review · Pharmaceuticals
Neurodegenerative conditions such as Alzheimer's and Parkinson's disease cause severe cognitive and motor impairments, driven significantly by glutamate-mediated excitotoxicity. While blocking N-methyl-D-aspartate (NMDA) receptors offers therapeutic potential, developing effective drugs has proved difficult. Standard blockers often trigger severe adverse effects or fail to cross the blood-brain barrier, largely because these receptors also manage vital physiological processes. To overcome this, research has shifted toward allosteric modulators that selectively target specific receptor subunits, particularly GluN2B, which features prominently in pathways leading to neuronal cell death. Existing candidates, including ifenprodil and radiprodil, suffer from poor bioavailability and incomplete selectivity in clinical trials. Emerging phenanthroic and naphthoic acid derivatives, alongside multifunctional molecules containing polycyclic moieties, show promise for improved selectivity and pharmacodynamics, pointing the way toward more viable therapeutic designs.
Neurodegenerative diseases place a massive social and economic burden on families and healthcare systems worldwide, yet disease-modifying therapies remain scarce. Understanding how to selectively block harmful excitotoxic pathways without disrupting normal brain function is essential for creating safer, more effective treatments that can halt or slow the progression of debilitating conditions like Alzheimer's and Parkinson's disease.
This work informs early-stage pharmaceutical discovery for neurodegenerative therapies, relevant primarily to biotechnology firms and medicinal chemists. The insights highlight phenanthroic and naphthoic acid derivatives as promising chemical starting points for GluN2B-selective or multitarget drug programmes. However, because clinical data remain sparse and previous candidates encountered serious pharmacokinetic barriers, these therapeutic candidates remain at an early, preclinical research stage and are distant from commercial application.
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Neurodegenerative disorders (NDs) include a range of chronic conditions characterized by progressive neuronal loss, leading to cognitive, motor, and behavioral impairments. Common examples include Alzheimer's disease (AD) and Parkinson's disease (PD). The global prevalence of NDs is on the rise, imposing significant economic and social burdens. Despite extensive research, the mechanisms underlying NDs remain incompletely understood, hampering the development of effective treatments. Excitotoxicity, particularly glutamate-mediated excitotoxicity, is a key pathological process implicated in NDs. Targeting the N-methyl-D-aspartate (NMDA) receptor, which plays a central role in excitotoxicity, holds therapeutic promise. However, challenges, such as blood-brain barrier penetration and adverse effects, such as extrapyramidal effects, have hindered the success of many NMDA receptor antagonists in clinical trials. This review explores the molecular mechanisms of NMDA receptor antagonists, emphasizing their structure, function, types, challenges, and future prospects in treating NDs. Despite extensive research on competitive and noncompetitive NMDA receptor antagonists, the quest for effective treatments still faces significant hurdles. This is partly because the same NMDA receptor that necessitates blockage under pathological conditions is also responsible for the normal physiological function of NMDA receptors. Allosteric modulation of NMDA receptors presents a potential alternative, with the GluN2B subunit emerging as a particularly attractive target due to its enrichment in presynaptic and extrasynaptic NMDA receptors, which are major contributors to excitotoxic-induced neuronal cell death. Despite their low side-effect profiles, selective GluN2B antagonists like ifenprodil and radiprodil have encountered obstacles such as poor bioavailability in clinical trials. Moreover, the selectivity of these antagonists is often relative, as they have been shown to bind to other GluN2 subunits, albeit minimally. Recent advancements in developing phenanthroic and naphthoic acid derivatives offer promise for enhanced GluN2B, GluN2A or GluN2C/GluN2D selectivity and improved pharmacodynamic properties. Additional challenges in NMDA receptor antagonist development include conflicting preclinical and clinical results, as well as the complexity of neurodegenerative disorders and poorly defined NMDA receptor subtypes. Although multifunctional agents targeting multiple degenerative processes are also being explored, clinical data are limited. Designing and developing selective GluN2B antagonists/modulators with polycyclic moieties and multitarget properties would be significant in addressing neurodegenerative disorders. However, advancements in understanding NMDA receptor structure and function, coupled with collaborative efforts in drug design, are imperative for realizing the therapeutic potential of these NMDA receptor antagonists/modulators.
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DOI: 10.3390/ph17050639
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