The Multi-Targeting Ligand ST-2223 with Histamine H3 Receptor and Dopamine D2/D3 Receptor Antagonist Properties Mitigates Autism-Like Repetitive Behaviors and Brain Oxidative Stress in Mice.

Autism spectrum disorder (ASD) is a complex heterogeneous neurodevelopmental disorder characterized by social and communicative impairments, as well as repetitive and restricted behaviors (RRBs). With the limited effectiveness of current pharmacotherapies in treating repetitive behaviors, the present study determined the effects of acute systemic treatment of the novel multi-targeting ligand ST-2223, with incorporated histamine H3 receptor (H3R) and dopamine D2/D3 receptor affinity properties, on ASD-related RRBs in a male Black and Tan BRachyury (BTBR) mouse model of ASD. ST-2223 (2.5, 5, and 10 mg/kg, i.p.) significantly mitigated the increase in marble burying and self-grooming, and improved reduced spontaneous alternation in BTBR mice (all p < 0.05). Similarly, reference drugs memantine (MEM, 5 mg/kg, i.p.) and aripiprazole (ARP, 1 mg/kg, i.p.), reversed abnormally high levels of several RRBs in BTBR (p < 0.05). Moreover, ST-2223 palliated the disturbed anxiety levels observed in an open field test (all p < 0.05), but did not restore the hyperactivity parameters, whereas MEM failed to restore mouse anxiety and hyperactivity. In addition, ST-2223 (5 mg/kg, i.p.) mitigated oxidative stress status by decreasing the elevated levels of malondialdehyde (MDA), and increasing the levels of decreased glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT) in different brain parts of treated BTBR mice (all p < 0.05). These preliminary in vivo findings demonstrate the ameliorative effects of ST-2223 on RRBs in a mouse model of ASD, suggesting its pharmacological prospective to rescue core ASD-related behaviors. Further confirmatory investigations on its effects on various brain neurotransmitters, e.g., dopamine and histamine, in different brain regions are still warranted to corroborate and expand these initial data.

Ameliorating effects of histamine H3 receptor antagonist E177 on acute pentylenetetrazole-induced memory impairments in rats.

Histamine H3 receptors (H3Rs) are involved in several neuropsychiatric diseases including epilepsy. Therefore, the effects of H3R antagonist E177 (5 and 10 mg/kg, intraperitoneal (i.p.)) were evaluated on acute pentylenetetrazole (PTZ)-induced memory impairments, oxidative stress levels (glutathione (GSH), malondialdehyde (MDA), catalase (CAT), and superoxide dismutase (SOD)), various brain neurotransmitters (histamine (HA), acetylcholine (ACh), γ-aminobutyric acid (GABA)), and glutamate (Glu), acetylcholine esterase (AChE) activity, and c-fos protein expression in rats. E177 (5 and 10 mg/kg, i.p.) significantly prolonged step-through latency (STL) time in single-trial passive avoidance paradigm (STPAP), and shortened transfer latency time (TLT) in elevated plus maze paradigm (EPMP) (all P < 0.05). Moreover, and in the hippocampus of PTZ-treated animals, E177 mitigated abnormal levels of AChE activity, ACh and HA (all P < 0.05), but failed to modify brain levels of GABA and Glu. Furthermore, E177 alleviated hippocampal oxidative stress by significantly decreasing the elevated levels of MDA, and increasing the abnormally decreased level of GSH (all P < 0.05). Furthermore, E177 reduced elevated levels of hippocampal c-fos protein expression in hippocampal tissues of PTZ-treated animals (all P < 0.05). The observed results propose the potential of H3R antagonist E177 with an added advantage of avoiding cognitive impairment, emphasizing the H3Rs as a prospective target for future pharmacological management of epilepsy with associated memory impairments.

Identification of N-phenyl-3-methoxy-4-pyridinones as orally bioavailable H3 receptor antagonists and ß-amyloid aggregation inhibitors for the treatment of Alzheimer's disease.

