Development Of Positive Allosteric Modulators Research Articles

Differential Activity of Orthosteric Agonists and Allosteric Modulators at Metabotropic Glutamate Receptor 7.

Metabotropic glutamate receptor 7 (mGlu7) is a G protein coupled receptor that has demonstrated promise as a therapeutic target across a number of neurologic and psychiatric diseases. Compounds that modulate the activity of mGlu7, such as positive and negative allosteric modulators, may represent new therapeutic strategies to modulate receptor activity. The endogenous neurotransmitter associated with the mGlu receptor family, glutamate, exhibits low efficacy and potency in activating mGlu7, and surrogate agonists, such as the compound L-(+)-2-Amino-4-phosphonobutyric acid (L-AP4), are often used for receptor activation and compound profiling. To understand the implications of the use of such agonists in the development of positive allosteric modulators (PAMs), we performed a systematic evaluation of receptor activation using a system in which mutations can be made in either protomer of the mGlu7 dimer; we employed mutations that prevent interaction with the orthosteric site as well as the G-protein coupling site of the receptor. We then measured increases in calcium levels downstream of a promiscuous G protein to assess the effects of mutations in one of the two protomers in the presence of two different agonists and three positive allosteric modulators. Our results reveal that distinct PAMs, for example N-[3-Chloro-4-[(5-chloro-2-pyridinyl)oxy]phenyl]-2-pyridinecarboxamide (VU0422288) and 3-(2,3-Difluoro-4-methoxyphenyl)-2,5-dimethyl-7-(trifluoromethyl)pyrazolo[1,5-a]pyrimidine (VU6005649), do exhibit different maximal levels of potentiation with L-AP4 versus glutamate, but there appear to be common stable receptor conformations that are shared among all of the compounds examined here. SIGNIFICANCE STATEMENT: This manuscript describes the systematic evaluation of the mGlu7 agonists glutamate and L-(+)-2-Amino-4-phosphonobutyric acid (L-AP4) in the presence and absence of three distinct potentiators examining possible mechanistic differences. These findings demonstrate that mGlu7 potentiators display subtle variances in response to glutamate versus L-AP4.

New insights in the development of positive allosteric modulators of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors belonging to 3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides: Introduction of (mono/difluoro)methyl groups at the 2-position of the thiadiazine ring

Positive allosteric modulators of the AMPA receptors (AMPAR PAMs) have been proposed as new drugs for the management of various neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, attention deficit hyperactivity disorder, depression, and schizophrenia.The present study explored new AMPAR PAMs belonging to 3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides (BTDs) characterized by the presence of a short alkyl substituent at the 2-position of the heterocycle and by the presence or absence of a methyl group at the 3-position. The introduction of a monofluoromethyl or a difluoromethyl side chain at the 2-position instead of the methyl group was examined.7-Chloro-4-cyclopropyl-2-fluoromethyl-3,4-dihydro-4H-1,2,4-benzothiadiazine 1,1-dioxide (15e) emerged as the most promising compound associating high in vitro potency on AMPA receptors, a favorable safety profile in vivo and a marked efficacy as a cognitive enhancer after oral administration in mice.Stability studies in aqueous medium suggested that 15e could be considered, at least in part, as a precursor of the corresponding 2-hydroxymethyl-substituted analogue and the known AMPAR modulator 7-chloro-4-cyclopropyl-3,4-dihydro-4H-1,2,4-benzothiadiazine 1,1-dioxide (3) devoid of an alkyl group at the 2-position.

Opportunities and challenges for the development of M1 muscarinic receptor positive allosteric modulators in the treatment for neurocognitive deficits.

Targeting allosteric sites of M1 muscarinic acetylcholine receptors (M1 receptors) is a promising strategy to treat neurocognitive disorders, such as Alzheimer's disease and schizophrenia. Indeed, the last two decades have seen an impressive body of work focussing on the design and development of positive allosteric modulators (PAMs) for the M1 receptor. This has led to the identification of a structurally diverse range of highly selective M1 PAMs. In preclinical models, M1 PAMs have shown rescue of cognitive deficits and improvement of endpoints predictive of symptom domains of schizophrenia. Yet, to date only a few M1 PAMs have reached early-stage clinical trials, with many of them failing to progress further due to on-target mediated cholinergic adverse effects that have plagued the development of this class of ligand. This review covers the recent preclinical and clinical studies in the field of M1 receptor drug discovery for the treatment of Alzheimer's disease and schizophrenia, with a specific focus on M1 PAM, highlighting both the undoubted potential but also key challenges for the successful translation of M1 PAMs from bench-side to bedside.

