Pharmacological activity of the second generation leukotriene B4 receptor antagonist,SC-53228:

Inflammatory bowel disease is a chronic inflammatory disorder of the gastrointestinal tract that includes ulcerative colitis and Crohn's disease. Leukotriene B₄ is thought to be a prominent proinflammatory mediator in these diseases, in that leukotriene B₄ levels are increased in the colonic mucosa of inflammatory bowel disease patients and there is increased polymorphonuclear leukocyte infiltration of these tissues. SC-53228(+)-(S)-7-[3-[2(-cyclopropylmethyl)-3-methoxy-4-[(methylamino)carbonyl]phenoxy]propoxy]-3,4-dihydro-8-propyl-2H-1-benzopyran-2-propanoic acid, a second generation LTB₄ receptor antagonist, was evaluated for therapeutic efficacy in a rodent model of acute colonic inflammation induced by short chain organic acids, as well as for effects on rodent liver. When given intracolonically to mice, SC-53228 inhibited neutrophil infiltration, assessed by myeloperoxidase (MPO) levels, with an ED₅₀ value of 9±1.2 mg/kg. When given by gavage, SC-53228 inhibited neutrophil influx in colitic mice with an ED₅₀ value of 30 mg/kg. These results were also confirmed histologically. Furthermore, high dose oral SC-53228 treatment had no effect on liver cytochrome P-450 content, fatty acyl CoA oxidase or liver weight in rats and mice. Together, these data suggest that SC-53228 may be efficacious orally and locally, as well as safe for use in trials for the medical management of IBD.     

Effect of a leukotriene B4 receptor antagonist on leukotriene B4-induced neutrophil chemotaxis in cavine dermis

Leukotriene B₄ (LTB₄) is a proinflammatory product of arachidonic acid metabolism that has been implicated as a mediator in a number of inflammatory diseases. When injected intradermally into the cavine, LTB₄ elicits a dose-dependent immigration (chemotaxis) of neutrophils (PMNs) into the injection sites as assessed by the presence of a neutrophil marker enzyme myeloperoxidase. SC-41930 {7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)propoxy]-3,4-dihydro-8-propyl-2H-l-benzopyran-2-carboxylic acid, a potent LTB₄ receptor antagonist inhibited the chemotactic actions of LTB₄ when coadministered into the dermal site and when given intravenously or orally with ED₅₀ values of 200 ng, 0.5 mg/kg, and 0.6 mg/ kg respectively. This compound may well have application in disease states, such as inflammatory bowel disease and psoriasis, where LTB₄ is implicated as a proinflammatory mediator.     

Pharmacological profile of mifentidine: A novel H2-receptor antagonist

Mifentidine, a representative compound of a novel class of H₂-antagonists, has been investigated for its ability to interact with H₂-receptors and to inhibit gastric acid secretion. Affinity estimates (K _B) of mifentidine obtained fromin vitro studies on cardiac and gastric mucosal histamine (H₂) receptors were in the 20–50 nM range. Mifentidine appeared to be endowed with strong antisecretory properties against histamine-stimulated secretion in the anaesthetized rat and in the conscious dog. Distinct features of mifentidine were considerable bioavailability and duration of anti-secretory effect.     

The pharmacokinetics and metabolism of SC-53228, a specific leukotriene B4 receptor antagonist

Inflammation Research -     

Inhibition of leukotriene formation and IL-8 release by the PAF-receptor antagonist SM-12502

We analyzed the effect of the PAF receptor antagonist (+)-cis-3,5-dimethyl-2-(3-pyridyl) thiazolidin-4-one hydrochloride (SM-12502) on the release of leukotriene B₄ and IL-8 from human leukocytes. Peripheral blood from healthy donors was separated in two different fractions: polymorphonuclear leukocytes (PMN) and a lymphocyte, monocyte and basophil granulocyte cell fraction (LMB). After incubation of the cell population with different concentrations of SM-12502 the cells were subsequently stimulated with either the Ca ionophore A23187, the bacterial derived peptide fMLP, or with an activator of heterotrimetric G-proteins, the sodium fluoride (NaF, in the presence of Al³⁺). The PAF receptor antagonist led to a concentration and time dependent inhibition of LTB₄ formation and IL-8 release from PMN and LMB. Our data clearly indicate an inhibitory effect of the PAF receptor antagonist SM-12502 on the formation of mediators of the lipoxygenase pathway and on the release of IL-8.     