Based on our previous work, a series of N-phenyl-3-methoxy-4-pyridinone derivatives were designed as orally bioavailable dual functional agents for therapy of Alzheimer's disease, through introducing alkyloxy moiety into 4-pyridinone ring to avoid the possible phase II metabolism of 3-hydroxy-4-pyridinone in lead compound 3-hydroxy-2-methyl-1-(4-(3-(pyrrolidin-1-yl)propoxy)phenyl)-pyridin-4(1H)-one (4). In vitro studies indicated that most of these compounds exhibit excellent H3 receptor antagonistic activities and potent self-induced Aß1-40/Aß1-42 aggregation inhibitory activities. In particular, 3-methoxy-1-(4-(3-(pyrrolidin-1-yl)propoxy)phenyl)-pyridin-4(1H)-one (7i) demonstrated IC50 value of 0.52 nM in H3R antagonism and good selectivity over other histamine receptor subtypes. The transmission electron microscopy (TEM) images showed that compound 7i can inhibit self-mediated Aß1-40/Aß1-42 aggregation efficiently. As expected, it exhibited desirable pharmacokinetic properties in plasma and good BBB permeability. Furthermore, compound 7i can efficiently block (R)-α-methylhistamine- induced dipsogenia and reverse scopolamine-induced learning deficits of rats. All above results indicated that compound 7i was a promising orally bioavailable dual functional agents with potential use in the treatment of Alzheimer's disease.

Novel compounds with dual S1P receptor agonist and histamine H3 receptor antagonist activities act protective in a mouse model of multiple sclerosis.

The sphingosine 1-phosphate (S1P) receptor 1 (S1P1) has emerged as a therapeutic target for the treatment of multiple sclerosis (MS). Fingolimod (FTY720) is the first functional antagonist of S1P1 that has been approved for oral treatment of MS. Previously, we have developed novel butterfly derivatives of FTY720 that acted similar to FTY720 in reducing disease symptoms in a mouse model of experimental autoimmune encephalomyelitis (EAE). In this study, we have synthesized a piperidine derivative of the oxazolo-oxazole compounds, denoted ST-1505, and its ring-opened analogue ST-1478, and characterised their in-vitro and in-vivo functions. Notably, the 3-piperidinopropyloxy moiety resembles a structural motif of pitolisant, a drug with histamine H3R antagonistic/inverse agonist activity approved for the treatment of narcolepsy. Both novel compounds exerted H3R affinities, and in addition, ST-1505 was characterised as a dual S1P1+3 agonist, whereas ST-1478 was a dual S1P1+5 agonist. Both multitargeting compounds were also active in mice and reduced the lymphocyte numbers as well as diminished disease symptoms in the mouse model of MS. The effect of ST-1478 was dependent on SK-2 activity suggesting that it is a prodrug like FTY720, but with a more selective S1P receptor activation profile, whereas ST-1505 is a fully active drug even in the absence of SK-2. In summary, these data suggest that the well soluble piperidine derivatives ST-1505 and ST-1478 hold promise as novel drugs for the treatment of MS and other autoimmune or inflammatory diseases, and by their H3R antagonist potency, they might additionally improve cognitive impairment during disease.

Central histaminergic transmission modulates the expression of chronic nicotine withdrawal induced anxiety-like and somatic behavior in mice.

The present study investigated the plausible modulatory role of central histaminergic transmission on the expression of nicotine withdrawal induced anxiety and somatic behavior in mice. Abrupt cessation of chronic nicotine (2 mg/kg, i.p. × 3/day) treatment for 12 days to mice, expressed increased anxiety in light & dark test and total abstinence (somatic) score at 24 h post nicotine withdrawal time. The somatic signs includes a composite score of all behaviors such as grooming, rearing, jumping, body shakes, forelimb tremors, head shakes, abdominal constrictions, scratching, empty mouth chewing or teeth chattering, genital licking, tail licking. Mice exhibited higher expression to nicotine withdrawal induced anxiety in light & dark test at 24 h post-nicotine withdrawal time on pre-treatment centrally (i.c.v) with histaminergic agents like histamine (0.1, 50 µg/mouse), histamine H3 receptor inverse agonist, thioperamide (2, 10 µg/mouse), histamine H1 receptor agonist, FMPH (2, 6.5 µg/mouse) or H2 receptor agonist amthamine (0.1, 0.5 µg/mouse) or intraperitoneally (i.p.) with histamine precursor, l-histidine (250, 500 mg/kg) as compared to control nicotine withdrawn animals. Furthermore, mice pre-treated with all these histaminergic agents except histamine H1 receptor agonist, FMPH shows exacerbated expression to post-nicotine withdrawal induced total abstinence (somatic) score in mice. On the other hand, central injection of selective histamine H1 receptor antagonist, cetirizine (0.1 µg/mouse, i.c.v.) or H2 receptor antagonist, ranitidine (50 µg/mouse, i.c.v) to mice 10 min before 24 h post-nicotine withdrawal time completely alleviated the expression of nicotine withdrawal induced anxiety and somatic behavior. Thus, it can be contemplated that the blockade of central histamine H1 or H2 receptor during the nicotine withdrawal phase could be a novel approach to mitigate the nicotine withdrawal associated anxiety-like manifestations. Contribution of endogenous histamine via H1 or H2 receptor stimulation in the nicotine withdrawal induced anxiety and somatic behavior is proposed.

