Bivalent Ligand Approach Research Articles

Dimeric-serotonin bivalent ligands induced gold nanoparticle aggregation for highly sensitive and selective serotonin biosensor

Chemically modulating monoamine neurotransmitter serotonin undergoes a physiological reaction of enzyme intermediated peroxidation to reconstruct dimeric self-assembled complex. A standard bivalent ligand approach dimeric serotonin increases structural and functional scaffolding with recognition-binding sites that are fundamentally more friendly than monovalent binding sites. Dimerization reaction accelerates the catalytic activity of one-electron oxidation at the C(4) position of serotonin to generate dual phenolic radicals in the presence of horseradish (HRP) and hydrogen peroxide (H2O2). Herein, we suggest the dimeric serotonin-based colorimetric assay, which presents a new rapid, sensitive, selective, and quantitative visualization. The dimeric serotonin possesses the capability to recognize intermolecular interaction units that cause aggregation scaffold of gold nanoparticles (GNPs), providing inexpensive and straightforward analytical needs. As a proof of visual and spectral analysis, peroxidative dimeric serotonin demonstrated sensitive and robust results. The calorimetric method enables highly sensitive detection of serotonin in phosphate buffer, and in human serum samples at nanomolar levels with a LOD of 2.6 nM and 2.81 nM, respectively, and the sensor possesses a dynamic range of 100–300 nM in buffer condition. Also, as proof of concept, visible color imaging of immunosensors which is appropriate for fast visible testing at detection limits as low as 2.90 nM concentration.

Novel Bivalent and D-Peptide Ligands of CXCR4 Mobilize Hematopoietic Progenitor Cells to the Blood in C3H/HeJ Mice

The interaction of SDF-1α (also known as CXCL12) with the CXCR4 receptor plays a critical role in the retention of hematopoietic stem cells (HSCs) in bone marrow. The viral macrophage inflammatory protein-II (vMIP-II), a human herpesvirus-8 (HHV-8)-encoded viral chemokine, can bind the CXCR4 receptor and inhibit endogenous ligand-induced calcium responses and cell migration. Previously, we used the bivalent ligand approach to link synthetically two unnatural D-amino acid peptides derived from the N-terminus of vMIP-II (DV1 and DV3, respectively) to generate a dimeric peptide, DV1-K-(DV3) (also named HC4319), which shows very high affinity for CXCR4. Here, we studied the biological effects of this dimeric peptide, HC4319, and its monomeric counterpart, DV1, on SDF-1α-induced signaling in CXCR4- or CXCR7-transfected Chinese hamster ovary cells and mobilization of hematopoietic progenitor cells (HPCs) in C3H/HeJ mice using an HPC assay. HC4319 and DV1 inhibited significantly the phosphorylation of Akt and Erk, known to be downstream signaling events of CXCR4. This in vivo study in C3H/HeJ mice showed that HC4319 and DV-1 strongly induced rapid mobilization of granulocyte–macrophage colony-forming units (CFUs), erythrocyte burst-forming units, and granulocyte–erythrocyte–monocyte–megakaryocyte CFUs from the bone marrow to the blood. These results provide the first reported experimental evidence that bivalent and D-amino acid peptides derived from the N-terminus of vMIP-II are potent mobilizers of HPCs in C3H/HeJ mice and support the further development of such agents for clinical application.

Design, physico-chemical and pre-clinical evaluation of a homo-bivalent99mTc-(BTZ)2DTPA radioligand for targeting dimeric 5-HT1A/5-HT7receptors

A99mTc-labelled bis-benzothiazolone-DTPA radio-complex as a SPECT neuroimaging agent.

Small Molecule Radiopharmaceuticals - A Review of Current Approaches.

Radiopharmaceuticals are an integral component of nuclear medicine and are widely applied in diagnostics and therapy. Though widely applied, the development of an “ideal” radiopharmaceutical can be challenging. Issues such as specificity, selectivity, sensitivity, and feasible chemistry challenge the design and synthesis of radiopharmaceuticals. Over time, strategies to address the issues have evolved by making use of new technological advances in the fields of biology and chemistry. This review presents the application of few advances in design and synthesis of radiopharmaceuticals. The topics covered are bivalent ligand approach and lipidization as part of design modifications for enhanced selectivity and sensitivity and novel synthetic strategies for optimized chemistry and radiolabeling of radiopharmaceuticals.

The design of multitarget ligands for chronic and neuropathic pain.

Monodrug therapy has been used with success to fight various pathologies. When one medicine fails, co-administration of two or more drugs at the same time may be successfully applied in the treatment of infections, hypertension, HIV and in many other fields. This approach has some weakness related to the pharmacokinetic of the two different substances administered, side effects, possible drug-drug interaction. Bivalent ligand approach would maintain the strength of the multidrug therapy (synergistic effect, lower doses, and little side effects) and overcome the weakness of a co-administration. In this review we have described the state-of-the-art of the multitarget approach for the control of pain. Several approaches adopted by different research groups and future perspectives have been discussed.

The Bivalent Ligand Approach as a Tool for Improving the in vitro Anti‐Alzheimer Multitarget Profile of Dimebon

The Bivalent Ligand Approach as a Tool for Improving the in vitro Anti‐Alzheimer Multitarget Profile of Dimebon

A synthetic bivalent ligand of CXCR4 inhibits HIV infection

G-protein-coupled receptors (GPCRs) are cell membrane protein receptors that transduce signals across the cell membrane and are important targets for therapeutic interventions. As members of the GPCR superfamily, chemokine receptors such as CXCR4 play critical roles in normal physiology as well as the pathology of many human diseases including cancer, inflammation, autoimmune diseases, and human immunodeficiency virus (HIV) infection. Here we report the discovery and study of a novel peptide ligand of CXCR4 using d-amino acids and bivalent ligand approach. This peptide, DV1-K-(DV3), shows very high affinity for CXCR4 with an IC50 of 4nM in anti-CXCR4 monoclonal antibody (mAb) 12G5 competitive assay, which is more potent than full length natural ligand SDF-1α, even though the peptide is less than half of the number of residues of SDF-1α. This peptide can block the calcium influx stimulated by SDF-1α and inhibit cancer cell migration in vitro via CXCR4, thus functioning as a CXCR4 antagonist. Furthermore, DV1-K-(DV3) peptide displayed anti-HIV activity by inhibiting HIV-1 infection mediated by CXCR4. With its high receptor affinity and stability from d-amino acids, this peptide may be a new probe of CXCR4 functions in physiology and pathology and promising lead for therapeutic development.

Synthesis, evaluation and structure–activity relationships of triazine dimers as novel antiviral agents

This letter reports the synthesis and structure–activity relationship (SAR) study of a series of triazine dimers as novel antiviral agents. These compounds were obtained through a bivalent ligand approach in which two triazine moieties are covalently connected by suitable linkers. Several compounds showed submicromolar activity against wild-type HIV-1 and moderate activity against single mutant strains.

Design and synthesis of a bivalent ligand to explore the putative heterodimerization of the mu opioid receptor and the chemokine receptor CCR5

The bivalent ligand approach has been utilized not only to study the underlying mechanism of G protein-coupled receptors dimerization and/or oligomerization, but also to enhance ligand affinity and/or selectivity for potential treatment of a variety of diseases by targeting this process. Substance abuse and addiction have made both the prevention and the treatment of human immunodeficiency virus (HIV) infection more difficult to tackle. Morphine, a mu opioid receptor (MOR) agonist, can accelerate HIV infection through up-regulating the expression of the chemokine receptor CCR5, a well-known co-receptor for HIV invasion to the host cells and this has been extensively studied. Meanwhile, two research groups have described the putative MOR-CCR5 heterodimers in their independent studies. The purpose of this paper is to report the design and synthesis of a bivalent ligand to explore the biological and pharmacological process of the putative MOR-CCR5 dimerization phenomenon. The developed bivalent ligand thus contains two distinct pharmacophores linked through a spacer; ideally one of which will interact with the MOR and the other with the CCR5. Naltrexone and Maraviroc were selected as the pharmacophores to generate such a bivalent probe. The overall reaction route to prepare this bivalent ligand was convergent and efficient, and involved sixteen steps with moderate to good yields. The preliminary biological characterization showed that the bivalent compound 1 retained the pharmacological characteristics of both pharmacophores towards the MOR and the CCR5 respectively with relatively lower binding affinity, which tentatively validated our original molecular design.

