Structural Insights into the Atomistic Mechanisms of Action of Small Molecule Inhibitors Targeting the KCa3.1 Channel Pore

Design and structural basis of selective 1,4-dihydropyridine inhibitors of the calcium-activated potassium channel KCa3.1

The 1,4-dihydropyridines, drugs with well-established bioavailability and toxicity profiles, have proven efficacy in treating human hypertension, peripheral vascular disorders, and coronary artery disease. Every 1,4-dihydropyridine in clinical use blocks L-type voltage-gated calcium channels. We now report our development, using selective optimization of a side activity (SOSA), of a class of 1,4-dihydropyridines that selectively and potently inhibit the intermediate-conductance calcium-activated K+ channel KCa3.1, a validated therapeutic target for diseases affecting many organ systems. One of these 1,4-dihydropyridines, DHP-103, blocked KCa3.1 with an IC50 of 6 nM and exhibited exquisite selectivity over calcium channels and a panel of >100 additional molecular targets. Using high-resolution structure determination by cryogenic electron microscopy together with mutagenesis and electrophysiology, we delineated the drug binding pocket for DHP-103 within the water-filled central cavity of the KCa3.1 channel pore, where bound drug directly impedes ion permeation. DHP-103 inhibited gain-of-function mutant KCa3.1 channels that cause hereditary xerocytosis, suggesting its potential use as a therapeutic for this hemolytic anemia. In a rat model of acute ischemic stroke, the second leading cause of death worldwide, DHP-103 administered 12 h postischemic insult in proof-of-concept studies reduced infarct volume, improved balance beam performance (measure of proprioception) and decreased numbers of activated microglia in infarcted areas. KCa3.1-selective 1,4-dihydropyridines hold promise for the many diseases for which KCa3.1 has been experimentally confirmed as a therapeutic target.

6,7-Dichloro-1H-indole-2,3-dione-3-oxime functions as a superagonist for the intermediate-conductance Ca2+-activated K+ channel KCa3.1

NS309 (6,7-dichloro-1H-indole-2,3-dione-3-oxime) is widely used as a pharmacological tool to increase the activity of small- and intermediate-conductance calcium-activated potassium channels. NS309 is assumed to function as a positive allosteric gating modulator. However, its binding site and the molecular details of its action remain unknown. Here, we show that NS309 has a profound effect on the calcium-dependent gating of the intermediate-conductance Ca2+-activated K+ channel KCa3.1. In inside-out experiments, 10 μM NS309 shifted the calcium EC50 from 430 to 31 nM. In whole-cell experiments, changing free intracellular calcium from 250 nM to 3 μM decreased the EC50 of NS309 from 74 to 8.6 nM. We further observed that NS309 could elicit greater responses than saturating calcium, making it a "superagonist." Molecular modeling suggested 2 possible binding sites for NS309 in KCa3.1, which we probed by mutagenesis and determined that NS309 is binding in the interface between the S45A segment of the intracellular S4-S5 linker and the N-lobe of the channel-associated calmodulin. Molecular dynamic simulations revealed that NS309 pushes several water molecules out of the interface pocket, establishes stable contacts with S181 and L185 in the S45A segment of KCa3.1 and E54 in calmodulin, and promotes longer sustained widening of the inner gate of KCa3.1 at V282 in the S6 segment. Polar substitutions of the hydrophobic-gating residues V282 and A279 resulted in constitutively open channels that could not be further potentiated by NS309, suggesting that NS309 produces its agonistic effects by increasing the open probability of the inner gate of KCa3.1. SIGNIFICANCE STATEMENT: The publication of the full-length cryo-electron microscopy structure of the intermediate-conductance Ca2+-activated K+ channel KCa3.1 suggested that the previously reported binding site of NS309 (6,7-dichloro-1H-indole-2,3-dione-3-oxime) was a crystallization artifact because this structure only included the C-terminus and the channel-associated calmodulin. This study demonstrates that the true binding site of NS309 is located between the S4 and S5 linker of KCa3.1 and the N-lobe of calmodulin. NS309 acts as a stabilizing force within the gating interface and increases the open probability of the inner hydrophobic gate.

Fluorescent Probes to Image the KCa3.1 Channel in Tumor Cells

Background/Objectives: The Ca2+-activated K+ channel KCa3.1 is not only involved in physiological processes such as immune reactions and control of vascular tone, but is highly expressed in various tumor entities. Thus, imaging of KCa3.1 channels comes into focus for the localization of high channel density, i.e., for tumor diagnosis. In particular, the physicochemical properties of the fluorescent probes should be improved compared to existing probes. Methods: The small molecule inhibitor of the KCa3.1 channel, senicapoc, was used as a warhead and was coupled with different fluorescent dyes. After synthesis of the novel probes, their physicochemical properties (lipophilicity, photophysical properties) and their ability to image KCa3.1 channels in A549-3R lung tumor cells were determined. Results: In order to increase the polarity and quantum yield of reported fluorescent probes, three strategies were followed: (1) An F-atom at the B-atom of bodipy-labeled senicapoc derivatives 9a, 9b, and 15a was replaced by a OCH3 moiety, which decreased the logP value by one log-unit. (2) The p-phenylene moiety of the linker was replaced by an aliphatic tetramethylene linker decreasing the lipophilicity by 0.3-0.5 log-units. (3) Instead of bodipy dyes, fluorescein was coupled with the senicapoc warhead resulting in very polar probes 21a and 21b with low logP values of 1.5 and 1.3, respectively. Introduction of an ethyl moiety at the bodipy core increased the quantum yield, which resulted in the best punctate staining pattern of fixed and living A549-3R lung tumor cells with the ethylbodipy-labeled senicapoc derivative 10b. The specificity was shown by various control experiments. Co-staining with 10b and an antibody did not result in overlapping signals. Conclusions: The well-balanced lipophilicity and fluorescent quantum yield render the ethylbodipy-labeled senicapoc derivative 10b a very good probe to image selectively KCa3.1 ion channels in fixed and living tumor cells. It was hypothesized that the antibody binds selectively at the closed channel (58.5%), whereas the senicapoc-bodipy conjugate 10b binds selectively at the open channel (41.5%). The ratio 58.5:41.5 reflects the ratio of the ion channel in closed and open conformations.

Harnessing Deep Learning Methods for Voltage-Gated Ion Channel Drug Discovery

Voltage-gated ion channels (VGICs) are pivotal in regulating electrical activity in excitable cells and are critical pharmaceutical targets for treating many diseases including cardiac arrhythmia and neuropathic pain. Despite their significance, challenges such as achieving target selectivity persist in VGIC drug development. Recent progress in deep learning, particularly diffusion models, has enabled the computational design of protein binders for any clinically relevant protein based solely on its structure. These developments coincide with a surge in experimental structural data for VGICs, providing a rich foundation for computational design efforts. This review explores the recent advancements in computational protein design using deep learning and diffusion methods, focusing on their application in designing protein binders to modulate VGIC activity. We discuss the potential use of these methods to computationally design protein binders targeting different regions of VGICs, including the pore domain, voltage-sensing domains, and interface with auxiliary subunits. We provide a comprehensive overview of the different design scenarios, discuss key structural considerations, and address the practical challenges in developing VGIC-targeting protein binders. By exploring these innovative computational methods, we aim to provide a framework for developing novel strategies that could significantly advance VGIC pharmacology and lead to the discovery of effective and safe therapeutics.