Targeting presynaptic H3 heteroreceptor in nucleus accumbens to improve anxiety and obsessive-compulsive-like behaviors.

Anxiety commonly co-occurs with obsessive-compulsive disorder (OCD). Both of them are closely related to stress. However, the shared neurobiological substrates and therapeutic targets remain unclear. Here we report an amelioration of both anxiety and OCD via the histamine presynaptic H3 heteroreceptor on glutamatergic afferent terminals from the prelimbic prefrontal cortex (PrL) to the nucleus accumbens (NAc) core, a vital node in the limbic loop. The NAc core receives direct hypothalamic histaminergic projections, and optogenetic activation of hypothalamic NAc core histaminergic afferents selectively suppresses glutamatergic rather than GABAergic synaptic transmission in the NAc core via the H3 receptor and thus produces an anxiolytic effect and improves anxiety- and obsessive-compulsive-like behaviors induced by restraint stress. Although the H3 receptor is expressed in glutamatergic afferent terminals from the PrL, basolateral amygdala (BLA), and ventral hippocampus (vHipp), rather than the thalamus, only the PrL- and not BLA- and vHipp-NAc core glutamatergic pathways among the glutamatergic afferent inputs to the NAc core is responsible for co-occurrence of anxiety- and obsessive-compulsive-like behaviors. Furthermore, activation of the H3 receptor ameliorates anxiety and obsessive-compulsive-like behaviors induced by optogenetic excitation of the PrL-NAc glutamatergic afferents. These results demonstrate a common mechanism regulating anxiety- and obsessive-compulsive-like behaviors and provide insight into the clinical treatment strategy for OCD with comorbid anxiety by targeting the histamine H3 receptor in the NAc core.

In vivo evaluation of effects of histamine H3 receptor antagonists on methamphetamine-induced hyperlocomotion in mice.

A single administration with METH (3 mg/kg) induced a hyperlocomotion in male ICR mice. Pretreatment of mice with pitolisant, a histamine H3 receptor antagonist (5 and 10 mg/kg), for 30 min showed a significant reduction of the hyperlocomotion induced by METH, as compared with vehicle (saline)-pretreated subjects. Pretreatment of mice with the histamine H3 receptor antagonists JNJ-10181457 (5 and 10 mg/kg) or conessine (20 mg/kg), also showed similar inhibitory effects on METH-induced hyperlocomotion, similar to pitolisant. No significant change in locomotion was observed in mice pretreated with pitolisant, JNJ-10181457, or conessine alone. The pitolisant (10 mg/kg) action on METH-induced hyperlocomotion was completely abolished by the histamine H1 receptor antagonist pyrilamine (10 mg/kg), but not by the peripherally acting histamine H1 receptor antagonist fexofenadine (20 mg/kg), the brain-penetrating histamine H2 receptor antagonist zolantidine (10 mg/kg), or the brain-penetrating histamine H4 receptor antagonist JNJ-7777120 (40 mg/kg). Pretreatment with a histamine H3 receptor agonist immepip (10 mg/kg) augmented METH--induced behavior, including hyperlocomotion and stereotyped biting, and combined pretreatment with pitolisant (10 mg/kg) significantly attenuated stereotyped biting. These observations suggest that pretreatment with histamine H3 receptor antagonists attenuate METH-induced hyperlocomotion via releasing histamine after blocking H3 receptors, which then bind to the post-synaptic histamine receptor H1 (but not H2 or H4). It is likely that activation of brain histamine systems may be a good strategy for the development of agents, which treat METH abuse and dependence.

