Novel KV7 ion channel openers for the treatment of epilepsy and implications for detrusor tissue contraction

Potassium channels in behavioral brain disorders. Molecular mechanisms and therapeutic potential: A narrative review

Potassium channels (K+-channels) selectively control the passive flow of potassium ions across biological membranes and thereby also regulate membrane excitability. Genetic variants affecting many of the human K+-channels are well known causes of Mendelian disorders within cardiology, neurology, and endocrinology. K+-channels are also primary targets of many natural toxins from poisonous organisms and drugs used within cardiology and metabolism. As genetic tools are improving and larger clinical samples are being investigated, the spectrum of clinical phenotypes implicated in K+-channels dysfunction is rapidly expanding, notably within immunology, neurosciences, and metabolism. K+-channels that previously were considered to be expressed in only a few organs and to have discrete physiological functions, have recently been found in multiple tissues and with new, unexpected functions. The pleiotropic functions and patterns of expression of K+-channels may provide additional therapeutic opportunities, along with new emerging challenges from off-target effects. Here we review the functions and therapeutic potential of K+-channels, with an emphasis on the nervous system, roles in neuropsychiatric disorders and their involvement in other organ systems and diseases.

The novel KV7 channel activator URO-K10 exerts enhanced pulmonary vascular effects independent of the KCNE4 regulatory subunit

KV7 channels exert a pivotal role regulating vascular tone in several vascular beds. In this context, KV7 channel agonists represent an attractive strategy for the treatment of pulmonary arterial hypertension (PAH). Therefore, in this study, we have explored the pulmonary vascular effects of the novel KV7 channel agonist URO-K10. Consequently, the vasodilator and electrophysiological effects of URO-K10 were tested in rat and human pulmonary arteries (PA) and PA smooth muscle cells (PASMC) using myography and patch-clamp techniques. Protein expression was also determined by Western blot. Morpholino-induced knockdown of KCNE4 was assessed in isolated PA. PASMC proliferation was measured by BrdU incorporation assay. In summary, our data show that URO-K10 is a more effective relaxant of PA than the classical KV7 activators retigabine and flupirtine. URO-K10 enhanced KV currents in PASMC and its electrophysiological and relaxant effects were inhibited by the KV7 channel blocker XE991. The effects of URO-K10 were confirmed in human PA. URO-K10 also exhibited antiproliferative effects in human PASMC. Unlike retigabine and flupirtine, URO-K10-induced pulmonary vasodilation was not affected by morpholino-induced knockdown of the KCNE4 regulatory subunit. Noteworthy, the pulmonary vasodilator efficacy of this compound was considerably increased under conditions mimicking the ionic remodelling (as an in vitro model of PAH) and in PA from monocrotaline-induced pulmonary hypertensive rats. Taking all together, URO-K10 behaves as a KCNE4-independent KV7 channel activator with much increased pulmonary vascular effects compared to classical KV7 channel activators. Our study identifies a promising new drug in the context of PAH.

A Role for KCNQ Channels on Cell Type-Specific Plasticity in Mouse Auditory Cortex after Peripheral Damage

Damage to sensory organs triggers compensatory plasticity mechanisms in sensory cortices. These plasticity mechanisms result in restored cortical responses, despite reduced peripheral input, and contribute to the remarkable recovery of perceptual detection thresholds to sensory stimuli. Overall, peripheral damage is associated with a reduction of cortical GABAergic inhibition; however, less is known about changes in intrinsic properties and the underlying biophysical mechanisms. To study these mechanisms, we used a model of noise-induced peripheral damage in male and female mice. We uncovered a rapid, cell type-specific reduction in the intrinsic excitability of parvalbumin-expressing neurons (PVs) in layer (L) 2/3 of auditory cortex. No changes in the intrinsic excitability of either L2/3 somatostatin-expressing or L2/3 principal neurons (PNs) were observed. The decrease in L2/3 PV excitability was observed 1, but not 7, d after noise exposure, and was evidenced by a hyperpolarization of the resting membrane potential, depolarization of the action potential threshold, and reduction in firing frequency in response to depolarizing current. To uncover the underlying biophysical mechanisms, we recorded potassium currents. We found an increase in KCNQ potassium channel activity in L2/3 PVs of auditory cortex 1 d after noise exposure, associated with a hyperpolarizing shift in the minimal voltage activation of KCNQ channels. This increase contributes to the decreased intrinsic excitability of PVs. Our results highlight cell-type- and channel-specific mechanisms of plasticity after noise-induced hearing loss and will aid in understanding the pathologic processes involved in hearing loss and hearing loss-related disorders, such as tinnitus and hyperacusis.SIGNIFICANCE STATEMENT Noise-induced damage to the peripheral auditory system triggers central plasticity that compensates for the reduced peripheral input. The mechanisms of this plasticity are not fully understood. In the auditory cortex, this plasticity likely contributes to the recovery of sound-evoked responses and perceptual hearing thresholds. Importantly, other functional aspects of hearing do not recover, and peripheral damage may also lead to maladaptive plasticity-related disorders, such as tinnitus and hyperacusis. Here, after noise-induced peripheral damage, we highlight a rapid, transient, and cell type-specific reduction in the excitability of layer 2/3 parvalbumin-expressing neurons, which is due, at least in part, to increased KCNQ potassium channel activity. These studies may highlight novel strategies for enhancing perceptual recovery after hearing loss and mitigating hyperacusis and tinnitus.

