Pharmacological profile of MEN91507, a new CysLT₁ receptor antagonist

Abstract

MEN91507 (8-[2-(E)-[4-[4-(4-fluorophenyl)butyloxy]phenyl]vinyl]-4-oxo-2-(5-1H-tetrazolyl)-4H-1-benzopyran sodium salt)) potently displaced [³H]leukotriene D₄ binding from guinea-pig lung and dimethylsulphoxide-differentiated U937 (dU937) cell membranes (K_i 0.50±0.16 and 0.65±0.29 nM, respectively). On the other hand, MEN91507 did not display significant binding affinity for a series of receptors or channels. In functional studies on dU937 cells, MEN91507 behaved as insurmountable antagonist of leukotriene D₄-induced calcium transients, with an apparent pK_B of 10.25±0.15. In anaesthetized guinea-pigs, MEN91507 antagonized in a dose-dependent manner leukotriene D₄-induced bronchoconstriction following i.v. or oral administration: the ED_50s were 3.0±0.3 and 140±90 nmol/kg, respectively. The inhibition of leukotriene D₄-induced bronchoconstriction by MEN91507 was long-lasting, since a dose of 0.6 μmol/kg produced 74% reduction of the response after 8 h from administration. Likewise, leukotriene D₄-induced microvascular leakage was antagonized by MEN91507 either following i.v. or oral administration: a significant inhibitory effect was still evident at 16 h from oral administration of a dose of 6 μmol/kg. It is concluded that MEN91507 is a potent and selective antagonist of both guinea-pig and human CysLT₁ receptors; in addition, in vivo studies on guinea-pigs indicate that MEN91507 is an orally available and long-lasting antagonist of the bronchomotor and pro-inflammatory effects induced by leukotriene D₄ through the stimulation of CysLT₁ receptors.

Introduction

Cysteinyl-leukotrienes, as leukotriene C₄, D₄ and E₄, are potent constrictors and pro-inflammatory mediators in guinea-pig and human airways. They play a crucial role in asthma pathophysiology by causing bronchoconstriction, mucus production, increase in vascular permeability and induce eosinophil-mediated inflammatory responses (Lane, 1998). Inhaled leukotriene D₄ and leukotriene E₄ provoke constriction of small and large airway smooth muscle and increase bronchial hyperresponsiveness to pharmacologic agents in both normal and asthmatic subjects. In addition, cysteinyl-leukotrienes has been identified in plasma, urine, nasal secretions, sputum and bronchoalveolar lavage fluid of patients during spontaneous exacerbations of asthma or after antigen challenge Smith, 1998, Claesson and Dahlen, 1999. Although the initial focus was linked to bronchoconstrictor activity, it is nowadays clear that the role of cysteinyl-leukotriene in asthma also involves a contribution to the underlying inflammation and in airway remodeling.

Cysteinyl-leukotrienes exert their biological actions by activating specific receptors on the membranes of target cells. Two types of CysLT receptors have been cloned and pharmacologically characterized, namely CysLT₁ and CysLT₂ Gorenne et al., 1996, Rovati et al., 1997, Lynch et al., 1999, Sarau et al., 1999, Heise et al., 2000, Nothacker et al., 2000, Takasaki et al., 2000: both receptors belong to the superfamily of seven segments trasmembrane-spanning G-protein-coupled receptors. The CysLT₁ receptor appears to be the main responsible of the actions of cystenyl-leukotrienes in asthma (Lynch et al., 1999) and is specifically blocked by recently developed leukotriene D₄-receptor antagonists such as Montelukast (Jones et al., 1995), Zafirlukast (Krell et al., 1990), and Pranlukast (Obata et al., 1992). In contrast, the human CysLT₂ receptor is insensitive to these compounds Heise et al., 2000, Nothacker et al., 2000.

Agents developed to specifically antagonize the actions of leukotriene D₄ or leukotriene E₄ at the receptor level, i.e., CysLT₁ receptor antagonists, represent a new class of drugs in therapy of asthma (Lipworth, 1999). Until now three CysLT₁ receptor antagonists, namely Montelukast, Pranlukast and Zafirlukast, have been developed and marketed Hamilton et al., 1998, Leff et al., 1998, Nathan et al., 1998. They are orally effective over a wide range of asthma severity, preventing the airway inflammatory response to cysteinyl-leukotrienes action as well as acting as bronchodilators to the leukotriene-induced bronchoconstriction. Furthermore, recent clinical data would suggest that CysLT₁ receptor antagonists are also beneficial in upper airways diseases since Montelukast reduce symptoms in seasonal allergic rhinitis (Wilson et al., 2001).

This work describes the pharmacodynamic profile of the new CysLT₁ receptor antagonist MEN91507 (8-[2-(E)-[4-[4-(4-fluorophenyl)butyloxy]phenyl]vinyl]-4-oxo-2-(5-1H-tetrazolyl)-4H-1-benzopyran sodium salt)) (Fig. 1). The investigation has been conducted by means of in vitro studies and in animals models of bronchoconstriction and airway inflammation induced by leukotriene D₄. MEN91507 is a new potent, selective and orally effective CysLT₁ receptor antagonist: its preclinical profile indicates MEN91507 as a promising candidate for the treatment of inflammatory conditions of the respiratory tract, such as asthma and allergic rhinitis.