Toward high-resolution modeling of small molecule-ion channel interactions

Ion channels are critical drug targets for a range of pathologies, such as epilepsy, pain, itch, autoimmunity, and cardiac arrhythmias. To develop effective and safe therapeutics, it is necessary to design small molecules with high potency and selectivity for specific ion channel subtypes. There has been increasing implementation of structure-guided drug design for the development of small molecules targeting ion channels. We evaluated the performance of two RosettaLigand docking methods, RosettaLigand and GALigandDock, on the structures of known ligand-cation channel complexes. Ligands were docked to voltage-gated sodium (NaV), voltage-gated calcium (CaV), and transient receptor potential vanilloid (TRPV) channel families. For each test case, RosettaLigand and GALigandDock methods frequently sampled a ligand-binding pose within a root mean square deviation (RMSD) of 1-2 Å relative to the experimental ligand coordinates. However, RosettaLigand and GALigandDock scoring functions cannot consistently identify experimental ligand coordinates as top-scoring models. Our study reveals that the proper scoring criteria for RosettaLigand and GALigandDock modeling of ligand-ion channel complexes should be assessed on a case-by-case basis using sufficient ligand and receptor interface sampling, knowledge about state-specific interactions of the ion channel, and inherent receptor site flexibility that could influence ligand binding.

Repurposing the KCa3.1 Blocker Senicapoc for Ischemic Stroke

Senicapoc, a small molecule inhibitor of the calcium-activated potassium channel KCa3.1, was safe and well-tolerated in clinical trials for sickle cell anemia. We previously reported proof-of-concept data suggesting that both pharmacological inhibition and genetic deletion of KCa3.1 reduces infarction and improves neurologic recovery in rodents by attenuating neuroinflammation. Here we evaluated the potential of repurposing senicapoc for ischemic stroke. In cultured microglia, senicapoc inhibited KCa3.1 currents with an IC50 of 7 nM, reduced Ca2+ signaling induced by the purinergic agonist ATP, suppressed expression of pro-inflammatory cytokines and enzymes (iNOS and COX-2), and prevented induction of the inflammasome component NLRP3. When transient middle cerebral artery occlusion (tMCAO, 60 min) was induced in male C57BL/6 J mice, twice daily administration of senicapoc at 10 and 40 mg/kg starting 12 h after reperfusion dose-dependently reduced infarct area determined by T2-weighted magnetic resonance imaging (MRI) and improved neurological deficit on day 8. Ultra-high-performance liquid chromatography/mass spectrometry analysis of total and free brain concentrations demonstrated sufficient KCa3.1 target engagement. Senicapoc treatment significantly reduced microglia/macrophage and T cell infiltration and activation and attenuated neuronal death. A different treatment paradigm with senicapoc started at 3 h and MRI on day 3 and day 8 revealed that senicapoc reduces secondary infarct growth and suppresses expression of inflammation markers, including T cell cytokines in the brain. Lastly, we demonstrated that senicapoc does not impair the proteolytic activity of tissue plasminogen activator (tPA) in vitro. We suggest that senicapoc could be repurposed as an adjunctive immunocytoprotective agent for combination with reperfusion therapy for ischemic stroke.

Gating kinetics and pharmacological properties of small-conductance Ca2+-activated potassium channels

Small-conductance (SK) calcium-activated potassium channels are a promising treatment target in atrial fibrillation. However, the functional properties that differentiate SK inhibitors remain poorly understood. The objective of this study was to determine how two unrelated SK channel inhibitors, apamin and AP14145, impact SK channel function in excised inside-out single-channel recordings. Surprisingly, both apamin and AP14145 exert much of their inhibition by inducing a class of very-long-lived channel closures (apamin: τc,vl = 11.8 ± 7.1 s, and AP14145: τc,vl = 10.3 ± 7.2 s), which were never observed under control conditions. Both inhibitors also induced changes to the three closed and two open durations typical of normal SK channel gating. AP14145 shifted the open duration distribution to favor longer open durations, whereas apamin did not alter open-state kinetics. AP14145 also prolonged the two shortest channel closed durations (AP14145: τc,s = 3.50 ± 0.81 ms, and τc,i = 32.0 ± 6.76 ms versus control: τc,s = 1.59 ± 0.19 ms, and τc,i = 13.5 ± 1.17 ms), thus slowing overall gating kinetics within bursts of channel activity. In contrast, apamin accelerated intraburst gating kinetics by shortening the two shortest closed durations (τc,s = 0.75 ± 0.10 ms and τc,i = 5.08 ± 0.49 ms) and inducing periods of flickery activity. Finally, AP14145 introduced a unique form of inhibition by decreasing unitary current amplitude. SK channels exhibited two clearly distinguishable amplitudes (control: Ahigh = 0.76 ± 0.03 pA, and Alow = 0.54 ± 0.03 pA). AP14145 both reduced the fraction of patches exhibiting the higher amplitude (AP14145: 4/9 patches versus control: 16/16 patches) and reduced the mean low amplitude (0.38 ± 0.03 pA). Here, we have demonstrated that both inhibitors introduce very long channel closures but that each also exhibits unique effects on other components of SK gating kinetics and unitary current. The combination of these effects is likely to be critical for understanding the functional differences of each inhibitor in the context of cyclical Ca2+-dependent channel activation in vivo.

Pancreatic KCa3.1 channels in health and disease

Ion channels play an important role for regulation of the exocrine and the endocrine pancreas. This review focuses on the Ca²⁺-regulated K⁺ channel K_Ca3.1, encoded by the KCNN4 gene, which is present in both parts of the pancreas. In the islets of Langerhans, K_Ca3.1 channels are involved in the regulation of membrane potential oscillations characterizing nutrient-stimulated islet activity. Channel upregulation is induced by gluco- or lipotoxic conditions and might contribute to micro-inflammation and impaired insulin release in type 2 diabetes mellitus as well as to diabetes-associated renal and vascular complications. In the exocrine pancreas K_Ca3.1 channels are expressed in acinar and ductal cells. They are thought to play a role for anion secretion during digestion but their physiological role has not been fully elucidated yet. Pancreatic carcinoma, especially pancreatic ductal adenocarcinoma (PDAC), is associated with drastic overexpression of K_Ca3.1. For pharmacological targeting of K_Ca3.1 channels, we are discussing the possible benefits K_Ca3.1 channel inhibitors might provide in the context of diabetes mellitus and pancreatic cancer, respectively. We are also giving a perspective for the use of a fluorescently labeled derivative of the K_Ca3.1 blocker senicapoc as a tool to monitor channel distribution in pancreatic tissue. In summary, modulating K_Ca3.1 channel activity is a useful strategy for exo-and endocrine pancreatic disease but further studies are needed to evaluate its clinical suitability.

