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Leukotriene B(4) (LTB(4)) is a potent, proinflammatory mediator involved in the pathogenesis of a number of diseases including inflammatory bowel disease, psoriasis, rheumatoid arthritis, and asthma. The enzyme LTA(4) hydrolase represents an attractive target for pharmacological intervention in these disease states, since the action of this enzyme is the rate-limiting step in the production of LTB(4). Our previous efforts focused on the exploration of a series of analogues related to screening hit SC-22716 (1, 1-[2-(4-phenylphenoxy)ethyl]pyrrolidine) and resulted in the identification of potent, orally active inhibitors such as 2. Additional structure-activity relationship studies around this structural class resulted in the identification of a series of alpha-, beta-, and gamma-amino acid analogues that are potent inhibitors of the LTA(4) hydrolase enzyme and demonstrated good oral activity in a mouse ex vivo whole blood LTB(4) production assay. The efforts leading to the identification of clinical candidate SC-57461A (8d, 3-[methyl[3-[4-(phenylmethyl)phenoxy]propyl]amino]propanoic acid) are described.

Leukotriene (LT) A(4) hydrolase is a dual function enzyme that is essential for the conversion of LTA(4) to LTB(4) and also possesses an aminopeptidase activity. SC-57461A (3-[methyl[3-[4-phenylmethyl)phenoxy]propyl]amino]propanoic acid HCl) is a potent inhibitor of human recombinant LTA(4) hydrolase (epoxide hydrolase and aminopeptidase activities, K(i) values = 23 and 27 nM, respectively) as well as calcium ionophore-induced LTB(4) production in human whole blood (IC(50) = 49 nM). In the present study, we investigated its action in several animal models. Oral activity was evident from the ability of the compound to inhibit mouse ex vivo calcium ionophore-stimulated blood LTB(4) production with ED(50) values at 1.0 and 3.0 h of 0.2 and 0.8 mg/kg, respectively. A single oral dose of 10 mg/kg SC-57461A blocked mouse ex vivo LTB(4) production 67% at 18 h and 44% at 24 h, suggesting a long pharmacodynamic half-life. In a rat model of ionophore-induced peritoneal eicosanoid production, SC-57461 inhibited LTB(4) production in a dose-dependent manner (ED(50) = 0.3-1 mg/kg) without affecting LTC(4) or 6-keto-prostaglandin F(1alpha) production. Oral pretreatment with SC-57461 in a rat reversed passive dermal Arthus model blocked LTB(4) production with an ED(90) value of 3 to 10 mg/kg, demonstrating good penetration of drug into skin. Plasma level of intact SC-57461 (3 h after oral gavage dosing with 3 mg/kg) was 0.4 microg/ml, which corresponds to >80% inhibition of dermal LTB(4) production. Oral or topical pretreatment with SC-57461A 1 h before challenge with arachidonic acid blocked ear edema in the mouse. SC-57461A is a competitive, selective, and orally active inhibitor of LTA(4) hydrolase in vivo, making it useful to explore the contribution of LTB(4) to a number of inflammatory diseases.

Leukotriene B(4) (LTB(4)) is a pro-inflammatory mediator that has been implicated in the pathogenesis of a number of diseases including inflammatory bowel disease (IBD) and psoriasis. Since the action of LTA(4) hydrolase is the rate-limiting step for LTB(4) production, this enzyme represents an attractive pharmacological target for the suppression of LTB(4) production. From an in-house screening program, SC-22716 (1, 1-[2-(4-phenylphenoxy)ethyl]pyrrolidine) was identified as a potent inhibitor of LTA(4) hydrolase. Structure-activity relationship (SAR) studies around this structural class resulted in the identification of a number of novel, potent inhibitors of LTA(4) hydrolase, several of which demonstrated good oral activity in a mouse ex vivo whole blood assay.