The Effectiveness in Activating M-Type K+ Current Produced by Solifenacin ([(3R)-1-azabicyclo[2.2.2]octan-3-yl] (1S)-1-phenyl-3,4-dihydro-1H-isoquinoline-2-carboxylate): Independent of Its Antimuscarinic Action

Solifenacin (Vesicare^®, SOL), known to be a member of isoquinolines, is a muscarinic antagonist that has anticholinergic effect, and it has been beneficial in treating urinary incontinence and neurogenic detrusor overactivity. However, the information regarding the effects of SOL on membrane ionic currents is largely uncertain, despite its clinically wide use in patients with those disorders. In this study, the whole-cell current recordings revealed that upon membrane depolarization in pituitary GH₃ cells, the exposure to SOL concentration-dependently increased the amplitude of M-type K⁺ current (I_K(M)) with effective EC₅₀ value of 0.34 μM. The activation time constant of I_K(M) was concurrently shortened in the SOL presence, hence yielding the K_D value of 0.55 μM based on minimal reaction scheme. As cells were exposed to SOL, the steady-state activation curve of I_K(M) was shifted along the voltage axis to the left with no change in the gating charge of the current. Upon an isosceles-triangular ramp pulse, the hysteretic area of I_K(M) was increased by adding SOL. As cells were continually exposed to SOL, further application of acetylcholine (1 μM) failed to modify SOL-stimulated I_K(M); however, subsequent addition of thyrotropin releasing hormone (TRH, 1 μM) was able to counteract SOL-induced increase in I_K(M) amplitude. In cell-attached single-channel current recordings, bath addition of SOL led to an increase in the activity of M-type K⁺ (K_M) channels with no change in the single channel conductance; the mean open time of the channel became lengthened. In whole-cell current-clamp recordings, the SOL application reduced the firing of action potentials (APs) in GH₃ cells; however, either subsequent addition of TRH or linopirdine was able to reverse SOL-mediated decrease in AP firing. In hippocampal mHippoE-14 neurons, the I_K(M) was also stimulated by adding SOL. Altogether, findings from this study disclosed for the first time the effectiveness of SOL in interacting with K_M channels and hence in stimulating I_K(M) in electrically excitable cells, and this noticeable action appears to be independent of its antagonistic activity on the canonical binding to muscarinic receptors expressed in GH₃ or mHippoE-14 cells.

Drug treatment of epilepsy: From serendipitous discovery to evolutionary mechanisms

Epilepsy is a chronic brain disorder caused by abnormal firing of neurons. Up to now, using antiepileptic drugs is the main method of epilepsy treatment. The development of antiepileptic drugs lasted for centuries. In general, most agents entering clinical practice act on the balance mechanisms of brain "excitability-inhibition". More specifically, they target voltage-gated ion channels, GABAergic transmission and glutamatergic transmission. In recent years, some novel drugs representing new mechanisms of action have been discovered. Although there are about 30 available drugs in the market, it is still in urgent need of discovering more effective and safer drugs. The development of new antiepileptic drugs is into a new era: from serendipitous discovery to evolutionary mechanism-based design. This article presents an overview of drug treatment of epilepsy, including a series of traditional and novel drugs.