Structural modeling of peptide toxin-ion channel interactions using RosettaDock

Voltage-gated ion channels play essential physiological roles in action potential generation and propagation. Peptidic toxins from animal venoms target ion channels and provide useful scaffolds for the rational design of novel channel modulators with enhanced potency and subtype selectivity. Despite recent progress in obtaining experimental structures of peptide toxin-ion channel complexes, structural determination of peptide toxins bound to ion channels in physiologically important states remains challenging. Here we describe an application of RosettaDock approach to the structural modeling of peptide toxins interactions with ion channels. We tested this approach on 10 structures of peptide toxin-ion channel complexes and demonstrated that it can sample near-native structures in all tested cases. Our approach will be useful for improving the understanding of the molecular mechanism of natural peptide toxin modulation of ion channel gating and for the structural modeling of novel peptide-based ion channel modulators.

Pharmacological targeting of the mitochondrial calcium-dependent potassium channel KCa3.1 triggers cell death and reduces tumor growth and metastasis in vivo

Ion channels are non-conventional, druggable oncological targets. The intermediate-conductance calcium-dependent potassium channel (K_Ca3.1) is highly expressed in the plasma membrane and in the inner mitochondrial membrane (mitoK_Ca3.1) of various cancer cell lines. The role mitoK_Ca3.1 plays in cancer cells is still undefined. Here we report the synthesis and characterization of two mitochondria-targeted novel derivatives of a high-affinity K_Ca3.1 antagonist, TRAM-34, which retain the ability to block channel activity. The effects of these drugs were tested in melanoma, pancreatic ductal adenocarcinoma and breast cancer lines, as well as in vivo in two orthotopic models. We show that the mitochondria-targeted TRAM-34 derivatives induce release of mitochondrial reactive oxygen species, rapid depolarization of the mitochondrial membrane, fragmentation of the mitochondrial network. They trigger cancer cell death with an EC₅₀ in the µM range, depending on channel expression. In contrast, inhibition of the plasma membrane K_Ca3.1 by membrane-impermeant Maurotoxin is without effect, indicating a specific role of mitoK_Ca3.1 in determining cell fate. At sub-lethal concentrations, pharmacological targeting of mitoK_Ca3.1 significantly reduced cancer cell migration by enhancing production of mitochondrial reactive oxygen species and nuclear factor-κB (NF-κB) activation, and by downregulating expression of Bcl-2 Nineteen kD-Interacting Protein (BNIP-3) and of Rho GTPase CDC-42. This signaling cascade finally leads to cytoskeletal reorganization and impaired migration. Overexpression of BNIP-3 or pharmacological modulation of NF-κB and CDC-42 prevented the migration-reducing effect of mitoTRAM-34. In orthotopic models of melanoma and pancreatic ductal adenocarcinoma, the tumors at sacrifice were 60% smaller in treated versus untreated animals. Metastasis of melanoma cells to lymph nodes was also drastically reduced. No signs of toxicity were observed. In summary, our results identify mitochondrial K_Ca3.1 as an unexpected player in cancer cell migration and show that its pharmacological targeting is efficient against both tumor growth and metastatic spread in vivo.

Single amino acid residue mediates reciprocal specificity in two mosquito odorant receptors

The southern house mosquito, Culex quinquefasciatus, utilizes two odorant receptors, CquiOR10 and CquiOR2, narrowly tuned to oviposition attractants and well conserved among mosquito species. They detect skatole and indole, respectively, with reciprocal specificity. We swapped the transmembrane (TM) domains of CquiOR10 and CquiOR2 and identified TM2 as a specificity determinant. With additional mutations, we showed that CquiOR10A73L behaved like CquiOR2. Conversely, CquiOR2L74A recapitulated CquiOR10 specificity. Next, we generated structural models of CquiOR10 and CquiOR10A73L using RoseTTAFold and AlphaFold and docked skatole and indole using RosettaLigand. These modeling studies suggested space-filling constraints around A73. Consistent with this hypothesis, CquiOR10 mutants with a bulkier residue (Ile, Val) were insensitive to skatole and indole, whereas CquiOR10A73G retained the specificity to skatole and showed a more robust response than the wildtype receptor CquiOR10. On the other hand, Leu to Gly mutation of the indole receptor CquiOR2 reverted the specificity to skatole. Lastly, CquiOR10A73L, CquiOR2, and CquiOR2L74I were insensitive to 3-ethylindole, whereas CquiOR2L74A and CquiOR2L74G gained activity. Additionally, CquiOR10A73G gave more robust responses to 3-ethylindole than CquiOR10. Thus, we suggest the specificity of these receptors is mediated by a single amino acid substitution, leading to finely tuned volumetric space to accommodate specific oviposition attractants.

Inhibition of platelet aggregation by activation of platelet intermediate conductance Ca2+ -activated potassium channels

BACKGROUND

Within the vasculature platelets and endothelial cells play crucial roles in hemostasis and thrombosis. Platelets, like endothelial cells, possess intermediate conductance Ca2+ -activated K+ (IKCa ) channels and generate nitric oxide (NO). Although NO limits platelet aggregation, the role of IKCa channels in platelet function and NO generation has not yet been explored.

OBJECTIVES

We investigated whether IKCa channel activation inhibits platelet aggregation, and per endothelial cells, enhances platelet NO production.

METHODS

Platelets were isolated from human volunteers. Aggregometry, confocal microscopy, and a novel flow chamber model, the Quartz Crystal Microbalance (QCM) were used to assess platelet function. Flow cytometry was used to measure platelet NO production, calcium signaling, membrane potential, integrin αIIb /β3 activation, granule release, and procoagulant platelet formation.

RESULTS

Platelet IKCa channel activation with SKA-31 inhibited aggregation in a concentration-dependent manner, an effect reversed by the selective IKCa channel blocker TRAM-34. The QCM model along with confocal microscopy demonstrated that SKA-31 inhibited platelet aggregation under flow conditions. Surprisingly, IKCa activation by SKA-31 inhibited platelet NO generation, but this could be explained by a concomitant reduction in platelet calcium signaling. IKCa activation by SKA-31 also inhibited dense and alpha-granule secretion and integrin αIIb /β3 activation, but maintained platelet phosphatidylserine surface exposure as a measure of procoagulant response.

CONCLUSIONS

Platelet IKCa channel activation inhibits aggregation by reducing calcium-signaling and granule secretion, but not by enhancing platelet NO generation. IKCa channels may be novel targets for the development of antiplatelet drugs that limit atherothrombosis, but not coagulation.

The erythroid K-Cl cotransport inhibitor [(dihydroindenyl)oxy]acetic acid blocks erythroid Ca2+-activated K+ channel KCNN4

Red cell volume is a major determinant of HbS concentration in sickle cell disease. Cellular deoxy-HbS concentration determines the delay time, the interval between HbS deoxygenation and deoxy-HbS polymerization. Major membrane transporter protein determinants of sickle red cell volume include the SLC12/KCC K-Cl cotransporters KCC3/SLC12A6 and KCC1/SLC12A4, and the KCNN4/KCa3.1 Ca2+-activated K+ channel (Gardos channel). Among standard inhibitors of KCC-mediated K-Cl cotransport, only [(dihydroindenyl)oxy]acetic acid (DIOA) has been reported to lack inhibitory activity against the related bumetanide-sensitive erythroid Na-K-2Cl cotransporter NKCC1/SLC12A2. DIOA has been often used to inhibit K-Cl cotransport when studying the expression and regulation of other K+ transporters and K+ channels. We report here that DIOA at concentrations routinely used to inhibit K-Cl cotransport can also abrogate activity of the KCNN4/KCa3.1 Gardos channel in human and mouse red cells and in human sickle red cells. DIOA inhibition of A23187-stimulated erythroid K+ uptake (Gardos channel activity) was chloride-independent and persisted in mouse red cells genetically devoid of the principal K-Cl cotransporters KCC3 and KCC1. DIOA also inhibited YODA1-stimulated, chloride-independent erythroid K+ uptake. In contrast, DIOA exhibited no inhibitory effect on K+ influx into A23187-treated red cells of Kcnn4-/- mice. DIOA inhibition of human KCa3.1 was validated (IC50 42 µM) by whole cell patch clamp in HEK-293 cells. RosettaLigand docking experiments identified a potential binding site for DIOA in the fenestration region of human KCa3.1. We conclude that DIOA at concentrations routinely used to inhibit K-Cl cotransport can also block the KCNN4/KCa3.1 Gardos channel in normal and sickle red cells.

Dextran sodium sulfate potentiates NLRP3 inflammasome activation by modulating the KCa3.1 potassium channel in a mouse model of colitis

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, has increased in incidence and prevalence in recent decades. Both clinical and animal studies are critical for understanding the pathogenesis of this disease. Dextran sodium sulfate (DSS)-induced colitis is a frequently used animal model of IBD, but the underlying mechanism of the model remains incompletely understood. In this study, we found that NOD-like receptor family pyrin containing 3 (NLRP3) depletion markedly mitigated DSS-induced colitis and was accompanied by decreased activation of the inflammasome in the colons of mice. However, in vitro assays showed that DSS did not directly trigger but instead potentiated NLRP3 inflammasome assembly in macrophages in response to suboptimal ATP or nigericin stimulation. Mechanistically, DSS potentiated NLRP3 inflammasome activation in macrophages by augmenting KCa3.1-mediated potassium ion (K+) efflux. Furthermore, we found that pharmacologic blockade of the K+ channel KCa3.1 with TRAM-34 or genetic depletion of the Kcnn4 gene (encoding KCa3.1) not only ameliorated the severity of DSS-induced colitis but also attenuated in vivo inflammasome assembly in the colonic tissues of mice, suggesting a causal link between KCa3.1-mediated augmentation of the NLRP3 inflammasome and DSS-induced inflammatory injuries. Collectively, these results indicate that KCa3.1 plays a critical role in mediating DSS-induced colitis in mice by potentiating NLRP3 inflammasome activation. Our data provide a previously unknown mechanism by which DSS induces colitis in mice and suggests that KCa3.1 is an alternative therapeutic target for treating IBD.

Pose Classification Using Three-Dimensional Atomic Structure-Based Neural Networks Applied to Ion Channel-Ligand Docking

The identification of promising lead compounds showing pharmacological activities toward a biological target is essential in early stage drug discovery. With the recent increase in available small-molecule databases, virtual high-throughput screening using physics-based molecular docking has emerged as an essential tool in assisting fast and cost-efficient lead discovery and optimization. However, the best scored docking poses are often suboptimal, resulting in incorrect screening and chemical property calculation. We address the pose classification problem by leveraging data-driven machine learning approaches to identify correct docking poses from AutoDock Vina and Glide screens. To enable effective classification of docking poses, we present two convolutional neural network approaches: a three-dimensional convolutional neural network (3D-CNN) and an attention-based point cloud network (PCN) trained on the PDBbind refined set. We demonstrate the effectiveness of our proposed classifiers on multiple evaluation data sets including the standard PDBbind CASF-2016 benchmark data set and various compound libraries with structurally different protein targets including an ion channel data set extracted from Protein Data Bank (PDB) and an in-house KCa3.1 inhibitor data set. Our experiments show that excluding false positive docking poses using the proposed classifiers improves virtual high-throughput screening to identify novel molecules against each target protein compared to the initial screen based on the docking scores.

Molecular modeling in cardiovascular pharmacology: Current state of the art and perspectives

Molecular modeling in pharmacology is a promising emerging tool for exploring drug interactions with cellular components. Recent advances in molecular simulations, big data analysis, and artificial intelligence (AI) have opened new opportunities for rationalizing drug interactions with their pharmacological targets. Despite the obvious utility and increasing impact of computational approaches, their development is not progressing at the same speed in different fields of pharmacology. Here, we review current in silico techniques used in cardiovascular diseases (CVDs), cardiological drug discovery, and assessment of cardiotoxicity. In silico techniques are paving the way to a new era in cardiovascular medicine, but their use somewhat lags behind that in other fields.

TRPM2 Oxidation Activates Two Distinct Potassium Channels in Melanoma Cells through Intracellular Calcium Increase

Tumor microenvironments are often characterized by an increase in oxidative stress levels. We studied the response to oxidative stimulation in human primary (IGR39) or metastatic (IGR37) cell lines obtained from the same patient, performing patch-clamp recordings, intracellular calcium ([Ca²⁺]_i) imaging, and RT-qPCR gene expression analysis. In IGR39 cells, chloramine-T (Chl-T) activated large K⁺ currents (KROS) that were partially sensitive to tetraethylammonium (TEA). A large fraction of KROS was inhibited by paxilline—a specific inhibitor of large-conductance Ca²⁺-activated BK channels. The TEA-insensitive component was inhibited by senicapoc—a specific inhibitor of the Ca²⁺-activated KCa3.1 channel. Both BK and KCa3.1 activation were mediated by an increase in [Ca²⁺]_i induced by Chl-T. Both KROS and [Ca²⁺]_i increase were inhibited by ACA and clotrimazole—two different inhibitors of the calcium-permeable TRPM2 channel. Surprisingly, IGR37 cells did not exhibit current increase upon the application of Chl-T. Expression analysis confirmed that the genes encoding BK, KCa3.1, and TRPM2 are much more expressed in IGR39 than in IGR37. The potassium currents and [Ca²⁺]_i increase observed in response to the oxidizing agent strongly suggest that these three molecular entities play a major role in the progression of melanoma. Pharmacological targeting of either of these ion channels could be a new strategy to reduce the metastatic potential of melanoma cells, and could complement classical radio- or chemotherapeutic treatments.

The role of potassium in atherosclerosis

BACKGROUND

Atherosclerosis (AS) is a chronic progressive inflammatory condition with a leading prevalence worldwide. Endothelial dysfunction leads to low-density lipoprotein trafficking into subendothelial space and the subsequent form of oxidized LDL (ox-LDL) within intimal layer, perpetuating the vicious cycle of endothelial dysfunction. K+ exerts beneficial effects in vascular wall by reducing LDL oxidization, vascular smooth muscle cells (VSMCs) proliferation, and free radical generation. K+ also modulates vascular tone through a regulatory effect on cell membrane potential.

MATERIALS AND METHODS

The most relevant papers on the association between 'potassium channels' and 'atherosclerosis' were selected among those deposited on PubMed from 1990 to 2020.

