leukotriene receptor/LTD4

Zafirlukast possesses an N-methylindole moiety with a 3-alkyl substituent on the indole ring, which makes it similar to 3-methylindole. Zafirlukast readily forms a GSH adduct with a molecular mass of 880 Da upon incubation with horseradish peroxidase (10% conversion in 60 min). CYP3A4 is inactivated in a concentration-, time-, and NADP(H)-dependent manner by zafirlukast. In one report, zafirlukast was shown to inhibit CYP3A enzyme activity in vitro (nonpreincubation inhibition) with a Ki of 2 μM; however, higher values have been published, and our KI for the inactivation process is 13.4 μM. The high plasma protein binding of zafirlukast (>99%) would reduce the concentration of free drug. A highly electrophilic α,β-unsaturated iminium species is produced by two consecutive one-electron oxidations of zafirlukast, which then spontaneously reacts with GSH to produce the observed adduct.[1]

Zafirlukast is a potent and selective antagonist of the cysteinyl leukotriene receptor that is primarily used in the prevention of bronchial asthma. When administered orally at a dose of 80 mg/kg, zafirlukast significantly lowers tissue levels of myeloperoxidase, reduced glutathione, and catalase while having no effect on these parameters when administered rectal route.[2]

Zafirlukast is a leukotriene antagonist indicated for the treatment of mild to moderate asthma, but the drug has been associated with occasional idiosyncratic hepatotoxicity. Structurally, zafirlukast is similar to 3-methylindole because it contains an N-methylindole moiety that has a 3-alkyl substituent on the indole ring. The results presented here describe the metabolic activation of zafirlukast via a similar mechanism to that described for 3-methylindole. NADP(H)-dependent biotransformation of zafirlukast by hepatic microsomes from rats and humans afforded a reactive metabolite, which was detected as its GSH adduct. Mass spectrometry and NMR data indicated that the GSH adduct was formed by the addition of GSH to the methylene carbon between the indole- and methoxy-substituted phenyl rings of zafirlukast. The formation of this reactive metabolite in human liver microsomes was shown to be exclusively catalyzed by CYP3A enzymes. Evidence for in vivo metabolic activation of zafirlukast was obtained when the same GSH adduct was detected in bile of rats given an iv or oral dose of the drug. On the basis of results with model peroxidases and of the structures of product alcohols from incubations containing H2(18)O, it appeared that zafirlukast underwent dehydrogenation by two sequential one-electron oxidations. In addition, zafirlukast proved to be a mechanism-based inhibitor of CYP3A4 activity in human liver microsomes and in microsomes containing cDNA-expressed CYP3A4. The enzyme inhibitory property of zafirlukast was selective for this enzyme among all of the P450 enzymes that were tested in human liver microsomes. The inactivation was characterized by a K(I) of 13.4 microM and k(inact) of 0.026 min(-1). In summary, zafirlukast dehydrogenation to an electrophilic alpha,beta-unsaturated iminium intermediate may be associated with idiosyncratic hepatotoxicity and/or cause drug-drug interactions through inactivation of CYP3A4[1].

