Prototypical Positive Allosteric Modulator Research Articles

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.

Effect of the mGlu2 positive allosteric modulator CBiPES on dyskinesia, psychosis-like behaviours and parkinsonism in the MPTP-lesioned marmoset.

Advanced Parkinson's disease (PD) is often complicated by the occurrence of dyskinesia, motor fluctuations and psychosis. To this day, few treatment options are available for each of these phenomena, and they are at times not effective or elicit adverse events, leaving some patients short of therapeutic options. We have recently shown that positive allosteric modulation of metabotropic 2 (mGlu2) receptors with the prototypical positive allosteric modulator (PAM) LY-487,379 is efficacious at alleviating both dyskinesia and psychosis-like behaviours (PLBs), while simultaneously enhancing the anti-parkinsonian action of L-3,4-dihydroxyphenylalanine (L-DOPA), in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset. Here, we assessed the effects of CBiPES, a mGlu2 PAM derived from LY-487,379, but with improved pharmacokinetic properties. Six MPTP-lesioned marmosets with reproducible dyskinesia and PLBs were administered L-DOPA in combination with vehicle or CBiPES (0.1, 1 and 10mg/kg), after which their behaviour was rated. CBiPES 10mg/kg reduced global dyskinesia by 60% (P < 0.0001), while peak dose dyskinesia was reduced by 66% (P < 0.001), compared to L-DOPA/vehicle. CBiPES 10mg/kg also diminished global PLBs by 56% (P < 0.0001), while peak dose PLBs were reduced by 64% (P < 0.001), compared to L-DOPA/vehicle. Lastly, CBiPES enhanced the anti-parkinsonian action of L-DOPA, by reducing global parkinsonian disability by 43% (P < 0.01), compared to L-DOPA/vehicle. Our results provide further evidence that mGlu2 positive allosteric modulation may be an approach that could be efficacious for the treatment of dyskinesia, psychosis and motor fluctuations in PD.

Biphenylindanone A, a prototypical mGlu2 positive allosteric modulator, alleviates dyskinesia and psychosis in the parkinsonian marmoset

ObjectiveTo determine the effect of the prototypical and selective metabotropic glutamate 2 (mGlu2) receptor positive allosteric modulator (PAM) biphenylindanone A (BINA) on L‐3,4‐dihydroxyphenylalanine (L‐DOPA)‐induced psychosis‐like behaviours (PLBs) and dyskinesia in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐lesioned marmoset model of Parkinson's disease (PD).BackgroundPsychosis and dyskinesia undermine the quality of life of as many as 50–95% of patients with advanced PD. Available therapies are few, and they may elicit important side effects. We have recently demonstrated that activation of mGlu2 receptors with another prototypical PAM, LY‐487,379, reduces both PLBs and dyskinesia in the MPTP‐lesioned primate. Here, we seek to determine the effects of PAM BINA on these 2 treatment‐related complications, in the MPTP‐lesioned marmoset.MethodsSix common marmosets (Callithrix jacchus) were rendered parkinsonian by MPTP injection. Following repeated administration of L‐DOPA/benserazide (L‐DOPA) to elicit stable PLBs and dyskinesia, they were administered acute challenges of BINA (0.1, 1 and 10 mg/kg) or vehicle, in combinaison with L‐DOPA after which the severity of PLBs, dyskinesia and parkinsonian disability was rated.ResultsBINA (0.1, 1 and 10 mg/kg) significantly reduced the severity of peak dose PLBs, by ≈33.3%, ≈ 55.6 and ≈ 61.1% (P &lt; 0.05, P &lt; 0.01 and P &lt; 0.01), respectively when compared to L‐DOPA/vehicle. Severity of peak dose dyskinesia was also reduced, by ≈ 28.9%, ≈ 52.3 and ≈57.8% (P &lt; 0.05, P &lt; 0.01 and P &lt; 0.01), respectively, when BINA (0.1, 1 and 10 mg/kg) was added to L‐DOPA, compared to L‐DOPA/vehicle. The anti‐psychotic and anti‐dyskinetic effects of BINA were achieved without interfering with the therapeutic effect of L‐DOPA on parkinsonian disability.ConclusionsBINA is the second mGlu2 PAM that was effective at alleviating PLBs and dyskinesia in the gold‐standard animal model of PD, the parkinsonian primate. The results presented here further add to the increasing data suggesting that mGlu2 positive allosteric modulation may be effective to diminish both PD psychosis and L‐DOPA‐induced dyskinesia.Support or Funding InformationFonds de Recherche Québec ‐ Santé, Parkinson Canada, Natural Sciences and Engineering Research Council of Canada, Weston Brain Institute, Michael J Fox Foundation for Parkinson's Research, Healthy Brains for Healthy Lives.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Structural Basis for Binding of Allosteric Drug Leads in the Adenosine A1 Receptor

