Characteristics of the antihistamine effect of TAK-427, a novel imidazopyridazine derivative

Exploring the untapped pharmacological potential of imidazopyridazines

Imidazopyridazines are fused heterocycles, like purines, with a pyridazine ring replacing the pyrimidine ring in purines. Imidazopyridazines have been primarily studied for their kinase inhibition activity in the development of new anticancer and antimalarial agents. In addition to this, they have also been investigated for their anticonvulsant, antiallergic, antihistamine, antiviral, and antitubercular properties. Herein, we review the background and development of different imidazopyridazines as potential pharmacological agents. Moreover, the scope of this relatively less charted heterocyclic scaffold is also highlighted.

Function and Role of Histamine H1 Receptor in the Mammalian Heart

Histamine can change the force of cardiac contraction and alter the beating rate in mammals, including humans. However, striking species and regional differences have been observed. Depending on the species and the cardiac region (atrium versus ventricle) studied, the contractile, chronotropic, dromotropic, and bathmotropic effects of histamine vary. Histamine is present and is produced in the mammalian heart. Thus, histamine may exert autocrine or paracrine effects in the mammalian heart. Histamine uses at least four heptahelical receptors: H₁, H₂, H₃ and H₄. Depending on the species and region studied, cardiomyocytes express only histamine H₁ or only histamine H₂ receptors or both. These receptors are not necessarily functional concerning contractility. We have considerable knowledge of the cardiac expression and function of histamine H₂ receptors. In contrast, we have a poor understanding of the cardiac role of the histamine H₁ receptor. Therefore, we address the structure, signal transduction, and expressional regulation of the histamine H₁ receptor with an eye on its cardiac role. We point out signal transduction and the role of the histamine H₁ receptor in various animal species. This review aims to identify gaps in our knowledge of cardiac histamine H₁ receptors. We highlight where the published research shows disagreements and requires a new approach. Moreover, we show that diseases alter the expression and functional effects of histamine H₁ receptors in the heart. We found that antidepressive drugs and neuroleptic drugs might act as antagonists of cardiac histamine H₁ receptors, and believe that histamine H₁ receptors in the heart might be attractive targets for drug therapy. The authors believe that a better understanding of the role of histamine H₁ receptors in the human heart might be clinically relevant for improving drug therapy.

[Verification of Pharmacokinetic Approaches in Prior Drug Development]

In this review, 9 compounds with insufficient absorption characteristics, safety or efficacy were selected from among the compounds for which the author was in charge of development between 2000 and 2005, in order to evaluate the pharmacokinetic (PK) approaches used to develop these compounds. Optimization of the PK characteristics of a compound at the early stage of chemical design was found to be the most important factor for successful development. For example, (i) selecting class I or II drugs in the biopharmaceutical classification system, while avoiding efflux transporters, and introducing an appropriate dissociation moiety into a compound to make it soluble lead to sufficient drug absorption; (ii) designing compounds whose production of reactive metabolites, such as acyl glucuronide, does not largely affect total metabolism, yet helps to prevent abnormal PK caused by reactive metabolites. Other factors include (i) selection of a drug efficacy evaluation system based on the correct understanding of the relationship between PK and pharmacodynamics (PD) helps to solve species differences in PD; (ii) the establishment of a nonclinical study based on the identification of the involvement of specific cytochrome P450 molecules in the total metabolic clearance of a drug (f_m,CYPs) helps to solve species differences in PK; and (iii) PK analysis using the tube model for hepatic extraction kinetics, and knowledge of the f_m,CYPs of the victim drug, lead to successful drug-drug interaction (DDI) prediction. I hope that this review aids in future drug discovery or development.

Antihistamines suppress upregulation of histidine decarboxylase gene expression with potencies different from their binding affinities for histamine H1 receptor in toluene 2,4-diisocyanate-sensitized rats

Antihistamines inhibit histamine signaling by blocking histamine H1 receptor (H1R) or suppressing H1R signaling as inverse agonists. The H1R gene is upregulated in patients with pollinosis, and its expression level is correlated with the severity of nasal symptoms. Here, we show that antihistamine suppressed upregulation of histidine decarboxylase (HDC) mRNA expression in patients with pollinosis, and its expression level was correlated with that of H1R mRNA. Certain antihistamines, including mepyramine and diphenhydramine, suppress toluene-2,4-diisocyanate (TDI)-induced upregulation of HDC gene expression and increase HDC activity in TDI-sensitized rats. However, d-chlorpheniramine did not demonstrate any effect. The potencies of antihistamine suppressive effects on HDC mRNA elevation were different from their H1R receptor binding affinities. In TDI-sensitized rats, the potencies of antihistamine inhibitory effects on sneezing in the early phase were related to H1R binding. In contrast, the potencies of their inhibitory effects on sneezing in the late phase were correlated with those of suppressive effects on HDC mRNA elevation. Data suggest that in addition to the antihistaminic and inverse agonistic activities, certain antihistamines possess additional properties unrelated to receptor binding and alleviate nasal symptoms in the late phase by inhibiting synthesis and release of histamine by suppressing HDC gene transcription.

