A 99Tcm-labelled leukotriene B4 receptor antagonist for scintigraphic detection of infection in rabbits

In a search for a rapid and accurate imaging agent for scintigraphic detection of infection and inflammation, an LTB4 receptor antagonist, 99Tcm-RP517, which contains the hydrazino nicotinamide moiety, has been developed recently. To study the in vivo behaviour of 99Tcm-RP517, rabbits with Escherichia coli infection were injected intravenously with 99Tcm-RP517. Gamma camera images were obtained and ex vivo bio-distribution was determined at several hours post-injection (p.i.). In a separate set of rabbits the choledochal duct was cannulated to quantitatively monitor the hepatobiliary clearance of the radiopharmaceutical. The receptor binding fraction of the radiolabelled RP517 exceeded 70%. Accumulation of 99Tcm-RP517 in the abscess was visualized as early as 1 h p.i. Due to rapid blood clearance (t1/2 alpha=18+/-0.6 min, t1/2 beta=6.5+/-0.4 h) and high abscess uptake, the abscess-to-muscle ratios increased with time from 7.0+/-2.3 at 1 h p.i. to 44.3+/-4.6 at 20 h p.i. The agent mainly cleared via the hepatobiliary route: 50% of the radiolabel was recovered in the small bowel at 1 h p.i., whereas 85% was found in cecum and sigmoid at 20 h p.i. In conclusion, 99Tcm-RP517 rapidly visualized E. coli abscesses in rabbits. The agent rapidly cleared from the blood, mainly via the hepatobiliary route. High abscess-to-background ratios were achieved. The accumulation in the intestines could limit the applicability of this agent for detecting infectious processes in the abdominal area. The development of a more hydrophilic analogue of 99Tcm-RP517 could improve the clinical applicability of this agent.

Effects of a BLT receptor antagonist on local and remote reperfusion injuries after transient ischemia of the superior mesenteric artery in rats

Reperfusion of ischemic vascular beds may lead to recruitment and activation of leukocytes, release of mediators of the inflammatory process and further injury to the affected vascular bed and to remote sites. Neutrophils appear to play a major role in the pathophysiology of reperfusion injury. Amongst inflammatory mediators shown to activate neutrophils and induce their recruitment in vivo, much interest has been placed on the role of leukotriene (LT)B(4). Here, we have assessed the effects of the BLT receptor antagonist (+)-1-(3S, 4R)-[3-(4-phenyl-benzyl)-4-hydroxy-chroman-7-yl]-cyclopentane carboxylic acid (CP 105,696) in a model of neutrophil-dependent ischemia and reperfusion injury in the rat. The superior mesenteric artery was isolated and ischemia was induced by its total occlusion for 30 min. After 30 min of reperfusion, injury was assessed by evaluating the extravasation of Evans blue, an index of vascular permeability, and the levels of myeloperoxidase, an index of neutrophil accumulation, in the intestine, mesentery and lung. The neutrophil-dependence of the local (intestine and mesentery) and remote (lung) injury was confirmed by using fucoidin, a selectin blocker, and WT-3, an anti-CD18 monoclonal antibody. Post-ischemic treatment with CP 105,696 dose-dependently inhibited vascular permeability and neutrophil accumulation in the intestine and mesentery. CP 105,696 also blocked the vascular permeability changes, but not neutrophil accumulation, in the lungs after reperfusion injury. Virtually identical results were obtained with another BLT receptor antagonist, 1-(5-ethyl-2-hydroxy-4-(6-methyl-6-(1H-tetrazol-5-yl)-heptoxy++ +)-phenyl )ethanone (LY255283). Our results suggest that post-ischemic treatment with BLT receptor antagonists may inhibit local and remote ischemia and reperfusion injury by blocking both the accumulation and/or activation of neutrophils.

Effects of the second-generation leukotriene B(4) receptor antagonist, LY293111Na, on leukocyte infiltration and collagen-induced arthritis in mice

