GABAA receptor pharmacology of fluorinated derivatives of the novel sedative-hypnotic pyrazolopyrimidine indiplon

Medicinal Chemistry of Pyrazolopyrimidine Scaffolds Substituted with Different Heterocyclic Nuclei

BACKGROUND

Medicinal chemistry of pyrazolopyrimidine scaffolds substituted with different heterocyclic nuclei has attracted great attention due to their wide range of biological activities that have been reported. Pyrazolopyrimidine scaffold is an important privileged heterocycle nucleus in drug discovery.

METHODS

All pharmacological activities of pyrazolopyrimidine scaffold have been mentioned, such as anticancer, anti-inflammatory, antihypertensive, antitubercular, antiviral, antibacterial, antifungal, antidiabetic, and anti-obesity agents. In addition, it was used in both osteoporosis and neurological disorders. The difference in potency and bioavailability of pyrazolopyrimidine derivatives refers to the substituent groups that can increase the activity against specific targets and enhance their selectivity.

RESULTS

This review provides an overview of different synthetic pathways, structure activity relationships, and preclinical studies of pyrazolopyrimidine scaffolds substituted with a variety of heterocyclic nuclei, as well as it provides a discussion on the significant biological findings of these important scaffolds. In addition, it provides some insights on the different macromolecular targets that pyrazolopyrimidine scaffold can effectively work on, such as; cyclin dependent kinases; CDK2, CDK7, and CDK9, checkpoint kinases; CHK1 and CHK2 and their correlation with the anticancer activity, PI3Kα, transient receptor potential canonical 6, B-Raf kinase, Interleukin- 1 receptor-associated kinase 4, B-cell lymphoma 6, TRKA-C kinase, potent kDa ribosomal protein S6 kinase, colon cancer cell line (CaCo-2), domain receptor kinase (KDR), HepG-2 carcinoma cell, FLT3. The antibacterial activity against B. subtilis and E. coli and antifungal activity against C. albicans, C. tropicalis, A. niger, and A. clavatus are discussed.

CONCLUSION

This review provides an overview of the different pharmacological activities of the pyrazolopyrimidine scaffold and its correlation with chemical structure. Some exciting new developments in pyrazolopyrimidine scaffolds are also presented in this review.

Synthesis and Pharmacological Evaluation of New 3,4-Dihydroisoquinolin Derivatives Containing Heterocycle as Potential Anticonvulsant Agents

Two novel series of 3,4-dihydroisoquinolin with heterocycle derivatives (4a–t and 9a–e) were synthesized and evaluated for their anticonvulsant activity using maximal electroshock (MES) test and pentylenetetrazole (PTZ)-induced seizure test. All compounds were characterized by IR, ¹H-NMR, ¹³C-NMR, and mass spectral data. Among them, 9-(exyloxy)-5,6-dihydro-[1,2,4]triazolo[3,4-a]isoquinolin-3(2H)-one (9a) showed significant anticonvulsant activity in MES tests with an ED₅₀ value of 63.31 mg/kg and it showed wide margins of safety with protective index (PI > 7.9). It showed much higher anticonvulsant activity than that of valproate. It also demonstrated potent activity against PTZ-induced seizures. A docking study of compound 9a in the benzodiazepine (BZD)-binding site of γ-aminobutyric acid_A (GABA_A) receptor confirmed possible binding of compound 9a with the BZD receptors.

Plasmid-Based Generation of Induced Neural Stem Cells from Adult Human Fibroblasts

Direct reprogramming from somatic to neural cell types has become an alternative to induced pluripotent stem cells. Most protocols employ viral expression systems, posing the risk of random genomic integration. Recent developments led to plasmid-based protocols, lowering this risk. However, these protocols either relied on continuous presence of a variety of small molecules or were only able to reprogram murine cells. We therefore established a reprogramming protocol based on vectors containing the Epstein-Barr virus (EBV)-derived oriP/EBNA1 as well as the defined expression factors Oct3/4, Sox2, Klf4, L-myc, Lin28, and a small hairpin directed against p53. We employed a defined neural medium in combination with the neurotrophins bFGF, EGF and FGF4 for cultivation without the addition of small molecules. After reprogramming, cells demonstrated a temporary increase in the expression of endogenous Oct3/4. We obtained induced neural stem cells (iNSC) 30 days after transfection. In contrast to previous results, plasmid vectors as well as a residual expression of reprogramming factors remained detectable in all cell lines. Cells showed a robust differentiation into neuronal (72%) and glial cells (9% astrocytes, 6% oligodendrocytes). Despite the temporary increase of pluripotency-associated Oct3/4 expression during reprogramming, we did not detect pluripotent stem cells or non-neural cells in culture (except occasional residual fibroblasts). Neurons showed electrical activity and functional glutamatergic synapses. Our results demonstrate that reprogramming adult human fibroblasts to iNSC by plasmid vectors and basic neural medium without small molecules is possible and feasible. However, a full set of pluripotency-associated transcription factors may indeed result in the acquisition of a transient (at least partial) pluripotent intermediate during reprogramming. In contrast to previous reports, the EBV-based plasmid system remained present and active inside the cells at all time points.

