The peptide leukotrienes LTC4, D4 and E4 collectively account for the biological activity known as slow-reacting substance of anaphylaxis (SRS-A). These metabolites of arachidonic acid are thought to play a role in lung pathophysiology. A role in asthma is postulated as a result of their potent bronchoconstrictor activity both in vitro (Dahlén et al. 1980; Drazen et al. 1980; Hanna et al. 1981; Piper et al. 1981; Jones et al. 1982; Peters et al. 1984) and in vivo (Manning et al. 1990; Holroyde et al. 1981; Griffin et al. 1983; Weiss et al. 1982; Barnes et al. 1984). Increased production of leukotrienes has been demonstrated following antigen challenge of the airways of allergic patients in vivo (Creticos et al. 1984; Ishihara et al. 1985; Isono et al. 1985) and in vitro (Dalhén et al. 1983).

A cDNA for endothelial leukocyte adhesion molecule 1 (ELAM-1) was isolated by transient expression in COS-7 cells of a subtracted cDNA library from cytokine-treated human umbilical vein endothelial cells (HUVECs), with selection of ELAM-1-expressing clones by adhesion of transfected cells to the human promyelocytic cell line HL-60. This cloning method requires neither antibody nor purified ligand. ELAM-1-expressing COS cells bind the promyelocytic cell line HL-60 by a Ca2(+)-dependent but temperature-independent mechanism. Although ELAM-1 is homologous to mammalian lectins, its interaction with HL-60 cells is not inhibited by simple carbohydrate structures. ELAM-1-expressing COS cells also bind human neutrophils and the human colon carcinoma cell line HT-29, but not the B-cell line Ramos. However, Ramos cells adhere to cytokine-treated HUVECs but not control HUVECs, confirming the existence of other inducible adhesion molecules. In addition, the binding of HL-60 cells or neutrophils to ELAM-1-expressing COS cells is not inhibited by a monoclonal antibody (60.3) directed to an inhibitory epitope on CD18, indicating that the ELAM-1 ligand, although uncharacterized, is not a member of the CD11/CD18 family.

L-663,536 (3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2, 2-dimethylpropanoic acid) is a potent inhibitor of leukotriene (LT) biosynthesis in intact human polymorphonuclear leukocytes (PMN) (IC50, 2.5 nM). Similarly, L-663,536 inhibited A23187-induced LTB4 formation by rat peripheral blood and elicited PMN. At concentrations where inhibition of leukotriene biosynthesis occurred in human whole blood (1.1 microM), no effect was seen on cyclooxygenase or 12-lipoxygenase, an effect also observed in washed human platelets. The compound had no effect on rat or porcine 5-lipoxygenase indicating that L-663,536 is not a direct 5-lipoxygenase inhibitor. When administered in vivo L-663,536 was a potent inhibitor of antigen-induced dyspnea in inbred rats pretreated with methysergide (ED50, 0.036 mg/kg p.o.) and of Ascaris-induced bronchoconstriction in squirrel monkeys (1 mg/kg p.o.). The compound inhibited leukotriene biosynthesis in vivo in a rat pleurisy model (ED50, 0.2 mg/kg p.o.), an inflamed rat paw model (ED50, 0.8 mg/kg), a model of leukotriene excretion in rat bile following antigen provocation, and a model in the guinea-pig ear where leukotriene synthesis was induced by topical challenge with ionophore A23187 (ED50, 2.5 mg/kg p.o. and 0.6 micrograms topically). The results indicate that L-663,536 is a potent inhibitor of leukotriene biosynthesis both in vitro and in vivo indicating that the compound is suitable for studying the role of leukotrienes in a variety of pathological situations.

The synthesis of a series of 2-(phenylmethyl)-4-hydroxy-3,5-dialkylbenzofurans and their inhibitory effects against leukotriene biosynthesis and 5-lipoxygenase activity in vitro are described. Many compounds in this series were found to be potent inhibitors of LTB4 production by human polymorphonuclear leukocytes with IC50 values ranging from 7 to 100 nM. Structure-activity relationships of the series are presented. Within this series, 2-[(4'-methoxyphenyl)methyl]-4-hydroxy-3-methyl-5-propyl-7-chlorobenz ofuran (L-656,224) showed extremely potent activity, inhibiting leukotriene biosynthesis in intact human leukocytes (IC50 = 11 nM), as well as the 5-lipoxygenase reaction catalyzed by cell-free preparations from rat leukocytes (IC50 = 36 nM), human leukocytes (IC50 = 0.4 microM), and the purified enzyme from porcine leukocytes (IC50 = 0.4 microM). The compound also shows oral activity in a number of animal models in vivo.

L-656,224 (7-chloro-2-[(4-methoxyphenyl)methyl]-3-methyl-5-propyl-4-benzofuranol) was a potent inhibitor of leukotriene biosynthesis in intact rat and human leukocytes and CXBG mastocytoma cells (IC50 values, 18-240 nM) and of crude human leukocyte and highly purified porcine leukocyte 5-lipoxygenase (IC50 value, 4 X 10(-7) M). The selectivity of L-656,224 for 5-lipoxygenase was shown through the relative lack of activity of the compound on 12-lipoxygenase, 15-lipoxygenase, cyclooxygenase, catalase, and myeloperoxidase. The compound showed (i) oral activity against hyperalgesia induced in the rat paw by injection of yeast or platelet-activating factor, (ii) dyspnea in sensitized inbred rats induced by an aerosol of antigen, and (iii) bronchoconstriction induced by an aerosol of Ascaris in squirrel monkeys, suggesting a role for 5-lipoxygenase inhibitors in the treatment of asthma and peripheral pain.

Exogenous synthetic 1,2-diacylglycerols (e.g. 1,2-dioctanoylglycerol, DiC8) and 4β Phorbol esters (e.g. phorbol myristate acetate, PMA) routinely are used to probe the effects of protein Kinase C (PKC) on cellular responsiveness. Such agents act either independently or synergistically with elevated [Ca2+]i to induce platelet activation, but also inhibit agonist-induced inositol lipid metabolism and Ca2+ flux. These findings led to the concept that activated PKC can function as a bi-directional regulator of platelet reactivity. Therefore, DiCg and PMA were utilized to examine the effects of activated PKC on receptor-mediated stimulation and inhibition of adenylate cyclase, as monitored by cAMP accumulation. All studies were performed using intact human platelets in a modified Tyrodes solution, and cAMP was quantified by radioimmunoassay. Pretreatment (2 min.; 37°C) of platelets with PMA (≤ 300 nM) but not DiCg (200 μM) attenuated the elevation of platelet cAMP content evoked by PGD2 300 nM) but not by PGE1 (≤300 nM), PGI2 (≤100 nM) or adenosine (≤ 100 μM). These effects of PMA were unaffected by ADP scavengers, by Flurbiprofen (10 μM) or by cAMP phosphodiesterase inhibitors (IBMX, 1 mM) but were abolished by the PKC inhibitor Staurosporine (STP, 100 nM). In contrast, DiC8 (200 μM), but not PMA ( ≤ 300 nM), reduced the inhibitory effect of adrenaline (5 μM) on PGE1 (300 nM)-induced cAMP formation. This effect of DiCg was unaltered by STP (100 nM). Selective inhibition of PGD2-induced cAMP formation by PMA most probably can be attributed to PKC catalysed phosphorylation of the DP receptor. Reduction of the inhibitory effect of adrenaline by DiC8 could occur via an action at the α2 adrenoreceptor or Ni. These differential effects of PMA and DiC8 may result from differences in their distribution or efficacy, or to heterogeneity of platelet PKC.