AMPA receptor agonists,antagonists and modulators: their potential for clinical utility

Ligands with four pharmacologically distinct actions at the AMPA receptor are discussed. The four classes of compounds include agonists, antagonists, positive allosteric modulators, and negative allosteric modulators of AMPA receptor function. To date, no partial agonists have been discovered. Agonists and positive allosteric modulators may have therapeutic potential in disease states where hypoactivity of glutamatergic tone exists. From our understanding of neuronal circuitry and its involvement in brain function, agonists and positive allosteric modulators are predicted to improve the negative symptomatology in schizophrenia, and to improve memory, behavioural and cognition skills in dementias associated with neurodegenerative disorders or trauma. Issues related to the structural overlap of competitive AMPA receptor antagonists and NMDA glycine site (GlyN) antagonists are addressed; emphasis is directed toward AMPA antagonist activity. Competitive antagonists and negative allosteric modulators (non-competitive antagonists) have consistently demonstrated efficacy as neuroprotective agents in models of stroke, heart attack, and brain injury. Agents from the two classes of antagonist have been selected for clinical development, and some have entered clinical trials. At least one positive allosteric modulator is in clinical trials to determine whether it can improve clinical end-points in patients with Alzheimer’s disease. No agonist has been investigated in clinical trials.     

Apoptosis modulators in the therapy of neurodegenerative diseases

Apoptosis is a prerequisite to model the developing nervous system. However, an increased rate of cell death in the adult nervous system underlies neurodegenerative disease and is a hallmark of multiple sclerosis (MS) Alzheimer’s- (AD), Parkinson- (PD), or Huntington’s disease (HD). Cell surface receptors (e.g., CD95/APO-1/Fas; TNF receptor) and their ligands (CD95-L; TNF) as well as evolutionarily conserved mechanisms involving proteases, mitochondrial factors (e.g., Bcl-2-related proteins, reactive oxygen species, mitochondrial membrane potential, opening of the permeability transition pore) or p53 participate in the modulation and execution of cell death. Effectors comprise oxidative stress, inflammatory processes, calcium toxicity and survival factor deficiency. Therapeutic agents are being developed to interfere with these events, thus conferring the potential to be neuroprotective. In this context, drugs with anti-oxidative properties, e.g., flupirtine, N-acetylcysteine, idebenone, melatonin, but also novel dopamine agonists (ropinirole and pramipexole) have been shown to protect neuronal cells from apoptosis and thus have been suggested for treating neurodegenerative disorders like AD or PD. Other agents like non-steroidal anti-inflammatory drugs (NSAIDs) partly inhibit cyclooxygenase (COX) expression, as well as having a positive influence on the clinical expression of AD. Distinct cytokines, growth factors and related drug candidates, e.g., nerve growth factor (NGF), or members of the transforming growth factor-β (TGF-β ) superfamily, like growth and differentiation factor 5 (GDF-5), are shown to protect tyrosine hydroxylase or dopaminergic neurones from apoptosis. Furthermore, peptidergic cerebrolysin has been found to support the survival of neurones in vitro and in vivo. Treatment with protease inhibitors are suggested as potential targets to prevent DNA fragmentation in dopaminergic neurones of PD patients. Finally, CRIB (cellular replacement by immunoisolatory biocapsule) is an auspicious gene therapeutical approach for human NGF secretion, which has been shown to protect cholinergic neurones from cell death when implanted in the brain. This review summarises and evaluates novel aspects of anti-apoptotic concepts and pharmacological intervention including gene therapeutical approaches currently being proposed or utilised to treat neurodegenerative diseases.     

Positive allosteric modulators of the metabotropic glutamate receptor 2 for the treatment of schizophrenia

Background: Normalization of excessive glutamate neurotransmission through activation of the metabotropic glutamate receptor 2 (mGluR2) represents a novel and promising approach for the treatment of schizophrenia. This strategy has gained support through the evaluation of dual mGluR2/3 agonists that act directly at the glutamate (orthosteric) binding site. Importantly, clinical validation of the mechanism was achieved in a Phase II study in schizophrenia patients with mGluR2/3 agonist LY404039. Selective positive allosteric modulators (potentiators) of mGluR2 that bind to the transmembrane region of the receptor have shown efficacy in rodent models predictive of antipsychotic activity, but have yet to be evaluated in the clinic. Allosteric mGluR2 potentiators may offer advantages over orthosteric mGluR2/3 agonists as a result of their unique mode of action and ability to achieve superior mGluR2 selectivity. Objective/method: This review focuses on the structures and biological activities of small molecule potentiators of mGluR2 that appeared in the patent literature between 2006 and early 2009. Conclusion: Potent mGluR2 potentiators that span a broad range of structural diversity have been disclosed. Narrow patent filings within select series and drug-like properties of corresponding preferred compounds suggest that development candidates have likely been nominated.     