The effects of the second-generation leukotriene B(4) receptor (LTB(4) receptor) antagonist, 2-[2-propyl-3-¿3-[2-ethyl-4-(4-fluorophenyl)-5-hydroxy-phenoxy]-propo xy¿phenoxy]benzoic acid sodium salt (LY293111Na), on leukotriene B(4)-induced leukocyte infiltration and interleukin-1-accelerated collagen-induced arthritis in mice were studied. Neutrophil infiltration induced into an air pouch by leukotriene B(4) was dose-dependently inhibited by LY293111Na and strongly so by another LTB(4) receptor antagonist, 4-[5-¿4-(aminoiminomethyl)phenoxy¿pentoxy]-3-methoxy-N, N-bis(1-methylethyl) (Z)-2butenedioate (1:1) (CGS25019C). Both compounds significantly inhibited the increase of the arthritis index and the ankle bone destruction in interleukin-1-accelerated collagen-induced arthritis. Phenidone, a 5-lipoxygenase inhibitor, also inhibited interleukin-1-accelerated collagen-induced arthritis, while indomethacin and tenidap, cyclooxygenase inhibitors, had slight inhibitory effects. Injection of interleukin-1 elicited a marked increase of the leukotriene B(4) level in arthritic paws, while the prostaglandin E(2) level was slightly increased. These findings indicate clearly that leukotriene B(4) is an important mediator of interleukin-1-accelerated collagen-induced arthritis in mice. If this can be extrapolated to man, LTB(4) receptor antagonists might be useful for treatment of the acute progressive phase of human arthritis.

Human granulocyte CD11b expression as a pharmacodynamic biomarker of inflammation

A method has been developed for the direct quantification of the CD11b integrin on granulocytes by flow cytometric analysis of whole blood specimens following either LTB(4) or lipopolysaccharide (LPS) stimulation. This method has utility in evaluating the pharmacodynamic action of either LTB(4) receptor antagonists or immune cell modulators in effecting CD11b integrin expression and granulocyte activation in human subjects administered such drugs. Previous studies using CD11b as a biomarker of granulocyte activation have faltered because of the difficulty in controlling the activation state of the granulocyte following removal of blood from subjects. The present study has made use of a newly validated method using either LTB(4) or LPS to stimulate CD11b expression on granulocytes and has been used, as one measure, in the evaluation of LPS activity when administered to normal human volunteers.

Effects of LTB4 receptor antagonist on myonephropathic metabolic syndrome: an experimental study

The aims of this study were to determine the involvement of leukocytes in reperfusion injury following acute arterial occlusion and to evaluate the effect of the leukotriene B4 (LTB4), which is a chemical mediator of inflammation, receptor antagonist. We examined the usefulness of LTB4 receptor antagonist, ONO-4057, as a preventative drug for myonephropathic metabolic syndrome (MNMS). The experimental leg ischemic model was developed using Wistar strain rats. The rats were divided into 4 groups. In Group R3, the infra-renal abdominal aorta was clamped for 3 hrs and the right femoral muscle tissue was cut to block the development of a collateral artery. In Group R6, the infra-renal abdominal aorta was clamped for 6 hrs and the right femoral muscle tissue was cut. In Group C, the controls, there was no clamping of the abdominal aorta and the right femoral muscle tissue was cut. In Group M, the medicated group, rats were pretreated with an LTB4 receptor antagonist, ONO-4057, just before reperfusion. Blood serum interleukin-1 (IL-1), interleukin-8 (IL-8), creatine phosphokinase (CPK), and aldolase were measured and compared in each of those 4 groups. We also examined the intercellular adhesion molecule-1 (ICAM-1) expression in various organs (liver, heart and kidney) by immunohistochemistry. We found that IL-1 beta levels were low in all groups. CPK, aldolase and IL-8 levels after reperfusion in Group R6 significantly high compared with the levels in Group C (P < 0.03 about CPK, P < 0.05 about aldolase, and P < 0.05 about IL-8). The levels of CPK, aldolase, and IL-8 in Group M were significantly lower than those in Group R6 (P < 0.02 about CPK, P < 0.04 about aldolase, and P < 0.03 about IL-8). We determined immunohistochemically that the expression of ICAM-1 was positive on endothelial cells at the coronary artery and the small vein in Group R6 and that the expression of ICAM-1 was negative on endothelial cells in Group C. Those data suggested that ICAM-1 may play an important role in the progression of reperfusion injury, and the adhesion of neutrophilic leukocytes on endothelial cells may play a significant role in MNMS. LTB4 receptor antagonist may be useful for preventing reperfusion injury following acute aortic occlusion.

[Effects of leukotriene B4 receptor antagonist on experimental autoimmune uveoretinitis in rats]

PURPOSE

We evaluated the potential of leukotriene B4 receptor antagonist (LTB4 RA) as an anti-inflammatory agent on experimental autoimmune uveoretinitis (EAU).

MATERIALS AND METHODS

LTB4 RA was administered to Lewis rats twice a day on days 0-10, 0-5, and 6-10 after immunization. Rats treated on days 0-10 after immunization were subdivided into three groups according to the dosage of LTB4 RA. The eyes were examined histopathologically, and the expression of CD 45 RC in CD 4+T cells was analyzed.

