Synthesis and characterization of a novel tritiated K_ATP channel opener with a benzopyran structure

Abstract

The synthesis of a tritiated benzopyran‐type opener of the ATP‐dependent K+ channel (KATP channel), [3H]‐PKF217 – 744 {(3S,4R)‐N‐[3,4‐dihydro‐2,2‐dimethyl‐3‐hydroxy‐6‐(2‐methyl‐4‐pyridinyl)‐2H‐1‐benzopyran‐4‐yl]‐3‐[2,6‐3H]pyridinecarboxamide} with a specific activity of 50 Ci mmol−1 is described. Binding of the ligand was studied in membranes from human embryonic kidney cells transfected with the sulphonylurea receptor isoforms, SUR2B and SUR2A, respectively. PKF217 – 744 was confirmed as being a KATP channel opener by its ability to open the Kir6.1/SUR2B channel, the recombinant form of the vascular KATP channel, and to inhibit binding of the pinacidil analogue, [3H]‐P1075, to SUR2B (Ki=26 nM). The kinetics of [3H]‐PKF217 – 744 binding to SUR2B was described by rate constants of association and dissociation of 6.9×106 M−1 min−1 and 0.09 min−1, respectively. Binding of [3H]‐PKF217 – 744 to SUR2B/2A was activated by MgATP (EC50∼3 μM) and inhibited (SUR2B) or enhanced (SUR2A) by MgADP. Binding of [3H]‐PKF217 – 744 to SUR2B was inhibited by representatives of the different structural classes of openers and sulphonylureas. Ki values were identical with those obtained using the opener [3H]‐P1075 as the radioligand. Glibenclamide accelerated dissociation of the SUR2B‐[3H]‐PKF217 – 744 complex. The data show that the affinity of [3H]‐PKF217 – 744 binding to SUR2B is ∼6 times lower than that of [3H]‐P1075. This is due to a surprisingly slow association rate of the benzopyran‐type ligand, suggesting a complex mechanism of opener binding to SUR. The other pharmacological properties of the two opener radioligands are identical. British Journal of Pharmacology (2001) 133, 275–285; doi:10.1038/sj.bjp.0704071

[125I]A-312110, a Novel High-Affinity 1,4-Dihydropyridine ATP-sensitive K+Channel Opener: Characterization and Pharmacology of Binding

“…The affinity for inhibition of [ 125 I]A-312110 binding to bladder membranes by glyburide (K i ϭ 3.7 M) is comparable with that reported for SUR2B-expressing K ATP channels using either [ 3 H]P1075 (K i ϭ 2.8 M; Hambrock et al, 1999) Manley et al, 2001). The precise nature of these cardiac high-and low-affinity antagonist sites remains to be elucidated, although it is likely that they may emerge from interactions with multiple SUR subtypes or discrete combinations of SURs with K IR 6.1 or 6.2 subunits.…”

“…3 H]PKF217-744, has emerged (Manley et al, 2001). Although the pharmacological profile of this novel ligand compares well with studies using [ 3 H]P1075, the affinity of [ 3 H]PKF217-744 is about 20-fold lower than [ 3 H]P1075.…”

KCO912: a potent and selective opener of ATP-dependent potassium (K ATP ) channels which suppresses airways hyperreactivity at doses devoid of cardiovascular effects

“…They are closed by the hypoglycaemic sulphonylureas exemplified by glibenclamide (Coghlan et al 2001;Fozard and Manley 2001). Both classes of compounds elicit their effects by binding to the SUR subunit of the channel (Hambrock et al 1998Schwanstecher et al 1998;Manley et al 2001).…”

Interaction of a novel dihydropyridine K+ channel opener, A‐312110, with recombinant sulphonylurea receptors and KATP channels: comparison with the cyanoguanidine P1075

“…A‐312110 carries an iodine and, after radioiodination, was shown to specifically bind to K ATP channels in membranes from guinea‐pig heart and bladder, with K D values of 5.8 and 4.9 n M , respectively. The high affinity and high specific activity (2000 Ci mmol −1 ) make [ 125 I]A‐312110 a very valuable addition to the other well‐characterised radiolabelled openers, which are both tritiated, for example, the cyanoguanidine [ 3 H] P1075 (Bray & Quast, 1992; Manley et al , 1993 ) and the benzopyran [ 3 H]217‐774 ( Manley et al , 2001 ). It was the aim of this study to compare the binding and the channel‐opening properties of A‐312110 to those of the standard cyanoguanidine opener P1075 in human embryonic kidney (HEK) 293 cells expressing recombinant SURx and Kir6.2.…”