Sonochemical synthesis and biological evaluation of isoquinolin-1(2H)-one/isoindolin-1-one derivatives: Discovery of a positive ago-allosteric modulator (PAAM) of 5HT2CR

Efforts have been devoted for the discovery and development of positive allosteric modulators (PAMs) of 5-HT2CR because of their potential advantages over the orthosteric agonist like Lorcaserin that was withdrawn from the market. On the other hand, pursuing a positive ago-allosteric modulator (PAAM) is considered as beneficial particularly when an agonist is not capable of affecting the potency of the endogenous agonist sufficiently. In search of a suitable PAAM of 5-HT2CR we adopted an in silico based approach that indicated the potential of the 3-(1-hydroxycycloalkyl) substituted isoquinolin-1-one derivatives against the 5-HT2CR as majority of these molecules interacted with the site other than that of Lorcaserin with superior docking scores. These compounds along with the regioisomeric 3-methyleneisoindolin-1-one derivatives were prepared via the Cu(OAc)2 catalyzed coupling of 2-iodobenzamide with 1-ethynylcycloalkanol under ultrasound irradiation. According to the in vitro studies, most of these compounds were not only found to be potent and selective agonists but also emerged as PAAM of 5-HT2CR whereas Lorcaserin did not show PAAM activities. According to the SAR study the isoquinolin-1(2H)-ones appeared as better PAAM than isoindolin-1-ones whereas the presence of hydroxyl group appeared to be crucial for the activity. With the potent PAAM activity for 5-HT2CR (EC50 = 1 nM) and 107 and 86-fold selectivity towards 5-HT2C over 5-HT2A and 5-HT2B the compound 4i was identified as a hit molecule. The compound showed good stability in male BALB/c mice brain homogenate (∼85 % remaining after 2 h), moderate stability in the presence of rat liver microsomes (42 % remaining after 1 h) and acceptable PK properties with fast reaching in the brain maintaining ∼ 1:1 brain/plasma concentration ratio. The compound at a dose of 50 mg/kg exhibited decreased trend in the food intake starting from day 3 in S.D. rats, which reached significant by 5th day, and the effect was comparable to Lorcaserin (10 mg/kg) on day 5. Thus, being the first example of PAAM of 5-HT2CR the compound 4i is of further medicinal interest.

Multisite Model of Allosterism for the Adenosine A1 Receptor.

Despite being a target for about one-third of approved drugs, G protein-coupled receptors (GPCRs) still represent a tremendous reservoir for therapeutic strategies against diseases. For example, several cardiovascular and central nervous system conditions could benefit from clinical agents that activate the adenosine 1 receptor (A1R); however, the pursuit of A1R agonists for clinical use is usually impeded by both on- and off-target side effects. One of the possible strategies to overcome this issue is the development of positive allosteric modulators (PAMs) capable of selectively enhancing the effect of a specific receptor subtype and triggering functional selectivity (a phenomenon also referred to as bias). Intriguingly, besides enforcing the effect of agonists upon binding to an allosteric site, most of the A1R PAMs display intrinsic partial agonism and orthosteric competition with antagonists. To rationalize this behavior, we simulated the binding of the prototypical PAMs PD81723 and VCP171, the full-agonist NECA, the antagonist 13B, and the bitopic agonist VCP746. We propose that a single PAM can bind several A1R sites rather than a unique allosteric pocket, reconciling the structure-activity relationship and the mutagenesis results.

Characterization of a New Positive Allosteric Modulator of AMPA Receptors - PAM-43: Specific Binding of the Ligand and its Ability to Potentiate AMPAR Currents.

Currently, the most dynamic areas in the glutamate receptor system neurobiology are the identification and development of positive allosteric modulators (PAMs) of glutamate ionotropic receptors. PAM-based drugs are of great interest as promising candidates for the treatment of neurological diseases, such as epilepsy, Alzheimer's disease, schizophrenia, etc. Understanding the molecular mechanisms underlying the biological action of natural and synthetic PAMs is a key point for modifying the original chemical compounds as well as for new drug design. We are trying to elaborate a system of molecular functional screening of ionotropic glutamate receptor probable PAMs. The system will be based on the radioligand - receptor method of analysis and will allow rapid quantification of new AMPAR probable PAMs molecular activity. We plan to use a tritiumlabeled analogue of recently elaborated ionotropic GluR probable PAM ([3H]PAM-43) as the main radioligand. Here, we characterized the specific binding of the ligand and its ability to potentiate ionotropic GluR currents. The existence of at least two different sites of [3H]PAM-43 specific binding has been shown. One of the above sites is glutamate-dependent and is characterized by higher affinity. "Patchclamp" technique showed the ability of PAM-43 to potentiate ionotropic GluR currents in rat cerebellar Purkinje neurons in a concentration-dependent manner. The possibility of using PAM-43 as a model compound to study different allosteric effects of potential regulatory drugs (AMPAR allosteric regulators) was shown. [3H]PAM-43 based screening system will allow rapid selection of new AMPAR probable PAM structures and quantification of their molecular activity.

