Homobivalent Ligands Research Articles

Homobivalent Dopamine D2 Receptor Ligands Modulate the Dynamic Equilibrium of D2 Monomers and Homo- and Heterodimers.

Dopamine D2 receptors (D2Rs) are major targets in the treatment of psychiatric and neurodegenerative diseases. As with many other G protein-coupled receptors (GPCRs), D2Rs interact within the cellular membrane, leading to a transient receptor homo- or heterodimerization. These interactions are known to alter ligand binding, signaling, and receptor trafficking. Bivalent ligands are ideally suited to target GPCR dimers and are composed of two pharmacophores connected by a spacer element. If properly designed, bivalent ligands are able to engange the two orthosteric binding sites of a GPCR dimer simultaneously. Taking advantage of previously developed ligands for heterodimers of D2R and the neurotensin receptor 1 (NTSR1), we synthesized homobivalent ligands targeting D2R. Employing bioluminescence resonance energy transfer, we found that the bivalent ligands 3b and 4b comprising a 92-atom spacer are able to foster D2R-homodimerization while simultaneously reducing interactions of D2R with NTSR1. Both receptors are coexpressed in the central nervous system and involved in important physiological processes. The newly developed bivalent ligands are excellent tools to further understand the pharmacological consequences of D2R homo- and heterodimerization. Not limited to the dopaminergic system, modifying class A GPCRs' dynamic equilibrium between monomers, homomers, and heteromers with bivalent ligands may represent a novel pharmacological concept paving the way toward innovative drugs.

Distance-Dependent Cellular Uptake of Oligoproline-Based Homobivalent Ligands Targeting GPCRs-An Experimental and Computational Analysis.

Tumor targeting with bivalent radiolabeled ligands for GPCRs is an attractive means for cancer imaging and therapy. Here, we studied and compared the distance dependence of homobivalent ligands for the human gastrin-releasing peptide receptor (hGRP-R) and the somatostatin receptor subtype II (hSstR2a). Oligoprolines were utilized as molecular scaffolds to enable distances of 10, 20, or 30 Å between two identical, agonistic recognition motifs. In vitro internalization assays revealed that ligands with a distance of 20 Å between the recognition motifs exhibit the highest cellular uptake in both ligand series. Structural modeling and molecular dynamics simulations support an optimal distance of 20 Å for accommodating ligand binding to both binding sites of a GPCR dimer. Translation of these findings to the significantly higher complexity in vivo proved difficult and showed only for the hGRP-R increased tumor uptake of the bivalent ligand.

Novel Bivalent 5-HT2A Receptor Antagonists Exhibit High Affinity and Potency in Vitro and Efficacy in Vivo.

The 5-HT2A receptor (5-HT2AR) plays an important role in various neuropsychiatric disorders, including substance use disorder and schizophrenia. Homodimerization of this receptor has been suggested, but tools that allow direct assessment of the relevance of the 5-HT2AR:5-HT2AR homodimer in these disorders are necessary. We chemically modified the selective 5-HT2AR antagonist M100907 to synthesize a series of homobivalent ligands connected by ethylene glycol linkers of varying lengths that may be useful tools for probing 5-HT2AR:5-HT2AR homodimer function. We tested these molecules for 5-HT2AR antagonist activity in a cell line stably expressing the functional 5-HT2AR and quantified a downstream signaling target, activation (phosphorylation) of extracellular regulated kinases 1/2 (ERK1/2), in comparison to in vivo efficacy of altering spontaneous or cocaine-evoked locomotor activity in rats. All of the synthetic compounds inhibited 5-HT-mediated phosphorylation of ERK1/2 in the cellular signaling assay; the potency of the bivalent ligands varied as a function of linker length, with the intermediate linker lengths being the most potent. The Ki values for the binding of bivalent ligands to 5-HT2AR were only slightly lower than the values for the parent (+)-M100907 compound, but significant selectivity for 5-HT2AR over 5-HT2BR or 5-HT2CR binding was retained. In addition, the 11-atom-linked bivalent 5-HT2AR antagonist (2 mg/kg, intraperitoneally) demonstrated efficacy on par with that of (+)-M100907 in inhibiting cocaine-evoked hyperactivity. As we develop further strategies for ligand-evoked receptor assembly and analyses of diverse signaling and functional roles, these novel homobivalent 5-HT2AR antagonist ligands will serve as useful in vitro and in vivo probes of 5-HT2AR structure and function.

