ABSTRACT
Serotonin 5-HT6 receptor has been proposed as a promising therapeutic target for cognition enhancement though the development of new antagonists is still needed to validate these molecules as a drug class for the treatment of Alzheimer's disease and other pathologies associated with memory deficiency. As part of our efforts to target the 5-HT6 receptor, new benzimidazole-based compounds have been designed and synthesized. Site-directed mutagenesis and homology models show the importance of a halogen bond interaction between a chlorine atom of the new class of 5-HT6 receptor antagonists identified herein and a backbone carbonyl group in transmembrane domain 4. In vitro pharmacological characterization of 5-HT6 receptor antagonist 7 indicates high affinity and selectivity over a panel of receptors including 5-HT2B subtype and hERG channel, which suggests no major cardiac issues. Compound 7 exhibited in vivo procognitive activity (1 mg/kg, ip) in the novel object recognition task as a model of memory deficit.
Subject(s)
Cognition/drug effects , Halogens/chemistry , Receptors, Serotonin/metabolism , Serotonin Antagonists/pharmacology , Animals , Benzimidazoles/chemical synthesis , Benzimidazoles/chemistry , Benzimidazoles/pharmacology , Humans , Ligands , Microsomes, Liver/metabolism , Mutagenesis, Site-Directed , Rats , Receptors, Serotonin/chemistry , Serotonin Antagonists/chemical synthesis , Serotonin Antagonists/chemistry , Structural Homology, Protein , Task Performance and AnalysisABSTRACT
The finding that ergotamine binds serotonin receptors in a less conserved extended binding pocket close to the extracellular entrance, in addition to the orthosteric site, allowed us to obtain 5-HT7R antagonist 6 endowed with high affinity (Ki=0.7 nM) and significant 5-HT1AR selectivity (ratio>1428). Compound 6 exhibits in vivo antidepressant-like effect (1 mg/kg, ip) mediated by the 5-HT7R, which reveals its interest as a putative research tool or pharmaceutical in depression disorders.
Subject(s)
Antidepressive Agents/chemistry , Indoles/chemistry , Isoquinolines/chemistry , Receptors, Serotonin/metabolism , Serotonin Antagonists/chemistry , Animals , Antidepressive Agents/chemical synthesis , Antidepressive Agents/pharmacology , Body Temperature/drug effects , Female , Hypothermia/chemically induced , Indoles/chemical synthesis , Indoles/pharmacology , Isoquinolines/chemical synthesis , Isoquinolines/pharmacology , Male , Mice, Inbred C57BL , Molecular Dynamics Simulation , Motor Activity/drug effects , Serotonin Antagonists/chemical synthesis , Serotonin Antagonists/pharmacology , Stereoisomerism , Structure-Activity RelationshipABSTRACT
On the basis of our previously described pharmacophore model for serotonin 5-HT(6) receptor (5-HT(6)R) antagonists, we have designed, synthesized, and pharmacologically characterized a series of benzimidazole derivatives 1-20 that represent a new family of potent antagonists at the human 5-HT(6)R. Site-directed mutagenesis and a beta(2)-adrenoceptor-based homology model of the 5-HT(6)R were used to predict the mode of binding of antagonist SB-258585 and the new synthesized ligands. Substitution of W6.48, F6.52, or N6.55 by Ala fully impedes compound 4 to block 5-HT-induced activation. Thus, we propose that D3.32 in TM 3 anchors the protonated piperazine ring, the benzimidazole ring expands parallel to EL 2 to hydrogen bond N6.55 in TM 6, and the aromatic ring is placed between TMs 3 and 5 in CH(2)-containing compounds and between TMs 3 and 6 in CO-containing compounds. This combined experimental and computational study has permitted to propose the molecular mechanisms by which the new benzimidazole derivatives act as 5-HT(6)R antagonists.
Subject(s)
Benzimidazoles/chemistry , Benzimidazoles/pharmacology , Receptors, Serotonin/chemistry , Receptors, Serotonin/metabolism , Serotonin Antagonists/chemical synthesis , Animals , Benzimidazoles/chemical synthesis , Binding, Competitive , COS Cells , Cells, Cultured , Chlorocebus aethiops , Computer Simulation , Cyclic AMP/metabolism , Enzyme-Linked Immunosorbent Assay , Humans , Kidney/cytology , Kidney/drug effects , Molecular Structure , Mutagenesis, Site-Directed , Protein Conformation , Radioligand Assay , Receptors, Serotonin/genetics , Serotonin Antagonists/chemistry , Serotonin Antagonists/pharmacology , Structure-Activity RelationshipABSTRACT
Forty-five structurally diverse 5-hydroxytryptamine(6) receptor (5-HT(6)R) antagonists were selected to develop a 3D pharmacophore model with the Catalyst software. The structural features for antagonism at this receptor are a positive ionizable atom interacting with Asp(3.32), a hydrogen bond acceptor group interacting with Ser(5.43) and Asn(6.55), a hydrophobic site interacting with residues in a hydrophobic pocket between transmembranes 3, 4, and 5, and an aromatic-ring hydrophobic site interacting with Phe(6.52).
