Pharmacologic and clinical effects of lonapalene (RS 43179), a 5-lipoxygenase inhibitor, in psoriasis

New and promising type of leukotriene B4 (LTB4) antagonists based on the 1,4-benzodioxine structure

New leukotriene B4 (LTB4) antagonists have been synthesized that can be considered as potential anti-inflammatory drugs. Structures containing the dioxygenated nucleus of 1,4-benzodioxine constitute a potential group of leukotriene B4 (LTB4) antagonists. The objective of this study was to access efficient and selective LTB4 antagonists as a way to elucidate the role of LTB4 in inflammatory processes and therefore allow the development of new types of structures based on 1,4-benzodioxine. Forty-one new 1,4-benzodioxine molecules substituted at different positions of the heterocyclic nucleus were synthesized to determine the minimum structural requirements by studying structure-activity relationships. Eighteen of them were tested in vitro and in vivo for their anti-inflammatory activity related to the antagonist character of LTB4. Pharmacological tests have shown satisfactory in vitro activity for compounds 24b, 24c and 24e with IC50's of 288, 439, 477 nM respectively. The results of the in vivo tests, carried out with the compound that presented greater activity in the in vitro tests 24b, have shown significant anti-inflammatory properties.

Do Sleep Disorders and Western Diet Influence Psoriasis? A Scoping Review

Western diet may trigger sleep disorders and vice versa, but their single and mutual effects on systemic inflammatory diseases (i.e., psoriasis) are far from being fully elucidated. At the same time, psoriatic patients display a great burden of sleep disorders and dysmetabolisms related to an unhealthy lifestyle (i.e., diet). These patients are also affected by a chronic disorder deeply modulated by environmental factors (i.e., sleep and diet) capable to influence drug-response and disease progression. Thus, we aimed to summarize the evidence in the literature that may highlight a potential link among psoriasis–diet–sleep in order to further promote a multidisciplinary approach to psoriatic patients in the scientific community.

Current understanding of the role of dietary lipids in the pathophysiology of psoriasis

Dietary lipids are fundamental nutrients for human health. They are typically composed of various long-chain fatty acids which include saturated fatty acids (SFAs) and unsaturated fatty acids (UFAs). UFAs are further classified into several groups, such as omega-3 polyunsaturated fatty acids (PUFAs) and omega-6 PUFAs, depending on their chemical structure. Epidemiological studies have suggested the involvement of dietary lipids in the progression or regulation of psoriasis, a common chronic inflammatory skin disease induced via the IL-23/IL-17 axis. Although the underlying mechanisms by which dietary lipids regulate psoriasis have remained unclear, with the advancement of experimental techniques and the development of psoriasis mouse models, various possible mechanisms have been proposed. For example, SFAs may facilitate psoriatic dermatitis by causing activation of the inflammasome in keratinocytes and macrophages or by inducing IL-17-producing cells, such as Th17 and IL-17-producing γδ T cells in the skin, while omega-3 PUFAs may play inhibitory roles by suppressing Th17 differentiation. In this review, we summarize current data on the roles of dietary lipids in the development of psoriasis as revealed by mouse studies, and we discuss potential therapeutic strategies for psoriasis from the perspective of dietary lipids.

Healing fats of the skin: the structural and immunologic roles of the omega-6 and omega-3 fatty acids

Linoleic acid (18:2omega6) and alpha-linolenic acid (18:3omega3) represent the parent fats of the two main classes of polyunsaturated fatty acids: the omega-6 (n-6) and the omega-3 (n-3) fatty acids, respectively. Linoleic acid and alpha-linolenic acid both give rise to other long-chain fatty acid derivatives, including gamma-linolenic acid and arachidonic acid (omega-6 fatty acids) and docosahexaenoic acid and eicosapentaenoic acid (omega-3 fatty acids). These fatty acids are showing promise as safe adjunctive treatments for many skin disorders, including atopic dermatitis, psoriasis, acne vulgaris, systemic lupus erythematosus, nonmelanoma skin cancer, and melanoma. Their roles are diverse and include maintenance of the stratum corneum permeability barrier, maturation and differentiation of the stratum corneum, formation and secretion of lamellar bodies, inhibition of proinflammatory eicosanoids, elevation of the sunburn threshold, inhibition of proinflammatory cytokines (tumor necrosis factor-alpha, interferon-gamma, and interleukin-12), inhibition of lipoxygenase, promotion of wound healing, and promotion of apoptosis in malignant cells, including melanoma. They fulfill these functions independently and through the modulation of peroxisome proliferator-activated receptors and Toll-like receptors.

