A new class of blockers of the voltage-gated potassium channel Kv1.3 via modification of the 4- or 7-position of khellinone

Synthesis, Herbicidal Activity, and Structure-Activity Relationships of O-Alkyl Analogues of Khellin and Visnagin

Khellin and visnagin furanochromones were recently reported as potential new bioherbicides with phytotoxic activities comparable to those of some commercially available herbicides. In this study, we examined the effect of O-alkylation and O-arylalkylation of both khellin and visnagin on its effect on herbicidal and antifungal activity. Synthetic analogues included O-demethyl khellin and visnagin, acetylated O-demethyl khellin and visnagin, O-benzylated demethyl khellin and visnagin, four O-demethyl alkylated khellin analogues, and six O-demethyl alkylated visnagin analogues, many of which are reported here for the first time. Both acetate analogues of khellin and visnagin indicated more activity as herbicides on Lemna pausicostata than visnagin, with IC50 values of 71.7 and 77.6 μM, respectively. Complete loss of activity for all O-alkyl analogues with a carbon chain length of greater than 14 carbons was observed. The O-demethyl butylated visnagin analogue was the most active compound with an IC50 of 47.2 μM against L. pausicostata. O-Demethyl ethylated analogues of both khellin and visnagin were as effective as khellin. In the antifungal bioautography bioassay against Colletotrichum fragariae at 100 μg, the only active O-alkyl and O-arylalkyl analogues were O-ethylated, O-butylated, and O-benzylated visnagin analogues with zones of inhibition of 10, 9, and 9 mm, respectively, an effect comparable to that of visnagin and khellin.

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.

Khellinoflavanone, a Semisynthetic Derivative of Khellin, Overcomes Benzo[a]pyrene Toxicity in Human Normal and Cancer Cells That Express CYP1A1

Cytochrome P450 family 1 (CYP1) enzymes catalyze the metabolic activation of environmental procarcinogens such as benzo[a]pyrene, B[a]P, into carcinogens, which initiates the process of carcinogenesis. Thus, stopping the metabolic activation of procarcinogens can possibly prevent the onset of cancer. Several natural products have been reported to show unique ability in inhibiting CYP1 enzymes. We found that khellin, a naturally occurring furanochromone from Ammi visnaga, inhibits CYP1A1 enzyme with an IC50 value of 4.02 μM in CYP1A1-overexpressing human HEK293 suspension cells. To further explore this natural product for discovery of more potent and selective CYP1A1 inhibitors, two sets of semisynthetic derivatives were prepared. Treatment of khellin with alkali results in opening of a pyrone ring, yielding khellinone (2). Claisen-Schmidt condensation of khellinone (2) with various aldehydes in presence of potassium hydroxide, at room temperature, provides a series of furanochalcones 3a-v (khellinochalcones). Treatment of khellinone (2) with aryl aldehydes in the presence of piperidine, under reflux, affords the flavanone series of compounds 4a-p (khellinoflavanones). The khellinoflavanone 4l potently inhibited CYP1A1 with an IC50 value of 140 nM in live cells, with 170-fold selectivity over CYP1B1 (IC50 for CYP1B1 = 23.8 μM). Compound 4l at 3× IC50 concentration for inhibition of CYP1A1 completely protected HEK293 cells from CYP1A1-mediated B[a]P toxicity. Lung cancer cells, A549 (p53+) and Calu-1 (p53-null), blocked in growth at the S-phase by B[a]P were restored into the cell cycle by compound 4l. The results presented herein strongly indicate the potential of these khellin derivatives for further development as cancer chemopreventive agents.

Feeling Nature's PAINS: Natural Products, Natural Product Drugs, and Pan Assay Interference Compounds (PAINS)

We have previously reported on classes of compounds that can interfere with bioassays via a number of different mechanisms and termed such compounds Pan Assay INterference compoundS, or PAINS. These compounds were defined on the basis of high-throughput data derived from vendor-supplied synthetics. The question therefore arises whether the concept of PAINS is relevant to compounds of natural origin. Here, it is shown that this is indeed the case, but that the context of the biological readout is an important factor that must be brought into consideration.

Novel Kv1.3 blockers for immunosuppression: WO2012155199

A recent patent application from Bionomics/Merck Serono describes novel compounds as blockers of the voltage-gated Kv1.3 ion channel. The blockade of this channel shows great promise as a new therapeutic target for the treatment of autoimmune disorders such as multiple sclerosis, psoriasis, diabetes and rheumatoid arthritis. The generic claim of this patent refers to a new chemotype of Kv1.3 blockers based on an amide core with potent IC50's which are potentially within the nanomolar range. This article briefly reviews the chemistry and biology found in the patent and compares it with previous discoveries in the field.

