Non-imidazole Histamine H3 Receptor Antagonists Research Articles

Structures 4-n-propyl Piperazines as Non-Imidazole Histamine H3 Antagonists.

Seven new low-temperature structures of 4-n-propylpiperazine derivatives, potential H3 receptor antagonists, have been determined by X-ray crystallography, with the following symmetry and unit cell parameters: 2-(4-propyl-piperazin-1-yl)oxazolo[4,5-c]pyridine (compound 1), P-1, 5.9496 Å, 12.4570 Å, 12.8656 Å, 112.445°, 95.687°, 103.040°; 2-(4-propyl-piperazin-1-yl)thia-zolo[4,5-c]pyridine (compound 2), I2/a, 22.2087 Å, 7.5519 Å, 19.9225 Å, β = 92.368°; 2-(4-propyl-piperazin-1-yl)oxazolo[5,4-c]pyridine (compound 3), C2/c, 51.1351 Å, 9.36026 Å, 7.19352 Å, β = 93.882°; 2-(4-propyl-piperazin-1-yl)thiazolo[5,4-c]pyridine (compound 4), Pbcn, 19.2189 Å, 20.6172 Å, 7.4439 Å; 2-(4-propylpiperazin-1-yl)[1,3]oxazolo[4,5-b]pyridine, hydrate (structure 5), Pbca, 7.4967 Å, 12.2531 Å, 36.9527 Å; 2-(4-propylpiperazin-1-yl)[1,3]oxazolo[4,5-b]pyridine, first polymorph (structure 6), P-1, 7.2634 Å, 11.1261 Å, 18.5460 Å, 80.561°, 80.848°, 76.840°; 2-(4-propylpiperazin-1-yl)[1,3]oxazolo[4,5-b]pyridine, second polymorph (structure 7), P21, 8.10852 Å, 7.06025 Å, 12.41650 Å, β = 92.2991°. All the compounds crystallized out as hydrobromides. Oxazole structures show a much greater tendency to form twin crystals than thiazole structures. All the investigated structures display N—H···Br hydrogen bonding. (ADME) analysis, including the assessment of absorption, distribution, metabolism, and excretion, determined the physicochemical properties, pharmacokinetics, drug similarity, and bioavailability radar, and confirmed the usefulness of the compounds in question for pharmaceutical utility. This work is a continuation of the research searching for a new lead of non-imidazole histamine H3 receptor antagonists.

Synthesis and antiseizure effectevaluation of nonimidazole histamine H3 receptor antagonists containing the oxazole moiety.

The use of histamine H3 receptor (H3 R) antagonists is becoming a promising therapeutic approach for epilepsy. In this paper, a series of novel nonimidazole H3 R antagonists was synthesized and screened as antiepileptic drugs. All of these prepared antagonists displayed micromolar or submicromolar H3 R antagonistic activities in the cAMP response element luciferase screening assay. Compounds 5a (IC50 = 0.11 μM), 5b (IC50 = 0.56 μM), and 5f (IC50 = 0.78 μM) displayed the most potent H3 R antagonistic activities, with considerable potency when compared with pitolisant (IC50 = 0.51 μM). In the maximal electroshock (MES)-induced seizure model, compounds 5c, 5e, and 5g showed obvious protection for the electrostimulated mice, and the protection of 5g against the MES-induced seizures was fully abrogated when mice were cotreated with R-(α)-methyl-histamine, a central nervous system-penetrant H3 R agonist, suggesting that the potential therapeutic effect of 5g was observed to work through H3 R. These results indicate that the attempt to find a new antiepileptic drug among H3 R antagonists is practicable, but it is necessary to consider the log P of the molecules to ensure penetration of the blood-brain barrier.

Studies on Anticonvulsant Effects of Novel Histamine H3R Antagonists in Electrically and Chemically Induced Seizures in Rats.

