Differential inhibition of T-type calcium channels by neuroleptics

Sulfide and polysulfide as pronociceptive mediators: Focus on Cav3.2 function enhancement and TRPA1 activation

Reactive sulfur species including sulfides, polysulfides and cysteine hydropersulfide play extensive roles in health and disease, which involve modification of protein functions through the interaction with metals bound to the proteins, cleavage of cysteine disulfide (S-S) bonds and S-persulfidation of cysteine residues. Sulfides over a wide micromolar concentration range enhance the activity of Cav3.2 T-type Ca2+ channels by eliminating Zn2+ bound to the channels, thereby promoting somatic and visceral pain. Cav3.2 is under inhibition by Zn2+ in physiological conditions, so that sulfides function to reboot Cav3.2 from Zn2+ inhibition and increase the excitability of nociceptors. On the other hand, polysulfides generated from sulfides activate TRPA1 channels via cysteine S-persulfidation, thereby facilitating somatic, but not visceral, pain. Thus, Cav3.2 function enhancement by sulfides and TRPA1 activation by polysulfides, synergistically accelerate somatic pain signals. The increased activity of the sulfide/Cav3.2 system, in particular, appears to have a great impact on pathological pain, and may thus serve as a therapeutic target for treatment of neuropathic and inflammatory pain including visceral pain.

Metabolic complications of psychotropic medications in psychiatric disorders: Emerging role of de novo lipogenesis and therapeutic consideration

Although significant advances have been made in understanding the patho-physiology of psychiatric disorders (PDs), therapeutic advances have not been very convincing. While psychotropic medications can reduce classical symptoms in patients with PDs, their long-term use has been reported to induce or exaggerate various pre-existing metabolic abnormalities including diabetes, obesity and non-alcoholic fatty liver disease (NAFLD). The mechanism(s) underlying these metabolic abnormalities is not clear; however, lipid/fatty acid accumulation due to enhanced de novo lipogenesis (DNL) has been shown to reduce membrane fluidity, increase oxidative stress and inflammation leading to the development of the aforementioned metabolic abnormalities. Intriguingly, emerging evidence suggest that DNL dysregulation and fatty acid accumulation could be the major mechanisms associated with the development of obesity, diabetes and NAFLD after long-term treatment with psychotropic medications in patients with PDs. In support of this, several adjunctive drugs comprising of anti-oxidants and anti-inflammatory agents, that are used in treating PDs in combination with psychotropic medications, have been shown to reduce insulin resistance and development of NAFLD. In conclusion, the above evidence suggests that DNL could be a potential pathological factor associated with various metabolic abnormalities, and a new avenue for translational research and therapeutic drug designing in PDs.

Voltage-gated Calcium Channels as Potential Therapeutic Targets in Migraine

Migraine is a complex and highly incapacitating neurological disorder that affects around 15% of the general population with greater incidence in women, often at the most productive age of life. Migraine physiopathology is still not fully understood, but it involves multiple mediators and events in the trigeminovascular system and the central nervous system. The identification of calcitonin gene-related peptide as a key mediator in migraine physiopathology has led to the development of effective and highly selective antimigraine therapies. However, this treatment is neither accessible nor effective for all migraine sufferers. Thus, a better understanding of migraine mechanisms and the identification of potential targets are still clearly warranted. Voltage-gated calcium channels (VGCCs) are widely distributed in the trigeminovascular system, and there is accumulating evidence of their contribution to the mechanisms associated with headache pain. Several drugs used in migraine abortive or prophylactic treatment target VGCCs, which probably contributes to their analgesic effect. This review aims to summarize the current evidence of VGGC contribution to migraine physiopathology and to discuss how current pharmacological options for migraine treatment interfere with VGGC function. PERSPECTIVE: Calcitonin gene-related peptide (CGRP) represents a major migraine mediator, but few studies have investigated the relationship between CGRP and VGCCs. CGRP release is calcium channel-dependent and VGGCs are key players in familial migraine. Further studies are needed to determine whether VGCCs are suitable molecular targets for treating migraine.

Voltage-gated calcium channels in genetic epilepsies

Voltage-gated calcium channels (VGCC) are abundant in the central nervous system and serve a broad spectrum of functions, either directly in cellular excitability or indirectly to regulate Ca2+ homeostasis. Ca2+ ions act as one of the main connections in excitation-transcription coupling, muscle contraction and excitation-exocytosis coupling, including synaptic transmission. In recent years, many genes encoding VGCCs main α or additional auxiliary subunits have been associated with epilepsy. This review sums up the current state of knowledge on disease mechanisms and provides guidance on disease-specific therapies where applicable.

Pimozide Increases a Delayed Rectifier K+ Conductance in Chicken Embryo Vestibular Hair Cells

Pimozide is a conventional antipsychotic drug largely used in the therapy for schizophrenia and Tourette's syndrome. Pimozide is assumed to inhibit synaptic transmission at the CNS by acting as a dopaminergic D₂ receptor antagonist. Moreover, pimozide has been shown to block voltage-gated Ca²⁺ and K⁺ channels in different cells. Despite its widespread clinical use, pimozide can cause several adverse effects, including extrapyramidal symptoms and cardiac arrhythmias. Dizziness and loss of balance are among the most common side effects of pimozide. By using the patch-clamp whole-cell technique, we investigated the effect of pimozide [3 μM] on K⁺ channels expressed by chicken embryo vestibular type-II hair cells. We found that pimozide slightly blocks a transient outward rectifying A-type K⁺ current but substantially increases a delayed outward rectifying K⁺ current. The net result was a significant hyperpolarization of type-II hair cells at rest and a strong reduction of their response to depolarizing stimuli. Our findings are consistent with an inhibitory effect of pimozide on the afferent synaptic transmission by type-II hair cells. Moreover, they provide an additional key to understanding the beneficial/collateral pharmacological effects of pimozide. The finding that pimozide can act as a K⁺ channel opener provides a new perspective for the use of this drug.