Discovery of HN37 as a Potent and Chemically Stable Antiepileptic Drug Candidate

We previously reported that P-retigabine (P-RTG), a retigabine (RTG) analogue bearing a propargyl group at the nitrogen atom in the linker of RTG, displayed moderate anticonvulsant efficacy. Recently, our further efforts led to the discovery of HN37 (pynegabine), which demonstrated satisfactory chemical stability upon deleting the ortho liable -NH₂ group and installing two adjacent methyl groups to the carbamate motif. HN37 exhibited enhanced activation potency toward neuronal Kv7 channels and high in vivo efficacy in a range of pre-clinical seizure models, including the maximal electroshock test and a 6 Hz model of pharmacoresistant limbic seizures. With its improved chemical stability, strong efficacy, and better safety margin, HN37 has progressed to clinical trial in China for epilepsy treatment.

Chemical modulation of Kv7 potassium channels

The rising interest in Kv7 modulators originates from their ability to evoke fundamental electrophysiological perturbations in a tissue-specific manner. A large number of therapeutic applications are, in part, based on the clinical experience with two broad-spectrum Kv7 agonists, flupirtine and retigabine. Since precise molecular structures of human Kv7 channel subtypes in closed and open states have only very recently started to emerge, computational studies have traditionally been used to analyze binding modes and direct the development of more potent and selective Kv7 modulators with improved safety profiles. Herein, the synthetic and medicinal chemistry of small molecule modulators and the representative biological properties are summarized. Furthermore, new therapeutic applications supported by in vitro and in vivo assay data are suggested.

Potassium (K+) channels in the pulmonary vasculature: Implications in pulmonary hypertension Physiological, pathophysiological and pharmacological regulation

The large K⁺ channel functional diversity in the pulmonary vasculature results from the multitude of genes expressed encoding K⁺ channels, alternative RNA splicing, the post-transcriptional modifications, the presence of homomeric or heteromeric assemblies of the pore-forming α-subunits and the existence of accessory β-subunits modulating the functional properties of the channel. K⁺ channels can also be regulated at multiple levels by different factors controlling channel activity, trafficking, recycling and degradation. The activity of these channels is the primary determinant of membrane potential (Em) in pulmonary artery smooth muscle cells (PASMC), providing an essential regulatory mechanism to dilate or contract pulmonary arteries (PA). K⁺ channels are also expressed in pulmonary artery endothelial cells (PAEC) where they control resting Em, Ca²⁺ entry and the production of different vasoactive factors. The activity of K⁺ channels is also important in regulating the population and phenotype of PASMC in the pulmonary vasculature, since they are involved in cell apoptosis, survival and proliferation. Notably, K⁺ channels play a major role in the development of pulmonary hypertension (PH). Impaired K⁺ channel activity in PH results from: 1) loss of function mutations, 2) downregulation of its expression, which involves transcription factors and microRNAs, or 3) decreased channel current as a result of increased vasoactive factors (e.g., hypoxia, 5-HT, endothelin-1 or thromboxane), exposure to drugs with channel-blocking properties, or by a reduction in factors that positively regulate K⁺ channel activity (e.g., NO and prostacyclin). Restoring K⁺ channel expression, its intracellular trafficking and the channel activity is an attractive therapeutic strategy in PH.

Kv7 Channels and Excitability Disorders

Kv7.1-Kv7.5 (KCNQ1-5) K⁺ channels are voltage-gated K⁺ channels with major roles in neurons, muscle cells and epithelia where they underlie physiologically important K⁺ currents, such as neuronal M current and cardiac I_Ks. Specific biophysical properties of Kv7 channels make them particularly well placed to control the activity of excitable cells. Indeed, these channels often work as 'excitability breaks' and are targeted by various hormones and modulators to regulate cellular activity outputs. Genetic deficiencies in all five KCNQ genes result in human excitability disorders, including epilepsy, arrhythmias, deafness and some others. Not surprisingly, this channel family attracts considerable attention as potential drug targets. Here we will review biophysical properties and tissue expression profile of Kv7 channels, discuss recent advances in the understanding of their structure as well as their role in various neurological, cardiovascular and other diseases and pathologies. We will also consider a scope for therapeutic targeting of Kv7 channels for treatment of the above health conditions.

