Leukotriene A4 Hydrolase Inhibitors Research Articles

Effects of JNJ-40929837, a leukotriene A4 hydrolase inhibitor, in a bronchial allergen challenge model of asthma

Leukotriene B4 (LTB4) is a chemotactic mediator implicated in the pathogenesis of asthma. JNJ-40929837 is an oral inhibitor of LTA4 hydrolase, which catalyzes LTB4 production. We evaluated the effects of JNJ-40929837 in a human bronchial allergen challenge (BAC) model. In this double-blind, 3-period crossover study, 22 patients with mild, atopic asthma were randomized to one of three treatments per period: 100 mg/day JNJ-40929837 for 6 days followed by 50 mg/day on day 7; 10 mg/day montelukast for 6 days; and matched placebo. The BAC was performed on day 6 of each treatment period. Primary outcome was BAC-induced late asthmatic response (LAR) measured by maximal percent reduction in forced expiratory volume (FEV1) in one second. Secondary outcomes included early asthmatic response (EAR) by maximal percent reduction in FEV1, EAR and LAR evaluated by area under the FEV1/time curve (AUC0-2, AUC3-10, respectively), change in baseline FEV1 after 5-day treatment, safety, and correlation of JNJ-40929837 to the divalent cation ionophore A23187-stimulated whole blood LTB4 levels and sputum basal LTB4 levels. No significant differences were observed in the primary or secondary FEV1 endpoints with JNJ-40929837 versus placebo. Compared with placebo (n = 17, LS mean = 27.7), there was no significant attenuation of the maximal percent reduction in the LAR FEV1 with JNJ-40929837 (n = 16, LS mean = 28.6, P = 0.63) but montelukast (n = 17, LS mean = 22.6, P = 0.01) significantly attenuated the LAR. JNJ-40929837 substantially inhibited LTB4 production in whole blood, decreased sputum LTB4 levels and was well-tolerated. The number of adverse events leading to study withdrawal was the same in JNJ-40929837 and placebo groups. In conclusion, JNJ-40929837 demonstrated target engagement in blood and sputum. No significant impact in response to allergen inhalation was observed with JNJ-40929837 versus placebo. RegistrationThis study is registered at ClinicalTrials.gov: NCT01241422.

Testicular distribution and toxicity of a novel LTA4H inhibitor in rats

JNJ 40929837, a novel leukotriene A4 hydrolase inhibitor in drug development, was reported to induce testicular toxicity in rats. The mechanism of toxicity was considered to be rodent specific and not relevant to humans. To further investigate this finding in rats, the distribution and toxicokinetics of JNJ 40929837 and its two metabolites, M1 and M2, were investigated. A quantitative whole body autoradiography study showed preferential distribution and retention of JNJ 40929837-derived radioactivity in the testes consistent with the observed site of toxicity. Subsequent studies with unlabeled JNJ 40929837 showed different metabolite profiles between the plasma and testes. Following a single oral 50mg/kg dose of JNJ 40929837, M2 was the primary metabolite in plasma whereas M1 was the primary metabolite in testes. The exposure of M1 was 386-fold higher in the testes compared to plasma whereas M2 had limited exposure in testes. Furthermore, the Tmax of M1 was 48h in testes suggesting a large accumulation potential of this metabolite in testes compared to plasma. Following six months of repeated daily oral dosing, M1 accumulated approximately five-fold in the testes whereas the parent did not accumulate. These results indicate that the toxicokinetic profiles of JNJ 40929837 and its two metabolites in testes are markedly different compared to plasma and support the importance of understanding the toxicokinetic profiles of compounds and their metabolites in organs/tissues where toxicity is observed.