Synthesis, Characterization, and Cytotoxicity of Some New 5-Aminopyrazole and Pyrazolo[1,5-a]pyrimidine Derivatives

5-Amino-N-aryl-3-[(4-methoxyphenyl)amino]-1H-pyrazole-4-carboxamides 4a–c were synthesized by the reaction of N-(aryl)-2-cyano-3-[(4-methoxyphenyl)amino]-3-(methylthio)acrylamides 3a–c with hydrazine hydrate in ethanol. The reaction of 5-amino-N-aryl-1H-pyrazoles 4a–c with acetylacetone 5 or 2-(4-methoxybenzylidene)malononitrile 8 yielded the pyrazolo[1,5-a]pyrimidine derivatives 7a–c and 10a–c, respectively. The structures of the synthesized compounds were established based on elemental analysis and spectral data (IR, MS, ¹H-NMR, and ¹³C-NMR). Representative examples of the new synthesized products were screened for their in vitro cytotoxic activity against Ehrlich Ascites Carcinoma (EAC) cells.

Functional differentiation of midbrain neurons from human cord blood-derived induced pluripotent stem cells

Introduction

Human induced pluripotent stem cells (hiPSCs) offer great promise for regenerative therapies or in vitro modelling of neurodegenerative disorders like Parkinson’s disease. Currently, widely used cell sources for the generation of hiPSCs are somatic cells obtained from aged individuals. However, a critical issue concerning the potential clinical use of these iPSCs is mutations that accumulate over lifetime and are transferred onto iPSCs during reprogramming which may influence the functionality of cells differentiated from them. The aim of our study was to establish a differentiation strategy to efficiently generate neurons including dopaminergic cells from human cord blood-derived iPSCs (hCBiPSCs) as a juvenescent cell source and prove their functional maturation in vitro.

Methods

The differentiation of hCBiPSCs was initiated by inhibition of transforming growth factor-β and bone morphogenetic protein signaling using the small molecules dorsomorphin and SB 431542 before final maturation was carried out. hCBiPSCs and differentiated neurons were characterized by immunocytochemistry and quantitative real time-polymerase chain reaction. Since functional investigations of hCBiPSC-derived neurons are indispensable prior to clinical applications, we performed detailed analysis of essential ion channel properties using whole-cell patch-clamp recordings and calcium imaging.

Results

A Sox1 and Pax6 positive neuronal progenitor cell population was efficiently induced from hCBiPSCs using a newly established differentiation protocol. Neuronal progenitor cells could be further maturated into dopaminergic neurons expressing tyrosine hydroxylase, the dopamine transporter and engrailed 1. Differentiated hCBiPSCs exhibited voltage-gated ion currents, were able to fire action potentials and displayed synaptic activity indicating synapse formation. Application of the neurotransmitters GABA, glutamate and acetylcholine induced depolarizing calcium signal changes in neuronal cells providing evidence for the excitatory effects of these ligand-gated ion channels during maturation in vitro.

Conclusions

This study demonstrates for the first time that hCBiPSCs can be used as a juvenescent cell source to generate a large number of functional neurons including dopaminergic cells which may serve for the development of novel regenerative treatment strategies.

Searching for perfect sleep: the continuing evolution of GABAA receptor modulators as hypnotics

The non-benzodiazepine GABA(A) receptor modulators ('Z-drugs') - zaleplon, zolpidem, zopiclone and eszopiclone - have become the accepted treatments for insomnia where they are available. However, recent randomized, placebo-controlled trials suggest that, for these drugs, there may be particular efficacy and tolerability profiles and distinct clinical outcomes in specific patient populations. This is particularly apparent when hypnotic/ selective serotonin reuptake inhibitor co-therapy is used to treat patients with co-morbid insomnia and psychiatric disorders, as patient recovery appears to be accelerated and enhanced by some drugs but not others. Emerging evidence of why this should be the case is that these hypnotic drugs may differ significantly from each other in their pharmacodynamic and pharmacokinetic profiles. Functional selectivity for specific GABA(A) receptor subtypes may determine each drug's clinical attributes, while the pharmacokinetic characteristics of Z-drugs also determine to a large extent how they perform in the clinic. For example, activity at GABA(A) alpha 1 receptor subtypes may be associated with sedative effects, whereas activity at alpha 2 and alpha 3 receptor subtypes may be associated with anxiolytic and antidepressant effects. In summary, the distinct clinical outcomes of zaleplon, zolpidem, zopiclone and eszopiclone may be explained by each drug's unique GABA(A) receptor subunit selectivity and pharmacokinetic profile. Further investigation of GABA( A) receptor subtype effects would help to increase understanding of current hypnotic drug effects, while knowledge of each drug's specific binding profile should enable clinicians to tailor treatment to individual patient's needs.

Functional and molecular analysis of GABA receptors in human midbrain-derived neural progenitor cells

GABA(A) receptor function is involved in regulating proliferation, migration, and differentiation of rodent neural progenitor cells (NPCs). However, little is known about the molecular composition and functional relevance of GABA(A) receptors in human neural progenitors. Here, we investigated human fetal midbrain-derived NPCs in respect to their GABA(A) receptor function and subunit expression using electrophysiology, calcium imaging, and quantitative real-time PCR. Whole-cell recordings of ligand- and voltage-gated ion channels demonstrate the ability of NPCs to generate action potentials and to express functional GABA(A) receptors after differentiation for 3 weeks in vitro. Pharmacological and molecular characterizations indicate a predominance of GABA(A) receptor heteromers containing subunits alpha2, beta1, and/or beta3, and gamma. Intracellular Ca(2+) measurements and the expression profile of the Na(+)-K(+)-Cl(-) co-transporter 1 and the K(+)-Cl(-) co-transporter 2 in differentiated NPCs suggest that GABA evokes depolarizations mediated by GABA(A) receptors. These data indicate that NPCs derived from human fetal midbrain tissue acquire essential GABA(A) receptor properties during neuronal maturation in vitro.