RESULTS

Here, we provide a short narrative review that elaborates on the role of K+ in atherosclerosis. This review also update the current knowledge about potential pharmacological agents targeting K+ channels with a special focus on pleiotropic activities of agents such as statins, sulfonylureas and dihydropyridines.

CONCLUSION

In this review, the mechanism of different K+ channels on vascular endothelium will be summarized, mainly focusing on their pathophysiological role in atherosclerosis and potential therapeutic application.

Identification of the Functional Binding Site for the Convulsant Tetramethylenedisulfotetramine in the Pore of the α 2 β 3 γ 2 GABAA Receptor

Tetramethylenedisulfotetramine (TETS) is a so-called "caged" convulsant that is responsible for thousands of accidental and malicious poisonings. Similar to the widely used GABA receptor type A (GABAA) antagonist picrotoxinin, TETS has been proposed to bind to the noncompetitive antagonist (NCA) site in the pore of the receptor channel. However, the TETS binding site has never been experimentally mapped, and we here set out to gain atomistic level insights into how TETS inhibits the human α 2 β 3 γ 2 GABAA receptor. Using the Rosetta molecular modeling suite, we generated three homology models of the α 2 β 3 γ 2 receptor in the open, desensitized, and closed/resting state. Three different ligand-docking algorithms (RosettaLigand, Glide, and Swissdock) identified two possible TETS binding sites in the channel pore. Using a combination of site-directed mutagenesis, electrophysiology, and modeling to probe both sites, we demonstrate that TETS binds at the T6' ring in the closed/resting-state model, in which it shows perfect space complementarity and forms hydrogen bonds or makes hydrophobic interactions with all five pore-lining threonine residues of the pentameric receptor. Mutating T6' in either the α 2 or β 3 subunit reduces the IC50 of TETS by ∼700-fold in whole-cell patch-clamp experiments. TETS is thus interacting at the NCA site in the pore of the GABAA receptor at a location that is overlapping but not identical to the picrotoxinin binding site. SIGNIFICANCE STATEMENT: Our study identifies the binding site of the highly toxic convulsant tetramethylenedisulfotetramine (TETS), which is classified as a threat agent by the World Health Organization. Using a combination of homology protein modeling, ligand docking, site-directed mutagenesis, and electrophysiology, we show that TETS is binding in the pore of the α2β3γ2 GABA receptor type A receptor at the so-called T6' ring, wherein five threonine residues line the permeation pathway of the pentameric receptor channel.

Synthesis of Small-Molecule Fluorescent Probes for the In Vitro Imaging of Calcium-Activated Potassium Channel KCa 3.1

Small-molecule probes for the in vitro imaging of KCa 3.1 channel-expressing cells were developed. Senicapoc, showing high affinity and selectivity for the KCa 3.1 channels, was chosen as the targeting component. BODIPY dyes 15-20 were synthesized and connected by a CuI -catalyzed azide-alkyne [3+2]cycloaddition with propargyl ether senicapoc derivative 8, yielding fluorescently labeled ligands 21-26. The dimethylpyrrole-based imaging probes 25 and 26 allow staining of KCa 3.1 channels in NSCLC cells. The specificity was shown by removing the punctate staining pattern by pre-incubation with senicapoc. The density of KCa 3.1 channels detected with 25 and by immunostaining was identical. The punctate structure of the labeled channels could also be observed in living cells. Molecular modeling showed binding of the senicapoc-targeting component towards the binding site within the ion channel and orientation of the linker with the dye along the inner surface of the ion channel.

Suppression of Ca2+ signals by EGR4 controls Th1 differentiation and anti-cancer immunity in vivo

While the zinc finger transcription factors EGR1, EGR2, and EGR3 are recognized as critical for T-cell function, the role of EGR4 remains unstudied. Here, we show that EGR4 is rapidly upregulated upon TCR engagement, serving as a critical "brake" on T-cell activation. Hence, TCR engagement of EGR4^-/- T cells leads to enhanced Ca²⁺ responses, driving sustained NFAT activation and hyperproliferation. This causes profound increases in IFNγ production under resting and diverse polarizing conditions that could be reversed by pharmacological attenuation of Ca²⁺ entry. Finally, an in vivo melanoma lung colonization assay reveals enhanced anti-tumor immunity in EGR4^-/- mice, attributable to Th1 bias, Treg loss, and increased CTL generation in the tumor microenvironment. Overall, these observations reveal for the first time that EGR4 is a key regulator of T-cell differentiation and function.

Comparison of the pharmacological profiles of arginine vasopressin and oxytocin analogs at marmoset, macaque, and human vasopressin 1a receptor

Arginine vasopressin (AVP) and oxytocin (OT) are nonapeptides that bind to G-protein coupled receptors and influence social behaviors. Consensus mammalian AVP and OT (Leu⁸-OT) sequences are highly conserved. In marmosets, an amino acid change in the 8th position of the peptide (Pro⁸-OT) exhibits unique structural and functional properties. There is ∼85 % structural homology between the OT receptor (OTR) and vasopressin 1a receptor (V1aR) resulting in significant cross-reactivity between the ligands and receptors. Chinese hamster ovary (CHO) cells expressing marmoset (mV1aR), macaque (qV1aR), or human vasopressin receptor 1a (hV1aR) were used to assess AVP, Leu⁸-OT and Pro⁸-OT pharmacological profiles. To assess activation of Gq, functional assays were performed using Fluo-3 to measure ligand-induced Ca²⁺ mobilization. In all three V1aR-expressing cell lines, AVP was more potent than the OT ligands. To assess ligand-induced hyperpolarization, FLIPR Membrane Potential (FMP) assays were performed. In all three V1aR lines, AVP was more potent than the OT analogs. The distinctive U-shaped concentration-response curve displayed by AVP may reflect enhanced desensitization of the mV1aR and hV1aR, which is not observed with qV1aR. Evaluation of Ca²⁺-activated potassium (K⁺) channels using the inhibitors apamin, paxilline, and TRAM-34 demonstrated that both intermediate and large conductance Ca²⁺-activated K⁺ channels contributed to membrane hyperpolarization, with different pharmacological profiles identified for distinct ligand-receptor combinations. Taken together, these data suggest differences in ligand-receptor signaling that may underlie differences in social behavior. Integrative studies of behavior, genetics and ligand-receptor interaction will help elucidate the connection between receptor pharmacology and social behaviors.

Ca2+ signalling in fibroblasts and the therapeutic potential of KCa3.1 channel blockers in fibrotic diseases

The role of Ca²⁺ signalling in fibroblasts is of great interest in fibrosis-related diseases. Intracellular free Ca²⁺ ([Ca²⁺ ]_i ) is a ubiquitous secondary messenger, regulating a number of cellular functions such as secretion, metabolism, differentiation, proliferation and contraction. The intermediate conductance Ca²⁺ -activated K⁺ channel K_Ca 3.1 is pivotal in Ca²⁺ signalling and plays a central role in fibroblast processes including cell activation, migration and proliferation through the regulation of cell membrane potential. Evidence from a number of approaches demonstrates that K_Ca 3.1 plays an important role in the development of many fibrotic diseases, including idiopathic pulmonary, renal tubulointerstitial fibrosis and cardiovascular disease. The K_Ca 3.1 selective blocker senicapoc was well tolerated in clinical trials for sickle cell disease, raising the possibility of rapid translation to the clinic for people suffering from pathological fibrosis. This review after analysing all the data, concludes that targeting K_Ca 3.1 should be a high priority for human fibrotic disease.

