Zileuton

IC50: Zileuton inhibited 5-hydroxyeicosatetraenoic aicd synthesis in rat basophilic leukemia cell and polymorphonuclear leukocytes (IC50 = 0.5 and 0.3 μM), respectively [1].
5-Lipoxygenase pathway is to form leukotrienes, including leukotriene B4 (LTB4), 5-oxo-6E,8Z,11Z,14Z-eicosatetranoic acid and the cysteinyl leukotrienes (LTC4, LTD4 and LTE4) and activates all four leukotriene receptors, BLT1, BLT2, cysLT1 and cysLT2. Zileuton is the only commercially available inhibitor of the 5-Lipoxygenase pathway.
In vitro: Treatment of H9c2 cells with zileuton efficiently induced COX-2 expression and PGE2 biosynthesis in a time- and dose-dependent manner. Zileuton also exerted a profound protective effect against H2O2-induced oxidative stress, a mimic of reperfusion damage in vitro, and this protective effect was abolished by COX-2-selective inhibitor. Furthermore, zileuton-stimulated ERK1/2 and Akt phosphorylation was attenuated by rottlerin, indicating that PKCδ might act upstream of ERK1/2 and Akt. These results suggest that zileuton-induced COX-2 expression is sequentially mediated through PKCδ-dependent activation of ERK1/2 and Akt. Based on these findings, we propose that zileuton might provide a new therapeutic strategy for ischemia/reperfusion injury of the heart [2].
In vivo: To investigate the mechanism underlying zileuton's neuroprotection, SD rats underwent permanent middle cerebral artery occlusion (MCAO), then received treatment with zileuton or vehicle after the onset of ischemia. Zileuton was found to significantly reduce neurological deficit scores, cerebral infarct volume, MPO activity, and the lipid peroxidation levels. It also inhibited the expression of NF-kappaB and decreased the expression and activity of iNOS in rat brain. In addition, zileuton attenuated the release of TNF-alpha and IL-1beta in serum. These results suggested that zileuton reduces inflammatory reaction and brain damage in a rat model of permanent focal cerebral ischemia. The neuroprotective effect of zileuton in cerebral ischemia might be associated with the inhibition of inflammatory reaction [3].
Clinical trial:
Zileuton (trade name ZYFLO) is an orally active inhibitor of 5-lipoxygenase, and thus inhibits leukotrienes (LTB4, LTC4, LTD4, and LTE4) formation. Zileuton is used for the maintenance treatment of asthma. Zileuton was introduced in 1996 by Abbott Laboratories and is now marketed in two formulations by Cornerstone Therapeutics Inc. under the brand names ZYFLO and ZYFLO CR. Given the important role that leukotrienes play in airway inflammation, zileuton provides an additional therapeutic option in the management of chronic, persistent asthma, particularly those asthmatics with more severe disease. In addition, zileuton has shown promise in a number of other conditions, including upper airway inflammatory conditions, dermatological disease and chronic obstructive pulmonary disease. The development of new formulations, including a controlled release tablet formulation for b.i.d. dosing and an intravenous preparation for acute asthma exacerbations may enhance clinical utility and expand therapeutic indications.
Reference:
[1] Carter GW, Young PR, Albert DH, Bouska J, Dyer R, Bell RL, Summers JB, Brooks DW. 5-lipoxygenase inhibitory activity of zileuton. J Pharmacol Exp Ther. 1991;256(3):929-37.
[2] Hyun-Jeong Kwak, Kyoung-Mi Park, Hye-Eun Choi, Hyun-Joung Lim, Jin-Hee Park, Hyun-Young Park. The cardioprotective effects of zileuton, a 5-lipoxygenase inhibitor, are mediated by COX-2 via activation of PKCδ. Cellular Signalling 22 (2010) 80-87
[3] Tu XK, Yang WZ, Wang CH, Shi SS, Zhang YL, Chen CM, Yang YK, Jin CD, Wen S.Zileuton reduces inflammatory reaction and brain damage following permanent cerebral ischemia in rats. Inflammation. 2010;33(5):344-52.

5-Lipoxygenase inhibitor zileuton inhibits Ca(2+)-responses induced by glutoxim and molixan in macrophages.[Pubmed:27599517]

Dokl Biochem Biophys. 2016 Jul;469(1):302-4.