A link between agrin signalling and Cav3.2 at the neuromuscular junction in spinal muscular atrophy

SMN protein deficiency causes motoneuron disease spinal muscular atrophy (SMA). SMN-based therapies improve patient motor symptoms to variable degrees. An early hallmark of SMA is the perturbation of the neuromuscular junction (NMJ), a synapse between a motoneuron and muscle cell. NMJ formation depends on acetylcholine receptor (AChR) clustering triggered by agrin and its co-receptors lipoprotein receptor-related protein 4 (LRP4) and transmembrane muscle-specific kinase (MuSK) signalling pathway. We have previously shown that flunarizine improves NMJs in SMA model mice, but the mechanisms remain elusive. We show here that flunarizine promotes AChR clustering in cell-autonomous, dose- and agrin-dependent manners in C2C12 myotubes. This is associated with an increase in protein levels of LRP4, integrin-beta-1 and alpha-dystroglycan, three agrin co-receptors. Furthermore, flunarizine enhances MuSK interaction with integrin-beta-1 and phosphotyrosines. Moreover, the drug acts on the expression and splicing of Agrn and Cacna1h genes in a muscle-specific manner. We reveal that the Cacna1h encoded protein Cav3.2 closely associates in vitro with the agrin co-receptor LRP4. In vivo, it is enriched nearby NMJs during neonatal development and the drug increases this immunolabelling in SMA muscles. Thus, flunarizine modulates key players of the NMJ and identifies Ca_v3.2 as a new protein involved in the NMJ biology.

T-Type Calcium Channels: A Mixed Blessing

The role of T-type calcium channels is well established in excitable cells, where they preside over action potential generation, automaticity, and firing. They also contribute to intracellular calcium signaling, cell cycle progression, and cell fate; and, in this sense, they emerge as key regulators also in non-excitable cells. In particular, their expression may be considered a prognostic factor in cancer. Almost all cancer cells express T-type calcium channels to the point that it has been considered a pharmacological target; but, as the drugs used to reduce their expression are not completely selective, several complications develop, especially within the heart. T-type calcium channels are also involved in a specific side effect of several anticancer agents, that act on microtubule transport, increase the expression of the channel, and, thus, the excitability of sensory neurons, and make the patient more sensitive to pain. This review puts into context the relevance of T-type calcium channels in cancer and in chemotherapy side effects, considering also the cardiotoxicity induced by new classes of antineoplastic molecules.

Evaluation of potential anticonvulsant fluorinated N-benzamide enaminones as T-type Ca2+ channel blockers

Trifluoromethylated N-benzamide enaminones have been identified as potential anticonvulsants for the treatment of drug-resistant epilepsy. T-type Ca²⁺ channels are an important target for anti-seizure medications. Our laboratory has developed several fluorinated N-benzamide enaminone analogs that were evaluated by their ability to target T-type Ca²⁺ channels. Using whole cell voltage-clamp recordings, we identified two meta-trifluoromethyl N-benzamide enaminones with a significant inhibitory effect on T-type Ca²⁺ channels. These compounds had no effect on voltage-activated Na⁺ channels. We also evaluated the effect of the fluorinated N-benzamide enaminone analogs on the T-type Ca²⁺ channel subunits Cav3.2 and Cav3.3. The meta-trifluoromethyl N-benzamide enaminone lead analogs altered the steady-state inactivation of Cav3.2 T-type Ca²⁺ channels, which resulted in a significant increase in the inactivation recovery time of the channels. There was no effect of fluorinated N-benzamide enaminone analogs on the gating mechanism of T-type Ca²⁺ channels, as proven by the lack of effect on the activation and inactivation time constant of Ca²⁺ currents. On the contrary, the meta-trifluoromethyl N-benzamide enaminone lead analogs altered the gating mechanism of Cav3.3 T-type Ca²⁺ channels, as proven by the reduction in the activation and inactivation time constant of the channels. There was no effect on the inactivation kinetics of Cav3.3 T-type Ca²⁺ channels. The present results demonstrate that meta-substituted trifluoromethyl N-benzamide enaminone analogs target T-type Ca²⁺ channels by different mechanisms depending on the channel subunit. Meta-trifluoromethyl N-benzamide enaminone analogs can potentially lead to the design of more specific blockers of T-type Ca²⁺ channels for the treatment of epileptic seizures.

Structure, gating, and pharmacology of human CaV3.3 channel

The low-voltage activated T-type calcium channels regulate cellular excitability and oscillatory behavior of resting membrane potential which trigger many physiological events and have been implicated with many diseases. Here, we determine structures of the human T-type Ca_V3.3 channel, in the absence and presence of antihypertensive drug mibefradil, antispasmodic drug otilonium bromide and antipsychotic drug pimozide. Ca_V3.3 contains a long bended S6 helix from domain III, with a positive charged region protruding into the cytosol, which is critical for T-type Ca_V channel activation at low voltage. The drug-bound structures clearly illustrate how these structurally different compounds bind to the same central cavity inside the Ca_V3.3 channel, but are mediated by significantly distinct interactions between drugs and their surrounding residues. Phospholipid molecules penetrate into the central cavity in various extent to shape the binding pocket and play important roles in stabilizing the inhibitor. These structures elucidate mechanisms of channel gating, drug recognition, and actions, thus pointing the way to developing potent and subtype-specific drug for therapeutic treatments of related disorders.

