15R-methyl-prostaglandin D2 is a potent and selective CRTH2/DP2 receptor agonist in human eosinophils

Prostaglandin D2 (PGD2) is a mast cell-derived mediator that seems to play a role in asthma and allergic diseases. It is the only primary prostanoid to activate human eosinophils, which it accomplishes through the DP2 receptor/chemoattractant receptor-homologous molecule expressed on T helper cell type 2 (Th2) cells (CRTH2). In addition, PGD2 has both pro- and anti-inflammatory effects via the adenylyl cyclase-coupled DP1 receptor. To attempt to identify potent and selective DP2 receptor agonists we compared the abilities of a series of PGD2 analogs to activate eosinophils via the DP2 receptor with their abilities to stimulate adenylyl cyclase in platelets via the DP1 receptor. All of the PGD2 analogs tested stimulated CD11b expression and actin polymerization with a rank order of potency of 15R-methyl-PGD2 > PGD2 > 17-phenyl-18,19,20-trinor-PGD2 > 15S-methyl-PGD2 approximately equal16,16-dimethyl-PGD2 > 11-keto-fluprostenol. Surprisingly, 15R-methyl-PGD2, which has the unnatural R-configuration at carbon 15, was about 5 times more potent than PGD2 and about 75 times more potent than 15S-methyl-PGD2. 15R-methyl-PGD2 (EC50 value of 1.7 nM) was also much more potent as an eosinophil chemoattractant than PGD2 (EC50 value of 10 nM) and 15S-methyl-PGD2 (EC50 value of 128 nM). Cross-desensitization experiments indicated that 15R-methyl-PGD2 acts through the DP2 receptor. None of the PGD2 analogs tested elevated platelet cAMP by more than 20% of the maximal level in response to PGD2. However, in contrast to eosinophils, the most active was 15S-methyl-PGD2. In conclusion, 15R-methyl-PGD2 is the most potent known DP2 receptor agonist, and because of its selectivity and resistance to metabolism, should be a useful tool in probing the physiological role of this receptor in inflammatory diseases.