A newly developed series of non-imidazole histamine H3 receptor (H3R) antagonists (1–16) was evaluated in vivo for anticonvulsant effects in three different seizure models in Wistar rats. Among the novel H3R antagonists examined, H3R antagonist 4 shortened the duration of tonic hind limb extension (THLE) in a dose-dependent fashion in the maximal electroshock (MES)-induced seizure and offered full protection against pentylenetetrazole (PTZ)-induced generalized tonic-clonic seizure (GTCS), following acute systemic administration (2.5, 5, 10, and 15 mg/kg, i.p.). However, only H3R antagonist 13, without appreciable protective effects in MES- and PTZ-induced seizure, fully protected animals in the strychnine (STR)-induced GTCS following acute systemic pretreatment (10 mg/kg, i.p.). Moreover, the protective effect observed with H3R antagonist 4 in MES-induced seizure was completely abolished when animals were co-administered with the H3R agonist (R)-α-methylhistamine (RAMH, 10 mg/kg, i.p.). However, RAMH failed to abolish the full protection provided by the H3R antagonist 4 in PTZ-induced seizure and H3R antagonist 13 in STR-induced seizure. Furthermore, in vitro antiproliferative effects or possible metabolic interactions could not be observed for compound 4. Additionally, the predictive in silico, as well as in vitro, metabolic stability for the most promising H3R antagonist 4 was assessed. The obtained results show prospective effects of non-imidazole H3R antagonists as innovative antiepileptic drugs (AEDs) for potential single use against epilepsy.

Anticonvulsant evaluation of novel non-imidazole histamine H3R antagonists in different convulsion models in rats

Novel non-imidazole histamine H3 receptor (H3R) antagonists (2–8) were developed and assessed for in-vitro antagonist binding affinities at the human histamine H1–H4R. These novel H3R antagonists (2–8) were examined in-vivo for anticonvulsant effects in three different convulsion models in male adult rats. Compound 6 significantly and dose-dependently exhibited decreased duration of tonic hind limb extension (THLE) in the maximal electroshock (MES)- and fully protected animals against pentylenetetrazole (PTZ)-induced convulsion, following acute systemic administration (5, 10, and 20 mg/kg, i.p.). Contrary, all compounds 2–8 showed moderate protection in the strychnine (STR)-induced convulsion model following acute pretreatment (10 mg/kg, i.p.). Moreover, the acute systemic administration of H3R antagonist 6 (10 mg/kg, i.p.) significantly prolonged latency time for MES convulsions. Furthermore, the anticonvulsant effect observed with compound 6 in MES-model was entirely abrogated when rats were co-injected with the brain penetrant H1R antagonist pyrilamine (PYR) but not the brain penetrant H2R antagonist zolantidine (ZOL). However, PYR and ZOL failed to abolish the full protection provided by the H3R antagonist 6 in PTZ- and STR-models. No mutagenic or antiproliferative effects or potential metabolic interactions were shown for compound 6 when assessing its antiproliferative activities and metabolic profiling applying in-vitro methods. These findings demonstrate the potential of non-imidazole H3R antagonists as novel antiepileptic drugs (AEDs) either for single use or in addition to currently available epilepsy medications.

4-Hydroxypiperidines and Their Flexible 3-(Amino)propyloxy Analogues as Non-Imidazole Histamine H₃ Receptor Antagonist: Further Structure⁻Activity Relationship Exploration and In Vitro and In Vivo Pharmacological Evaluation.