Comparison of the pharmacologic profiles of arginine vasopressin and oxytocin analogs at marmoset, titi monkey, macaque, and human oxytocin receptors

The oxytocin-arginine vasopressin (OT-AVP) ligand-receptor family influences a variety of physiological, behavioral, and social behavioral processes in the brain and periphery. The OT-AVP family is highly conserved in mammals, but recent discoveries have revealed remarkable diversity in OT ligands and receptors in New World Monkeys (NWMs) providing a unique opportunity to assess the effects of genetic variation on pharmacological signatures of peptide ligands. The consensus mammalian OT sequence has leucine in the 8^th position (Leu⁸-OT), whereas a number of NWMs, including the marmoset, have proline in the 8^th position (Pro⁸-OT) resulting in a more rigid tail structure. OT and AVP bind to OT’s cognate G-protein coupled receptor (OTR), which couples to various G-proteins (G_i/o, G_q, G_s) to stimulate diverse signaling pathways. CHO cells expressing marmoset (mOTR), titi monkey (tOTR), macaque (qOTR), or human (hOTR) OT receptors were used to compare AVP and OT analog-induced signaling. Assessment of G_q-mediated increase in intracellular calcium (Ca²⁺) demonstrated that AVP was less potent than OT analogs at OTRs from species whose endogenous ligand is Leu⁸-OT (tOTR, qOTR, hOTR), relative to Pro⁸-OT. Likewise, AVP-induced membrane hyperpolarization was less potent at these same OTRs. Evaluation of (Ca²⁺)-activated potassium (K⁺) channels using the inhibitors apamin, paxilline, and TRAM-34 demonstrated that both intermediate and large conductance Ca²⁺-activated K⁺ channels contributed to membrane hyperpolarization, with different pharmacological profiles identified for distinct ligand-receptor combinations. Understanding more fully the contributions of structure activity relationships for these peptide ligands at vasopressin and OT receptors will help guide the development of OT-mediated therapeutics.

Impaired Endothelium-Dependent Hyperpolarization Underlies Endothelial Dysfunction during Early Metabolic Challenge: Increased ROS Generation and Possible Interference with NO Function

Endothelial dysfunction is a hallmark of diabetic vasculopathies. Although hyperglycemia is believed to be the culprit causing endothelial damage, the mechanism underlying early endothelial insult in prediabetes remains obscure. We used a nonobese high-calorie (HC)-fed rat model with hyperinsulinemia, hypercholesterolemia, and delayed development of hyperglycemia to unravel this mechanism. Compared with aortic rings from control rats, HC-fed rat rings displayed attenuated acetylcholine-mediated relaxation. While sensitive to nitric oxide synthase (NOS) inhibition, aortic relaxation in HC-rat tissues was not affected by blocking the inward-rectifier potassium (Kir) channels using BaCl2 Although Kir channel expression was reduced in HC-rat aorta, Kir expression, endothelium-dependent relaxation, and the BaCl2-sensitive component improved in HC rats treated with atorvastatin to reduce serum cholesterol. Remarkably, HC tissues demonstrated increased reactive species (ROS) in smooth muscle cells, which was reversed in rats receiving atorvastatin. In vitro ROS reduction, with superoxide dismutase, improved endothelium-dependent relaxation in HC-rat tissues. Significantly, connexin-43 expression increased in HC aortic tissues, possibly allowing ROS movement into the endothelium and reduction of eNOS activity. In this context, gap junction blockade with 18-β-glycyrrhetinic acid reduced vascular tone in HC rat tissues but not in controls. This reduction was sensitive to NOS inhibition and SOD treatment, possibly as an outcome of reduced ROS influence, and emerged in BaCl2-treated control tissues. In conclusion, our results suggest that early metabolic challenge leads to reduced Kir-mediated endothelium-dependent hyperpolarization, increased vascular ROS potentially impairing NO synthesis and highlight these channels as a possible target for early intervention with vascular dysfunction in metabolic disease. SIGNIFICANCE STATEMENT: The present study examines early endothelial dysfunction in metabolic disease. Our results suggest that reduced inward-rectifier potassium channel function underlies a defective endothelium-mediated relaxation possibly through alteration of nitric oxide synthase activity. This study provides a possible mechanism for the augmentation of relatively small changes in one endothelium-mediated relaxation pathway to affect overall endothelial response and highlights the potential role of inward-rectifier potassium channel function as a therapeutic target to treat vascular dysfunction early in the course of metabolic disease.

The Trials and Tribulations of Structure Assisted Design of KCa Channel Activators

Calcium-activated K⁺ channels constitute attractive targets for the treatment of neurological and cardiovascular diseases. To explain why certain 2-aminobenzothiazole/oxazole-type K_Ca activators (SKAs) are K_Ca3.1 selective we previously generated homology models of the C-terminal calmodulin-binding domain (CaM-BD) of K_Ca3.1 and K_Ca2.3 in complex with CaM using Rosetta modeling software. We here attempted to employ this atomistic level understanding of K_Ca activator binding to switch selectivity around and design K_Ca2.2 selective activators as potential anticonvulsants. In this structure-based drug design approach we used RosettaLigand docking and carefully compared the binding poses of various SKA compounds in the K_Ca2.2 and K_Ca3.1 CaM-BD/CaM interface pocket. Based on differences between residues in the K_Ca2.2 and K_Ca.3.1 models we virtually designed 168 new SKA compounds. The compounds that were predicted to be both potent and K_Ca2.2 selective were synthesized, and their activity and selectivity tested by manual or automated electrophysiology. However, we failed to identify any K_Ca2.2 selective compounds. Based on the full-length K_Ca3.1 structure it was recently demonstrated that the C-terminal crystal dimer was an artefact and suggested that the "real" binding pocket for the K_Ca activators is located at the S4-S5 linker. We here confirmed this structural hypothesis through mutagenesis and now offer a new, corrected binding site model for the SKA-type K_Ca channel activators. SKA-111 (5-methylnaphtho[1,2-d]thiazol-2-amine) is binding in the interface between the CaM N-lobe and the S4-S5 linker where it makes van der Waals contacts with S181 and L185 in the S₄₅A helix of K_Ca3.1.

Pharmacology of Small- and Intermediate-Conductance Calcium-Activated Potassium Channels

The three small-conductance calcium-activated potassium (K_Ca2) channels and the related intermediate-conductance K_Ca3.1 channel are voltage-independent K⁺ channels that mediate calcium-induced membrane hyperpolarization. When intracellular calcium increases in the channel vicinity, it calcifies the flexible N lobe of the channel-bound calmodulin, which then swings over to the S4-S5 linker and opens the channel. K_Ca2 and K_Ca3.1 channels are highly druggable and offer multiple binding sites for venom peptides and small-molecule blockers as well as for positive- and negative-gating modulators. In this review, we briefly summarize the physiological role of K_Ca channels and then discuss the pharmacophores and the mechanism of action of the most commonly used peptidic and small-molecule K_Ca2 and K_Ca3.1 modulators. Finally, we describe the progress that has been made in advancing K_Ca3.1 blockers and K_Ca2.2 negative- and positive-gating modulators toward the clinic for neurological and cardiovascular diseases and discuss the remaining challenges.