Toward Defining the Pharmacophore for Positive Allosteric Modulation of PTH1 Receptor Signaling by Extracellular Nucleotides.

The parathyroid hormone 1 receptor (PTH1R) is a Class B G-protein-coupled receptor that is a target for osteoporosis therapeutics. Activated PTH1R couples through Gs to the stimulation of adenylyl cyclase. As well, β-arrestin is recruited to PTH1R leading to receptor internalization and MAPK/ERK signaling. Previously, we reported that the agonist potency of PTH1R is increased in the presence of extracellular ATP, which acts as a positive allosteric modulator of PTH signaling. Another nucleotide, cytidine 5'-monophosphate (CMP), also enhances PTH1R signaling, suggesting that ATP and CMP share a moiety responsible for positive allostery, possibly ribose-5-phosphate. Therefore, we examined the effect of extracellular sugar phosphates on PTH1R signaling. cAMP levels and β-arrestin recruitment were monitored using luminescence-based assays. Alone, ribose-5-phosphate had no detectable effect on adenylyl cyclase activity in UMR-106 rat osteoblastic cells, which endogenously express PTH1R. However, ribose-5-phosphate markedly enhanced the activation of adenylyl cyclase induced by PTH. Other sugar phosphates, including glucose-1-phosphate, glucose-6-phosphate, fructose-6-phosphate, and fructose-1,6-bisphosphate, also potentiated PTH-induced adenylyl cyclase activation. As well, some sugar phosphates enhanced PTH-induced β-arrestin recruitment to human PTH1R heterologously expressed in HEK293H cells. Interestingly, the effects of glucose-1-phosphate were greater than those of its isomer glucose-6-phosphate. Our results suggest that phosphorylated monosaccharides such as ribose-5-phosphate contain the pharmacophore for positive allosteric modulation of PTH1R. At least in some cases, the extent of modulation depends on the position of the phosphate group. Knowledge of the pharmacophore may permit future development of positive allosteric modulators to increase the therapeutic efficacy of PTH1R agonists.

Positive Allosteric Modulators (PAMs) of Metabotropic Glutamate Receptor 5 (mGluR5) Attenuate Microglial Activation

Traumatic brain injury causes progressive neurodegeneration associated with chronic microglial activation. Recent studies show that neurodegeneration and neuroinflammation after traumatic brain injury can be inhibited as late as one month in animals by the activation of the metabotropic glutamate receptor 5 in microglia using (RS)-2-chloro-5- hydroxy-phenylglycine. However, the therapeutic potential of this agonist is limited due to its relatively weak potency and brain permeability. To address such concerns, we evaluated the anti-inflammatory activities of several positive allosteric modulators using various in vitro assays, and found that 3,3'-difluorobenzaldazine, 3-cyano-N-(1,3-diphenyl-1H-pyrazol- 5-yl)benzamide and 4-nitro-N-(1-(2-fluorophenyl)-3-phenyl-1H-pyrazol-5-yl)benzamide showed significantly improved potency which makes them potential lead compounds for further development of positive allosteric modulators for the treatment of traumatic brain injury.

Functional insight into development of positive allosteric modulators of AMPA receptors

Positive allosteric modulators of α-amino-3-hydroxy-5-methyl-isoxazole-propionic acid (AMPA) ionotropic glutamate receptors facilitate synaptic plasticity and contribute essentially to learning and memory, properties which make AMPA receptors targets for drug discovery and development. One region at which several different classes of positive allosteric modulators bind lies at the dimer interface between the ligand-binding core of the second, membrane-proximal, extracellular domain of AMPA receptors. This solvent-accessible binding pocket has been the target of drug discovery efforts, leading to the recent delineation of five “subsites” which differentially allow access to modulator moieties, and for which distinct modulator affinities and apparent efficacies are attributed. Here we use the voltage-clamp technique in conjunction with rapid drug application to study the effects of mutants lining subsites “A” and “B” of the allosteric modulator pocket to assess affinity and efficacy of allosteric modulation by cyclothiazide, CX614, CMPDA and CMPDB. A novel analysis of the decay of current produced by the onset of desensitization has allowed us to estimate both affinity and efficacy from single concentrations of modulator. Such an approach may be useful for effective high throughput screening of new target compounds.