Presynaptic histamine H3 receptors (H3R) act as auto- or heteroreceptors controlling, respectively, the release of histamine and of other neurotransmitters in the central nervous system (CNS). The extracellular levels of several neurotransmitters are enhanced by H3R antagonists, and there is a great interest for potent, brain-penetrating H3 receptor antagonists/inverse agonists to compensate for the neurotransmitter deficits present in various neurological disorders. We have shown that 1-[(benzylfuran-2-yl)methyl]piperidinyl-4-oxyl- and benzyl- derivatives of N-propylpentan-1-amines exhibit high in vitro potencies toward the guinea pig H3 receptor (jejunum), with pA2 = 8.47 and 7.79, respectively (the reference compound used was thioperamide with pA2 = 8.67). Furthermore, following the replacement of 4-hydroxypiperidine with a 3-(methylamino)propyloxy chain, the pA2 value for the first group decreased, whereas it increased for the second group. Here, we present data on the impact of elongating the aliphatic chain between the nitrogen of 4-hydroxypiperidine or 3-(methylamino)propan-1-ol and the lipophilic residue. Additionally, the most active compound in this series of non-imidazole H3 receptor antagonists/inverse agonists, i.e., ADS-003, was evaluated for its affinity to the recombinant rat and human histamine H3 receptors transiently expressed in HEK-293T cells. It was shown that ADS-003, given parenterally for 5 days, reduced the food intake of rats, as well as changed histamine and noradrenaline concentrations in the rats’ brain in a manner and degree similar to the reference H3 antagonist Ciproxifan.

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.

Efficient Approaches to S-alkyl-N-alkylisothioureas and Application to Novel Histamine H3R Antagonists.

S-Alkyl-N-alkylisothiourea compounds, which contain various cyclic amines, were synthesized using 3-phenylpropionyl isothiocyanate (PPI) to discover novel non-imidazole histamine H3 receptor (H3R) antagonists. The synthetic route was improved remarkably by using 2-nitrophenylacetyl isothiocyanate (NPAI). Among the synthesized compounds, N-[4-(4-chlorophenyl)butyl]-S-[3-piperidin-1-yl)propyl]isothiourea (1k, OUP-186) exhibited potent and selective antagonism against human H3R but not human H4R, in vitro. Of particular interest, they did not show antagonism for the histamine release in rat brain microdialysis in vivo, suggesting species-selective differences in antagonist affinities. Furthermore, in silico docking studies of OUP-186 and its C2-homolog (OUP-181) in human/rat H3Rs suggested that the structural difference of antagonist-docking sites between human and rat H3Rs was attributable to the Ala122/Val122 mutation.

Anticonvulsant and procognitive properties of the non-imidazole histamine H3 receptor antagonist DL77 in male adult rats

It has become clear that histamine H3 receptors (H3Rs) are implicated in modulating epilepsy and memory in laboratory animals. The new non-imidazole H3R antagonist DL77 has excellent selectivity profile and shows high in-vivo potency as well as in-vitro antagonist affinity with ED50 values of 2.1 ± 0.2 mg/kg and 8.4 ± 1.3 [nM], respectively. In the present study, the anticonvulsant effects of DL77 on maximal electroshock (MES)-, pentylenetetrazole (PTZ)-, and strychnine (STR)-induced seizure models were investigated. Moreover, the procognitive properties of DL77 were tested on acquisition, consolidation and retrieval processes in a one-trial inhibitory avoidance task in male Wistar rats. The results indicate that DL77 (5, 10, and 15 mg/kg, i.p.) significantly and dose-dependently reduced MES-induced seizure duration, whereas no protection was observed in PTZ- or STR-induced seizures. Importantly, the protective action observed for DL77 in MES-induced seizure was comparable to that of the reference antiepileptic drug (AED) phenytoin (PHT), and was also reversed when rats were pretreated with the CNS penetrant pyrilamine (PYR) (10 mg/kg, i.p.), or with the selective H3R agonist R-(α)-methyl-histamine (RAMH) (10 mg/kg, i.p.). Furthermore, the procognitive studies indicate that acute pre-training systemic administration of DL77 (2.5 mg/kg, i.p.) facilitated acquisition, whereas pre-testing acute administration of DL77 (5 and 10 mg/kg, i.p.) improved retrieval. Interestingly, the procognitive effect of DL77 on retrieval was completely abrogated when rats were pretreated with the centrally-acting H2R antagonist zolantidine (ZOL) but not the centrally acting H1R antagonist PYR, indicating that histaminergic pathways through activation of H2Rs appear to be participating in neuronal circuits involved in retrieval processes. Taken together, our results show that DL77 demonstrates anticonvulsant properties in the MES-induced seizure model and improves cognitive performance through actions on different memory stages. Therefore, H3Rs may have implications for the treatment of degenerative disorders associated with impaired memory function and may represent a novel therapeutic pharmacological target to tackle cognitive problems associated with the chronic use of antiepileptic drugs.This article is part of the Special Issue entitled ‘Histamine Receptors’.