A Comparison of the Ability of Leu8- and Pro8-Oxytocin to Regulate Intracellular Ca2+ and Ca2+-Activated K+ Channels at Human and Marmoset Oxytocin Receptors

The neurohypophyseal hormone oxytocin (OT) regulates biologic functions in both peripheral tissues and the central nervous system. In the central nervous system, OT influences social processes, including peer relationships, maternal-infant bonding, and affiliative social relationships. In mammals, the nonapeptide OT structure is highly conserved with leucine in the eighth position (Leu8-OT). In marmosets (Callithrix), a nonsynonymous nucleotide substitution in the OXT gene codes for proline in the eighth residue position (Pro8-OT). OT binds to its cognate G protein-coupled receptor (OTR) and exerts diverse effects, including stimulation (Gs) or inhibition (Gi/o) of adenylyl cyclase, stimulation of potassium channel currents (Gi), and activation of phospholipase C (Gq). Chinese hamster ovary cells expressing marmoset or human oxytocin receptors (mOTRs or hOTRs, respectively) were used to characterize OT signaling. At the mOTR, Pro8-OT was more efficacious than Leu8-OT in measures of Gq activation, with both peptides displaying subnanomolar potencies. At the hOTR, neither the potency nor efficacy of Pro8-OT and Leu8-OT differed with respect to Gq signaling. In both mOTR- and hOTR-expressing cells, Leu8-OT was more potent and modestly more efficacious than Pro8-OT in inducing hyperpolarization. In mOTR cells, Leu8-OT-induced hyperpolarization was modestly inhibited by pretreatment with pertussis toxin (PTX), consistent with a minor role for Gi/o activation; however, the Pro8-OT response in mOTR and hOTR cells was PTX insensitive. These findings are consistent with membrane hyperpolarization being largely mediated by a Gq signaling mechanism leading to Ca2+-dependent activation of K+ channels. Evaluation of the influence of apamin, charybdotoxin, paxilline, and TRAM-34 demonstrated involvement of both intermediate and large conductance Ca2+-activated K+ channels.

Structural basis for antiarrhythmic drug interactions with the human cardiac sodium channel

Voltage-gated sodium channels play a central role in cellular excitability and are key targets for drug development. Recent breakthroughs in high-resolution cryo-electron microscopy protein structure determination, Rosetta computational protein structure modeling, and multimicrosecond molecular dynamics simulations are empowering advances in structural biology to study the atomistic details of channel−drug interactions. We used Rosetta structural computational modeling and molecular dynamics simulations to study the interactions of antiarrhythmic and local anesthetic drugs with cardiac sodium channel. Our results provide crucial atomic-scale mechanistic insights into the channel–drug interactions, necessary for the rational design of novel modulators of the human cardiac sodium channel to be used for the treatment of cardiac arrhythmias.

The human voltage-gated sodium channel, hNa_V1.5, is responsible for the rapid upstroke of the cardiac action potential and is target for antiarrhythmic therapy. Despite the clinical relevance of hNa_V1.5-targeting drugs, structure-based molecular mechanisms of promising or problematic drugs have not been investigated at atomic scale to inform drug design. Here, we used Rosetta structural modeling and docking as well as molecular dynamics simulations to study the interactions of antiarrhythmic and local anesthetic drugs with hNa_V1.5. These calculations revealed several key drug binding sites formed within the pore lumen that can simultaneously accommodate up to two drug molecules. Molecular dynamics simulations identified a hydrophilic access pathway through the intracellular gate and a hydrophobic access pathway through a fenestration between DIII and DIV. Our results advance the understanding of molecular mechanisms of antiarrhythmic and local anesthetic drug interactions with hNa_V1.5 and will be useful for rational design of novel therapeutics.

Ca2+-Activated K+ Channel KCa3.1 as a Therapeutic Target for Immune Disorders

In lymphoid and myeloid cells, membrane hyperpolarization by the opening of K⁺ channels increases the activity of Ca²⁺ release-activated Ca²⁺ (CRAC) channels and transient receptor potential (TRP) Ca²⁺ channels. The intermediate-conductance Ca²⁺-activated K⁺ channel K_Ca3.1 plays an important role in cell proliferation, differentiation, migration, and cytokine production in innate and adaptive immune systems. K_Ca3.1 is therefore an attractive therapeutic target for allergic, inflammatory, and autoimmune disorders. In the past several years, studies have provided new insights into 1) K_Ca3.1 pharmacology and its auxiliary regulators; 2) post-transcriptional and proteasomal regulation of K_Ca3.1; 3) K_Ca3.1 as a regulator of immune cell migration, cytokine production, and phenotypic polarization; 4) the role of K_Ca3.1 in the phosphorylation and nuclear translocation of Smad2/3; and 5) K_Ca3.1 as a therapeutic target for cancer immunotherapy. In this review, we have assembled a comprehensive overview of current research on the physiological and pathophysiological significance of K_Ca3.1 in the immune system.

Functional Roles of the Ca2+-activated K+ Channel, KCa3.1, in Brain Tumors

BACKGROUND

Glioblastoma is the most aggressive and deadly brain tumor, with low disease-free period even after surgery and combined radio and chemotherapies. Among the factors contributing to the devastating effect of this tumor in the brain are the elevated proliferation and invasion rate, and the ability to induce a local immunosuppressive environment. The intermediateconductance Ca2+-activated K+ channel KCa3.1 is expressed in glioblastoma cells and in tumorinfiltrating cells.

METHODS

We first describe the researches related to the role of KCa3.1 channels in the invasion of brain tumor cells and the regulation of cell cycle. In the second part we review the involvement of KCa3.1 channel in tumor-associated microglia cell behaviour.

RESULTS

In tumor cells, the functional expression of KCa3.1 channels is important to substain cell invasion and proliferation. In tumor infiltrating cells, KCa3.1 channel activity is required to regulate their activation state. Interfering with KCa3.1 activity can be an adjuvant therapeutic approach in addition to classic chemotherapy and radiotherapy, to counteract tumor growth and prolong patient's survival.

CONCLUSION

In this mini-review we discuss the evidence of the functional roles of KCa3.1 channels in glioblastoma biology.

Inhibitory effects of candesartan on KCa3.1 potassium channel expression and cell culture and proliferation in peripheral blood CD4+T lymphocytes in Kazakh patients with hypertension from the Xinjiang region

BACKGROUND AND AIM

Increasing evidence confirms that potassium channels are essential for lymphocyte activation, suggesting an involvement in the development of hypertension. Moreover, chronic inflammation is regarded as a direct or indirect manifestation of hypertension, highlighting the theoretical mechanisms. In this study, we investigated changes in KCa3.1 potassium channel expression in the blood of hypertensive and healthy Kazakh people in north-west China.

