Identification, substrate specificity, and inhibition of the Streptococcus pneumoniae beta-ketoacyl-acyl carrier protein synthase III (FabH).

In the bacterial type II fatty acid synthase system, beta-ketoacyl-acyl carrier protein (ACP) synthase III (FabH) catalyzes the condensation of acetyl-CoA with malonyl-ACP. We have identified, expressed, and characterized the Streptococcus pneumoniae homologue of Escherichia coli FabH. S. pneumoniae FabH is approximately 41, 39, and 38% identical in amino acid sequence to Bacillus subtilis, E. coli, and Hemophilus influenzae FabH, respectively. The His-Asn-Cys catalytic triad present in other FabH molecules is conserved in S. pneumoniae FabH. The apparent K(m) values for acetyl-CoA and malonyl-ACP were determined to be 40.3 and 18.6 microm, respectively. Purified S. pneumoniae FabH preferentially utilized straight short-chain CoA primers. Similar to E. coli FabH, S. pneumoniae FabH was weakly inhibited by thiolactomycin. In contrast, inhibition of S. pneumoniae FabH by the newly developed compound SB418011 was very potent, with an IC(50) value of 0.016 microm. SB418011 also inhibited E. coli and H. influenzae FabH with IC(50) values of 1.2 and 0.59 microm, respectively. The availability of purified and characterized S. pneumoniae FabH will greatly aid in structural studies of this class of essential bacterial enzymes and facilitate the identification of small molecule inhibitors of type II fatty acid synthase with the potential to be novel and potent antibacterial agents active against pathogenic bacteria.

Pharmacology of SB-273779, a nonpeptide calcitonin gene-related peptide 1 receptor antagonist.

Calcitonin gene-related peptide (CGRP), a potent vasodilatory and cardiotonic peptide, has a potential role for CGRP in diverse physiologic and pathophysiologic situations such as congestive heart failure, diabetes, migraine, and neurogenic inflammation. Although a peptide CGRP receptor antagonist, CGRP(8-37,) is available, its utility presents significant limitations for these indications. Here, we describe the properties of SB-(+)-273779 [N-methyl-N-(2-methylphenyl)-3-nitro-4-(2-thiazolylsulfinyl)nitrobenzanilide], a selective nonpeptide antagonist of CGRP(1) receptor. SB-(+)-273779 inhibited (125)I-labeled CGRP binding to SK-N-MC (human neuroblastoma cells) and human cloned CGRP(1) receptor with K(i) values of 310 +/- 40 and 250 +/-15 nM, respectively. SB-(+)-273779 also inhibited CGRP (3 nM)-activated adenylyl cyclase in these systems with IC(50) values of 390 +/-10 nM (in SK-N-MC) and 210 +/-16 nM (recombinant human CGRP receptors). Prolonged treatment (>30 min) of SK-N-MC cells with SB-(+)-273779 followed by extensive washing resulted in reduction in maximum CGRP-mediated adenylyl cyclase activity, suggesting that this compound has irreversible binding characteristics. In addition, SB-(+)-273779 antagonized CGRP-mediated 1) stimulation of intracellular Ca(2+) in recombinant CGRP receptors in HEK-293 cells, 2) inhibition of insulin-stimulated [(14)C]deoxyglucose uptake in L6 cells, 3) vasodilation in rat pulmonary artery, and 4) decrease in blood pressure in anesthetized rats. SB-(+)-273779 tested at 3 microM had no significant affinity for calcitonin, endothelin, angiotensin II, and alpha-adrenergic receptors under standard ligand binding assays. SB-(+)-273779 also did not inhibit forskolin and pituitary adenylate cyclase-activating polypeptide. These results suggest that SB-(+)-273779 is a valuable tool for studying CGRP-mediated functional responses in complex biological systems.

In vitro and in vivo pharmacological characterization of SB 201993, an eicosanoid-like LTB4 receptor antagonist with anti-inflammatory activity.

Leukotriene B4 (LTB4) and 12-(R)-hydroxy-5,8,10,14-eicosatetraenoic acid (12-[R]-HETE) have been postulated to contribute to the pathophysiology of inflammatory diseases. SB 201993, (E)-3-[[[[6-(2-carboxyethenyl)-5-[[8-(4-methoxyphenyl)octyl] oxy]-2-pyridinyl] methyl] thio] methyl] benzoic acid, identified from a chemical series designed as ring-fused analogs of LTB4, was evaluated as an antagonist of LTB4- and 12-(R)-HETE-induced responses in vitro and for anti-inflammatory activity in vivo. SB 201993 competitively antagonized [3-H]-LTB4 binding to intact human neutrophils (Ki = 7.6 nM) and to membranes of RBL 2H3 cells expressing the LTB4 receptor (RBL 2H3-LTB4R; IC50 = 154 nM). This compound demonstrated competitive antagonism of LTB4- and 12-(R)-HETE-induced Ca2+ mobilization responses in human neutrophils (IC50s of 131 nM and 105 nM, respectively) and inhibited LTB4-induced Ca2+ mobilization in human cultured keratinocytes (IC50 = 61 nM), RBL 2H3-LTB4R cells (IC50 = 255 nM) and mouse neutrophils (IC50 = 410 nM). SB 201993 showed weak LTD4-receptor binding affinity (Ki = 1.9 microM) and inhibited 5-lipoxygenase (IC50 of 3.6 microM), both in vitro and ex vivo. In vivo, SB 201993 inhibited LTB4-induced neutrophil infiltration in mouse skin and produced dose-related, long lasting topical anti-inflammatory activity against the fluid and cellular phases of arachidonic acid-induced mouse ear inflammation (ED50 of 580 microg/ear and 390 microg/ear, respectively). Similarly, anti-inflammatory activity was also observed in the murine phorbol ester-induced cutaneous inflammation model (ED50 of 770 and 730 microg/ear, respectively, against the fluid and cellular phases). These results indicate that SB 201993 blocks the actions of LTB4 and 12-(R)-HETE and inhibits a variety of inflammatory responses; and thus may be a useful compound to evaluate the role of these mediators in disease models.

