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

Macrophage polarisation and inflammatory mechanisms in atherosclerosis: Implications for prevention and treatment

Atherosclerosis is a chronic inflammatory disease characterised by plaque accumulation in the arteries. Macrophages are immune cells that are crucial in the development of atherosclerosis. Macrophages can adopt different phenotypes, with the M1 phenotype promoting inflammation while the M2 phenotype counteracting it. This review focuses on the factors that drive the polarisation of M1 macrophages towards a pro-inflammatory phenotype during AS. Additionally, we explored metabolic reprogramming mechanisms and cytokines secretion by M1 macrophages. Hyperlipidaemia is widely recognised as a major risk factor for atherosclerosis. Modified lipoproteins released in the presence of hyperlipidaemia can trigger the release of cytokines and recruit circulating monocytes, which adhere to the damaged endothelium and differentiate into macrophages. Macrophages engulf lipids, leading to the formation of foam cells. As atherosclerosis progresses, foam cells become the necrotic core within the atherosclerotic plaques, destabilising them and triggering ischaemic disease. Furthermore, we discuss recent research focusing on targeting macrophages or inflammatory pathways for preventive or therapeutic purposes. These include statins, PCSK9 inhibitors, and promising nanotargeted drugs. These new developments hold the potential for the prevention and treatment of atherosclerosis and its related complications.

Role of Kv1.3 Channels in Platelet Functions and Thrombus Formation

Objective:

Platelet activation by stimulatory factors leads to an increase in intracellular calcium concentration ([Ca 2+ ] i ), which is essential for almost all platelet functions. Modulation of Ca 2+ influx and [Ca 2+ ] i in platelets has been emerging as a possible strategy for preventing and treating platelet-dependent thrombosis. Voltage-gated potassium 1.3 channels (Kv1.3) are highly expressed in platelets and able to regulate agonist-evoked [Ca 2+ ] i increase. However, the role of Kv1.3 channels in regulating platelet functions and thrombosis has not yet been elucidated. In addition, it is difficult to obtain a specific blocker for this channel, since Kv1.3 shares identical drug-binding sites with other K + channels. Here, we investigate whether specific blockade of Kv1.3 channels by monoclonal antibodies affects platelet functions and thrombosis.

Approach and Results:

In this study, we produced the anti-Kv1.3 monoclonal antibody 6E12#15, which could specifically recognize both human and mouse Kv1.3 proteins and sufficiently block Kv1.3 channel currents. We found Kv1.3 blockade by 6E12#15 inhibited platelet aggregation, adhesion, and activation upon agonist stimulation. In vivo treatment with 6E12#15 alleviated thrombus formation in a mesenteric arteriole thrombosis mouse model and protected mice from collagen/epinephrine-induced pulmonary thromboembolism. Furthermore, we observed Kv1.3 regulated platelet functions by modulating Ca 2+ influx and [Ca 2+ ] i elevation, and that this is mediated in part by P2X 1 . Interestingly, Kv1.3 −/− mice showed impaired platelet aggregation while displayed no abnormalities in in vivo thrombus formation. This phenomenon was related to more megakaryocytes and platelets produced in Kv1.3 −/− mice compared with wild-type mice.

Conclusions:

We showed specific inhibition of Kv1.3 by the novel monoclonal antibody 6E12#15 suppressed platelet functions and platelet-dependent thrombosis through modulating platelet [Ca 2+ ] i elevation. These results indicate that Kv1.3 could act as a promising therapeutic target for antiplatelet therapies.

Contributions of natural products to ion channel pharmacology

Covering: Up to 2020Ion channels are a vast super-family of membrane proteins that play critical physiological roles in excitable and non-excitable cells. Their biomedical importance makes them valuable and attractive drug targets for neurological, cardiovascular, gastrointestinal and metabolic diseases, and for cancer therapy and immune modulation. Current therapeutics target only a minor subset of ion channels, leaving a large unexploited space within the ion channel field. Natural products harnessed from the almost unlimited and diverse universe of compounds within the bioenvironment have been used to modulate channels for decades. In this review we highlight the impact made by natural products on ion channel pharmacology, specifically on K⁺, Na_V and Ca_V channels, and use case studies to describe the development of ion channel-modulating drugs from natural sources for the treatment of pain, heart disease and autoimmune diseases.

