George Chandy

Nanyang Technological University | ntu · Lee Kong Chian School of Medicine (LKCSoM)

Background: Tumours create an immunosuppressive microenvironment that limits the antitumor function of infiltrating T-cells. In particular, K+ ions released from dying necrotic tumour cells accumulate in the tumour microenvironment and increase the local K+ concentration to 50 mM (high-[K+]e). This study aims to investigate functional impact of hig...

The Concise Guide to PHARMACOLOGY 2023/24 is the sixth in this series of biennial publications. The Concise Guide provides concise overviews, mostly in tabular format, of the key properties of approximately 1800 drug targets, and over 6000 interactions with about 3900 ligands. There is an emphasis on selective pharmacology (where available), plus l...

The voltage-gated potassium channel KV1.3 is an important therapeutic target for the treatment of autoimmune and neuroinflammatory diseases. The recent structures of KV1.3, Shaker-IR (wild-type and inactivating W434F mutant) and an inactivating mutant of rat KV1.2-KV2.1 paddle chimera (KVChim-W362F+S367T+V377T) reveal that the transition of voltage...

The 6TM family of K channels comprises the voltage-gated KV subfamilies, the EAG subfamily (which includes hERG channels), the Ca2+-activated Slo subfamily (actually with 7TM, termed BK) and the Ca2+-activated SK subfamily. These channels possess a pore-forming α subunit that comprise tetramers of identical subunits (homomeric) or of different subu...

Calcium- and sodium- activated potassium channels are members of the 6TM family of K channels which comprises the voltage-gated KV subfamilies, including the KCNQ subfamily, the EAG subfamily (which includes hERG channels), the Ca2+-activated Slo subfamily (actually with 6 or 7TM) and the Ca2+- and Na+-activated SK subfamily (nomenclature as agreed...

The tumour microenvironment (TME) imposes a major obstacle to infiltrating T-lymphocytes and suppresses their function. Several immune checkpoint proteins that interfere with ligand/receptor interactions and impede T-cell anti-tumour responses have been identified. Immunotherapies that block immune checkpoints have revolutionized the treatment para...

Simple Summary Cancer immunotherapy has shown huge potential in the fight against cancer but few patients respond durably to treatment. Durable immunological responses are associated with the generation of memory T cells. A subset of memory T cells, effector memory T cells, have been shown to be associated with tumours responding to immune checkpoi...

Significance Voltage-gated potassium channels (Kv) open with membrane depolarization and allow the flow of K ⁺ ions. Ion flow is tightly governed by time-dependent entry into nonconducting inactivated states. Here, we focus on Kv1.3, a channel of physiological importance in immune cells. We used cryogenic electron microscopy to determine structures...

The Concise Guide to PHARMACOLOGY 2021/22 is the fifth in this series of biennial publications. The Concise Guide provides concise overviews, mostly in tabular format, of the key properties of nearly 1900 human drug targets with an emphasis on selective pharmacology (where available), plus links to the open access knowledgebase source of drug targe...

Calcium- and sodium- activated potassium channels are members of the 6TM family of K channels which comprises the voltage-gated KV subfamilies, including the KCNQ subfamily, the EAG subfamily (which includes hERG channels), the Ca2+-activated Slo subfamily (actually with 6 or 7TM) and the Ca2+- and Na+-activated SK subfamily (nomenclature as agreed...

The 6TM family of K channels comprises the voltage-gated KV subfamilies, the EAG subfamily (which includes hERG channels), the Ca2+-activated Slo subfamily (actually with 7TM, termed BK) and the Ca2+-activated SK subfamily. These channels possess a pore-forming α subunit that comprise tetramers of identical subunits (homomeric) or of different subu...

Voltage-gated Kv1.3 potassium channels are key regulators of T lymphocyte activation, proliferation and cytokine production, by providing the necessary membrane hyper-polarization for calcium influx following immune stimulation. It is noteworthy that an accumulating body of in vivo and in vitro evidence links these channels to multiple sclerosis pa...

