NS19504: A Novel BK Channel Activator with Relaxing Effect on Bladder Smooth Muscle Spontaneous Phasic Contractions

Abstract

Large-conductance Ca 21 -activated K 1 channels (BK, K Ca 1.1, MaxiK) are important regulators of urinary bladder function and may be an attractive therapeutic target in bladder disorders. In this study, we established a high-throughput fluorometric imaging plate reader-based screening assay for BK channel activators and identified a small-molecule positive modulator, NS19504 (5-[(4-bromophenyl)methyl]-1,3-thiazol-2-amine), which activated the BK channel with an EC 50 value of 11.0 6 1.4 mM. Hit validation was performed using high-throughput electrophysiology (QPatch), and further characterization was achieved in manual whole-cell and inside-out patch-clamp studies in human embryonic kidney 293 cells expressing hBK channels: NS19504 caused distinct activation from a concentration of 0.3 and 10 mM NS19504 left-shifted the voltage activation curve by 60 mV. Furthermore, whole-cell recording showed that NS19504 activated BK channels in native smooth muscle cells from guinea pig urinary bladder. In guinea pig urinary bladder strips, NS19504 (1 mM) reduced spontaneous phasic contractions, an effect that was significantly inhibited by the specific BK channel blocker iberiotoxin. In contrast, NS19504 (1 mM) only modestly inhibited nerve-evoked contractions and had no effect on contractions induced by a high K 1 concentration consistent with a K 1 channel-mediated action. Collectively, these results show that NS19504 is a positive modulator of BK channels and provide support for the role of BK channels in urinary bladder function. The pharmacologic profile of NS19504 indicates that this compound may have the potential to reduce nonvoiding contractions associated with spontaneous bladder overactivity while having a minimal effect on normal voiding.

Vasodilation of rat skeletal muscle arteries by the novel BK channel opener GoSlo is mediated by the simultaneous activation of BK and Kv7 channels

“…The response to GoSlo‐SR‐5‐6 (10 −5 M) was not blocked by the selective BK channel blocker IBTX (Figure d,g) and penitrem A (10 −7 M, Figure f,g; Knaus et al, ) or low concentrations of the non‐selective K + channel blocker TEA (1 × 10 −3 M, Figure e; Nelson & Quayle, ). A similar observation was made for another BK channel opener, NS19504 (Nausch et al, ), which induced relaxation not affected by IBTX (10 −7 M) and paxilline (10 −7 M; Figure h).…”

“…Given these important roles, BK channels have been targeted in a number of drug development programmes (reviewed in Kaczorowski & Garcia, ). Many different BK channel openers have been discovered (dehydrosoyasaponin 1, McManus et al, ; Maxikdiol, Singh et al, ; DiBAC 4 , Morimoto et al, ) or synthesised including NS1619 (Holland, Langton, Standen, & Boyle, ; Olesen, Munch, Moldt, & Drejer, ), the pimaranes (Imaizumi et al, ), NS11021 (Bentzen et al, ) and NS19504 (Nausch et al, ). Recently, a more efficacious family of BK channel openers called the GoSlo‐SR compounds have been developed (Roy et al, ; Roy et al, ).…”

BK channel activators and their therapeutic perspectives

“…Subunit dependent potency and efficacy was also recently demonstrated for a series of N-arylbenzamide, with loss of effect when β-1 subunits were co-expressed (Kirby et al, 2013 ). We recently reported a novel positive BK channel modulator, NS19504 identified in a HTS FLIPR screen (Nausch et al, 2014 ). This compound represent a novel chemical scaffold and was observed to activate endogenous BK channels in native smooth muscle cells from guinea pig bladder, and to reduce spontaneous contractions in bladder strips in an iberiotoxin-sensitive manner.…”

Effects of the novel BK (KCa1.1) channel opener GoSlo‐SR‐5‐130 are dependent on the presence of BKβ subunits

“…BK channels are therefore attractive targets for novel drugs and over the past two decades a number of small‐molecule BK channel modulators have been developed (Argentieri and Butera, ; Nardi et al ., ; Garcia et al ., ; Nardi and Olesen, 2007; 2008). These include the Neurosearch compounds, NS1608 (Strøbaek et al ., ), NS1619 (Olesen et al ., ) and more recently NS19504 (Nausch et al ., ). However, no BK channel opener has yet progressed to market as a therapeutic treatment.…”