Synthesis and biological evaluation of bivalent cannabinoid receptor ligands based on hCB2R selective benzimidazoles reveal unexpected intrinsic properties

The design of bivalent ligands targeting G protein-coupled receptors (GPCRs) often leads to the development of new, highly selective and potent compounds. To date, no bivalent ligands for the human cannabinoid receptor type 2 (hCB2R) of the endocannabinoid system (ECS) are described. Therefore, two sets of homobivalent ligands containing as parent structure the hCB2R selective agonist 13a and coupled at different attachment positions were synthesized. Changes of the parent structure at these positions have a crucial effect on the potency and efficacy of the ligands. However, we discovered that bivalency has an influence on the effect at both cannabinoid receptors. Moreover, we found out that the spacer length and the attachment position altered the efficacy of the bivalent ligands at the receptors by turning agonists into antagonists and inverse agonists.

Investigation of novel ropinirole analogues: synthesis, pharmacological evaluation and computational analysis of dopamine D2 receptor functionalized congeners and homobivalent ligands

This study includes the synthesis, pharmacological evaluation and molecular modeling study of novel ropinirole-based monovalent and homobivalent ligands.

Synthesis, functional and binding profile of (R)-apomorphine based homobivalent ligands targeting the dopamine D2 receptor

Bivalent ligands represent useful tools to investigate the phenomenon of GPCR dimerization. We synthesized bivalent ligands based on (R)-apomorphine with variations in spacer length, and assessed these compounds in functional and binding assays at the dopamine D2 receptor. The results present novel SAR for bivalent ligands targeting the D2R, and identify a relationship for spacer length with ligand potency, efficacy and affinity.

Homobivalent Ligands of the Atypical Antipsychotic Clozapine: Design, Synthesis, and Pharmacological Evaluation

To date all typical and atypical antipsychotics target the dopamine D(2) receptor. Clozapine represents the best-characterized atypical antipsychotic, although it displays only moderate (submicromolar) affinity for the dopamine D(2) receptor. Herein, we present the design, synthesis, and pharmacological evaluation of three series of homobivalent ligands of clozapine, differing in the length and nature of the spacer and the point of attachment to the pharmacophore. Attachment of the spacer at the N4' position of clozapine yielded a series of homobivalent ligands that displayed spacer-length-dependent gains in affinity and activity for the dopamine D(2) receptor. The 16 and 18 atom spacer bivalent ligands were the highlight compounds, displaying marked low nanomolar receptor binding affinity (1.41 and 1.35 nM, respectively) and functional activity (23 and 44 nM), which correspond to significant gains in affinity (75- and 79-fold) and activity (9- and 5-fold) relative to the original pharmacophore, clozapine. As such these ligands represent useful tools with which to investigate dopamine receptor dimerization and the atypical nature of clozapine.

Bivalent Ligands for the Serotonin 5-HT3 Receptor.

The serotonin 5-HT3 receptor is a ligand-gated ion channel, which by virtue of its pentameric architecture, can be considered to be an intriguing example of intrinsically multivalent biological receptors. This paper describes a general design approach to the study of multivalency in this multimeric ion channel. Bivalent ligands for 5-HT3 receptor have been designed by linking an arylpiperazine moiety to probes showing different functional features. Both homobivalent and heterobivalent ligands have shown 5-HT3 receptor affinity in the nanomolar range, providing evidence for the viability of our design approach. Moreover, the high affinity shown by homobivalent ligands suggests that bivalency is a promising approach in 5-HT3 receptor modulation and provides the rational basis for applying the concepts of multivalency to the study of 5-HT3 receptor function.