1. We investigated the inhibitory effects of the cysteinyl leukotriene (CysLT1) receptor antagonists, pranlukast and zafirlukast, on 35SO4 labelled mucus output, in vitro, in guinea-pig trachea, induced by leukotriene D4 (LTD4) or by antigen challenge of sensitized animals. Agonists and antagonists were administered mucosally, except in selected comparative experiments where drugs were administered both mucosally and serosally to assess the influence of the epithelium on evoked-secretion. 2. LTD4 increased 35SO4 output in a concentration-related manner with a maximal increase of 23 fold above controls at 100 microM and an approximate EC50 of 2 microM. Combined mucosal and serosal addition of LTD4 did not significantly affect the secretory response compared with mucosal addition alone. Neither LTC4 nor LTE4 (10 microM each) affected 35SO4 output. Pranlukast or zafirlukast significantly inhibited 10 microM LTD4-evoked 35SO4 output in a concentration-dependent fashion, with maximal inhibitions of 83% at 10 microM pranlukast and 78% at 10 microM zafirlukast, and IC50 values of 0.3 microM for pranlukast and 0.6 microM for zafirlukast. Combined mucosal and serosal administration of the antagonists (5 microM each) gave degrees of inhibition of mucosal-serosal 10 microM LTD4-evoked 35SO4 output similar to those of the drugs given mucosally. Pranlukast (0.5 microM) caused a parallel rightward shift of the LTD4 concentration-response curve with a pKB of 7. Pranlukast did not inhibit ATP-induced 35SO4 output. 3. Ovalbumin (10-500 microg ml(-1) challenge of tracheae from guinea-pigs actively sensitized with ovalbumin caused a concentration-related increase in 35SO4 output with a maximal increase of 20 fold above vehicle controls at 200 microg ml(-1). The combination of the antihistamines pyrilamine and cimetidine (0.1 mM each) did not inhibit ovalbumin-induced 35SO4 output in sensitized guinea-pigs. Neither mucosal (10 microM or 100 microM) nor mucosal-serosal (100 microM) histamine had any significant effect on 35SO4 output. 4. Pranlukast or zafirlukast (5 microM each) significantly suppressed ovalbumin-induced secretion in tracheae from sensitized guinea-pigs by 70% and 65%, respectively. 5 We conclude that LTD4 or ovalbumin challenge of sensitized animals provokes mucus secretion from guinea-pig trachea in vitro and this effect is inhibited by the CysLT1 receptor antagonists pranlukast and zafirlukast. These antagonists may be beneficial in the treatment of allergic airway diseases in which mucus hypersecretion is a clinical symptom, for example asthma and allergic rhinitis[3].

Mice: It uses A/J female mice that are 5–6 weeks old. The first of two intraperitoneal injections (i.p.) of vinyl carbamate (16 mg/kg each, spaced seven days apart) is given to the mice when they are seven to eight weeks old. In their diet, the mice are given leukotriene inhibitors two weeks following their second dosage of vinyl carbamate. The meal should contain the prescribed mg/kg concentrations of zafirlukast (270 or 540 mg/kg), zileuton (600 or 1200 mg/kg), and MK-886 (30 mg/kg). After being exposed to leukotriene inhibitors for the first six weeks, mice are weighed every week. They are weighed every two to four weeks until they are sacrificed after that. Before being embedded in paraffin for histology, the lungs are removed, fixed for one night in formalin, moved to 70% alcohol, and checked for tumors.

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The present work was conducted to assess the possible protective effects of zafirlukast against the toxic damage induced by acetic acid in rat colon. Zafirlukast is a potent and selective cysteinyl leukotriene receptor antagonist which is used mainly in the prophylaxis of bronchial asthma. Two doses of zafirlukast were used (40 and 80 mg/kg) dissolved in gum acacia and given either orally or rectally (0.5 ml/kg). Several parameters including, macroscopic score, histopathological and biochemical such as malondialdehyde (MDA), myeloperoxidase (MPO), catalase and reduced glutathione (GSH) levels were measured using standard assay procedures. The study showed that pretreatment with zafirlukast in a dose of 80 mg/kg orally produced a significant decrease in tissue malondialdehyde, myeloperoxidase, and an increase in both reduced glutathione and catalase levels, while there was no significant changes with the rectal route. The 40 mg/kg dose had no significant protective effects when given either orally or rectally. The available data indicate that the inhibition of leukotriene synthesis or action may have a role in inflammatory bowel disease (IBD) as they are considered as important mediators in this condition.[3]

Absorption, Distribution and Excretion
Rapidly absorbed following oral administration, reduced following a high-fat or high-protein meal.
The most common metabolic products are hydroxylated metabolites which are excreted in the feces.
70 L
apparent oral CL=20 L/h
11.4 L/h [7-11 yrs]
9.2 L/h [5-6 yrs]

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Metabolism / Metabolites
Hepatic
Zafirlukast has known human metabolites that include cyclopentyl N-[1-(hydroxymethyl)-3-({2-methoxy-4-[(2-methylbenzenesulfonyl)carbamoyl]phenyl}methyl)indol-5-yl]carbamate and 3-hydroxycyclopentyl N-[3-({2-methoxy-4-[(2-methylbenzenesulfonyl)carbamoyl]phenyl}methyl)-1-methylindol-5-yl]carbamate.