Cannabinoids, loratadine and allopurinol as novel additions to the antipsoriatic ammunition

As the current antipsoriatic medications are commonly associated with deleterious side-effects, a determined search for safer agents, which could be used alone or in combination with current antipsoriatic drugs, would be very imperative. Psoriasis is believed to be characterized by a type 1 cytokine pattern; interferon-gamma, interleukin (IL)-2 and tumour necrosis factor (TNF)-alpha are predominantly expressed in this disorder. Nitric oxide, reactive oxygen species, histamine, leukotriene B4, and decreased [corrected] keratinocyte cyclic adenosine monophosphate/cyclic guanosine monophosphate (cAMP/cGMP) ratio are supposed to play roles in the pathogenesis of this disorder. Based on the immunopathogenesis of psoriasis, this paper introduces three novel, potential treatments for this clinical conundrum: (i) cannabinoids, which exert inhibitory effects on antigen processing and macrophage/T-cell interaction and also on the release of IL-2, TNF-alpha and nitric oxide from immune cells; (ii) loratadine, which is an antihistamine capable of increasing [corrected] the cAMP/cGMP ratio and the production of leukotriene B4; and (iii) allopurinol, which scavenges free radicals, inhibits the production of TNF-alpha, and downregulates the expression of intercellular adhesion molecule-1 and P2X7 receptors on monocytes/macrophages, which are involved in antigen presentation and production of the inflammatory response, respectively. Importantly, allopurinol, especially in combination with cyclosporin, has been shown to be effective against experimental autoimmune uveitis, which, like psoriasis, is a cell-mediated autoimmune disorder.

Evidence of 5-lipoxygenase overexpression in the skin of patients with systemic sclerosis: a newly identified pathway to skin inflammation in systemic sclerosis

OBJECTIVE

Leukotrienes are a family of arachidonic acid derivatives with potent proinflammatory and profibrotic properties, and 5-lipoxygenase (5-LOX) catalyzes two key steps in the leukotriene biosynthetic pathway. Since inflammatory cell infiltrates and excessive fibrosis are hallmarks of systemic sclerosis (SSc) skin lesions, we undertook the present study to investigate the expression of 5-LOX in skin biopsy specimens from patients with SSc.

METHODS

Expression of 5-LOX in skin sections from 10 SSc patients and 8 healthy controls was examined by in situ hybridization with specific riboprobes and by immunohistochemistry analysis with 5-LOX monoclonal antibodies. Synthesis of 5-LOX by cultured dermal fibroblasts from 7 patients with SSc and 4 controls was measured by fluorescence-activated cell sorter analysis. In addition, concentrations of leukotriene B4 (LTB4) and LTE4 in fibroblast supernatants after stimulation were determined using enzyme immunoassays.

RESULTS

Expression of 5-LOX was found in all skin sections from SSc patients as well as from controls. However, the number and percentage of 5-LOX-positive cells were significantly higher in SSc skin sections compared with control sections. Expression of 5-LOX was seen in cells within perivascular inflammatory infiltrates as well as in fibroblasts throughout the skin. The experiments with cultured skin fibroblasts revealed that 5-LOX was constitutively expressed in these cells, which resulted in the production of leukotrienes after cell stimulation. Whereas no difference was found for LTE4, SSc fibroblasts produced significantly higher amounts of LTB4 after stimulation, compared with healthy control fibroblasts.

CONCLUSION

The results of this study suggest that the 5-LOX pathway may be of significance in the pathogenesis of SSc and may represent a target for new treatment strategies.