The novel non-imidazole histamine H3 receptor antagonist DL77 reduces voluntary alcohol intake and ethanol-induced conditioned place preference in mice

It has become clear that histamine H3 receptors (H3R) have been implicated in modulating ethanol intake and preference in laboratory animals. The novel non-imidazole H3R antagonist DL77 with excellent selectivity profile shows high in-vivo potency as well as in-vitro antagonist affinity with ED50 of 2.1±0.2mg/kg and pKi=8.08, respectively. In the present study, and applying an unlimited access two-bottle choice procedure, the anti-alcohol effects of the H3R antagonist, DL77 (0, 3, 10 and 30mg/kg; i.p.), were investigated in adult mice. In this C57BL/6 line, effects of DL77 on voluntary alcohol intake and preference, as well as on total fluid intake were evaluated. Results have shown that DL77, dose-dependently, reduced both ethanol intake and preference. These effects were very selective as both saccharin and quinine, used to control for taste sensitivity, and intakes were not affected following DL77 pre-application. More importantly, systemic administration of DL77 (10mg/kg) during acquisition inhibited ethanol-induced conditioned-place preference (EtOH-CPP) as measured using an unbiased protocol. The anti-alcohol activity observed for DL77 was abrogated when mice 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). These results suggest that DL77 has a predominant role in two in vivo effects of ethanol. Therefore, signaling via H3R is essential for ethanol-related consumption and conditioned reward and may represent a novel therapeutic pharmacological target to tackle ethanol abuse and alcoholism.

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%.

Anticonvulsive effect of nonimidazole histamine H3 receptor antagonists.

To determine the potential of histamine H3 receptor (H3R) ligands as new antiepileptic drugs (AEDs), aromatic ether, and diether derivatives (1-12) belonging to the nonimidazole class of ligands, with high in-vitro binding affinity at human H3R, were tested for their in-vivo anticonvulsive activity in the maximal electroshock (MES)-induced and pentylenetetrazole (PTZ)-kindled seizure models in rats. The anticonvulsive effects of a systemic injection of 1-12 on MES-induced and PTZ-kindled seizures were evaluated against the reference AED phenytoin (PHT) and the structurally related H3R antagonist/inverse agonist pitolisant (PIT). Among the most promising ligands 2, 4, 5, and 11, there was a significant and dose-dependent reduction in the duration of tonic hind limb extension (THLE) in MES-induced seizure subsequent to administration of 4 and 5 [(5, 10, and 15 mg/kg, intraperitoneally (i.p.)]. The protective effects observed for the 1-(3-(3-(4-chlorophenyl)propoxy)propyl)-3-methylpiperidine derivative 11 at 10 mg/kg, i.p. were significantly greater than those of PIT, and were reversed by pretreatment with the central nervous system penetrant H1R antagonist pyrilamine (PYR) (10 mg/kg). Moreover, the protective action of the reference AED PHT, at a dose of 5 mg/kg (without considerable protection in the MES model), was significantly augmented when coadministered with derivative 11 (5 mg/kg, i.p.). Surprisingly, pretreatment with derivative 7 (10 mg/kg, i.p.), an ethylphenoxyhexyl-piperidine derivative without considerable protection in the MES model, potently altered PTZ-kindled seizure, significantly prolonged myoclonic latency time, and clearly shortened the total seizure time when compared with control, PHT, and PIT. These interesting results highlight the potential of H3R ligands as new AEDs or as adjuvants to available AED therapeutics.

Anxiolytic and antidepressant-like activities of the novel and potent non-imidazole histamine H₃ receptor antagonist ST-1283.

