Identification of a New Class of Prostaglandin Transporter Inhibitors and Characterization of Their Biological Effects on Prostaglandin E2 Transport □S

Prostaglandins (PGs) are involved in several major signaling pathways. Their effects are terminated when they are transported across cell membranes and oxidized intracellularly. The transport step of PG metabolism is carried out by the prostaglandin transporter (PGT). Inhibition of PGT would therefore be expected to change local or circulating concentrations of prostaglandins, and thus their biological effects. To develop PGT-specific inhibitors with high affinity, we designed a library of triazine compounds and screened 1842 small molecules by using Madin-Darby canine kidney cells stably expressing rat PGT. We found several effective PGT inhibitors. Among them, the most potent inhibitor had a Ki of 3.7 0.2 M. These inhibitors allowed us to isolate the efflux process of PGE2 and to demonstrate that PGT does not transport PGE2 outwardly under physiological conditions. Prostaglandins (PGs) are synthesized from arachidonic acid by cyclooxygenases (COX1 and COX2) and corresponding synthases (Helliwell et al., 2004). PGs play an important role in physiology and clinical settings. Their biological effects include triggering inflammation, fever, and pain (Blatteis and Sehic, 1997; Bley et al., 1998; Vanegas and Schaible, 2001; Samad et al., 2002); induction of labor (Ulmann et al., 1992); modulation of renal hemodynamics and of water and solute reabsorption (Epstein, 1986; Wang et al., 1998; Yokoyama et al., 2002); and arterial vasodilatation (Clyman et al., 1978; Coceani and Olley, 1988; Smith et al., 1994). PG analogs, such as latanoprost and unoprostone, have been used to treat glaucoma (Stjernschantz, 1995, 2004; Alm, 1998; Susanna et al., 2002). At the cellular level, PGs are involved in several major signaling pathways, including the mitogen-activated protein kinase and protein kinase A pathways by up-regulation of cAMP (Narumiya et al., 1999; Bos et al., 2004). The magnitude of PG effects depends not only on their production but also their metabolism. We identified the prostaglandin transporter (PGT) (Kanai et al., 1995) and have reported that PGT removes PGs from the extracellular compartment and thereby terminates their interactions with receptors on cell membranes. PGT delivers PGs to cytoplasmic 15-OH PG dehydrogenase (Schuster, 2002; Nomura et al., 2004), resulting in oxidation and inactiva-