A homodimeric bivalent radioligand derived from 1-(2-methoxyphenyl)piperazine with high affinity for in vivo 5-HT1A receptor imaging

The bivalent ligand approach is very promising and can give rise to molecular probes with enhanced conformational flexibility for tissue selective modulation. In this study we describe the synthesis of a homodimeric 5-HT1A receptor ligand by incorporating two identical pharmacophores , 1-(2-methoxyphenyl)piperazine, linked through DTPA. This bivalent derivative was efficiently synthesized and characterized by 1H, 13C NMR and mass spectroscopy. 99mTc-labeling was performed with a high radiolabeling yield (>95%) and radiochemical purity (>98%) using very low ligand concentration. In vitro studies were carried out on hippocampal cultures and PC3 cell lines which express 5-HT1A receptors. The selectivity of the complex for 5-HT1A receptors is 1000 times more than it is for 5-HT2A receptors, with Kd in picomolar range. Hill coefficients between 1.9 and 2.3 were observed, indicating that the homodimeric binding pharmacophores appear to be essential for the cooperative binding mode. In vitro binding assays in rat hippocampal cultures demonstrated the high affinity of the complex for 5-HT1A receptors. Further studies include in vivo organ distribution and gamma scintigraphy carried out in rat and rabbit. Plasma clearance rate (CR) revealed a value of 4.86 μg mL−1 min−1 in normal rabbit. Dynamic imaging performed in rabbit showed the beginning of radiolabeled uptake in brain as early as 2 min. The tumor-to-contralateral muscle tissue ratio of 99mTc–DTPA–bis(MPBA) in athymic mice with PC3 xenograft was found to be 65 ± 3.3 at 1 h. Significant accumulation was seen in mice and rat brain at 10 min with 2.07 ± 0.76% ID g−1 and 2.81% ID g−1 respectively. The high uptake in hippocampus and cerebral cortex was accredited to the 5-HT1A receptor rich regions in post mortem rat brain. This imaging agent holds a promising future in imaging 5-HT1A receptors for the effective diagnosis of neuropathological disorders.

Bivalent ligand approach on N-{2-[(3-methoxyphenyl)methylamino]ethyl}acetamide: Synthesis, binding affinity and intrinsic activity for MT1 and MT2 melatonin receptors

We report the synthesis, binding properties and intrinsic activity at MT1 and MT2 melatonin receptors of new dimeric melatonin receptor ligands in which two units of the monomeric agonist N-{2-[(3-methoxyphenyl)methylamino]ethyl}acetamide (1) are linked together through different anchor points. Dimerization of compound 1 through the methoxy substituent leads to a substantial improvement in selectivity for the MT1 receptor, and to a partial agonist behavior. Compound 3a, with a trimethylene linker, was the most selective for the MT1 subtype (112-fold selectivity) and compound 3d, characterized by a hexamethylene spacer, had the highest MT1 binding affinity (pKiMT1=8.47) and 54-fold MT1-selectivity. Dimerization through the aniline nitrogen of 1 abolished MT1 selectivity, leading to compounds with either a full agonist or an antagonist behavior depending on the nature of the linker.

Discovery of a Competitive Apelin Receptor (APJ) Antagonist

The apelin receptor (APJ) is a class A G-protein-coupled receptor (GPCR) and is a putative target for the treatment of cardiovascular and metabolic diseases. Apelin-13 (NH₂-QRPRLSHKGPMPF-COOH) is a vasoactive peptide and one of the most potent endogenous inotropic agents identified to date. We report the design and discovery of a novel APJ antagonist. By using a bivalent ligand approach, we have designed compounds with two 'affinity' motifs and a short series of linker groups with different conformational and non-bonded interaction properties. One of these, cyclo(1-6)CRPRLC-KH-cyclo(9-14)CRPRLC is a competitive antagonist at APJ. Radioligand binding in CHO cells transfected with human APJ gave a K(i) value of 82 nM, competition binding in human left ventricle gave a K(D) value of 3.2 μM, and cAMP accumulation assays in CHO-K1-APJ cells gave a K(D) value of 1.32 μM.