Previous studies have suggested a potential link between histamine H3 receptors (H3R) signaling and anxiolytic-like and antidepressant-like effects. The aim of this study was to investigate the acute effects of ST-1283, a novel H3R antagonist, on anxiety-related and depression-related behaviors in comparison with those of diazepam and fluoxetine. The effects of ST-1283 were evaluated using the elevated plus maze test, open field test, marbles burying test, tail suspension test, novelty suppressed feeding test, and forced swim test in male C57BL/6 mice. The results showed that, like diazepam, ST-1283 (7.5 mg/kg) significantly modified all the parameters observed in the elevated plus maze test. In addition, ST-1283 significantly increased the amount of time spent in the center of the arena without altering general motor activity in the open field test. In the same vein, ST-1283 reduced the number of buried marbles as well as time spent digging in the marbles burying test. The tail suspension test and forced swim test showed that ST-1283 was able to reduce immobility time, like the recognized antidepressant drug fluoxetine. In the novelty suppressed feeding test, treatment with ST-1283 decreased latency to feed with no effect on food intake in the home cage. Importantly, pretreatment with the H3R agonist R-α-methylhistamine abrogated the anxiolytic and antidepressant effects of ST-1283. Taken together, the present series of studies demonstrates the novel effects of this newly synthesized H3R antagonist in a number of preclinical models of psychiatric disorders and highlights the histaminergic system as a potential therapeutic target for the treatment of anxiety-related and depression-related disorders.

Structure–Activity Relationships of New 1‐substitutedmethyl‐4‐[5‐(N‐methyl‐N‐propylamino)pentyloxy]piperidines and Selected 1‐[(N‐substituted‐N‐methyl)‐3‐propyloxy]‐5‐(N‐methy‐l‐N‐propyl)‐pentanediamines as H3‐Antagonists

Novel, potent non-imidazole histamine H3 receptor antagonists have been prepared and in vitro tested as H3 -receptor antagonists (the electrically evoked contraction of the guinea-pig jejunum). The present compounds contain a 4-hydroxypiperidine core, which behaves as a conformationally restricted version of the 3-amino-1-propanol moiety common to the many previously described non-imidazole H3 ligands. Detailed structure-activity studies revealed that 1-(2-benzofuranylmethyl)- 5c (pA2 = 8.47 ± 0.05) and 1-(3-benzofuranylmethyl)-4-[5-(N-methyl-N-propyl)pentyloxy]piperidine 5d (pA2 = 8.15 ± 0.07) exhibit high potency for the H3 histamine receptor. In addition, the potency of selected 1-[(N-substituted-N-methyl)-3-propyloxy]-5-(N-methyl-N-propyl)pentanediamines as antagonist of the H3 histamine receptor was also evaluated. Replacement of the 4-hydroxypiperidine of the leads 7 and 5c by a highly flexible 3-(methylamino)propyloxy chain yields compounds 6a (pA2 = 8.02) and 6b (pA2 = 6.23) with higher and lower potency than their piperidine analogues (7, pA2 = 7.79; 5c, pA2 = 8.47), respectively. The histaminergic H1 antagonism of selected compounds 5c, 5d and 6a has been established on the isolated guinea-pig ileum by conventional methods; the pA2 values have compared with the potency of pyrilamine. None of them showed any H1 -antagonistic activity (pA2 < 4; for pyrilamine pA2 = 8.5).

Synthesis and evaluation of N-alkyl-S-[3-(piperidin-1-yl)propyl]isothioureas: High affinity and human/rat species-selective histamine H3 receptor antagonists

S-Alkyl-N-alkylisothiourea compounds containing various cyclic amines were synthesized in the search for novel nonimidazole histamine H3 receptor (H3R) antagonists. Among them, four N-alkyl S-[3-(piperidin-1-yl)propyl]isothioureas 18, 19, 22, and 23 were found to exhibit potent and selective H3R antagonistic activities against in vitro human H3R, but were inactive against in vitro human H4R. Furthermore, three alkyl homologs 18–20 showed inactivity for histamine release in in vivo rat brain microdialysis, suggesting differences in antagonist affinities between species. In addition, in silico docking studies of N-[4-(4-chlorophenyl)butyl]-S-[3-piperidin-1-yl)propyl]isothiourea 19 and a shorter homolog 17 with human/rat H3Rs revealed that structural differences between the antagonist-docking cavities of rat and human H3Rs were likely caused by the Ala122/Val122 mutation.

