"Dual Anta-Inhibitors" of the A2A Adenosine Receptor and Casein Kinase CK1delta: Synthesis, Biological Evaluation, and Molecular Modeling Studies.

Based on a screening of a chemical library of A2A adenosine receptor (AR) antagonists, a series of di- and tri-substituted adenine derivatives were synthesized and tested for their ability to inhibit the activity of the enzyme casein kinase 1 delta (CK1δ) and to bind adenosine receptors (ARs). Some derivatives, here called "dual anta-inhibitors", demonstrated good CK1δ inhibitory activity combined with a high binding affinity, especially for the A2AAR. The N6-methyl-(2-benzimidazolyl)-2-dimethyamino-9-cyclopentyladenine (17, IC50 = 0.59 µM and KiA2A = 0.076 µM) showed the best balance of A2AAR affinity and CK1δ inhibitory activity. Computational studies were performed to simulate, at the molecular level, the protein-ligand interactions involving the compounds of our series. Hence, the dual anta-inhibitor 17 could be considered the lead compound of new therapeutic agents endowed with synergistic effects for the treatment of chronic neurodegenerative and cancer diseases.

Dual Anta-Inhibitors Targeting Protein Kinase CK1δ and A2A Adenosine Receptor Useful in Neurodegenerative Disorders.

Currently, the number of patients with neurodegenerative pathologies is estimated at over one million, with consequences also on the economic level. Several factors contribute to their development, including overexpression of A2A adenosine receptors (A2AAR) in microglial cells and up-regulation and post-translational alterations of some casein kinases (CK), among them, CK-1δ. The aim of the work was to study the activity of A2AAR and CK1δ in neurodegeneration using in-house synthesized A2A/CK1δ dual anta-inhibitors and to evaluate their intestinal absorption. Experiments were performed on N13 microglial cells, which were treated with a proinflammatory CK cocktail to simulate an inflammatory state typical of neurodegenerative diseases. Results showed that the dual anta-inhibitors have the ability to counteract the inflammatory state, even if compound 2 is more active than compound 1. In addition, compound 2 displayed an important antioxidant effect similar to the reference compound ZM241385. Since many known kinase inhibitors are very often unable to cross lipid bilayer membranes, the ability of A2A/CK1δ double anta-inhibitors to cross the intestinal barrier was investigated by an everted gut sac assay. HPLC analysis revealed that both compounds are able to cross the intestinal barrier, making them promising candidates for oral therapy.

The possible role of the nucleoside adenosine in countering skin aging: A review.

Skin aging is a complex biological process. Skin aspect is considered as a sign of well-being and of beauty. In view of this, noninvasive and/or minimally invasive anti-aging strategies were developed. Adenosine, a well-known nucleoside, may play a role in skin rejuvenation. Adenosine receptors belong to the G protein-coupled receptors superfamily and are divided into four subtypes: A1 , A2A , A2B , and A3 . The adenosine receptors expressed by skin are mainly the A1 and A2A subtypes. In the hypodermis, adenosine through the A1 receptor stimulates lipogenesis and adipogenesis. In the dermis, adenosine through the A2A receptor subtype stimulates collagen production. Moreover, the nucleoside increases new DNA synthesis and subsequently protein synthesis in dermal cells. Activation of adenosine receptors by interacting with various skin layers may induce a decrease in the amount of wrinkles, roughness, dryness, and laxity. This article has reviewed the mechanisms through which adenosine modulates biological mechanisms in the skin tissues and the effect of preparations containing adenosine or its derivatives on the skin.

A2A Adenosine Receptor Antagonists: Are Triazolotriazine and Purine Scaffolds Interchangeable?

The A2A adenosine receptor (A2AAR) is one of the four subtypes activated by nucleoside adenosine, and the molecules able to selectively counteract its action are attractive tools for neurodegenerative disorders. In order to find novel A2AAR ligands, two series of compounds based on purine and triazolotriazine scaffolds were synthesized and tested at ARs. Compound 13 was also tested in an in vitro model of neuroinflammation. Some compounds were found to possess high affinity for A2AAR, and it was observed that compound 13 exerted anti-inflammatory properties in microglial cells. Molecular modeling studies results were in good agreement with the binding affinity data and underlined that triazolotriazine and purine scaffolds are interchangeable only when 5- and 2-positions of the triazolotriazine moiety (corresponding to the purine 2- and 8-positions) are substituted.

