The consensus that ketamine can produce rapid-onset antidepressant effects in patients combined with the recent approval of S(+)-ketamine (esketamine, Spravato) as an antidepressant, has fueled the ...search for other compounds that might recapitulate the remarkable therapeutic benefits of ketamine. At the same time, discovery efforts have been additionally directed toward minimization of the tolerability, side-effect, and safety issues associated with ketamine. The history of thought on the viability of metabotropic 2/3 (mGlu2/3) receptor antagonism as a potential mechanism for inducing rapid-acting antidepressant effects is reviewed here. The biological basis for predicting antidepressant efficacy of mGlu2/3 receptor antagonists in depressed patients is also presented. This prediction is based upon convergent biochemical, neurochemical, electrophysiological, and behavioral data that indicate a striking homology in the substrates that underlie the effects of mGlu2/3 receptor antagonists and the known antidepressant ketamine. The data reviewed to date also demonstrate that the preclinical side-effect/tolerability and toxicology profile of mGlu2/3 receptor antagonists are not concerning. Finally, preclinical data on a relatively new mGlu2/3 receptor antagonist, LY3020371, and its orally-bioavailable prodrug, LY3027788, are reviewed. The data on this mechanism provides optimism for successful translation of the mGlu2/3 receptor antagonist hypothesis into therapeutics for those suffering from depression.
•mGlu2/3 receptor antagonists produce antidepressant-associated biological and behavioral effects.•mGlu2/3 receptor antagonists do not produce ketamine-like side-effects.•mGlu2/3 receptor antagonists are predicted to be rapid-acting antidepressants.•LY3020371 is a new mGlu2/3 receptor antagonists with antidepressant potential.
11-O-Debenzoyltashironin (1) is a member of the neurotrophic sesquiterpenes, trace plant metabolites that enhance neurite outgrowth in cultured neurons. We report its synthesis in six steps from a ...butenolide heterodimer via its likely biosynthetic precursor, 3,6-dideoxy-10-hydroxypseudoanisatin, here identified as the chain tautomer of 1. Access to the tashironin chemotype fills a gap in a comparison set of convulsive and neurotrophic sesquiterpenes, which we hypothesized to share a common target. Here we show that both classes mutually hyperexcite rat cortical neurons, consistent with antagonism of inhibitory channels and a mechanism of depolarization-induced neurite outgrowth.
The root extract, curcumin (diferuloylmethane), is a constituent of the ancient herbal medicine Jiawei-Xiaoyaosan that has been used for dyspepsia, stress, and mood disorders. Curcumin engenders a ...diverse profile of biological actions that result in changes in oxidative stress, inflammation, and cell-death pathways. Combined with its historical use in medical practice and its safety profile, curcumin has been studied for its potential therapeutic applications in cancer, aging, endocrine, immunological, gastrointestinal, and cardiac diseases. In addition, data in animal models and in humans have also begun to be collected in stroke, Alzheimer's disease, and Parkinson's disease. A compelling new body of literature is also mounting to support the efficacy of curcumin in stress and mood disorders. Current understanding of the biological basis for antidepressant-relevant biochemical and behavioral changes shows convergence with some mechanisms known for standard antidepressants. In addition, the mechanisms of the antidepressant-like pharmacology of curcumin also appear to overlap with those of other disease states. Thus, ancient wisdom might be built into this interesting and newly-appreciated natural molecule. Although curcumin is a primary ingredient in anti-aging pills, cosmetic creams, eye treatments, diet products, etc, a key hurdle to the development of curcumin for disease treatment and prevention is overcoming its low oral bioavailability. Although multiple approaches to this problem are being examined, a solution to the bioavailability issue will be needed to ensure appropriate tissue exposures of curcumin in clinical investigation. Progress in this regard is underway.
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Patients with epilepsy require improved medications. Purinergic receptors were identified as late as 1976 and are slowly emerging as potential drug targets for the discovery of ...antiseizure medications. While compounds interacting with these receptors have been approved for use as medicines (e.g., gefapixant for cough) and continue to be explored for a number of diseases (e.g., pain, cancer), there have been no purinergic receptor antagonists that have been advanced for epilepsy. There are very few studies on the channel conducting receptors, P2X3 and P2X4, that suggest their possible role in seizure generation or control. However, the limited data available provides some compelling reasons to believe that they could be valuable antiseizure medication drug targets. The data implicating P2X3 and P2X4 receptors in epilepsy includes the role played by ATP in neuronal excitability and seizures, receptor localization, increased receptor expression in epileptic brain, the involvement of these receptors in seizure-associated inflammation, crosstalk between these purinergic receptors and neuronal processes involved in seizures (GABAergic and glutamatergic neurotransmission), and the significant attenuation of seizures and seizure-like activity with P2X receptor blockade. The discovery of new and selective antagonists for P2X3 and P2X4 receptors is ongoing, armed with new structural data to guide rational design. The availability of safe, brain-penetrant compounds will likely encourage the clinical exploration of epilepsy as a disease entity.