Positive Allosteric Modulators of Type 5 Metabotropic Glutamate Receptors (mGluR5) and Their Therapeutic Potential for the Treatment of CNS Disorders

Studies utilizing selective pharmacological antagonists or targeted gene deletion have demonstrated that type 5 metabotropic glutamate receptors (mGluR5) are critical mediators and potential therapeutic targets for the treatment of numerous disorders of the central nervous system (CNS), including depression, anxiety, drug addiction, chronic pain, Fragile X syndrome, Parkinson’s disease, and gastroesophageal reflux disease. However, in recent years, the development of positive allosteric modulators (PAMs) of the mGluR5 receptor have revealed that allosteric activation of this receptor may also be of potential therapeutic benefit for the treatment of other CNS disorders, including schizophrenia, cognitive deficits associated with chronic drug use, and deficits in extinction learning. Here we summarize the discovery and characterization of various mGluR5 PAMs, with an emphasis on those that are systemically active. We will also review animal studies showing that these molecules have potential efficacy as novel antipsychotic agents. Finally, we will summarize findings that suggest that mGluR5 PAMs have pro-cognitive effects such as the ability to enhance synaptic plasticity, improve performance in various learning and memory tasks, including extinction of drug-seeking behavior, and reverse cognitive deficits produced by chronic drug use.

Neuronal Nicotinic Acetylcholine Receptors - Targets for the Development of Drugs to Treat Cognitive Impairment Associated with Schizophrenia and Alzheimers Disease

Nicotinic acetylcholine receptors (nAChR) have been strongly implicated as therapeutic targets for treating cognitive deficits in disorders such as schizophrenia and Alzheimer's disease (AD). In particular alpha7 and alpha4beta2 subtype-selective nAChR agonists and partial agonists have been developed as potential candidates for the treatment of schizophrenia, cognitive disorders (including Alzheimer's disease), and inflammation. Further development of positive allosteric modulators and antagonists were also recently reported in the literature. In this review we will cover recent developments focused on the above mentioned nAChR subtypes, starting from the most advanced clinical candidate followed by an overview of literature compounds where potency, selectivity, central nervous system access, pharmacological activity and pharmacokinetic properties are disclosed.

Recent Patents on Positive Allosteric Modulators of the Metabotropic Glutamate 5 Receptor as a Potential Treatment for Schizophrenia

The glutamate hypothesis of schizophrenia suggests that hypofunction of N-methyl-D-aspartate (NMDA) receptors may be critical for schizophrenic symptoms; therefore, pharmacological approaches that enhance NMDA function may be beneficial for the treatment of schizophrenia. Several lines of evidence indicate that NMDA and metabotropic glutamate (mGlu) 5 receptors are closely associated signaling partners and that a selective mGlu5 receptor agonist might provide a viable approach for increasing NMDA receptor function in the treatment of schizophrenia. The orthosteric binding sites across members of the mGlu receptor subtype for a particular endogenous ligand are often highly conserved, making it difficult to achieve high selectivity for the specific mGlu5 receptor. The advanced currents of drug discovery have developed multiple highly selective allosteric modulators of mGlu5 receptors. In the present review, we provide an update of the recent patents and development of positive allosteric modulators of the mGlu5 receptor and explore their therapeutic potential for schizophrenia.

P2.105 The development of positive allosteric modulators of mGluR4 for the treatment of Parkinson's disease

P2.105 The development of positive allosteric modulators of mGluR4 for the treatment of Parkinson's disease

New Trends in the Development of Positive Allosteric Modulators of AMPA Receptors

The 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propanoic acid (AMPA) receptors, a subtype of glutamate receptors, are involved in important neuronal functions such as long-term memory. A decrease of the number and activity of these receptors seems to play a role in schizophrenia and in the impairment of cognitive function associated to Alzheimers disease. Therefore, research has been focused on the development of drugs acting on those receptors, in particular of AMPA receptors positive allosteric modulators. Although agonists have an intrinsic activity, allosteric modulators need the release of glutamate to be active. Therefore, these drugs are expected to exhibit a decreasing risk of toxicity compared to pure agonists. In this article, we review the recent advances in the design of positive allosteric modulators of AMPA receptors.