ABT-299, a potent antagonist of platelet activating factor.
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Animals↗
Biomedical subjects
J B Summers
Publications and source records attributed to J B Summers.
N-(acyloxyalkyl)pyridinium salts as soluble prodrugs of a potent platelet activating factor antagonist.
Pyrrolothiazole 4 is a potent antagonist of platelet activating factor-mediated effects in a variety of in vitro and in vivo assays. Despite its positive activity in models of inflammation and septic shock, 4 lacks the aqueous solubility necessary for intravenous administration. This deficit was overcome by conversion of 4 to water-soluble pyridinium prodrugs. A two-step procedure was used to prepare a series of N-(acyloxyalkyl)pyridinium salts, all of which exhibited aqueous solubility of greater than 20 mg/mL. The rate of conversion of these prodrugs to 4 was faster in human plasma than in pH 7 aqueous buffer. This rate difference was shown to be due to serum enzymes since the conversion in plasma was significantly slower in the presence of a serine esterase inhibitor. A strong correlation between prodrug structure and buffer/plasma half-life was established. The N-(acetyloxymethyl)pyridinium prodrug 11 (ABT-299) is currently undergoing clinical evaluation for the treatment of sepsis.
Animals↗
The 5-lipoxygenase inhibitory activity of zileuton in in vitro and in vivo models of antigen-induced airway anaphylaxis.
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.
Anaphylaxis↗
The properties of A-69412: a small hydrophilic 5-lipoxygenase inhibitor.
A compound which inhibits leukotriene biosynthesis could be clinically useful in treating several allergic and inflammatory diseases. One site for such inhibition is at the enzyme 5-lipoxygenase. Most inhibitors of this enzyme thus far described are poorly bioavailable. A-69412 is a small, relatively hydrophilic compound of the N-hydroxyurea class, which exhibits minimal plasma protein binding (6-12%). The compound was found to be a potent long-acting inhibitor of leukotriene formation in vivo in the rat (oral ED50 = 5 mg/kg) and ex vivo in several species. In addition, the compound exhibits excellent bioavailability in dogs and monkeys with a relatively long elimination half-life in both the species (6 and 3 h, respectively). The biochemical activity and pharmacological profile of A-69412 indicates its potential utility in asthma and ulcerative colitis, and possibly other inflammatory and allergic conditions.
Anaphylaxis↗
Synthesis and structure-activity relationships of a series of novel benzopyran-containing platelet activating factor antagonists.
A class of N-substituted tetrahydrobenzopyrano[3,4-c]pyridines, I, have been identified as antagonists of platelet activating factor (PAF). The structural features essential for PAF binding were determined by systematic modification of three sites in the molecule. While O-alkyl analogues had little effect on binding potency, N-alkyl analogues exhibited a wide range of activity. Structural changes in the core ring system generally resulted in a loss of binding activity. Optimization of the N- and O-substituents resulted in the analogues 25-27 which exhibited Ki values ranging between 131 and 167 nM in a [3H]PAF binding assay. Compound 23 was also active in a model of PAF-induced shock in the mouse following intravenous administration.
Alkylation↗
The discovery and development of zileuton: an orally active 5-lipoxygenase inhibitor.
The enzyme 5-lipoxygenase is a key target in the effort to discover drugs which inhibit the pathophysiology associated with the formation of leukotrienes. The research efforts of these laboratories have focused on the discovery of direct enzyme inhibitors of 5-lipoxygenase. In particular, compounds with hydroxamate or N-hydroxyurea functionalities have proven to be potent inhibitors of leukotriene biosynthesis in vitro and more importantly in vivo. One of these compounds, zileuton (N-(1-benzo-[b]-thien-2-ylethyl)-N-hydroxyurea) has been shown recently to be an effective leukotriene inhibitor in man. The critical approaches and breakthroughs in the discovery and development of zileuton are described. In addition, some recent results with zileuton in animals and man are detailed.
Animals↗
Inhibition of leukotriene biosynthesis in the rat peritoneal cavity.
In the search for a model of leukotriene (LT) production to provide a method to determine in vivo 5-lipoxygenase (5-LO) inhibitory activity by various compounds, a passive anaphylactic reaction in the rat peritoneal cavity was examined, refined and characterized. The reaction, produced by passive sensitization with an i.p. injection of rabbit anti-bovine serum albumin (anti-BSA) followed by an i.p. injection of BSA, resulted in the biosynthesis of large amounts of sulfidopeptide LTs measurable by immunoassay or by reversed phase high performance liquid chromatography. The oral activity of several 5-LO inhibitors has been examined using this model. An example of these is zileuton (Abbott-64077), a potent 5-lipoxygenase inhibitor now under clinical evaluation. Zileuton inhibited sulfidopeptide LT biosynthesis in the rat peritoneal cavity in a dose-dependent manner (ED50 = 3 mg/kg). WY-49,232, MK-866, BW A4C and phenidone also produced good activity with ED50 values of 6, 8, 11 and 17 mg/kg, respectively. This modified rat peritoneal anaphylaxis model appears to be a valuable tool for establishing in vivo activity of 5-LO inhibitors.
Administration, Oral↗
5-lipoxygenase inhibitory activity of zileuton.