In Silico Identification of Novel Leukotriene A4 Hydrolase Inhibitors as Potential Anti-Inflammatory Agents

Leukotriene A4 Hydrolase (LTA4H) is considered an indispensable enzyme in the cascade of producing inflammatory mediators. Overproducing inflammatory mediators will end with inflammatory diseases that are disturbing to the patient. Selective inhibition of this enzyme will alleviate the symptoms of inflammation and promote the patient’s lifestyle. Within this study, a solitary 3D structure-based pharmacophore has been constructed for this enzyme that contains a distinguished “Zinc Binding Feature” that selectively extracts candidate inhibitors which contain functional groups that coordinate with zinc atom, a property that increases selectivity and affinity for this enzyme. The selection process for potential inhibitors was performed by screening commercially available Aldrich CPR over the generated pharmacophore combined with advanced docking procedures. Twelve compounds were introduced to be potential inhibitors containing different functional groups and all are possessing drug likeness

A sensitive fluorigenic substrate for selective in vitro and in vivo assay of leukotriene A4 hydrolase activity

Leukotriene A4 hydrolase (LTA4H) is a bifunctional zinc-dependent metalloprotease bearing both an epoxide hydrolase, producing the pro-inflammatory LTB4 leukotriene, and an aminopeptidase activity, whose physiological relevance has long been ignored. Distinct substrates are commonly used for each activity, although none is completely satisfactory; LTA4, substrate for the hydrolase activity, is unstable and inactivates the enzyme, whereas aminoacids β-naphthylamide and para-nitroanilide, used as aminopeptidase substrates, are poor and nonselective. Based on the three-dimensional structure of LTA4H, we describe a new, specific, and high-affinity fluorigenic substrate, PL553 [l-(4-benzoyl)phenylalanyl-β-naphthylamide], with both in vitro and in vivo applications. PL553 possesses a catalytic efficiency (kcat/Km) of 3.8±0.5×104M−1s−1 using human recombinant LTA4H and a limit of detection and quantification of less than 1 to 2ng. The PL553 assay was validated by measuring the inhibitory potency of known LTA4H inhibitors and used to characterize new specific amino-phosphinic inhibitors. The LTA4H inhibition measured with PL553 in mouse tissues, after intravenous administration of inhibitors, was also correlated with a reduction in LTB4 levels. This authenticates the assay as the first allowing the easy measurement of endogenous LTA4H activity and in vitro specific screening of new LTA4H inhibitors.

Development of Predictive Quantitative Structure–Activity Relationship Model and Its Application in the Discovery of Human Leukotriene A4 Hydrolase Inhibitors

Human LTA4H catalyzes the conversion of LTA4 to LTB4 and plays a key role in innate immune responses. Inhibition of this enzyme can be a valid method in the treatment of inflammatory response exhibited through LTB4. The quantitative structure-activity relationship (QSAR) models were developed using genetic function approximation and validated. A training set of 26 diverse compounds and their molecular descriptors were used to develop highly correlating QSAR models. A six-descriptor model explaining the biological activity of the training and test sets with correlation values of 0.846 and 0.502, respectively, was selected as the best model and used in a database screening of drug-like Maybridge database followed by molecular docking. Based on the predicted potent inhibitory activities, expected binding mode and molecular interactions at the active site of hLTA4H final leads were selected as to be utilized in designing future hLTA4H inhibitors.

Identification of benzofuran central cores for the inhibition of leukotriene A4 hydrolase

Leukotrienes (LT’s) are known to play a physiological role in inflammatory immune response. Leukotriene A4 hydrolase (LTA4H) is a cystolic enzyme that stereospecifically catalyzes the transformation of LTA4 to LTB4. LTB4 is a known pro-inflammatory mediator. This paper describes the identification and synthesis of substituted benzofurans as LTH4H inhibitors. The benzofuran series demonstrated reduced mouse and human whole blood LTB4 levels in vitro and led to the identification one analog for advanced profiling. Benzofuran 28 showed dose responsive target engagement and provides a useful tool to explore a LTA4H inhibitor for the treatment of inflammatory diseases, such as asthma and inflammatory bowel disease (IBD).