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Biological Half-Life
10 hours

Hepatotoxicity
Prospective studies have shown that ALT elevations occur in 1.5% of patients receiving zafirlukast, most of which are mild, asymptomatic and self limited even with continuing therapy. A similar rate of transient ALT elevations is often found in placebo recipients. Clinically apparent liver disease from zafirlukast is rare, but many convincing cases have been reported, several of which were severe and resulted in hepatic failure, need for liver transplantation or death. The onset of symptoms of liver injury is typically within 2 to 6 months of starting therapy, but cases with longer latency periods have been reported (8-13 months). Symptoms include fatigue, nausea, and right upper quadrant pain followed by dark urine, jaundice and pruritus. The pattern of liver enzyme elevation is usually hepatocellular and resembles acute viral hepatitis. Eosinophilia is common but immunoallergic features are usually not prominent and autoantibodies are uncommon (eosinophilia may be due to the underlying allergic asthmatic condition). Fatal cases have been described. Reexposure can lead to more rapid and severe reappearance of injury and should be avoided. Zafirlukast can also cause systemic vasculitis and eosinophilia (Churg-Strauss Syndrome) which may be accompanied by hepatic involvement and mild enzyme elevations.
Likelihood score: C (probable cause of clinical apparent liver injury).

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Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
No published information is available on the use of zafirlukast during breastfeeding; however, manufacturer's data indicate that the dose in milk is low. Zafirlukast has been used in children as young as 12 months of age. International guidelines consider that leukotriene receptor antagonists can be used during breastfeeding.
◉ Effects in Breastfed Infants
Relevant published information was not found as of the revision date.
◉ Effects on Lactation and Breastmilk
Relevant published information was not found as of the revision date.

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Protein Binding
99%

[1]. Chem Res Toxicol. 2005 Sep;18(9):1427-37.

[2]. Toxicol Lett. 2003 Nov 1;145(1):79-87.

[3]. Br J Pharmacol. 1998 Jun;124(3):563-71.

Zafirlukast is a member of indoles, a carbamate ester and a N-sulfonylcarboxamide. It has a role as an anti-asthmatic agent and a leukotriene antagonist.
Zafirlukast is an oral leukotriene receptor antagonist (LTRA) for the maintenance treatment of asthma, often used in conjunction with an inhaled steroid and/or long-acting bronchodilator. It is available as a tablet and is usually dosed twice daily. Another leukotriene receptor antagonist is montelukast (Singulair), which is usually taken just once daily. Zafirlukast blocks the action of the cysteinyl leukotrienes on the CysLT1 receptors, thus reducing constriction of the airways, build-up of mucus in the lungs and inflammation of the breathing passages.
Zafirlukast is a Leukotriene Receptor Antagonist. The mechanism of action of zafirlukast is as a Leukotriene Receptor Antagonist, and Cytochrome P450 2C9 Inhibitor.
Zafirlukast is an orally available leukotriene receptor antagonist which is widely used for the prophylaxis and chronic treatment of asthma. Zafirlukast has been linked to rare, but occasionally severe cases of acute liver injury.
Zafirlukast is a tolyl compound and leukotriene receptor antagonist (LTRA), with anti-asthmatic and potential capsular contracture-preventing activities. Upon administration, zafirlukast selectively and competitively binds to and blocks the cysteinyl leukotriene 1 receptor (CYSLTR1), thereby preventing the potent pro-inflammatory mediators leukotriene C4, D4 and E4 from binding. This prevents leukotriene-mediated actions, including enhanced migration of eosinophils and neutrophils, increased adhesion of leukocytes, increased monocyte and neutrophil aggregation, increased airway edema, inflammation, capillary permeability and bronchoconstriction. In addition, zafirlukast may decrease collagen deposition, fibrosis, and capsular thickness after implantation, thereby preventing scar tissue.