Preclinical evaluation of non-imidazole histamine H3 receptor antagonists in comparison to atypical antipsychotics for the treatment of cognitive deficits associated with schizophrenia

Cognitive deficits associated with schizophrenia (CDS) are implicated as a core symptom cluster of the disease and are associated with poor daily life functioning. Unfortunately, current antipsychotic agents provide little alleviation of CDS, representing a critical unmet therapeutic need. Here we investigated the effects of ABT-239 and A-431404, non-imidazole histamine H(3) receptor (H(3)R) antagonists, in animal models with relevance to CDS. As N-methyl-d-aspartate receptor hypofunction is considered an important factor in the pathogenesis of schizophrenia, acute administration of ketamine or MK-801 was used to induce cognitive impairments. The assays employed in the current studies were spontaneous alternation in cross-maze, used as an indication of working memory, and inhibitory avoidance (IA), used to assess long-term memory retention. Risperidone and olanzapine were also tested to directly compare the effects of H(3)R antagonists to two widely used antipsychotics. ABT-239 and A-431404, but not risperidone and olanzapine, attenuated ketamine-induced deficits on spontaneous alternation in cross-maze, while none of these compounds affected alternation performance on their own. ABT-239 and A-431404 also attenuated MK-801-induced impairments in IA; no effects were observed when given alone. Risperidone and olanzapine, however, failed to attenuate MK-801-induced deficits in IA and produced dose-dependent impairments when given alone. ABT-239 was also investigated in methylazoxymethanol acetate (MAM) treated rats, a neurodevelopmental model for schizophrenia. Chronic, but not acute, treatment with ABT-239 significantly improved spontaneous alternation impairments in MAM rats tested in cross-maze. In summary, these results suggest H(3)R antagonists may have the potential to ameliorate CDS.

Selective brain region activation by histamine H3 receptor antagonist/inverse agonist ABT-239 enhances acetylcholine and histamine release and increases c-Fos expression

Histamine axons originate solely from the tuberomamillary nucleus (TMN) to innervate almost all brain regions. This feature is consistent with a function for histamine over a host of physiological processes, including regulation of appetite, body temperature, cognitive processes, pain perception and sleep–wake cycle. An important question is whether these diverse physiological roles are served by different histamine neuronal subpopulations. Here we report that systemic administration of the non-imidazole histamine H3 receptor antagonist 4-(2-{2-[(2R)-2-methylpyrrolidinyl]ethyl}-benzofuran-5-yl)benzonitrile (ABT-239, 3 mg/kg) increased c-Fos expression dose-dependently in rat cortex and nucleus basalis magnocellularis (NBM) but not in the nucleus accumbens (NAcc) nor striatum, and augmented acetylcholine and histamine release from rat prefrontal cortex. To further understand functional histaminergic pathways in the brain, dual-probe microdialysis was used to pharmacologically block H3 receptors in the TMN. Perfusion of the TMN with ABT-239 (10 μM) increased histamine release from the TMN, NBM, and cortex, but not from the striatum or NAcc. When administered locally, ABT-239 increased histamine release from the NBM, but not from the NAcc. Systemic as well as intra-TMN administration of ABT-239 increased c-Fos expression in the NBM, and cortex, but not in the striatum or NAcc. Thus, as defined by their sensitivity to ABT-239, histaminergic neurons establish distinct pathways according to their terminal projections, and can differentially modulate neurotransmitter release in a brain region-specific manner. This implies independent functions of subsets of histamine neurons according to their terminal projections, with relevant consequences for the development of specific compounds that affect only subsets of histamine neurones, thus increasing target specificity.

