Selective, Direct Activation of High-Conductance, Calcium-Activated Potassium Channels Causes Smooth Muscle Relaxation

Abstract

High-conductance calcium-activated potassium (Maxi-K) channels are present in smooth muscle where they regulate tone. Activation of Maxi-K channels causes smooth muscle hyperpolarization and shortening of action-potential duration, which would limit calcium entry through voltage-dependent calcium channels leading to relaxation. Although Maxi-K channels appear to indirectly mediate the relaxant effects of a number of agents, activators that bind directly to the channel with appropriate potency and pharmacological properties useful for proof-of-concept studies are not available. Most agents identified to date display significant polypharmacy that severely compromises interpretation of experimental data. In the present study, a high-throughput, functional, cell-based assay for identifying Maxi-K channel agonists was established and used to screen a large sample collection (Ͼ1.6 million compounds). On the basis of potency and selectivity, a family of tetrahydroquinolines was further characterized. Medicinal chemistry efforts afforded identification of compound X, from which its two enantiomers, Y and Z, were resolved. In in vitro assays, Z is more potent than Y as a channel activator. The same profile is observed in tissues where the ability of either agent to relax precontracted smooth muscles, via a potassium channeldependent mechanism, is demonstrated. These data, taken together, suggest that direct activation of Maxi-K channels represents a mechanism to be explored for the potential treatment of a number of diseases associated with smooth muscle hyperexcitability.

Cerebrovascular Dilation via Selective Targeting of the Cholane Steroid-Recognition Site in the BK Channel β1-Subunit by a Novel Nonsteroidal Agent

“…For example, the voltage-sensitive oxonol dye and related analogs can activate b1-containing and neuronally abundant, b4-containing BK channels (Morimoto et al, 2007) [4-chloro-7-(trifluoromethyl)-10H-benzofuro[3,2-b]indole-1-carboxylic acid], and the tetrahydroquinoline termed compound Z [(3aR,4S,9bS)-4-(Naphthalen-1-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline-8-carboxylic acid] (Lee et al, 2012;Ponte et al, 2012) all induce BK channel activation in absence of BK b1, with drug action being likely mediated by the ubiquitously distributed BK a subunit. It remains unknown whether NS1619 amido derivatives promote relaxation of KClprecontracted isolated thoracic aortic rings via BK b1 subunits (Calderone et al, 2008).…”

Novel cell-free high-throughput screening method for pharmacological tools targeting K + channels

“…. Human mutations that cause asthma and mouse genetic and pharmacological studies suggest that Slo1 activators might provide benefit in the treatment of asthma, hypertension and over-reactive bladder (9)(10)(11)(12)(13)(14)(15). We thus applied LFA to the Slo1 channel to identify molecules that would open the channel.…”

“…The hERG channel is the dangerous off-target of many drugs that, by inadvertently inhibiting hERG, cause drug-induced long QT syndrome with the potential of torsades de pointes and sudden death (8). High-conductance Ca 2+ -activated K + (Slo1) channel of the K Ca subfamily regulates smooth muscle contraction, and activators of the Slo1 channel are drug candidates for asthma, over-reactive bladder, and hypertension (9)(10)(11)(12)(13)(14)(15). These channels are just a small subset of examples illustrating the important roles of K + channels to different physiological functions.…”

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

“…More recent studies have identified the bisarylthiourea NS11021 [5-(2-{3-[3,5-bis(trifluoromethyl) phenyl]thioureido}-5-bromophenyl)-1H-1,2,3,4-tetrazole], the oxindole BMS-204352 [(3S)-3-(5-chloro-2-methoxyphenyl)-3-fluoro-6-(trifluoromethyl)-2-indolinone], the natural modulator dihydrosoyasaponin-1 (for review, see Ghatta et al, 2006;Nardi and Olesen, 2008), the GoSlo-SR family of anthraquinone analogs (Roy et al, 2012(Roy et al, , 2014, as well as the tetrahydroquinoline racemate "X" and its two enantiomers "Y" and "Z" (Ponte et al, 2012). Several of these modulators have shown activity in pharmacological studies in ex vivo organ bath studies using bladder strips (Imai et al, 2001;Tanaka et al, 2003;Malysz et al, 2004; Mora and Suarez-Kurtz, 2005; Ponte et al, 2012).…”