RESULTS

The inflammatory changes in the eyes of EAU were decreased in all groups treated with LTB4 RA in a dose-dependent manner. The treatment with LTB4 RA on days 0-10 after immunization achieved much higher uveitis suppression. The infiltration into eye tissues by neutrophils and lymphocytes was decreased by treatment with LTB4 RA. In treated groups, the CD 45 RChigh subset decreased in the induction phase of EAU as compared with the untreated group.

CONCLUSION

The suppressive mechanisms of LTB4 RA on EAU may be dependent on suppression of the activation of neutrophils and CD 4+T cells.

Pharmacologic actions of the second generation leukotriene B4 receptor antagonist LY29311: in vivo pulmonary studies

We examined the in vivo actions of LY293111 sodium (2-[2-propyl-3-[3-[2-ethyl-4-(4-fluorophenyl)-5-hydroxyphenoxy]pro poxy]phenoxy] benzoic acid sodium salt). Guinea pigs were used to evaluate the effect of this agent on (1) acute airway obstruction produced by intravenous leukotriene B4, (2) pulmonary granulocyte infiltration and delayed onset airway obstruction resulting from a 4-h leukotriene B4 inhalation and (3) lung inflammation after aerosol challenge with the divalent cationic ionophore A23187 (6S-[6alpha(2S*,3S*),8beta(R*),9beta,11alpha]-5- (methylamino)-2-[[3,9,11-trimethyl-8-[1-methyl-2-oxo-2-(1H-pyrrol-2-yl)e thyl]-1,7-dioxaspiro[5.5]undec-2-yl]methyl]-4-benzoxazole carboxylic acid). Airway obstruction was quantitated using pulmonary gas trapping measurements and lung inflammation was evaluated by bronchoalveolar lavage (BAL) and histology. LY293111 sodium produced a dose-related inhibition of acute leukotriene B4-induced airway obstruction when administered i.v. (ED50=14 microg/kg) or p.o. (ED50=0.4 mg/kg). In contrast, LY293111 sodium did not inhibit the pulmonary gas trapping caused by aerosols of histamine, leukotriene D4, or the thromboxane mimetic U46619 (15 [(S)-hydroxy11a,9a-(epoxymethano)prosta-5Z,13E-dienoic acid]). Oral LY293111 sodium inhibited leukotriene B4-induced bronchoalveolar lavage granulocyte infiltration and delayed onset airway obstruction at doses as low as 0.3 mg/kg. In A23187-challenged animals, pulmonary inflammation was markedly inhibited at 1 h, but not 2 h and 4 h post-exposure. We conclude that LY293 11 sodium is a selective leukotriene B4 receptor antagonist with potent pulmonary anti-inflammatory activity.

The potential of various lipopolysaccharides to release IL-8 and G-CSF

Lipopolysaccharide (LPS) derived from Pseudomonas aeruginosa is less cytotoxic than that from Escherichia coli. But P. aeruginosa induces a prominent sustained lung inflammation as in cystic fibrosis and diffuse panbronchiolotis. The present study examined the potential for several LPSs obtained from E. coli and P. aeruginosa to release neutrophil chemotactic activity (NCA) from lung cells. LPSs differently stimulated A549 cells, BEAS-2B cells, and lung fibroblasts to release NCA [P. aeruginosa > E. coli 0127:B8 (Difco) > E. coli 055:B5 (Sigma) > E. coli 026:B6 (Sigma)]. E. coli 0127:B8 (Sigma) and 0111:B4 (Sigma) did not stimulate these cells. NCA was chemotactic by checkerboard analysis. Molecular-sieve column chromatography revealed three chemotactic peaks. The release of NCA was inhibited by cycloheximide and lipoxygenase inhibitors. Experiments with blocking antibodies suggested that much of the NCA was secondary to the release of interleukin (IL)-8 and granulocyte colony-stimulating factor (G-CSF). Thus we examined the concentrations of IL-8 and G-CSF and found that the potency of the various LPSs to stimulate NCA closely paralleled the potency in releasing IL-8 and G-CSF. But a difference among LPSs to stimulate A549 cells was observed. Finally, the release of IL-6 showed similar results. These data suggest that P. aeruginosa LPS may stimulate lung cells to release more NCA than E. coli LPSs, leading to sustained lung inflammation.