A patent review of adenosine A2B receptor antagonists (2016-present).

INTRODUCTION: A2B adenosine receptor (A2BAR) plays a crucial role in pathophysiologic conditions associated with high adenosine release, typical of airway inflammatory pathologies, gastrointestinal disorders, cancer, asthma, type 2 diabetes, and atherosclerosis. In some pathologies, simultaneous inactivation of A2A and A2BARs is desirable to have a synergism of action that leads to a greater efficacy of the pharmacological treatment and less side effects due to the dose of drug administered. In this context, it is strongly required to identify molecules capable of selectively antagonizing A2BAR or A2A/A2BARs. AREAS COVERED: The review provides a summary of patents, published from 2016 to present, on chemicals and their clinical use. In this paper, information on the biological activity of representative structures of recently developed A2B or A2A/A2B receptor ligands is reported. EXPERT OPINION: Among the four P1 receptors, A2BAR is the most inscrutable and the least studied until a few years ago, but its involvement in various inflammatory pathologies has recently made it a pharmacological target of high interest. Many efforts by the academy and pharmaceutical companies have been made to discover potential A2BAR and A2A/A2BARs drugs. Although several compounds have been synthesized only a few molecules have entered clinical trials.

A3 Adenosine Receptor Antagonists with Nucleoside Structures and Their Anticancer Activity.

The overexpression of the A3 adenosine receptor (AR) in a number of cancer cell types makes it an attractive target for tumor diagnosis and therapy. Hence, in the search for new A3AR ligands, a series of novel 2,N6-disubstituted adenosines (Ados) was synthesized and tested in radioligand binding and functional assays at ARs. Derivatives bearing a 2-phenethylamino group in the N6-position were found to exert higher A3AR affinity and selectivity than the corresponding N6-(2,2-diphenylethyl) analogues. 2-Chloro-N6-phenylethylAdo (15) was found to be a potent full A3AR agonist with a Ki of 0.024 nM and an EC50 of 14 nM, in a cAMP accumulation assay. Unlike 15, the other ligands behaved as A3AR antagonists, which concentration-dependently reduced cell growth and exerted cytostatic activity on the prostate cancer cell line PC3, showing comparable and even more pronounced effects with respect to the ones elicited by the reference full agonist Cl-IB-MECA. In particular, the N6-(2,2-diphenylethyl)-2-phenylethynylAdo (12: GI50 = 14 µM, TGI = 29 µM, and LC50 = 59 µM) showed the highest activity proving to be a potential antitumor agent. The cytostatic effect of both A3AR agonist (Cl-IB-MECA) and antagonists (12 and other newly synthesized compounds) confirm previous observations according to which, in addition to the involvement of A3ARs, other cellular mechanisms are responsible for the anticancer effects of these ligands.

Design and Synthesis of Novel Thiazolo[5,4-d]pyrimidine Derivatives with High Affinity for Both the Adenosine A1 and A2A Receptors, and Efficacy in Animal Models of Depression.

New compounds with a 7-amino-2-arylmethyl-thiazolo[5,4-d]pyrimidine structure were synthesized and evaluated in vitro for their affinity and/or potency at the human (h) A1, hA2A, hA2B, and hA3 adenosine receptors (ARs). Several compounds (5, 8-10, 13, 18, 19) were characterized by nanomolar and subnanomolar binding affinities for the hA1 and the hA2A AR, respectively. Results of molecular docking studies supported the in vitro results. The 2-(2-fluorobenzyl)-5-(furan-2yl)-thiazolo[5,4-d]pyrimidin-7-amine derivative 18 (hA1 Ki = 1.9 nM; hA2A Ki = 0.06 nM) was evaluated for its antidepressant-like activity in in vivo studies, the forced swimming test (FST), the tail suspension test (TST), and the sucrose preference test (SPT) in mice, showing an effect comparable to that of the reference amitriptyline.

