Histamine H3 Receptor Ligands Research Articles

Therapeutic potential of histamine H4 receptor agonists in triple‐negative human breast cancer experimental model

The presence of the histamine H₄ receptor (H₄R) was previously reported in benign and malignant lesions and cell lines derived from the human mammary gland. The aim of this work was to evaluate the effects of H₄R ligands on the survival, tumour growth rate and metastatic capacity of breast cancer in an experimental model. Xenograft tumours of the highly invasive human breast cancer cell line MDA-MB-231 were established in immune deficient nude mice. The following H₄R agonists were employed: histamine (5 mg kg⁻¹), clozapine (1 mg kg⁻¹) and the experimental compound JNJ28610244 (10 mg kg⁻¹). Data indicate that developed tumours were highly undifferentiated, expressed H₄R and exhibited high levels of histamine content and proliferation marker (PCNA) while displaying low apoptosis. Mice of the untreated group displayed a median survival of 60 days and a tumour doubling time of 7.4 ± 0.6 days. A significant decrease in tumour growth evidenced by an augment of the tumour doubling time was observed in the H₄R agonist groups (13.1 ± 1.2, P < 0.01 in histamine group; 15.1 ± 1.1, P < 0.001 in clozapine group; 10.8 ± 0.7, P < 0.01 in JNJ28610244 group). This effect was associated with a decrease in the PCNA expression levels, and also reduced intratumoural vessels in histamine and clozapine treated mice. Histamine significantly increased median survival (78 days; Log rank Mantel-Cox Test, P = 0.0025; Gehan-Breslow-Wilcoxon Test, P = 0.0158) and tumoural apoptosis. Histamine through the H₄R exhibits a crucial role in tumour progression. Therefore, H₄R ligands offer a novel therapeutic potential as adjuvants for breast cancer treatment.

Anticonvulsant properties of histamine H3 receptor ligands belonging to N-substituted carbamates of imidazopropanol

Ligands targeting central histamine H3 receptors (H3Rs) for epilepsy might be a promising therapeutic approach. Therefore, the previously described and structurally strongly related imidazole-based derivatives belonging to carbamate class with high H3R in vitro affinity, in-vivo antagonist potency, and H3R selectivity profile were investigated on their anticonvulsant activity in maximal electroshock (MES)-induced and pentylenetetrazole (PTZ)-kindled seizure models in Wistar rats. The effects of systemic injection of H3R ligands 1–13 on MES-induced and PTZ-kindled seizures were screened and evaluated against the reference antiepileptic drug (AED) Phenytoin (PHT) and the standard histamine H3R inverse agonist/antagonist Thioperamide (THP) to determine their potential as new antiepileptic drugs. Following administration of the H3R ligands 1–13 (5, 10 and 15mg/kg, ip) there was a significant dose dependent reduction in MES-induced seizure duration. The protective action observed for the pentenyl carbamate derivative 4, the most protective H3R ligand among 1–13, was significantly higher (P <0.05) than that of standard H3R antagonist THP, and was reversed when rats were pretreated with the selective H3R agonist R-(α)-methyl-histamine (RAMH) (10mg/kg), or with the CNS penetrant H1R antagonist Pyrilamine (PYR) (10mg/kg). In addition, subeffective dose of H3R ligand 4 (5mg/kg, ip) significantly potentiated the protective action in rats pretreated with PHT (5mg/kg, ip), a dose without appreciable protective effect when given alone. In contrast, pretreatment with H3R ligand 4 (10mg/kg ip) failed to modify PTZ-kindled convulsion, whereas the reference drug PHT was found to fully protect PTZ-induced seizure. These results indicate that some of the investigated imidazole-based H3R ligands 1–13 may be of future therapeutic value in epilepsy.

ChemInform Abstract: Copper(I)‐Catalyzed Borylative exo‐Cyclization of Alkenyl Halides Containing Unactivated Double Bond.

AbstractSeveral synthetic applications of the reaction products are demonstrated, including the synthesis of histamine H3 receptorligand (XV).

