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Abstract
CXC chemokine receptor 2 (CXCR2) is a key receptor in the chemotaxis of neutrophils to sites of inflammation. The studies reported here describe the pharmacological characterization of danirixin, a CXCR2 antagonist in the diaryl urea chemical class. Danirixin has high affinity for CXCR2, with a negative log of the 50% inhibitory concentration (pIC50) of 7.9 for binding to Chinese hamster ovary cell (CHO)-expressed human CXCR2, and 78-fold selectivity over binding to CHO-expressed CXCR1. Danirixin is a competitive antagonist against CXCL8 in Ca2+-mobilization assays, with a KB (the concentration of antagonist that binds 50% of the receptor population) of 6.5 nM and antagonist potency (pA2) of 8.44, and is fully reversible in washout experiments over 180 minutes. In rat and human whole-blood studies assessing neutrophil activation by surface CD11b expression following CXCL2 (rat) or CXCL1 (human) challenge, danirixin blocks the CD11b upregulation with pIC50s of 6.05 and 6.3, respectively. Danirixin dosed orally also blocked the influx of neutrophils into the lung in vivo in rats following aerosol lipopolysaccharide or ozone challenge, with median effective doses (ED50s) of 1.4 and 16 mg/kg respectively. Thus, danirixin would be expected to block chemotaxis in disease states in which neutrophils are increased in response to inflammation, such as pulmonary diseases. In comparison with navarixin, a CXCR2 antagonist from a different chemical class, the binding characterization of danirixin is distinct. These observations may offer insight into the previously observed clinical differences in induction of neutropenia between these compounds.
Highlights
Sustained neutrophil influx to the lung plays a key role of the pathology of diseases such chronic obstructive pulmonary disease (COPD), severe asthma, cystic fibrosis, acute lung injury, and respiratory syncytial virus infection (Wareing et al, 2007; Chapman et al, 2009; Stadtmann and Zarbock, 2012)
Danirixin (B form) competed with [125I] CXCL8 binding to membranes prepared from Chinese hamster ovary cell (CHO) stably transfected with human CXC chemokine receptor 2 (CXCR2) or CXC chemokine receptor 1 (CXCR1) cells, with pIC50s, respectively, of 7.90 6 0.04 (n 5 3; IC50 12.5 nM) and of 6.03 6 0.05 (n 5 3) (IC50 977 nM), or 78-fold higher affinity for CXCR2
Binding affinity for CXCR2 was assessed in the presence of 0.4% human serum albumin to more closely approximate physiologic conditions, and danirixin competed with [125I] CXCL8 (0.23 nM) with a pIC50 of 6.95 (n 5 2) (IC50 5 113.5 nM)
Summary
Sustained neutrophil influx to the lung plays a key role of the pathology of diseases such chronic obstructive pulmonary disease (COPD), severe asthma, cystic fibrosis, acute lung injury, and respiratory syncytial virus infection (Wareing et al, 2007; Chapman et al, 2009; Stadtmann and Zarbock, 2012). In these conditions, tissue cells at the site of injury produce ELR1 chemokines (containing a Glu-Leu-Arg motif before the first cysteine), which in turn activate neutrophils through interaction with the G protein-coupled CXC chemokine receptor 1 (CXCR1) and CXC chemokine receptor 2 (CXCR2). Additional consequences of more or less selective compounds, such as host defense functions, have not been studied in detail in the clinic at this time
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