Inverse agonistic activity of antihistamines and suppression of histamine H1 receptor gene expression

Histamine H(1) receptor (H1R) expression influences the severity of allergy symptoms. We examined the effect of inverse agonists on H1R gene expression. Two inverse agonists (carebastine and mepyramine), but not the neutral antagonist oxatomide, decreased inositol phosphate accumulation. The inverse agonists also decreased H1R gene expression and down-regulated H1R mRNA below basal expression, while basal H1R mRNA expression was maintained after oxatomide treatment. These results suggest that inverse agonists more potently alleviate allergy symptoms by not only inhibiting stimulus-induced up-regulation of H1R gene expression but also by suppressing basal histamine signaling through their inverse agonistic activity.

Effect of a Chinese herbal formula, Shi-Bi-Lin, on an experimental model of allergic rhinitis

BACKGROUND

Jia Wei Cang Er Zi San, a traditional Chinese herbal formula, has been used to treat allergic rhinitis (AR) for several centuries. However, its effect on experimental animal models and its therapeutic mechanism remain unclear.

OBJECTIVE

To study the effect of Shu-Bi-Lin, a modified Jia Wei Cang Er Zi San, on an animal model of AR.

METHODS

Shu-Bi-Lin was administered to the guinea pig model of AR. Meanwhile, an antihistamine-treated group for the treatment control, an ovalbumin-sensitized and untreated group for the positive control, and a sham-sensitized, sham-challenged group for the sham control were studied in parallel. Symptomatic and some pathophysiologic variables were evaluated.

RESULTS

Sneezing and nasal scratching after challenges were significantly ameliorated in the Shu-Bi-Lin-treated group compared with the ovalbumin-sensitized and untreated group, but rhinorrhea volume was not reduced. Shu-Bi-Lin significantly suppressed the production of IgG1 in the passive cutaneous anaphylaxis test. The thromboxane B2 level in nasal lavage fluid was significantly deceased in the Shu-Bi-Lin-treated group; however, the reduction in histamine and peptide leukotriene levels did not reach statistical significance. In addition, eosinophil infiltration and endothelial nitric oxide synthase immunoreactivity in the nasal tissues were reduced in the Shu-Bi-Lin-treated group.

CONCLUSIONS

Shu-Bi-Lin could alleviate the nasal symptoms of AR, and its mechanism might be related to its inhibitory effect on type I anaphylaxis reactions and eosinophil infiltration in the nasal tissues, as well as the inhibition of some mediators related to AR.

Effects of poor sleep in allergic rhinitis

PURPOSE OF REVIEW

Allergic rhinitis affects a large portion of the population. These patients often suffer from daytime fatigue, both as a result of the mechanics of the nasal airway in patients with allergic rhinitis as well as through central effects on sleep by immune mediators. By understanding these mechanisms and by becoming familiar with effective treatments for allergic rhinitis that are beneficial in alleviating rather than worsening daytime somnolence, physicians may improve patient quality of life.

RECENT FINDINGS

Children with rhinitis and snoring have poorer school performance compared with controls. The role of rhinitis in chronic fatigue remains controversial despite an increase in literature on this subject. The role of immune mediators on rhinitis and sleep is evolving as well. Nasal steroids effectively treat rhinitis and improve daytime fatigue. Second-generation antihistamines are preferred to first-generation antihistamines based on efficacy and safety studies.

SUMMARY

Understanding the relationship between rhinitis in sleep abnormalities and subsequent daytime fatigue is still developing. Nasal steroids are the mainstay of treatment, but the role of future agents is promising although undefined.

Effects of TAK-427 on acute nasal symptoms and nasal obstruction in guinea pig model of experimental allergic rhinitis

TAK-427 (2-[6-[[3-[4-(diphenylmethoxy)piperidino]propyl]amino]imidazo[1,2-b]pyridazin-2-yl]-2-methylpropionic acid dihydrate) is a novel anti-allergic agent that has both histamine H1-receptor antagonist and anti-inflammatory activities. In this study, we evaluated the efficacy of TAK-427 on acute nasal responses and nasal obstruction using various guinea pig models of allergic rhinitis. TAK-427 inhibited the histamine-induced nasal reactions with an ID50 value of 0.633 mg/kg, p.o. TAK-427 (0.1-10 mg/kg, p.o.) and most histamine H1-receptor antagonists tested inhibited the increase in intranasal pressure, nasal hypersecretion, sneezing and nasal itching caused by a single antigen challenge in sensitized guinea pigs. In addition, TAK-427 (0.3, 30 mg/kg, p.o.) significantly inhibited the development of nasal obstruction when sensitized guinea pigs were repeatedly challenged via inhalation with Japanese cedar pollen, whereas the histamine H1-receptor antagonist, azelastine (1 mg/kg, p.o.), and ketotifen (1 mg/kg, p.o.) were without effect. These results suggest that TAK-427 might not only suppress acute nasal symptoms but also ameliorate nasal obstruction via the effects other than those as a histamine H1-receptor antagonist.