Inhibition of ovulation in the rat by a leukotriene B(4) receptor antagonist

The involvement of leukotriene (LT) B(4) in the ovulatory process of the rat was investigated by the use of a LTB(4)-receptor antagonist (ZK158252 = L-ANT) administered either intrabursally in vivo or to the in-vitro perfused ovary. The in-vivo experiments revealed inhibition of human chorionic gonadotrophin (HCG)-induced ovulation by 500 micromol/l L-ANT (median 5.5, 25-75% range 1.0-6.0) compared with controls (median 9.0, range 6.25-13.5). In vitro, ovulation was induced by LH (0.2 microg/ml) + 3-isobutyl-1-methylxanthine (IBMX; 0.2 mmol/l). The ovary was perfused either for 20 h, to study ovulation rate, or for 10 h to examine ovarian concentrations of the ovulatory mediators matrix metalloproteinase (MMP)-2 and MMP-9, plasminogen activator (PA), prostaglandin (PG)E(2) and PGF(2 alpha). Addition of LH+IBMX resulted in a marked stimulation of steroid release and ovulations occurred in all ovaries (median 11.0, range 10.0-14.0). The L-ANT inhibited ovulation in a dose-dependent way (median 10.0, range 8.0-13.0 at 1 micromol/l; median 6.0, range 3.5-10.0 at 10 micromol/l; median 2.0, range 0.75-5.75 at 100 micromol/l). The intra-ovarian activity of PA was increased 1.5-fold by L-ANT (100 micromol/l), but the concentrations of PGE(2) and PGF(2 alpha) remained unaltered. While no changes in MMP-9 were observed, conversion from pro-MMP-2 to active MMP-2 was inhibited by L-ANT. These results suggest that activation of the LTB(4)-receptor within the ovary is involved in the ovulatory process and that the effects of LTB(4)-receptor activation are partly mediated via MMP-2.     

Anti-inflammatory activity of the leukotriene B4 receptor antagonist,SC-41930, in colitic cotton-top tamarins

Cotton-top tamarins (CTTs) with histologically confirmed persistent and active colitis were given the leukotriene B₄ (LTB₄) receptor antagonist, SC-41930, (10 mg/kg BW, by gavage b.i.d.) for eight weeks. Anti-inflammatory activity was evaluated by colonic biopsy, stool consistency and the level of the lipid mediators LTB₄ and prostaglandin E₂ (PGE₂) in rectal dialysates. Stool consistency did not improve with treatment but did not worsen. Blood chemistry (ALT, AST, LDH) and hematological parameters neither showed any untoward effects of SC-41930 treatment nor was there any effect on body weight. In rectal dialysate LTB₄ levels were significantly reduced from pretreatment level of 4.87±1.46 ng/ml to 1.07±0.67 and 2.45±0.13 ng/ml at 4 and 8 weeks, respectively, and higher prostaglandin E₂ (PGE₂) over time. Histologically, 5/7 improved, 1/7 remained the same and 1/7 worsened.

Oral SC-41930 treatment was safe and associated with an anti-colitic effect. The reduced LTB₄ levels (affecting granulocyte degranulation and recruitment into tissues) and increased PGE₂ (perhaps exerting a mucosal protective effect) may, in part explain the observed efficacy of this compound in active tamarin colitis. Use of the CTT model could provide insight into the inflammatory mediator contribution to idiopathic colitis and serve as a useful bridge between preclinical pharmacology and the assessment of these compounds in the medical management of human inflammatory bowel disease.

     

Effect of a leukotriene B4 antagonist on substance P-induced granulocyte infiltration in mouse skin]

Substance P causes granulocyte (neutrophil and eosinophil) infiltration in mouse skin by inducing mast cell degranulation. However, the mediator responsible for this granulocyte infiltration has not been determined. In this study, we examined the effect of a leukotriene B4 (LTB4) antagonist ONO-4057 on substance P-induced granulocyte infiltration in the skin of BALB/c mice. Pretreatment with the LTB4 antagonist decreased substance P-induced neutrophil and eosinophil infiltrations in mouse skin at 6 h to the same extent that an inhibitor of mast cell degranulation disodium cromoglycate decreased those responses. The LTB4 antagonist also decreased substance P-induced neutrophil, but not eosinophil, infiltration in mouse skin at 24 h. We conclude that LTB4 is a major mast cell-derived chemotactic mediator for initiating substance P-induced neutrophil and eosinophil infiltrations in mouse skin.     

