Design and Synthesis of Novel Positive Allosteric Modulators of α7 Nicotinic Acetylcholine Receptors with the Ability To Rescue Auditory Gating Deficit in Mice

1,4-Disubstituted Piperazin-2-Ones as Selective Late Sodium Current Inhibitors with QT Interval Shortening Properties in Isolated Rabbit Hearts

Late sodium current (INa) inhibitors are a new subclass of antiarrhythmic agents. To overcome the drawbacks, e.g., low efficacy and inhibition effect on K+ current, of the FDA-approved late INa inhibitor ranolazine, chain amide 6a-6q, 1,4-disubstituted piperazin-2-ones 7a-7s, and their derivatives 8a-8n were successively designed, synthesized, and evaluated in vitro on the NaV1.5-transfected HEK293T cells by the whole-cell patch clamp recording assay at the concentration of 40 μM. Among the new skeleton compounds, 7d showed the highest efficacy (IC50 = 2.7 μM) and good selectivity (peak/late ratio >30 folds), as well as excellent pharmacokinetics properties in mice (T1/2 of 3.5 h, F = 90%, 3 mg/kg, po). It exhibited low hERG inhibition and was able to reverse the ATX-II-induced augmentation of late INa phenotype of LQT3 model in isolated rabbit hearts. These results suggest the application potentials of 7d in the treatments of arrhythmias related to the enhancement of late INa.

Allosteric Activation of α7 Nicotinic Acetylcholine Receptors by Novel 2-Arylamino-thiazole-5-carboxylic Acid Amide Derivatives for the Improvement of Cognitive Deficits in Mice

Enhancing α7 nAChR function serves as a therapeutic strategy for cognitive disorders. Here, we report the synthesis and evaluation of 2-arylamino-thiazole-5-carboxylic acid amide derivatives 6-9 that as positive allosteric modulators (PAMs) activate human α7 nAChR current expressed in Xenopus ooctyes. Among the 4-amino derivatives, a representative atypical type I PAM 6p exhibits potent activation of α7 current with an EC50 of 1.3 μM and the maximum activation effect on the current over 48-fold in the presence of acetylcholine (100 μM). The structure-activity relationship (SAR) analysis reveals that the 4-amino group is crucial for the allosteric activation of α7 currents by compound 6p as the substitution of 4-methyl group results in its conversion to compound 7b (EC50 = 2.1 μM; max effect: 58-fold) characterized as a typical type I PAM. Furthermore, both 6p and 7b are able to rescue auditory gating deficits in mouse schizophrenia-like model of acoustic startle prepulse inhibition.

Small molecule ligands for α9* and α7 nicotinic receptors: a survey and an update, respectively

The α9- and α7-containing nicotinic acetylcholine receptors (nAChRs) mediate numerous physiological and pathological processes by complex mechanisms that are currently the subject of intensive study and debate. In this regard, selective ligands serve as invaluable investigative tools and, in many cases, potential therapeutics for the treatment of various CNS disfunctions and diseases, neuropathic pain, inflammation, and cancer. However, the present scenario differs significantly between the two aforementioned nicotinic subtypes. Over the past few decades, a large number of selective α7-nAChR ligands, including full, partial and silent agonists, antagonists, and allosteric modulators, have been described and reviewed. Conversely, reports on selective α9-containing nAChR ligands are relatively scarce, also due to a more recent characterization of this receptor subtype, and hardly any focusing on small molecules. In this review, we focus on the latter, providing a comprehensive overview, while providing only an update over the last five years for α7-nAChR ligands.

Traceless Solid-Phase Synthesis of 7-Aminothiazolo[4,5-d]pyrimidine-Based Library via Dimroth Rearrangement

Thiazolo[4,5-d]pyrimidine is one of the purine isosteres that possesses a variety of pharmaceutical activities and is an attractive scaffold for drug discovery. In this work, a novel protocol for the synthesis of 7-aminothiazolo[4,5,-d]pyrimidine scaffold libraries on solid support has been developed using a traceless linker. Dimroth rearrangement afforded the desired intermediate with a fused heterocyclic thiazolo[4,5,-d]pyrimidine core skeleton. To diversify the synthesized library, three types of building blocks were introduced to the resin-bound thiazolo[4,5,-d]pyrimidine through N-acylation, N-alkylation, and nucleophilic substitution with amines during cleavage from the resin. The synthesized compounds were produced in seven steps with overall yields of 11-48%. Additionally, physicochemical properties, as well as drug-likeness of the library, were calculated.