T-type calcium channels are implicated in many diseases. Here, multiple structures of CaV3.3 channel elucidate molecular mechanisms of T-type CaV channels activation at low voltage and interaction with different clinically used channel blockers.

Cav3 T-Type Voltage-Gated Ca2+ Channels and the Amyloidogenic Environment: Pathophysiology and Implications on Pharmacotherapy and Pharmacovigilance

Voltage-gated Ca²⁺ channels (VGCCs) were reported to play a crucial role in neurotransmitter release, dendritic resonance phenomena and integration, and the regulation of gene expression. In the septohippocampal system, high- and low-voltage-activated (HVA, LVA) Ca²⁺ channels were shown to be involved in theta genesis, learning, and memory processes. In particular, HVA Ca_v2.3 R-type and LVA Ca_v3 T-type Ca²⁺ channels are expressed in the medial septum-diagonal band of Broca (MS-DBB), hippocampal interneurons, and pyramidal cells, and ablation of both channels was proven to severely modulate theta activity. Importantly, Ca_v3 Ca²⁺ channels contribute to rebound burst firing in septal interneurons. Consequently, functional impairment of T-type Ca²⁺ channels, e.g., in null mutant mouse models, caused tonic disinhibition of the septohippocampal pathway and subsequent enhancement of hippocampal theta activity. In addition, impairment of GABA A/B receptor transcription, trafficking, and membrane translocation was observed within the septohippocampal system. Given the recent findings that amyloid precursor protein (APP) forms complexes with GABA B receptors (GBRs), it is hypothesized that T-type Ca²⁺ current reduction, decrease in GABA receptors, and APP destabilization generate complex functional interdependence that can constitute a sophisticated proamyloidogenic environment, which could be of potential relevance in the etiopathogenesis of Alzheimer’s disease (AD). The age-related downregulation of T-type Ca²⁺ channels in humans goes together with increased Aβ levels that could further inhibit T-type channels and aggravate the proamyloidogenic environment. The mechanistic model presented here sheds new light on recent reports about the potential risks of T-type Ca²⁺ channel blockers (CCBs) in dementia, as observed upon antiepileptic drug application in the elderly.

Novel Fluorescence-Based High-Throughput FLIPR Assay Utilizing Membrane-Tethered Genetic Calcium Sensors to Identify T-Type Calcium Channel Modulators

T-type voltage-gated Ca²⁺ channels have been implicated in many human disorders, and there has been increasing interest in developing highly selective and potent T-type Ca²⁺ channel modulators for potential clinical use. However, the unique biophysical properties of T-type Ca²⁺ channels are not conducive for developing high-throughput screening (HTS) assays to identify modulators, particularly potentiators. To illustrate, T-type Ca²⁺ channels are largely inactivated and unable to open to allow Ca²⁺ influx at -25 mV, the typical resting membrane potential of the cell lines commonly used in cellular screening assays. To address this issue, we developed cell lines that express K_ir2.3 channels to hyperpolarize the membrane potential to -70 mV, thus allowing T-type channels to return to their resting state where they can be subsequently activated by membrane depolarization in the presence of extracellular KCl. Furthermore, to simplify the HTS assay and to reduce reagent cost, we stably expressed a membrane-tethered genetic calcium sensor, GCaMP6s-CAAX, that displays superior signal to the background compared to the untethered GCaMP6s or the synthetic Ca²⁺ sensor Fluo-4AM. Here, we describe a novel GCaMP6s-CAAX-based calcium assay utilizing a high-throughput fluorometric imaging plate reader (Molecular Devices, Sunnyvale, CA) format that can identify both activators and inhibitors of T-type Ca²⁺ channels. Lastly, we demonstrate the utility of this novel fluorescence-based assay to evaluate the activities of two distinct G-protein-coupled receptors, thus expanding the use of GCaMP6s-CAAX to a wide range of applications relevant for developing cellular assays in drug discovery.

Repurposing Antipsychotics for Cancer Treatment

Cancer is a leading cause of death worldwide, with approximately 19 million new cases each year. Lately, several novel chemotherapeutic drugs have been introduced, efficiently inhibiting tumor growth and proliferation. However, developing a new drug is a time- and money-consuming process, requiring around 1 billion dollars and nearly ten years, with only a minority of the initially effective anti-cancer drugs experimentally finally being efficient in human clinical trials. Drug repurposing for cancer treatment is an optimal alternative as the safety of these drugs has been previously tested, and thus, in case of successful preclinical studies, can be introduced faster and with a lower cost into phase 3 clinical trials. Antipsychotic drugs are associated with anti-cancer properties and, lately, there has been an increasing interest in their role in cancer treatment. In the present review, we discussed in detail the in-vitro and in-vivo properties of the most common typical and atypical antipsychotics, along with their mechanism of action.

Cyclic Peptides as T-Type Calcium Channel Blockers: Characterization and Molecular Mapping of the Binding Site

T-type calcium (Ca_V3) channels play a crucial role in the generation and propagation of action potentials in excitable cells and are considered potential drug targets for the treatment of neurological and cardiovascular diseases. Given the limited pharmacological repertoire for these channels, there is a great need for novel potent and selective Ca_V3 channel inhibitors. In this study, we used Xenopus oocytes to heterologously express Ca_V3.1 channels and characterized the interaction with a small cyclic peptide, PnCS1. Using molecular modeling, PnCS1 was docked into the cryo-electron microscopy structure of the human Ca_V3.1 channel and molecular dynamics were performed on the resultant complex. The binding site of the peptide was mapped with the involvement of critical amino acids located in the pore region and fenestrations of the channel. More specifically, we found that PnCS1 reclines in the central cavity of the pore domain of the Ca_V3.1 channel and resides stably between the selectivity filter and the intracellular gate, blocking the conduction pathway of the channel. Using Multiple Attribute Positional Scanning approaches, we developed a series of PnCS1 analogues. These analogues had a reduced level of inhibition, confirming the importance of specific residues and corroborating our modeling. In summary, functional studies of PnCS1 on the Ca_V3.1 channel combined with molecular dynamics results provide the basis for understanding the molecular interactions of PnCS1 with Ca_V3.1 and are fundamental to structure-based drug discovery for treating Ca_V3 channelopathies.