Using Fura-2AM microfluorimetry, we have shown for the first time that 5-lipoxygenase specific inhibitor antiasthmatic agent Zileuton significantly inhibits Ca(2+)-responses induced by glutoxim and molixan in macrophages. The results support 5-lipoxygenase involvement in the effect of glutoxim and molixan on intracellular Ca(2+) concentration in macrophages and indicate the inadvisability of a combined use of drugs glutoxim and molixan and antiasthmatic agent Zileuton.

5-LOX Inhibitor Zileuton Reduces Inflammatory Reaction and Ischemic Brain Damage Through the Activation of PI3K/Akt Signaling Pathway.[Pubmed:27380038]

Neurochem Res. 2016 Oct;41(10):2779-2787.

Previous studies from our laboratories showed that an anti-inflammatory drug, 5-lipoxygenase inhibitor Zileuton, attenuates ischemic brain damage via inhibiting inflammatory reaction. However, it was elusive whether Zileuton attenuates inflammatory reaction and ischemic brain damage through the modulation of PI3K/Akt signaling pathway. In the present study, we, for the first time, investigated whether PI3K/Akt pathway was involved in Zileuton's anti-inflammatory and neuroprotective properties against brain damage following experimental ischemic stroke. Adult male Sprague-Dawley rats underwent middle cerebral artery occlusion (MCAO), then received treatment with Zileuton or vehicle after the onset of ischemia. LY294002 was injected intracerebroventricularly to inhibit the activation of PI3K/Akt signaling pathway selectively. Neurological deficit scores, cerebral infarct volume, morphological characteristic and cerebral water content were assessed 24 h after cerebral ischemia. The enzymatic activity of myeloperoxidase (MPO) was measured 24 h after cerebral ischemia. Expression of p-Akt, t-Akt and COX-2 in ischemic brain were determined by western blot. NF-kappaB p65 immuno-positive cells in ischemic brain were detected 24 h after cerebral ischemia. The content of TNF-alpha in blood was examined by ELISA. 5-LOX inhibitor Zileuton significantly reduces neurological deficit scores, cerebral infarct volume, cerebral water content, ischemic neuronal injury and the enzymatic activity of MPO, all of which were abolished by LY294002 administration. Zileuton significantly up-regulates the expression of p-Akt, which was inhibited by LY294002 administration. Zileuton significantly down-regulates the over-expression of NF-kappaB p65 and COX-2, and attenuates the release of TNF-alpha, all of which were disminished by LY294002 administration. These results suggest that Zileuton attenuates ischemic brain damage by inhibiting inflammatory reaction through the activation of PI3K/Akt signaling pathway.

Inhibition of 5-lipoxygenase by zileuton in a rat model of myocardial infarction.[Pubmed:27849187]

Anatol J Cardiol. 2017 Apr;17(4):269-275.

OBJECTIVE: The goal of the present study was to investigate the effects of 5-lipoxygenase (5-LOX) inhibition, alone and with cyclooxygenase (COX) inhibitors, on inflammatory parameters and apoptosis in ischemia/reperfusion (I/R)-induced myocardial damage in rats. For this purpose, Zileuton, a selective and potent inhibitor of 5-LOX, resulting in suppression leukotriene production, was used. METHODS: Male Wistar rats (200-250 g; n=12 per group) were used in the study. I/R was performed by occluding the left coronary artery for 30 minutes and 2 hours of reperfusion of the heart. Experimental groups were I/R group, sham I/R group, Zileuton (5 mg/kg orally, twice daily)+I/R group, Zileuton+indomethacin (5 mg/kg intraperitoneally)+I/R group, Zileuton+ketorolac (10 mg/kg subcutaneously)+I/R group, and Zileuton+nimesulide (5 mg/kg subcutaneously)+I/R group. Following I/R, blood samples were collected to measure tumor necrosis factor alpha (TNF-alpha), and left ventricles were excised for evaluation of microscopic damage; malondialdehyde (MDA), glutathione, nuclear factor (NF)-kappaB assays; and evaluation of apoptosis. RESULTS: Left ventricle MDA in I/R group was higher compared to sham group; however, it did not show significant change with Zileuton. Although tissue injury in I/R group was less severe in all treatment groups, it was not statistically significant. NF-kappaB H-score and apoptotic index, which were higher in I/R group compared to sham I/R, were decreased with application of Zileuton (H-score: p<0.01; apoptotic index: p<0.001). Zileuton had no significant effect on increased serum TNF-alpha levels in I/R group. CONCLUSION: 5-LOX inhibition in rat myocardial infarction model attenuated increased left ventricle NF-kappaB expression and apoptosis and these actions were not modulated by COX inhibitors.

