CP 671,305 is a potent inhibitor of phosphodiesterase 4D (PDE4D; IC50 = 3 nM). It is selective for PDE4D over PDE4A, -B, and -C (IC50s = 310, 287, and 3,858 nM, respectively), as well as over PDE1-3 and 5 (IC50s = >5,000 nM for all). CP 671,305 inhibits release of leukotriene E4 (LTE4; ) from eosinophils (IC50 = 52 nM) and LTB4 from neutrophils (IC50 = 106 nM). In vivo, CP 671,305 inhibits antigen-induced pulmonary eosinophil influx in cynomolgus monkeys in a dose-dependent manner.
