Abstract

Prostaglandin E₂ (PGE₂) triggers a vast array of biological signals and physiological events. The prostaglandin transporter (PGT) controls PGE₂ influx and is rate-limiting for PGE₂ 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 affects PGE₂ synthesis. In Madin-Darby canine kidney cells stably transfected with PGT, T26A blocked PGE₂ metabolism, resulting in retention of PGE₂ in the extracellular compartment and the negligible appearance of PGE₂ metabolites in the intracellular compartment. Compared with vehicle, T26A injected intravenously into rats effectively doubled the amount of endogenous PGE₂ in the circulation and reduced the level of circulating endogenous PGE₂ metabolites to 50%. Intravenous T26A was also able to slow the metabolism of exogenously injected PGE₂. These results confirm that PGT directly regulates PGE₂ metabolism and demonstrate that a high-affinity inhibitor of PGT can effectively prevent PGE₂ metabolism and prolong the half-life of circulating PGE₂.