Combined Therapy of A1AR Agonists and A2AAR Antagonists in Neuroinflammation.

Alzheimer's, Parkinson's, and multiple sclerosis are neurodegenerative diseases related by neuronal degeneration and death in specific areas of the central nervous system. These pathologies are associated with neuroinflammation, which is involved in disease progression, and halting this process represents a potential therapeutic strategy. Evidence suggests that microglia function is regulated by A1 and A2A adenosine receptors (AR), which are considered as neuroprotective and neurodegenerative receptors, respectively. The manuscript's aim is to elucidate the role of these receptors in neuroinflammation modulation through potent and selective A1AR agonists (N6-cyclopentyl-2'- or 3'-deoxyadenosine substituted or unsubstituted in 2 position) and A2AAR antagonists (9-ethyl-adenine substituted in 8 and/or in 2 position), synthesized in house, using N13 microglial cells. In addition, the combined therapy of A1AR agonists and A2AAR antagonists to modulate neuroinflammation was evaluated. Results showed that A1AR agonists were able, to varying degrees, to prevent the inflammatory effect induced by cytokine cocktail (tumor necrosis factor (TNF)-α, interleukin (IL)-1ß, and interferon (IFN)-γ), while A2AAR antagonists showed a good ability to counteract neuroinflammation. Moreover, the effect achieved by combining the two most effective compounds (1 and 6) in doses previously found to be non-effective was greater than the treatment effect of each of the two compounds used separately at maximal dose.

Efficacy of acetylcholinesterase inhibitors in Alzheimer's disease.

Alzheimer's disease (AD), the most common cause of adult-onset dementia is characterized by a progressive decline of cognitive functions accompanied by behavioral manifestations. The main class of drugs currently used for the treatment of AD are acetylcholinesterase/cholinesterase inhibitors (ChE-Is). The first ChE-I licensed for symptomatic treatment of AD was tacrine. The ChE-Is currently available in the market are donepezil, rivastigmine and galantamine as tacrine is no longer in use, due to its hepatotoxicity. According to mechanism of action the ChE-Is are classified as short-acting or reversible agents such as tacrine, donepezil, and galantamine, as intermediate-acting or pseudo-irreversible agent such as rivastigmine. Overall, the efficacy of the three ChE-Is available in the market is similar and the benefit of administration of these compounds is mild and may not be clinically significant. Due to gastrointestinal side effects of these drugs, medicinal chemistry and pharmaceutical delivery studies have investigated solutions to improve the pharmacological activity of these compounds. In spite of the limited activity of ChE-Is, waiting for more effective approaches, these drugs still represent a pharmacotherapeutic resource for the treatment of AD. Other approaches in which ChE-Is were investigated is in their use in combination with other classes of drugs such as cholinergic precursors, N-methyl-d-aspartate (NMDA) receptor antagonists and antioxidant agents. After many years from the introduction in therapy of ChE-Is, the combination with other classes of drugs may represent the chance for a renewed interest of ChE-Is in the treatment of adult-onset dementia disorders.

Acetylshikonin isolated from Lithospermum erythrorhizon roots inhibits dihydrofolate reductase and hampers autochthonous mammary carcinogenesis in Δ16HER2 transgenic mice.