VML 295 (LY-293111), a novel LTB4 antagonist, is not effective in the prevention of relapse in psoriasis

Leukotriene B4 (LTB4) receptor antagonists have been the subject of several studies in the treatment of inflammatory diseases, including psoriasis. A novel oral LTB4 antagonist, VML 295 (LY-293111) has recently been developed and has a pronounced effect on epidermal inflammatory parameters. However, oral treatment of psoriasis for 4 weeks did not result in a decrease in disease severity. The present study was performed in order to investigate whether prolonged treatment with VML 295 up to 8 weeks has a beneficial effect on the overall severity of psoriasis. Moreover, we studied to what extent VML 295 is able to prevent relapse in psoriasis. In the present study, 35 patients with stable chronic plaque psoriasis were included. A representative plaque of at least 16 cm2 was initially treated with clobetasol-17-propionate lotion under hydrocolloid occlusion in all patients. Clearance was achieved within 6 weeks in 31 patients. After clearance, the patients were randomized to treatment and received oral VML 295 capsules 200 mg twice daily or placebo for 8 weeks. Twenty-five patients completed the study. The psoriasis area and severity index (PASI) was assessed before treatment, at clearance, and on days 15, 29, 43 and 5 7 of the treatment period. Biopsies were taken from the treated lesion before treatment, after clearance and at relapse, and cells were analysed by flow cytometry with markers for differentiation (keratin 10), inflammation (vimentin), and proliferation (DNA content). After 8 weeks of treatment, 14 of 15 VML 295-treated patients had relapsed and 11 of 16 placebo-treated patients had relapsed. A total of six patients were withdrawn. The time to relapse and the number of relapsed patients was not significantly different comparing the treatment groups. There was no significant difference in PASI scores between VML 295-treated patients and placebo-treated patients after 8 weeks of treatment. Flow cytometric parameters for differentiation, inflammation and proliferation did not show significant differences between VML 295- and placebo-treated patients. We conclude that oral VML 295 (LY-293111) is not effective in preventing relapse in psoriasis, either clinically or at the cellular level, and that in our group of patients VML 295 had no beneficial effect on overall psoriasis severity. Moreover, we conclude that further development of LTB4 modulating drugs for the treatment of psoriasis is not indicated.

Psoriasis and the arachidonic acid cascade

Arachidonic acid (5.8,11,14-eicosatetraenoic acid C20:4, n-6) is released from the cell membrane by the action of phospholipases on membrane phospholipids. Metabolites of arachidonic acid, which are generically termed eicosanoids, including prostaglandins, thromboxane, leukotrienes and hydroxyeicosatetraenoic acids, have been implicated as mediators or modulators of a number of physiological functions and pathological conditions in both normal and diseased human skin. Particularly, eicosanoids have been suspected to play an important role in the pathogenesis of psoriasis, because a number of phenomena observed in psoriasis can be explained, at least in part, by the action of eicosanoids. This review will focus on recent progress regarding the significance of eicosanoids in the pathogenesis of psoriasis. Recent developments in the molecular biology in the eicosanoids have renewed interest in the role of eicosanoids in psoriasis. New understanding of the etiology of psoriasis and advances in its treatment due to recent progress in eicosanoid biology will also be presented.

The role of interleukins 1, 6 and 8 as lymphocyte attractants in the photodermatoses polymorphic light eruption and chronic actinic dermatitis

The two photodermatoses, polymorphic light eruption (PLE) and chronic actinic dermatitis (CAD), are characterized by lymphocyte-rich inflammatory infiltrates, the pathogeneses of which are not fully understood. We have therefore studied suction blister fluid (SBF) samples from patients with these conditions before and at two time points after the induction of experimental lesions by means of a solar simulator; this SBF was then tested for the presence of selected cytokines known to induce peripheral blood lymphocyte (PBL) migration in vitro. A specific EL-4 NOB-1 bioassay was used to detect interleukin (IL)-1 activity, which has already been noted in normal skin and this was found in pre-irradiation control samples as well as 1-3 h and 24 h post-irradiation in both patient groups, but at levels not significantly different from those of controls. Use of a B9 cell proliferation assay showed no detectable IL-6-like activity pre-irradiation, but there was substantial activity in samples at both post-irradiation time points in both patient groups. Further, in other experiments, retained SBF samples were tested in an in vitro PBL migration assay in the presence and absence of neutralizing antibodies against IL-1 alpha, IL-1 beta, IL-6 and IL-8; considerable PBL attractant activity was noted in the pre-irradiation SBF from both patient groups; a finding consistent with previous reports of such activity in samples from normal skin, and at least in CAD patients, a proportion of this activity appeared to be due to IL-1, pre-incubation of SBF with neutralizing antibodies against IL-1 alpha and IL-1 beta reducing the effect significantly. Substantial PBL attractant activity was present also in the SBF from 1-3 h and 24 h post-irradiation samples in both patient groups and again, IL-1 neutralizing antibodies reduced this in the 1-3 h and 24 h CAD samples. In addition, neutralizing antibodies against IL-6 and IL-8 reduced the activity in the 24 h PLE samples significantly and although not fully conclusive in the case of IL-1, these data suggest that IL-6, IL-8 and possibly IL-1 may be involved in the induction of PBL infiltrates, and perhaps other events, in both PLE and CAD.

Pharmacokinetics and pharmacodynamics of the leukotriene B4 receptor antagonist CP-105,696 in man following single oral administration

AIMS

CP-105,696, (+)-1-(3S,4R)-[3-(4-phenylbenzyl)-4-hydroxy-chroman-7-yl] cyclopropane carboxylic acid is a potent, novel LTB4 receptor antagonist advanced to clinical trials to determine its efficacy in inflammatory diseases. The pharmacokinetics and pharmacodynamics of CP-105,696 were investigated in healthy male volunteers following oral administration of single doses of 5 to 640 mg.

METHODS

Forty-eight subjects participated in a randomized, double-blind, parallel group study. Plasma and urine concentrations of CP-105,696 were determined at intervals after drug administration. As an indication of LTB4 receptor antagonism following oral administration of CP-105,696, the inhibiton of LTB4-induced upregulation of the neutrophil cell surface complement receptor (CR3), CD11b/CD18, was monitored at 4 h following drug administration using an ex vivo whole blood flow cytometry assay.

RESULTS

Cmax and AUC(0, infinity) increased in a dose-related manner. Respective mean Cmax values were 0.54 to 30.41 microg ml(-1) following doses of 5 to 640 mg. Respective mean AUC(0, infinity) values were 1337 to 16819 microg ml(-1) h for the 40 to 640 mg dose groups. Plasma concentrations declined in a monoexponential manner, with terminal elimination half-lives ranging from 289 to 495 h. Group mean terminal elimination half-lives were dose-independent. Urinary excretion of unchanged drug accounted for < 1% of the administered dose. A linear relationship was observed between CP-105,696 plasma concentrations and inhibition of LTB4-mediated CD11b upregulation on human neutrophils in whole blood. CP-105,696 plasma concentrations of 5-6 microg ml(-1) were necessary to elicit a two-fold shift to the right of the LTB4 concentration response curve for CD11b upregulation.

CONCLUSIONS

These studies demonstrate pharmacologically significant LTB4-receptor antagonism following a single dose of CP-105,696 and pharmacokinetics consistent with once-daily dosing.

The regulation of CD11b integrin levels on human blood leukocytes and leukotriene B4-stimulated skin by a specific leukotriene B4 receptor antagonist (LY293111)

CD11b is part of the beta2-integrin Mac-1 and plays an important role in neutrophil adhesion. Leukotriene B4 (LTB4) is an active upregulator of neutrophil CD11b-expression, acts as a potent chemoattractant to neutrophils and is also known to upmodulate epidermal proliferation. We performed a placebo-controlled study on LY293111, an oral LTB4 receptor antagonist. Twenty healthy male volunteers were randomised over three treatment groups that received placebo, 48 mg, or 200 mg drug twice daily for 10 days. Before and after treatment, flow cytometrical CD11b assessment was performed on in vitro LTB4-stimulated peripheral blood neutrophils. Additionally, skin biopsies were taken at 24 and 72 h after epicutaneous LTB4 application, before and after treatment. The effects on skin were assessed immunohistochemically using various markers. All observed effects were dose related. CD11b upregulation on blood neutrophils was significantly suppressed in both treatment groups compared to placebo. In skin, a significant suppression of inflammation and hyperproliferation occurred. Pronounced inhibition was observed on neutrophil migration into the epidermis and the inflammatory infiltrate was decreased. A similar but weaker response was seen in the dermis. The number of cycling cells as well as suprabasal keratin-16 expression were decreased in both treatment groups. LY293111 proved to be a potent inhibitor of LTB4-induced cutaneous inflammation and hyperproliferation. The potent antiinflammatory effect in vivo and the fact that in the present study the compound showed no clinically significant side effects make it an interesting drug in the future treatment of inflammatory conditions predominated by neutrophils.

