In vitro activity: Taprenepag (formerly known as CP-544326) is a potent and selective agonist of EP2 (prostaglandin EP receptor 2) with IC50 of 10 nM and EC50 of 2.8 nM. Its corneal permeability and ocular bioavailability were significantly increased when the compound was dosed as the isopropyl ester prodrug, PF-04217329. Recently PF-04217329 (Taprenepag isopropyl), a prodrug of CP-544326 (active acid metabolite), a potent and selective EP(2) receptor agonist, was successfully evaluated for its ocular hypotensive activity in a clinical study involving patients with primary open angle glaucoma. Topical ocular dosing of PF-04217329 was well tolerated in preclinical species and caused an elevation of cAMP in aqueous humor/iris-ciliary body indicative of in vivo EP(2) target receptor activation. Topical ocular dosing of PF-04217329 resulted in ocular exposure of CP-544326 at levels greater than the EC(50) for the EP(2) receptor. PF-04217329 when dosed once daily caused between 30 and 50% IOP reduction in single day studies in normotensive Dutch-belted rabbits, normotensive dogs, and laser-induced ocular hypertensive cynomolgus monkeys and 20-40% IOP reduction in multiple day studies compared to vehicle-dosed eyes. IOP reduction was sustained from 6 h through 24 h following a single topical dose. In conclusion, preclinical data generated thus far appear to support the clinical development of PF-04217329 as a novel compound for the treatment of glaucoma.

Kinase Assay: CP-544326 is a novel, selective and potent EP2 agonist. CP-544326 with an IC50 for human EP2 equal to 10 nM (average of two independent experiments; 9 and 11 nM), is at least 270 times more selective for human EP2 subtype as compared with the other human EP subtypes, 1, 3, and 4. Based on the cell-based efficacy data using rat EP2-HEP293 cells, cAMP levels increased in a dose- and time-dependent manner yielding an average EC50of 1.9 nM (1.5 and 2.4 nM; from two independent experiments). In human EP2-HEK293 cells, CP-544326-mediated cAMP production yielded an EC50 of 2.8 nM (2.5 and 3.1 nM; from two independent experiments), which was similar to that observed for PGE2(EC50 = 2.6 nM)

Cell Assay: