4-Phenoxybutoxy-substituted heterocycles--a structure-activity relationship study of blockers of the lymphocyte potassium channel Kv1.3

Kv1.3 in the spotlight for treating immune diseases

INTRODUCTION

Kv1.3 is the main voltage-gated potassium channel of leukocytes from both the innate and adaptive immune systems. Channel function is required for common processes such as Ca2+ signaling but also for cell-specific events. In this context, alterations in Kv1.3 are associated with multiple immune disorders. Excessive channel activity correlates with numerous autoimmune diseases, while reduced currents result in increased cancer prevalence and immunodeficiencies.

AREAS COVERED

This review offers a general view of the role of Kv1.3 in every type of leukocyte. Moreover, diseases stemming from dysregulations of the channel are detailed, as well as current advances in their therapeutic research.

EXPERT OPINION

Kv1.3 arises as a potential immune target in a variety of diseases. Several lines of research focused on channel modulation have yielded positive results. However, among the great variety of specific channel blockers, only one has reached clinical trials. Future investigations should focus on developing simpler administration routes for channel inhibitors to facilitate their entrance into clinical trials. Prospective Kv1.3-based treatments will ensure powerful therapies while minimizing undesired side effects.

Bergapten attenuates microglia-mediated neuroinflammation and ischemic brain injury by targeting Kv1.3 and Carbonyl reductase 1

Microglia-mediated neuroinflammation plays a vital role in the pathogenesis of ischemic stroke, which serves as a prime target for developing novel therapeutic agent. However, feasible and effective agents for controlling neuroinflammation are scarce. Bergapten were acknowledged to hold therapeutic potential in restricting inflammation in multiple diseases, including peripheral neuropathy, migraine headaches and osteoarthritis. Here, we aimed to investigate the impact of bergapten on microglia-mediated neuroinflammation and its therapeutic potential in ischemic stroke. Our study demonstrated that bergapten significantly reduced the expression of pro-inflammatory cytokines and the activation of NF-κB signaling pathway in LPS-stimulated primary microglia. Mechanistically, bergapten suppressed cellular potassium ion efflux by inhibiting Kv1.3 channel and inhibits the degradation of Carbonyl reductase 1 induced by LPS, which might contribute to the anti-inflammatory effect of bergapten. Furthermore, bergapten suppressed microglial activation and post-stroke neuroinflammation in an experimental stroke model, leading to reduced infarct size and improved functional recovery. Thus, our study identified that bergapten might be a potential therapeutic compound for the treatment of ischemic stroke.

Discovery of KV 1.3 ion channel inhibitors: Medicinal chemistry approaches and challenges

The KV 1.3 voltage-gated potassium ion channel is involved in many physiological processes both at the plasma membrane and in the mitochondria, chiefly in the immune and nervous systems. Therapeutic targeting KV 1.3 with specific peptides and small molecule inhibitors shows great potential for treating cancers and autoimmune diseases, such as multiple sclerosis, type I diabetes mellitus, psoriasis, contact dermatitis, rheumatoid arthritis, and myasthenia gravis. However, no KV 1.3-targeted compounds have been approved for therapeutic use to date. This review focuses on the presentation of approaches for discovering new KV 1.3 peptide and small-molecule inhibitors, and strategies to improve the selectivity of active compounds toward KV 1.3. Selectivity of dalatazide (ShK-186), a synthetic derivate of the sea anemone toxin ShK, was achieved by chemical modification and has successfully reached clinical trials as a potential therapeutic for treating autoimmune diseases. Other peptides and small-molecule inhibitors are critically evaluated for their lead-like characteristics and potential for progression into clinical development. Some small-molecule inhibitors with well-defined structure-activity relationships have been optimized for selective delivery to mitochondria, and these offer therapeutic potential for the treatment of cancers. This overview of KV 1.3 inhibitors and methodologies is designed to provide a good starting point for drug discovery to identify novel effective KV 1.3 modulators against this target in the future.

Targeting mitochondrial ion channels for cancer therapy

Pharmacological targeting of mitochondrial ion channels is emerging as a promising approach to eliminate cancer cells; as most of these channels are differentially expressed and/or regulated in cancer cells in comparison to healthy ones, this strategy may selectively eliminate the former. Perturbation of ion fluxes across the outer and inner membranes is linked to alterations of redox state, membrane potential and bioenergetic efficiency. This leads to indirect modulation of oxidative phosphorylation, which is/may be fundamental for both cancer and cancer stem cell survival. Furthermore, given the crucial contribution of mitochondria to intrinsic apoptosis, modulation of their ion channels leading to cytochrome c release may be of great advantage in case of resistance to drugs triggering apoptotic events upstream of the mitochondrial phase. In the present review, we give an overview of the known mitochondrial ion channels and of their modulators capable of killing cancer cells. In addition, we discuss state-of-the-art strategies using mitochondriotropic drugs or peptide-based approaches allowing a more efficient and selective targeting of mitochondrial ion channel-linked events.

Synthesis of linear hetarenochromones based on 7-hydroxy-6-formyl(acetyl)chromones

Fused chromones are attracting increasing attention as novel therapeutic agents due to their wide distribution in nature, effective bioactivities and low toxicity. 6-Carbonyl-7-hydroxychromones proved to be versatile synthons for the synthesis of linear hetarenochromones by annulation of heterocycle to the chromone core. The present review is focused on the syntheses of furo[3,2-g]chromones, pyrano[3,2-g]chromones and some of their N-containing analogues, namely chromeno[6,7-d]isoxazoles, pyrano[3’,2’:6,7]chromeno[4,3-b]pyridine-5,11-diones and pyrano[3’,2’:6,7]chromeno[4,3-c]pyridine-5,11-diones based on the 7-hydroxy-6-formylchromones or 7-hydroxy-6-acetylchromones and shows the current state of research to date. The methods for the synthesis of the starting 7-hydroxy-6-formylchromones and 7-hydroxy-6-acetylchromones have been also mentioned. The biological activity of naturally occurring and modified synthetic linear hetarenochromones has been also represented.

Insight into the mechanism of cytotoxicity of membrane-permeant psoralenic Kv1.3 channel inhibitors by chemical dissection of a novel member of the family

The potassium channel Kv1.3, involved in several important pathologies, is the target of a family of psoralen-based drugs whose mechanism of action is not fully understood. Here we provide evidence for a physical interaction of the mitochondria-located Kv1.3 (mtKv1.3) and Complex I of the respiratory chain and show that this proximity underlies the death-inducing ability of psoralenic Kv1.3 inhibitors. The effects of PAP-1-MHEG (PAP-1, a Kv1.3 inhibitor, with six monomeric ethylene glycol units attached to the phenyl ring of PAP-1), a more soluble novel derivative of PAP-1 and of its various portions on mitochondrial physiology indicate that the psoralenic moiety of PAP-1 bound to mtKv1.3 facilitates the diversion of electrons from Complex I to molecular oxygen. The resulting massive production of toxic Reactive Oxygen Species leads to death of cancer cells expressing Kv1.3. In vivo, PAP-1-MHEG significantly decreased melanoma volume. In summary, PAP-1-MHEG offers insights into the mechanisms of cytotoxicity of this family of compounds and may represent a valuable clinical tool.

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The mitochondrial channel mitoKv1.3 is a promising pharmacological target.

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MitoKv1.3 interacts with Complex I of the respiratory chain.

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Psoralenic inhibitors of Kv1.3 facilitate the diversion of e⁻ from complex I to O₂.

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A novel psoralenic Kv1.3 inhibitor with increased solubility reduces melanoma volume.

Suppression of connexin 43 phosphorylation promotes astrocyte survival and vascular regeneration in proliferative retinopathy