Structure-activity relationship exploration of Kv1.3 blockers based on diphenoxylate

Diphenoxylate, a well-known opioid agonist and anti-diarrhoeal agent, was recently found to block Kv1.3 potassium channels, which have been proposed as potential therapeutic targets for a range of autoimmune diseases. The molecular basis for this Kv1.3 blockade was assessed by the selective removal of functional groups from the structure of diphenoxylate as well as a number of other structural variations. Removal of the nitrile functional group and replacement of the C-4 piperidinyl substituents resulted in several compounds with submicromolar IC(50) values.

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.

The Lymphocyte Potassium Channels Kv1.3 and KCa3.1 as Targets for Immunosuppression

The voltage-gated Kv1.3 and the calcium-activated KCa3.1 potassium channel modulate many calcium-dependent cellular processes in immune cells, including T-cell activation and proliferation, and have therefore been proposed as novel therapeutic targets for immunomodulation. Kv1.3 is highly expressed in CCR7(-) effector memory T cells and is emerging as a target for T-cell mediated diseases like multiple sclerosis, rheumatoid arthritis, type-1 diabetes mellitus, allergic contact dermatitis, and psoriasis. KCa3.1 in contrast is expressed in CCR7(+) naïve and central memory T cells, as well as in mast cells, macrophages, dedifferentiated vascular smooth muscle cells, fibroblasts, vascular endothelium, and airway epithelium. Given this expression pattern, KCa3.1 is a potential therapeutic target for conditions ranging from inflammatory bowel disease, multiple sclerosis, arthritis, and asthma to cardiovascular diseases like atherosclerosis and post-angioplasty restenosis. Results from animal studies have been supportive of the therapeutic potential of both Kv1.3 and KCa3.1 blockers and have also not shown any toxicities associated with pharmacological Kv1.3 and KCa3.1 blockade. To date, two compounds targeting Kv1.3 are in preclinical development but, so far, no Kv1.3 blocker has advanced into clinical trials. KCa3.1 blockers, on the other hand, have been evaluated in clinical trials for sickle cell anemia and exercise-induced asthma, but have so far not shown efficacy. However, the trial results support KCa3.1 as a safe therapeutic target, and will hopefully help enable clinical trials for other medical conditions that might benefit from KCa3.1 blockade.

Spiro azepane-oxazolidinones as Kv1.3 potassium channel blockers: WO2010066840

This article evaluates a patent application from Solvay Pharmaceuticals, which claims spiro azepane-oxazolidinones as novel blockers of the voltage-gated potassium channel Kv1.3 for the treatment of diabetes, psoriasis, obesity, transplant rejection and T-cell mediated autoimmune diseases such as rheumatoid arthritis and MS. The patent describes a new chemotype of Kv1.3 blockers and thus illustrates the growing interest of the pharmaceutical industry in Kv1.3 as a target of immunosuppression and metabolic disorders. This article briefly summarizes the chemistry and biological data provided in the patent and then compares the new compounds to Kv1.3 blockers previously disclosed by both academia and pharmaceutical companies.

Pharmacological modulation of voltage-gated potassium channels as a therapeutic strategy

IMPORTANCE OF THE FIELD

The human genome encodes at least 40 distinct voltage-gated potassium channel subtypes, which vary in regional expression, pharmacological and biophysical properties. Voltage-dependent potassium (Kv) channels help orchestrate many of the physiological and pathophysiological processes that promote and sometimes hinder the healthy functioning of our bodies.

AREAS COVERED IN THIS REVIEW

This review summarizes patent and scientific literature reports from the past decade highlighting the opportunities that Kv channels offer for the development of new therapeutic interventions for a wide variety of disorders.

WHAT THE READER WILL GAIN

The reader will gain an insight from an analysis of the associations of different Kv family members with disease processes, summary and evaluation of the development of therapeutically relevant pharmacological modulators of these channels, particularly focusing on proprietary agents being developed.

TAKE HOME MESSAGE

Development of new drugs that target Kv channels continue to be of great interest but is proving to be challenging. Nevertheless, opportunities for Kv channel modulators to have an impact on a wide range of disorders in the future remain an exciting prospect.

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.