Pitolisant for treating patients with narcolepsy.

Introduction: Narcolepsy is a rare sleep disorder characterized by excessive daytime sleepiness, cataplexy, disturbed nocturnal sleep, hypnagogic hallucinations, and sleep paralysis. Pitolisant is a first-in-class drug acting on histamine 3 receptors and indicated for the treatment of narcolepsy. This article aims to review pitolisant.Areas covered: In this paper the chemical properties, mechanism of action, pharmacokinetics, clinical efficacy and safety of pitolisant was introduced, and the development course of drugs for treating narcolepsy is also briefly described. We performed a systematic review of the literature using PubMed and the following keywords were used: 'pitolisant' and 'narcolepsy', 'cataplexy' and 'excessive daytime sleepiness' and 'histamine 3 receptor'.Expert opinion: Pitolisant is a histamine 3 receptor antagonist/inverse agonist. It can activate histamine release in the brain and enhances wakefulness. Clinical studies showed that pitolisant significantly decreased excessive daytime sleepiness and cataplexy rate versus placebo. Pitolisant was well tolerated, common adverse reactions were headache, insomnia, nausea, and anxiety.

KSK19 - Novel histamine H3 receptor ligand reduces body weight in diet induced obese mice.

AIMS: Histamine H3 receptors ligands act anorectic by blocking the H3 autoreceptors in the CNS, that results in increased synthesis and disinhibition of histamine release. Histamine further influencing H1 receptors participates in the leptin-dependent inhibition of food intake. It also affects the peripheral metabolism by increasing white adipose tissue lipolysis. Thus, ligands such as KSK19 with significant antagonistic properties at the H3 receptor might serve as an useful treatment for obesity. MATERIALS AND METHODS: To induce obesity, female CD-1 mice were fed a high-fat diet for 14 weeks. The test compound at the doses of 10 or 15 mg/kg, i.p. was administrated for 21 days. Glucose and insulin tolerance tests was performed at the beginning of week 15. At the end of study, amount of intraperitoneal fat pads, AlAT, IL-6 and TNF-α plasma levels were determined. RESULTS: Animals fed with high-fat diet and treated with test compound at the dose of 15 mg/kg showed significantly less weight gain, than mice from the control group. The use of KSK19 for 21 days in obese mice also significantly improved glucose tolerance and insulin resistance. In the tested doses KSK19 did not affect locomotor activity neither in lean nor in obese mice after single i.p. administration, but spontaneous activity increased during three hour after twentieth administrations. CONCLUSION: KSK19 is a strong, selective histamine H3 receptor antagonist with a favorable influence on body weight after multiple administration at the dose of 15 mg/kg. Moreover it significantly improves glucose tolerance.

Design, synthesis, and biological evaluation of novel oxadiazole- and thiazole-based histamine H3R ligands.

Histamine H3 receptor (H3R) is largely expressed in the CNS and modulation of the H3R function can affect histamine synthesis and liberation, and modulate the release of many other neurotransmitters. Targeting H3R with antagonists/inverse agonists may have therapeutic applications in neurodegenerative disorders, gastrointestinal and inflammatory diseases. This prompted us to design and synthesize azole-based H3R ligands, i.e. having oxadiazole- or thiazole-based core structures. While ligands of oxadiazole scaffold were almost inactive, thiazole-based ligands were very potent and several exhibited binding affinities in a nanomolar concentration range. Ligands combining 4-cyanophenyl moiety as arbitrary region, para-xylene or piperidine carbamoyl linkers, and/or pyrrolidine or piperidine basic heads were found to be the most active within this series of thiazole-based H3R ligands. The most active ligands were in silico screened for ADMET properties and drug-likeness. They fulfilled Lipinski's and Veber's rules and exhibited potential activities for oral administration, blood-brain barrier penetration, low hepatotoxicity, combined with an overall good toxicity profile.

Novel naphthyloxy derivatives - Potent histamine H3 receptor ligands. Synthesis and pharmacological evaluation.

