Acknowledgments br PGD is an arachadonic

Acknowledgments
PGD is an arachadonic acid-derived prostaglandin produced in large quantities when asthmatic lung tissues are challenged by allergens. PGD contracts the airway tissue as well as stimulating an inflammatory response. PGD was also found to be the ligand for a second receptor, DP2 (originally known as CRTH2). Chemoattractant receptor homologous molecule expressed on TH lymphocytes (CRTH2) are activated by PGD and a range of responses such as chemotaxis and mediator release are triggered. These findings have resulted in considerable interest in the development of CRTH2 antagonists as treatments for alk pathway and allergic rhinitis. The structures of some known CRTH2 antagonists and examples of generic structures that have been patented are shown in . The non-selective cyclooxygenase (COX) inhibitor indomethacin , is also a potent CRTH2 agonist, whereas the thomboxane receptor antagonist Ramatroban is a CRTH2 antagonist. As part of Pfizer’s effort towards discovering a novel CRTH2 antagonist, an analysis of the CRTH2 ligand patent literature (>60 patents) revealed the common motif/pharmacophore to be an aryl group attached to a carboxylic acid.
Introduction In allergic rhinitis inflammation, lymphocytes and eosinophils play pivotal role, being the chief inflammatory cell types infiltrating the nasal mucosa. Recruitment of eosinophils in large numbers into the allergic inflamed nose during the late phase reaction entails a complex process of directed cell migration against concentration gradient of the chemokine (chemotaxis). For this to happen, the chemokine interaction with its specific receptor mediates signal transduction via Ca mobilization, protein kinase C, and heterotrimeric GTP-binding proteins [1], [2], [3] or Kinases and phosphatases, adaptor proteins, and a small GTP-binding proteins [4], [5]. CRTH2 is expressed on eosinophils, basophils and T Helper Type 2 lymphocytes. CRTH2 gained a lot of attention as promotor for PGD2-induced eosinophilia in allergic airway diseases [6], [7], [8], [9], [10]. In an allergic rhinitis murine model, it has been demonstrated that the PGD2-CRTH2 interaction is elevated following pollen sensitization. Additionally, CRTH2 mRNA in nasal mucosa was significantly elevated in Cry j 1-sensitized mice [11]. Moreover, in nasal tissue, ligation of PGD2 to CRTH2 appeared to be selectively involved in eosinophil recruitment [12]. Recently we showed that VIP amounts are significantly higher in AR patients nasal secretions compared to control subjects and that VIP competes with PGD2 for CRTH2 receptor signaling for eosinophil chemotaxis [13]. This highlighted a novel neuro-immuno-axis in recruiting eosinophils via CRTH2. Tyrosine kinases is an important factor for cell differentiation and mediates many cellular biological effects. Interestingly, our previous biochemical assays showed that tyrosine kinase activity in human eosinophils is an essential down-stream signal that promotes eotaxin induced eosinophil chemotaxis via CCR3 receptor [14]. On the other hand, tyrosine kinase inhibition was not involved in PGD2/VIP-induced eosinophil chemotaxis, but rather augmented eosinophil chemotaxis against VIP and PGD2 [13], [15], [16].