Pharmacological effects of a specific leukotriene B(4) receptor antagonist (VML 295) on blood leukocytes, cutaneous inflammation and epidermal proliferation

VML 295 (LY 293111) is a potent and specific leukotriene(4) receptor antagonist. It has previously been shown in human volunteers that VML 295 at a dosage of 48 mg twice daily inhibits the ex vivo leukotriene B(4) (LTB(4))-induced upregulation of CD11b on peripheral blood neutrophils. A clear dose-response relatinship was shown. In addition, VML 295 inhibits various inflammatory aspects resulting from LTB(4) challenge of the skin, again showing a dose-response relationship. In view of the large variation in the elimination half-life of VML 295 (25-88.5 h) in individual human subjects, the present pharmacological study was designed to provide information on the pharmacodynamics of the drug by the assessment of VML 295 plasma concentrations, ex vivo LTB(4)-induced CD11b upregulation of neutrophils, neutrophil accumulation in the skin following epicutaneous application of LTB(4) and epidermal regeneration following standardized surface trauma. A group of 36 healthy volunteers were treated in a double-blind study with VML 295 at 200 mg twice daily, VML 295 at 200 mg once daily or placebo for 7 days. Before treatment, at the end of treatment and following discontinuation of treatment, VML 295 plasma concentrations and CD11b upregulation of blood neutrophils were assessed. In 18 subjects, the effects of the three treatments on LTB(4)-induced inflammatory were assessed before and at the end of treatment, and in the remaining 18 subjects the effects of these treatments on epidermal regeneration were assessed similarly. VML 295 at 200 mg either twice or once daily has a profound inhibitory effect on ex vivo LTB(4)-induced CD11b upregulation of blood neutrophils, LTB(4)-induced neutrophil accumulation in the skin, trauma-induced hyperproliferation of the epidermis and regenerative keratinization. The twice daily dose schedule was significantly more effective than the once daily regimen in reducing ex vivo CD11b stimulation of neutrophils, in blood samples collected 24 h after discontinuation of VML 295 treatment. The twice daily schedule tended to be more efficient in skin biopsies, although this difference was not statistically significant in the number of subjects investigated. A plasma concentration of 100 ng/ml proved to be the threshold for these effects. The profound biological effects, both systemically and cutaneously, as well as the safety profile, make VML 295 a promising drug for skin disorders characterized by epidermal proliferation and neutrophil accumulation.

An in vivo approach showing the chemotactic activity of leukotriene B(4) in acute renal ischemic-reperfusion injury

Neutrophil migration protects the body against foreign invasion. Sequestration and activation of neutrophils, however, require stringent regulation because they may also cause tissue damage by the release of lysosomal enzymes and reactive oxygen species. The activity of various chemoattractants [e.g., leukotriene B(4) (LTB(4)), interleukin-8, and complements] has been documented by in vitro assays, whereas in vivo data have been limited mostly to histology. To examine in an in vivo model the chemotactic activity and subsequent tissue infiltration and the role of a specific chemoattractant, LTB(4), we used a rat renal ischemia-reperfusion injury model. Fluorescence-labeled Chinese hamster ovary (CHO) cells stably expressing the LTB(4) receptor (CHO-BLT) were able to accumulate along with neutrophils in the postischemic kidney, in contrast to vector control CHO cells. Furthermore, LTB(4) antagonists that protect against the decrease in renal function and diminish the tissue myeloperoxidase activity also led to the marked decrease in the number of CHO-BLT cells and neutrophils. Thus, LTB(4) alone appears sufficient to cause cells to migrate into postischemic tissues, and its dominant role in reperfusion injury has been demonstrated. The utilization of transfectants to pinpoint the role of LTB(4) in these in vivo experiments suggests their potential use with other ligands and/or in other pathological conditions.

Synthesis and structure-activity relationships of new 1, 3-disubstituted cyclohexanes as structurally rigid leukotriene B(4) receptor antagonists

A series of 1-hydroxy-3-¿3-hydroxy-7-phenyl-1-hepten-1-yl cyclohexane acetic acid derivatives was designed based on postulated active conformation of leukotriene B(4) (LTB(4)) and evaluated as human cell surface LTB(4) receptor (BLTR) antagonists. Binding was determined through ¿(3)HLTB(4) displacement from human neutrophils and receptor antagonistic assays by in vitro measurements of inhibition of leukocyte chemotaxis induced by LTB(4). On the basis of these assays, a structure-affinity relationship was investigated. Optimization of the acid chain length and omega-substitution of a phenyl group on the lipophilic tail were shown to be critical for binding activity. These modifications led to the discovery of compounds with submicromolar potency and selective BLTR antagonism. The most potent compound 3balpha (IC(50) = 250 nM) was found to significantly inhibit oedema formation in a topical model of phorbolester-induced inflammation. Substantial improvement of in vitro potency was achieved by modification of the carboxylic acid function leading to the identification of the N,N-dimethylamide series. Compound 5balpha, free of agonist activity, displayed higher potency in receptor binding with an IC(50) of 40 nM. These results support the hypothesis that the spatial relationship between the carboxylic acid and allylic hydroxyl functions is crucial for high binding affinity with BLTR.