Antipsoriatic anthrones: aspects of oxygen radical formation, challenges and prospects

1. Antipsoriatic anthrones are among the most commonly used topical agents for the treatment of psoriasis. 2. These drugs generate reactive oxygen species during their auto-oxidation under physiological conditions. 3. Recent studies have indicated that activation of molecular oxygen by anthrones may play a critical role in their mechanism of action at the molecular level. 4. This article summarizes the evidence pointing toward the significance of oxygen activation and radical formation in the antipsoriatic action and induction of skin inflammation of anthrones. 5. Also, the role of oxygen radical formation in the development of novel anthrones devoid of inflammatory and staining properties is discussed.

Human keratinocytes lack the components to produce leukotriene B4

The cellular origin of leukotriene B4 (LTB4), a potent pro-inflammatory molecule present in psoriatic lesions, has yet to be determined. In the present study, cultured human keratinocytes were evaluated for their ability to produce LTB4. Keratinocytes stimulated under a variety of conditions did not produce detectable amounts of LTB4, as measured by enzyme immunoassay and liquid chromatographic techniques. Prostaglandin E2 and 15-hydroxyeicosatetraenoic acid were the only eicosanoids detected. The capacity of keratinocytes to synthesize 5-lipoxygenase (5-LO) products, or lack thereof, was further evaluated by preparing subcellular fractions and examining them for the presence of 5-LO activity and the proteins responsible for LTB4 production. Using Western blot analysis, we detected no bands that migrated with the 78-kDa 5-LO enzyme. Subcellular fractions were also examined for the presence of the 5-LO-activating protein (FLAP). This protein, which is essential to 5-LO activity, could not be detected in any keratinocyte preparation examined. Consistent with the absence of proteins, the mRNAs for 5-LO and FLAP were undetectable by reverse transcriptase polymerase chain reactions analysis. These results demonstrate that human keratinocytes lack the crucial proteins necessary for LTB4 production.

Potent antagonism of calmodulin activity in vitro, but lack of antiproliferative effects on keratinocytes by the novel leukotriene biosynthesis inhibitor MK-886

MK-886, a leukotriene biosynthesis inhibitor, which prevents the translocation and activation of 5-lipoxygenase, has been proposed as an effective drug for the treatment of inflammatory disorders, including psoriasis. In the present study, we investigated the effects of MK-886 on calmodulin as a potential target protein of anti-inflammatory drug activity, and on the proliferation of cultured human keratinocytes, a calmodulin-dependent cellular response with indicative value for antipsoriatic drug activity. Despite potent calmodulin-antagonistic activity in vitro, MK-886 failed to block cell proliferation in a human keratinocyte line, whereas trifluoperazine, a well characterized calmodulin antagonist with similar effects on calmodulin activity in our in vitro assays, inhibited cell proliferation in a dose-dependent manner. Further investigations on the mechanism of action revealed that, in contrast with trifluoperazine, calmodulin antagonism by MK-886 in vitro is likely to be mediated at the level of the allosteric calmodulin-recognition site of phosphodiesterase, rather than by binding to calmodulin itself. Therefore, our data do not conflict with the proposed role of calmodulin in the regulation of cell proliferation, but demonstrate that drug-induced antagonism of calmodulin, detected by inhibition of calmodulin-dependent enzymes in vitro, is not necessarily linked to antiproliferative activity in human keratinocytes.

Clinical activity of leukotriene inhibitors

Data from the emerging clinical trials with compounds such as zileuton, ICI 204,219, Bay X1005, MK571, MK679, and MK591 are demonstrating the importance of the leukotrienes as mediators of asthma and possibly other diseases such as rheumatoid arthritis, psoriasis, and inflammatory bowel disease. One of the major questions facing the asthma community is how much improvement in the FEV1 is needed to improve the quality of life of the asthmatic patient. Comparing the various approaches to asthma treatment, there is typically 15-20% improvement in the lung function with inhaled steroids. Leukotriene interventions apparently will improve lung function to similar levels as with inhaled steroids, and thus may offer an alternative to steroids. Like the steroids, zileuton appears to also reduce the inflammatory cell influx into the antigen-challenged site, which may have the long-term effect of reversing some of the tissue alterations that occur as a result of the inflammation seen with asthma. Importantly, the reported experience to date has shown that the leukotriene modulators do not have the same side-effects as the current therapies, and thus offer the hope that both safe and effective treatment may be derived from this approach. The clinical data reported do not yet define a preferred approach to the modulation of leukotriene pathology. As more studies are published in other diseases the broad spectrum use of these inhibitors will become known.