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Drug Indication
For the prophylaxis and chronic treatment of asthma.
FDA Label

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Mechanism of Action
Zafirlukast is a selective and competitive receptor antagonist of leukotriene D4 and E4 (LTD₄ and LTE4), components of slow-reacting substance of anaphylaxis (SRSA). Cysteinyl leukotriene production and receptor occupation have been correlated with the pathophysiology of asthma, including airway edema, smooth muscle constriction, and altered cellular activity associated with the inflammatory process, which contribute to the signs and symptoms of asthma.

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Pharmacodynamics
Zafirlukast is a synthetic, selective peptide leukotriene receptor antagonist (LTRA) indicated for the prophylaxis and chronic treatment of asthma. Patients with asthma were found in one study to be 25-100 times more sensitive to the bronchoconstricting activity of inhaled LTD₄ than nonasthmatic subjects. In vitro studies demonstrated that zafirlukast antagonized the contractile activity of three leukotrienes (LTC₄, LTD₄ and LTE₄) in conducting airway smooth muscle from laboratory animals and humans. Zafirlukast prevented intradermal LTD₄-induced increases in cutaneous vascular permeability and inhibited inhaled LTD₄-induced influx of eosinophils into animal lungs.

C31H33N3O6S

575.6752

575.208

C, 64.68; H, 5.78; N, 7.30; O, 16.67; S, 5.57

107753-78-6

Zafirlukast-d7; 1217174-18-9; Zafirlukast-13C,d3; Zafirlukast-13C,d6

5717

Off-white to pink solid powder

1.3±0.1 g/cm3

139°C

1.641

6.15

2

6

9

41

1010

0

S(C1=C([H])C([H])=C([H])C([H])=C1C([H])([H])[H])(N([H])C(C1C([H])=C([H])C(=C(C=1[H])OC([H])([H])[H])C([H])([H])C1=C([H])N(C([H])([H])[H])C2C([H])=C([H])C(=C([H])C1=2)N([H])C(=O)OC1([H])C([H])([H])C([H])([H])C([H])([H])C1([H])[H])=O)(=O)=O

YEEZWCHGZNKEEK-UHFFFAOYSA-N

InChI=1S/C31H33N3O6S/c1-20-8-4-7-11-29(20)41(37,38)33-30(35)22-13-12-21(28(17-22)39-3)16-23-19-34(2)27-15-14-24(18-26(23)27)32-31(36)40-25-9-5-6-10-25/h4,7-8,11-15,17-19,25H,5-6,9-10,16H2,1-3H3,(H,32,36)(H,33,35)

cyclopentyl N-[3-[[2-methoxy-4-[(2-methylphenyl)sulfonylcarbamoyl]phenyl]methyl]-1-methylindol-5-yl]carbamate

ICI-204219; ICI204219; ICI 204219; ICI-204,219; ICI 204,219; ICI204,219; Zafirlukast; brand names Accolate, Accoleit, and Vanticon; Olmoran; Cyclopentyl (3-(2-methoxy-4-((o-tolylsulfonyl)carbamoyl)benzyl)-1-methyl-1H-indol-5-yl)carbamate;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO: ~100 mg/mL (~173.7 mM)

Solubility in Formulation 1: ≥ 2.08 mg/mL (3.61 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.08 mg/mL (3.61 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 3: 5%DMSO + 40%PEG300 + 5%Tween 80 + 50%ddH2O: 5.0mg/ml (8.69mM)

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 (Please use freshly prepared in vivo formulations for optimal results.)