The hydroxamic acid-containing peptide kelatorphan, a known inhibitor of enkephalin-degrading enzymes, is a potent, non-competitive inhibitor of leukotriene A4 (LTA4) hydrolase. Analogs of kelatorphan were prepared and several significantly and selectively inhibited both the hydrolase and aminopeptidase activity of the enzyme.

The synthesis and biological evaluation of a series of heterocyclic analogues of the previously reported LTA(4) hydrolase inhibitor 1b are described. Imidazopyridine and purine analogues are specifically highlighted with several demonstrating excellent potency in our in vitro assays, as well as good oral activity in a mouse ex vivo assay.

Nonsteroidal anti-inflammatory drugs (NSAIDs) exert their effect by inhibiting the target enzyme cyclooxygenase (prostaglandin H2 synthase); however, little is known about the peptides comprising its NSAID binding site. Hydroxyprostaglandin dehydrogenases also bind NSAIDs, but their NSAID binding sites have not been well characterized. Using existing synthetic strategies, we have incorporated the bromoacetoxy affinity labeling moiety around the perimeter of two potent NSAIDs, indomethacin and mefenamate, a N-phenylanthranilate. The compounds synthesized were 1-(4-(bromoacetamido)benzyl)-5-methoxy-2-methylindole-3-acetic acid (1), 3-(2-(2-bromoacetoxy)ethyl)-1-(4-chlorobenzyl)-5-methoxy-2-methylindole (2), 4-(bromoacetamido)-N-(2,3-dimethylphenyl)anthranilic acid (3), N-(3-(bromoacetamido)phenyl)-anthranilic acid (4), and N-(4-(bromoacetamido)phenyl)anthranilic acid (5). To access whether these compounds have general utility in labeling NSAID binding sites, the compounds were evaluated as affinity labeling agents for 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD) from rat liver cytosol. This enzyme displays 9-, 11-, and 15-hydroxyprostaglandin dehydrogenase activity, is inhibited potently by NSAIDs, and is homologous to bovine lung prostaglandin F synthase. Compounds 1-5 were shown to affinity label the NSAID binding site of 3 alpha-HSD. They inactivated 3 alpha-HSD through an E.I complex in a time- and concentration-dependent manner with t1/2 values ranging from seconds to hours. Ligands that compete for the active site of 3 alpha-HSD (NAD+ and indomethacin) afforded protection against inactivation, and the inactivators could demonstrate competitive kinetics against 3 alpha-hydroxysteroid substrates by forming an E.NAD+.I complex.(ABSTRACT TRUNCATED AT 250 WORDS)

The acetylenic analogue of adenosine 9-(5',6'-dideoxy-beta-D-ribo-hex-5'-ynofuranosyl)adenine has been synthesized, and its behavior as an inhibitor of bovine S-adenosylhomocysteine hydrolase has been examined. Incubation of the enzyme with excess inhibitor caused a time-dependent, irreversible inactivation of the enzyme that was accompanied by the reduction of two equivalents of NAD+ to NADH and the loss of the two remaining equivalents of NAD+. With use of radiolabeled inhibitor, it was established that 4 equiv of the acetylenic analog bind irreversibly to the enzyme and that 4 equiv were required to inactivate the enzyme completely. The inactivated enzyme could not be reactivated by incubation with NAD+. Denaturation studies revealed that 2 equiv of the inhibitor are bound more tightly to the enzyme than the remainder, suggesting the formation of a covalent linkage between the oxidized inhibitor and the enzyme. The putative covalent linkage was found to be acid sensitive but stable to mild base. The linkage could not be stabilized by treatment of the enzyme-inhibitor complex with either borohydride or cyanoborohydride. A Kl of 173 nM was measured for the inhibitor, making it one of the more potent inhibitors that have been reported. The enzyme used in these studies was isolated by modification of an affinity chromatography method reported by Narayanan and Borchardt [(1988) Biochim. Biophys. Acta 965, 22-28]. The affinity chromatography unexpectedly led to the isolation of two forms of the enzyme. The major form contained 4.0 mol of nucleotide cofactor/mol of enzyme tetramer, while the minor form carried only 2.0 mol/tetramer.