Determination of the binding mode and interacting amino-acids for dibasic H3 receptor antagonists

Due to its involvement in major CNS functions, the histamine H3 receptor (H3R) is the subject of intensive medicinal chemistry investigation, supported by the range of modern drug discovery tools, such as receptor modeling and ligand docking. Although the receptor models described to date share a majority of common traits, they display discrete alternatives in amino-acid conformation, rendering ligand binding modes quite different. Such variations impede structure-based drug design in the H3R field. In the present study, we used a combination of medicinal chemistry, receptor-guided and ligand-based methods to elucidate the binding mode of antagonists. The approaches converged towards a ligand orientation perpendicular to the membrane plane, bridging Glu206 of the transmembrane helix 5 to acidic amino acids of the extracellular loops. This consensus will help future structure-based drug design for H3R ligands.

Bispyrimidines as Potent Histamine H4 Receptor Ligands: Delineation of Structure–Activity Relationships and Detailed H4 Receptor Binding Mode

The basic methylpiperazine moiety is considered a necessary substructure for high histamine H4 receptor (H4R) affinity. This moiety is however also the metabolic hot spot for various classes of H4R ligands (e.g., indolcarboxamides and pyrimidines). We set out to investigate whether mildly basic 2-aminopyrimidines in combination with the appropriate linker can serve as a replacement for the methylpiperazine moiety. In the series of 2-aminopyrimidines, the introduction of an additional 2-aminopyrimidine moiety in combination with the appropriate linker lead to bispyrimidines displaying pKi values for binding the human H4R up to 8.2. Furthermore, the methylpiperazine replacement results in compounds with improved metabolic properties. The attempt to transfer the knowledge generated in the class of bispyrimidines to the indolecarboxamides failed. Combining the derived structure-activity relationships with homology modeling leads to new detailed insights in the molecular aspects of ligand-H4R binding in general and the binding mode of the described bispyrimidines in specific.

Novel and highly potent histamine H3 receptor ligands. Part 3: An alcohol function to improve the pharmacokinetic profile

Synthesis and biological evaluation of potent histamine H3 receptor antagonists incorporating a hydroxyl function are described. Compounds in this series exhibited nanomolar binding affinities for human receptor, illustrating a new possible component for the H3 pharmacophore. As demonstrated with compound BP1.4160 (cyclohexanol 19), the introduction of an alcohol function counter-intuitively allowed to reach high in vivo efficiency and favorable pharmacokinetic profile with reduced half-life.

Cellular distribution of the histamine H3 receptor in the basal ganglia: Functional modulation of dopamine and glutamate neurotransmission

Histamine H3 receptors (H3R) are widely expressed in the brain where they participate in sleep–wake cycle and cognition among other functions. Despite their high expression in some regions of the basal ganglia, their functional role in this forebrain neural network remains unclear. The present findings provide in situ hybridization and immunohistochemical evidence for H3R expression in several neuronal populations of the rat basal ganglia but not in astrocytes (glial fibrillary acidic protein immunoreactive cells). We demonstrate the presence of H3R mRNA and protein in dopaminergic neurons (tyrosine hydroxylase positive) of the ventral tegmental area and substantia nigra. In the dorsal and ventral (nucleus accumbens) striatal complex we show H3R immunoreactivity in cholinergic (choline acetyltransferase immunoreactive) and GABAergic neurons (substance P, proenkephalin or dopamine D1 receptor positive) as well as in corticostriatal terminals (VGLUT1-immunoreactive). Double-labelling experiments in the medial prefrontal cortex show that H3R is expressed in D1R-positive interneurons and VGLUT1-positive corticostriatal output neurons. Our functional experiments confirm that H3R ligands modulate dopamine synthesis and the probability of glutamate release in the striatum from cortico-striatal afferents. The presence of H3R in such different neuronal populations and its involvement in the control of striatal dopaminergic and glutamatergic transmission ascribes a complex role to H3R in the function of the basal ganglia neural network.

Histamine H3 Receptor Function and Ligands: Recent Developments

Histamine H3 Receptor Function and Ligands: Recent Developments

Bodilisant-a novel fluorescent, highly affine histamine h3 receptor ligand.

A piperidine-based lead structure for the human histamine H3 receptor (hH3R) was coupled with the BODIPY fluorophore and resulted in a strong green fluorescent (quantum yield, 0.92) hH3R ligand with affinity in the nanomolar concentration range (K i hH3R = 6.51 ± 3.31 nM), named Bodilisant. Screening for affinities at histamine and dopamine receptor subtypes showed high hH3R preference. Bodilisant was used for visualization of hH3R in hH3R overexpressing HEK-293 cells with fluorescence confocal laser scanning microscopy. In addition, in native human brain tissues, Bodilisant showed clear and displaceable images of labeled hH3R.