CGS 26529: The biological profile of a novel,orally active 5-lipoxygenase inhibitor with an extended duration of action

Inflammation Research -     

Assessment of thein vivo biochemical efficacy of orally active leukotriene biosynthesis inhibitors

In man, the therapeutic effectiveness of specific inhibitors of leukotriene (LT) biosynthesis against allergen-induced bronchoconstriction appears to be related to thein vivo biochemical efficacy of these compounds, as measured by inhibition of whole blood LTB₄ generation (upon A23187 stimulus) and, particularly, urinary LTE₄ excretion. Accordingly, we have assessed the ability of two clinically documented LT biosynthesis inhibitors, zileuton and MK-886, and the structurally novel 5-lipoxygenase activatig protein antagonist, MK-0591, to inhibit the production of these inflammatory arachidonic acid metabolites in laboratory dogs. Zileuton (2 mg/kg) was extremely bioavailable in dogs (>10 M plasma concentrations), and inhibited the A23187-inducedex vivo production of LTB₄ by venous blood by >90%, in concordance with its potency in canine bloodin vitro (IC₅₀=1.1 M). Despite this degree of inhibition in whole blood, urinary LTE₄ excretion was reduced by only 52%, a profile of activity similar to that seen in clinical studies. MK-886 was less well absorbed, with plasma concentrations of 3 M being achieved only at 25 mg/kg. These levels resulted in <45% inhibition of LTB₄ production, but a significant (p<0.05) 47% inhibition of urinary LTE₄ excretion. MK-0591 was similarly bioavailable (compared with MK-886), but 10-fold more activein vivo as a 2 mg/kg dose resulted in 41–62% inhibition of urinary LTE₄ excretion (p<0.05 vs controls;n=4, 28). Significant inhibition ofex vivo LTB₄ synthesis was also observed at this dose (49%), in accord with peak plasma concentrations of 0.5 M and anin vitro potency of 0.2–0.4 M (IC₅₀) in whole blood from these animals. At higher dose (10 mg/kg), MK-0591 inhibited LTE₄ excretion by 69%, with 88% inhibition of the LT biosynthetic capacity of whole blood. These data demonstrate that the biochemical efficacy of structurally diverse leukotriene biosynthesis inhibitors can be assessedin vivo in normal laboratory dogs. Such measurements, combined with bioavailability data from other species, may be useful for predicting biochemical activity in man.     

Biosynthesis of leukotriene B4

Leukotriene B₄ (LTB₄) is a lipid mediator derived from arachidonic acid (AA) by the sequential action of 5-lipoxygenase (5-LOX), 5-lipoxygenase-activating protein (FLAP) and LTA₄ hydrolase (LTA₄H). It was initially recognized for its involvement in the recruitment of neutrophils and is one of the most potent chemotactic agents known to date. A large body of data has indicated that LTB₄ plays a significant role in many chronic inflammatory diseases, such as arthritis, chronic obstructive pulmonary disease (COPD), cardiovascular disease, cancer and more recently, metabolic disorder. In this review, we focus on the biosynthesis of LTB₄ and its biological effects. In particular, we will describe a basic biochemical understanding integrated with recent developments in the field of structural biology of the three key enzymes (5-LOX, FLAP and LTA₄H) in LTB₄ biosynthesis, and also summarize the most outstanding work on in vivo biological and pathogenic roles of these enzymes and the development of enzyme inhibitors.     

Metiamide — An orally active histamine H2-receptor antagonist

Metiamide has been found to be about 10 times more active than burimamide in vitro in antagonizing histamine H₂-receptors and nearly 5 times more active in vivo as an antagonist of histamine or pentagastrin-stimulated secretion. Effective oral ED₅₀ doses for inhibition have been estimated as 25 mole kg^–1 against basal secretion in rats and 16 mole kg^–1 against maximal histamine-stimulated secretion in dogs. Administration of metiamide orally daily for 90 days with doses of 1,500 mole kg^–1 to rats and 700 mole kg^–1 to dogs produced signs of kidney damage as the dominant lesion in both species. These toxic doses are roughly 60 and 44 times greater than the ED₅₀ doses in the rat and dog, respectively. These results show that metiamide has the degree of activity and safety needed for a compound to be a candidate for through clinical evaluation.     