Non-alcoholic fatty liver disease (NAFLD) has been on a global rise. While animal models have rendered valuable insights to the pathogenesis of NAFLD, discrepancy with patient data still exists. Since non-alcoholic steatohepatitis (NASH) involves chronic inflammation, and CD4⁺ T cell infiltration of the liver is characteristic of NASH patients, we...

We describe a cysteine-rich, membrane-penetrating, joint-targeting and remarkably stable peptide, EgK5, that modulates voltage-gated KV1.3 potassium channels in T lymphocytes by a distinctive mechanism. EgK5 enters plasma membranes and binds to KV1.3, causing current rundown by a phosphatidylinositol 4,5-bisphosphate-dependent mechanism. EgK5 exhib...

Covering: Up to 2020 Ion 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 modulatio...

The Concise Guide to PHARMACOLOGY 2019/20 is the fourth in this series of biennial publications. The Concise Guide provides concise overviews of the key properties of nearly 1800 human drug targets with an emphasis on selective pharmacology (where available), plus links to the open access knowledgebase source of drug targets and their ligands (www....

Calcium- and sodium- activated potassium channels are members of the 6TM family of K channels which comprises the voltage-gated KV subfamilies, including the KCNQ subfamily, the EAG subfamily (which includes herg channels), the Ca2+-activated Slo subfamily (actually with 6 or 7TM) and the Ca2+- and Na+-activated SK subfamily (nomenclature as agreed...

The 6TM family of K channels comprises the voltage-gated KV subfamilies, the EAG subfamily (which includes hERG channels), the Ca2+-activated Slo subfamily (actually with 7TM, termed BK) and the Ca2+-activated SK subfamily. These channels possess a pore-forming α subunit that comprise tetramers of identical subunits (homomeric) or of different subu...

Dying tumor cells release intracellular potassium (K+), raising extracellular K+ ([K+]e) in the tumor microenvironment (TME) to 40–50 mM (high-[K+]e). Here, we investigated the effect of high-[K+]e on T cell functions. Exposure to high-[K+]e suppressed the proliferation of central memory and effector memory T cells, while T memory stem cells were u...

Host-cell chromatin changes are thought to play an important role in the pathogenesis of infectious diseases. Here, we describe the first histone acetylome-wide association study (HAWAS) of an infectious disease, based on genome-wide H3K27 acetylation profiling of peripheral granulocytes and monocytes from subjects with active Mycobacterium tubercu...

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, a...

Activation of brown adipose tissue, treatment of obesity and/or treatment of obesity-related disorders in human or non-human animals subjects by administering to the subject a potassium channel inhibiting agent. The potassium channel inhibiting agent may comprise ShK toxin or a modified ShK toxin. Examples of modified ShK toxins include ShK-186.

Background: Platinum-based drugs such as Cisplatin are commonly employed for cancer treatment. Despite an initial therapeutic response, Cisplatin treatment often results in the development of chemoresistance. To identify novel approaches to overcome Cisplatin resistance, we tested Cisplatin in combination with K+ channel modulators on colorectal c...

Traditionally, ocular surface cytology is studied with techniques such as spatula technology and brush technology. The problem with these techniques is that they may induce traumatic lesions on the surface of the eye, which can progress to scarring, eyelid deformity, limbal stem cell deficiency and in some cases, cause great discomfort to the subje...

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...

The voltage-gated Kv1.3 channel in T lymphocytes is a validated therapeutic target for diverse autoimmune diseases. Here we review the discovery of Kv1.3, its physiological role in T cells, and why it is an attractive target for modulating autoimmune responses. We focus on peptide inhibitors because the first Kv1.3-selective inhibitor in human tria...

Dry eye disease is a very common condition that causes morbidity and healthcare burden and decreases the quality of life. There is a need for a suitable dry eye animal model to test novel therapeutics to treat autoimmune dry eye conditions. This protocol describes a chronic autoimmune dry eye rat model. Lewis rats were immunized with an emulsion co...