Histamine H3 Receptor Function and Ligands: Recent Developments

Histamine H3 receptors are found mostly in central nervous system involved in the regulation of release of various neurotransmitters in brain. They have been implicated in diverse potential therapeutic applications such as sleep-wake disorders, attention-deficient hyperactivity disorder, epilepsy, cognitive impairment and obesity. This review is an attempt to elucidate the function of H3 receptors and their role in various CNS disorders. Also, it is aimed at collating the information on efforts of various medicinal chemists to synthesize the H3 receptor agonists and antagonists in single article.

Histamine H3 Receptor Function and Ligands: Recent Developments

Histamine H3 Receptor Function and Ligands: Recent Developments

Development of a Profiling Strategy for Metabolic Mixtures by Combining Chromatography and Mass Spectrometry with Cell-Based GPCR Signaling

In this study, we developed an in-line methodology that combines analytical with pharmacological techniques to characterize metabolites of human histamine H4 receptor (hH4R) ligands. Liquid chromatographic separation of metabolic mixtures is coupled to high-resolution fractionation into 96- or 384-well plates and directly followed by a cell-based reporter gene assay to measure receptor signaling. The complete methodology was designed, optimized, validated, and ultimately miniaturized into a high-density well plate format. Finally, the methodology was demonstrated in a metabolic profiling setting for three hH4R lead compounds and the drug clozapine. This new methodology comprises integrated analytical separations, mass spectrometry, and a cell-based signal transduction–driven reporter gene assay that enables the implementation of comprehensive metabolic profiling earlier in the drug discovery process.

Effects of Histamine H4 Receptor Ligands in a Mouse Model of Gastric Ulceration

Aim: In the present study we examined whether histamine H₄ receptors (H₄Rs) have a role in gastric ulcerogenesis using a mouse model of gastric damage. Methods: The H₄R antagonist JNJ7777120 and the H₄R agonists VUF8430 and VUF10460 were investigated in fasted CD-1 mice against the ulcerogenic effect induced by co-administration of indomethacin (IND, 30 mg/kg s.c.) and bethanechol (BET, 5 mg/kg i.p.). Both macroscopic and histologic lesions were examined. Strain-related differences were investigated by testing JNJ7777120 also in NMRI, BALB/c and C57BL/6J mice. Results: Neither JNJ7777120 nor the H₄R agonists displayed effects in the normal stomach at any dose tested (10 and 30 mg/kg s.c.). As expected, IND+BET provoked several lesions in the fundic mucosa, which were significantly reduced by JNJ7777120 (10 and 30 mg/kg s.c.). The gastroprotective effect of JNJ7777120 (10 and 30 mg/kg s.c.) was observed in CD-1, NMRI and BALB/c, but not in C57BL/6J, mice. In CD-1 mice, the H₄R agonists VUF8430 and VUF10460 (both at 10 and 30 mg/kg s.c.) did not modify the damage induced by IND+BET, however VUF8430 (10 mg/kg s.c.) prevented the gastroprotection induced by JNJ7777120 (10 mg/kg s.c.). Conclusions: Data obtained with selective ligands suggest that the H₄R may have a role in mouse gastric ulcerogenesis. If confirmed in humans, these data would emphasize the potential advantage of H₄R blockers as gastrosparing anti-inflammatory drugs. The lack of effects of JNJ7777120 in C57BL/6J mice has to be carefully considered in the pharmacological characterization of H₄R functions and/or new selective ligands.

In vivo receptor occupancy assay of histamine H3 receptor antagonist in rats using non-radiolabeled tracer