Synthesis and Biological Evaluation of Novel Triazine Derivatives as Positive Allosteric Modulators of α7 Nicotinic Acetylcholine Receptors

Enhancing neuronal α7 nicotinic acetylcholine receptor (α7 nAChR) function can alleviate cognitive deficits. Here, we report the design, synthesis, and evaluation of N-(4-(trifluoromethoxy)phenyl)-1,3,5-triazin-2-amine derivatives 8-10 as a series of novel α7 nAChR positive allosteric modulators (PAMs). The representative compound 10e functions as a type I PAM with an EC50 of 3.0 μM and approximately 38-fold enhancement of α7 current in the presence of agonist acetylcholine (100 μM). It specifically enhances α7 current with high selectivity. Compound 10e shows good pharmacokinetic property in mice. Intraperitoneal injection of 10e (3 mg/kg) exhibits sufficient blood-brain barrier penetration in mice. Furthermore, 10e can also rescue the auditory gating deficit in mice with schizophrenia-like behavior. Molecular docking of 10e with homopentameric α7 nAChR reveals a new mode of action. These results support the potential of 10e for treatment for schizophrenia and Alzheimer's disease.

HTS-based discovery and optimization of novel positive allosteric modulators of the α7 nicotinic acetylcholine receptor

HTS campaign of the corporate compound collection resulted in a novel, oxalic acid diamide scaffold of α7 nACh receptor positive allosteric modulators. During the hit expansion, several derivatives, such as 4, 11, 17 demonstrated not only high in vitro potency, but also in vivo efficacy in the mouse place recognition test. The advanced hit molecule 11 was further optimized by the elimination of the putatively mutagenic aromatic-amine building block that resulted in a novel, aminomethylindole compound family. The most balanced physico-chemical and pharmacological profile was found in case of compound 55. Docking study revealed an intersubunit binding site to be the most probable for our compounds. 55 demonstrated favorable cognitive enhancing profile not only in scopolamine-induced amnesia (place recognition test in mice) but also in natural forgetting (novel object recognition test in rats). Compound 55 was, furthermore, active in a cognitive paradigm of high translational value, namely in the rat touch screen visual discrimination test. Therefore, 55 was selected as a lead compound for further optimization. Based on the obtained favorable results, the invented aminomethylindole cluster may provide a viable approach for cognitive enhancement through positive allosteric modulation of α7 nAChRs.

Discovery of novel positive allosteric modulators of the α7 nicotinic acetylcholine receptor: Scaffold hopping approach

The paper focuses on the scaffold hopping-based discovery and characterization of novel nicotinic alpha 7 receptor positive modulator (α7 nAChR PAM) ligands around the reference molecule (A-867744). First, substantial efforts were carried out to assess the importance of the various pharmacophoric elements on the in vitro potency (SAR evaluation) by chemical modifications. Subsequently, several new derivatives with versatile, heteroaromatic central cores were synthesized and characterized. A promising, pyrazole-containing new chemotype with good physicochemical and in vitro parameters was identified. Retrospective analysis based on homology modeling was also carried out. Besides its favorable in vitro characteristics, the most advanced derivative 69 also showed in vivo efficacy in a rodent model of cognition (scopolamine-induced amnesia in the mouse place recognition test) and acceptable pharmacokinetic properties. Based on the in vivo data, the resulting molecule with advanced drug-like characteristics has the possibility to improve cognitive performance in a biologically relevant dose range, further strengthening the view of the supportive role of α7 nACh receptors in the cognitive processes.

Selective α7 nicotinic receptor agonists and positive allosteric modulators for the treatment of schizophrenia - a review

INTRODUCTION

Alpha 7 nicotinic acetylcholine receptor (α7 nAChR) partial agonists, agonists, and positive allosteric modulators (PAMs) have been in development for over a decade. The initial candidates were in clinical trials for a wide variety of diseases including schizophrenia, but there has yet to be a successful compound to make it to the market for any disorder. Although difficult to assess the cause of all the clinical failures, the lack of efficacy played a major role. The development of more selective compounds, may bring a successful compound to long-suffering schizophrenia patients.

AREAS COVERED

This article examines investigational agonists and positive allosteric modulators of the α7 nicotinic receptor in preclinical studies as well as clinical trials. Our search included the use of SciFinder, Google, and clinicaltrials.gov with search dates of 2015 to the present.