Degeneration of retinal astrocytes precedes hypoxia-driven pathologic neovascularization and vascular leakage in ischemic retinopathies. However, the molecular events that underlie astrocyte loss remain unclear. Astrocytes abundantly express connexin 43 (Cx43), a transmembrane protein that forms gap junction (GJ) channels and hemichannels. Cx channels can transfer toxic signals from dying cells to healthy neighbors under pathologic conditions. Here we show that Cx43 plays a critical role in astrocyte apoptosis and the resulting preretinal neovascularization in a mouse model of oxygen-induced retinopathy. Opening of Cx43 hemichannels was not observed following hypoxia. In contrast, GJ coupling between astrocytes increased, which could lead to amplification of injury. Accordingly, conditional deletion of Cx43 maintained a higher density of astrocytes in the hypoxic retina. We also identify a role for Cx43 phosphorylation in mediating these processes. Increased coupling in response to hypoxia is due to phosphorylation of Cx43 by casein kinase 1δ (CK1δ). Suppression of this phosphorylation using an inhibitor of CK1δ or in site-specific phosphorylation-deficient mice similarly protected astrocytes from hypoxic damage. Rescue of astrocytes led to restoration of a functional retinal vasculature and lowered the hypoxic burden, thereby curtailing neovascularization and neuroretinal dysfunction. We also find that absence of astrocytic Cx43 does not affect developmental angiogenesis or neuronal function in normoxic retinas. Our in vivo work directly links phosphorylation of Cx43 to astrocytic coupling and apoptosis and ultimately to vascular regeneration in retinal ischemia. This study reveals that targeting Cx43 phosphorylation in astrocytes is a potential direction for the treatment of proliferative retinopathies.

Rhodium-catalyzed cyclization of acceptor-substituted biphenyl α-diazoketones: a study of the substitution effect on chemoselectivity

A range of biphenyl α-diazoketones containing different α-electron withdrawing groups exhibits divergent chemoselectivity toward rhodium(ii) catalysis, delivering phenanthrols, benz[α]azulenones, aromatic ketones and/or 1,2-diketones in varying ratios.

Direct Pharmacological Targeting of a Mitochondrial Ion Channel Selectively Kills Tumor Cells In Vivo

The potassium channel Kv1.3 is highly expressed in the mitochondria of various cancerous cells. Here we show that direct inhibition of Kv1.3 using two mitochondria-targeted inhibitors alters mitochondrial function and leads to reactive oxygen species (ROS)-mediated death of even chemoresistant cells independently of p53 status. These inhibitors killed 98% of ex vivo primary chronic B-lymphocytic leukemia tumor cells while sparing healthy B cells. In orthotopic mouse models of melanoma and pancreatic ductal adenocarcinoma, the compounds reduced tumor size by more than 90% and 60%, respectively, while sparing immune and cardiac functions. Our work provides direct evidence that specific pharmacological targeting of a mitochondrial potassium channel can lead to ROS-mediated selective apoptosis of cancer cells in vivo, without causing significant side effects.

Understanding autoimmunity: The ion channel perspective

Ion channels are integral membrane proteins that orchestrate the passage of ions across the cell membrane and thus regulate various key physiological processes of the living system. The stringently regulated expression and function of these channels hold a pivotal role in the development and execution of various cellular functions. Malfunction of these channels results in debilitating diseases collectively termed channelopathies. In this review, we highlight the role of these proteins in the immune system with special emphasis on the development of autoimmunity. The role of ion channels in various autoimmune diseases is also listed out. This comprehensive review summarizes the ion channels that could be used as molecular targets in the development of new therapeutics against autoimmune disorders.

Synthesis, reactions and biological activities of furochromones: a review

Furochromone derivatives are important synthetic targets which showed a myriad of interesting biological activities. Ammi visnaga (Umbelliferae) is the most famous source of these derivatives, which has been used in folk medicine for millennia targeting different ailments. Since the isolation of furochromone derivatives, different synthetic methodologies were developed for their preparation. Despite the recent interesting findings on this class of compounds, the chemical literatures lack a comprehensive summary on the synthetic methodologies and biological activities of furochromone derivatives. This review highlights recent advances in furochromones chemistry by discussing different synthetic procedures developed for the preparation of naturally occurring derivatives as well as other unique derivatives which showed promising biological activities. It also sheds light on the most common reactions of furochromone derivatives and the utilization of these derivatives as the blocks for many biologically active compounds.