Preclinical investigations into the antipsychotic potential of the novel histamine H3 receptor antagonist GSK207040

To test the novel nonimidazole histamine H3 receptor antagonist 5-[(3-cyclobutyl-2,3,4,5-tetrahydro-1H-3-benzazapin-7-yl)oxy]-N-methyl-2-pyrazinecarboxamide (GSK207040) in a series of behavioral and neurochemical paradigms designed to evaluate its antipsychotic potential. Acute orally administered GSK207040 was investigated for its capacity to reverse a 24-h-induced deficit in novel object recognition memory, deficits in prepulse inhibition (PPI) induced by isolation rearing, and hyperlocomotor activity induced by amphetamine. The acute neurochemical effects of GSK207040 were explored by analyzing rat anterior cingulate cortex microdialysates for levels of dopamine, noradrenaline, and acetylcholine and by c-fos immunohistochemistry. The potential for interaction with the antipsychotic dopamine D2 receptor antagonist haloperidol was explored behaviorally (spontaneous locomotor activity and catalepsy), biochemically (plasma prolactin), and via ex vivo receptor occupancy determinations. GSK207040 significantly enhanced object recognition memory (3 mg/kg) and attenuated isolation rearing-induced deficits in PPI (1.0 and 3.2 mg/kg) but did not reverse amphetamine-induced increases in locomotor activity. There was no evidence of an interaction of GSK207040 with haloperidol. GSK207040 (3.2 mg/kg) raised extracellular concentrations of dopamine, noradrenaline, and acetylcholine in the anterior cingulate cortex and c-fos expression in the core of the nucleus accumbens was increased at doses of 3.2 and 10.0 mg/kg. The behavioral and neurochemical profile of GSK207040 supports the potential of histamine H3 receptor antagonism to treat the cognitive and sensory gating deficits of schizophrenia. However, the failure of GSK207040 to reverse amphetamine-induced locomotor hyperactivity suggests that the therapeutic utility of histamine H(3) receptor antagonism versus positive symptoms is less likely, at least following acute administration.

O3-05-02: Peptidomimetics derived from the amyloid precursor protein (APP) as potential therapeutic agents in Alzheimer’s disease

of several neurotransmitters in the brain and enhance cognition in rodent models. Several H3 antagonists are being developed as symptomatic agents for the treatment of cognitive deficits in Alzheimer’s Disease and other dementias. Objective: To investigate the in vitro and in vivo properties of GSK189254, a novel non-imidazole histamine H3 receptor antagonist. Methods: GSK189254 was profiled in standard in vitro binding and functional assays. In vivo oral activity of GSK189254 was assessed in several assays including ex vivo binding, cognition models and EEG. Results: GSK189254 had high affinity for native H3 receptors expressed in human and rat cerebral cortex (pKi 9.59 and 8.58 respectively) and for human and rat recombinant H3 receptors (pKi 9.90 and 9.17 respectively). GSK189254 was highly selective for H3 receptors ( 10000-fold vs other receptors, ion channels and transporters) and exhibited high functional antagonist potency at the human recombinant H3 receptor in vitro (pA2 9.1 vs imetit-induced inhibition of forskolin-stimulated cAMP accumulation). In vitro autoradiography studies with [3H]-GSK189254 in rat brain slices demonstrated a specific binding pattern consistent with H3 receptor distribution in cortex, hippocampus, striatum and hypothalamus. Specific [3H]-GSK189254 labelling was also observed in post-mortem cortex and hippocampus from human control and Alzheimer’s disease brains. Following oral administration in rats, GSK189254 exhibited high H3 receptor occupancy in the cerebral cortex (ED50 0.17mg/kg from ex vivo binding studies) indicative of good brain penetration, and potently reversed drinking induced by the H3 selective agonist (R)-alpha-methylhistamine (ID50 0.05mg/kg), supporting functional blockade of H3 receptors in vivo. GSK189254 (0.1-3mg/kg) exhibited efficacy in a number of rodent models of cognitive function including object recognition (48h delay), passive avoidance (scopolamine-induced amnesia) and water maze (aged animals). In addition, GSK189254 induced a transient increase in wakefulness in the rat during the light phase, and a corresponding decrease in slow wave sleep 2. Conclusion: Given these effects on cognition and alertness in preclinical species, the H3 antagonist GSK189254 has the potential to be a new therapeutic agent for the symptomatic treatment of Alzheimer’s Disease and other dementias.

