Thromboxane A2 antagonist inhibits leukotriene D4-induced smooth muscle contraction in guinea-pig lung parenchyma, but not in trachea

Ramatroban-Based Analogues Containing Fluorine Group as Potential 18F-Labeled Positron Emission Tomography (PET) G-Protein Coupled Receptor 44 (GPR44) Tracers

Diabetes remains one of the fastest growing chronic diseases and is a leading source of morbidity and accelerated mortality in the world. Loss of beta cell mass (BCM) and decreased sensitivity to insulin underlie diabetes pathogenesis. Yet, the ability to safely and directly assess BCM in individuals with diabetes does not exist. Measures such as blood glucose provide only a crude indirect picture of beta cell health. PET imaging could, in theory, allow for safe, direct, and precise characterization of BCM. However, identification of beta cell-specific radiolabeled tracers remains elusive. G-protein coupled receptor 44 (GPR44) is a transmembrane protein that was characterized in 2012 as highly beta cell-specific within the insulin-positive islets of Langerhans. Accordingly, radiolabeling of existing GPR44 antagonists could be a viable method to accelerate PET tracer development. The present study aims to evaluate and summarize published analogues of the GPR44 antagonist ramatroban to develop ¹⁸F-labeled PET tracers for BCM analysis. The 77 corresponding ramatroban analogues containing a fluorine nuclide were characterized for properties including binding affinity, selectivity, and pharmacokinetic and metabolic profile, and 32 compounds with favorable properties were identified. This review illustrates the potential of GPR44 analogues for the development of PET tracers.

Airway mechanics and methods used to visualize smooth muscle dynamics in vitro

Contraction of airway smooth muscle (ASM) is regulated by the physiological, structural and mechanical environment in the lung. We review two in vitro techniques, lung slices and airway segment preparations, that enable in situ ASM contraction and airway narrowing to be visualized. Lung slices and airway segment approaches bridge a gap between cell culture and isolated ASM, and whole animal studies. Imaging techniques enable key upstream events involved in airway narrowing, such as ASM cell signalling and structural and mechanical events impinging on ASM, to be investigated.

G protein-coupled receptor pharmacogenetics

Common G protein-coupled receptor (GPCR) gene variants that encode receptor proteins with a distinct sequence may alter drug efficacy without always resulting in a disease phenotype. GPCR genetic loci harbor numerous variants, such as DNA insertions or deletions and single-nucleotide polymorphisms that alter GPCR expression and function, thereby contributing to interindividual differences in disease susceptibility/progression and drug responses. In this chapter, these pharmacogenetic phenomena are reviewed with respect to a limited sampling of GPCR systems, including the beta(2)-adrenergic receptors, the cysteinyl leukotriene receptors, and the calcium-sensing receptor. In each example, the nature of the disruption to receptor function that results from each variant is discussed with respect to the regulation of gene expression, expression on cell surface (affected by receptor trafficking, dimerization, desensitization/downregulation), or perturbation of receptor function (by altering ligand binding, G protein coupling, and receptor constitutive activity). Despite the breadth of pharmacogenetic knowledge available, assessment for genetic variants is only occasionally applied to drug development projects involving pharmacogenomics or to optimizing the clinical use of GPCR drugs. The continued effort by the basic science of pharmacogenetics may draw the attention of drug discovery projects and clinicians alike to the utility of personalized pharmacogenomics as a means to optimize novel GPCR drug targets.

Effects of KP-496, a novel dual antagonist at the cysteinyl leukotriene receptor 1 and the thromboxane A(2) receptor, on airway obstruction in guinea pigs

BACKGROUND AND PURPOSE

KP-496 is a novel dual antagonist for cysteinyl leukotriene receptor 1 (CysLT(1)) and thromboxane A(2) (TXA(2)) receptor (TP). The aim of this study was to evaluate the pharmacological profile of inhaled KP-496 and its effects on airway obstruction.

EXPERIMENTAL APPROACH

Antagonist activities of inhaled KP-496 were investigated using bronchoconstriction induced in guinea pigs by LTD(4) or U46619, a stable TXA(2) mimetic. Guinea pigs sensitized with injections of ovalbumin were used to assess the effects of inhaled KP-496 on bronchoconstriction induced by antigen (i.v.). Another set of guinea pigs were sensitized and challenged with ovalbumin by inhalation and the effects of inhaled KP-496 on immediate and late airway responses and airway hyperresponsiveness were investigated.

KEY RESULTS

KP-496 significantly inhibited LTD(4)- and U46619-induced bronchoconstriction in a dose-dependent manner. The inhibitory effects of KP-496 (1%) were comparable to those of montelukast (a CysLT(1) antagonist, p.o., 0.3 mg kg(-1)) or seratrodast (a TP antagonist, p.o., 3 mg kg(-1)). KP-496 (1%) and oral co-administration of montelukast (10 mg kg(-1)) and seratrodast (20 mg kg(-1)) significantly inhibited antigen-induced bronchoconstriction, whereas administration of montelukast or seratrodast separately did not inhibit antigen-induced bronchoconstriction. KP-496 exhibited dose-dependent and significant inhibitory effects on the immediate and late airway responses and airway hyperresponsiveness following antigen challenge.

CONCLUSIONS AND IMPLICATIONS

KP-496 exerts effects in guinea pigs which could be beneficial in asthma. These effects of KP-496 were greater than those of a CysLT(1) antagonist or a TP antagonist, in preventing antigen-induced airway obstruction.

Synergism between cysteinyl leukotrienes and thromboxane A2 to induce allergic late phase nasal blockage in guinea pigs

We examined whether cysteinyl leukotrienes (CysLTs) and thromboxane (TX) A2 are synergistically involved in a cedar pollen-induced allergic late phase nasal blockage in guinea pigs. Sensitized animals were repeatedly challenged by pollen inhalation once every week. Combined treatment with pranlukast (a CysLT antagonist) and seratrodast (a TXA2 antagonist) inhibited late phase nasal blockage, but the magnitude of inhibition (approximately 50%) was equal to those of the respective single treatments, suggesting that CysLTs produced late after challenge induces TXA2 production in the nasal tissue, as in the case of the lung of this species. However, pranlukast did not affect TXB2 increase in the nasal tissue. In contrast, combined intranasal instillation of LTD4 and U-46619 (a TXA2 mimetic) produced much greater nasal blockage than single administration of each agonist in sensitized animals. Therefore, allergic late phase nasal blockage should be induced by synergistic activity of CysLTs and TXA2 at the effector organ.

Effect of combined leukotriene D(4) and thromboxane A(2) receptor antagonist on mediator-controlled resistance in guinea pigs

The effects of YM158 (3-[(4-tert-butylthiazol-2-yl)methoxy]-5'-[3-(4-chlorobenzenesu lfonyl )propyl]-2'-(1H-tetrazol-5-ylmethoxy)benzanilide monosodium salt monohydrate), a new dual antagonist for leukotriene D(4) and thromboxane A(2) receptors, on antigen-induced increases in airway resistance were investigated in mediator-controlled novel asthmatic models using actively sensitized guinea pigs. While the predominant mediator was thromboxane A(2), complete inhibition of cyclooxygenase induced mediation by cysteinyl-leukotrienes. About 1-mg/kg indomethacin induced a state where both mediators participated equally. YM158 inhibited increases in resistance whether only one or both mediators were involved. When leukotriene D(4) and thromboxane A(2) equally participated, ED(50) values for 4-oxo-8-[4-(4-phenylbutoxy)benzoylamino]-2-(tetrazol-5-yl)-4 H-1-benzo pyran hemihydrate (pranlukast; 3.9 mg/kg) and 7-(3,5,6-trimethyl-1, 4-benzoquinon-2-yl)-7-phenylheptanoic acid (seratrodast; 2.1 mg/kg) were similar to that for YM158 (8.3 mg/kg), although those effects on the corresponding mediator-induced reaction were 10 times stronger than those of YM158. Additionally, the maximum inhibition of YM158 was stronger than those of either single receptor antagonist. In conclusion, YM158 has a potentially greater efficacy in wider types of experimental asthmatic models than single receptor antagonists.

In vivo pharmacologic profile of YM158, a new dual antagonist for leukotriene D4 and thromboxane A2 receptors

