Molecular exploration of the α1A-adrenoceptor orthosteric site: Binding site definition for epinephrine, HEAT and prazosin

Structural basis of α1A-adrenergic receptor activation and recognition by an extracellular nanobody

The α_1A-adrenergic receptor (α_1AAR) belongs to the family of G protein-coupled receptors that respond to adrenaline and noradrenaline. α_1AAR is involved in smooth muscle contraction and cognitive function. Here, we present three cryo-electron microscopy structures of human α_1AAR bound to the endogenous agonist noradrenaline, its selective agonist oxymetazoline, and the antagonist tamsulosin, with resolutions range from 2.9 Å to 3.5 Å. Our active and inactive α_1AAR structures reveal the activation mechanism and distinct ligand binding modes for noradrenaline compared with other adrenergic receptor subtypes. In addition, we identified a nanobody that preferentially binds to the extracellular vestibule of α_1AAR when bound to the selective agonist oxymetazoline. These results should facilitate the design of more selective therapeutic drugs targeting both orthosteric and allosteric sites in this receptor family.

Structural and Functional Diversity of Animal Toxins Interacting With GPCRs

Peptide toxins from venoms have undergone a long evolutionary process allowing host defense or prey capture and making them highly selective and potent for their target. This has resulted in the emergence of a large panel of toxins from a wide diversity of species, with varied structures and multiple associated biological functions. In this way, animal toxins constitute an inexhaustible reservoir of druggable molecules due to their interesting pharmacological properties. One of the most interesting classes of therapeutic targets is the G-protein coupled receptors (GPCRs). GPCRs represent the largest family of membrane receptors in mammals with approximately 800 different members. They are involved in almost all biological functions and are the target of almost 30% of drugs currently on the market. Given the interest of GPCRs in the therapeutic field, the study of toxins that can interact with and modulate their activity with the purpose of drug development is of particular importance. The present review focuses on toxins targeting GPCRs, including peptide-interacting receptors or aminergic receptors, with a particular focus on structural aspects and, when relevant, on potential medical applications. The toxins described here exhibit a great diversity in size, from 10 to 80 amino acids long, in disulfide bridges, from none to five, and belong to a large panel of structural scaffolds. Particular toxin structures developed here include inhibitory cystine knot (ICK), three-finger fold, and Kunitz-type toxins. We summarize current knowledge on the structural and functional diversity of toxins interacting with GPCRs, concerning first the agonist-mimicking toxins that act as endogenous agonists targeting the corresponding receptor, and second the toxins that differ structurally from natural agonists and which display agonist, antagonist, or allosteric properties.

INPHARMA-Based Determination of Ligand Binding Modes at α1 -Adrenergic Receptors Explains the Molecular Basis of Subtype Selectivity

The structural poses of ligands that bind weakly to protein receptors are challenging to define. In this work we have studied ligand interactions with the adrenoreceptor (AR) subtypes, α_1A -AR and α_1B -AR, which belong to the G protein-coupled receptor (GPCR) superfamily, by employing the solution-based ligand-observed NMR method interligand NOEs for pharmacophore mapping (INPHARMA). A lack of receptor crystal structures and of subtype-selective drugs has hindered the definition of the physiological roles of each subtype and limited drug development. We determined the binding pose of the weakly binding α_1A -AR-selective agonist A-61603 relative to an endogenous agonist, epinephrine, at both α_1A -AR and α_1B -AR. The NMR experimental data were quantitatively compared, by using SpINPHARMA, to the back-calculated spectra based on ligand poses obtained from all-atom molecular dynamics simulations. The results helped mechanistically explain the selectivity of (R)-A-61603 towards α_1A -AR, thus demonstrating an approach for targeting subtype selectivity in ARs.

Synthesis, Molecular Modeling of Novel Substituted Pyridazinones and their Vasorelaxant Activities

BACKGROUND

Hypertension, one of the most common cardiovascular diseases that can cause coronary disease, stroke, myocardial infarction, and sudden death, it is the major contributor to cardiac failure as well as renal insufficiency.

OBJECTIVES

As there are many cardio-active pyridazinone-base derivatives in clinical use, therefore, we aimed to synthesize a new series of pyridazin-3-ones and evaluate their vasorelaxant activity.