IntroductionRapid and reliable preclinical receptor occupancy measurement at the target organ in relevant species is critical in accelerating the drug hunting process. The aim of this study was to develop in vivo receptor occupancy assay for histamine H3 receptors (H3R) using the non-radiolabeled GSK189254 as a tracer and to correlate the occupancy–exposure relationship for H3R antagonists in the rats. MethodsIn vivo tracer characterization studies like brain regional distribution, dose and time dependent uptake were carried out for GSK189254 in the male Wistar rats after intravenous administration. The tracer specificity was validated by pretreatment with H3 antagonists like ciproxifan, thioperamide, and GSK334429. The brain regional tracer levels and H3R antagonist concentrations in plasma and brain were quantified using liquid chromatography tandem mass spectrometry. Receptor occupancy was calculated using the ratio of total binding (striatum or frontal cortex) to the nonspecific binding (cerebellum) of the tracer in animals pretreated with H3R antagonist. ResultsHigh degree of selective distribution of GSK189254 was found in striatum, frontal cortex, and low level in the cerebellum. Regional distribution of GSK189254 in the rat brain was consistent to that of H3R distribution mapped using 3H or 11C-GSK189254 in human, porcine, and rat. The calculated occupancy ED50 values in the frontal cortex were 0.14, 1.58, and 0.14mg/kg for ciproxifan, thioperamide, and GSK334429, respectively. The plasma EC50 values (ng/mL) were found to be 2.33, 292.2, and 3.54 for ciproxifan, thioperamide and GSK334429, respectively. DiscussionResults from mass spectroscopy based approach to determine H3R occupancy in rat brain is comparable with reported radiolabeled method by scintillation spectroscopy. In conclusion, non-radiolabeled GSK189254 was successfully employed as a tracer for assessing the H3R occupancy in rats and it can be used as a preclinical tool for evaluation of novel H3R ligands in the drug discovery.

High-resolution metabolic profiling towards G protein-coupled receptors: Rapid and comprehensive screening of histamine H4 receptor ligands

In the past years we developed high-resolution screening platforms involving separation of bioactive mixtures and on-line or at-line bioassays for a wide variety of biological targets with parallel mass spectrometric detection and identification. In the current research, we make a major step forward in the development of at-line bioassays by implementation of radioligand receptor binding and functional cellular assays to evaluate bioactvity and selectivity. We demonstrate a new platform for high-resolution metabolic profiling of lead compounds for functional activity and selectivity toward the human histamine H4 receptor (hH4R), a member of the large family of membrane-bound G protein-coupled receptors. In this platform analytical chemistry, cell biology and pharmacology are merged. The methodology is based on chromatographic separation of metabolic mixtures by HPLC coupled to high-resolution fractionation onto (multiple) microtiter well plates for complementary assaying. The methodology was used for efficient and rapid metabolic profiling of the drug clozapine and three selective hH4R lead compounds. With this new platform metabolites with undesired alterations in target selectivity profiles can be readily identified. Moreover, the parallel identification of metabolite structures, with accurate-mass measurements and MS/MS, allowed identification of liable metabolic ‘hotspots’ for further lead optimization and plays a central role in the workflow and in this study. The methodology can be easily adapted for use with other receptor screening formats. The efficient combination of pharmacological assays with analytical techniques by leveraging high-resolution at-line fractionation as a linking technology will allow implementation of comprehensive metabolic profiling in an early phase of the drug discovery process.

Reversal of Oxidative Stress by Histamine H3 Receptor-Ligands in Experimental Models of Schizophrenia

Schizophrenia (SCZ) is a debilitating disorder afflicting around 1% of the world population. Recent literature reveals oxidative injuries contribute enormously to the pathophysiology of SCZ alongside other psychopathological disturbances. Histamine H3R-antagonists have shown dual mechanism of action in experimental models of SCZ. Firstly it prevents oxidative stress and secondly alleviates schizophrenic symptoms, particularly the negative symptoms and cognitive deficits. In the present study, histamine H3R-antagonists used were ciproxifan (3.0 mg/kg, ip) and clobenpropit (15 mg/kg, ip) markedly controlled the elevated levels of various oxidative stress markers, for example, thiobarbituric acid reactive substance (TBARS), glutathione (GSH), superoxide dismutase, catalase, etc., as a result of augmented oxidative stress in the experimental models of SCZ such as amphetamine (0.5 mg/kg, sc) and dizocilpine (MK-801) (0.2 mg/kg, ip) induced locomotor hyperactivity, apomorphine (1.5 mg/kg, sc) induced climbing behavior and haloperidol (2.0 mg/kg, po) induced catalepsy. The results of the present study revealed that H3R-antagonists possess antioxidant activity and could serve with dual mechanism by supplementing antioxidant needs of SCZ and at the same time controlling symptoms of SCZ.