Acute wake-promoting actions of JNJ-5207852, a novel, diamine-based H3 antagonist.

1 1-[4-(3-piperidin-1-yl-propoxy)-benzyl]-piperidine (JNJ-5207852) is a novel, non-imidazole histamine H3 receptor antagonist, with high affinity at the rat (pKi=8.9) and human (pKi=9.24) H3 receptor. JNJ-5207852 is selective for the H3 receptor, with negligible binding to other receptors, transporters and ion channels at 1 microm. 2 JNJ-5207852 readily penetrates the brain tissue after subcutaneous (s.c.) administration, as determined by ex vivo autoradiography (ED50 of 0.13 mg kg(-1) in mice). In vitro autoradiography with 3H-JNJ-5207852 in mouse brain slices shows a binding pattern identical to that of 3H-R-alpha-methylhistamine, with high specific binding in the cortex, striatum and hypothalamus. No specific binding of 3H-JNJ-5207852 was observed in brains of H3 receptor knockout mice. 3 In mice and rats, JNJ-5207852 (1-10 mg kg(-1) s.c.) increases time spent awake and decreases REM sleep and slow-wave sleep, but fails to have an effect on wakefulness or sleep in H3 receptor knockout mice. No rebound hypersomnolence, as measured by slow-wave delta power, is observed. The wake-promoting effects of this H3 receptor antagonist are not associated with hypermotility. 4 A 4-week daily treatment of mice with JNJ-5207852 (10 mg kg(-1) i.p.) did not lead to a change in body weight, possibly due to the compound being a neutral antagonist at the H3 receptor. 5 JNJ-5207852 is extensively absorbed after oral administration and reaches high brain levels. 6 The data indicate that JNJ-5207852 is a novel, potent and selective H3 antagonist with good in vitro and in vivo efficacy, and confirm the wake-promoting effects of H3 receptor antagonists.

Piperidino-Hydrocarbon compounds as novel non-Imidazole histamine H3-Receptor antagonists

In search for novel non-imidazole histamine H3-receptor antagonists, piperidino-hydrocarbon compounds were synthesized using the known non-imidazole histamine H3-receptor antagonist FUB 637 (3-phenylpropyl 3-piperidinopropyl ether) as lead structure. Piperidino-alkyl derivatives containing highly flexible side chains (2, 4–7) were prepared via N-alkylation. Compounds containing unsaturated alkyl groups were synthesized in order to investigate the impact of rigidifying the side chain (8–16). Terminal alkynes were prepared by alkylation of lithium acetylide-ethylenediamine complex, disubstituted alkynes were synthesized by alkylation of the appropriate acetylene in the presence of n-butyllithium-N,N,N′,N′-tetramethylene-ethylene-diamine complex. The novel compounds were investigated in an in vitro functional assay on the guinea-pig ileum, in which N-(7-phenylhept-3-ynyl)piperidine (14) proved to be of good potency in this class (pA2=7.21). In an in vivo assay the compounds were additionally screened for their abilities to influence central H3-histaminergic neuron activity in mice with regard to their oral availabilities and distribution properties. In this screening, N-pent-4-ynylpiperidine (9) and N-hex-5-ynylpiperidine (10) proved to be highly potent and orally available histamine H3-receptor antagonists. The ED50 values for 9 and 10 were 1.3 and 1.4mg/kg po, respectively, which is in the potency range of the reference antagonist thioperamide.