Efferent Duct Toxicity with Secondary Testicular Changes in Rats Following Administration of a Novel Leukotriene A4 Hydrolase Inhibitor

The efferent ducts represent an important site of toxicity in the male reproductive tract but are not routinely examined in toxicity studies. This article describes a primary efferent duct toxicity that resulted in secondary testicular changes in rats. Male rats were administered LTI-1, a leukotriene A₄ hydrolase inhibitor, at doses up to 250 mg/kg/d for 3 month or 150 mg/kg/d for 6 month. At the highest dose levels, testicular changes were predominantly unilateral and characterized by diffuse dilation or atrophy of the seminiferous tubules. These testicular changes correlated with granulomatous inflammation in the corresponding efferent ducts, suggesting that the mechanism for the testicular changes involves obstruction and impaired fluid reabsorption in the efferent ducts. Subsequent buildup in fluid volume and back-pressure upstream of the blockage cause dilation of the seminiferous tubules, which, in its late stages, progress to tubular atrophy. There are important differences in efferent duct anatomy between rats and larger mammals, including humans, such that the latter are less susceptible to testicular injury by this mechanism. Because of the limited relevance of this rat-specific finding to humans, it is important to distinguish testicular changes secondary to efferent duct toxicity from primary drug-induced testicular toxicity.

Diastereoselective ruthenium porphyrin-catalyzed tandem nitrone formation/1,3-dipolar cycloaddition for isoxazolidines. Synthesis, in silico docking study and in vitro biological activities

Ruthenium porphyrin catalyzes tandem nitrone formation/1,3-dipolar cycloaddition of diazo compounds, nitrosoarenes and alkenes to form isoxazolidines in good to high yields and with excellent regio-, chemo- and diastereo-selectivities. A broad substrate scope of alkenes is applicable to this protocol and various functional groups are compatible with the reaction conditions. In silico analysis and in vitro biological experiments revealed that some of the new isoxazolidines synthesized in this work could act as leukotriene A4 hydrolase inhibitors.

Leukotriene A4 hydrolase: an anti-inflammatory role for a proinflammatory enzyme

Neutrophils represent a prominent source of pathology in an array of persistent pulmonary diseases. A recent article published in Science describes a novel anti-inflammatory pathway that degrades the neutrophil chemoattractant...

Pharmacophore-based virtual screening and Bayesian model for the identification of potential human leukotriene A4 hydrolase inhibitors

Leukotriene A4 hydrolase (LTA4H), an enzyme involved in the conversion of LTA4 to LTB4, is an emerging and important anti-inflammatory target. This study demonstrates the development of quantitative pharmacophore hypothesis and Bayesian model and their applications in identification of potential human LTA4H (hLTA4H) inhibitors. The best hypothesis with a high correlation coefficient value of 0.951 was validated using different methods including a test set containing 136 compounds. It was further used as a three-dimensional query in database searching to retrieve virtual leads for hLTA4H inhibition. Molecular docking study was employed to identify the compounds that bind the active site with high affinity. Developed Bayesian model suggested molecular features favoring and not favoring the inhibition of hLTA4H.

English

Leukotriene A4 hydrolase (LTA4H) is a hydrolase with a bifunctional zinc enzyme, which plays a role in inflammation. LTA4H may also play an important role in carcinogenesis, especially chronic inflammation-associated carcinogenesis. In this study, chemical feature based pharmacophore models based on 22 currently available LTA4H inhibitors have been developed with the aid of HipHop and HypoRefine modules within Catalyst program package. 3D pharmacophore model developed was, characterized by distinct chemical features such as Hydrogen-bond acceptor (HA), Hydrogen-bond donor (HD), Hydrophobic aliphatic (HPAli), Hydrophobic aromatic (HPAr) that are found to be responsible for the activity of the LTA4H inhibitors. The correlation coefficient, root mean square deviation and cost difference were 0.92, 1.0867 and 53.62 respectively, suggesting that a highly predictive pharmacophore model was successfully obtained. The results of our study provide a valuable tool in designing new leads with desired biological activity for virtual screening.

Leukotriene A4Hydrolase Inhibition Attenuates Allergic Airway Inflammation and Hyperresponsiveness