Comparison of single- and repeated-ischemia-induced changes in expression of flip and flop splice variants of AMPA receptor subtypes GluR1 and GluR2 in the rats hippocampus CA1 subregion

In addition to their role in physiological activities, ionotropic glutamate alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors (AMPARs) play an important role in neuronal death, especially that following ischemic insults. In this study, we examined the effect of single (SI) and twice repeated (RI)-4-vessel occlusion-ischemia on rat performance in the 8-armed radial maze test. Moreover, the effects of SI and RI on the AMPARs subunits glutamate receptor (GluR) 1 and GluR2 flip and flop variants composition in the CA1 subregion of the hippocampus were investigated using RT-PCR, normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and expressed as their ratios to the latter. The results showed that SI and RI impaired the maze performance by decreasing correct choices and increasing the error choices, but RI increased error choices to a greater extent than the SI. The SI reduced only GluR1 flip/GAPDH on day 1. The SI did not alter ratios of GluR2 variants to those of GluR1. On the other hand, the RI decreased GluR2 flip and flop variants after 1 and 3 days, respectively, whereas after 7 days, it increased the flip variant of both GluR1 and GluR2. Moreover, the RI reduced ratios of GluR2 variants to those of GluR1. These results reveal the differential effects of the SI and RI on memory and expression of the AMPARs subunits GluR1 and GluR2 and their flip and flop variants in the CA1.     

Challenges for and current status of research into positive modulators of AMPA receptors

AMPA receptors consist of a family of hetero-oligomeric (tetrameric) receptors arising from four genes, each of which encodes a distinct receptor subunit (GluA1-4). Recombinant homo-tetrameric AMPA receptors, comprising four identical subunits, are functionally active and have been used in in vitro assays. However, the many different subunit permutations make possible the functional and anatomical diversity of AMPA receptors throughout the CNS. Furthermore, AMPA receptor subunit stoichiometry influences the biophysical and functional properties of the receptor. A number of chemically diverse positive modulators of AMPA receptor have been identified which potentiate AMPA receptor-mediated activity in vitro as well as improving cognitive performance in rodents and non-human primates with several being taken further in the clinic. This review article summarizes the current status in the research on positive allosteric modulation of AMPA receptors and outlines the challenges involved in identifying a chemically distinct series of AMPA receptor positive modulators, addressing the challenges created by the heterogeneity of the AMPA receptor populations and the development of structure-activity relationships driven by homomeric, recombinant systems on high-throughput platforms. We also review the role of X-ray crystallography in the selection and prioritization of targets for lead optimization for AMPA receptor positive modulators.     

新型AMPA受体正向变构调节剂抗疲劳活性筛选

目的寻找以AMPA(α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid)受体为靶点的新型抗疲劳化合物。方法以胡椒酸、3,4,5-三甲氧基苯甲酸、3,4-二甲氧基苯甲酸,这3个化合物分别作为母体结构,对苯甲酰胺的酰胺氮原子引入基团进行结构修饰,设计合成43个化合物,结构经1H-NMR确认。采用MTT法评价新化合物的细胞毒性,通过戊巴比妥钠镇静催眠实验进行中枢兴奋性筛选,最后采用小鼠负重游泳实验评价目标新化合物抗疲劳活性。结果化合物2j细胞毒性低,具有一定的中枢兴奋性与抗疲劳活性。结论化合物2j具有较好的抗疲劳作用,具有进一步开发潜力。     

Targeting glucose-dependent insulinotropic polypeptide receptor for neurodegenerative disorders

Introduction: Incretin hormones, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide-1 (GLP-1) exert pleiotropic effects on endocrine pancreas and nervous system. Expression of GIP and GIP receptor (GIPR) in neurons, their roles in neurogenesis, synaptic plasticity, neurotransmission, and neuromodulation uniquely position GIPR for therapeutic applications in neurodegenerative disorders. GIP analogs acting as GIPR agonists attenuate neurobehavioral and neuropathological sequelae of neurodegenerative disorders in preclinical models, e.g. Alzheimer’s disease (AD), Parkinson’s disease (PD), and cerebrovascular disorders. Modulation of GIPR signaling offers an unprecedented approach for disease modification by arresting neuronal viability decline, enabling neuronal regeneration, and reducing neuroinflammation. Growth-promoting effects of GIP signaling and broad-based neuroprotection highlight the therapeutic potential of GIPR agonists.

