and Ca 2+ channels. As in the previous attempts, the tacrine scaffold was used as template for ChE inhibition while the 3,4‐dihydropyrimidin‐2(1 H )‐thione fragment (Figure ) was selected on the basis of the well known capacity of 3,4‐dihydropyrimidin‐2(1 H )‐thiones to act not only as good CCB,, but also as neuroprotective agents toward A β ‐induced toxicity, likely by attenuating the metal‐mediated toxicity of A β …”