Structure-Activity Analysis of Biased Agonism at the Human Adenosine A 3 Receptor s

ABSTRACT Biased agonism at G protein-coupled receptors (GPCRs) has significant implications for current drug discovery, but molecular determinants that govern ligand bias remain largely unknown. The adenosine A 3 GPCR (A 3 AR) is a potential therapeutic target for various conditions, including cancer, inflammation, and ischemia, but for which biased agonism remains largely unexplored. We now report the generation of bias "fingerprints" for prototypical ribose containing A 3 AR agonists and rigidified (N)-methanocarba 59-N-methyluronamide nucleoside derivatives with regard to their ability to mediate different signaling pathways. Relative to the reference prototypical agonist IB-MECA, (N)-methanocarba 59-Nmethyluronamide nucleoside derivatives with significant N 6 or C2 modifications, including elongated aryl-ethynyl groups, exhibited biased agonism. Significant positive correlation was observed between the C2 substituent length (in Å) and bias toward cell survival. Molecular modeling suggests that extended C2 substituents on (N)-methanocarba 59-N-methyluronamide nucleosides promote a progressive outward shift of the A 3 AR transmembrane domain 2, which may contribute to the subset of A 3 AR conformations stabilized on biased agonist binding

Designing adenosine receptors antagonists using an in silico approach

The neuromodulator adenosine affects a wide variety of physiopathological processes through activation of four receptors, classified as A1, A2A, A2B, and A3 subtypes. Adenosine receptors (ARs) belong to family A of G protein-coupled receptors (GPCRs) and are ubiquitously expressed in the human body. Activation or blockade of ARs is responsible for a wide range of effects in numerous organ systems; and therefore the regulation of ARs can have many potential therapeutic applications. The main objective of this project has been the investigation of the in silico molecular pharmacology of adenosine receptors and, in particular, of the human A2A and A3 adenosine receptors to guide the discovery and the structural refinement of new potent and selective AR antagonists. The recently published crystal structures of the human A2A adenosine receptor (hA2AAR) provide detailed three-dimensional information useful to support homology modeling studies and receptor-based drug design approaches. In particular, the 2.6 Å crystallographic structure of the hA2AAR in complex with the potent and selective antagonist ZM241385 was used as template to build a homology model of the hA3AR. In order to validate the molecular docking protocols for the adenosine receptors family, the hA2AAR crystal structure was used to perform in parallel molecular docking studies using different docking software. Then RMSD values between predicted and crystallographic poses of ZM241385 were calculated to select the docking protocol able to better reproduce this molecular system and to be used in the following molecular docking studies. Subsequently, molecular docking studies of different ARs antagonists were performed at the hA3AR model and at the hA2AAR crystal structure, enabling the exploration of the potential effects of chemical modifications of these compounds, and thus facilitating the lead optimization process. Different series of new compounds belonging to known adenosine antagonists classes, including triazolo-triazines and pyrazolo-triazolo-pyrimidines, have been analyzed and modified with the aim to modulate their affinity towards different adenosine receptor subtypes, to increase their solubility, or to overcome their metabolic instability. Moreover, several compounds with simplified scaffolds have been proposed as new adenosine receptor antagonists; such as pyrazolo-pyrimidinones, phthalazinones and triazolo-pyrimidines. Finally, the knowledge gained through the docking studies led to the identification of structural features of antagonist compounds important for the interaction with the hA3AR and was applied to the design of fluorescent ligands for this subtype, of particular interest as pharmacological probes. In conclusion, the integration of in silico studies with synthetic work and pharmacological tests resulted to be a good strategy for the development of new compounds as adenosine receptors antagonists and led to a better understanding at the molecular level of this class of GPCRs.L’adenosina è un neuromodulatore che regola molti processi fisiopatologici attraverso l’attivazione di quattro diversi recettori accoppiati a proteine G (GPCRs), classificati come sottotipi A1, A2A, A2B e A3. I recettori adenosinici sono ubiquitari nell’organismo umano e la loro attivazione è responsabile di numerosi effetti in diversi organi. Proprio per questo motivo la regolazione dell’attività di questi recettori può avere interessanti applicazioni terapeutiche. Il principale obiettivo di questo progetto è stato l’analisi in silico a livello molecolare dei recettori adenosinici, ed in particolare dei recettori adenosinici umani A2A e A3, per guidare la scoperta e l’ottimizzazione strutturale di nuovi antagonisti adenosinici potenti e selettivi. Le strutture cristallografiche del recettore adenosinico umano A2A, recentemente pubblicate, forniscono dettagliate informazioni strutturali utili per supportare studi di homology modeling e approcci di drug design di tipo structure-based. In particolare, la struttura cristallografica del recettore adenosinico umano A2A, in complesso con l’antagonista potente e selettivo ZM241385, è stata utilizzata come templato per la costruzione di un modello per omologia del recettore adenosinico umano A3. Inoltre, con l’intento di selezionare il protocollo di docking molecolare più adatto per la famiglia dei recettori adenosinici, la struttura cristallografica del recettore adenosinico A2A è stata utilizzata per effettuare simulazioni di docking con diversi softwares in parallelo. Successivamente, le conformazioni ottenute dal docking sono state confrontate con la pose cristallografica di ZM241385 per selezionare il protocollo di docking che fosse in grado di riprodurre al meglio questo sistema molecolare e che potesse quindi essere usato per i successivi studi di docking. Sono stati quindi effettuati studi di docking molecolare di vari antagonisti adenosinici sul modello del recettore A3 e sulla struttura cristallografica del recettore A2A, in modo da ricavare informazioni che potessero facilitare il processo di ottimizzazione dei composti. Sono stati infatti analizzati numerosi nuovi composti appartenenti a classi note di antagonisti adenosinici, tra cui composti triazolotriazinici e tirazolotriazolopirimidinici, in modo da suggerire modifiche strutturali in grado di modularne l’affinità nei confronti dei vari sottotipi recettoriali adenosinici, di aumentarne la solubilità o di superarne i punti di instabilità metabolica. Diversi derivati con strutture semplificate, come per esempio composti pirazolopirimidinonici, ftalazinonici e triazolotriazinici, sono stati inoltre proposti come nuovi composti con attività antagonista nei confronti dei recettori adenosinici. Le informazioni ricavate grazie agli studi di docking hanno permesso l’identificazione di caratteristiche strutturali degli antagonisti adenosinici fondamentali per l’interazione con questi recettori. Queste informazioni sono state quindi applicate alla progettazione di derivati fluorescenti per il recettore adenosinico A3, che risultano particolarmente interessanti per il loro potenziale utilizzo in saggi farmacologici. In conclusione, quindi, questo studio sui recettori adenosinici dimostra come l’integrazione di metodologie computazionali con il lavoro sintetico e farmacologico risulta essere una strategia efficace per lo sviluppo di nuovi ligandi dei recettori adenosinici, a potenziale interesse terapeutico, e per il chiarimento di importanti aspetti strutturali riguardanti questa famiglia recettoriale e più in generale tutti i GPCRs