The agonistic action of URO-K10 on Kv7.4 and 7.5 channels is attenuated by co-expression of KCNE4 ancillary subunit

KCNQ family constitutes slowly-activating potassium channels among voltage-gated potassium channel superfamily. Recent studies suggested that KCNQ4 and 5 channels are abundantly expressed in smooth muscle cells, especially in lower urinary tract including corpus cavernosum and that both channels can exert membrane stabilizing effect in the tissues. In this article, we examined the electrophysiological characteristics of overexpressed KCNQ4, 5 channels in HEK293 cells with recently developed KCNQ-specific agonist. With submicromolar EC50, the drug not only increased the open probability of KCNQ4 channel but also increased slope conductance of the channel. The overall effect of the drug in whole-cell configuration was to increase maximal whole-cell conductance, to prolongate the activation process, and left-shift of the activation curve. The agonistic action of the drug, however, was highly attenuated by the co-expression of one of the β ancillary subunits of KCNQ family, KCNE4. Strong in vitro interactions between KCNQ4, 5 and KCNE4 were found through Foster Resonance Energy Transfer and co-immunoprecipitation. Although the expression levels of both KCNQ4 and KCNE4 are high in mesenteric arterial smooth muscle cells, we found that 1 μM of the agonist was sufficient to almost completely relax phenylephrine-induced contraction of the muscle strip. Significant expression of KCNQ4 and KCNE4 in corpus cavernosum together with high tonic contractility of the tissue grants highly promising relaxational effect of the KCNQ-specific agonist in the tissue.

Uncovered Contribution of Kv7 Channels to Pulmonary Vascular Tone in Pulmonary Arterial Hypertension

K + channels play a fundamental role regulating membrane potential of pulmonary artery (PA) smooth muscle cells and their impairment is a common feature in pulmonary arterial hypertension (PAH). K + voltage-gated channel subfamily Q ( KCNQ1-5 ) or Kv7 channels and their regulatory subunits subfamily E (KCNE) regulatory subunits are known to regulate vascular tone, but whether Kv7 channel function is impaired in PAH and how this can affect the rationale for targeting Kv7 channels in PAH remains unknown. Here, we have studied the role of Kv7/KCNE subunits in rat PA and their possible alteration in PAH. Using the patch-clamp technique, we found that the total K + current is reduced in PA smooth muscle cells from pulmonary hypertension animals (SU5416 plus hypoxia) and Kv7 currents made a higher contribution to the net K + current. Likewise, enhanced vascular responses to Kv7 channel modulators were found in pulmonary hypertension rats. Accordingly, KCNE4 subunit was highly upregulated in lungs from pulmonary hypertension animals and patients. Additionally, Kv7 channel activity was enhanced in the presence of Kv1.5 and TASK-1 channel inhibitors and this was associated with an increased KCNE4 membrane abundance. Compared with systemic arteries, PA showed a poor response to Kv7 channel modulators which was associated with reduced expression and membrane abundance of Kv7.4 and KCNE4. Our data indicate that Kv7 channel function is preserved and KCNE4 is upregulated in PAH. Therefore, compared with other downregulated channels, the contribution of Kv7 channels is increased in PAH resulting in an enhanced sensitivity to Kv7 channel modulators. This study provides insight into the potential usefulness of targeting Kv7 channels in PAH.

Detrusor Smooth Muscle KV7 Channels: Emerging New Regulators of Urinary Bladder Function

Relaxation and contraction of the urinary bladder smooth muscle, also known as the detrusor smooth muscle (DSM), facilitate the micturition cycle. DSM contractility depends on cell excitability, which is established by the synchronized activity of multiple diverse ion channels. K+ channels, the largest family of channels, control DSM excitability by maintaining the resting membrane potential and shaping the action potentials that cause the phasic contractions. Among the members of the voltage-gated K+ (KV) channel superfamily, KV type 7 (KV7) channels - KV7.1-KV7.5 members encoded by KCNQ1-KCNQ5 genes - have been recently identified as functional regulators in various cell types including vascular, cardiac, and neuronal cells. Their regulatory roles in DSM, however, are just now emerging and remain to be elucidated. To address this gap, our research group has initiated the systematic investigation of human DSM KV7 channels in collaboration with clinical urologists. In this comprehensive review, we summarize the current understanding of DSM Kv7 channels and highlight recent discoveries in the field. We describe KV7 channel expression profiles at the mRNA and protein levels, and further elaborate on functional effects of KV7 channel selective modulators on DSM excitability, contractility, and intracellular Ca2+ dynamics in animal species along with in vivo studies and the limited data on human DSM. Within each topic, we highlight the main observations, current gaps in knowledge, and most pressing questions and concepts in need of resolution. We emphasize the lack of systematic studies on human DSM KV7 channels that are now actively ongoing in our laboratory.