EXPERT OPINION

Researchers must rethink their approach should look more closely at the selectivity of new compounds and how to tackle the translational gap. Perhaps new positive allosteric modulators that can help minimize receptor desensitization and selectivity profiles can be a path forward for α7 nAChRs in schizophrenia.

Discovery of fused heterocyclic carboxamide derivatives as novel α7-nAChR agonists: Synthesis, preliminary SAR and biological evaluation

The α7 nicotinic acetylcholine receptor (α7 nAChR) has emerged as a promising therapeutic target for schizophrenia. In our previous work, a novel series of α7-nAChR agonists bearing scaffold of indolizine were discovered. To explore the effect of aromaticity on the activity and find more active agents, herein, fused heterocyclic carboxamide derivatives were designed and synthesized in this study. Based on the evaluation by two-electrode voltage clamp in Xenopus oocytes, 27 of the synthesized compounds showed obvious agonism of α7 nAChR. Particularly, compounds 10a and 10e showed significantly higher E_max than EVP-6124. The result illustrated the importance of aromaticity to the activity of agonism. Compound 10a, which showed EC₅₀ of 1.88 μM and E_max of 72.4%, was further characterized comprehensively, including co-application with type II positive allosteric modulator PNU-120596, selectivity with other closely related ligand-gated ion channel, etc. The results showed that 10a showed moderate selectivity over other subtypes such as α4β2 and α3β4 nAChR. 10a evoked α7-like currents that were inhibited by MLA and enhanced in the presence of the α7 PAM PNU-120596. The analysis of binding mode and understanding of structure-activity relationship provided insights to develop more potent novel α7-nAChR agonists.

Chemical conversion of nicotinamide into type I positive allosteric modulator of α7 nAChRs

Structural modifications of nicotinamide, a form of vitamin B3, gave rise to a series of compounds (8aa-8ce) that exhibit activities as type I positive allosteric modulators (PAMs) of human α7 nAChR expressed in Xenopus oocytes in two-electrode voltage clamp assay. The compound 8ai was a potent and efficacious PAM with an EC₅₀ = 3.34 ± 1.13 μM and the maximum activation effect of α7 current over 1474 ± 246% in the presence of acetylcholine (100 μM). It is highly specific to α7 nAChR over other subtypes of nAChR and 5-HT_3A receptors. The structure-activity relationship analysis identified a key skeleton of nicotinamide nucleus critical for biological activity. Taken together, the 8ai as a type I PAM of α7 nAChR may be beneficial for improvement of cognitive deficit.

The visualization of hERG channels in living cells via a fluorescent probe regulated by the synergy between solvatochromism and molecular rotation based on simple targeting of the group 4-benzylaniline

A highly sensitive fluorescent probe CBH based on solvatochromism and molecular rotation was designed and developed for imaging of hERG channels by employing a novel targeting group 4-benzylaniline. More importantly, CBH has the potential for the quantitative analysis of the hERG channels expressed in tumor cells.

Multi-Target Approach for Drug Discovery against Schizophrenia

Polypharmacology is nowadays considered an increasingly crucial aspect in discovering new drugs as a number of original single-target drugs have been performing far behind expectations during the last ten years. In this scenario, multi-target drugs are a promising approach against polygenic diseases with complex pathomechanisms such as schizophrenia. Indeed, second generation or atypical antipsychotics target a number of aminergic G protein-coupled receptors (GPCRs) simultaneously. Novel strategies in drug design and discovery against schizophrenia focus on targets beyond the dopaminergic hypothesis of the disease and even beyond the monoamine GPCRs. In particular these approaches concern proteins involved in glutamatergic and cholinergic neurotransmission, challenging the concept of antipsychotic activity without dopamine D₂ receptor involvement. Potentially interesting compounds include ligands interacting with glycine modulatory binding pocket on N-methyl-d-aspartate (NMDA) receptors, positive allosteric modulators of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, positive allosteric modulators of metabotropic glutamatergic receptors, agonists and positive allosteric modulators of α7 nicotinic receptors, as well as muscarinic receptor agonists. In this review we discuss classical and novel drug targets for schizophrenia, cover benefits and limitations of current strategies to design multi-target drugs and show examples of multi-target ligands as antipsychotics, including marketed drugs, substances in clinical trials, and other investigational compounds.