Prodrugs Activated by Vascular Ectopeptidases: Proof of Concept ^†

Several vascular ectopeptidases reside in blood vessels and efficiently regulate peptide hormones. For instance, bradykinin (BK) is inactivated by angiotensin converting enzyme (ACE) or arginine-carboxypeptidases (Arg-CPs), and aminopeptidase N (APN) cleaves several substrates. Whether such peptidases may activate latent prodrugs of vasoactive agents has been tested. The contractility of the isolated human umbilical vein, radioligand binding assays, immunolocalization of peptidases, the internalization cycle of fluorescent receptors (microscopy), blood pressure measurements in anesthetized rats, and specific inhibitors of peptidases have been exploited to show the feasibility of prodrug activation by vascular peptidases. L-alanyl-histamine has virtually no affinity for the human histamine H1 receptor, but releases histamine and contracts the vein following cleavage by endogenous APN. Prolonged sequences of BK, such as BK-Arg, Arg⁰-BK-Arg-Arg, and BK-His-Leu have little affinity for the BK B2 receptor, but are contractile in the umbilical vein and hypotensive in anesthetized rats via their action on this receptor type following cleavage of the C-terminal extensions by Arg-CPs for the first two peptides, as well as by ACE for the last two. Vascular ectopeptidases were shown to activate latent agonists of the H1 and B2 receptors, a concept that could be extended to various classes of drugs for a local action on the vasculature.