Reversal of human neutrophil survival by leukotriene B(4) receptor blockade and 5-lipoxygenase and 5-lipoxygenase activating protein inhibitors

Persistent neutrophilia is a feature of chronic obstructive pulmonary disease (COPD). Leukotriene synthesis inhibitors and cysteinyl leukotriene receptor antagonists have shown efficacy in the treatment of asthma. Antagonism of leukotriene (LT)B(4) receptors is being considered as a mode of treating COPD. We examined the capacity for inhibition of leukotriene synthesis and LTB(4) receptor antagonism to reduce survival of neutrophils from patients with COPD and those from normal subjects. The basal apoptosis level of these cells was 55.4 +/- 2.4% (mean +/- SEM) of total cells. Separate exposure to lipopolysaccharide (LPS), granulocyte-macrophage colony-stimulating factor (GM-CSF), dexamethasone (DEX), and LTB(4) increased neutrophil survival (p < 0. 001). The LTB(4) receptor antagonist SB201146 abolished LPS-induced survival in a concentration-dependent manner (10 pmol to 0.1 microM), with an IC(50) of 1.9 nM. Combined exposure to SB201146 and to the cysteinyl leukotriene antagonist SKF104353 did not have a greater effect on survival than did exposure to SB201146 alone. Inhibition of 5-lipoxygenase (5-LO) with BWA4C and of 5-LO-activating protein (FLAP) with MK886 abolished GM-CSF- and DEX-induced neutrophil survival. BWA4C and MK886 abolished GM-CSF- induced neotrophil survival in a concentration-dependent manner (1 nM to 10 microM), with IC(50) values of 182.0 nM and 63.1 nM, respectively. These findings demonstrate reversal of LPS-, GM-CSF-, and DEX-induced neutrophil survival by LTB(4) receptor antagonism and inhibitors of 5-LO and FLAP. They also suggest a potential additional antiinflammatory mode of action of these compounds through reduction of cell survival.

Endogenous monocyte chemoattractant protein-1 (MCP-1) protects mice in a model of acute septic peritonitis: cross-talk between MCP-1 and leukotriene B4

We investigated the involvement of monocyte chemoattractant protein (MCP)-1 in a murine model of septic peritonitis induced by cecal ligation and puncture (CLP). Initial studies demonstrated that CLP induced a dramatic increase in MCP-1 production in the peritoneum, followed by an increase in the recruitment of leukocytes. MCP-1 blockade with anti-MCP-1 antiserum significantly decreased the survival rate following CLP, which was accompanied by an enhanced recovery of viable bacteria from the peritoneum. This was likely due to the reduction in the recruitment and activation of both macrophages and neutrophils. To understand the mechanisms whereby MCP-1 may influence neutrophil infiltration, levels of chemokines known to attract neutrophils were monitored, which showed that peritoneal levels of macrophage-inflammatory protein (MIP)-2, KC, and MIP-1alpha were not altered with anti-MCP-1 Abs. However, anti-MCP-1 Abs reduced the peritoneal levels of leukotriene B4 (LTB4) by 59%. The i.p. injection of MCP-1 into normal mice resulted in elevated levels of LTB4 in the peritoneum. In vitro, MCP-1 stimulated the production of LTB4 from peritoneal macrophages, in a dose-dependent manner. A specific LTB4 receptor antagonist (CP-105, 696) inhibited CLP-induced recruitment of both neutrophils and macrophages, which was accompanied by a reduced level of MCP-1 in the peritoneum. Finally, administration of CP-105,696 was extremely detrimental to the survival of mice following CLP. These experiments demonstrate that endogenous MCP-1 serves as an indirect mediator to attract neutrophils via the production of LTB4, and suggest the cross-talk can occur between MCP-1 and the lipid mediator LTB4 during septic peritonitis.

Metabolism of CP-195,543, a leukotriene B4 receptor antagonist, in the Long-Evans rat and Cynomolgus monkey

1. The fate of [14C]CP-195,543, a novel leukotriene B4 receptor antagonist, was studied following oral administration to the Long-Evans rat and Cynomolgus monkey. 2. Most of the radioactivity was primarily excreted in the faeces, and urine was a minor route of excretion. 3. CP-195,543 was extensively metabolized in the two species, primarily by two metabolic pathways: glucuronidation of unchanged CP-195,543 and oxidative metabolism, presumably by cytochrome P450. 4. The sites of glucuronidation were the carboxylic acid moiety and the hydroxy group. The ester glucuronide was the predominant glucuronide conjugate detected in the rat, whereas the monkey generated the ether as well as the ester glucuronide. 5. The structures of oxidative metabolites were elucidated using mass spectrometry (in the positive- and negative-ion mode) and 1H-NMR. The sites of hydroxylation were the benzylic group and the 3-position of the benzopyran ring. 6. This study has indicated that CP-195,543 was mainly eliminated by Phase II metabolism in both species.

