Effect of JTV-506, a novel vasodilator, on coronary blood flow in conscious dogs

KATP channel openers: structure-activity relationships and therapeutic potential

ATP-sensitive potassium channels (K(ATP) channels) are heteromeric complexes of pore-forming inwardly rectifying potassium channel subunits and regulatory sulfonylurea receptor subunits. K(ATP) channels were identified in a variety of tissues including muscle cells, pancreatic beta-cells, and various neurons. They are regulated by the intracellular ATP/ADP ratio; ATP induces channel inhibition and MgADP induces channel opening. Functionally, K(ATP) channels provide a means of linking the electrical activity of a cell to its metabolic state. Shortening of the cardiac action potential, smooth muscle relaxation, inhibition of both insulin secretion, and neurotransmitter release are mediated via K(ATP) channels. Given their many physiological functions, K(ATP) channels represent promising drug targets. Sulfonylureas like glibenclamide block K(ATP) channels; they are used in the therapy of type 2 diabetes. Openers of K(ATP) channels (KCOs), for example, relax smooth muscle and induce hypotension. KCOs are chemically heterogeneous and include as different classes as the benzopyrans, cyanoguanidines, thioformamides, thiadiazines, and pyridyl nitrates. Examples for new chemical entities more recently developed as KCOs include cyclobutenediones, dihydropyridine related structures, and tertiary carbinols.

ATP-sensitive K+ channels of vascular smooth muscle cells

ATP-sensitive potassium channels (K(ATP)) of vascular smooth muscle cells represent potential therapeutic targets for control of abnormal vascular contractility. The biophysical properties, regulation and pharmacology of these channels have received intense scrutiny during the past twenty years, however, the molecular basis of vascular K(ATP) channels remains ill-defined. This review summarizes the recent advancements made in our understanding of the molecular composition of vascular K(ATP) channels with a focus on the evidence that hetero-octameric complexes of Kir6.1 and SUR2B subunits constitute the vascular K(ATP) subtype responsible for control of arterial diameter by vasoactive agonists.

K(+) channels as therapeutic drug targets

K(+) channels play critical roles in a wide variety of physiological processes, including the regulation of heart rate, muscle contraction, neurotransmitter release, neuronal excitability, insulin secretion, epithelial electrolyte transport, cell volume regulation, and cell proliferation. As such, K(+) channels have been recognized as potential therapeutic drug targets for many years. Unfortunately, progress toward identifying selective K(+) channel modulators has been severely hampered by the need to use native currents and primary cells in the drug-screening process. Today, however, more than 80 K(+) channel and K(+) channel-related genes have been identified, and an understanding of the molecular composition of many important native K(+) currents has begun to emerge. The identification of these molecular K(+) channel drug targets should lead to the discovery of novel drug candidates. A summary of progress is presented.

Potassium channel openers as potential therapeutic weapons in ion channel disease

The opening of potassium (K+) channels, causing hyperpolarization of the cell membrane, is a physiological means of decreasing cell excitability. Thus, drugs with this property will demonstrate a broad clinical potential. The identification of synthetic molecules that evoke physiological responses (for example smooth muscle relaxation) by the opening of K+ channels led to a new direction in the pharmacology of ion channels. The term "potassium channel openers" was initially associated with a group of chemically diverse agents (for example, cromakalim, pinacidil, nicorandil) that evoke K+ efflux through adenosine 5'-triphosphate (ATP)-sensitive K+ channels (KATP). This finding initiated a search to identify molecules that specifically open other K+ channel subtypes (for example large conductance calcium-activated K+ channels [BKCa]). K+ channel opening properties have been demonstrated in a diverse range of synthetic chemical structures and endogenous substances. Second generation KATP channel openers (KATPCOs) demonstrate heterogeneous pharmacology indicative of independent sites of action for the different agents. Successful cloning of the KATP channel has shed light on the heterogeneity of the structure targeted by KATPCOs. Expression of the actions of KATPCOs involves three isoforms of the sulfonylurea (SUR) receptor (which forms the beta subunit of the KATP channel). The distribution of the SUR isoforms (and potential of identifying new isoforms) provides unique targets for the development of selective KATPCOs giving focused therapeutic approaches to clinical conditions for example cardiac ischemia, urinary incontinence, neurodegeneration, obesity and autoimmune diseases. BKCa channels are found in a diverse array of tissues and due to voltage and Ca sensitivity may work as a negative feedback process. A variety of small synthetic molecules (for example, NS004, fenamates) and natural product-derived compounds (DHS-I, maxikdiol) have been identified as selective BKCa channel openers which should have a profound impact in controlling diseases. The discovery of numerous variants of the alpha subunit (ion conductance pore) and beta subunit (contributes biophysical and pharmacological properties) complex of the BKCa channel gives potential to target specific tissues with selective openers. Little is known, however, about the site(s) of interaction of openers of these channels. The discovery of K+ channel subtype-specific openers and their evaluation in different diseases will determine the degree to which these channels (KATP, BKCa), or their isoforms, represent realistic therapeutic targets. Drugs already marketed that open K+ channels were discovered empirically, and most have serious safety and efficacy problems. New scientific methods, utilizing molecular insight, are implicating K+ channel dysfunction in numerous disease states and are identifying new targets for the future generation of K+ channel opening drugs.

Effect of JTV-506, a novel vasodilator, on experimental angina model in rats

The antianginal effects of JTV-506, a newly synthesized 2,2-bis-methoxymethyl benzopyran-derivative potassium channel opener, were evaluated in experimental angina models in rats and compared with those of levcromakalim, nicorandil, and nifedipine. JTV-506 (0.01-0.1 mg/kg, i.d.) dose-dependently inhibited S-wave elevation induced by injection of methacholine but caused almost no changes in blood pressure or heart rate. Other vasodilators including levcromakalim, nicorandil, and nifedipine, when administered intraduodenally, also inhibited the S-wave elevation and elicited a decrease in blood pressure. Oral administration of JTV-506 (1 and 3 mg/kg), levcromakalim (1 and 3 mg/kg), and nicorandil (30 mg/kg) significantly inhibited the S-wave depression induced by intravenous administration of arginine vasopressin (AVP). Thus JTV-506 exerts a potent protective effect on angina pectoris models to an extent similar to those of levcromakalim, nicorandil, and nifedipine, whereas its action on systemic blood pressure is different from that of other vasodilators, including reference potassium channel openers. These results suggest that JTV-506 may clinically be useful as an antianginal agent.