From pan-reactive KV7 channel opener to subtype selective opener/inhibitor by addition of a methyl group.

The voltage-gated potassium channels of the KV7 family (KV7.1-5) play important roles in controlling neuronal excitability and are therefore attractive targets for treatment of CNS disorders linked to hyperexcitability. One of the main challenges in developing KV7 channel active drugs has been to identify compounds capable of discriminating between the neuronally expressed subtypes (KV7.2-5), aiding the identification of the subunit composition of KV7 currents in various tissues, and possessing better therapeutic potential for particular indications. By taking advantage of the structure-activity relationship of acrylamide KV7 channel openers and the effects of these compounds on mutant KV7 channels, we have designed and synthesized a novel KV7 channel modulator with a unique profile. The compound, named SMB-1, is an inhibitor of KV7.2 and an activator of KV7.4. SMB-1 inhibits KV7.2 by reducing the current amplitude and increasing the time constant for the slow component of the activation kinetics. The activation of KV7.4 is seen as an increase in the current amplitude and a slowing of the deactivation kinetics. Experiments studying mutant channels with a compromised binding site for the KV7.2-5 opener retigabine indicate that SMB-1 binds within the same pocket as retigabine for both inhibition of KV7.2 and activation of KV7.4. SMB-1 may serve as a valuable tool for KV7 channel research and may be used as a template for further design of better subtype selective KV7 channel modulators. A compound with this profile could hold novel therapeutic potential such as the treatment of both positive and cognitive symptoms in schizophrenia

Activation of K_V7.4 by SMB-1.

<p>(<b>A</b>) Representative current traces for K_V7.4 in the absence and presence of 10 µM SMB-1. (<b>B</b>) Effect of SMB-1 on current-voltage relationship. (<b>C</b>) Effect of SMB-1 on voltage-dependence of activation. (<b>D</b>) Effect of SMB-1 on deactivation kinetics. Statistical significance was determined by paired, two-tailed Student's <i>t</i>-test. Representative tail current traces in the absence and presence of 10 µM SMB-1 are shown in the inset. (<b>E</b>) Effect of SMB-1 on activation kinetics. Statistical significance was determined by two-way repeated measurements ANOVA followed by Bonferroni post-test. (<b>F</b>) Dose-response relationship of SMB-1 on K_V7.4. *** <i>p<</i>0.001. Bars represent S.E.M and <i>n = </i>5–8.</p

Effect of SMB-1 on K_V7.4-W242L.

<p>(<b>A</b>) Representative current traces for K_V7.4-W242L in the absence and presence of 10 µM SMB-1. (<b>B</b>) Effect of SMB-1 on current-voltage relationship. (<b>C</b>) Effect of SMB-1 on voltage-dependence of activation. (<b>D</b>) Effect of SMB-1 on deactivation kinetics. Statistical significance was determined by paired, two-tailed Student's <i>t</i>-test. Representative tail current traces in the absence and presence of 10 µM SMB-1 are shown in the inset (note that the traces are completely overlapping). (<b>E</b>) Effect of SMB-1 on activation kinetics. Statistical significance was determined by two-way repeated measurements ANOVA followed by Bonferroni post-test. Bars represent S.E.M and <i>n = </i>5.</p

Effect of SMB-1 on channels with mutations in the refined retigabine binding site.

<p>Effect of 10 µM SMB-1 on the current-voltage relationship of (A) K_V7.2-L275V, (B) K_V7.2-L299V and (C) K_V7.4-L305V. Bars represent S.E.M. and <i>n = </i>4–6.</p

Inhibition of K_V7.2 by SMB-1.

<p>Chemical structure of (S)-2 (<b>A</b>) and SMB-1 (<b>B</b>). (<b>C</b>) Representative current traces for K_V7.2 in the absence and presence of 10 µM SMB-1 (<b>D</b>) Effect of SMB-1 on current-voltage relationship. (<b>E</b>) Effect of SMB-1 on voltage-dependence of activation. (<b>F</b>) Effect of SMB-1 on deactivation kinetics. Statistical significance was determined by paired, two-tailed Student's <i>t</i>-test. Representative tail current traces in the absence and presence of 10 µM SMB-1 are shown in the inset. Effect of SMB-1 on the fast (<b>G</b>) and slow (<b>H</b>) component of the activation kinetics. Statistical significance was determined by two-way repeated measurements ANOVA followed by Bonferroni post-test. Y-values were log-transformed before the statistical analysis to meet the assumption of normality. (<b>I</b>) Dose-response relationship for the effect of SMB-1 on K_V7.2. *** <i>p<</i>0.001. Bars represent S.E.M and <i>n = </i>5–9. Note that the error bars in some instances are too small to be visible.</p

Effect of SMB-1 on K_V7.2-W236L.

<p>(<b>A</b>) Representative current traces for K_V7.2-W236L in the absence and presence of 10 µM SMB-1 (<b>B</b>) Effect of SMB-1 on current-voltage relationship. (<b>C</b>) Effect of SMB-1 on voltage-dependence of activation. (<b>D</b>) Effect of SMB-1 on deactivation kinetics. Statistical significance was determined by paired, two-tailed Student's <i>t</i>-test. Representative tail current traces in the absence and presence of 10 µM SMB-1 are shown in the inset. Effect of SMB-1 on the fast (<b>E</b>) and slow (<b>F</b>) component of the activation kinetics. Statistical significance was determined by two-way repeated measurements ANOVA followed by Bonferroni post-test. Y-values were log-transformed before the statistical analysis to meet the assumption of normality. * <i>p<</i>0.05, ** <i>p<</i>0.01, *** <i>p<</i>0.001. Bars represent S.E.M and <i>n = </i>4–6.</p

Plasma and brain exposure of SMB-1 in rats following subcutaneous administration of 20 mg/kg.

<p>Data shown as mean total concentrations ± S.E.M (n = 3).</p