Areas covered: This review focuses on the role of GIPR-mediated signaling in the central nervous system in neurophysiological and neuropathological conditions. In context of neurodegeneration, the article summarizes potential of targeting GIPR signaling for neurodegenerative conditions such as AD, PD, traumatic brain injury, and cerebrovascular disorders.

Expert opinion: GIPR represents a validated therapeutic target for neurodegenerative disorders. GIPR agonists impart symptomatic improvements, slowed neurodegeneration, and enhanced neuronal regenerative capacity in preclinical models. Modulation of GIPR signaling is potentially a viable therapeutic approach for disease modification in neurodegenerative disorders.     

Psychiatric Drug Discovery and Development

This new conference on Psychiatric Drug Research was organised by the Strategic Research Institute and was chaired by P McGonigle (Wyeth Research, USA) and D Schoepp (Eli Lilly, USA). The 2-day meeting featured presentations from an international assembly of industrial and academic experts who have significantly contributed to the current body of knowledge in the field of psychotherapeutics. D Weinberger (NIMH, USA) gave an elegant keynote lecture on the application of genomics in psychopharmacology. Other presentations covered the latest technological advances, animal models and mechanistic approaches utilised in drug discovery for neuropsychiatric disorders and reviewed the current status of numerous novel targets resulting from these strategies.     

Targeting GSK3 signaling as a potential therapy of neurodegenerative diseases and aging

ABSTRACT

Introduction: Glycogen synthase kinase 3 (GSK3) is at the center of cellular signaling and controls various aspects of brain functions, including development of the nervous system, neuronal plasticity and onset of neurodegenerative disorders.

Areas covered: In this review, recent efforts in elucidating the roles of GSK3 in neuronal plasticity and development of brain pathologies; Alzheimer’s and Parkinson’s disease, schizophrenia, and age-related neurodegeneration are described. The effect of microglia and astrocytes on development of the pathological states is also discussed.

Expert opinion: GSK3β and its signaling pathway partners hold great promise as therapeutic target(s) for a multitude of neurological disorders. Activity of the kinase is often elevated in brain disorders. However, due to the wide range of GSK3 cellular targets, global inhibition of the kinase leads to severe side-effects and GSK3 inhibitors rarely reach Phase-2 clinical trials. Thus, a selective modulation of a specific cellular pool of GSK3 or specific down- or upstream partners of the kinase might provide more efficient anti-neurodegenerative therapies.     

Nicotinic acetylcholine receptor ligands as potential therapeutics

The nicotinic acetylcholine receptors (nAChRs) belong to a superfamily of ligand-gated ion channels. Neuronal nAChRs are involved in a variety of complex cognitive processes (learning and memory) and therefore in CNS disorders. These include, for example, Alzheimer’s and Parkinson’s disease, attention deficit hyperactivity disorder, Tourette’s syndrome, schizophrenia, depression, pain and tobacco dependence. Thus, nAChRs present a rational target for the treatment of these pathological processes. Over the past years an increasing number of ligands, especially for the α₄β₂ subtype has been synthesised. Recent developments reveal increased interest in α₇ ligands for the treatment of CNS diseases as well as for pain and inflammation. Unfortunately, only a few companies provide biological data in detail, especially regarding subtype selectivity and functionality. This review provides an overview of the recent patent literature focusing mainly on small molecule ligands.     

5-Arylbenzothiadiazine Type Compounds as Positive Allosteric Modulators of AMPA/Kainate Receptors

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Cardiovascular & Renal: Novel ET receptor antagonists

The socio-economic costs of caring for patients with Alzheimer’s disease (AD), both in institutions and in the community, are immense. Since increasing age is a significant risk factor for the development of AD, these costs are set to rise commensurate with demographic changes in the age structure of the population. The need for effective treatments to combat the decline in cognitive functions in AD is therefore obvious. The realisation over the past decade of the importance of the amyloid precursor protein (APP) and its metabolites, the amyloid β-peptides (Aβ), in the pathogenesis of AD has suggested that these may be likely therapeutic targets, at several points along their synthetic and metabolic pathways. This review will cover patenting activity concerning APP and Aβ for the period 1995 - 1996. Special emphasis is placed on the patent applications aimed at preventing Aβ aggregation since this seems to be a key event in potentiating Aβ neurotoxicity.     