Comparison of oral montelukast with oral zileuton in acute asthma: A randomized, double-blind, placebo-controlled study.[Pubmed:27185992]

Lung India. 2016 May-Jun;33(3):281-6.

BACKGROUND: Leukotriene modifiers have an established role in the management of chronic asthma but their role in acute asthma is still under evaluation. OBJECTIVE: To study and compare the effects of oral montelukast with oral Zileuton in acute asthma. MATERIALS AND METHODS: This study included 120 asthmatics and was conducted from September 2012 to March 2014. Patients were randomized into three different groups to receive montelukast or Zileuton or placebo in addition to standard treatment for asthma exacerbation. Peak expiratory flow rate (PEFR) values, details of rescue medication and vital signs were recorded at 6 h, 12 h, 24 h, and 48 h of drug or placebo administration and at discharge. Additional recording was done in the morning (8-10 am) following admission. The primary endpoint was the mean PEFR of each group at these time points; the secondary end point being the need for rescue medications. RESULTS: The mean PEFR recordings of the three study groups - placebo, montelukast, and Zileuton - respectively, at various time points were as follows: at 6 h (223.25 +/- 90.40, 199.00 +/- 82.52, 233.75 +/- 84.05; P = 0.240); at 12 h (271.00 +/- 109.38, 251.50 +/- 101.44, 309.50 +/- 129.63; P = 0.048); at 24 h (288.25 +/- 114.26, 269.00 +/- 107.51, 324.50 +/- 127.88; P = 0.080); and at 48 h (295.00 +/- 114.80, 293.50 +/- 113.24, 344.75 +/- 119.91; P = 0.015); discharge (305.00 +/- 118.56, 305.25 +/- 119.51, 361.25 +/- 119.70; P = 0.010). The mean PEFR for the three study groups at 8-10 am on the morning following admission was 268.75 +/- 111.43, 252.50 +/- 99.99, 306.75 +/- 114.44; P = 0.047. Total rescue doses needed were 10, 1, and 0, respectively (P = 0.049). CONCLUSION: Zileuton is better than montelukast as an additional drug in acute asthma and results in significant improvement in lung function, and reduction in the need for rescue medications.

Mechanism-based inhibition of human liver microsomal cytochrome P450 1A2 by zileuton, a 5-lipoxygenase inhibitor.[Pubmed:14570767]

Drug Metab Dispos. 2003 Nov;31(11):1352-60.

Zileuton, a 5-lipoxygenase inhibitor, was evaluated as an inhibitor of cytochrome P450 activity in human liver microsomes. In the absence of preincubation, the racemate was found to be a weak inhibitor (IC50 > 100 microM) of phenacetin O-deethylation (POD) (CYP1A2), paclitaxel 6alpha-hydroxylation (CYP2C8), diclofenac 4'-hydroxylation (CYP2C9), (S)-mephenytoin 4'-hydroxylation (CYP2C19), bufuralol 1'-hydroxylation (CYP2D6), testosterone 6beta-hydroxylation (CYP3A4), chlorzoxazone 6-hydroxylation (CYP2E1), and bupropion hydroxylation (CYP2B6). When preincubated with NADPH-fortified human liver microsomes in the absence of substrate, Zileuton (racemate) was shown to inhibit POD. The effect was NADPH-, time-, and concentration-dependent, and was characterized by a kinact (maximal rate of enzyme inactivation) and apparent KI(inhibitor concentration that supports half the maximal rate of inactivation) of 0.035 min(-1) and 117 microM, respectively (kinact/KIratio of 0.0003 min-1 microM(-1)). Preincubation-dependent inhibition of POD activity was also observed with the individual (S)-(-)- and (R)-(+)-enantiomers of Zileuton [(S)-(-)-Zileuton; kinact, 0.037 min(-1), KI, 98.2 microM, kinact/KIratio, 0.0004 min(-1) microM(-1); (R)-(+)-Zileuton; kinact, 0.012 min(-1), KI, 66.6 microM, kinact/KIratio, 0.0002 min(-1) microM(-1)]. In addition, the inhibition of CYP1A2 was not reversed in the presence of reduced glutathione, catalase, and superoxide dismutase and was refractory to dialysis. Therefore, Zileuton was characterized as a mechanism-based inhibitor of human liver microsomal CYP1A2. Mechanism-based inhibition of CYP1A2 may explain why Zileuton decreases the oral clearance of antipyrine, propranolol, (R)-warfarin, and theophylline, at doses that have a minimal effect on the pharmacokinetics of (S)-warfarin, phenytoin, and terfenadine.