Anti-prion Drugs Targeting the Protein Folding Activity of the Ribosome Reduce PABPN1 Aggregation

Prion diseases are caused by the propagation of PrPSc, the pathological conformation of the PrPC prion protein. The molecular mechanisms underlying PrPSc propagation are still unsolved and no therapeutic solution is currently available. We thus sought to identify new anti-prion molecules and found that flunarizine inhibited PrPSc propagation in cell culture and significantly prolonged survival of prion-infected mice. Using an in silico therapeutic repositioning approach based on similarities with flunarizine chemical structure, we tested azelastine, duloxetine, ebastine, loperamide and metixene and showed that they all have an anti-prion activity. Like flunarizine, these marketed drugs reduced PrPSc propagation in cell culture and in mouse cerebellum organotypic slice culture, and inhibited the protein folding activity of the ribosome (PFAR). Strikingly, some of these drugs were also able to alleviate phenotypes due to PABPN1 nuclear aggregation in cell and Drosophila models of oculopharyngeal muscular dystrophy (OPMD). These data emphasize the therapeutic potential of anti-PFAR drugs for neurodegenerative and neuromuscular proteinopathies.

Effects of Bepridil and Pimozide, Existing Medicines Capable of Blocking T-Type Ca2+ Channels, on Visceral Pain in Mice

T-Type Ca²⁺ channels (T-channels), particularly Ca_v3.2, are now considered as therapeutic targets for treatment of intractable pain including visceral pain. Among existing medicines, bepridil, a multi-channel blocker, used for treatment of arrhythmia and angina, and pimozide, a dopamine D₂ receptor antagonist, known as a typical antipsychotic, have potent T-channel blocking activity. We thus tested whether bepridil and pimozide could suppress visceral pain in mice. Colonic and bladder pain were induced by intracolonic administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS) and systemic administration of cyclophosphamide (CPA), respectively. Referred hyperalgesia was assessed by von Frey test, and colonic hypersensitivity to distension by a volume load with intracolonic water injection and spontaneous bladder pain were evaluated by observing nociceptive behaviors in conscious mice. The mice exhibited referred hyperalgesia and colonic hypersensitivity to distension on day 6 after TNBS treatment. Systemic administration of bepridil at 10-20 mg/kg or pimozide at 0.1-0.5 mg/kg strongly reduced the referred hyperalgesia on the TNBS-induced referred hyperalgesia and colonic hypersensitivity to distension. CPA treatment caused bladder pain-like nociceptive behavior and referred hyperalgesia, which were reversed by bepridil at 10-20 mg/kg or pimozide at 0.5-1 mg/kg. Our data thus suggest that bepridil and pimozide, existing medicines capable of blocking T-channels, are useful for treatment of colonic and bladder pain, and serve as seeds for the development of new medicines for visceral pain treatment.

Circadian photoperiod alters TREK-1 channel function and expression in dorsal raphe serotonergic neurons via melatonin receptor 1 signaling

Seasonal day length has been linked to the prevalence of mood disorders, and however, the mechanisms underlying this relationship remain unknown. Previous work in our laboratory has shown that developmental exposure to seasonal photoperiods has enduring effects on the activity of mouse dorsal raphe serotonergic neurons, their intrinsic electrical properties, as well as on depression and anxiety-related behaviors. Here we focus on the possible ionic mechanisms that underlie the observed programming of the electrophysiological properties of serotonin neurons, focusing on the twin-pore K + channels TREK-1 and TASK-1 that set resting membrane potential and regulate excitability. Pharmacological inhibition of TREK-1 significantly increased spike frequency in Short and Equinox photoperiods, but did not further elevate the firing rate in slices from Long photoperiod mice, suggesting that TREK-1 function is reduced in Long photoperiods. In contrast, inhibition of TASK-1 resulted in increases in firing rates across all photoperiods, suggesting that it contributes to setting excitability, but is not regulated by photoperiod. We then quantified Kcnk2 mRNA levels specifically in dorsal raphe 5-HT neurons using triple-label RNAscope. We found that Long photoperiod significantly reduced levels of Kcnk2 in serotonin neurons co-expressing Tph2, and Pet-1. Photoperiodic effects on the function and expression of TREK-1 were blocked in melatonin 1 receptor knockout (MT-1KO) mice, consistent with previous findings that MT-1 signaling is necessary for photoperiodic programming of dorsal raphe 5-HT neurons. Taken together these results indicate that photoperiodic regulation of TREK-1 expression and function plays a key role in photoperiodic programming the excitability of dorsal raphe 5-HT neurons.

Ion Channels as Therapeutic Targets in High Grade Gliomas

Simple Summary

Glioblastoma multiforme is an aggressive grade IV lethal brain tumour with a median survival of 14 months. Despite surgery to remove the tumour, and subsequent concurrent chemotherapy and radiotherapy, there is little in terms of effective treatment options. Because of this, exploring new treatment avenues is vital. Brain tumours are intrinsically electrically active; expressing unique patterns of ion channels, and this is a characteristic we can exploit. Ion channels are specialised proteins in the cell’s membrane that allow for the passage of positive and negatively charged ions in and out of the cell, controlling membrane potential. Membrane potential is a crucial biophysical signal in normal and cancerous cells. Research has identified that specific classes of ion channels not only move the cell through its cell cycle, thus encouraging growth and proliferation, but may also be essential in the development of brain tumours. Inhibition of sodium, potassium, calcium, and chloride channels has been shown to reduce the capacity of glioblastoma cells to grow and invade. Therefore, we propose that targeting ion channels and repurposing commercially available ion channel inhibitors may hold the key to new therapeutic avenues in high grade gliomas.