Azines as histamine H4 receptor antagonists

Since 2000, when the histamine H4 receptor (H4R) was cloned, it has constituted an interesting target for drug development. Pharmacological studies suggest the potential utility of histamine H4R antagonists/inverse agonists in the treatment of inflammatory diseases, e.g. allergic rhinitis, asthma, atopic dermatitis, colitis, or pruritus. The first H4R ligands were non-selective compounds, but intensive chemical and pharmacological work has led to the discovery of highly potent and selective H4R antagonists (e.g. JNJ7777120, CZC-13788, PF-2988403, A-940894, A-987306). The first compound (UR-63325) has finally entered into clinical studies for the treatment of allergic respiratory diseases (completing the phase I ascending dose trial) and has been found to be safe and well tolerated. The number of scientific publications and patent applications in the H4 field is increasing annually. Among the diverse chemical structures of the H4R antagonists described a 2-aminopyrimidine scaffold is repeatedly found. This review looked at recent advances in the search for H4R antagonists as reflected in patent applications/patents and peer-reviewed publications over the last two years. The work concerns azines (mono-, di-, triazines) and their fused analogues. The chemistry and pharmacology has been described.

Molecular pharmacology of histamine H4 receptors

The histamine H4 receptor (H4R) is the youngest member of the histamine receptor family. Based on its predominant expression pattern in hematopoietic cells, the H4R is considered to be an interesting drug target for inflammatory disorders such as allergy and asthma. Since the identification and cloning of the H4R in 2000, drug discovery programs boosted the development of various H4R (specific) ligands. Differences between H4R orthologs in combination with available three-dimensional G protein-coupled receptor (GPCR) models have guided site-directed mutagenesis studies to gain insight in ligand binding and receptor activation. In addition, ongoing characterization of H4R-mediated signaling in transfected and native cells contributes to further unravel the (patho-) physiological functions of H4Rs.

Novel Chalcone-Based Fluorescent Human Histamine H3 Receptor Ligands as Pharmacological Tools

Novel fluorescent chalcone-based ligands at human histamine H3 receptors (hH3R) have been designed, synthesized, and characterized. Compounds described are non-imidazole analogs of ciproxifan with a tetralone motif. Tetralones as chemical precursors and related fluorescent chalcones exhibit affinities at hH3R in the same concentration range like the reference antagonist ciproxifan (hH3R pKi value of 7.2). Fluorescence characterization of our novel ligands shows emission maxima about 570 nm for yellow fluorescent chalcones and ≥600 nm for the red fluorescent derivatives. Interferences to cellular autofluorescence could be excluded. All synthesized chalcone compounds could be used to visualize hH3R proteins in stably transfected HEK-293 cells using confocal laser scanning fluorescence microscopy. These novel fluorescent ligands possess high potential to be used as pharmacological tools for hH3R visualization in different tissues.

Protective effects of histamine H3-receptor ligands in schizophrenic behaviors in experimental models

Schizophrenia (SCZ) afflicts around 1% of the world’s population with characteristic symptoms such as hallucinations, delusions, and cognitive disorders. Several experimental studies in the past have indicted brain histaminergic neuronal system involvement in the pathogenesis of psychotic disorders including SCZ. Present study investigates anti-schizophrenic activity using two histamine H3-receptor (H3R)-antagonists/inverse agonists, ciproxifan (3.0mg/kg, ip) and clobenpropit (15mg/kg, ip), on some of the established animal model of schizophrenia, for example, amphetamine (AMPH) and dizocilpine (MK-801)-induced hyperactivity, apo-morphine (APO)-induced climbing behavior, scopolamine and MK-801-induced learning and memory deficits and haloperidol-induced catalepsy including determination of acetylcholinesterase (AChE) activity. Results of the present study demonstrate that ciproxifan and clobenpropit were able to control AMPH and MK-801-induced hyperlocomotor activities demonstrated as reduced horizontal activity and reduced number of movements made by rats. Further, there was overall reduction in APO-induced climbing behavior. Learning and memory deficits, as evaluated on elevated plus maze, followed by estimation of brain AChE activity demonstrated positive results with these protypical imidazole H3R-antagonists/inverse agonists.In conclusion, present study demonstrates anti-schizophrenic like activities of ciproxifan and clobenpropit and supports the therapeutic interest of histamine H3R antagonists/inverse agonists to improve symptomatic treatment of psychotic disorders.