Inhibition of exercise-induced bronchoconstriction by MK-571, a potent leukotriene D4-receptor antagonist

BACKGROUND. Exercise is a common stimulus of bronchoconstriction in subjects with asthma, who also have bronchoconstriction after inhaling the sulfidopeptide leukotriene D4 (LTD4). The purpose of this study was to investigate the importance of LTD4 as a mediator of exercise-induced bronchoconstriction. METHODS. In a double-blind, randomized, crossover study, 12 subjects with stable asthma were treated intravenously with MK-571 (160 mg), a selective and potent LTD4-receptor antagonist, or placebo, 20 minutes before each of two challenges involving exercise at a level previously demonstrated to cause a fall of at least 20 percent in the forced expiratory volume in one second (FEV1). The two exercise challenges were separated by one week. The results of the challenges were expressed as both the maximal fall in FEV1 after exercise and the time to recovery from bronchoconstriction. RESULTS. Treatment with MK-571 attenuated exercise-induced bronchoconstriction in all the subjects. The mean (+/- SEM) maximal percent decrease in FEV1 after exercise was 25.2 +/- 3.5 percent in the subjects taking placebo and 9.2 +/- 2.5 percent in the subjects taking MK-571 (P less than 0.001). The mean percent inhibition for the entire group was 69.5 percent. The mean time to recovery after exercise was 33.4 +/- 4.0 minutes in the placebo group and 8.4 +/- 2.5 minutes in the MK-571 group (P less than 0.001). CONCLUSIONS. This study demonstrates that pretreatment with a potent and selective LTD4 antagonist markedly attenuates exercise-induced bronchoconstriction, and it suggests that LTD4 is a major mediator of this type of bronchoconstriction.     

Effects of a leukotriene receptor antagonist on exhaled leukotriene E4 and prostanoids in children with asthma

BACKGROUND: Leukotriene (LT) E(4) and 8-isoprostane concentrations are elevated in exhaled breath condensate in children with asthma. The effects of leukotriene receptor antagonists (LTRAs) on exhaled leukotriene and prostanoids in children with asthma are unknown. OBJECTIVE: (1) To study the effect of montelukast, a LTRA, on exhaled LTE(4), 8-isoprostane, and prostaglandin E(2) in children with asthma and atopic children; (2) to measure exhaled nitric oxide. METHODS: An open-label study with oral montelukast (5 mg once daily for 4 weeks) was undertaken in 17 atopic children with asthma and 16 atopic children without asthma. RESULTS: Pretreatment exhaled LTE(4) (P < .0001) and 8-isoprostane (P < .0001) values were higher in atopic children with asthma than in atopic children without asthma. In atopic children with asthma, montelukast reduced exhaled LTE(4) by 33% (P < .001), and this reduction was correlated with pretreatment LTE(4) values (r = -0.90; P = .0001). Posttreatment exhaled LTE(4) levels in children with asthma were higher than pretreatment LTE(4) values in atopic children without asthma (P < .004). Montelukast had no effect on exhaled LTE(4) in atopic children without asthma (P = .74), or on exhaled 8-isoprostane (atopic children with asthma, P = .94; atopic children without asthma, P = .55) and PGE(2) (atopic children with asthma, P = .56; atopic children without asthma, P = .93) in both groups. In atopic children with asthma, exhaled nitric oxide concentrations were reduced by 27% (P < .05) after montelukast. CONCLUSION: Leukotriene receptor antagonists decrease exhaled LTE(4) in atopic children with asthma. This reduction is dependent on baseline exhaled LTE(4) values. CLINICAL IMPLICATIONS: Measurement of exhaled LTE(4) might help identify children with asthma most likely to benefit from LTRAs.     

Biological activities of leukotriene B4

Leukotriene B₄ isomer III is released from polymorphonuclear leucocytes, monocytes, eosinophils and macrophagesin vitro and has been detected and measured in human synovial fluidin vivo. Its most prominent biological activities are to induce the aggregation of and to stimulate the movement (chemokinesis and chemotaxis) of leucocytesin vitro and it acts as a cytotaxinin vivo. In addition, it increases vascular permeabilityin vivo when administered together with the vasodilator, PGE₂.     

The effect of inhalation of the leukotriene receptor antagonist, SK&F 104353, on leukotriene C4- and leukotriene E4-induced bronchoconstriction in subjects with asthma.

The effect of prior inhalation of the sulfidopeptide leukotriene receptor antagonist, SK&F 104353 (963 +/- 43.7 micrograms; mean +/- SEM), on (LTC4)- and leukotriene E4 (LTE4)-induced bronchoconstriction has been studied in six subjects with asthma (six male subjects, aged 24 to 36 years). Inhalation challenges with either synthetic LTC4 or LTE4 were performed after prior inhalation of aerosolized SK&F 104353 or placebo in a double-blind, randomized fashion. Airway responsiveness to each agonist was determined by the cumulative dose of agonist required to induce a 35% fall in specific airway conductance (PD35) as determined by linear interpolation of the log dose-response curve. There was no change in baseline specific airway conductance after inhalation of either placebo or SK&F 104353. LTC4- and LTE4-induced bronchoconstrictions were significantly inhibited by aerosolized inhalation of SK&F 104353 30 minutes before challenge. The geometric mean (GM) PD35 of LTC4 on the open-therapy and placebo-therapy days was 0.043 nmol (range, 0.01 to 0.1 nmol) and 0.036 nmol (range, 0.01 to 0.1 nmol), respectively. On the treatment day with SK&F 104353, it was not possible to obtain a GM PD35 LTC4 up to a maximum concentration of 0.52 nmol LTC4 (p less than 0.01). The GM PD35 of LTE4 on the open-therapy and placebo-therapy days was 0.30 nmol (range, 0.13 to 0.76 nmol) and 0.39 nmol (range, 0.14 to 0.9 nmol), respectively. On the treatment day with SK&F 104353, it was not possible to obtain a GM PD35 LTE4 up to a maximum concentration of 5 nmol LTE4 (p less than 0.005). Thus, LTC4- and LTE4-induced bronchoconstrictions are both inhibited by SK&F 104353.     

Generation of leukotriene B4 by hemodialyzer membranes: A novel index of biocompatibility

Summary Leukotriene B₄ (LTB₄) plays an important role in acute and chronic inflammatory and hypersensitive reactions. We studied the time course of LTB₄ biosynthesis in whole blood in 18 patients with end-stage renal failure maintained on regular hemodialysis with two different membranes, cuprophane and polyacrylonitrile (AN 69). The basal levels of LTB₄ from dialysis patients did not differ significantly from a normal control group. Compared to predialytic values, the cuprophane membrane caused a maximal release of LTB₄ by a factor of about 4.5 (p<0.01) within the first 10 to 20 minutes. Thereafter the level fell and returned to baseline range at the end of the hemodialysis session. With the use of the AN 69 membrane no significant increase of LTB₄ could be demonstrated. The changes in LTB₄ concentration showed a close temporal correlation to the alterations in white blood cell count. We conclude that (1) LTB4 is a biologically important mediator of neutrophil activation during hemodialysis, and (2) LTB₄ may be a sensitive marker of biocompatibility in vivo.Abbreviations LTB₄ Leukotriene B₄ - 5-HETE 5-Hydroxyeicosatetraenoic acid     

Dermal inflammation in primates,mice, and guinea pigs: Attenuation by second-generation leukotriene B4 receptor antagonist,SC-53228

Granulocyte infiltration is a prominent feature of human psoriasis. Psoriatic lesional skin contains abnormally high amounts of immunoreactive leukotriene B₄ (LTB₄), a potent granulocyte chemotaxin in vivo and in vitro. SC-53228 [(+)-(S)-7-(3-{2-(cyclopropylmethyl)-3-methoxy-4-[(methylamino)carbonyl]phenoxy}propoxy)-3, 4-dihydro-8-propyl-2H-1-benzopyran-2-propanoic acid], a second-generation LTB₄ receptor antagonist, was tested topically and orally in phorbol ester-induced dermal inflammation in three species. Skin inflammation was induced by topical application of phorbol-12-myristate-13-acetate-(PMA/TPA) and assessed by ear thickness, levels of the neutrophil marker enzyme myeloperoxidase (MPO) and histological examination. In mice, SC-53228 inhibited inflammation with a topical ED₅₀ value of 200 ± 18 g. When applied to guinea pigs, SC-53228 (100 g) inhibited the MPO increase by 86%, while 1000 g abrogated inflammation in rhesus macaques with no plasma accumulation of the drug. A 1 % gel formulation was also efficacious in guinea pig PMA-induced epidermal inflammation. Furthermore, single oral dose administration to mice was efficacious (ED₅₀ < 2.5 mg/kg) as was multidose administration to rhesus macaques. PMA-induced skin inflammation possesses some of the attributes of human psoriasis and an agent such as SC-53228 may have utility in the medical management of this condition.