Breast cancer (BC) is the most common cancer in women and, among different BC subtypes, triple negative (TN) and human epidermal growth factor receptor 2 (HER2)-positive BCs have the worst prognosis. In this study, we investigated the anticancer activity of the root ethanolic and hexane extracts from Lithospermum erythrorhizon, a traditional Chinese herbal medicine known also as tzu ts'ao or tzu-ken, against in vitro and in vivo models of TNBC and HER2-positive BC. Treatment with L. erythrorhizon root extracts resulted in a dose-dependent inhibition of BC cell viability and in a significant reduction of the growth of TNBC cells transplanted in syngeneic mice. Acetylshikonin, a naphthoquinone, was identified as the main bioactive component in extracts and was responsible for the observed antitumor activity, being able to decrease BC cell viability and to interfere with autochthonous mammary carcinogenesis in Δ16HER2 transgenic mice. Acetylshikonin anticancer effect depends on its ability to act as a potent inhibitor of dihydrofolate reductase (DHFR), to down-regulate key mediators governing cancer growth and progression, such as HER2, Src and STAT3, and to induce apoptosis by caspase-3 activation. The accumulation of acetylshikonin in blood samples as well as in brain, kidney, liver and tumor tissues was also investigated by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) highlighting that L. erythrorhizon treatment is effective in delivering the active compound into the target tissues. These results provide evidence that L. erythrorhizon extract and in particular its main component acetylshikonin are effective against aggressive BC subtypes and reveal new acetylshikonin mechanisms of action.

Adenosine Receptors as Neuroinflammation Modulators: Role of A1 Agonists and A2A Antagonists.

The pathological condition of neuroinflammation is caused by the activation of the neuroimmune cells astrocytes and microglia. The autacoid adenosine seems to be an important neuromodulator in this condition. Its main receptors involved in the neuroinflammation modulation are A1AR and A2AAR. Evidence suggests that A1AR activation produces a neuroprotective effect and A2AARs block prevents neuroinflammation. The aim of this work is to elucidate the effects of these receptors in neuroinflammation using the partial agonist 2'-dCCPA (2-chloro-N6-cyclopentyl-2'-deoxyadenosine) (C1 KiA1AR = 550 nM, KiA2AAR = 24,800 nM, and KiA3AR = 5560 nM, α = 0.70, EC50A1AR = 832 nM) and the newly synthesized in house compound 8-chloro-9-ethyl-2-phenethoxyadenine (C2 KiA2AAR = 0.75 nM; KiA1AR = 17 nM and KiA3AR = 227 nM, IC50A2AAR = 251 nM unpublished results). The experiments were performed in in vitro and in in vivo models of neuroinflammation. Results showed that C1 was able to prevent the inflammatory effect induced by cytokine cocktail (TNF-α, IL-1ß, and IFN-γ) while C2 possess both anti-inflammatory and antioxidant properties, counteracting both neuroinflammation in mixed glial cells and in an animal model of neuroinflammation. In conclusion, C2 is a potential candidate for neuroinflammation therapy.

Discovery of first-in-class multi-target adenosine A2A receptor antagonists-carbonic anhydrase IX and XII inhibitors. 8-Amino-6-aryl-2-phenyl-1,2,4-triazolo [4,3-a]pyrazin-3-one derivatives as new potential antitumor agents.

This paper describes identification of the first-in-class multi-target adenosine A2A receptor antagonists-carbonic anhydrase (CA) IX and XII inhibitors, as new potential antitumor agents. To obtain the multi-acting ligands, the 8-amino-2,6-diphenyltriazolo[4,3-a]pyrazin-3-one, a potent adenosine hA2A receptor (AR) antagonist, was taken as lead compound. To address activity against the tumor-associated CA isoforms, it was modified by introduction of different substituents (OH, COOH, CONHOH, SO2NH2) on the 6-phenyl ring or on a phenyl pendant connected to the former through different spacers. Among the new triazolopyrazines 1-23, the most active were those featuring the sulfonamide residue. Derivative 20, featuring a 4-sulfonamidophenyl residue attached through a CONH(CH2)2CONH spacer at the para-position of the 6-phenyl ring, showed the best combination of activity at the three targets. In fact, it inhibited both the tumor-associated hCA IX and XII isozymes at nanomolar concentration (Ki = 5.0 and 27.0 nM), and also displayed a quite good affinity for the hA2A AR (Ki = 108 nM). Compound 14, bearing the 4-sulfonamidophenyl residue linked at the para-position of the 6-phenyl ring by a CONH spacer, was remarkable because both its hA2A AR affinity and hCA XII inhibitory potency were in the low nanomolar range (Ki = 6.4 and 6.2 nM, respectively). Molecular docking studies highlighted the interaction mode of selected triazolopyrazines in the hA2A AR recognition pocket and in the active site of hCA II, IX and XII isoforms.