The present invention is related generally to a method for screening subjects to determine those subjects more likely to develop diabetes by quantization of insulin producing cells. The present invention is also related to the diagnosis of diabetes and related to monitor disease progression or treatment efficacy of candidate drugs.

Non-recirculating resident memory (TRM) and recirculating T cells mount vigorous immune responses to both self and foreign antigens in barrier tissues like the skin, lung and gastrointestinal tract. Using impression cytology followed by flow cytometry we identified two TRM subsets and four recirculating T-subsets in the healthy human ocular surface...

Asubset of potassium channels is regulated primarily by changes in the cytoplasmic concentration of ions, including calcium, sodium, chloride, and protons. The eight members of this subfamily were originally all designated as calcium-activated channels. More recent studies have clarified the gating mechanisms for these channels and have documented...

Potassium released from dying tumour cells has now been found to suppress the activity of T cells of the immune system. Enhancing the removal of potassium from T cells restores their ability to attack cancer. See Letter p.539

The voltage-gated potassium (Kv) 1.3 channel is widely regarded as a therapeutic target for immunomodulation in autoimmune diseases. ShK-186, a selective inhibitor of Kv1.3 channels, ameliorates autoimmune diseases in rodent models, and human phase 1 trials of this agent in healthy volunteers have been completed. In this study, we identified and ch...

Parasites have coexisted with their human hosts for thousands of years and are known mainly for their harmful disease-causing role in humans. However, probiotic worm therapy is beneficial in human autoimmune diseases, suggesting the existence of immunomodulators in parasitic worms. By screening a cDNA library and searching genome databases we ident...

Background Tumors affecting the head, neck, and brain account for significant morbidity and mortality. The curative efficacy of radiotherapy for these tumors is well established, but radiation carries a significant risk of neurologic injury. So far, neuroprotective therapies for radiation-induced brain injury are still limited. In this study we dem...

The molecular targets and neural circuits that underlie general anesthesia are not fully elucidated. Here, we directly demonstrate that Kv1-family (Shaker-related) delayed rectifier K(+) channels in the central medial thalamic nucleus (CMT) are important targets for volatile anesthetics. The modulation of Kv1 channels by volatiles is network specif...

MMP23 is a member of the matrix metalloprotease family of zinc- and calcium-dependent endopeptidases, which are involved in a wide variety of cellular functions. Its catalytic domain displays a high degree of structural homology with those of other metalloproteases, but its atypical domain architecture suggests that it may possess unique functional...

Significance Obesity is a global epidemic in need of novel and safe therapeutics. We show that ShK-186, a selective blocker of the Kv1.3 potassium channel, has powerful antiobesity effects in a mouse model of diet-induced obesity. ShK-186 increases energy expenditure by activating brown adipose tissue, causes profound changes in liver metabolism an...

Matrix metalloproteases (MMPs) are endopeptidases that regulate diverse biological processes. They are synthesized as zymogens and become active after removal of their prodomains. Much is known about the metalloprotease activity of these enzymes, but non-canonical functions are poorly defined, and functions of the prodomains have been largely ignor...

Matrix metalloproteases (MMPs) are endopeptidases that regulate diverse biological processes. Synthesized as zymogens, MMPs become active after removal of their prodomains. Much is known about the metalloprotease activity of these enzymes, but noncanonical functions are poorly defined, and functions of the prodomains have been largely ignored. Here...

Voltage-gated sodium (Na(V)) and potassium (K(V)) channels are critical components of neuronal action potential generation and propagation. Here, we report that Na(V)β1 encoded by SCN1b, an integral subunit of Na(V) channels, coassembles with and modulates the biophysical properties of K(V)1 and K(V)7 channels, but not K(V)3 channels, in an isoform...