Activation of leukotriene synthesis in human neutrophils by exogenous arachidonic acid: inhibition by adenosine A(2a) receptor agonists and crucial role of autocrine activation by leukotriene B(4)

We report here that the apparent inability of isolated human polymorphonuclear leukocytes (PMNs) to efficiently transform arachidonic acid (AA) is the consequence of A(2a) receptor engagement by endogenous adenosine accumulating in incubation media. Indeed, when adenosine is eliminated from PMN suspensions by the addition of adenosine deaminase, or when cells are incubated with adenosine A(2a) receptor antagonists, important quantities (40-80 pmol/10(6) cells) of 5-lipoxygenase products are synthesized by PMN incubated with 1 to 5 microM exogenous AA. The selective A(2a) receptor agonist CGS21680 was a very potent inhibitor of the AA-induced leukotriene (LT) synthesis, showing an IC(50) of approximately 1 nM. The mechanism of AA-induced stimulation of LT synthesis observed in the absence of extracellular adenosine was investigated. In adenosine deaminase-treated PMN, exogenous AA induced Ca(2+) mobilization and the translocation of 5-lipoxygenase to nuclear structures. A time lag of 20 to 60 s (variable between PMN preparations) was observed consistently between the addition of AA and the elevation of intracellular Ca(2+) concentration (and LT synthesis), indicating that AA itself did not trigger the Ca(2+) mobilization in PMN. This AA-induced Ca(2+) mobilization, as well as the corresponding 5-lipoxygenase translocation and stimulation of LT synthesis, was blocked efficiently by the LT synthesis inhibitor MK0591, the LTB(4) receptor antagonists CP105696 and LY223982, and the LTA(4) hydrolase inhibitor SC57461A. These data demonstrate that AA is a highly potent and effective activator of LT synthesis and acts through a mechanism that requires an autocrine stimulatory loop by LTB(4).

Immunosuppressive effect of leukotriene B(4) receptor antagonist in vitro

Leukotriene B(4) (LTB(4)), which is an arachidonic acid metabolite produced by the 5-lipoxygenase pathway and a well-characterized chemical mediator of inflammation, has been proposed to be an immune response modulator. Here we showed the constitutive expression of the LTB(4) receptor (LTB(4)R) in resting and activated T cells. We found that the LTB(4)R antagonist inhibited T cell proliferation induced by Con A, immobilized anti-CD3 mAb, or IL-2. This inhibitory effect was abolished by addition of LTB(4)R agonist. The LTB(4)R antagonist inhibited IL-2, IFN-gamma, and IL-4 production by anti-CD3-stimulated T cells and also inhibited IL-12-induced IFN-gamma production. Moreover, the LTB(4)R antagonist exerted an additive inhibitory effect to FK506 on T cell proliferation. These results suggest that LTB(4) is intrinsically involved in T cell activation to upregulate cytokine production and proliferation, and thus the LTB(4)R antagonist might be useful as an immunosuppressive agent.

In vitro and in vivo pharmacological characterization of SB 201993, an eicosanoid-like LTB4 receptor antagonist with anti-inflammatory activity