Abstract

Glioblastoma multiforme (GBM) is a lethal brain cancer with an average survival of 14–15 months even with exhaustive treatment. High grade gliomas (HGG) represent the leading cause of CNS cancer-related death in children and adults due to the aggressive nature of the tumour and limited treatment options. The scarcity of treatment available for GBM has opened the field to new modalities such as electrotherapy. Previous studies have identified the clinical benefit of electrotherapy in combination with chemotherapeutics, however the mechanistic action is unclear. Increasing evidence indicates that not only are ion channels key in regulating electrical signaling and membrane potential of excitable cells, they perform a crucial role in the development and neoplastic progression of brain tumours. Unlike other tissue types, neural tissue is intrinsically electrically active and reliant on ion channels and their function. Ion channels are essential in cell cycle control, invasion and migration of cancer cells and therefore present as valuable therapeutic targets. This review aims to discuss the role that ion channels hold in gliomagenesis and whether we can target and exploit these channels to provide new therapeutic targets and whether ion channels hold the mechanistic key to the newfound success of electrotherapies.

Pathophysiological roles and therapeutic potential of voltage-gated ion channels (VGICs) in pain associated with herpesvirus infection

Herpesvirus is ranked as one of the grand old members of all pathogens. Of all the viruses in the superfamily, Herpes simplex virus type 1 (HSV-1) is considered as a model virus for a variety of reasons. In a permissive non-neuronal cell culture, HSV-1 concludes the entire life cycle in approximately 18–20 h, encoding approximately 90 unique transcriptional units. In latency, the robust viral gene expression is suppressed in neurons by a group of noncoding RNA. Historically the lesions caused by the virus can date back to centuries ago. As a neurotropic pathogen, HSV-1 is associated with painful oral lesions, severe keratitis and lethal encephalitis. Transmission of pain signals is dependent on the generation and propagation of action potential in sensory neurons. T-type Ca²⁺ channels serve as a preamplifier of action potential generation. Voltage-gated Na⁺ channels are the main components for action potential production. This review summarizes not only the voltage-gated ion channels in neuropathic disorders but also provides the new insights into HSV-1 induced pain.

STF-62247 and pimozide induce autophagy and autophagic cell death in mouse embryonic fibroblasts

Induction of autophagy can have beneficial effects in several human diseases, e.g. cancer and neurodegenerative diseases (ND). Here, we therefore evaluated the potential of two novel autophagy-inducing compounds, i.e. STF-62247 and pimozide, to stimulate autophagy as well as autophagic cell death (ACD) using mouse embryonic fibroblasts (MEFs) as a cellular model. Importantly, both STF-62247 and pimozide triggered several hallmarks of autophagy in MEFs, i.e. enhanced levels of LC3B-II protein, its accumulation at distinct cytosolic sites and increase of the autophagic flux. Intriguingly, autophagy induction by STF-62247 and pimozide resulted in cell death that was significantly reduced in ATG5- or ATG7-deficient MEFs. Consistent with ACD induction, pharmacological inhibitors of apoptosis, necroptosis or ferroptosis failed to protect MEFs from STF-62247- or pimozide-triggered cell death. Interestingly, at subtoxic concentrations, pimozide stimulated fragmentation of the mitochondrial network, degradation of mitochondrial proteins (i.e. mitofusin-2 and cytochrome c oxidase IV (COXIV)) as well as a decrease of the mitochondrial mass, indicative of autophagic degradation of mitochondria by pimozide. In conclusion, this study provides novel insights into the induction of selective autophagy as well as ACD by STF-62247 and pimozide in MEFs.

Mibefradil and Flunarizine, Two T-Type Calcium Channel Inhibitors, Protect Mice against Lipopolysaccharide-Induced Acute Lung Injury

Recent studies have illuminated that blocking Ca²⁺ influx into effector cells is an attractive therapeutic strategy for lung injury. We hypothesize that T-type calcium channel may be a potential therapeutic target for acute lung injury (ALI). In this study, the pharmacological activity of mibefradil (a classical T-type calcium channel inhibitor) was assessed in a mouse model of lipopolysaccharide- (LPS-) induced ALI. In LPS challenged mice, mibefradil (20 and 40 mg/kg) dramatically decreased the total cell number, as well as the productions of TNF-α and IL-6 in bronchoalveolar lavage fluid (BALF). Mibefradil also suppressed total protein concentration in BALF, attenuated Evans blue extravasation, MPO activity, and NF-κB activation in lung tissue. Furthermore, flunarizine, a widely prescripted antimigraine agent with potent inhibition on T-type channel, was also found to protect mice against lung injury. These data demonstrated that T-type calcium channel inhibitors may be beneficial for treating acute lung injury. The important role of T-type calcium channel in the acute lung injury is encouraged to be further investigated.

Penfluridol as a Candidate of Drug Repurposing for Anticancer Agent

Penfluridol has robust antipsychotic efficacy and is a first-generation diphenylbutylpiperidine. Its effects last for several days after a single oral dose and it can be administered once a week to provide better compliance and symptom control. Recently; strong antitumour effects for penfluridol were discovered in various cancer cell lines; such as breast; pancreatic; glioblastoma; and lung cancer cells via several distinct mechanisms. Therefore; penfluridol has drawn much attention as a potentially novel anti-tumour agent. In addition; the anti-cancer effects of penfluridol have been demonstrated in vivo: results showed slight changes in the volume and weight of organs at doses tested in animals. This paper outlines the potential for penfluridol to be developed as a next-generation anticancer drug.