Allergic asthma is characterized by reversible airway obstruction, lung inflammation, and airway hyperresponsiveness (AHR). Previous studies using leukotriene B(4) (LTB(4)) receptor 1-deficient mice and adoptive transfer experiments have suggested that LTB(4) plays a role in lung inflammation and AHR. In this study, we used a leukotriene A(4) hydrolase (LTA(4)H) inhibitor as a pharmacological tool to directly examine the role of LTB(4) in a mast cell-dependent murine model of allergic airway inflammation. We used the forced oscillation technique to test the effects of an LTA(4)H inhibitor dosed during the challenge phase on AHR. Lung tissue and lavage were collected for analysis. Treatment with an LTA(4)H inhibitor improved multiple parameters encompassing AHR and lung function. Significant decreases in inflammatory leukocytes, cytokines, and mucin were observed in the lung lumen. Serum levels of antigen-specific IgE and IgG1 were also decreased. Labeled antigen uptake by lung dendritic cells and subsequent trafficking to draining lymph nodes and the lung were decreased on LTA(4)H inhibitor treatment. Provocatively, inhibition of LTA(4)H increased lipoxin A(4) levels in lung lavage fluid. These data suggest that LTB(4) plays a key role in driving lung inflammation and AHR. Mechanistically, we provide evidence that inhibition of LTA(4)H, affects recruitment of both CD4(+) and CD8(+) T cells, as well as trafficking of dendritic cells to draining lymph nodes, and may beneficially modulate other pro- and antiinflammatory eicosanoids in the lung. Inhibition of LTA(4)H is thus a potential therapeutic strategy that could modulate key aspects of asthma.

Development of a Scalable Synthetic Process for DG-051B, A First-in-Class Inhibitior of LTA4H

DG-051B is a first-in-class small molecule inhibitor of leukotriene A4 hydrolase (LTA4H), currently in Phase II clinical development for the prevention of heart attack. Process optimization led from a linear seven-step synthetic procedure to a convergent four-step manufacturing sequence that has been used to manufacture at 100-kg scale. The entire process can be telescoped due to high conversion reactions, low impurity levels, efficient separations, and a very effective final purification. Two key aspects of the process are: (a) bypassing the isolation of a reactive electrophile by using its aqueous-washed reaction mixture directly into a coupling reaction with a phenoxide nucleophile and (b) modulating the properties of the final product solutions for optimal extraction, purification, and crystallization.

Discovery of Leukotriene A4 Hydrolase Inhibitors Using Metabolomics Biased Fragment Crystallography

We describe a novel fragment library termed fragments of life (FOL) for structure-based drug discovery. The FOL library includes natural small molecules of life, derivatives thereof, and biaryl protein architecture mimetics. The choice of fragments facilitates the interrogation of protein active sites, allosteric binding sites, and protein−protein interaction surfaces for fragment binding. We screened the FOL library against leukotriene A4 hydrolase (LTA4H) by X-ray crystallography. A diverse set of fragments including derivatives of resveratrol, nicotinamide, and indole were identified as efficient ligands for LTA4H. These fragments were elaborated in a small number of synthetic cycles into potent inhibitors of LTA4H representing multiple novel chemotypes for modulating leukotriene biosynthesis. Analysis of the fragment-bound structures also showed that the fragments comprehensively recapitulated key chemical features and binding modes of several reported LTA4H inhibitors.

New Roles for LTA4 Hydrolase, LTB4 and BLT1 in Multiple Sclerosis and Experimental Allergic Encephalomyelitis (48.9)

Abstract 5-lipoxygenase (5-LO), leukotriene A4 hydrolase (LTA4h), leukotriene B4 (LTB4) and its high affinity receptor BLT1 are known drivers of allergy, adaptive immunity and vascular inflammation, but have unknown roles in human multiple sclerosis (MS) and experimental allergic encephalomyelitis (EAE). We show that LTA4h and BLT1 are markers of inflammatory perivascular cuffs and actively demyelinating plaques in relapsing-remitting and progressive human MS, as well as spinal cord inflammatory foci in rodent EAE. Encephalitogenic murine CD3+ T cells experienced with proteolipid protein peptide antigen (PLP139-151) migrate to LTB4 and express functional BLT1. Peripheral blood immune cell LTB4 synthetic capacity is markedly primed prior to/during onset of rat and mouse EAE and mouse spleen 5-LO/LTA4h/BLT1 mRNAs are dynamically regulated during the immune response after T cell adoptive transfer. Potent, selective LTA4h inhibitors decrease clinical score and cumulative disease burden in rat antigen-induced and murine adoptive T cell transfer EAE. LTA4h inhibitors are also synergistic in suppressing rat EAE when combined with agents having an orthogonal mode of immunomodulatory action, such as the PDE-IV inhibitor mesopram. The results define new roles for the 5-LO / LTA4h / LTB4 / BLT1 pathway in autoimmunity and disease progression in EAE. Human MS may be a therapeutic target for inhibitors of LTB4 synthesis.