New 8-amino-1,2,4-triazolo[4,3-a]pyrazin-3-one derivatives. Evaluation of different moieties on the 6-aryl ring to obtain potent and selective human A2A adenosine receptor antagonists.

In this work, further structural investigations on the 8-amino-2-phenyl-6-aryl-1,2,4-triazolo[4,3-a]pyrazin-3-one series were carried out to achieve potent and selective human A2A adenosine receptor (AR) antagonists. Different ether and amide moieties were attached at the para-position of the 6-phenyl ring, thus leading to compounds 1-9 and 10-18, respectively. Most of these moieties contained terminal basic rings (pyrrolidine, morpholine, piperidine and substituted piperazines) which were thought to confer good physicochemical and drug-like properties. Compounds 11-16, bearing the amide linker, possessed high affinity and selectivity for the hA2A AR (Ki = 3.6-11.8 nM). Also derivatives 1-9, featuring an ether linker, preferentially targeted the hA2A AR but with lower affinity, compared to those of the relative amide compounds. Docking studies, carried out at the hA2A AR binding site, highlighted some crucial ligand-receptor interactions, particularly those provided by the appended substituent whose nature deeply affected hA2A AR affinity.

Outstanding insecticidal activity and sublethal effects of Carlina acaulis root essential oil on the housefly, Musca domestica, with insights on its toxicity on human cells.

Carlina acaulis (Compositae) is traditionally used for food and medicinal purposes in central and southern Europe. Its root essential oil (EO), mainly composed by carlina oxide, is included in the BELFRIT botanical list of food supplements. It is also recognized as a potent mosquito larvicide. It is matter of concern whether this EO could be endowed with intrinsic toxicity to limit its use on a food level. Focusing on the insecticidal activity of this EO, we investigated the acute toxicity and sublethal effects on Musca domestica. In topical assays, the EO was extremely effective (LD50 = 2.74 and 5.96 µg fly-1, on males and females, respectively). The exposure to a sublethal dose (LD30) led to significant reductions of female longevity (LT50 = 6.7-9.0 days vs. control LT50 = 12.9-13.7 days). Treated females laid 2.5 times fewer eggs over control ones. F1 vitality decreased: F1 larvae and pupae showed high mortality, 2-4-fold higher over the control. The EO also showed high cytotoxicity on normal human fibroblasts (NHF-A12, IC50 = 9.4-14.2 µg mL-1 after 6-48 h). Overall, our findings support the employ of this EO for developing botanical insecticides. At the same time, they encourage food safety authorities to perform a full toxicological assessment for possible restrictions at food level.

Structure-Based Optimization of Coumarin hA3 Adenosine Receptor Antagonists.

Adenosine receptors participate in many physiological functions. Molecules that may selectively interact with one of the receptors are favorable multifunctional chemical entities to treat or decelerate the evolution of different diseases. 3-Arylcoumarins have already been studied as neuroprotective agents by our group. Here, differently 8-substituted 3-arylcoumarins are complementarily studied as ligands of adenosine receptors, performing radioligand binding assays. Among the synthesized compounds, selective A3 receptor antagonists were found. 3-(4-Bromophenyl)-8-hydroxycoumarin (compound 4) displayed the highest potency and selectivity as A3 receptor antagonist (Ki = 258 nM). An analysis of its X-ray diffraction provided detailed information on its structure. Further evaluation of a selected series of compounds indicated that it is the nature and position of the substituents that determine their activity and selectivity. Theoretical modeling calculations corroborate and explain the experimental data, suggesting this novel scaffold can be involved in the generation of candidates as multitarget drugs.

Update on novel purinergic P2X3 and P2X2/3 receptor antagonists and their potential therapeutic applications.