The Hard-To-Close Window of T-Type Calcium Channels

T-Type calcium channels (TTCCs) are key regulators of membrane excitability, which is the reason why TTCC pharmacology is subject to intensive research in the neurological and cardiovascular fields. TTCCs also play a role in cancer physiology, and pharmacological blockers such as tetralols and dihydroquinazolines (DHQs) reduce the viability of cancer cells in vitro and slow tumor growth in murine xenografts. However, the available compounds are better suited to blocking TTCCs in excitable membranes rather than TTCCs contributing window currents at steady potentials. Consistently, tetralols and dihydroquinazolines exhibit cytostatic/cytotoxic activities at higher concentrations than those required for TTCC blockade, which may involve off-target effects. Gene silencing experiments highlight the targetability of TTCCs, but further pharmacological research is required for TTCC blockade to become a chemotherapeutic option.

Effects of the T-type calcium channel antagonist Z944 on paired associates learning and locomotor activity in rats treated with the NMDA receptor antagonist MK-801

RATIONALE

Currently available antipsychotics are unsatisfactory given their side effects and limited efficacy for the cognitive symptoms of schizophrenia. Many currently available drugs, such as haloperidol, are T-type calcium channel antagonists in addition to their well-established antagonism of dopamine D2 receptors. Thus, preclinical research into the effects of T-type calcium channel antagonists/blockers in behavioral assays related to schizophrenia may inform novel therapeutic strategies.

OBJECTIVES

We explored the effects of a recently developed highly selective T-type calcium channel antagonist, Z944 (2.5, 5.0, 10.0 mg/kg), on the MK-801 (0.15 mg/kg) model of acute psychosis.

METHODS

To examine the effects of Z944 on behaviors relevant to schizophrenia, we tested touchscreen-based paired associates learning given its relevance to the cognitive symptoms of the disorder and locomotor activity given its relevance to the positive symptoms.

RESULTS

Acute treatment with Z944 failed to reverse the visuospatial associative memory impairments caused by MK-801 in paired associates learning. The highest dose of drug (10.0 mg/kg) given alone produced subtle impairments on paired associates learning. In contrast, Z944 (5.0 mg/kg) blocked the expected increase in locomotion following MK-801 treatment in a locomotor assay.

CONCLUSIONS

These experiments provide support that Z944 may reduce behaviors relevant to positive symptoms of schizophrenia, although additional study of its effects on cognition is required. These findings and other research suggest T-type calcium channel antagonists may be an alternative to currently available antipsychotics with less serious side effects.

T-type Calcium Channels in Health and Disease

Low Voltage-Activated (LVA) T-type calcium channels are characterized by transient current and Low Threshold Spikes (LTS) that trigger neuronal firing and oscillatory behavior. Combined with their preferential localization in dendrites and their specific "window current", T-type calcium channels are considered to be key players in signal amplification and synaptic integration. Assisted by the emerging pharmacological tools, the structural determinants of channel gating and kinetics, as well as novel physiological and pathological functions of T-type calcium channels, are being uncovered. In this review, we provide an overview of structural determinants in T-type calcium channels, their involvement in disorders and diseases, the development of novel channel modulators, as well as Structure-Activity Relationship (SAR) studies that lead to rational drug design.

The Cooperative Relationship between STAT5 and Reactive Oxygen Species in Leukemia: Mechanism and Therapeutic Potential

Reactive oxygen species (ROS) are now recognized as important second messengers with roles in many aspects of signaling during leukemogenesis. They serve as critical cell signaling molecules that regulate the activity of various enzymes including tyrosine phosphatases. ROS can induce inactivation of tyrosine phosphatases, which counteract the effects of tyrosine kinases. ROS increase phosphorylation of many proteins including signal transducer and activator of transcription-5 (STAT5) via Janus kinases (JAKs). STAT5 is aberrantly activated through phosphorylation in many types of cancer and this constitutive activation is associated with cell survival, proliferation, and self-renewal. Such leukemic activation of STAT5 is rarely caused by mutation of the STAT5 gene itself but instead by overactive mutant receptors with tyrosine kinase activity as well as JAK, SRC family protein tyrosine kinases (SFKs), and Abelson murine leukemia viral oncogene homolog (ABL) kinases. Interestingly, STAT5 suppresses transcription of several genes encoding antioxidant enzymes while simultaneously enhancing transcription of NADPH oxidase. By doing so, STAT5 activation promotes an overall elevation of ROS level, which acts as a feed-forward loop, especially in high risk Fms-related tyrosine kinase 3 (FLT3) mutant leukemia. Therefore, efforts have been made recently to target ROS in cancer cells. Drugs that are able to either quench ROS production or inversely augment ROS-related signaling pathways both have potential as cancer therapies and may afford some selectivity by activating feedback inhibition of the ROS-STAT5 kinome. This review summarizes the cooperative relationship between ROS and STAT5 and explores the pros and cons of emerging ROS-targeting therapies that are selective for leukemia characterized by persistent STAT5 phosphorylation.