METHODS

Flow cytometry technology was used for T-lymphocyte subtype analysis. Changes in the messenger RNA and protein expression of the KCa3.1 potassium channel in CD4⁺ T lymphocytes were detected using real-time quantitative polymerase chain reaction and western blots, using CD4⁺ T-cell samples from hypertensive Kazakh patients divided into candesartan and TRAM-34 treatment groups, and healthy case controls. Peripheral blood CD4⁺ T lymphocytes were activated and proliferated in vitro and then incubated for 0, 24, and 48 h under various treatment conditions. Changes in CD4⁺ T-lymphocytic proliferation were determined using Cell Counting Kit-8 and electron microscope photography.

RESULTS

Expression of KCa3.1 was significantly higher in the hypertensive patients than in the controls (p < 0.05). Compared with the healthy group, Kazakh hypertensive patients had a reduced proportion of CD4⁺ T lymphocytes (p < 0.05).Candesartan and TRAM-34 intervention for 24 h and 48 h inhibited the expression of Kv1.3 and KCa3.1 at mRNA and protein level (p < 0.05).

CONCLUSIONS

Increase in functional KCa3.1 channels expressed in CD4⁺ T lymphocytes of Kazakh patients with hypertension was blocked by candesartan, providing theoretical support for hypertension treatment at the cellular ion channel level. Candesartan may potentially regulate hypertensive inflammatory responses by inhibiting T-lymphocytic proliferation and KCa3.1 potassium channel expression in CD4 ⁺ T lymphocytes.

Sickle cell dehydration: Pathophysiology and therapeutic applications

Cell dehydration is a distinguishing characteristic of sickle cell disease and an important contributor to disease pathophysiology. Due to the unique dependence of Hb S polymerization on cellular Hb S concentration, cell dehydration promotes polymerization and sickling. In double heterozygosis for Hb S and C (SC disease) dehydration is the determining factor in disease pathophysiology. Three major ion transport pathways are involved in sickle cell dehydration: the K-Cl cotransport (KCC), the Gardos channel (KCNN4) and Psickle, the polymerization induced membrane permeability, most likely mediated by the mechano-sensitive ion channel PIEZO1. Each of these pathways exhibit unique characteristics in regulation by oxygen tension, intracellular and extracellular environment, and functional expression in reticulocytes and mature red cells. The unique dependence of K-Cl cotransport on intracellular Mg and the abnormal reduction of erythrocyte Mg content in SS and SC cells had led to clinical studies assessing the effect of oral Mg supplementation. Inhibition of Gardos channel by clotrimazole and senicapoc has led to Phase 1,2,3 trials in patients with sickle cell disease. While none of these studies has resulted in the approval of a novel therapy for SS disease, they have highlighted the key role played by these pathways in disease pathophysiology.

KCa3.1 Channel Modulators as Potential Therapeutic Compounds for Glioblastoma

BACKGROUND

The intermediate-conductance Ca2+-activated K+ channel KCa3.1 is widely expressed in cells of the immune system such as T- and B-lymphocytes, mast cells, macrophages and microglia, but also found in dedifferentiated vascular smooth muscle cells, fibroblasts and many cancer cells including pancreatic, prostate, leukemia and glioblastoma. In all these cell types KCa3.1 plays an important role in cellular activation, migration and proliferation by regulating membrane potential and Ca2+ signaling.

METHODS AND RESULTS

KCa3.1 therefore constitutes an attractive therapeutic target for diseases involving excessive proliferation or activation of one more of these cell types and researchers both in academia and in the pharmaceutical industry have developed several potent and selective small molecule inhibitors of KCa3.1. This article will briefly review the available compounds (TRAM-34, senicapoc, NS6180), their binding sites and mechanisms of action, and then discuss the potential usefulness of these compounds for the treatment of brain tumors based on their brain penetration and their efficacy in reducing microglia activation in animal models of ischemic stroke and Alzheimer's disease.

CONCLUSION

Senicapoc, which has previously been in Phase III clinical trials, would be available for repurposing, and could be used to quickly translate findings made with other KCa3.1 blocking tool compounds into clinical trials.

Structural insights into the potency of SK channel positive modulators

Small-conductance Ca2+-activated K+ (SK) channels play essential roles in the regulation of cellular excitability and have been implicated in neurological and cardiovascular diseases through both animal model studies and human genetic association studies. Over the past two decades, positive modulators of SK channels such as NS309 and 1-EBIO have been developed. Our previous structural studies have identified the binding pocket of 1-EBIO and NS309 that is located at the interface between the channel and calmodulin. In this study, we took advantage of four compounds with potencies varying over three orders of magnitude, including 1-EBIO, NS309, SKS-11 (6-bromo-5-methyl-1H-indole-2,3-dione-3-oxime) and SKS-14 (7-fluoro-3-(hydroxyimino)indolin-2-one). A combination of x-ray crystallographic, computational and electrophysiological approaches was utilized to investigate the interactions between the positive modulators and their binding pocket. A strong trend exists between the interaction energy of the compounds within their binding site calculated from the crystal structures, and the potency of these compounds in potentiating the SK2 channel current determined by electrophysiological recordings. Our results further reveal that the difference in potency of the positive modulators in potentiating SK2 channel activity may be attributed primarily to specific electrostatic interactions between the modulators and their binding pocket.

Structural Determinants for the Selectivity of the Positive KCa3.1 Gating Modulator 5-Methylnaphtho[2,1-d]oxazol-2-amine (SKA-121)

Intermediate-conductance (KCa3.1) and small-conductance (KCa2) calcium-activated K+ channels are gated by calcium binding to calmodulin (CaM) molecules associated with the calmodulin-binding domain (CaM-BD) of these channels. The existing KCa activators, such as naphtho[1,2-d]thiazol-2-ylamine (SKA-31), 6,7-dichloro-1H-indole-2,3-dione 3-oxime (NS309), and 1-ethylbenzimidazolin-2-one (EBIO), activate both channel types with similar potencies. In a previous chemistry effort, we optimized the benzothiazole pharmacophore of SKA-31 toward KCa3.1 selectivity and identified 5-methylnaphtho[2,1-d]oxazol-2-amine (SKA-121), which exhibits 40-fold selectivity for KCa3.1 over KCa2.3. To understand why introduction of a single CH3 group in five-position of the benzothiazole/oxazole system could achieve such a gain in selectivity for KCa3.1 over KCa2.3, we first localized the binding site of the benzothiazoles/oxazoles to the CaM-BD/CaM interface and then used computational modeling software to generate models of the KCa3.1 and KCa2.3 CaM-BD/CaM complexes with SKA-121. Based on a combination of mutagenesis and structural modeling, we suggest that all benzothiazole/oxazole-type KCa activators bind relatively "deep" in the CaM-BD/CaM interface and hydrogen bond with E54 on CaM. In KCa3.1, SKA-121 forms an additional hydrogen bond network with R362. In contrast, NS309 sits more "forward" and directly hydrogen bonds with R362 in KCa3.1. Mutating R362 to serine, the corresponding residue in KCa2.3 reduces the potency of SKA-121 by 7-fold, suggesting that R362 is responsible for the generally greater potency of KCa activators on KCa3.1. The increase in SKA-121's KCa3.1 selectivity compared with its parent, SKA-31, seems to be due to better overall shape complementarity and hydrophobic interactions with S372 and M368 on KCa3.1 and M72 on CaM at the KCa3.1-CaM-BD/CaM interface.