Overcoming the resistance of tumours to chemotherapy, often due to downregulation of Bax and Bak, represents a significant clinical challenge. It is therefore important to identify novel apoptosis inducers that bypass Bax and Bak. Potassium channels are emerging as oncological targets and a crucial role of mitochondrial Kv1.3 in apoptosis has been...

The Kv1.3 channel is a recognized target for pharmaceutical development to treat autoimmune diseases and organ rejection. ShK-186, a specific peptide inhibitor of Kv1.3, has shown promise in animal models of multiple sclerosis and rheumatoid arthritis. Here, we describe the pharmacokinetic-pharmacodynamic relationship for ShK-186 in rats and monkey...

Increasing evidence suggests ion channels have critical functions in the differentiation and plasticity of T cells. Kv1.3, a voltage-gated K(+) channel, is a functional marker and a pharmacological target for activated effector memory T cells. Selective Kv1.3 blockers have been shown to inhibit proliferation and cytokine production by human and rat...

The Potassium Kv1.3 channel on effector memory T cells is a target to treat autoimmune diseases. ShK-186, a specific peptide inhibitor of Kv1.3, has shown promise in animal models of multiple sclerosis and rheumatoid arthritis. Here, we describe the development of methods to establish a pharmacokinetic (PK) - pharmacodynamic (PD) relationship for S...

Although voltage‐gated Nav1 sodium channels and Kv1 potassium channels are both known for their tandem function in action potential firing and have ubiquitous tissue expressions, to date, no functional association between members of the Nav1.x channel family and the Kv1 channel family have been reported. Here we report that SCN1b modulates the Kv1‐...

We describe the anti‐obesity effects of ShK‐186, a Kv1.3‐selective peptide inhibitor. C57BL/J mice fed a diet containing high fat (21%) diet and fructose solution (60%) were administered ShK‐186 (500 μg/kg) or vehicle on alternate days by subcutaneous injection. ShK‐186‐treatment caused a dose‐dependent reduction in weight gain over the 45‐day tria...

Obesity is a global health problem and there is a pressing need for safe therapeutics. Here, we describe the anti-obesity effects of ShK-186, a Kv1.3-selective peptide inhibitor with picomolar potency and an excellent safety profile in rodents and monkeys. C57BL/J mice fed a diet containing high fat (21%) diet and fructose solution (60%) were admin...

Sodium channel beta subunits (SCN1b-SCN4b) are integral members of voltage-gated sodium channel (VGSC)-complexes at nodes of Ranvier, axon initial segments, and cardiac intercalated disks, where they modulate the function of VGSCs. Mutations of these genes results in neurological (e.g. epilepsy) and cardiovascular (e.g. Brugada syndrome) diseases....

Sulfated glycolipids (SGs) and glycosaminoglycans (GAGs) present on the surface of colonic, vaginal epithelial and neuroglial cells bind to HIV GP120, suggesting that these glycoconjugates may have a role in HIV infection. The main goal of this work was to test the ability of the human milk glycoconjugates (SGs and GAGs) to inhibit the infection of...

Traditional healthcare systems in China, India, Greece and the Middle East have for centuries exploited venomous creatures as a resource for medicines. This review focuses on one class of pharmacologically active compounds from venom, namely peptide toxins that target ion channels. We highlight their therapeutic potential and the specific channels...

Electrophysiological and pharmacological studies coupled with molecular identification have revealed a unique network of ion channels--Kv1.3, KCa3.1, CRAC (Orai1 + Stim1), TRPM7, Cl(swell)--in lymphocytes that initiates and maintains the calcium signaling cascade required for activation. The expression pattern of these channels changes during lymph...

Islet cell loss in the pancreas results in diabetes. A noninvasive method that measures islet cell loss and also tracks the fate of transplanted islets would facilitate the development of novel therapeutics and improve the management of diabetes. We describe a novel dopamine D(2)/D(3) receptor (D(2)/D(3)R)-based PET method to study islet cells in t...

