Development of a high-affinity inhibitor of the prostaglandin transporter

Prostaglandin E ₂ (PGE ₂) triggers a vast array of biological signals and physiological events. The prostaglandin transporter (PGT) controls PGE2 influx and is rate-limiting for PGE ₂ metabolism and signaling termination. PGT global knockout mice die on postnatal day 1 from patent ductus arteriosus. A high-affinity PGT inhibitor would thus be a powerful tool for studying PGT function in adult animals. Moreover, such an inhibitor could be potentially developed into a therapeutic drug targeting PGT. Based on structure-activity relationship studies that built on recently identified inhibitors of PGT, we obtained N-(2- (2-(2-azidoethoxy)ethoxy)ethyl)-4-((4-((2- (2-(2-benzamidoethoxy) ethoxy)ethyl)amino)-6-((4-hydroxyphenyl)amino)-1,3,5- triazin-2- yl)amino)benzamide (T26A), a competitive inhibitor of PGT, with a K _i of 378 nM. T26A seems to be highly selective for PGT, because it neither interacts with a PGT homolog in the organic anion transporter family nor affectsPGE ₂ synthesis. In Madin-Darby canine kidney cells stably transfected with PGT, T26A blocked PGE ₂ metabolism, resulting in retention of PGE ₂ in the extracellular compartment and the negligible appearance of PGE ₂ metabolites in the intracellular compartment. Compared with vehicle, T26A injected intravenously into rats effectively doubled the amount of endogenous PGE ₂ in the circulation and reduced the level of circulating endogenous PGE ₂ metabolites to 50%. Intravenous T26A was also able to slow the metabolism of exogenously injected PGE ₂. These results confirm that PGT directly regulates PGE ₂ metabolism and demonstrate that a high-affinity inhibitor of PGT can effectively prevent PGE ₂ metabolism and prolong the half-life of circulating PGE ₂.