Lynn E. Rinkema

Evidence for multiple leukotriene D4 receptors in smooth muscle

Using pure leukotriene D4 (LTD4) as the agonist, we determined the dissociation constants, Kb and pA2 values, for the selective leukotriene antagonist FPL 55712 on guinea pig ileum, trachea, and parenchyma. Responses of the 3 tissues to LTD4 were competitively antagonized by FPL 55712. Kb and pA2 values were similar for trachea and parenchyma. However, these values differed from those obtained in ileum. We propose the existence of multiple LTD4 receptors, with those in lung differing from LTD4 receptors in ileum.

Evaluation of LY163443, 1-[2-hydroxy-3-propyl-4-{[4-(1H-tetrazol-5-ylmethyl)phenoxy]methyl}phenyl]ethanone, as a pharmacologic antagonist of leukotrienes D4 and E4

SummaryLY163443,1-[2-hydroxy-3-propyl-4-{[4-(1H-tetrazol-5-ylmethyl)-phenoxy]methyl}phenyl]ethanone, antagonized LTD4-induced contractions of guinea pig ileum, trachea, and lung parenchyma. Tracheal contractions to LTE4 were also inhibited by LY163443. The compound had minimal effect against ileal responses to LTC4 and parenchymal contractions to LTB4. Furthermore, LY163443.had little to no effect against contractions of isolated smooth muscles to histamine, bradykinin, PGF2α, carbachol, serotonin or U46619. LY163443, given by oral administration to guinea pigs, blocked LTD4-induced increases in total pulmonary impedance (TPI). Similar responses elicited by histamine or U46619 were unaffected. Increases in TPI in response to i.v. administration of LTC4 were antagonized by LY163443 given by the same route. Ovalbumin challenge also increased TPI in guinea pigs previously sensitized against this antigen. In such animals, pretreated with pyrilamine, propranolol, and indomethacin, oral administration of LY163443 blocked the increase in TPI caused by ovalbumin. Additionally, LTD4 given intradermally to guinea pigs caused a vascular leakage which was suppressed by prior oral administration of LY163443. Finally, LY163443 relaxed isolated guinea pig trachea previously contracted with LTD4, histamine, or carbachol. Relaxation of tissues contracted by these latter two agonists suggested some inherent airway smooth muscle relaxant properties of the molecule. This was further demonstrated by showing some bronchodilator activity in an in vivo setting. Thus, this pharmacologic profile indicates that LY163443, or a member of the same chemical family, warrants consideration as a possible therapeutic agent in the treatment of asthma and in diseases characterized by an overproduction of LTD4 and LTE4.

Pharmacologic analysis of LY188695 (KB-2413), 1-(2-ethoxyethyl)-2-(4-methyl-1-homopiperazinyl)-benzimidazole difumarate, a potent histamine1 receptor antagonist

LY188695 was evaluated bothin vitro andin vivo in the guinea pig to determine its pharmacologic profile. The compound antagonized histamine-induced contractions of ileum, aorta, and trachea, with pKB values of 9.9, 9.9, and 9.2 respectively. In the lung parenchymal strip, LY188695 caused a rightward shift of the histamine concentration-response curve with a reduction in the maximal response at all antagonist concentrations tested. The reason for this effect is unknown, but it was not due to a nonspecific depressant action of the compound on the parenchyma. Selectivity was shown by its inactivity against leukotriene D4, bradykinin, prostaglandin F2α, acetylcholine, norepinephrine, and serotonin on various guinea pig and rat smooth muscles. Similary, H2 receptor-mediated relaxation of the rat uterus was unaltered by LY188695. Increases in total pulmonary impedance caused by i.v. histamine to anesthetized guinea pigs were reduced by as little as 3 μg/kg given orally 1 hour prior to histamine challenge. In this system, LY188695 was 15 times more potent than chloropheniramine and 100 times more potent than terfenadine. Similar responses elicited by acetylcholine were not antagonized by LY188695. A duration of action greater than 4 hours was observed in this model. Ovalbumin given i.v. to sensitized guinea pigs increased total pulmonary impedance which was markedly decreased after oral administration of 30 or 100 μg/kg LY188695. These results indicate that LY188695 is a very potent antagonist of H1-mediated responses and suggest that this agent might be useful in disease states characterized by an overproduction of histamine.

Structure-activity relationships (SAR) of the 3-alkyl substituents among a series of hydroxyacetophenone leukotriene antagonists

LY171883 is an orally active antagonist of leukotriene (LT) D4 and LTE4. A series of related compounds varying the position and nature of the alkyl side chain were synthesized and evaluated for their ability to block LTD4-induced contraction of guinea pig ileum. Maximal activity was obtained with n-propyl, n-butyl, and n-pentyl substituents with slightly reduced activity for longer side chains. Polar groups on the side chain substantially reduced activity. Thus, it appears that the leukotriene receptor site requires a nonpolar alkyl group of moderate size at the 3-position on this type of receptor antagonist.