Introduction: Purinergic P2X3-P2X2/3 receptors are placed in nociceptive neurons' strategic location and show unique desensitization properties; hence, they represent an attractive target for many pain-related diseases. Therefore, a broad interest from academic and pharmaceutical scientists has focused on the search for P2X3 and P2X2/3 receptor ligands and has led to the discovery of numerous new selective antagonists. Some of them have been studied in clinical trials for the treatment of pathological conditions such as bladder disorders, gastrointestinal and chronic obstructive pulmonary diseases.Areas covered: This review provides a summary of the patents concerning the discovery of P2X3 and/or P2X2/3 receptor antagonists published between 2015 and 2019 and their potential clinical use. Thus, the structures and biological data of the most representative molecules are reported.Expert opinion: The 2016 publication of the crystallographic structure of the human P2X3 receptor subtype gave an improvement of published patents in 2017. Hence, a great number of small molecules with dual antagonist activity on P2X3-P2X2/3 receptors, a favorable pharmacokinetic profile, and reasonable oral bioavailability was discovered. The most promising compounds are the phenoxy-diaminopyrimidines including gefapixant (AF-219), and the imidazo-pyridines like BLU-5937, which are in phase III and phase II clinical trials, respectively, for refractory chronic cough.

Non-Nucleoside Agonists of the Adenosine Receptors: An Overview.

Potent and selective adenosine receptor (AR) agonists are of pharmacological interest for the treatment of a wide range of diseases and conditions. Among these derivatives, nucleoside-based agonists represent the great majority of molecules developed and reported to date. However, the limited availability of compounds selective for a specific AR subtype (i.e., A2BAR) and a generally long and complex synthetic route for largely substituted nucleosides are the main drawbacks of this category of molecules. Non-nucleoside agonists represent an alternative set of compounds able to stimulate the AR function and based on simplified structures. This review provides an updated overview on the structural classes of non-nucleoside AR agonists and their biological activities, with emphasis on the main derivatives reported in the literature. A focus is also given to the synthetic routes employed to develop these derivatives and on molecular modeling studies simulating their interaction with ARs.

Antioxidant-Conjugated 1,2,4-Triazolo[4,3-a]pyrazin-3-one Derivatives: Highly Potent and Selective Human A2A Adenosine Receptor Antagonists Possessing Protective Efficacy in Neuropathic Pain.

New 8-amino-6-aryl-1,2,4-triazolo[4,3-a]pyrazin-3-ones were designed to obtain dual antioxidant-human A2A adenosine receptor (hA2A AR) antagonists. Two sets of compounds were synthesized, the first featuring phenol rings at the 6-position, the second bearing the lipoyl and 4-hydroxy-3,5-di-tertbut-benzoyl residues appended by different linkers on the 6-phenyl ring. Several new triazolopyrazines (1-21) were potent and selective hA2A AR antagonists (Ki = 0.17-54.5 nM). Compounds 11, 15, and 21, featuring antioxidant moieties, and compound 12, lacking the antioxidant functionality, reduced oxaliplatin-induced toxicity in microglia cells, the most active being the lipoyl-derivative 15 and the (4-hydroxy-3,5-di-tert-butyl)benzoyl-analogue 21 which were effective in reducing the oxygen free radical level. The lipoyl-derivative 15 was also able to revert oxaliplatin-induced neuropathy in the mouse. In vivo efficacy of 15 makes it a promising neuroprotective agent in oxidative stress-related diseases.

New A2A adenosine receptor antagonists: a structure-based upside-down interaction in the receptor cavity.

Adenosine receptor antagonists are generally based on heterocyclic core structures presenting substituents of various volumes and chemical-physical profiles. Adenine and purine-based adenosine receptor antagonists have been reported in literature. In this work we combined various substituents in the 2, 6, and 8-positions of 9-ethylpurine to depict a structure-affinity relationship analysis at the human adenosine receptors. Compounds were rationally designed trough molecular modeling analysis and then synthesized and evaluated at radioligand binding studies at human adenosine receptors. The new compounds showed affinity for the human adenosine receptors, with some derivatives endowed with low nanomolar Ki data, in particular at the A2AAR subtype. The purine core proves to be a versatile core structure for the development of novel adenosine receptor antagonists with nanomolar affinity for these membrane proteins.