Recent advances towards the discovery of dopamine receptor ligands

Dopamine is a key regulator in the CNS, contributing importantly to functions of arousal and attention, initiation of movement, perception, motivation and emotion. Its imbalance has been implicated in the pathophysiology, and more clearly in the pharmacology, of a number of neurobehavioural disorders, including Parkinson’s disease, schizophrenia, mania and depression, alcohol and drug abuse, as well as attention and eating disorders. Five major dopamine receptor subtypes (D1 – D5) have been identified, with distinct differences in their genes and peptide composition, molecular functions and neuropharmacology. These receptors represent the rational targets for the treatment of a large number of neurological and psychiatric disorders. In recent years, substantial efforts have addressed the most recently described dopamine receptor types, particularly types D3, D4 and D5, although most research involves the longer-known D1 and D2 dopamine receptors. Current pharmacological efforts in medicinal chemistry and neuropharmacology include the development of D1 full agonists and D2 partial agonists, as well as agents with dopaminergic activity combined with effects at CNS serotonergic, muscarinic, adrenergic and histaminic receptors. This review provides an overview of the recent patent literature during 2003 – 2005 on the development of therapeutic agents, mainly targeting the five dopamine receptors.     

New trends in the development of AMPA receptor antagonists

The interest in AMPA glutamate receptors has grown enormously in recent years, due to their crucial role in physiological and pathological processes. This led to the development of AMPA ligands as research tools and potential therapeutic agents. In particular, extensive work was addressed towards the development of selective antagonists, which proved to be particularly useful in the prevention and treatment of a variety of neurological and non-neurological diseases. This review focuses on the primary and patent literature from 2000 onwards.     

Review of the acetylcholinesterase inhibitor galanthamine

Galanthamine (or galantamine, Reminyl^®) is a tertiary alkaloid acetylcholinesterase inhibitor (AChEI) which has been approved in several countries for the symptomatic treatment of senile dementia of the Alzheimer’s type. Derived from bulbs of the common snowdrop and several Amaryllidaceae plants, (-)-galanthamine (GAL) has long been used in anaesthetics to reverse neuromuscular paralysis induced by turbocurarine-like muscle relaxants and more recently, has been shown to attenuate drug- and lesion-induced cognitive deficits in animal models of learning and memory. GAL directly inhibits acetylcholinesterase activity, while demonstrating much weaker activity on butyrylcholinesterase (BuChE). GAL also stimulates pre- and postsynaptic nicotinic receptors, although the clinical significance of this finding is yet unclear. Numerous variants and analogues of GAL have also been developed, with varying potency in inhibiting AChE activity. GAL is readily absorbed after oral administration, with a t_maxof 52 min and a plasma elimination t_½ of 5.7 h. The efficacy of GAL administered to Alzheimer’s disease (AD) patients has been well demonstrated by large-scale clinical trials. Typical of AChEIs, the most common adverse events associated with GAL are nausea and vomiting. In conclusion, evidence to date suggests galanthamine to be similar to other AChEIs in improving cognitive function in AD patients.     

P-糖蛋白在神经退行性疾病中的作用

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Recent trends in the transdermal delivery of therapeutic agents used for the management of neurodegenerative diseases

With the increasing proportion of the global geriatric population, it becomes obvious that neurodegenerative diseases will become more widespread. From an epidemiological standpoint, it is necessary to develop new therapeutic agents for the management of Alzheimer’s disease, Parkinson’s disease, multiple sclerosis and other neurodegenerative disorders. An important approach in this regard involves the use of the transdermal route. With transdermal drug delivery systems (TDDS), it is possible to modulate the pharmacokinetic profiles of these medications and improve patient compliance. Transdermal drug delivery has also been shown to be useful for drugs with short half-life and low or unpredictable bioavailability. In this review, several transdermal drug delivery enhancement technologies are being discussed in relation to the delivery of medications used for the management of neurodegenerative disorders.     

茚酮氨基甲酸酯衍生物的设计合成及其对乙酰胆碱酯酶抑制活性的研究

目的设计合成茚酮氨基甲酸酯衍生物并进行乙酰胆碱酯酶(AChE)抑制活性测试。方法以羟基苯丙酸为起始原料,经分子内Friedel-Crafts酰化、羟基的氨基甲酸酯化和羟醛缩合3步反应合成目标物;采用Ellman法,以拉多替吉(ladostigil)为阳性对照,测试目标化合物对AChE的抑制活性。结果合成了8个未见文献报道的新化合物,其结构和纯度均经1H-NMR、MS谱测定。结论目标化合物对AChE均表现出一定的抑制活性,可作为先导化合物做进一步的改造和修饰。