Zileuton [N-(1-benzo[b]thien-2-ylethyl)-N-hydroxyure] inhibited 5-hydroxyeicosatetraenoic acid synthesis by rat basophilic leukemia cell 20,000 x g supernatant and rat polymorphonuclear leukocytes (PMNL) (IC50 = 0.5 and 0.3 microM) respectively. It also inhibited leukotriene (LT)B4 biosynthesis by rat PMNL (IC50 = 0.4 microM), human PMNL (IC50 = 0.4 microM) and human whole blood (IC50 = 0.9 microM). Inhibition of human PMNL LTB4 biosynthesis was removed readily by a simple wash procedure. At concentrations up to 100 microM, the compound produced little or no inhibition of several related enzymes, such as platelet 12-lipoxygenase, soybean and rabbit reticulocyte 15-lipoxygenase and sheep seminal vesicle cyclooxygenase. At p.o. doses from 0.5 to 5 mg/kg in the dog, zileuton produced a rapid and sustained inhibition of ex vivo blood LTB4 biosynthesis which correlated with the pharmacokinetic behavior of the compound. In a similar ex vivo study in the rat, the compound displayed an p.o. ED50 of 2 mg/kg. Zileuton was highly effective in preventing 6-sulfidopeptide LT formation in the rat peritoneal cavity triggered by an antigen-antibody reaction with an ED50 of 3 mg/kg. In experimental models of inflammation, zileuton significantly reduced arachidonic-acid induced mouse ear edema (ED50 = 31 mg/kg) and also attenuated inflammatory cell accumulation in the rat pleural Arthus reaction. The effectiveness of this compound for preventing LT formation in vitro, ex vivo and in vivo suggests its utility for preventing the pathophysiological effects of the LTs and other 5-lipoxygenase products in animals and in humans.
Administration, Oral↗
Hydroxamic acid inhibitors of 5-lipoxygenase: quantitative structure-activity relationships.
An evaluation of the quantitative structure-activity relationships (QSAR) for more than 100 hydroxamic acids revealed that the primary physicochemical feature influencing the in vitro 5-lipoxygenase inhibitory potencies of these compounds is the hydrophobicity of the molecule. A significant correlation was observed between the octanol-water partition coefficient of the substituent attached to the carbonyl of the hydroxamate and in vitro inhibitory activity. This correlation held for hydroxamic acids of diverse structure and with potencies spanning 4 orders of magnitude. Although the hydrophobicity may be packaged in a variety of structural ways and still correlate with potency, the QSAR study revealed two major exceptions. Specifically, the hydrophobicity of portions of compounds in the immediate vicinity of the hydroxamic acid functionality does not appear to contribute to increased inhibition and the hydrophobicity of fragments beyond approximately 12 A from the hydroxamate do not influence potency. The QSAR study also demonstrated that inhibitory activity was enhanced when there was an alkyl group on the hydroxamate nitrogen, when electron-withdrawing substituents were present and when the hydroxamate was conjugated to an aromatic system. These observations provide a simple description of the lipoxygenase-hydroxamic acid binding site.
Arachidonate Lipoxygenases↗
Structure-activity analysis of a class of orally active hydroxamic acid inhibitors of leukotriene biosynthesis.
The nature of the carbonyl and nitrogen substituents of hydroxamic acids has a major influence on the biological profile of these compounds. Hydroxamates with small groups such as methyl appended to the carbonyl and relatively large nitrogen substituents generally have longer duration in vivo, produce greater plasma concentrations, and often are more potent inhibitors of in vivo leukotriene biosynthesis than hydroxamic acids with the opposite arrangement. The structure-activity relationships that describe in vitro 5-lipoxygenase inhibitory activity and in vivo leukotriene biosynthesis inhibitory potency for a group of these hydroxamic acids were investigated. While most of the compounds examined were potent in vitro inhibitors of 5-lipoxygenase, their in vivo potencies varied widely. This discrepancy was usually attributable to differences in bioavailability. Substitution patterns are described that produce potent, orally active inhibitors of leukotriene biosynthesis.
Acylation↗
Orally active hydroxamic acid inhibitors of leukotriene biosynthesis.
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Administration, Oral↗
Hydroxamic acid inhibitors of 5-lipoxygenase.
The hydroxamic acid functionality can be incorporated in a variety of simple molecules to produce potent inhibitors of 5-lipoxygenase. As an example of this, the structure-activity relationships in a series of omega-phenylalkyl and omega-naphthylalkyl hydroxamic acids are presented. Among the features described are the influence of hydrophobicity, aryl substitution, and modifications of the hydroxamate group on enzyme inhibitory potency. To assist in the selection of more potent hydroxamic acid inhibitors, a simple hypothesis about the nature of enzyme-inhibitor binding was devised. In this hypothesis, the structures of compounds were matched to a proposed geometry of arachidonic acid when bound to the enzyme. Compounds that match best without extending into disfavored regions were predicted to be the best inhibitors. Three series of hydroxamates selected according to this approach are described. Within these series are some of the most potent inhibitors of 5-lipoxygenase reported to date.
Arachidonate Lipoxygenases↗
In vivo characterization of hydroxamic acid inhibitors of 5-lipoxygenase.
The hydroxamic acid functionally can be incorporated into simple molecules to produce potent inhibitors of 5-lipoxygenase. The ability of many of these hydroxamates to inhibit leukotriene synthesis in vivo has been measured directly with a rat peritoneal anaphylaxis model. Despite their potent enzyme inhibitory activity in vitro, many orally dosed hydroxamic acids only weakly inhibited leukotriene synthesis in vivo. This discrepancy is attributable at least in part to the rapid metabolism of hydroxamates to the corresponding carboxylic acids, which are inactive against the enzyme. A study of the structural features that affect this metabolism revealed that 2-arylpropionohydroxamic acids are relatively resistant to metabolic hydrolysis. Several members of this class of hydroxamates are described that are orally active inhibitors of leukotriene synthesis.
Administration, Oral↗