Loperamide, pimozide, and STF-62247 trigger autophagy-dependent cell death in glioblastoma cells

Autophagy is a well-described degradation mechanism that promotes cell survival upon nutrient starvation and other forms of cellular stresses. In addition, there is growing evidence showing that autophagy can exert a lethal function via autophagic cell death (ACD). As ACD has been implicated in apoptosis-resistant glioblastoma (GBM), there is a high medical need for identifying novel ACD-inducing drugs. Therefore, we screened a library containing 70 autophagy-inducing compounds to induce ATG5-dependent cell death in human MZ-54 GBM cells. Here, we identified three compounds, i.e. loperamide, pimozide, and STF-62247 that significantly induce cell death in several GBM cell lines compared to CRISPR/Cas9-generated ATG5- or ATG7-deficient cells, pointing to a death-promoting role of autophagy. Further cell death analyses conducted using pharmacological inhibitors revealed that apoptosis, ferroptosis, and necroptosis only play minor roles in loperamide-, pimozide- or STF-62247-induced cell death. Intriguingly, these three compounds induce massive lipidation of the autophagy marker protein LC3B as well as the formation of LC3B puncta, which are characteristic of autophagy. Furthermore, loperamide, pimozide, and STF-62247 enhance the autophagic flux in parental MZ-54 cells, but not in ATG5 or ATG7 knockout (KO) MZ-54 cells. In addition, loperamide- and pimozide-treated cells display a massive formation of autophagosomes and autolysosomes at the ultrastructural level. Finally, stimulation of autophagy by all three compounds is accompanied by dephosphorylation of mammalian target of rapamycin complex 1 (mTORC1), a well-known negative regulator of autophagy. In summary, our results indicate that loperamide, pimozide, and STF-62247 induce ATG5- and ATG7-dependent cell death in GBM cells, which is preceded by a massive induction of autophagy. These findings emphasize the lethal function and potential clinical relevance of hyperactivated autophagy in GBM.

Neuroleptics as therapeutic compounds stabilizing neuromuscular transmission in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing, fatal disorder with no effective treatment. We used simple genetic models of ALS to screen phenotypically for potential therapeutic compounds. We screened libraries of compounds in C. elegans, validated hits in zebrafish, and tested the most potent molecule in mice and in a small clinical trial. We identified a class of neuroleptics that restored motility in C. elegans and in zebrafish, and the most potent was pimozide, which blocked T-type Ca2+ channels in these simple models and stabilized neuromuscular transmission in zebrafish and enhanced it in mice. Finally, a short randomized controlled trial of sporadic ALS subjects demonstrated stabilization of motility and evidence of target engagement at the neuromuscular junction. Simple genetic models are, thus, useful in identifying promising compounds for the treatment of ALS, such as neuroleptics, which may stabilize neuromuscular transmission and prolong survival in this disease.

Exploring mechanochemistry to turn organic bio-relevant molecules into metal-organic frameworks: a short review

Mechanochemistry is a powerful and environmentally friendly synthetic technique successfully employed in different fields of synthetic chemistry. Application spans from organic to inorganic chemistry including the synthesis of coordination compounds. Metal-organic frameworks (MOFs) are a class of compounds with numerous applications, from which we highlight herein their application in the pharmaceutical field (BioMOFs), whose importance has been growing and is now assuming a relevant and promising domain. The need to find cleaner, greener and more energy and material-efficient synthetic procedures led to the use of mechanochemistry into the synthesis of BioMOFs.

Discovery and Development of Calcium Channel Blockers

In the mid 1960s, experimental work on molecules under screening as coronary dilators allowed the discovery of the mechanism of calcium entry blockade by drugs later named calcium channel blockers. This paper summarizes scientific research on these small molecules interacting directly with L-type voltage-operated calcium channels. It also reports on experimental approaches translated into understanding of their therapeutic actions. The importance of calcium in muscle contraction was discovered by Sidney Ringer who reported this fact in 1883. Interest in the intracellular role of calcium arose 60 years later out of Kamada (Japan) and Heibrunn (USA) experiments in the early 1940s. Studies on pharmacology of calcium function were initiated in the mid 1960s and their therapeutic applications globally occurred in the the 1980s. The first part of this report deals with basic pharmacology in the cardiovascular system particularly in isolated arteries. In the section entitled from calcium antagonists to calcium channel blockers, it is recalled that drugs of a series of diphenylpiperazines screened in vivo on coronary bed precontracted by angiotensin were initially named calcium antagonists on the basis of their effect in depolarized arteries contracted by calcium. Studies on arteries contracted by catecholamines showed that the vasorelaxation resulted from blockade of calcium entry. Radiochemical and electrophysiological studies performed with dihydropyridines allowed their cellular targets to be identified with L-type voltage-operated calcium channels. The modulated receptor theory helped the understanding of their variation in affinity dependent on arterial cell membrane potential and promoted the terminology calcium channel blocker (CCB) of which the various chemical families are introduced in the paper. In the section entitled tissue selectivity of CCBs, it is shown that characteristics of the drug, properties of the tissue, and of the stimuli are important factors of their action. The high sensitivity of hypertensive animals is explained by the partial depolarization of their arteries. It is noted that they are arteriolar dilators and that they cannot be simply considered as vasodilators. The second part of this report provides key information about clinical usefulness of CCBs. A section is devoted to the controversy on their safety closed by the Allhat trial (2002). Sections are dedicated to their effect in cardiac ischemia, in cardiac arrhythmias, in atherosclerosis, in hypertension, and its complications. CCBs appear as the most commonly used for the treatment of cardiovascular diseases. As far as hypertension is concerned, globally the prevalence in adults aged 25 years and over was around 40% in 2008. Usefulness of CCBs is discussed on the basis of large clinical trials. At therapeutic dosage, they reduce the elevated blood pressure of hypertensive patients but don't change blood pressure of normotensive subjects, as was observed in animals. Those active on both L- and T-type channels are efficient in nephropathy. Alteration of cognitive function is a complication of hypertension recognized nowadays as eventually leading to dementia. This question is discussed together with the efficacy of CCBs in cognitive pathology. In the section entitled beyond the cardiovascular system, CCBs actions in migraine, neuropathic pain, and subarachnoid hemorrhage are reported. The final conclusions refer to long-term effects discovered in experimental animals that have not yet been clearly reported as being important in human pharmacotherapy.

