PHARMACOLOGY AND STRUCTURE-ACTIVITY-RELATIONSHIPS FOR K-ATP MODULATORS - TISSUE-SELECTIVE K-ATP OPENERS

K-ATP openers are recognized as having a therapeutic potential for the treatment of various cardiovascular and noncardiovascular diseases. However, the first-generation agents open K-ATP in a variety of tissues that limit their potential clinical utility. This review describes our studies aimed at the identification of a common pharmacophore among structurally diverse K-ATP openers and the discovery of tissue-selective agents that may offer advantages over the first-generation agents for the treatment of cardiovascular diseases. Compounds (e.g., BMS-182264) combining the structural features of K-ATP openers cromakalim and pinacidil, show smooth-muscle relaxing and antihypertensive activities comparable to their predecessors, indicating cromakalim and pinacidil may express their biologic effects through similar structural requirements. The hypothesis about common features is further supported by radioligand-binding studies showing cromakalim, pinacidil, and the combination compound BMS-182264 bind to a similar receptor site in rat aortic smooth-muscle cells. Regardless of having a pharmacologic profile similar to cromakalim and pinacidil in vascular smooth muscle, BMS-182264 had no effect on action potential duration in guinea pig papillary muscle, indicating smooth-muscle selectivity for BMS-182264. We demonstrate that no correlation exists between antiischemic and smooth-muscle relaxing potencies for a variety of structurally different K-ATP openers. Efforts to find K-ATP openers selective for the ischemic myocardium led to the identification of BMS-180448 which, despite having similar anti-ischemic potency to cromakalim, was significantly less active as a smooth-muscle relaxant. This compound was shown to be efficacious as an anti-ischemic agent in vivo without affecting hemodynamic variables, a potential liability of first-generation compounds. The mechanism of tissue selectivity is not clear at present but it may be related to the existence of receptor subtypes in different tissues. Further work is required to identify the binding proteins for K-ATP openers and probe their relationship with K-ATP in different tissues. The identification of agents such as BMS-180448 has provided important pharmacologic and clinical tools to address these and other questions regarding the role of K-ATP in a disease state.