Inhibition of hepatitis C virus replication by chalepin and pseudane IX isolated from Ruta angustifolia leaves

Hepatitis C virus (HCV) infection is highly prevalent among global populations, with an estimated number of infected patients being 170 million. Approximately 70-80% of patients acutely infected with HCV will progress to chronic liver disease, such as liver cirrhosis and hepatocellular carcinoma, which is a substantial cause of morbidity and mortality worldwide. New therapies for HCV infection have been developed, however, the therapeutic efficacies still need to be improved. Medicinal plants are promising sources for antivirals against HCV. A variety of plants have been tested and proven to be beneficial as antiviral drug candidates against HCV. In this study, we examined extracts, their subfractions and isolated compounds of Ruta angustifolia leaves for antiviral activities against HCV in cell culture. We isolated six compounds, chalepin, scopoletin, γ-fagarine, arborinine, kokusaginine and pseudane IX. Among them, chalepin and pseudane IX showed strong anti-HCV activities with 50% inhibitory concentration (IC₅₀) of 1.7 ± 0.5 and 1.4 ± 0.2 μg/ml, respectively, without apparent cytotoxicity. Their anti-HCV activities were stronger than that of ribavirin (2.8 ± 0.4 μg/ml), which has been widely used for the treatment of HCV infection. Mode-of-action analyses revealed that chalepin and pseudane IX inhibited HCV at the post-entry step and decreased the levels of HCV RNA replication and viral protein synthesis. We also observed that arborinine, kokusaginine and γ-fagarine possessed moderate levels of anti-HCV activities with IC₅₀ values being 6.4 ± 0.7, 6.4 ± 1.6 and 20.4 ± 0.4 μg/ml, respectively, whereas scopoletin did not exert significant anti-HCV activities at 30 μg/ml.

Targeting potassium channels Kv1.3 and KC a 3.1: routes to selective immunomodulators in autoimmune disorder treatment?

The Kv1.3 and KC a 3.1 potassium channels are promising targets for the treatment of autoimmune disorders. Many Kv1.3 and KC a 3.1 blockers have a more favorable adverse event profiles than existing immunosuppressants, suggesting the selectivity of Kv1.3 and KC a 3.1 blockade. The Kv1.3 and KC a 3.1 blockers exert differential effects in different autoimmune diseases. The Kv1.3 inhibitors or gene deletion have been shown to have benefits in multiple sclerosis, type 1 diabetes, rheumatoid arthritis, psoriasis, and rapidly progressive glomerulonephritis. The KC a 3.1 blockers have demonstrated efficacy in human primary biliary cirrhosis and showed protective effects in animal models of severe colitis, allergic encephalomyelitis, inflammatory bowel disease, and multiple sclerosis. The KC a 3.1 blockers are not considered candidates for treatment of multiple sclerosis. The selective immunosuppressive effects of the Kv1.3 and KC a 3.1 blockers are due to the differences in their distribution on autoimmune-related immune cells and tissues and β1 integrin (very late activating antigen)-Kv1.3 channel cross-talk.

The antibody targeting the E314 peptide of human Kv1.3 pore region serves as a novel, potent and specific channel blocker

Selective blockade of Kv1.3 channels in effector memory T (T(EM)) cells was validated to ameliorate autoimmune or autoimmune-associated diseases. We generated the antibody directed against one peptide of human Kv1.3 (hKv1.3) extracellular loop as a novel and possible Kv1.3 blocker. One peptide of hKv1.3 extracellular loop E3 containing 14 amino acids (E314) was chosen as an antigenic determinant to generate the E314 antibody. The E314 antibody specifically recognized 63.8KD protein stably expressed in hKv1.3-HEK 293 cell lines, whereas it did not recognize or cross-react to human Kv1.1(hKv1.1), Kv1.2(hKv1.2), Kv1.4(hKv1.4), Kv1.5(hKv1.5), KCa3.1(hKCa3.1), HERG, hKCNQ1/hKCNE1, Nav1.5 and Cav1.2 proteins stably expressed in HEK 293 cell lines or in human atrial or ventricular myocytes by Western blotting analysis and immunostaining detection. By the technique of whole-cell patch clamp, the E314 antibody was shown to have a directly inhibitory effect on hKv1.3 currents expressed in HEK 293 or Jurkat T cells and the inhibition showed a concentration-dependence. However, it exerted no significant difference on hKv1.1, hKv1.2, hKv1.4, hKv1.5, hKCa3.1, HERG, hKCNQ1/hKCNE1, L-type Ca(2+) or voltage-gated Na(+) currents. The present study demonstrates that the antibody targeting the E314 peptide of hKv1.3 pore region could be a novel, potent and specific hKv1.3 blocker without affecting a variety of closely related K(v)1 channels, KCa3.1 channels and functional cardiac ion channels underlying central nervous system (CNS) disorders or drug-acquired arrhythmias, which is required as a safe clinic-promising channel blocker.