Urinary bladder smooth muscle ion channels: expression, function, and regulation in health and disease

Urinary bladder smooth muscle (UBSM), also known as detrusor smooth muscle, forms the bladder wall and ultimately determines the two main attributes of the organ: urine storage and voiding. The two functions are facilitated by UBSM relaxation and contraction, respectively, which depend on UBSM excitability shaped by multiple ion channels. In this review, we summarize the current understanding of key ion channels establishing and regulating UBSM excitability and contractility. They include excitation-enhancing voltage-gated Ca2+ (Cav) and transient receptor potential channels, excitation-reducing K+ channels, and still poorly understood Cl- channels. Dynamic interplay among UBSM ion channels determines the overall level of Cav channel activity. The net Ca2+ influx via Cav channels increases global intracellular Ca2+ concentration, which subsequently triggers UBSM contractility. Here, for each ion channel type, we describe UBSM tissue/cell expression (mRNA and protein) profiles and their role in regulating excitability and contractility of UBSM in various animal species, including the mouse, rat, and guinea pig, and, most importantly, humans. The currently available data reveal certain interspecies differences, which complicate the translational value of published animal research results to humans. This review highlights recent developments, findings on genetic knockout models, pharmacological data, reports on UBSM ion channel dysfunction in animal bladder disease models, and the very limited human studies currently available. Among all gaps in present-day knowledge, the unknowns on expression and functional roles for ion channels determined directly in human UBSM tissues and cells under both normal and disease conditions remain key hurdles in the field.

Synthesis and Optimization of Kv7 (KCNQ) Potassium Channel Agonists: The Role of Fluorines in Potency and Selectivity

Based on the potent K_v7 agonist RL-81, we prepared new lead structures with greatly improved selectivity for K_v7.2/K_v7.3 over related potassium channels, i.e., K_v7.3/K_v7.5, K_v7.4, and K_v7.4/7.5. RL-36 and RL-12 maintain an agonist EC_2x of ca. 1 μM on K_v7.2/K_v7.3 in a high-throughput assay on an automated electrophysiology platform in HEK293 cells but lack activity on K_v7.3/K_v7.5, K_v7.4, and K_v7.4/7.5, resulting in a selectivity index SI > 10. RL-56 is remarkably potent, EC_2x 0.11 ± 0.02 μM, and still shows an SI = 2.5. We also identified analogues with significant selectivity for K_v7.4/K_v7.5 over K_v7.2/K_v7.3. The extensive use of fluorine in iterative core structure modifications highlights the versatility of these substituents, including F, CF₃, and SF₅, to span orders of magnitude of potency and selectivity in medicinal chemistry lead optimizations.

Ion Channel Expression in Human Melanoma Samples: In Silico Identification and Experimental Validation of Molecular Targets

Expression of 328 ion channel genes was investigated, by in silico analysis, in 170 human melanoma samples and controls. Ninety-one members of this gene-family (i.e., about 28%) show a significant (p < 0.05) differential expression in melanoma- vs. nevi-biopsies, taken from the GEO database. ROC (receiver operating characteristic) analysis selected 20 genes as potential markers showing the highest discrimination ability of melanoma vs. nevi (AUC > 0.90 and p < 0.0001). These 20 genes underwent a first in silico-validation round in an independent patients-dataset from GEO. A second-in silico-validation step was then carried out on a third human dataset in Oncomine. Finally, five genes were validated, showing extremely high sensitivity and specificity in melanoma detection (>90% in most cases). Such five genes (namely, SCNN1A, GJB3, KCNK7, GJB1, KCNN2) are novel potential melanoma markers or molecular targets, never previously related to melanoma. The “druggable genome” analysis was then carried out. Miconazole, an antifungal drug commonly used in clinics, is known to target KCNN2, the best candidate among the five identified genes. Miconazole was then tested in vitro in proliferation assays; it dose-dependently inhibited proliferation up to 90% and potently induced cell-death in A-375 and SKMEL-28 melanoma cells, while it showed no effect in control cells. Moreover, specific silencing of KCNN2 ion channel was achieved by siRNA transfection; under such condition miconazole strongly increases its anti-proliferative effect. In conclusion, the present study identified five ion channels that can potentially serve as sensitive and specific markers in human melanoma specimens and demonstrates that the antifungal drug miconazole, known to target one of the five identified ion channels, exerts strong and specific anti-melanoma effects in vitro.