Leukotriene B4 (LTB4) and 12-(R)-hydroxy-5,8,10,14-eicosatetraenoic acid (12-[R]-HETE) have been postulated to contribute to the pathophysiology of inflammatory diseases. SB 201993, (E)-3-[[[[6-(2-carboxyethenyl)-5-[[8-(4-methoxyphenyl)octyl] oxy]-2-pyridinyl] methyl] thio] methyl] benzoic acid, identified from a chemical series designed as ring-fused analogs of LTB4, was evaluated as an antagonist of LTB4- and 12-(R)-HETE-induced responses in vitro and for anti-inflammatory activity in vivo. SB 201993 competitively antagonized [3-H]-LTB4 binding to intact human neutrophils (Ki = 7.6 nM) and to membranes of RBL 2H3 cells expressing the LTB4 receptor (RBL 2H3-LTB4R; IC50 = 154 nM). This compound demonstrated competitive antagonism of LTB4- and 12-(R)-HETE-induced Ca2+ mobilization responses in human neutrophils (IC50s of 131 nM and 105 nM, respectively) and inhibited LTB4-induced Ca2+ mobilization in human cultured keratinocytes (IC50 = 61 nM), RBL 2H3-LTB4R cells (IC50 = 255 nM) and mouse neutrophils (IC50 = 410 nM). SB 201993 showed weak LTD4-receptor binding affinity (Ki = 1.9 microM) and inhibited 5-lipoxygenase (IC50 of 3.6 microM), both in vitro and ex vivo. In vivo, SB 201993 inhibited LTB4-induced neutrophil infiltration in mouse skin and produced dose-related, long lasting topical anti-inflammatory activity against the fluid and cellular phases of arachidonic acid-induced mouse ear inflammation (ED50 of 580 microg/ear and 390 microg/ear, respectively). Similarly, anti-inflammatory activity was also observed in the murine phorbol ester-induced cutaneous inflammation model (ED50 of 770 and 730 microg/ear, respectively, against the fluid and cellular phases). These results indicate that SB 201993 blocks the actions of LTB4 and 12-(R)-HETE and inhibits a variety of inflammatory responses; and thus may be a useful compound to evaluate the role of these mediators in disease models.

Bleomycin stimulates lung epithelial cells to release neutrophil and monocyte chemotactic activities

Although bleomycin, an antineoplastic drug, is used in the treatment of a variety of tumors, the mechanisms of bleomycin-induced lung injury and fibrosis are not fully elucidated. We postulated that bleomycin might stimulate A549 cells, a type II pneumocyte cell line, to release neutrophil and monocyte chemotactic activities (NCA and MCA, respectively). To test this hypothesis, A549 cell supernatant fluids were harvested and evaluated for NCA and MCA. A549 cell supernatant fluids showed NCA and MCA in response to bleomycin in a dose- and time-dependent manner (P < 0.05). Checkerboard analysis revealed that both NCA and MCA were predominantly chemotactic. Partial characterization of the released NCA and MCA showed that the activities were partially heat labile, trypsin digested, and predominantly ethyl acetate extractable. Lipoxygenase inhibitors and cycloheximide inhibited the release of chemotactic activities significantly. Molecular-sieve column chromatography revealed that the released activities were heterogeneous. However, low-molecular-weight activity was prominent. Leukotriene B4-receptor antagonist, anti-interleukin-8, anti-granulocyte colony-stimulating factor, and anti-monocyte chemoattractant protein-1 antibodies attenuated the chemotactic activities. Immunoreactive leukotriene B4 receptor, interleukin-8, granulocyte colony-stimulating factor, and monocyte chemoattractant protein-1 significantly increased in supernatant fluids in response to bleomycin. These data demonstrate that bleomycin stimulates type II epithelial cells to release chemotactic activities and plays a role in inflammatory cell recruitment into the lung.

Synergistic effects of pranlukast and leukotriene B4 receptor antagonist on antigen-induced pulmonary reaction

We now attempted to differentiate effects of cysteinyl-leukotrienes and leukotriene B4 on antigen-induced pulmonary reaction by using a selective leukotriene D4/E4 (CysLT1) receptor antagonist and a selective LTB4 (BLT) receptor antagonist in rats. An intratracheal challenge with ovalbumin to Brown-Norway rats actively sensitized with ovalbumin produced two phases of airway responses which were estimated based on airway resistance, the immediate-type airway response within 30 min, and the delayed-type airway response beginning from 4 to 6 h after the challenge. Pretreatment of the rats with a CysLT1 receptor antagonist (pranlukast) failed to reduce the elevation of airway resistance, and pretreatment with a BLT receptor antagonist (ONO-4057; 5-[2-(2-carboxyethyl)-3-[6-(4-methoxyphenyl)-5E-hexenyl]- oxyphenoxy] valeric acid) also produced no decrease. In contrast, combined pretreatment of the rats with pranlukast and ONO-4057 did not reduce the amplitude of the immediate-type airway response, but did allow the elevated airway resistance to return to its baseline level and also significantly inhibited the delayed-type airway response. Histological examination at 6 h after ovalbumin challenge showed infiltration of inflammatory cells with a predominance of neutrophils and scattered eosinophils in the bronchial submucosa. While pretreatment with neither pranlukast nor with ONO-4057 inhibited the infiltration of inflammatory cells in the bronchial submucosa, pretreatment with the two antagonists combined significantly inhibited the infiltration of granulocytes into the bronchial submucosa. On the contrary, intratracheal administration of either leukotriene D4 or leukotriene B4 up to 10 microg resulted in the infiltration of granulocytes into the bronchial submucosa, but no synergism for the infiltration of granulocytes was observed after combined administration. These results suggest that leukotriene B4 appears to play a significant role in the antigen-induced pulmonary reaction in association with cysteinyl-leukotrienes. Accordingly, the combined antagonism at the CysLT1 receptor and BLT receptor may be a useful intervention for the treatment of bronchial asthma.

