Leukotriene (LT) B 4 is an inflammatory mediator that has been implicated in the pathogenesis of various diseases, including inflammatory bowel disease and psoriasis. As the rate-limiting step for LTB 4 production, LTA 4 hydrolase represents an attractive target for therapeutic agents that interfere with LTB 4 production. In the present study we evaluated a chemically novel compound designated phenoxy]propyl]amino]propanoic acid HCl) as an inhibitor of LTA 4 hydrolase. Pharmacological comparisons are made to its free acid SC-57461. SC-57461A is a potent competitive inhibitor of recombinant human LTA 4 hydrolase when either LTA 4 (IC 50 ϭ 2.5 nM, K i ϭ 23 nM) or peptide substrates (IC 50 ϭ 27 nM) are used. In human whole blood, the IC 50 for calcium ionophore-induced LTB 4 production was 49 nM, indicative of good cell penetration. Whole blood production of the cyclooxygenase metabolite thromboxane B 2 was not affected. SC-57461A was also active in several other species, including mouse, rat, dog, and rhesus monkey. The data indicate that SC-57461A is a potent and selective inhibitor of LTA 4 hydrolase.

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. phenoxy]propyl]amino]propanoic acid HCl) is a potent inhibitor of human recombinant LTA 4 hydrolase (epoxide hydrolase and aminopeptidase activities, K i values ϭ 23 and 27 nM, respectively) as well as calcium ionophore-induced LTB 4 production in human whole blood (IC 50 ϭ 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 ϭ 0.3-1 mg/kg) without affecting LTC 4 or 6-ketoprostaglandin F 1␣ 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 g/ml, which corresponds to Ͼ80% 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. -57461A (3-[methyl[3-[4-(phenylmethyl)phenoxy]propyl]amino]propanoic acid HCl) is a potent and competitive inhibitor of recombinant human leukotriene A 4 hydrolase in vitro (Askonas et al., 2002). It inhibits recombinant human leukotriene A 4 at nanomolar concentrations when either LTA 4 (epoxide hydrolase, K i ϭ 23 nM) or peptide substrates (aminopeptidase, K i ϭ 27 nM) are used. SC-57461A is selective for LTA 4 hydrolase and does not inhibit other enzymes involved in the metabolism of arachidonic acid (AA) [e.g., 5-lipoxygenase (5-LO), LTC 4 synthase, or various isoforms of cyclooxygenase] as well as other zinccontaining aminopeptidases (e.g., human leukocyte elastase, rabbit lung angiotensin-converting enzyme) (Askonas et al., 2002). SCSC-57461A is also active in mammalian whole blood under conditions in which both 5-LO and cyclooxygenase pathways were simultaneously stimulated with calcium ionophore A23187. The IC 50 values for inhibition of LTB 4 are less than 0.5 M in the blood of several species (Askonas et al., 2002), suggesting that SC-57461A is metabolically stable and can penetrate cells to inhibit the cytosolic enzyme.To characterize SC-57461A in vivo, we used several rodent models to assess oral activity, selectivity for inhibiting LTB 4 synthesis, and efficacy in several mode...

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