Pharmacological inhibition of Kv1.3 fails to modulate insulin sensitivity in diabetic mice or human insulin-sensitive tissues

Genetic ablation of the voltage-gated potassium channel Kv1.3 improves insulin sensitivity and increases metabolic rate in mice. Inhibition of Kv1.3 in mouse adipose and skeletal muscle is reported to increase glucose uptake through increased GLUT4 translocation. Since Kv1.3 represents a novel target for the treatment of diabetes, the present study investigated whether Kv1.3 is functionally expressed in human adipose and skeletal muscle and whether specific pharmacological inhibition of the channel is capable of modulating insulin sensitivity in diabetic mouse models. Voltage-gated K(+) channel currents in human skeletal muscle cells (SkMC) were insensitive to block by the specific Kv1.3 blockers 5-(4-phenoxybutoxy)psoralen (PAP-1) and margatoxin (MgTX). Glucose uptake into SkMC and mouse 3T3-L1 adipocytes was also unaffected by treatment with PAP-1 or MgTX. Kv1.3 protein expression was not observed in human adipose or skeletal muscle from normal and type 2 diabetic donors. To investigate the effect of specific Kv1.3 inhibition on insulin sensitivity in vivo, PAP-1 was administered to hyperglycemic mice either acutely or for 5 days prior to an insulin tolerance test. No effect on insulin sensitivity was observed at free plasma PAP-1 concentrations that are specific for inhibition of Kv1.3. Insulin sensitivity was increased only when plasma concentrations of PAP-1 were sufficient to inhibit other Kv1 channels. Surprisingly, acute inhibition of Kv1.3 in the brain was found to decrease insulin sensitivity in ob/ob mice. Overall, these findings are not supportive of a role for Kv1.3 in the modulation of peripheral insulin sensitivity.

Antitubercular chromones and flavonoids from Pisonia aculeata

Three new chromones, pisonins A (1), B (2), and D (4), two new flavonoids, pisonivanone [(2S)-5,7,2'-trihydroxy-8-methylflavanone] (7) and pisonivanol [(2R,3R)-3,7-dihydroxy-5,6-dimethoxyflavanone] (8), one new isoflavonoid, pisonianone (5,7,2'-trihydroxy-6-methoxy-8-methylisoflavone) (9), and five compounds first isolated from nature, namely, pisonins C (3), E (5), and F (6), pisoniamide (10), and pisonolic acid (11), together with 18 known compounds have been isolated from the methanol extract of the combined stem and root of Pisonia aculeata. Among these isolates, 2, 7, 14, 16, and 19 exhibited antitubercular activities (MICs≤50.0 μg/mL) against Mycobacterium tuberculosis H37Rv in vitro.

Concise synthesis of 5-methoxy-6-hydroxy-2-methylchromone-7-O- and 5-hydroxy-2-methylchromone-7-O-rutinosides. Investigation of their cytotoxic activities against several human tumor cell lines

The synthesis of two novel 2-methylchromone-7-O-rutinosides is reported, and the in vitro biological activities of these compounds and their synthetic precursors have been investigated on the basis of their cytotoxicity against several human tumor cell lines. The synthesis features early stage assembly of the acidic labile glycosidic bond between sugar and 2-methylchromone aglycon under phase transfer catalyzed glycosidation conditions, whereas all the other standard glycosylation conditions specific to a wide array of rutinosyl donors bearing different anomeric leaving groups (e.g., SPh, OC(NH)CCl(3), Br, OH groups) failed to furnish any detectable products.

Substituted N-{3-[(1,1-dioxido-1,2-benzothiazol-3-yl)(phenyl)amino]propyl}benzamide analogs as potent Kv1.3 ion channel blockers. Part 2

We report the synthesis and in vitro activity of a series of novel substituted N-{3-[(1,1-dioxido-1,2-benzothiazol-3-yl)(phenyl)amino]propyl}benzamide analogs. These analogs showed potent inhibitory activity against Kv1.3. Several demonstrated similar potency to the known Kv1.3 inhibitor PAP-1 when tested under the IonWorks patch clamp assay conditions. Two compounds 13i and 13rr were advanced further as potential tool compounds for in vivo validation studies.