Voltage-gated potassium channels as therapeutic targets

The human genome encodes 40 voltage-gated K(+) channels (K(V)), which are involved in diverse physiological processes ranging from repolarization of neuronal and cardiac action potentials, to regulating Ca(2+) signalling and cell volume, to driving cellular proliferation and migration. K(V) channels offer tremendous opportunities for the development of new drugs to treat cancer, autoimmune diseases and metabolic, neurological and cardiovascular disorders. This Review discusses pharmacological strategies for targeting K(V) channels with venom peptides, antibodies and small molecules, and highlights recent progress in the preclinical and clinical development of drugs targeting the K(V)1 subfamily, the K(V)7 subfamily (also known as KCNQ), K(V)10.1 (also known as EAG1 and KCNH1) and K(V)11.1 (also known as HERG and KCNH2) channels.

The functional network of ion channels in T lymphocytes

For more than 25 years, it has been widely appreciated that Ca2+ influx is essential to trigger T-lymphocyte activation. Patch clamp analysis, molecular identification, and functional studies using blockers and genetic manipulation have shown that a unique contingent of ion channels orchestrates the initiation, intensity, and duration of the Ca2+ signal. Five distinct types of ion channels--Kv1.3, KCa3.1, Orai1+ stromal interacting molecule 1 (STIM1) [Ca2+-release activating Ca2+ (CRAC) channel], TRPM7, and Cl(swell)--comprise a network that performs functions vital for ongoing cellular homeostasis and for T-cell activation, offering potential targets for immunomodulation. Most recently, the roles of STIM1 and Orai1 have been revealed in triggering and forming the CRAC channel following T-cell receptor engagement. Kv1.3, KCa3.1, STIM1, and Orai1 have been found to cluster at the immunological synapse following contact with an antigen-presenting cell; we discuss how channels at the synapse might function to modulate local signaling. Immuno-imaging approaches are beginning to shed light on ion channel function in vivo. Importantly, the expression pattern of Ca2+ and K+ channels and hence the functional network can adapt depending upon the state of differentiation and activation, and this allows for different stages of an immune response to be targeted specifically.

Enantioselective total synthesis of (-)-candelalides A, B and C: potential Kv1.3 blocking immunosuppressive agents

Novel Kv1.3 blocking immunosuppressants, (-)-candelalides A, B and C, were efficiently synthesized for the first time in a convergent and unified manner starting from (+)-5-methyl-Wieland-Miescher ketone. The synthetic method involved the following key steps: i) a strategic [2,3]-Wittig rearrangement of a stannylmethyl ether to install the stereogenic center at C9 and the exo-methylene function at C8 present in the decalin portion; ii) a straightforward coupling of a trans-decalin portion (BC ring) and a gamma-pyrone moiety through the C16-C3' bond to assemble the requisite carbon framework; and iii) a construction of a characteristic di or tetrahydropyran ring (A ring) by internal nucleophilic ring closure of a hydroxy aldehyde or a hydroxy epoxide. The present total synthesis has fully established the absolute configuration of these natural products.

Inhibitors of potassium channels KV1.3 and IK-1 as immunosuppressants

New structural classes of K(V)1.3 and IK-1 ion channel blockers have been identified based on a virtual high throughput screening approach using a homology model of KcsA. These compounds display inhibitory effects on T-cell and/or keratinocyte proliferation and immunosuppressant activity within a DTH animal model.

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

The voltage-gated potassium channel Kv1.3 constitutes an attractive pharmacological target for the treatment of effector memory T cell-mediated autoimmune diseases such as multiple sclerosis and psoriasis. Using 5-methoxypsoralen (5-MOP, 1), a compound isolated from Ruta graveolens, as a template we previously synthesized 5-(4-phenoxybutoxy)psoralen (PAP-1, 2) which inhibits Kv1.3 with an IC(50) of 2nM. Since PAP-1 is more than 1000-fold more potent than 5-MOP, we here investigated whether attaching a 4-phenoxybutoxy side chain to other heterocyclic systems would also produce potent Kv1.3 blockers. While 4-phenoxybutoxy-substituted quinolines, quinazolines and phenanthrenes were inactive, 4-phenoxybutoxy-substituted quinolinones, furoquinolines, coumarins or furochromones inhibited Kv1.3 with IC(50)s of 150 nM to 10 microM in whole-cell patch-clamp experiments. Our most potent new compound is 4-(4-phenoxybutoxy)-7H-furo[3,2-g]chromene-7-thione (73, IC(50) 17 nM), in which the carbonyl oxygen of PAP-1 is replaced by sulfur. Taken together, our results demonstrate that the psoralen system is a crucial part of the pharmacophore of phenoxyalkoxypsoralen-type Kv1.3 blockers.