The synthesis and biological evaluation of a series of functionalized pyrrolidine- and piperidine-containing analogues of our lead LTA(4) hydrolase inhibitor, SC-57461A, is described. A number of compounds showed excellent potency in our in vitro screens and several demonstrated good oral activity in a mouse ex vivo assay. These efforts led to the identification of SC-56938 (14) as a potent, orally active inhibitor of LTA(4) hydrolase.

Leukotriene (LT) A(4) hydrolase is a dual function enzyme that is essential for the conversion of LTA(4) to LTB(4) and also possesses an aminopeptidase activity. SC-57461A (3-[methyl[3-[4-phenylmethyl)phenoxy]propyl]amino]propanoic acid HCl) is a potent inhibitor of human recombinant LTA(4) hydrolase (epoxide hydrolase and aminopeptidase activities, K(i) values = 23 and 27 nM, respectively) as well as calcium ionophore-induced LTB(4) production in human whole blood (IC(50) = 49 nM). In the present study, we investigated its action in several animal models. Oral activity was evident from the ability of the compound to inhibit mouse ex vivo calcium ionophore-stimulated blood LTB(4) production with ED(50) values at 1.0 and 3.0 h of 0.2 and 0.8 mg/kg, respectively. A single oral dose of 10 mg/kg SC-57461A blocked mouse ex vivo LTB(4) production 67% at 18 h and 44% at 24 h, suggesting a long pharmacodynamic half-life. In a rat model of ionophore-induced peritoneal eicosanoid production, SC-57461 inhibited LTB(4) production in a dose-dependent manner (ED(50) = 0.3-1 mg/kg) without affecting LTC(4) or 6-keto-prostaglandin F(1alpha) production. Oral pretreatment with SC-57461 in a rat reversed passive dermal Arthus model blocked LTB(4) production with an ED(90) value of 3 to 10 mg/kg, demonstrating good penetration of drug into skin. Plasma level of intact SC-57461 (3 h after oral gavage dosing with 3 mg/kg) was 0.4 microg/ml, which corresponds to80% inhibition of dermal LTB(4) production. Oral or topical pretreatment with SC-57461A 1 h before challenge with arachidonic acid blocked ear edema in the mouse. SC-57461A is a competitive, selective, and orally active inhibitor of LTA(4) hydrolase in vivo, making it useful to explore the contribution of LTB(4) to a number of inflammatory diseases.

Prostaglandin H2 (PGH) synthase (EC 1.14.99.1) catalyzes the bis-dioxygenation of arachidonic acid to yield PGG2 (cyclooxygenase reaction) and the peroxidative cleavage of PGG2 to yield PGH2 (peroxidase reaction). PGH synthase (Mr: 72 kDa) functions as a homodimer and is a target for nonsteroidal antiinflammatory drugs (NSAIDs), which inhibit the cyclooxygenase reaction only.

Affinity-labeling agents, 1-[4-(bromoacetamido)benzyl]-5-methoxy-2-methylindole-3-acetic acid (I) and 4-(bromoacetamido)-N-(2,3-dimethylphenyl)anthranilic acid (II), were synthesized on the basis of their respective nonsteroidal anti-inflammatory drugs (NSAIDs), indomethacin and mefenamic acid [Askonas & Penning (1991) Biochemistry 30, 11553-11560]. Compounds I and II are now shown to inhibit homogeneous ram seminal vesicle prostaglandin H2 (PGH2) synthase by two kinetically distinct complexes. They are competitive inhibitors versus arachidonic acid via the formation of high-affinity E.I complexes, and they cause time-dependent inactivation of the holoenzyme via low-affinity E.I complexes. Compounds I and II, unlike classical NSAIDs, were found to inactivate both the cyclooxygenase and peroxidase reactions of the synthase in a parallel manner. Inactivation was accompanied by the incorporation of 2 mol of either radiolabeled I or II per synthase monomer. The covalent bonds that result were stable to boiling in SDS, indicating that I and II offer alternatives to aspirin in locating NSAID binding sites. Incubation of aspirin-treated PGH2 synthase with radiolabeled I reduced the stoichiometry of incorporation to 1.0, suggesting that one of the sites modified corresponds to the cyclooxygenase site. By saturating the cyclooxygenase site with mefenamic acid, I and II only abolished the peroxidase activity of the enzyme, suggesting that the second site of modification corresponds to the peroxidase site. When PGH2 synthase was incubated with mefenamic acid and I or II, only the peroxidase activity was inactivated. Subsequent removal of all drugs by dialysis gave a preparation of PGH2 synthase that could perform the cyclooxygenase reaction, but lacked the ability to cleave ethyl hydroperoxide to ethanol and water.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat liver 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD) (EC 1.1.1.50) is an NAD(P)(+)-dependent oxidoreductase that is potently inhibited at its active site by non-steroidal anti-inflammatory drugs (NSAIDs). Initial-velocity and product-inhibition studies performed in either direction at pH 7.0 are consistent with a sequential ordered Bi Bi mechanism in which pyridine nucleotide binds first and leaves last. This mechanism is supported by fluorescence titrations of the E-NADH complex, and by the failure to detect the binding of either [3H]androsterone or [3H]androstanedione to free enzyme by equilibrium dialysis. Dead-end inhibition studies with NSAIDs also support this mechanism. Initial-velocity studies with indomethacin show that this drug is an uncompetitive inhibitor against NAD+, but a potent competitive inhibitor against androsterone, indicating the ordered formation of an E.NAD+.indomethacin complex. Calculation of the individual rate constants reveals that the binding and release of pyridine nucleotide is rate-limiting and that isomerization of the central complex is favoured in the forward direction. Equilibrium dialysis experiments with [14C]indomethacin reveal the presence of two abortive NSAID complexes, a high-affinity ternary complex corresponding to E.NAD+.indomethacin (Kd = 1-2 microM for indomethacin) and a low-affinity binary complex corresponding to E.indomethacin (Kd = 22 microM for indomethacin). Since indomethacin has a low affinity for free enzyme, the formation of this abortive binary complex does not complicate kinetic measurements which are made in the presence of NAD+, but may contribute to the inhibition of the enzyme by NSAIDs. Using either pro-R-[4-3H]NADH or pro-S-[4-3H]NADH as cofactor, radiolabelled androsterone was formed only when the pro-R-[4-3H]NADH was used, confirming that purified 3 alpha-HSD is a Class A dehydrogenase.

3 alpha-HSD appears to be a multifunctional enzyme. In addition to its traditional role of catalyzing early steps in androgen metabolism, it will also oxidoreduce prostaglandins and detoxify trans-dihydrodiols (proximate carcinogens). Since these novel reactions have been quantified using homogeneous enzyme it is necessary to interpret the role of the enzyme in these processes in vivo with some caution. However, it is rare that such observations on a purified hydroxysteroid dehydrogenase have led to such important questions. Is the 3 alpha-HSD the only steroid dehydrogenase that transforms prostaglandins and trans-dihydrodiols? Are hydroxysteroid dehydrogenases and prostaglandin dehydrogenases the same enzymes in certain tissues? Does 3 alpha-HSD protect against chemical carcinogenesis in vivo? The inhibition of the purified dehydrogenase by therapeutically relevant concentrations of anti-inflammatory drugs also deserves comment. Is this hydroxysteroid dehydrogenase really an in vivo target for anti-inflammatory drug action? Could these drugs exert some of their pharmacological effect either by preventing glucocorticoid metabolism in some tissues or by preventing the transformation of PGF2 alpha (non-inflammatory prostanoid) to PGE2 (a pro-inflammatory prostanoid)? Could these drugs, by inhibiting trans-dihydrodiol oxidation, potentiate the initiation of chemical carcinogenesis? These and other important questions can be answered only by developing specific inhibitors for the dehydrogenase to decipher its function in vivo.