Tissue and substrate specificity of inhibition by alkoxy-aryl-lactams of platelet and arterial smooth muscle cyclic nucleotide phosphodiesterases relationship to pharmacological activity

Alkoxy-aryl-lactams (cilostamide, AAL 05, ZK 62 711, Ro 20-1724) inhibit differently cAMP or cGMP phosphodiesterases from blood platelets or vascular smooth muscle. Cilostamide (IC50 0.23 microM) and AAL 05 (IC50 0.15 microM) are 100 times more potent towards platelet cAMP phosphodiesterase whereas ZK 62 711 (IC50 2 microM) and Ro 20-1724 (IC50 33 microM) inhibit more selectively the enzyme from aorta. The substrate specificity of the inhibitors is different in the two tissues: ZK 62 711 and cilostamide are respectively 345 and 290 times more potent as inhibitor of cAMP than cGMP phosphodiesterase from vascular smooth muscle (ZK 62 711) or platelets (cilostamide). M + B 22,948 selectively inhibits cGMP phosphodiesterase with an IC50 of 9 or 24 microM on platelet or aorta enzyme, respectively. In general, the potencies of spasmolytic and platelet inhibitor effects vary from one drug to the other with the potency of inhibition of phosphodiesterase from the corresponding tissue. These data suggest that phosphodiesterases from platelets are different from those of arterial smooth muscle.