Pharmacologic and pharmacokinetic profile of SK&F S-106203, a potent, orally active peptidoleukotriene receptor antagonist, in guinea-pig

Identification of potent, selective non-peptide CC chemokine receptor-3 antagonist that inhibits eotaxin-, eotaxin-2-, and monocyte chemotactic protein-4-induced eosinophil migration

Eosinophils have been implicated in the pathogenesis of asthma and other allergic diseases. Several CC chemokines including eotaxin (CCL-11), eotaxin-2 (CCL-24), RANTES (CCL-5), and monocyte chemotactic protein-3 (MCP-3, CCL-7) and 4 (MCP-4, CCL-13) are potent eosinophil chemotactic and activating peptides acting through CC chemokine receptor-3 (CCR3). Thus, antagonism of CCR3 could have a therapeutic role in asthma and other eosinophil-mediated diseases. A high throughput, cellular functional screen was configured using RBL-2H3 cells stably expressing CCR3 (RBL-2H3-CCR3) to identify non-peptide receptor antagonists. A small molecule CCR3 antagonist was identified, SK&F 45523, and chemical optimization led to the generation of a number of highly potent, selective CCR3 antagonists including SB-297006 and SB-328437. These compounds were further characterized in vitro and demonstrated high affinity, competitive inhibition of (125)I-eotaxin and (125)I-MCP-4 binding to human eosinophils. The compounds were potent inhibitors of eotaxin- and MCP-4-induced Ca(2+) mobilization in RBL-2H3-CCR3 cells and eosinophils. Additionally, SB-328437 inhibited eosinophil chemotaxis induced by three ligands that activate CCR3 with similar potencies. Selectivity was affirmed using a panel of 10 seven-transmembrane receptors. This is the first description of a non-peptide CCR3 antagonist, which should be useful in further elucidating the pathophysiological role of CCR3 in allergic inflammatory diseases.

Identification of a potent, selective non-peptide CXCR2 antagonist that inhibits interleukin-8-induced neutrophil migration

Interleukin-8 (IL-8) and closely related Glu-Leu-Arg (ELR) containing CXC chemokines, including growth-related oncogene (GRO)alpha, GRObeta, GROgamma, and epithelial cell-derived neutrophil-activating peptide-78 (ENA-78), are potent neutrophil chemotactic and activating peptides, which are proposed to be major mediators of inflammation. IL-8 activates neutrophils by binding to two distinct seven-transmembrane (7-TMR) G-protein coupled receptors CXCR1 (IL-8RA) and CXCR2 (IL-8RB), while GROalpha, GRObeta, GROgamma, and ENA-78 bind to and activate only CXCR2. A chemical lead, which selectively inhibited CXCR2 was discovered by high throughput screening and chemically optimized. SB 225002 (N-(2-hydroxy-4-nitrophenyl)-N'-(2-bromophenyl)urea) is the first reported potent and selective non-peptide inhibitor of a chemokine receptor. It is an antagonist of 125I-IL-8 binding to CXCR2 with an IC50 = 22 nM. SB 225002 showed >150-fold selectivity over CXCR1 and four other 7-TMRs tested. In vitro, SB 225002 potently inhibited human and rabbit neutrophil chemotaxis induced by both IL-8 and GROalpha. In vivo, SB 225002 selectively blocked IL-8-induced neutrophil margination in rabbits. The present findings suggest that CXCR2 is responsible for neutrophil chemotaxis and margination induced by IL-8. This selective antagonist will be a useful tool compound to define the role of CXCR2 in inflammatory diseases where neutrophils play a major role.

Pharmacology of leukotriene receptor antagonists. More than inhibitors of bronchoconstriction

The cysteinyl leukotrienes (LTs) are chemical mediators that are thought to contribute to the pathophysiologic condition of asthma and other inflammatory diseases. The biological effects of the cysteinyl LTs in the lung are pleiotropic, including both bronchoconstrictor and a growing list of nonbronchoconstrictor activities that extend to inflammatory cell recruitment, vascular leakage, mucus production, neuronal dysfunction, and airways remodeling. This spectrum of effects of cysteinyl LTs is consistent with an expanded view of asthma that extends beyond simply bronchoconstriction and inflammation. Consequently, the clinical efficacy of cysteinyl LT receptor antagonists (LTRAs) in asthma may be related to antagonism of more than cysteinyl LT-induced bronchoconstriction. The relationship of antagonism of the multiple effects of cysteinyl LTs by cysteinyl LTRAs to their utility in the therapy of asthma is addressed, and the preclinical and clinical pharmacology of cysteinyl LTRAs is reviewed.

Column-switching high-performance liquid chromatographic method for the determination of SK&F 106203 in human plasma after fluorescence derivatization with 9-anthryldiazomethane

A sensitive and selective high-performance liquid chromatographic method was developed for the determination of SK&F 106203 3-(2-carboxyethylthio)-3-[2-(8-phenyloctyl)phenyl]propanoic acid, a potent peptidoleukotriene end organ receptor antagonist, in human plasma. The method involves isolation of SK&F 106203 and the internal standard (SK&F 104736) from plasma samples by liquid-liquid extraction prior to derivatization with 9-anthryldiazomethane. The derivatized samples were first subjected to a solid-phase extraction procedure prior to injection onto a short silica column, which is part of a chromatographic system equipped with an automated column-switching device. Column switching was used to heart-cut the chromatographic zone containing the peaks of interest from this first column and transfer it to an analytical silica column for further chromatographic separation. The peaks were quantified with an in-line fluorometer by measuring the fluorescence emission intensity at 415 nm after excitation at 365 nm. An on-column detection limit of 0.625 ng was achieved for SK&F 106203 by optimizing the derivatization and chromatography conditions. The limit of quantification for SK&F 106203, using 250 microliters of plasma, was 20 ng/ml. Linear response in SK&F 106203/internal standard peak-height ratios was observed for SK&F 106203 concentrations ranging from 10 to 5000 ng/ml of plasma. Precision and accuracy were within 5% across the calibration range. The assay was sufficiently sensitive, accurate, and precise to support pharmacokinetic studies in humans.