A series of 1- and 2-naphthyloxy derivatives were synthesized and evaluated for histamine H3 receptor affinity. Most compounds showed high affinities with Ki values below 100 nM. The most potent ligand, 1-(5-(naphthalen-1-yloxy)pentyl)azepane (11) displayed high affinity for the histamine H3 receptor with a Ki value of 21.9 nM. The antagonist behaviour of 11 was confirmed both in vitro in the cAMP assay (IC50 = 312 nM) and in vivo in the rat dipsogenia model (ED50 = 3.68 nM). Moreover, compound 11 showed positive effects on scopolamine induced-memory deficits in mice (at doses of 10 and 15 mg/kg) and an analgesic effect in the formalin test in mice with ED50 = 30.6 mg/kg (early phase) and ED50 = 20.8 mg/kg (late phase). Another interesting compound, 1-(5-(Naphthalen-1-yloxy)pentyl)piperidine (13; H3R Ki = 53.9 nM), was accepted for Anticonvulsant Screening Program at the National Institute of Neurological Disorders and Stroke/National Institute of Health (Rockville, USA). The screening was performed in the maximal electroshock seizure (MES), the subcutaneous pentylenetetrazole (scPTZ) and the 6-Hz psychomotor animal models of epilepsy. Neurologic deficit was evaluated by the rotarod test. Compound 13 inhibited convulsions induced by the MES with ED50 of 19.2 mg/kg (mice, i.p.), 17.8 (rats, i.p.), and 78.1 (rats, p.o.). Moreover, 13 displayed protection against the 6-Hz psychomotor seizures (32 mA) in mice (i.p.) with ED50 of 33.1 mg/kg and (44 mA) ED50 of 57.2 mg/kg. Furthermore, compounds 11 and 13 showed in vitro weak influence on viability of tested cell lines (normal HEK293, neuroblastoma IMR-32, hepatoma HEPG2), weak inhibition of CYP3A4 activity, and no mutagenicity. Thus, these compounds may be used as leads in a further search for histamine H3 receptor ligands with promising in vitro and in vivo activity.

Possible use of a H3R antagonist for the management of nonmotor symptoms in the Q175 mouse model of Huntington's disease.

Huntington's disease (HD) is an autosomal dominant, neurodegenerative disorder characterized by motor as well as nonmotor symptoms for which there is currently no cure. The Q175 mouse model of HD recapitulates many of the symptoms identified in HD patients including disruptions of the sleep/wake cycle. In this study, we sought to determine if the daily administration of the histamine-3 receptor (H3R) antagonist/inverse agonist 6-[(3-cyclobutyl-2,3,4,5-tetrahydro-1H-3-benzazepin-7-yl)oxy]-N-methyl-3-pyridinecarboxamide hydrochloride (GSK189254) would improve nonmotor symptoms in the Q175 line. This class of drugs acts on autoreceptors found at histaminergic synapses and results in increased levels of histamine (HA). HA is a neuromodulator whose levels vary with a daily rhythm with peak release during the active cycle and relatively lower levels during sleep. H3Rs are widely expressed in brain regions involved in cognitive processes and activation of these receptors promotes wakefulness. We administered GSK189254 nightly to homozygote and heterozygote Q175 mice for 4 weeks and confirmed that the plasma levels of the drug were elevated to a therapeutic range. We demonstrate that daily treatment with GSK189254 improved several behavioral measures in the Q175 mice including strengthening activity rhythms, cognitive performance and mood as measured by the tail suspension test. The treatment also reduced inappropriate activity during the normal sleep time. The drug treatment did not alter motor performance and coordination as measured by the challenging beam test. Our findings suggest that drugs targeting the H3R system may show benefits as cognitive enhancers in the management of HD.

Ciproxifan improves cholinergic transmission, attenuates neuroinflammation and oxidative stress but does not reduce amyloid level in transgenic mice.