Synthesis of Specific Bivalent Probes That Functionally Interact with 5-HT4 Receptor Dimers

G-protein-coupled receptor dimerization directs the design of new drugs that specifically bind to receptor dimers. Here, we generated a targeted series of homobivalent ligands for serotonin 5-HT(4) receptor (5-HT(4)R) dimers composed of two 5-HT(4)R-specific ML10302 units linked by a spacer. The design of spacers was assisted by molecular modeling using our previously described 5-HT(4)R dimer model. Their syntheses were based on Sonogashira-Linstrumelle coupling methods. All compounds retained high-affinity binding to 5-HT(4)R but lost the agonistic character of the monomeric ML10302 compound. Direct evidence for the functional interaction of both pharmacophores of bivalent ligands with the 5-HT(4)R was obtained using a bioluminescence resonance energy transfer (BRET) based assay that monitors conformational changes within 5-HT(4) dimers. Whereas the monovalent ML10302 was inactive in this assay, several bivalent derivatives dose-dependently increased the BRET signal, indicating that both pharmacophores functionally interact with the 5-HT(4) dimer. These bivalent ligands may serve as a new basis for the synthesis of potential drugs for 5-HT(4)-associated disorders.

Synthesis and Evaluation of Bivalent NDP-α-MSH(7) Peptide Ligands for Binding to the Human Melanocortin Receptor 4 (hMC4R)

We demonstrate the potential utility of multivalent ligands as targeting agents for cancer imaging or therapy by determining the binding of homobivalent ligands to their corresponding receptors. This manuscript details the synthesis and evaluation of a series of bivalent ligands containing two copies of the truncated heptapeptide version of [Nle4-D-Phe7]-alpha-melanocyte stimulating hormone (NDP-alpha-MSH), referred to as MSH(7). These were connected with various semirigid linkers containing Pro-Gly repeats, with or without flexible poly(ethylene glycol) (PEGO) moieties at their termini. Modeling data suggest a distance of 20-50 A between the ligand binding sites of two adjacent G-protein coupled receptors, GPCRs. These bivalent ligands were observed to bind with higher affinity compared to their monovalent counterparts. Data suggest these ligands may be capable of cross-linking adjacent receptors. An optimal linker length of 25 +/- 10 A, inferred from these ligands, correlated well with the inter-receptor distance estimated through modeling. Although there was no difference in maximal binding affinities between the ligands constructed with the Pro-Gly repeats versus those constructed with the PEGO inserts, the PEGO-containing ligands bound with high affinities over a greater range of linker lengths.

Specific targeting of acetylcholinesterase and butyrylcholinesterase recognition sites. Rational design of novel, selective, and highly potent cholinesterase inhibitors.

Tacrine-based AChE and BuChE inhibitors were designed by investigating the topology of the active site gorge of the two enzymes. The homobivalent ligands characterized by a nitrogen-bridged atom at the tether level could be considered among the most potent and selective cholinesterase inhibitors described to date. The nitrogen-containing homobivalent ligands 3e,g and the sulfur-containing 3h validated the hypothesis of extra sites of interaction in the AChE and BuChE active site gorges.

ChemInform Abstract: Novel and Potent Tacrine‐Related Hetero‐ and Homobivalent Ligands for Acetylcholinesterase and Butyrylcholinesterase.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Novel and potent tacrine-related hetero- and homobivalent ligands for acetylcholinesterase and butyrylcholinesterase

Based upon synthetic and biochemical results, a novel and potent tacrine analogue and heterobivalent analogues of tacrine, were designed. The role played by the amino groups of homo- and heterobivalent ligands in the interaction with the peripheral and catalytic sites of AChE and BuChE were investigated. The syntheses of these materials together with the results of AChE/BuChE inhibition assays are detailed.