Antibodies and venom peptides: new modalities for ion channels

Ion channels play fundamental roles in both excitable and non-excitable tissues and therefore constitute attractive drug targets for myriad neurological, cardiovascular and metabolic diseases as well as for cancer and immunomodulation. However, achieving selectivity for specific ion channel subtypes with small-molecule drugs has been challenging, and there currently is a growing trend to target ion channels with biologics. One approach is to improve the pharmacokinetics of existing or novel venom-derived peptides. In parallel, after initial studies with polyclonal antibodies demonstrated the technical feasibility of inhibiting channel function with antibodies, multiple preclinical programmes are now using the full spectrum of available technologies to generate conventional monoclonal and engineered antibodies or nanobodies against extracellular loops of ion channels. After a summary of the current state of ion channel drug discovery, this Review discusses recent developments using the purinergic receptor channel P2X purinoceptor 7 (P2X7), the voltage-gated potassium channel KV1.3 and the voltage-gated sodium channel NaV1.7 as examples of targeting ion channels with biologics.

A multiplatform strategy for the discovery of conventional monoclonal antibodies that inhibit the voltage-gated potassium channel Kv1.3

Identifying monoclonal antibodies that block human voltage-gated ion channels (VGICs) is a challenging endeavor exacerbated by difficulties in producing recombinant ion channel proteins in amounts that support drug discovery programs. We have developed a general strategy to address this challenge by combining high-level expression of recombinant VGICs in Tetrahymena thermophila with immunization of phylogenetically diverse species and unique screening tools that allow deep-mining for antibodies that could potentially bind functionally important regions of the protein. Using this approach, we targeted human Kv1.3, a voltage-gated potassium channel widely recognized as a therapeutic target for the treatment of a variety of T-cell mediated autoimmune diseases. Recombinant Kv1.3 was used to generate and recover 69 full-length anti-Kv1.3 mAbs from immunized chickens and llamas, of which 10 were able to inhibit Kv1.3 current. Select antibodies were shown to be potent (IC₅₀<10 nM) and specific for Kv1.3 over related Kv1 family members, hERG and hNav1.5.

Venom-derived peptide inhibitors of voltage-gated potassium channels

Voltage-gated potassium channels play a key role in human physiology and pathology. Reflecting their importance, numerous channelopathies have been characterised that arise from mutations in these channels or from autoimmune attack on the channels. Voltage-gated potassium channels are also the target of a broad range of peptide toxins from venomous organisms, including sea anemones, scorpions, spiders, snakes and cone snails; many of these peptides bind to the channels with high potency and selectivity. In this review we describe the various classes of peptide toxins that block these channels and illustrate the broad range of three-dimensional structures that support channel blockade. The therapeutic opportunities afforded by these peptides are also highlighted. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'

Macrophage-mediated cholesterol handling in atherosclerosis

Formation of foam cells is a hallmark at the initial stages of atherosclerosis. Monocytes attracted by pro-inflammatory stimuli attach to the inflamed vascular endothelium and penetrate to the arterial intima where they differentiate to macrophages. Intimal macrophages phagocytize oxidized low-density lipoproteins (oxLDL). Several scavenger receptors (SR), including CD36, SR-A1 and lectin-like oxLDL receptor-1 (LOX-1), mediate oxLDL uptake. In late endosomes/lysosomes of macrophages, oxLDL are catabolysed. Lysosomal acid lipase (LAL) hydrolyses cholesterol esters that are enriched in LDL to free cholesterol and free fatty acids. In the endoplasmic reticulum (ER), acyl coenzyme A: cholesterol acyltransferase-1 (ACAT1) in turn catalyses esterification of cholesterol to store cholesterol esters as lipid droplets in the ER of macrophages. Neutral cholesteryl ester hydrolases nCEH and NCEH1 are involved in a secondary hydrolysis of cholesterol esters to liberate free cholesterol that could be then out-flowed from macrophages by cholesterol ATP-binding cassette (ABC) transporters ABCA1 and ABCG1 and SR-BI. In atherosclerosis, disruption of lipid homoeostasis in macrophages leads to cholesterol accumulation and formation of foam cells.

New Horizons in Therapeutic Antibody Discovery

Antibody drugs have become an increasingly significant component of the therapeutic landscape. Their success has been driven by some of their unique properties, in particular their very high specificity and selectivity, in contrast to the off-target liabilities of small molecules (SMs). Antibodies can bring additional functionality to the table with their ability to interact with the immune system, and this can be further manipulated with advances in antibody engineering. This review summarizes what antibody therapeutics have achieved to date and what opportunities and challenges lie ahead. The target landscape for large molecules (LMs) versus SMs and some of the challenges for antibody drug development are discussed. Effective penetration of membrane barriers and intracellular targeting is one challenge, particularly across the highly resistant blood-brain barrier. The expanding pipeline of antibody-drug conjugates offers the potential to combine SM and LM modalities in a variety of creative ways, and antibodies also offer exciting potential to build bi- and multispecific molecules. The ability to pursue more challenging targets can also be further exploited but highlights the need for earlier screening in functional cell-based assays. I discuss how this might be addressed given the practical constraints imposed by high-throughput screening sample type and process differences in antibody primary screening.