Antagonizing leukotriene B4 receptors delays cardiac allograft rejection in mice

BACKGROUND

Allograft rejection is a cellular immunological/inflammatory response that is, in part, directed by potent proinflammatory mediators. This study was designed to test the hypothesis that leukotriene B4 (LTB4) may have a role in graft rejection and that LTB4 receptor antagonists may be clinically useful in the treatment of allograft rejection.

METHODS

We evaluated the potent and selective LTB4 receptor antagonist CP-105696 in a murine heterotopic cardiac allograft model with oral dosing daily for 28 days or in an induction protocol (day -1 to day 3).

RESULTS

At a dose of 50 mg/kg/day (28 days), B10.BR (H2k) allografts transplanted into C57Bl/6 (H2b) recipients were significantly protected, as reflected by the mean survival time versus control grafts (27+/-20 days [n=10] vs. 12+/-6 days [n=14]; P=0.0146). Using an induction protocol (day -1 to day 3), CP-105696 at 100 mg/kg/day significantly prolonged allograft survival (33+/-23 days [n=9]; P=0.0026), but CP-105696 at 10 mg/kg/day did not (18+/-16 days [n=8]; P=0.1433). Syngeneic grafts survived indefinitely (n=11). Immunohistological evaluation of allografts at rejection revealed a mononuclear cell infiltrate composed primarily of CD3+ and CD11b+ (Mac-1+) cells, which were infrequent in syngeneic grafts. Allografts from mice treated with CP-105696 at 50 or 100 mg/kg/day demonstrated a selective reduction in beta2-integrin (Mac-1) expression on monocytes/macrophages, as demonstrated by CD11b staining density compared with allograft controls.

CONCLUSIONS

The results suggest that LTB4 or other potential ligands for LTB4 receptors may be important mediators of allograft rejection and support the clinical evaluation of LTB4 receptor antagonists in human organ transplantation.

The leukotriene B4 receptor antagonist ONO-4057 inhibits nephrotoxic serum nephritis in WKY rats

To evaluate the role of leukotriene B4 (LTB4) in glomerulonephritis, this study was conducted to examine whether ONO-4057, an LTB4 receptor antagonist, moderated nephritis caused by the injection of nephrotoxic serum (NTS) into Wistar-Kyoto rats. Rats were given intraperitoneal injections of ONO-4057 or phosphate-buffered saline 24 h before the injection of NTS. These rats subsequently received equal doses of ONO-4057 or phosphate-buffered saline 3 h and 1, 2, 3, 4, 5, and 6 d later. Compared with the control groups, ONO-4057 treatment significantly reduced proteinuria and hematuria, suppressed the glomerular accumulation of monocytes/macrophages, and reduced the formation of crescentic glomeruli in a dose-dependent manner. These results suggest that LTB4 is responsible for the crescentic formations and renal dysfunction associated with NTS nephritis. The LTB4 receptor antagonist ONO-4057 may thus be beneficial in the treatment of crescentic glomerulonephritis.

Carboxy-substituted cinnamides: a novel series of potent, orally active LTB4 receptor antagonists

A series of carboxy-substituted cinnamides were investigated as antagonists of the human cell surface leukotriene B4 (LTB4) receptor. Binding was determined through measurement of [3H]LTB4 displacement from human neutrophils. Receptor antagonism was confirmed through a functional assay, which measures inhibition of Ca2+ release in human neutrophils. Potent antagonists were discovered through optimization of a random screening hit, a p-(alpha-methylbenzyloxy)cinnamide, having low-micromolar activity. Substantial improvement of in vitro potency was realized by the attachment of a carboxylic acid moiety to the cinnamide phenyl ring through a flexible tether, leading to identification of compounds with low-nanomolar potency. Modification of the benzyloxy substituent, either through ortho-substitution on the benzyloxy phenyl group or through replacement of the ether oxygen with a methylene or sulfur atom, produced achiral antagonists of equal or greater potency. The most potent compounds in vitro were assayed for oral activity using the arachidonic acid-induced mouse ear edema model of inflammation. Several compounds in this series were found to significantly inhibit edema formation and myeloperoxidase activity in this model up to 17 h after oral administration. Representatives of this series have been shown to be potent and long-acting orally active inhibitors of the LTB4 receptor.