Synthesis and opioid receptor binding affinities of 2-substituted and 3-aminomorphinans: ligands for mu, kappa, and delta opioid receptors.

The phenolic group of the potent mu and kappa opioid morphinan agonist/antagonists cyclorphan and butorphan was replaced by phenylamino and benzylamino groups including compounds with para-substituents in the benzene ring. These compounds are highly potent mu and kappa ligands, e.g., p-methoxyphenylaminocyclorphan showing a K(i) of 0.026 nM at the mu receptor and a K(i) of 0.03 nM at the kappa receptor. Phenyl carbamates and phenylureas were synthesized and investigated. Selective o-formylation of butorphan and levorphanol was achieved. This reaction opened the way to a large set of 2-substituted 3-hydroxymorphinans, including 2-hydroxymethyl-, 2-aminomethyl-, and N-substituted 2-aminomethyl-3-hydroxymorphinans. Bivalent ligands bridged in the 2-position were also synthesized and connected with secondary and tertiary aminomethyl groups, amide bonds, and hydroxymethylene groups, respectively. Although most of the 2-substituted morphinans showed considerably lower affinities compared to their parent compounds, the bivalent ligand approach led to significantly higher affinities compared to the univalent 2-substituted morphinans.

Modular synthesis of non-peptidic bivalent NPY Y 1 receptor antagonists

According to a ‘bivalent ligand approach’ to increase the affinity of the potent argininamide-type NPY Y 1 receptor antagonist BIBP-3226, dimeric ligands were synthesized in which two molecules of the parent compound were linked by different spacers via N G-acylation at the guanidino groups. A synthetic route for the preparation of the title compounds was developed, which includes a copper(I)-catalyzed azide alkyne cycloaddition as the key step. Three bivalent analogues of BIBP-3226 were prepared showing nanomolar antagonistic activity and binding affinity to the NPY Y 1 receptor (calcium assay on HEL cells, radioligand binding assay on SK-N-MC cells), but these ligands were not superior to the parent compound and there was no correlation with the length or the chemical nature of the spacer. A trivalent BIBP-3226 derivate showed, surprisingly, no affinity to the NPY Y 1 receptor at all.

Bivalent ligand approach on 4-[2-(3-methoxyphenyl)ethyl]-1-(2-methoxyphenyl)piperazine: Synthesis and binding affinities for 5-HT 7 and 5-HT 1A receptors

We here report on the synthesis and binding properties at 5-HT 7 and 5-HT 1A receptors of ligands 3– 12, that were designed according to the ‘bivalent ligand’ approach. Two moieties of the 5-HT 7/5-HT 1A ligand 4-[2-(3-methoxyphenyl)ethyl]-1-(2-methoxyphenyl)piperazine ( 1) were linked through their 3-methoxy substituent by polymethylene chains of variable length, with the aim to increase the affinity for 5-HT 7 receptor and the selectivity over 5-HT 1A receptors. In the best cases, the dimers showed affinities for 5-HT 7 receptors as high as the monomer with no improvement in selectivity. Some dimers displayed 5-HT 1A receptor affinities slightly higher than monomer 1.