Supplementary Figures S1-S7 and Supplementary Tables S1-S2

How environmental factors combine with genetic risk at the molecular level to promote complex trait diseases such as multiple sclerosis (MS) is largely unknown. In mice, N-glycan branching by the Golgi enzymes Mgat1 and/or Mgat5 prevents T cell hyperactivity, cytotoxic T-lymphocyte antigen 4 (CTLA-4) endocytosis, spontaneous inflammatory demyelinat...

Peptide toxins found in a wide array of venoms block K+ channels, causing profound physiological and pathological effects. Here we describe the first functional K+ channel-blocking toxin domain in a mammalian protein. MMP23 (matrix metalloprotease 23) contains a domain (MMP23TxD) that is evolutionarily related to peptide toxins from sea anemones. M...

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+ s...

We discuss the potential use of inhibitors of Kv1.3 potassium channels in T lymphocytes as therapeutics for multiple sclerosis. Current treatment strategies target the immune system in a non-selective manner. The resulting general immunosuppression, toxic side-effects and increased risk of opportunistic infections create the need for more selective...

Kv1.3 potassium channels maintain the membrane potential of effector memory (T(EM)) T cells that are important mediators of multiple sclerosis, type 1 diabetes mellitus, and rheumatoid arthritis. The polypeptide ShK-170 (ShK-L5), containing an N-terminal phosphotyrosine extension of the Stichodactyla helianthus ShK toxin, is a potent and selective...

Effector memory T (Tem) cells are essential mediators of autoimmune disease and delayed-type hypersensitivity (DTH), a convenient model for two-photon imaging of Tem cell participation in an inflammatory response. Shortly (3 hr) after entry into antigen-primed ear tissue, Tem cells stably attached to antigen-bearing antigen-presenting cells (APCs)....

Atherosclerosis remains a major cause of death in the developed world despite the success of therapies that lower cholesterol and BP. The intermediate-conductance calcium-activated potassium channel KCa3.1 is expressed in multiple cell types implicated in atherogenesis, and pharmacological blockade of this channel inhibits VSMC and lymphocyte activ...

Delayed type hypersensitivity (DTH) is an immune reaction in which the main players are CCR7(-) effector / memory T lymphocytes. Here, we demonstrate a method for inducing and recording the progress of a DTH reaction in the rat ear. This is followed by a demonstration of the preparation of rat ear tissue for two-photon imaging of the CCR7(-) effect...

The polypeptide toxin ShK is a potent blocker of Kv1.3 potassium channels, which are crucial in the activation of human effector memory T cells (TEM); selective blockers constitute valuable therapeutic leads for the treatment of autoimmune diseases mediated by TEM cells, such as multiple sclerosis, rheumatoid arthritis, and type-1 diabetes. The cri...

Adrenal medullary chromaffin cell culture systems are extremely useful for the study of excitation-secretion coupling in an in vitro setting. This protocol illustrates the method used to dissect the adrenals and then isolate the medullary region by stripping away the adrenal cortex. The digestion of the medulla into single chromaffin cells is then...

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) that commonly affects young adults. It is characterized by demyelination and glial scaring in areas disseminated in the brain and spinal cord. These lesions alter nerve conduction and induce the disabling neurological deficits that vary with the location o...

Maintenance of antigen-specific T cell lines or clones in culture requires rounds of antigen-induced activation separated by phases of cell expansion. Addition of interleukin 2 to the culture media during the expansion phase is necessary to prevent cell death and sufficient to maintain short-term T cell lines but has been shown to increase Th1 pola...

Whether studying an autoimmune disease directed to the central nervous system (CNS), such as experimental autoimmune encephalomyelitis (EAE, 1), or the immune response to an infection of the CNS, such as poliomyelitis, Lyme neuroborreliosis, or neurosyphilis, it is often necessary to isolate the CNS-infiltrating immune cells.In this video-protocol...