Despite intense interest in designing positive allosteric modulators (PAMs) as selective drugs of the adenosine A1 receptor (A1AR), structural binding modes of the receptor PAMs remain unknown. Using the first X-ray structure of the A1AR, we have performed all-atom simulations using a robust Gaussian accelerated molecular dynamics (GaMD) technique to determine binding modes of the A1AR allosteric drug leads. Two prototypical PAMs, PD81723 and VCP171, were selected. Each PAM was initially placed at least 20 Å away from the receptor. Extensive GaMD simulations using the AMBER and NAMD simulation packages at different acceleration levels captured spontaneous binding of PAMs to the A1AR. The simulations allowed us to identify low-energy binding modes of the PAMs at an allosteric site formed by the receptor extracellular loop 2 (ECL2), which are highly consistent with mutagenesis experimental data. Furthermore, the PAMs stabilized agonist binding in the receptor. In the absence of PAMs at the ECL2 allosteric site, the agonist sampled a significantly larger conformational space and even dissociated from the A1AR alone. In summary, the GaMD simulations elucidated structural binding modes of the PAMs and provided important insights into allostery in the A1AR, which will greatly facilitate the receptor structure-based drug design.

Mechanism of Allosteric Modulator Binding to the Adenosine A1 Receptor

The adenosine A1 receptor (A1AR) is a key G-protein-coupled receptor (GPCR) that has served as a therapeutic target for treating cardiovascular and neurological diseases. Activation of the A1AR is able to protect the myocardium against ischemia-reperfusion injury and reduce neuropathic pain. In contrast to traditional agonists that often cause off-target side effects, positive allosteric modulators (PAMs) that increase the receptor responsiveness to endogenous adenosine in local regions are promising selective drug candidates of the A1AR. However, the binding modes of PAMs in the A1AR and mechanism of the receptor allosteric modulation remain unclear. Here, all-atom computer simulations using the robust Gaussian accelerated molecular dynamics (GaMD) method are performed to capture spontaneous binding of prototypical PAMs to the A1AR. The GaMD simulations allow free energy calculations to identify low-energy binding modes of the PAMs in the receptor. The predicted binding modes are consistent with previous mutation and binding assay experiments. These results provide important insights into the mechanism of A1AR allostery at an atomistic level. The work will be also useful for future computer-aided drug design efforts targeting the A1AR and other GPCRs.

Molecular Mechanisms of Action of M5 Muscarinic Acetylcholine Receptor Allosteric Modulators

Recently, the first subtype-selective allosteric modulators of the M5 muscarinic acetylcholine receptor (mAChR) have been described, but their molecular mechanisms of action remain unknown. Using radioligand-binding and functional assays of inositol phosphate (IP) accumulation and Ca(2+) mobilization in a recombinant cell line stably expressing the human M5 mAChR, we investigated the effects of the positive allosteric modulator (PAM), ML380, and negative allosteric modulator, ML375. In functional assays, ML380 caused robust enhancements in the potency of the full agonists, acetylcholine (ACh), carbachol, and oxotremorine-M, while significantly increasing the maximal response to the partial agonist, pilocarpine. ML380 also demonstrated direct allosteric agonist activity. In contrast, ML375 displayed negative cooperativity with each of the agonists in a manner that varied with the pathway investigated and progressively reduced the maximal pilocarpine response. Radioligand-binding affinity cooperativity estimates were consistent with values derived from functional assays in some instances but not others, suggesting additional allosteric effects on orthosteric ligand efficacy. For ML375 this was confirmed in IP assays performed after reduction of receptor reserve by the alkylating agent, phenoxybenzamine, as it reduced the maximal ACh response. In contrast, ML380 enhanced only ACh potency after receptor alkylation, with no effect on maximal response, consistent with studies of the M1 mAChR with the prototypical PAM, BQZ12. Interaction studies between ML380 and ML375 also indicated that they most likely used an overlapping allosteric site. Our findings indicate that novel small-molecule modulators of the M5 mAChR display mixed mechanisms of action compared with previously characterized modulators of other mAChRs.

Novel Fused Arylpyrimidinone Based Allosteric Modulators of the M1 Muscarinic Acetylcholine Receptor.

Benzoquinazolinone 1 is a positive allosteric modulator (PAM) of the M1 muscarinic acetylcholine receptor (mAChR), which is significantly more potent than the prototypical PAM, 1-(4-methoxybenzyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (BQCA). In this study, we explored the structural determinants that underlie the activity of 1 as a PAM of the M1 mAChR. We paid particular attention to the importance of the tricyclic scaffold of compound 1, for the activity of the molecule. Complete deletion of the peripheral fused benzene ring caused a significant decrease in affinity and binding cooperativity with acetylcholine (ACh). This loss of affinity was rescued with the addition of either one or two methyl groups in the 7- and/or 8-position of the quinazolin-4(3H)-one core. These results demonstrate that the tricyclic benzo[h]quinazolin-4(3H)-one core could be replaced with a quinazolin-4(3H)-one core and maintain functional affinity. As such, the quinazolin-4(3H)-one core represents a novel scaffold to further explore M1 mAChR PAMs with improved physicochemical properties.