Novel antibody against a glutamic acid-rich human fibrinogen-like protein 2-derived peptide near Ser91 inhibits hfgl2 prothrombinase activity

Fibrinogen-like protein 2 (fgl2) is highly expressed in microvascular endothelial cells in diseases associated with microcirculatory disturbances and plays a crucial role in microthrombosis. Previous studies have demonstrated that the Ser89 residue is a critical site for mouse fgl2 prothrombinase activity. The aim of this study was to investigate the prothrombinase inhibitory ability of antibodies against an hfgl2-derived peptide. The peptide was termed NPG-12 because it is located at the N-terminus of membrane-bound hfgl2, contains 12 amino acid residues (corresponding to residues 76 to 87), and is rich in Glu. This peptide was selected as an antigenic determinant to produce antibodies in immunized rabbits using the DNAStar and HomoloGene software program. Abundant hfgl2 expression was induced in human umbilical vein endothelial cells through treatment with TNF-α. The generated anti-NPG-12 antibodies specifically recognize fgl2, as determined by ELISA, Western Blot and immunostaining. Moreover, one-stage clotting and thrombin generation tests provide evidence that the antibodies can reduce the hfgl2 prothrombinase activity without affecting the platelet-poor plasma prothrombin time (PT) or the activated partial thromboplastin time (APTT). In addition, the antibodies exerted undetectable influence on the proliferation or activation of bulk T cell populations. In conclusion, the selected peptide sequence NPG-12 may be a critical domain for hfgl2 prothrombinase activity, and the development of inhibitors against this sequence may be promising for research or management of hfgl2-associated microcirculatory disturbances.

Antibody-mediated targeting of the Orai1 calcium channel inhibits T cell function

Despite the attractiveness of ion channels as therapeutic targets, there are no examples of monoclonal antibodies directed against ion channels in clinical development. Antibody-mediated inhibition of ion channels could offer a directed, specific therapeutic approach. To investigate the potential of inhibiting ion channel function with an antibody, we focused on Orai1, the pore subunit of the calcium channel responsible for store-operated calcium entry (SOCE) in T cells. Effector T cells are key drivers of autoimmune disease pathogenesis and calcium signaling is essential for T cell activation, proliferation, and cytokine production. We show here the generation of a specific anti-human Orai1 monoclonal antibody (mAb) against an extracellular loop of the plasma membrane-spanning protein. The anti-Orai1 mAb binds native Orai1 on lymphocytes and leads to cellular internalization of the channel. As a result, T cell proliferation, and cytokine production is inhibited in vitro. In vivo, anti-Orai1 mAb is efficacious in a human T cell-mediated graft-versus host disease (GvHD) mouse model. This study demonstrates the feasibility of antibody-mediated inhibition of Orai1 function and, more broadly, reveals the possibility of targeting ion channels with biologics for the treatment of autoimmunity and other diseases.

New screening system for selective blockers of voltage-gated K(+) channels using recombinant cell lines dying upon single action potential

To develop a simple screening system for blockers of voltage-gated Kv1.3 and Kv1.5 channels, new cell lines co-expressing mutated Nav1.5 (IFM/Q3), Kir2.1 (Kir), and Kv1.3 or Kv1.5 were introduced as IFM/Q3+Kir+Kv1.3 and IFM/Q3+Kir+Kv1.5, respectively. Electrical stimulation (ES) of a cell line, IFM/Q3+Kir, induced prolonged action potentials due to the slow inactivation of IFM/Q3 and subsequent cell death. Additional co-expression of Kv1.3 or Kv1.5 to IFM/Q3+Kir shortened the evoked action potentials and prevented cell death. In the presence of margatoxin, a selective Kv1.3-blocker, ES induced cell death in IFM/Q3+Kir+Kv1.3, but not in IFM/Q3+Kir+Kv1.5. In the presence of 4-aminopyridine, a non-selective Kv-channel blocker, ES application elicited cell death in both cell lines. The IC50s of acacetin, a Kv1.5-blocker, was 10.2 μM in IFM/Q3+Kir+Kv1.3 and almost identical to that in IFM/Q3+Kir+Kv1.5 (7.6 μM). The IC50s of citalopram, a 5-HT uptake-inhibitor, were 1.8 μM in IFM/Q3+Kir+Kv1.3 and 1.5 μM in IFM/Q3+Kir+Kv1.5, respectively. These IC50s were comparable to those determined electrophysiologically. In conclusion, acacetin and citalopram block both Kv1.3 and Kv1.5 without selectivity. The Kv1.3 or Kv1.5 channel inhibition assay using these new cell lines may be applicable to high-throughput screening because of its simplicity, accuracy, and high cost-performance.