Agonistic and Antagonistic Bivalent Ligands for Serotonin and Dopamine Receptors Including their Transporters

This review deals with the literature (1982-2006) concerning bivalent ligands for dopamine (D) and serotonin (5-HT) receptors, as well as for their respective transporters. The design, synthesis, and pharmacological evaluation of bivalent agonists and antagonists for dopamine and serotonin receptors have been successfully pursued. Increased potencies for 5-HT(1B/1D) receptor agonists were achieved as well as improved selectivities. At these receptors, selectivity seems to depend strongly on spacer length, whereas the improved affinities seem to be based on the presence of two pharmacophores within one molecule. Intrinsic activities and pharmacokinetic properties may differ from those of the respective monovalent ligands. Additionally, improved central nervous system penetration was achieved. Bivalent dopamine receptor agonists and antagonists can exhibit selectivity profiles different from their monomeric analogues with no loss in potency. For dopamine antagonists, affinities depend strongly on spacer length. For agonistic dimers different pharmacokinetic properties were observed. Bivalency was also applied to inhibitors of monoamine re-uptake transporters. Selectivity profiles and affinities depend strongly on the length of the alkylene-spacer: For some dimeric inhibitors the norepinephrine transporter (NET) and the dopamine transporter (DAT) affinities changed gradually, but for the serotonin transporter (SERT) a pentamethylene spacer showed the highest potency. Because the bivalent ligand approach has just begun to be applied to these versatile, therapeutically important targets, many advances in affinity enhancement, as well as the achievement of novel selectivity profiles and improved pharmacokinetics can be expected.

Bivalent ligands for G protein-coupled receptors.

Bivalent ligands have been developed for a variety of G protein-coupled receptor targets, including opioid, dopamine, serotonin and muscarinic receptors. The most successful application of the bivalent ligand approach has been in the development of selective opioid antagonists, such as norbinaltorphimine. Several important principles have emerged from the study of norbinaltorphimine and related compounds, including the utility of bivalent ligands for targeting particular receptor classes and serving as a scaffold for specific interactions with unique amino acid residues that render receptor subtype selectivity. In recent years, several novel bivalent compounds were synthesized and characterized for activity at muscarinic receptors. The compounds display an interesting profile of high binding affinity, strong agonist potency and receptor subtype selectivity. Bivalent ligands represent an important starting point for the development of selective muscarinic agonists with potential utility in treating a variety of neurological disorders, including Alzheimer's disease and schizophrenia. The bivalent ligand approach may be generally applicable to other G protein-coupled receptors.

Dopamine/serotonin receptor ligands, part III [1]: synthesis and biological activities of 7, 7'-alkylene-bis-6, 7, 8, 9, 14, 15-hexahydro-5H-benz[d]indolo[2, 3-g]azecines -- application of the bivalent ligand approach to a novel type of dopamine receptor antagonist.

A series of 7, 7'-alkylene-bridged dimers(7a-e) of the benz [d]indolo[3, 2-f]azecine derivative LE300 was synthesized. Affinity and functional activity at dopamine D(1) and D(2) receptors were estimated by radioligand binding and a functional Ca(2+) assay. All the new bivalent ligands showed significant binding affinities to both D(1) and D(2) receptors with an optimal distance between the two monomeric recognition units of 6 methylene moieties. The D(1)/D(2)-selectivity pattern was dependent on the spacer length. No (7a, b) or only moderate (7c-e) functional activity was detected for all bivalent compounds by measuring the inhibition of agonist-induced increase in intracellular Ca(2+).

Application of the Bivalent Ligand Approach to the Design of Novel Dimeric Serotonin Reuptake Inhibitors

Application of the Bivalent Ligand Approach to the Design of Novel Dimeric Serotonin Reuptake Inhibitors

Use of hydrophilic diamines for bridging of two opioid peptide pharmacophores

The bivalent ligand approach, which assumes that two pharmacophores are connected by a spacer, was used to design receptor type-selective ligands for opioid receptors. The first two opioid peptide bivalent ligands with different spacer lengths containing different numbers of hydroxyl groups, (Tyr-D-Ala-Gly-Phe-NH-CH2-CHOH-)2 (Tyr-D-Ala-Gly-Phe-NH-CH2-CHOH-CHOH-)2, were synthesized and their binding to mu, delta, and kappa opioid receptors was characterized. Both analogues were found to possess high opioid in vitro activities. The length of the hydrophilic spacer does not affect the affinity for delta receptors, whereas shorter spacer length increases affinity for mu and even more so for kappa receptors. Thus receptor type-selective peptides for opioid receptors can be designed using the bivalent approach.