The design and synthesis of second generation leukotriene B4 (LTB4) receptor antagonists related to SC-41930

SC-41930, 7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)propoxy]-3,4- dihydro-8-propyl-2H-1-benzopyran-2-carboxylic acid, is a selective, orally active, LTB4 receptor antagonist currently in clinical trials for psoriasis and ulcerative colitis. Exhaustive SAR studies found a potential backup compound, SC-50605, which was 7-16 times more potent than SC-41930 in LTB4 receptor binding, chemotaxis and degranulation assays. SC-50605 also inhibited LTB4-induced intradermal chemotaxis in cavine skin at an oral dose of 0.10 mg/kg and displayed good activity in animal models of colitis and epidermal inflammation both orally and topically.

Designing therapeutically effective 5-lipoxygenase inhibitors

Metabolism of arachidonic acid by the enzyme 5-lipoxygenase leads to the formation of a group of biologically active lipids known as leukotrienes. Peptidoleukotrienes are powerful bronchoconstrictor agents while leukotriene B4 is a potent chemotactic agent for a variety of leukocytes. In view of these properties, leukotrienes have been proposed as important mediators in allergic and inflammatory disorders, and inhibitors of 5-lipoxygenase, by blocking leukotriene synthesis, have therapeutic potential in a range of diseases including arthritis and asthma. This review by Rodger McMillan and Ed Walker summarizes the biology of leukotrienes and the current knowledge of the mechanism of 5-lipoxygenase, providing a framework for consideration of the discovery, development and clinical status of drugs in the three major classes of 5-lipoxygenase inhibitors: 'redox' inhibitors, iron ligand inhibitors and 'non-redox' inhibitors.

Enhanced synthesis of cysteinyl leukotrienes in psoriasis

Cysteinyl leukotriene synthesis was investigated in patients with psoriasis. A non-invasive test requiring no stimulation was employed by measuring the major index metabolite of LTC4, which appears in urine. The presence of this metabolite, LTE4, was shown unequivocally by gas chromatography-mass spectrometry. Routinely LTE4 was quantitated by specific radio immunoassay after its isolation by reversed-phase high-performance liquid chromatography. Furthermore, in representative samples amounts of LTE4 obtained by radioimmunoassay were validated by gas chromatography-mass spectrometry. We demonstrate a significant (p less than 0.01) more than fourfold increase of urinary LTE4 in psoriasis compared to healthy volunteers. Urinary LTE4 was log normally distributed with geometric mean values (95% confidence intervals) of 11 (9-14) nmol LTE4/mol creatinine in healthy volunteers (n = 11) and 51 (28-95) nmol LTE4/mol creatinine in psoriasis (n = 9). The present study shows that cysteinyl leukotriene synthesis is enhanced in patients with psoriasis and that measurement of urinary LTE4 is a useful parameter to monitor its rate of synthesis.