AIM: The present study is aimed to investigate the ability of ciproxifan, a histamine H3 receptor antagonist to inhibit ß-amyloid (Aß)-induced neurotoxicity in SK-N-SH cells and APP transgenic mouse model. MATERIALS AND METHODS: In vitro studies was designed to evaluate the neuroprotective effects of ciproxifan in Aß25-35 - induced SK-N-SH cells. For the in vivo study, ciproxifan (1 and 3mg/kg, i.p.) was administrated to transgenic mice for 15days and behaviour was assessed using the radial arm maze (RAM). Brain tissues were collected to measure Aß levels (Aß1-40 and Aß1-42), acetylcholine (ACh), acetylcholinesterase (AChE), nitric oxide (NO), lipid peroxidation (LPO), antioxidant activities, cyclooxygenases (COX) and cytokines (IL-1α, IL-1ß and IL-6), while plasma was collected to measure TGF-1ß. RESULTS: The in vitro studies demonstrated neuroprotective effect of ciproxifan by increasing cell viability and inhibiting reactive oxygen species (ROS) in Aß25-35-induced SK-N-SH cells. Ciproxifan significantly improved the behavioural parameters in RAM. Ciproxifan however, did not alter the Aß levels in APP transgenic mice. Ciproxifan increased ACh and showed anti-oxidant properties by reducing NO and LPO levels as well as enhancing antioxidant levels. The neuroinflammatory analysis showed that ciproxifan reduced both COX-1 and COX-2 activities, decreased the level of pro-inflammatory cytokines IL-1α, IL-1ß and IL-6 and increased the level of anti-inflammatory cytokine TGF-1ß. CONCLUSION: This present study provides scientific evidence of the use of ciproxifan via antioxidant and cholinergic pathways in the management of AD.

Non-imidazole-based histamine H3 receptor antagonists with anticonvulsant activity in different seizure models in male adult rats.

A series of twelve novel non-imidazole-based ligands (3-14) was developed and evaluated for its in vitro binding properties at the human histamine H3 receptor (hH3R). The novel ligands were investigated for their in vivo protective effects in different seizure models in male adult rats. Among the H3R ligands (3-14) tested, ligand 14 showed significant and dose-dependent reduction in the duration of tonic hind limb extension in maximal electroshock (MES)-induced seizure model subsequent to acute systemic administration (5, 10, and 20 mg/kg, intraperitoneally), whereas ligands 4, 6, and 7 without appreciable protection in MES model were most promising in pentylenetetrazole (PTZ) model. Moreover, the protective effect observed for ligand 14 in MES model was lower than that observed for the reference drug phenytoin and was entirely abrogated when rats were co-administered with the brain-penetrant H1R antagonist pyrilamine (PYR) but not the brain-penetrant H2R antagonist zolantidine (ZOL), demonstrating that histaminergic neurotransmission by activation of postsynaptically located H1Rs seems to be involved in the protective action. On the contrary, PYR and ZOL failed to abrogate the full protection provided by 4 in PTZ model and the moderate protective effect by 14 in strychnine (STR) model. Moreover, the experimental and in silico estimation of properties such as metabolism was performed for five selected test compounds. Also, lipophilicity using planar reversed-phase thin-layer chromatography method was included for better understanding of the molecular properties of the tested compounds. Additionally, the absorption, distribution, metabolism, and elimination and toxicity parameters were evaluated for the most promising compounds 2, 4, 6, 7, and 14 utilizing in vitro methods. These interesting results highlight the potential of H3R ligands as new antiepileptic drugs or as adjuvants to available epilepsy medications.

Anticonvulsant effects of isomeric nonimidazole histamine H3 receptor antagonists.