Positive allosteric modulators of γ-aminobutyric acid-A (GABAA) receptors or GABAkines have been widely used medicines for over 70 years for anxiety, epilepsy, sleep, and other disorders. Traditional ...GABAkines like diazepam have safety and tolerability concerns that include sedation, motor-impairment, respiratory depression, tolerance and dependence. Multiple GABAkines have entered clinical development but the issue of side-effects has not been fully solved. The compounds that are presently being developed and commercialized include several neuroactive steroids (an allopregnanolone formulation (brexanolone), an allopregnanolone prodrug (LYT-300), Sage-324, zuranolone, and ganaxolone), the α2/3-preferring GABAkine, KRM-II-81, and the α2/3/5-preferring GABAkine PF-06372865 (darigabat). The neuroactive steroids are in clinical development for post-partum depression, intractable epilepsy, tremor, status epilepticus, and genetic epilepsy disorders. Darigabat is in development for epilepsy and anxiety. The imidazodiazepine, KRM-II-81 is efficacious in animal models for the treatment of epilepsy and post-traumatic epilepsy, acute and chronic pain, as well as anxiety and depression. The efficacy of KRM-II-81 in models of pharmacoresistant epilepsy, preventing the development of seizure sensitization, and in brain tissue of intractable epileptic patients bodes well for improved therapeutics. Medicinal chemistry efforts are also ongoing to identify novel and improved GABAkines. The data document gaps in our understanding of the molecular pharmacology of GABAkines that drive differential pharmacological profiles, but emphasize advancements in the ability to successfully utilize GABAA receptor potentiation for therapeutic gain in neurology and psychiatry.
Nociceptin/Orphanin FQ (N/OFQ) is a 17 amino acid peptide that was deorphanized in 1995. The generation of specific agonists, antagonists and receptor deficient mice and rats has enabled progress in ...elucidating the biological functions of N/OFQ. Additionally, radio-imaging technologies have been advanced for investigation of this system in animals and humans. Together with traditional neurobehavioral techniques, these tools have been utilized to identify the biological significance of the N/OFQ system and its interacting partners. The present review focuses on the role of N/OFQ in the regulation of feeding, body weight homeostasis, stress, the stress-related psychiatric disorders of depression and anxiety, and in drug and alcohol dependence. Critical evaluation of the current scientific preclinical literature suggests that small molecule modulators of nociceptin opioid peptide receptors (NOP) might be useful in the treatment of diseases related to these biological functions. In particular, the literature data suggest that antagonism of NOP receptors will produce anti-obesity and antidepressant activities in humans. However, there are also contradictory data discussed. The current literature on the role of N/OFQ in anxiety and addiction, on the other hand points primarily to a role of agonist modulation being potentially therapeutic. Some drug-like molecules that function either as agonists or antagonists of NOP receptors have been optimized for human clinical study to test some of these hypotheses. The discovery of PET ligands for NOP receptors, combined with the pharmacological tools and burgeoning preclinical data set discussed here bodes well for a rapid advancement of clinical understanding and potential therapeutic benefit.
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The ‘neurotrophic sesquiterpenes’ refer to a group of molecules derived from the Illicium genus of flowering plant. They display neurotrophic effects in cultured neuron preparations ...and have been suggested to be cognitive enhancers and potential therapeutics for neurodegenerative disorders and dementias. Recent synthetic advances generated sufficient quantities of jiadifenolide for in vivo investigation into its biological effects. Jiadifenolide did not induce convulsions in mice nor did it enhance or diminish convulsions induced by pentylenetetrazole. Other negative allosteric modulators of GABAA receptors, picrotoxin, tetramethylenedisulfotetramine (TETS), and bilobalide all induced convulsions. Either i.p. or i.c.v. dosing generated micromolar plasma and brain levels of jiadifenolide but only small effects on locomotion of mice. However, jiadifenolide decreased d-amphetamine-induced hyperlocomotion in mice, an antipsychotic-like drug effect. Jiadifenolide did not significantly alter body temperature or behavior in the forced-swim test in mice. Molecular simulation data suggested a potential site in the pore/M2 helix region that is at an overlapping, yet lower position than those observed for other ‘cage convulsant’ compounds such as TETS and picrotoxin. We hypothesize that a position nearer to the entrance of the pore channel may allow for easier displacement of jiadifenolide from its blocking location leading to lower potency and lower side-effect liability. Like jiadifenolide, memantine (Namenda), one of the few drugs used in the symptomatic treatment of dementias, occupies a unique site on the NMDA receptor complex that creates low binding affinity that is associated with its reduced side-effect profile. Given the potential therapeutic applications of jiadifenolide and its relatively inert effects on overt behavior, the possibility of clinical utility for jiadifenolide and related compounds becomes intriguing.
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