Current status of leukotriene A4 hydrolase inhibitors

Background: Leukotriene A4 hydrolase (LTA4H) is a ubiquitously distributed 69-kDa zinc-containing cytosolic enzyme with both hydrolase and aminopeptidase activity. As a hydrolase, LTA4H stereospecifically catalyzes the transformation of the unstable epoxide LTA4 to the diol leukotriene B4 (LTB4), a potent chemoattractant and activator of neutrophils and a chemoattractant of eosinophils, macrophages, mast cells, T cells, dendritic cells, smooth muscle cells and keratinocytes. Inhibiting the formation of LTB4 is expected to be beneficial in the treatment of inflammatory diseases such as inflammatory bowel disease, asthma and atherosclerosis. Objective: The focus of this review will be on patent applications/patents containing LTA4H inhibitors that were published between 1996 and March 2008 from four different companies. The documents reviewed are presented in a tabular manner. Method: The first part of this review focuses on the primary literature supporting LTA4H as a potential target. The second part covers the patent literature organized by applicant identified during the prescribed period. Conclusion: Activity towards identifying small molecule inhibitors of LTA4H has escalated in the last few years in line with important scientific and clinical developments involving the leukotriene pathway. One inhibitor from deCODE, DG-051, is reported to be in clinical trials for myocardial infarction and future reports of clinical efficacy will undoubtedly stimulate further work in the field by others.

Characterization of the aminopeptidase activity of epidermal leukotriene A4 hydrolase against the opioid dynorphin fragment 1-7.

Leukotriene A4 hydrolase is a bifunctional cytosolic enzyme, which both hydrolyses leukotriene A4 (LTA4) into leukotriene B4 (LTB4) and exerts aminopeptidase activity against opioid peptides. In the present study we have investigated whether the peptides angiotensin I and II, bradykinin, kallidine, histamine, dynorphin fragment 1-7 and substance P can act as substrates for epidermal and neutrophil LTA4 hydrolase. Among the tested substrates, dynorphin fragment 1-7 was found to be the best substrate for the enzyme. The aminopeptidase activity of epidermal and neutrophil LTA4 hydrolase against dynorphin fragment 1-7 was further characterized. The enzyme was purified from human epidermis and human neutrophils by anion exchange chromatography (Q-Sepharose) and affinity chromatography on a column with the LTA4 hydrolase inhibitor bestatin coupled to AH-Sepharose. The incubation of the dynorphin fragment 1-7 with LTA4 hydrolase resulted in the formation of tyrosine. The presence of the N-terminal amino acid tyrosine is essential for the interaction of opioids with their receptors, and this finding indicates that the LTA4 hydrolase can inactivate dynorphin fragment 1-7. After the two purification steps no other aminopeptidases acting at the N-terminal tyrosine of dynorphin fragment 1-7 was present in the preparation. This was demonstrated by the abolishment of the degradation at the N-terminal end of dynorphin fragment 1-7 when preincubating the enzyme preparation with LTA4 before the incubation with the dynorphin fragment 1-7. The abolishment of the aminopeptidase activity shows that activation of the hydrolase part of the enzyme, with conversion of LTA4 into the potent proinflammatory compound LTB4, results in an inhibition of the aminopeptidase activity of the enzyme. As a result, the catabolism of dynorphin fragment 1-7 and probably of other opioid peptides is inhibited, resulting in sustained biological effects of these opioids. This phenomenon may be important for the maintenance of inflammation in skin conditions, such as psoriasis and atopic dermatitis, in which LTB4 is formed.

Leukotriene A4 hydrolase as a target for cancer prevention and therapy.

Leukotriene A4 hydrolase (LTA4H) is a bifunctional zinc enzyme with the activities of epoxide hydrolase and aminopeptidase. As an epoxide hydrolase, LTA4H catalyzes the hydrolysis of the epoxide LTA4 to the diol, leukotriene B4 (LTB4), which mainly functions as a chemoattractant and an activator of inflammatory cells. As an aminopeptidase, LTA4H may process peptides related to inflammation and host defense. In a chronic inflammation-associated animal model of esophageal adenocarcinoma, we have shown that LTA4H was overexpressed in tumor as compared to normal tissues. Bestatin, an LTA4H inhibitor, suppresses tumorigenesis in this animal model. Since LTA4H has long been regarded as an anti-inflammatory target, we propose LTA4H as a target for prevention and therapy of cancers, especially those associated with chronic inflammation. Here we review the gene structure, expression, regulation and functions of LTA4H, as well as its involvement in carcinogenesis. We believe LTA4H/LTB4 may play an important role in chronic inflammation associated carcinogenesis by at least two mechanisms: a) the inflammation-augmenting effect on inflammatory cells through positive feedback mediated by its receptors and downstream signaling molecules; and b) the autocrine growth-stimulatory effect of LTB4 produced by epithelial cells, and the paracrine growth-stimulatory effect of LTB4 produced by inflammatory cells, on precancerous and cancer cells. Based on our present knowledge, inhibitors of LTA4H or antagonists of LTB4 receptors may be used alone or in combination with other agents (e.g., cyclooxygenase 2 inhibitors) in cancer prevention and treatment trials to test their effectiveness.

Leukotriene A4 hydrolase in rat and human esophageal adenocarcinomas and inhibitory effects of bestatin.

Esophageal adenocarcinoma (EAC) is increasing at the most rapid rate of any cancer in the United States. An esophagogastroduodenal anastomosis (EGDA) surgical model in rats mimics human gastroesophageal reflux and results in EAC. Leukotriene A4 hydrolase (LTA4H), a protein overexpressed in EAC in this model, is a rate-limiting enzyme in the biosynthesis of leukotriene B4 (LTB4), a potent inflammatory mediator. We used this model and human EAC and non-tumor tissues to elucidate the expression pattern of LTA4H and to evaluate it as a target for chemoprevention. LTA4H expression was examined by western blotting and immunohistochemistry. The functional role of LTA4H in carcinogenesis was investigated by use of an LTA4H inhibitor, bestatin, in the rat EGDA model. All statistical tests were two-sided. LTA4H was overexpressed in all 10 rat EACs examined, compared with its level in normal rat tissue; it was also overexpressed in four of six human EAC tumor samples, compared with its level in adjacent non-tumor tissue. In tissue sections from 20 EGDA rats and 92 patients (86 with EAC, one with dysplasia, and five with columnar-lined esophagus), LTA4H was expressed in infiltrating inflammatory cells and overexpressed in the columnar cells of preinvasive lesions and cancers, especially in well-differentiated EACs, as compared with the basal cells of the normal esophageal squamous epithelium. Bestatin statistically significantly inhibited LTB4 biosynthesis in the esophageal tissues of EGDA rats (without bestatin = 8.28 ng/mg of protein; with bestatin = 4.68 ng/mg of protein; difference = 3.60, 95% CI = 1.59 to 5.61; P = .002) and reduced the incidence of EAC in the EGDA rats from 57.7% (15 of 26 rats) to 26.1% (6 of 23 rats) (difference = 31.6%, 95% CI = 0.3% to 56.2%; P = .042). LTA4H overexpression appears to be an early event in esophageal adenocarcinogenesis and is a potential target for the chemoprevention of EAC.

Protein structure similarity as guiding principle for combinatorial library design.

Proteins are modularly built from a limited set of approximately 1000 structural domains. The evolutionary relationship within a domain family suggests that the knowledge about a common fold structure can be exploited for the design of small molecule libraries in the development of inhibitors and ligands. This principle has been used for the synthesis of inhibitors for kinases sharing the same fold. It can also be applied for proteins which share the same fold architecture yet belong to different functional classes. Bestatin--originally known as an aminopeptidase inhibitor--was employed as guiding structure for the development of leukotriene A4 hydrolase inhibitors. A combinatorial approach helped to identify inhibitors for sulfotransferases which share structural similarity with nucleotide kinases using a kinase inhibitor core structure as guiding principle.