Phenytoin (PHT), valproic acid, and modern antiepileptic drugs (AEDs), eg, remacemide, loreclezole, and safinamide, are only effective within a maximum of 70%-80% of epileptic patients, and in many cases the clinical use of AEDs is restricted by their side effects. Therefore, a continuous need remains to discover innovative chemical entities for the development of active and safer AEDs. Ligands targeting central histamine H3 receptors (H3Rs) for epilepsy might be a promising therapeutic approach. To determine the potential of H3Rs ligands as new AEDs, we recently reported that no anticonvulsant effects were observed for the (S)-2-(4-(3-(piperidin-1-yl)propoxy)benzylamino)propanamide (1). In continuation of our research, we asked whether anticonvulsant differences in activities will be observed for its R-enantiomer, namely, (R)-2-(4-(3-(piperidin-1-yl)propoxy)benzylamino)propaneamide (2) and analogs thereof, in maximum electroshock (MES)-, pentylenetetrazole (PTZ)-, and strychnine (STR)-induced convulsion models in rats having PHT and valproic acid (VPA) as reference AEDs. Unlike the S-enantiomer (1), the results show that animals pretreated intraperitoneally (ip) with the R-enantiomer 2 (10 mg/kg) were moderately protected in MES and STR induced models, whereas proconvulsant effect was observed for the same ligand in PTZ-induced convulsion models. However, animals pretreated with intraperitoneal doses of 5, 10, or 15 mg/kg of structurally bulkier (R)-enantiomer (3), in which 3-piperidinopropan-1-ol in ligand 2 was replaced by (4-(3-(piperidin-1-yl)propoxy)phenyl)methanol, and its (S)-enantiomer (4) significantly and in a dose-dependent manner reduced convulsions or exhibited full protection in MES and PTZ convulsions model, respectively. Interestingly, the protective effects observed for the (R)-enantiomer (3) in MES model were significantly greater than those of the standard H3R inverse agonist/antagonist pitolisant, comparable with those observed for PHT, and reversed when rats were pretreated with the selective H3R agonist R-(α)-methyl-histamine. Comparisons of the observed antagonistic in vitro affinities among the ligands 1-6 revealed profound stereoselectivity at human H3Rs with varying preferences for this receptor subtype. Moreover, the in vivo anticonvulsant effects observed in this study for ligands 1-6 showed stereoselectivity in different convulsion models in male adult rats.

Histamine H3 receptor antagonist OUP-186 attenuates the proliferation of cultured human breast cancer cell lines.

Histamine is involved in various physiological functions, including its neurotransmitter actions in the central nervous system and its action as a causative agent of inflammation, allergic reactions, and gastric acid secretions. Histamine expression and biosynthesis have been detected in breast cancer cells. It was recently suggested that the histamine H3 receptor (H3R) plays a role in the proliferation of breast cancer cells. We recently developed the non-imidazole H3R antagonist OUP-186 which exhibited a potent and selective human H3R antagonistic activity as well as no activity against the human histamine H4 receptor (H4R). In this study, we compared the effects of OUP-186 on the proliferation of estrogen receptor negative (ER-) breast cancer cells (MDA-MB-231) and ER+ breast cancer cells (MCF7) to the effects of clobenpropit (potent imidazole-containing H3R antagonist). OUP-186 and clobenpropit suppressed the proliferation of breast cancer cells. The IC50 values at 48 h for OUP-186 and clobenpropit were approximately 10 µM and 50 µM, respectively. Furthermore, OUP-186 potently induced cell death by activating caspase-3/7, whereas cell death was only slightly induced by clobenpropit. In addition, OUP-186 treatment blocked the proliferation increase triggered by 100 µM (R)-(-)-α-methylhistamine (H3R agonist). The use of 4-methylhistamine (H4R agonist) and JNJ10191584 (selective H4R antagonist) did not affect breast cancer proliferation. These results indicate that OUP-186 potently suppresses proliferation and induces caspase-dependent apoptotic death in both ER+ and ER-breast cancer cells.

Benzamide derivatives and their constrained analogs as histamine H3 receptor antagonists.

A series of 4-(1-substituted piperidin-4-yloxy) benzamides and 6-(1-substituted piperidin-4-yloxy)-3,4-dihydro-2H-isoquinolin-1-one derivatives have been synthesized and tested for their binding affinity towards H3 receptor. Most of these synthesized compounds have displayed potent binding affinity for H3 receptor when tested in in vitro binding assay. Preliminary SAR studies, functional activity, pharmacokinetic profile and efficacy profile constitute the subject matter of this communication.

Pharmacokinetics and tissue distribution of the new non-imidazole histamine H3 receptor antagonist 1-[3-(4-tert-butylphenoxy) propyl]piperidine in rats.

1. The aim of this study was to evaluate pharmacokinetics and tissue distribution of novel histamine H3 receptor antagonist 1-[3-(4-tert-butylphenoxy)propyl]piperidine (compound DL76). 2. Following intravenous administration of DL76 at the dose of 3 mg/kg, pharmacokinetic parameters were calculated using non-compartmental analysis. The systemic serum clearance was 10.08 L/h/kg and the estimated blood clearance was 5.64 L/h/kg. The volume of distribution at steady state was 16.1 L/kg which was greater than total body water, terminal half-life and MRT equalled 1.41 h and 1.6 h, respectively. The two-compartment pharmacokinetic model with enterohepatic circulation was also successfully fitted to the experimental data. 3. After systemic administration, DL76 was rapidly distributed into all organs studied (liver, kidney, brain, and lung). The highest AUC of DL76 was observed in lungs followed by brain, where the exposure to the investigated compound expressed as AUC was almost 30 times higher than in serum. 4. Bioavailability, calculated based on the area-under-the-concentration-time curve extrapolated to infinity after intravenous and intragastric administration of the dose 3 mg/kg, equalled 60.9%.