METHODS

A new series of synthesized compounds were carried out first by the synthesis of 6- flouroarylpyridazinones by cyclization of 3-(4-flourobenzoyl) propionic acid with hydrazine hydrate or arylhydrazines to provide the corresponding pyridazinone derivatives 2a-d. Mannich reaction was performed using morpholine or piperidine formaldehyde to obtain compounds 3a,b. On the other hand, reaction of 2a with various chloroacetamide intermediates, in dimethylformamide and potassium carbonate as a catalyst, afforded the target compounds 5a-c. The aromatic acid hydrazide intermediates 6a-g were prepared in 50-90% yield, by reacting to the prepared esters with hydrazine hydrate under reflux in ethanol. The two compounds 8a,b were prepared via condensation of 7a,b with ethyl chloroacetate in dry acetone. Finally, the target 2,4,6-trisubstituted pyridazinones 9a-c derivatives were obtained by the reaction of 7a with the appropriate aromatic aldehyde or substituted acetophenones. The new compounds were then evaluated for their vasorelaxant properties using isolated thoracic rat aortic rings. In addition, a homology model was built and molecular modeling simulation of these compounds into the active sites of the newly created α1a-adrenoceptor model was performed in order to predict and rationalize their affinities toward this receptor.

RESULTS

Among these compounds; 5a was the most potent, it exhibited approximately two-times the activity of prazosin (IC50 = 0.250, 0.487 mmol, respectively) also, fourteen compounds were more potent than prazosin.

The (R)-enantiomer of the 6-chromanol derivate SUL-121 improves renal graft perfusion via antagonism of the α1-adrenoceptor

SUL-compounds are protectants from cold-induced ischemia and mitochondrial dysfunction. We discovered that adding SUL-121 to renal grafts during warm machine reperfusion elicits a rapid improvement in perfusion parameters. Therefore, we investigate the molecular mechanisms of action in porcine intrarenal arteries (PIRA). Porcine kidneys were stored on ice overnight and perfusion parameters were recorded during treatment with SUL-compounds. Agonist-induced vasoconstriction was measured in isolated PIRA after pre-incubation with SUL-compounds. Receptor binding and calcium transients were assessed in α₁-adrenoceptor (α₁-AR) transgenic CHO cells. Molecular docking simulation was performed using Schrödinger software. Renal pressure during warm reperfusion was reduced by SUL-121 (−11.9 ± 2.50 mmHg) and its (R)-enantiomer SUL-150 (−13.2 ± 2.77 mmHg), but not by the (S)-enantiomer SUL-151 (−1.33 ± 1.26 mmHg). Additionally, SUL-150 improved renal flow (16.21 ± 1.71 mL/min to 21.94 ± 1.38 mL/min). SUL-121 and SUL-150 competitively inhibited PIRA contraction responses to phenylephrine, while other 6-chromanols were without effect. SUL-150 similarly inhibited phenylephrine-induced calcium influx and effectively displaced [7-Methoxy-³H]-prazosin in CHO cells. Docking simulation to the α₁-AR revealed shared binding characteristics between prazosin and SUL-150. SUL-150 is a novel α₁-AR antagonist with the potential to improve renal graft perfusion after hypothermic storage. In combination with previously reported protective effects, SUL-150 emerges as a novel protectant in organ transplantation.

Template selection and refinement considerations for modelling aminergic GPCR-ligand complexes

G protein-coupled receptors (GPCRs) are important targets for development of drugs for the treatment of many diseases. However, crystal structures are available for only a small fraction of these membrane bound proteins. Accurate homology models will provide opportunities for effective drug design targeting GPCRs. Recently, several serotonin receptor crystal structures were solved and needed to be evaluated as potential templates. In the first part of this work different measures of similarity in template selection were explored and methods for homology modelling, docking and refinement of aminergic GPCR-ligand complexes were developed and evaluated by comparing models of the D₃-R/eticlopride complex with the crystal structure. Homology models of the three α₁ adrenergic receptor subtypes and of a serotonin receptor subtype were then constructed using these methods These models were evaluated by docking a range of antagonists into them.

Synthesis and structure-activity relationships of novel arylpiperazines as potent antagonists of α1-adrenoceptor

Arylpiperazines 2-11 were synthesized, and their biological profiles at α1-adrenergic receptors (α1-ARs) assessed by binding assays in CHO cells expressing human cloned subtypes and by functional experiments in isolated rat vas deferens (α1A), spleen (α1B), and aorta (α1D). Modifications at the 1,3-benzodioxole and phenyl phamacophoric units resulted in the identification of a number of potent compounds (moderately selective with respect to the α1b-AR), in binding experiments. Notably, compound 7 (LDT451) showed a subnanomolar pKi of 9.41 towards α1a-AR. An encouragingly lower α1B-potency was a general trend for all the series of compounds, which showed α1A/D over α1B selectivity in functional assays. If adequately optimized, such peculiar selectivity could have relevance for a potential LUTS/BPH therapeutic application.

Insights into a defined secondary binding region on β-adrenoceptors and putative roles in ligand binding and drug design

Putative roles of a secondary binding region shared among beta-adrenoceptors.