Structural Investigations on a Novel Class of [1,2,4]Triazolo[1,5-c]pyrimidines as Adenosine Receptor Antagonists.

Adenosine receptors (ARs) are members of the superfamily of G protein-coupled receptors (GPCRs). There are four subtypes currently recognized: the A1AR, A2AAR, A2BAR and A3AR. The classical AR antagonist caffeine is the most consumed drug in the world. Its effects on the nervous system, such as enhancement of awareness and learning, have encouraged the investigation of selective AR antagonists for the treatment of various nervous system conditions. (1) Several classes of heterocyclic derivatives have been reported as AR antagonists with high levels of both affinity and selectivity. (2) The [1,2,4]-triazolo[1,5-c]pyrimidine nucleus possesses a low molecular weight and four nitrogen atoms, thus it may be a scaffold with promising pharmacokinetics properties. We have investigated substitutions at the 2, 5 and 8 positions, with the aim of obtaining potent antagonists selective only for one of the four adenosine receptor subtypes. A receptor-driven molecular modeling investigation has been carried out in order to support the experimental binding data and to justify the selectivity against the other receptor subtypes. (1) Moro, S.; Gao, Z.G.; Jacobson, K.A.; Spalluto, G. Med. Res. Rev. 2006, 26, 131-159. (2) Muller, C.E.; Jacobson, K.A. Biochim. Biophys. Acta. 2011, 1808, 1290\u2013130

Structural Probing of Off-Target G Protein-Coupled Receptor Activities within a Series of Adenosine/Adenine Congeners

