Novel Organic Nitrate Prodrug 4(R)-N-(2-Nitroxyethyl)-2-Oxothiazolidine-4-Carboxamide (RS-7897) Serves as a Xenobiotic Substrate for Pyroglutamyl Aminopeptidase I in Dogs

Summary: RS-7897, a novel organic nitrate, structurally contains aminoethylnitrate (AEN) and L-2oxothiazolidine-4-carboxylic acid (L-OTCA), which are linked together via an amide bond. Vasodilating activity of RS-7897 was 130 times weaker than that of AEN in vitro , while in vivo it was comparable to but longer lasting than those of AEN and nitroglycerin in anesthetized dogs. Intravenous administration of RS-7897 to dogs resulted in the appearance in plasma of AEN, which decreased with about 2.5 times longer t 1/2 (0.49 h) than that after administration of AEN itself. The T max value of AEN (0.25 h) after RS-7897 dosing agreed with the time showing the maximum vasodilating effect, indicating that RS-7897 serves as a prodrug releasing AEN slowly in vivo . The activity to hydrolyze RS-7897 to AEN and L-OTCA was localized in the cytosolic fractions of dog tissues, inhibited by thiol-blocking agents and was strongly inhibited by thyrotropin-releasing hormone, a substrate of pyroglutamyl aminopeptidase I (PAP-I). Furthermore, the RS-7897-hydrolyzing activity in dog liver cytosol was completely inhibited by an antibody against rat PAP-I. Therefore, it was found that PAP-I is involved in bioactivation of RS-7897 by amide bond hydrolysis, recognizing the sulfur-substituted L-pyroglutamyl moiety (L-OTCA) of this xenobiotic substrate.