The 5-lipoxygenase inhibitory activity of zileuton in in vitro and in vivo models of antigen-induced airway anaphylaxis.[Pubmed:8081074]

Pulm Pharmacol. 1994 Apr;7(2):73-9.

Leukotrienes are biologically active lipid mediators capable of producing airway inflammation, hyperresponsiveness and bronchoconstriction. The first enzyme in the metabolic pathway of arachidonic acid leading to the leukotrienes is 5-lipoxygenase (5-LO). A selective and potent 5-LO inhibitor, Zileuton (N-1(1-benzo[b]thien-2-ylethyl)-N-hydroxyurea, A-64077) was evaluated in models of airway anaphylaxis, where leukotrienes are a major component. In vitro, Zileuton inhibited antigen-induced contractions of guinea-pig tracheal strips (GPTS) from actively sensitized animals with an IC50 of 6 microM. Similar results were obtained in human bronchial strips passively sensitized to IgE. Zileuton had little or no effect on contractions elicited by acetylcholine, prostaglandin D2 (PGD2), or the thromboxane agonist, U-44069. In anesthetized sensitized guinea-pigs pretreated with meclofenamic acid and mepyramine, a single aerosol exposure of antigen produced a substantial decrease in dynamic lung compliance (Cdyn). These profound changes in lung function were dose-dependently inhibited by orally administered Zileuton (ED50 = 12 mg/kg). These results demonstrate that Zileuton is a potent, selective inhibitor of in vitro contraction of GPTS and antigen-induced bronchoconstriction in vivo. These data also confirm the participation of 5-LO products in these models of airway anaphylaxis and suggest the usefulness of the guinea-pig for identifying and characterizing the pulmonary effects of 5-LO inhibitors.

Pre-clinical pharmacology of ICI D2138, a potent orally-active non-redox inhibitor of 5-lipoxygenase.[Pubmed:1334748]

Br J Pharmacol. 1992 Dec;107(4):1042-7.

1. This paper describes the pre-clinical pharmacology of ICI D2138, a potent orally-active non-redox inhibitor of 5-lipoxygenase which is undergoing clinical evaluation. 2. ICI D2138 potently inhibited leukotriene synthesis in murine peritoneal macrophages (IC50 = 3 nM) and human blood (IC50 = 20 nM). In human and dog blood, ICI D2138 did not inhibit thromboxane B2 synthesis at a concentration of 500 microM, thus the selectivity ratio (cyclo-oxygenase: 5-lipoxygenase) was greater than 20,000. In contrast, Zileuton (a 5-lipoxygenase inhibitor also undergoing clinical evaluation) exhibited a selectivity ratio of 15-100. 3. ICI D2138 potently and dose-dependently inhibited ex vivo leukotriene B4 (LTB4) synthesis by rat blood with ED50 values of 0.9, 4.0 and 80.0 mg kg-1 p.o. at 3, 10 and 20 h respectively after dosing. Similar activity was observed for inhibition of LTB4 production in a zymosan-inflamed rat air pouch model. Zileuton produced ED50 values of 5 and 20 mg kg-1 at 3 and 10 h respectively. 4. Oral administration of 1, 3 or 10 mg kg-1 ICI D2138 to dogs produced maximal inhibition of ex vivo LTB4 synthesis by blood for 5, 9 and 31 h respectively. A dose of 5 mg kg-1 p.o. of Zileuton caused maximal inhibition of LTB4 for 24 h. 5. Oral administration of 10 mg kg-1 ICI D2138 caused total inhibition of LTB4 production in zymosan-inflamed rabbit knee joint. 6. Topical administration of ICI D2138 to rabbit skin caused a dose-related inhibition of arachidonic acid-induced plasma extravasation with an ID30 of 1.08 nmol per site. Zileuton was approximately 40 times less potent.7. Oral anti-inflammatory activity was assessed in an arachidonic acid-induced mouse ear oedema model in animals treated with indomethacin to block pro-inflammatory prostanoids. ICI D2138, given orally, caused dose-dependent inhibition of oedema with an approximate ID50 of 1.8 mg kg'. Zileuton was approximately 10 times less potent.8. ICI D2138 caused a dose-dependent inhibition of antigen-induced broncho-constriction in guineapigs with an approximate ID50 of 0.1 mg kg-', i.v. Zileuton was approximately 10 times less potent.9. In view of the pharmacological profile described here, ICI D2138 has the potential to provide improved clinical efficacy compared to existing lipoxygenase inhibitors such as Zileuton.