(E)-3-[6-[[(2,6-dichlorophenyl)thio]methyl]-3-(2-phenylethoxy)-2- pyridinyl]-2-propenoic acid: a high-affinity leukotriene B4 receptor antagonist with oral antiinflammatory activity.

An extensive structure-activity study based around the high-affinity leukotriene B4 (LTB4) receptor antagonist SB 201146 (1) led to the identification of (E)-3-[6-[[(2,6-dichlorophenyl)-thio]methyl]-3-(2-phenylethoxy)-2- pyridinyl]-2-propenoic acid (3). This compound displays high affinity for the human neutrophil LTB4 receptor (Ki = 0.78 nM), blocks LTB4-induced Ca2+ mobilization with an IC50 of 6.6 +/- 1.5 nM, and demonstrates potent oral and topical antiinflammatory activity in a murine model of dermal inflammation.

(E)-3-[[[[6-(2-carboxyethenyl)-5-[[8-(4- methoxyphenyl)octyl]oxy]-2-pyridinyl]-methyl]thio]methyl]benzoic acid and related compounds: high affinity leukotriene B4 receptor antagonists.

(E)-3-[[[[6-(2-Carboxyethenyl)-5-[[8-(4- methoxyphenyl)octyl]oxy]-2-pyridinyl]methyl]thio]methyl]benzoic acid (11, SB 201993) is a novel, potent LTB4 receptor antagonist. Compound 11 arose from a structure-activity study of a series of trisubstituted pyridines that demonstrated LTB4 receptor antagonist activity. The placement of an additional methylene unit in the sulfur containing chain linking the pyridine and benzoic acid moieties of lead compound 8 (K(i) = 80 nM) resulted in a greater than 10-fold increase in receptor affinity. Additionally, in this new series of compounds, the oxidation state of the sulfur was found to be critical to the activity, i.e., the sulfoxide and sulfone showed substantially lower affinity for the LTB4 receptor. Compound 11 competitively inhibits the binding of [3H]LTB4 to LTB4 receptors on human polymorphonuclear leukocytes with a Ki of 7.1 nM and blocks both the LTB4-induced calcium mobilization and the LTB4-induced degranulation responses in these cells with IC50 values of 131 and 271 nM, respectively. Compound 11 demonstrated oral LTB4 antagonist activity as well as topical antiinflammatory activity in the mouse.

Synthesis of structural analogs of leukotriene B4 and their receptor binding activity.

Structural analogs of leukotriene B4 (LTB4) were designed using a preferred conformation of LTB4 (1). Appending an aromatic ring scaffold between LTB4 carbons 7 and 11 led to quinoline analogs 3 and 15. A similar modification to the LTB4 structure between carbons 7 and 9 led to the pyridine analogs 41 and 46. The compounds of this study were evaluated in receptor binding assays using [3H]LTB4 and intact human DMSO differentiated U-937 cells. The first analog prepared, quinoline 3, displayed moderate potency in the LTB4 receptor binding assay (Ki = 0.9 microM). Modification of 3 by appending an aromatic ring between carbons 2 and 4 of the acid side chain produced a dramatic increase in receptor binding (15, Ki = 0.01 microM); a further improvement in receptor binding was achieved in the pyridine series (e.g., 41; Ki = 0.001 microM). The LTB4 receptor agonist/antagonist activity of the test compounds was determined using a functional assay that relies upon intracellular calcium mobilization induced by LTB4. Of the analogs prepared in this report only 47 demonstrated LTB4 receptor antagonist activity.

Trisubstituted pyridine leukotriene B4 receptor antagonists: synthesis and structure-activity relationships.

A series of trisubstituted pyridines have been prepared that exhibit in vitro leukotriene B4 (LTB4, 1) receptor antagonist activity. Previous disubstituted pyridines from these labs showed high affinity for the LTB4 receptor but demonstrated agonist activity in functional assays (e.g., 2, Ki = 1 nM). Compound 4, the initial lead compound of this new series, showed only modest affinity by comparison (Ki = 282 nM); however, 4 was a receptor antagonist with no demonstrable agonist activity up to 10 microM. Subsequent modifications of the lipid tail and aryl head group region led to the discovery of aniline 50 (SB 201146). This compound, also free of agonist activity, possesses high affinity for the LTB4 receptor (Ki = 4.7 nM).