5-lipoxygenase inhibitors and their anti-inflammatory activities

A wide variety of agents have been reported as 5-LO inhibitors. The majority of the series appear to be lipophilic reducing agents, including phenols, partially saturated aromatics, and compounds containing heteroatom-heteroatom bonds. Many of these are not selective 5-LO inhibitors, but often affect CO and other LOs as well. In vivo systemic activity for many of these has been, in general, disappointing, probably because of poor bioavailability caused by lipophilicity and metabolic instability (oxidation, and conjugation of phenolic compounds). However, topically a number of agents have shown promise for skin inflammation, with Syntex's lonapalene the most advanced of these. Most results published to date appear more disappointing in the allergy/asthma field. More excitingly, a few structural types are selective 5-LO inhibitors which have shown systemic activity in vivo and in the clinic. Abbott's zileuton (136) appears to be one of the leading compounds in this category, along with other hydroxamates such as BW-A4C (129) from Burroughs-Wellcome. Recent selective non-reducing agents such as Wyeth-Ayerst's Wy-50,295 (143) and the similar ICI compounds such as ICI 216800 (145) also hold promise. The enantiospecific effects of (106) and (145) are especially interesting for the design of new inhibitors. If compounds like these validate the hypothesis that inhibition of 5-LO will have a significant anti-inflammatory effect, a redoubling of effort throughout the industry to find second- and third-generation selective agents may be expected. Part of the difficulty in interpreting and comparing the 5-LO literature is the plethora of test methods and activity criteria. As pointed out in the introduction, inhibition of product release from cells, often stimulated with A23187, has commonly been used to demonstrate 5-LO inhibition. However, this type of assay cannot be assumed to be diagnostic for 5-LO inhibition. Only if specificity for 5-LO product generation and (ideally) activity in cell-free enzymes is also shown should mechanistic interpretations be made. Recently, a new class of compounds was found at Merck which inhibited LT biosynthesis without inhibiting 5-LO, but apparently by a novel, specific mechanism. L-655,240 (169) and L-663,536 (MK-886) (170) were both active in human ISN, with IC50 values in the low micromolar range. Both also orally inhibited GPB (< 1 mg/kg). MK-886 was effective in Ascaris-induced asthma in squirrel monkeys, in rat carrageenan pleurisy, in rat Arthus pleurisy, and (topically) in guinea-pig ear oedema induced by A23187.(ABSTRACT TRUNCATED AT 400 WORDS)

Leukotriene B4 and platelet-activating factor in human skin

Acute inflammatory reactions are characterized by leukocyte infiltration associated with increases in vascular permeability and in local blood flow. Leukocyte infiltration can be induced by chemotactic factors such as leukotriene B4 (LTB4) and paf-acether (formerly known as platelet-activating factor) that can be generated within inflammatory lesions. Vascular permeability and increase in blood flow are also affected by LTB4 and paf-acether, as well as by several other substances, including histamine and prostaglandins. Derived from arachidonic acid via the 5 lipo-oxygenase pathway, LTB4 is one of the most potent leukocyte chemotactic substances known. Intradermal injections of LTB4 induce dermal neutrophil infiltration in animal models and in humans. Topical application of LTB4 to human skin induces intraepidermal micro-abscesses containing numerous intact neutrophils. LTB4 has been found to be increased in psoriatic lesions, but its synthesis by epidermal cells remains undecided. Like other leukotrienes, LTB4 can stimulate DNA synthesis in cultured human epidermal keratinocytes. However, receptors for LTC4 but not for LTB4 have been found on human keratinocytes in culture. Paf-acether is an ether-linked phospholipid identified as 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine and is considered to be one of the most potent mediators of acute allergic and inflammatory reactions. For instance, intradermal injection of paf-acether induces inflammatory events such as neutrophil infiltration and increase in vascular permeability. Recent data suggest that cutaneous cells, such as fibroblasts and keratinocytes, are capable of producing paf and that paf is released during the development of allergic cutaneous reactions.(ABSTRACT TRUNCATED AT 250 WORDS)

CGS 22745: a selective orally active inhibitor of 5-lipoxygenase

CGS 22745, and aralkyl hydroxamic acid, inhibited 5-hydroxyeicosatetraenoic acid (5-HETE) and leukotriene B4 (LTB4) synthesis in guinea pig leukocytes (IC50 = 0.6 microM). The compound did not appreciably affect cyclooxygenase (ram seminal vesicles), 12-lipoxygenase and thromboxane synthase (human platelets) or 15-lipoxygenase (human neutrophils). CGS 22745 inhibited A23187-induced formation of LTB4 in blood (IC50's of 4.3, 0.56 and 3.2 microM for human, dog and rat, respectively). At 1 mg/kg i.v. in dogs, it caused 96% inhibition of A23187-stimulated LTB4 formation ex vivo after 5 min. Its effective biological half-life was greater than 160 min. In dogs at 3 and 10 mg/kg p.o., CGS 22745 inhibited ex vivo A23187-stimulated LTB4 formation at 3 hr by 48% and 97%, respectively. The inhibition persisted up to 6 hr (26% at 3 mg/kg; 49% at 10 mg/kg). CGS 22745 (3, 10 and 30 mg/kg p.o.) inhibited exudate formation, mononuclear cells and PMN accumulation in a dose-dependent manner during the late phase (48 and 72 hr) of carrageenan-induced pleurisy in the rat.