Hippocampal-Dependent Antidepressant Action of the H3 Receptor Antagonist Clobenpropit in a Rat Model of Depression.

BACKGROUND: Histamine is a modulatory neurotransmitter regulating neuronal activity. Antidepressant drugs target modulatory neurotransmitters, thus ultimately regulating glutamatergic transmission and plasticity. Histamine H3 receptor (H3R) antagonists have both pro-cognitive and antidepressant effects; however, the mechanism by which they modulate glutamate transmission is not clear. We measured the effects of the H3R antagonist clobenpropit in the Flinders Sensitive Line (FSL), a rat model of depression with impaired memory and altered glutamatergic transmission. METHODS: Behavioral tests included the forced swim test, memory tasks (passive avoidance, novel object recognition tests), and anxiety-related paradigms (novelty suppressed feeding, social interaction, light/dark box tests). Hippocampal protein levels were detected by Western blot. Hippocampal plasticity was studied by in slice field recording of CA3-CA1 long-term synaptic potentiation (LTP), and glutamatergic transmission by whole-cell patch clamp recording of excitatory postsynaptic currents (EPSCs) in CA1 pyramidal neurons. RESULTS: Clobenpropit, administered systemically or directly into the hippocampus, decreased immobility during the forced swim test; systemic injections reversed memory deficits and increased hippocampal GluN2A protein levels. FSL rats displayed anxiety-related behaviors not affected by clobenpropit treatment. Clobenpropit enhanced hippocampal plasticity, but did not affect EPSCs. H1R and H2R antagonists prevented the clobenpropit-induced increase in LTP and, injected locally into the hippocampus, blocked clobenpropit's effect in the forced swim test. CONCLUSIONS: Clobenpropit's antidepressant effects and the enhanced synaptic plasticity require hippocampal H1R and H2R activation, suggesting that clobenpropit acts through disinhibition of histamine release. Clobenpropit reverses memory deficits and increases hippocampal GluN2A expression without modifying anxiety-related phenotypes or EPSCs in CA1 pyramidal neurons.

Clobenpropit enhances anti-tumor effect of gemcitabine in pancreatic cancer.

AIM: To evaluate the anti-tumor effect of clobenpropit, which is a specific H3 antagonist and H4 agonist, in combination with gemcitabine in a pancreatic cancer cell line. METHODS: Three kinds of human pancreatic cancer cell lines (Panc-1, MiaPaCa-2, and AsPC-1) were used in this study. Expression of H3 and H4 receptors in pancreatic cancer cells was identified with Western blotting. Effects of clobenpropit on cell proliferation, migration and apoptosis were evaluated. Alteration of epithelial and mesenchymal markers after administration of clobenpropit was analyzed. An in vivo study with a Panc-1 xenograft mouse model was also performed. RESULTS: H4 receptors were present as 2 subunits in human pancreatic cancer cells, while there was no expression of H3 receptor. Clobenpropit inhibited cell migration and increased apoptosis of pancreatic cancer cells in combination with gemcitabine. Clobenpropit up-regulated E-cadherin, but down-regulated vimentin and matrix metalloproteinase 9 in real-time polymerase chain reaction. Also, clobenpropit inhibited tumor growth (gemcitabine 294 ± 46 mg vs combination 154 ± 54 mg, P = 0.02) and enhanced apoptosis in combination with gemcitabine (control 2.5%, gemcitabine 25.8%, clobenpropit 9.7% and combination 40.9%, P = 0.001) by up-regulation of E-cadherin and down-regulation of Zeb1 in Panc-1 xenograft mouse. CONCLUSION: Clobenpropit enhanced the anti-tumor effect of gemcitabine in pancreatic cancer cells through inhibition of the epithelial-mesenchymal transition process.