Antibody-guided photoablation of voltage-gated potassium currents

A family of 40 mammalian voltage-gated potassium (Kv) channels control membrane excitability in electrically excitable cells. The contribution of individual Kv channel types to electrophysiological signaling has been difficult to assign, as few selective inhibitors exist for individual Kv subunits. Guided by the exquisite selectivity of immune system interactions, we find potential for antibody conjugates as selective Kv inhibitors. Here, functionally benign anti-Kv channel monoclonal antibodies (mAbs) were chemically modified to facilitate photoablation of K currents. Antibodies were conjugated to porphyrin compounds that upon photostimulation inflict localized oxidative damage. Anti-Kv4.2 mAb–porphyrin conjugates facilitated photoablation of Kv4.2 currents. The degree of K current ablation was dependent on photon dose and conjugate concentration. Kv channel photoablation was selective for Kv4.2 over Kv4.3 or Kv2.1, yielding specificity not present in existing neurotoxins or other Kv channel inhibitors. We conclude that antibody–porphyrin conjugates are capable of selective photoablation of Kv currents. These findings demonstrate that subtype-specific mAbs that in themselves do not modulate ion channel function are capable of delivering functional payloads to specific ion channel targets.

Selective Kv1.3 channel blocker as therapeutic for obesity and insulin resistance

Obesity is an epidemic, calling for innovative and reliable pharmacological strategies. Here, we show that ShK-186, a selective and potent blocker of the voltage-gated Kv1.3 channel, counteracts the negative effects of increased caloric intake in mice fed a diet rich in fat and fructose. ShK-186 reduced weight gain, adiposity, and fatty liver; decreased blood levels of cholesterol, sugar, HbA1c, insulin, and leptin; and enhanced peripheral insulin sensitivity. These changes mimic the effects of Kv1.3 gene deletion. ShK-186 did not alter weight gain in mice on a chow diet, suggesting that the obesity-inducing diet enhances sensitivity to Kv1.3 blockade. Several mechanisms may contribute to the therapeutic benefits of ShK-186. ShK-186 therapy activated brown adipose tissue as evidenced by a doubling of glucose uptake, and increased β-oxidation of fatty acids, glycolysis, fatty acid synthesis, and uncoupling protein 1 expression. Activation of brown adipose tissue manifested as augmented oxygen consumption and energy expenditure, with no change in caloric intake, locomotor activity, or thyroid hormone levels. The obesity diet induced Kv1.3 expression in the liver, and ShK-186 caused profound alterations in energy and lipid metabolism in the liver. This action on the liver may underlie the differential effectiveness of ShK-186 in mice fed a chow vs. an obesity diet. Our results highlight the potential use of Kv1.3 blockers for the treatment of obesity and insulin resistance.

Specific Kv1.3 blockade modulates key cholesterol-metabolism-associated molecules in human macrophages exposed to ox-LDL

Cholesterol-metabolism-associated molecules, including scavenger receptor class A (SR-A), lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), CD36, ACAT1, ABCA1, ABCG1, and scavenger receptor class B type I, can modulate cholesterol metabolism in the transformation from macrophages to foam cells. Voltage-gated potassium channel Kv1.3 has increasingly been demonstrated to play an important role in the modulation of macrophage function. Here, we investigate the role of Kv1.3 in modulating cholesterol-metabolism-associated molecules in human acute monocytic leukemia cell-derived macrophages (THP-1 macrophages) and human monocyte-derived macrophages exposed to oxidized LDL (ox-LDL). Human Kv1.3 and Kv1.5 channels (hKv1.3 and hKv1.5) are expressed in macrophages and form a heteromultimeric channel. The hKv1.3-E314 antibody that we had generated as a specific hKv1.3 blocker inhibited outward delayed rectifier potassium currents, whereas the hKv1.5-E313 antibody that we had generated as a specific hKv1.5 blocker failed. Accordingly, the hKv1.3-E314 antibody reduced percentage of cholesterol ester and enhanced apoA-I-mediated cholesterol efflux in THP-1 macrophages and human monocyte-derived macrophages exposed to ox-LDL. The hKv1.3-E314 antibody downregulated SR-A, LOX-1, and ACAT1 expression and upregulated ABCA1 expression in THP-1 macrophages and human monocyte-derived macrophages. Our results reveal that specific Kv1.3 blockade represents a novel strategy modulating cholesterol metabolism in macrophages, which benefits the treatment of atherosclerotic lesions.