N-{3-[(1,1-dioxido-1,2-benzothiazol-3-yl)(phenyl)amino]propyl}benzamide analogs as potent Kv1.3 inhibitors. Part 1

We report the synthesis and in vitro activity of a series of novel N-{3-[(1,1-dioxido-1,2-benzothiazol-3-yl)(phenyl)amino]propyl}benzamide analogs. These analogs showed potent inhibitory activity against Kv1.3. Several compounds, including compound 8b, showed similar potency to the known Kv1.3 inhibitor PAP-1 when tested under the IonWorks patch clamp assay conditions.

Catalytic asymmetric synthesis of R207910

The first asymmetric synthesis of a very promising antituberculosis drug candidate, R207910, was achieved by developing two novel catalytic transformations; a catalytic enantioselective proton migration and a catalytic diastereoselective allylation of an intermediate alpha-chiral ketone. Using 2.5 mol % of a Y-catalyst derived from Y(HMDS)(3) and the new chiral ligand 9, 1.25 mol % of p-methoxypyridine N-oxide (MEPO), and 0.5 mol % of Bu(4)NCl, alpha-chiral ketone 3 was produced from enone 4 with 88% ee. This reaction proceeded through a catalytic chiral Y-dienolate generation via deprotonation at the gamma-position of 4, followed by regio- and enantioselective protonation at the alpha-position of the resulting dienolate. Preliminary mechanistic studies suggested that a Y: 9: MEPO = 2: 3: 1 ternary complex was the active catalyst. Bu(4)NCl markedly accelerated the reaction without affecting enantioselectivity. Enantiomerically pure 3 was obtained through a single recrystallization. The second key catalytic allylation of ketone 3 was promoted by CuF.3PPh(3).2EtOH (10 mol %) in the presence of KO(t)Bu (15 mol %), ZnCl(2) (1 equiv), and Bu(4)PBF(4) (1 equiv), giving the desired diastereomer 2 in quantitative yield with a 14: 1 ratio without any epimerization at the alpha-stereocenter. It is noteworthy that conventional organometallic addition reactions did not produce the desired products due to the high steric demand and a fairly acidic alpha-proton in substrate ketone 3. This first catalytic asymmetric synthesis of R207910 includes 12 longest linear steps from commercially available compounds with an overall yield of 5%.

Potassium channel block by a tripartite complex of two cationophilic ligands and a potassium ion

Voltage-gated potassium channels (Kv) are targets for drugs of large chemical diversity. Although hydrophobic cations block Kv channels with Hill coefficients of 1, uncharged electron-rich (cationophilic) molecules often display Hill coefficients of 2. The mechanism of the latter block is unknown. Using a combination of computational and experimental approaches, we mapped the receptor for the immunosuppressant PAP-1 (5-(4-phenoxybutoxy)psoralen), a high-affinity blocker of Kv1.3 channels in lymphocytes. Ligand-docking using Monte Carlo minimizations suggested a model in which two cationophilic PAP-1 molecules coordinate a K(+) ion in the pore with their coumarin moieties, whereas the hydrophobic phenoxyalkoxy side chains extend into the intrasubunit interfaces between helices S5 and S6. We tested the model by generating 58 point mutants involving residues in and around the predicted receptor and then determined their biophysical properties and sensitivity to PAP-1 by whole-cell patch-clamp. The model correctly predicted the key PAP-1-sensing residues in the outer helix, the P-loop, and the inner helix and explained the Hill coefficient of 2 by demonstrating that the Kv1.3 pore can accommodate two or even four PAP-1 molecules. The model further explained the voltage-dependence of block by PAP-1 and its thousand-fold selectivity for Kv1.3 over non-Kv1 channels. The 23- to 125-fold selectivity of PAP-1 for Kv1.3 over other Kv1 channels is probably due to its preferential affinity to the C-type inactivated state, in which cessation of K(+) flux stabilizes the tripartite PAP-1:K(+):PAP-1 complex in the pore. Our study provides a new concept for potassium channel block by cationophilic ligands.