<div><p>We studied patterns of off-target receptor interactions, mostly at G protein-coupled receptors (GPCRs) in the µM range, of nucleoside derivatives that are highly engineered for nM interaction with adenosine receptors (ARs). Because of the considerable interest of using AR ligands for treating diseases of the CNS, we used the Psychoactive Drug Screening Program (PDSP) for probing promiscuity of these adenosine/adenine congeners at 41 diverse receptors, channels and a transporter. The step-wise truncation of rigidified, trisubstituted (at N⁶, C2, and 5′ positions) nucleosides revealed unanticipated interactions mainly with biogenic amine receptors, such as adrenergic receptors and serotonergic receptors, with affinities as high as 61 nM. The unmasking of consistent sets of structure activity relationship (SAR) at novel sites suggested similarities between receptor families in molecular recognition. Extensive molecular modeling of the GPCRs affected suggested binding modes of the ligands that supported the patterns of SAR at individual receptors. In some cases, the ligand docking mode closely resembled AR binding and in other cases the ligand assumed different orientations. The recognition patterns for different GPCRs were clustered according to which substituent groups were tolerated and explained in light of the complementarity with the receptor binding site. Thus, some likely off-target interactions, a concern for secondary drug effects, can be predicted for analogues of this set of substructures, aiding the design of additional structural analogues that either eliminate or accentuate certain off-target activities. Moreover, similar analyses could be performed for unrelated structural families for other GPCRs.</p></div

Bone fragility during the COVID-19 pandemic: the role of macro- and micronutrients

Bone fragility is the susceptibility to fracture due to poor bone strength. This condition is usually associated with aging, comorbidities, disability, poor quality of life, and increased mortality. International guidelines for the management of patients with bone fragility include a nutritional approach, mainly aiming at optimal protein, calcium, and vitamin D intakes. Several biomechanical features of the skeleton, such as bone mineral density (BMD), trabecular and cortical microarchitecture, seem to be positively influenced by micro- and macronutrient intake. Patients with major fragility fractures are usually poor consumers of dairy products, fruit, and vegetables as well as of nutrients modulating gut microbiota. The COVID-19 pandemic has further aggravated the health status of patients with skeletal fragility, also in terms of unhealthy dietary patterns that might adversely affect bone health. In this narrative review, we discuss the role of macro- and micronutrients in patients with bone fragility during the COVID-19 pandemic

L'Auto-vélo : automobilisme, cyclisme, athlétisme, yachting, aérostation, escrime, hippisme / dir. Henri Desgranges

25 mars 19121912/03/25 (A13,N4179)

Simplification of Pyrazolo-triazolo-pyrimidine Nucleus for Searching New Adenosine Receptor Antagonists.

Blockade of adenosine receptors (ARs) lead to a broad variety of effects in several organ systems permitting to consider antagonists for ARs as potential therapeutic targets. Several classes of heterocyclic derivatives have been reported as ARs antagonists with high levels of both affinity and selectivity. [1] In particular, in the last years, the nucleus of pyrazolo-triazolo-pyrimidines as ARs antagonists was deeply investigated. Modulating the substitution at the N5, N7 and N8 positions potent and selective A2A (1) and A3 (2) ARs antagonists have been synthesized.[2,3] Nevertheless this class of compounds, such as other tricyclic structures, showed several problems such as poor water solubility and most importantly tangled synthetic preparation. On these bases we tried to simplify the nucleus in order to avoid the problems related to this structure. In particular we developed triazolo-triazines [4], triazolopyrimidines and the extremely basic arylstyrenes derivatives. All the obtained results will be summarized

Docking at 5HT₇ serotonergic receptor.

<p>Hypothetical binding mode of compounds <b>4</b> (green carbons) and <b>7</b> (pale pink carbons) at a homology model of the h5HT₇ serotonergic receptor based on the h5HT_1B receptor structure. Ligands are shown in ball and stick, and some residues important for ligand recognition are shown in stick (gray carbons). Hydrogen atoms are not displayed. H-bonds are shown as black dashed lines. The Connolly surface of the amino acids surrounding the binding site is displayed. Surface color indicates the lipophilic potential: lipophilic regions (green), neutral regions (white) and hydrophilic regions (magenta).</p

Docking at α adrenergic receptors.

<p>Hypothetical binding modes of selected compounds at homology models of the hα_2B and hα_2C adrenergic receptors based on the h5HT_1B receptor structure. (A) Compounds <b>8</b> (yellow carbons) and <b>9</b> (cyan carbons) at the α_2B receptor. (B) Compounds <b>1</b> (orange carbons), <b>8</b> (yellow carbons) and <b>9</b> (cyan carbons) at the α_2C receptor. Ligands are show in ball and stick and some residues important for ligand recognition are shown in stick (gray carbons). Hydrogen atoms are not displayed. H-bonds are shown as black dashed lines. The Connolly surface of the amino acids surrounding the binding site is displayed. Surface color indicates the lipophilic potential: lipophilic regions (green), neutral regions (white) and hydrophilic regions (magenta).</p