Contraction of guinea pig inferior vena cava by eicosanoids

SummaryGuinea pig inferior vena cava contracted in response to leukotriene (LT)C4, LTD4, LTE4 U46619, phenylephrine, histamine, and KCl. Although LTC4, LTD4, and U46619 were the most potent agonists, active tension generated by these eicosanoids was only about half that of histamine or KCl. LTE4 and phenylephrine were marginally active. Biochemical analysis showed vena cava able to convert about 23% LTC4 to LTD4 and LTE4 in 45 min. Pretreatment with acivicin prevented this by abrogating conversion of LTC4 to LTD4. A subthreshold concentration of LTE4 reduced responses to LTC4 and LTD4. LY171883 and WY-48252 competitively antagonized LTD4-induced contractions of vena cava. In contrast, these antagonists blocked contractions to LTC4 in a biphasic manner. Lower segments of the LTC4 concentration-response curves were less affected than the upper portion suggesting the possibility of 2 LTC4 receptor subtypes. Our results indicate that LTE4 is a weak or partial agonist in this tissue and furthermore they suggest a lack of high affinity receptors for LTE4 favoring LTC4 and LTD4. Indomethacin did not influence contractions to the leukotrienes or histamine. However, the response to U46619 was greatly enhanced suggesting release of a vasodilator prostaglandin as part of the overall response of the vena cava to the thromboxane A2 mimetic.

Leukotriene (LT) receptor antagonists. Heterocycle-linked tetrazoles and carboxylic acids. LY203647

LY171883, 1-[2-hydroxy-3-propyl-4-[4-(1H-tetrazol-5-yl)butoxy]phenyl] ethanone, is an orally active antagonist of LTD4- and LTE4-induced responses in a variety of test systems. We prepared a new series of LT antagonists based on a proposed model of LY171883 binding to the LTE4 receptor in which then-propyl and tetrazole moieties of LY171883 occupy those parts of the receptor to which the C1-C5 chain and the cysteinyl carboxyl of LTE4 bind, respectively. The new compounds have an acidic function corresponding to the glycine carboxyl of LTD4 linked through a heterocyclic group which is proposed to bind to the LTD4 receptor where the cysteinyl glycine amide bond of LTD4 binds. LY203647, 1-[2-hydroxy-3-propyl-4-[4-[2-[4-(1H-tetrazol-5-yl) butyl]-2H-tetrazol-5-yl]butoxy]phenyl] ethanone, showed good LTD4 antagonist activity with a suitable pharmacologic and toxicologic profile and has been chosen for clinical evaluation.

Leukotriene Receptor Antagonism and Augmentation of β‐Receptor‐mediated Events by LY1718831

Abstract— LY171883, (1‐[2‐hydroxy‐3‐propyl‐4‐((4(1H‐tetrazol‐5‐yl)butoxy)phenyl]ethanone), a leukotriene (LT) D4/E4 receptor antagonist, was assessed in comparison with two well known phosphodiesterase inhibitors, isobutylmethyl‐xanthine (IBMX) and theophylline, for its ability to augment β‐receptormediated responses. Relaxation of carbachol‐contracted guinea‐pig trachea by isoprenaline was enhanced by the three agents in a dose‐dependent manner. A two‐fold enhancement of isoprenaline‐induced smooth muscle relaxation was produced by 2.5 μM IBMX, 28 μM LY171883, or 140 μM theophylline. Similar concentrations of IBMX or theophylline did not antagonize LTE4‐induced tracheal contractions; LY171883 totally inhibited the response and had significant LTE4 receptor antagonist activity even at 10‐fold lower concentrations. Antigen‐induced release of histamine and LTC4 from guinea‐pig lung was reduced by isoprenaline. Prior treatment with LY171883, IBMX, or theophylline did not enhance this action. Isoprenaline reduced histamine‐induced bronchospasm in anaesthetized guinea‐pigs. LY171883, 30 mg kg−1, or IBMX, 1 mg kg−1, did not affect the isoprenaline‐induced decrease in the histamine response. IBMX, 3 mg kg−1, and theophylline, 30 mg kg−1, augmented the isoprenaline‐induced bronchodilation. LTE4‐induced bronchoconstriction was not affected by IBMX or theophylline whereas LY171883 antagonized this response at doses as low as 3 mg kg−1. Therefore, in both in‐vitro and in‐vivo test systems, LY171883 functioned primarily as a leukotriene receptor antagonist with minimal pharmacological activity attributable to its ability to potentiate isoprenaline.

Synthesis and Leukotriene D4/E4 Receptor Antagonist Activity of LY223468 and LY281761, “Carba” Analogues of LY171883

Structures containing the 3-propyl-4-alkoxy-o-hydroxyacetophenone moiety have an affinity for leukotriene D,/E, receptors.’ Compounds containing this group are represented by LY 171 883 and LY 137123.2,3 In considering the structure-activity relationships for members of this series, we asked what contribution the oxygen atom para to the acetyl group made to the observed antagonist activity. Analogues of LY171883 and LY137123 were synthesized in which the tetrazole was linked to the hydroxyacetophenone moiety by an all-methylene carbon chain (FIGURE 1). A key step in the synthesis involved a Wittig olefin-forming reaction between 3-methoxy-2-propylbenzaldehyde and the ylide derived from (4-carboxybuty1)triphenylphosphonium bromide to form the desired carbon chain. A regioselective Fries rearrangement was employed to form the ortho-hydroxyacetophenone. Compounds in which the tetrazole was separated from the acetophenone by four (LY223468) and five (LY281761) methylene groups were compared to the corresponding derivatives in which an oxygen atom linked the tetrazole chain to the aromatic ring for their ability to antagonize LTD,or LTE,-induced contractions of the isolated guinea pig ileum (TABLE 1). LY171883 and its “carba” analogue, LY28 1761, showed nearly identical LTD, antagonist activity. The LTE, antagonist activity of these two compounds also was very similiar, with both showing somewhat