The antagonistic activity of oral YM158 (3-[(4-tert-butylthiazol-2-yl)methoxy]-5'-[3-(4-chlorobenzenesu lfonyl)propyl]-2'-(1H-tetrazol-5-ylmethoxy)benzanilide monosodium salt monohydrate), a new dual antagonist for leukotriene (LT) D4 and thromboxane (TX) A2 receptors, was investigated. Oral YM158 caused dose-dependent inhibition of LTD4-induced increases in plasma leakage and LTD4- or U46619-induced increases in airway resistance, with ED50 values of 6.6, 8.6 and 14 mg/kg, respectively. The dose-range of YM158's inhibitions was almost the same for both LTD4 and TXA2 receptors, and repeated oral doses did not affect its efficacy. Furthermore, oral YM158 inhibited antigen-induced bronchoconstriction. Although the potency of pranlukast for LTD4 receptor antagonism (ED50 = 0.34 mg/kg) is greater than that of YM158 (ED50 = 8.6 mg/kg), the doses of both pranlukast and YM158 for significant inhibition of the antigen-evoked airway response were the same, indicating that the TXA2 receptor antagonism of YM158 plays an important role in its anti-asthmatic effects. In conclusion, YM158 promises to be a novel agent for treating bronchial asthma.

Can urinary eicosanoids be a potential predictive marker of clinical response to thromboxane A2 receptor antagonist in asthmatic patients?

Thromboxane (TX) A2 is an important bronchoconstrictor in the pathogenesis of asthma. Seratrodast, known as AA-2414, is a new oral TXA2 receptor antagonist which is currently prescribed in asthma therapy in Japan. However its clinical effects have been very different in individual subjects. To assess whether the clinical efficacy of TXA2 antagonist is predictable on the basis of urinary arachidonic acid metabolites in urine of patients with asthma, an open and multicentre trial was conducted. Fifty adult asthmatic subjects (women/men = 28/22) were enrolled [resting mean forced expiratory volume in 1 sec (FEV1)% was 82%; range, 50-96%]. Urinary levels of 11-dehydro-TXB2, leukotriene (LT) E4, 2,3-dinor-6-keto-prostaglandin F1alpha and creatinine in 3-h urine collected in the morning at the start of seratrodast (80 mg day(-1), once a day at evening for 4 weeks) were measured. Responders were defined by improvements of asthma symptoms score and peak expiratory flow rate (PEFR). Of the 50 subjects, 45 completed this study. Eighteen patients were responders and the other 27 were nonresponders. There were no significant differences between the two groups in patients' characteristics, baseline lung functions, treatments and baseline urinary eicosanoids. The 11-dehydro-TXB2/LTE4 ratio of responders was significantly higher (P = 0.0091) than that of non-responders (mean +/- SE, 7.49+/-0.71 vs. 5.09+/-0.67). Eleven patients out of 18 responders agreed to continue this drug for 6 months, the 11-dehydro-TXB2/LTE4 ratio decreased during this period, but not significantly. Our data demonstrated that responders and non-responders to TXA2 receptor antagonist existed in patients with asthma, and it suggests that the ratio of urinary eicosanoids might be a possible predictor of the effects of TXA2 receptor antagonist.

Leukotriene (LT)-receptor antagonist is more effective in asthmatic patients with a low baseline ratio of urinary LTE4 to 2,3-dinor-6-keto-prostaglandin (PG)F1alpha

BACKGROUND

To test the hypothesis that urinary levels of arachidonic acid metabolites may be a predicting factor of the effects of pranlukast, a selective leukotriene (LT) antagonist, on chronic adult asthma, we investigated the relationship between its clinical efficacy and urinary eicosanoid levels.

METHODS

An open, multicenter trial was conducted involving 38 stable moderate and severe asthmatic patients (mean percent predicted FEV1 was 71%). All patients received pranlukast (225 mg twice daily) for 4 weeks after a 2-week run-in period. Urinary levels of LTE4, 11-dehydro-thromboxane (TX) B2, 2,3-dinor-6-keto-prostaglandin (PG) F1alpha, and creatinine were measured in 3-h urine collected on day 1 of the treatment. The responder was defined by an improvement of asthma symptom scores and peak expiratory flow rate (PEFR).

RESULTS

One patient was excluded because of an adverse effect, nausea. Thirteen out of 37 subjects were responders and 24 were nonresponders. There were no significant differences in patients' backgrounds and urinary arachidonate levels between the two groups. The urinary LTE4 to 2,3-dinor-6-keto-PGF1alpha ratio in the responder was significantly lower (P=0.01) than that in the nonresponder. In all patients, a significant inverse correlation was revealed between the baseline urinary LTE4/2,3-dinor-6-keto-PGF1alpha ratio and the improvement of PEFR in the morning (r=-0.43, P=0.007).

CONCLUSIONS

These data suggested that the urinary ratio of LTE4 to 2,3-dinor-6-keto-PGF1alpha might be one of the predictive markers of the clinical efficacy of this LT-receptor antagonist in asthmatic subjects.