C-Glycosylflavones Against Alzheimer's Disease: From Discovery to Mechanism of Action.

Abstract

Alzheimer’s disease (AD) is the most common neurodegenerative disease worldwide and is the sixth leading cause of death in the U.S. Current AD medications only temporarily relieve symptoms, and none can prevent, cure, or even slow AD. There is an urgent demand for effective drugs for AD prevention and treatment. C-Glycosylflavones, a class of phytochemicals, display diverse benefits to human health and recently noted for their neuroprotective effects. They are a novel and valuable source of anti-AD agents. Identification and validation of therapeutic targets of C-glycosylflavones for neuroprotection against AD are crucial to convey the mechanistic understanding of these agents in pharmaceutical applications. The principal objectives of the dissertation research aim to unravel the mechanistic basis of natural and synthetic C-glycosylflavones for potential AD therapies. Different research strategies such as target/phenotype-based screening and chemical proteomics approaches were adopted and integrated into an innovative drug discovery paradigm for target identification and validation of C-glycosylflavones. Our efforts to search for natural anti-AD agents led to the discovery that a C-glycosylflavone called isoorientin from corn silks is neuroprotective. Isoorientin selectively inhibits glycogen synthase kinase-3β (GSK-3β), an enzyme most relevant to AD tauopathy. Molecular docking and enzyme kinetics indicated that isoorientin selectively inhibits GSK-3β via a substrate competition rather than the common ATP competition. Cellular studies demonstrated that isoorientin effectively attenuates tau hyperphosphorylation and amyloid neurotoxicity in human SH-SY5Y cells. By applying computer-aided drug design approach, novel analogues of C-glycosylflavones as GSK-3β inhibitors were synthesized. The new analogues show significant improvements of potency and passive membrane permeability compared to isoorientin. In addition, they have distinct kinase selectivity to GSK-3β and effectively block GSK-3β–mediated tau and amyloid neurotoxicities. Finally, by harnessing the chemical proteomics and bioinformatics technologies, we revealed that C-glycosylflavones are novel multitarget ligands for potential AD prevention. Collectively, the present dissertation elaborates a hypothesis-driven research on AD drug discovery. The new findings and knowledge gained through this study will broaden the understanding of mechanism of actions of C-glycosylflavones for potential AD therapies.