High-throughput screening with a miniaturized radioligand competition assay identifies new modulators of human α2-adrenoceptors

Structural Insight into the Mechanism of 4-Aminoquinolines Selectivity for the alpha2A-Adrenoceptor

Background

α_2A-adrenoceptor (AR) is a potential target for the treatment of degenerative diseases of the central nervous system, and α_2A-AR agonists are effective drugs for this condition. However, the lack of high selectivity for α_2A-AR subtype of traditional drugs greatly limits their clinic usage.

Methods

A series of homobivalent 4-aminoquinolines conjugated by two 4-aminoquinoline moieties via varying alkane linker length (C2-C12) were characterized for their affinities for each α₂-AR subtype. Subsequently, docking, molecular dynamics and mutagenesis were applied to uncover the molecular mechanism.

Results

Most 4-aminoquinolines (4-aminoquinoline monomer, C2-C6, C8-C10) were selective for α_2A-AR over α_2B- and α_2C-ARs. Besides, the affinities are of similar linker length-dependence for each α₂-AR subtype. Among all the compounds tested, C10 has the highest affinity for α_2A-AR (pKi=−7.45±0.62), which is 12-fold and 60-fold selective over α_2B-AR and α_2C-AR, respectively. Docking and molecular dynamics suggest that C10 simultaneously interacts with orthosteric and “allosteric” sites of the α_2A-AR. The mutation of F205 decreases the affinity by 2-fold. The potential allosteric residues include S90, N93, E94 and W99.

Conclusion

The specificity of C10 for the α_2A-AR and the potential orthosteric and allosteric binding sites proposed in this study provide valuable guidance for the development of novel α_2A-AR subtype selective compounds.

Ergotamine and nicergoline - facts and myths

Ergotamine, being a representative of naturally occurring ergoline alkaloids, derived from d-lysergic acid, and nicergoline, a d-lumilysergic acid derivative belonging to semi-synthetic ergot-derived alkaloids, display diversified affinity for adrenergic, serotoninergic, and dopamine receptors. Although introduction of triptans marginalized use of ergotamine, nicergoline is used in cerebral metabolic-vascular disorders, and dementia. Additionally, nicergoline exhibits a safety profile comparable to that of placebo, and none of the reviewed studies reported any incidence of fibrosis or ergotism with nicergoline treatment. In line with the recent data, activation of 5-HT2B receptor by ergot derivatives i.e. ergotamine, methysergide, pergolide, and carbegoline is involved in pathogenesis of drug-induced valvulopathy. In contrary structurally related drugs - lisuride and terguride do not increase the risk of valvular heart disease. It seems, that more detailed mechanistic studies on nicergoline and ergotamine might be beneficial for determining structural requirements related to activation of G-protein as well as alternative signal transduction pathways e.g. β-arrestins or different kinases, and responsible for drug liabilities.

Fluorinated analogues of marsanidine, a highly α2-AR/imidazoline I1 binding site-selective hypotensive agent. Synthesis and biological activities

The aim of these studies was to establish the influence of fluorination of the indazole ring on the pharmacological properties of two selective α2-adrenoceptor (α2-AR) agonists: 1-[(imidazolidin-2-yl)imino]-1H-indazole (marsanidine, A) and its methylene analogue 1-[(4,5-dihydro-1H-imidazol-2-yl)methyl]-1H-indazole (B). Introduction of fluorine into the indazole ring of A and B reduced both binding affinity and α2-AR/I1 imidazoline binding site selectivity. The most α2-AR-selective ligands were 6-fluoro-1-[(imidazolidin-2-yl)imino]-1H-indazole (6c) and 7-fluoro-1-[(imidazolidin-2-yl)imino]-1H-indazole (6d). The in vivo cardiovascular properties of fluorinated derivatives of A and B revealed that in both cases the C-7 fluorination leads to compounds with the highest hypotensive and bradycardic activities. The α2-AR partial agonist 6c was prepared as a potential lead compound for development of a radiotracer for PET imaging of brain α2-ARs.

A novel aptamer-based competition strategy for ultrasensitive electrochemical detection of leukemia cells

A robust, nanobiotechnology-based electrochemical cytosensing platform for the detection of acute leukemia cells was developed with high sensitivity, selectivity, acceptable rapidity and excellent extensibility. It utilized the competitive binding of cell-specific aptamers to acute leukemia cells and subsequent voltammetric quantification of the metal signature. Greatly enhanced sensitivity was achieved with dual signal amplification by using Fe3O4 magnetic nanoparticles (MNPs) as carriers to load a large amount of gold nanoparticles (AuNPs) and AuNP-catalyzed silver deposition. The proposed competitive cytosensor showed high sensitivity with a detection limit down to 10 cells. This simple and low-cost electrochemical cytosensing approach offers great promise to extend its application to early detection of human leukemia and possibly to other cancer cells.