Clinically Approved Ion Channel Inhibitors Close Gates for Hepatitis C Virus and Open Doors for Drug Repurposing in Infectious Viral Diseases

Chronic hepatitis C virus (HCV) infection causes severe liver disease and affects ca. 146 million individuals. Novel directly acting antivirals targeting HCV have revolutionized treatment. However, high costs limit access to therapy. Recently, several related drugs used in humans to treat allergies or as neuroleptics emerged as potent HCV cell entry inhibitors. Insights into their antiviral modes of action may increase opportunities for drug repurposing in hepatitis C and possibly other important human viral infections.

Sigma-1 receptor antagonist haloperidol attenuates Ca2+ responses induced by glutoxim and molixan in macrophages

Using Fura-2AM microfluorimetry, we have shown for the first time that sigma-1 receptor antagonist, antipsychotic haloperidol, significantly inhibits glutoxim- and molixan-induced Ca2+-response in peritoneal macrophages. These results indicate possible involvement of sigma-1 receptors in the signal cascade induced by glutoxim or molixan and leading to intracellular Ca2+ concentration increase in macrophages.

P2X1 Receptor-Mediated Ca2+ Influx Triggered by DA-9801 Potentiates Nerve Growth Factor-Induced Neurite Outgrowth

Nerve growth factor (NGF)-induced neuronal regeneration has emerged as a strategy to treat neuronal degeneration-associated disorders. However, direct NGF administration is limited by the occurrence of adverse effects at high doses of NGF. Therefore, development of a therapeutic strategy to promote the NGF trophic effect is required. In view of the lack of understanding of the mechanism for potentiating the NGF effect, this study investigated molecular targets of DA-9801, a well-standardized Dioscorea rhizome extract, which has a promoting effect on NGF. An increase in intracellular calcium ion level was induced by DA-9801, and chelation of extracellular calcium ions with ethylene-bis(oxyethylenenitrilo)tetraacetic acid (EGTA) suppressed the potentiating effect of DA-9801 on NGF-induced neurite outgrowth. In addition, EGTA treatment reduced the DA-9801-induced phosphorylation of extracellular signal-regulated kinase1/2 (ERK1/2), the major mediators of neurite outgrowth. To find which calcium ion-permeable channel contributes to the calcium ion influx induced by DA-9801, we treated PC12 cells with various inhibitors of calcium ion-permeable channels. NF449, a P2X1 receptor selective antagonist, significantly abolished the potentiating effect of DA-9801 on NGF-induced neurite outgrowth and abrogated the DA-9801-induced ERK1/2 phosphorylation. In addition, transfection with siRNA of P2X1 receptor significantly reduced the DA-9801-enhanced neurite outgrowth. In conclusion, calcium ion influx through P2X1 receptor mediated the promoting effect of DA-9801 on NGF-induced neurite outgrowth via ERK1/2 phosphorylation.

Dysregulated corticostriatal activity in open-field behavior and the head-twitch response induced by the hallucinogen 2,5-dimethoxy-4-iodoamphetamine

The substituted amphetamine, 2,5-dimethoxy-4-iodoamphetamine (DOI), is a hallucinogen that has been used to model a variety of psychiatric conditions. Here, we studied the effect of DOI on neural activity recorded simultaneously in the primary motor cortex (M1) and dorsal striatum of freely behaving FvB/N mice. DOI significantly decreased the firing rate of individually isolated neurons in M1 and dorsal striatum relative to pre-drug baseline. It also induced a bursting pattern of activity by increasing both the number of spikes within a burst and burst duration. In addition, DOI increased coincident firing between simultaneously recorded neuron pairs within the striatum and between M1 and dorsal striatum. Local field potential (LFP) activity also increased in coherence between M1 and dorsal striatum after DOI in the low frequency gamma band (30-50 Hz), while corticostriatal coherence in delta, theta, alpha, and beta activity decreased. We also assessed corticostriatal LFP activity in relation to the DOI-induced head-twitch response (HTR), a readily identifiable behavior used to assess potential treatments for the conditions it models. The HTR was associated with increased delta and decreased theta power in both M1 and dorsal striatum. Together, our results suggest that DOI dysregulates corticostriatal communication and that the HTR is associated with this dysregulation.

Synthesis and characterization of a disubstituted piperazine derivative with T-type channel blocking action and analgesic properties

Background

T-type calcium channels are important contributors to signaling in the primary afferent pain pathway and are thus important targets for the development of analgesics. It has been previously reported that certain piperazine-based compounds such as flunarizine are able to inhibit T-type calcium channels. Thus, we hypothesized that novel piperazine compounds could potentially act as analgesics.

Results

Here, we have created a series of 14 compound derivatives around a diphenyl methyl-piperazine core pharmacophore. Testing their effects on transiently expressed Cav3.2 calcium channels revealed one derivative (3-((4-(bis(4-fluorophenyl)methyl)piperazin-1-yl)methyl)-4-(2-methoxyphenyl)-1,2,5-oxadiazole 2-oxide, compound 10e) as a potent blocker. 10e mediate tonic block of these channels with an IC50 of around 4 micromolar. 10e also blocked Cav3.1 and Cav3.3 channels, but only weakly affected high-voltage-activated Cav1.2 and Cav2.2 channels. Intrathecal delivery of 10e mediated relief from formalin and complete Freund’s adjuvant induced inflammatory pain that was ablated by genetic knockout of Cav3.2 channels.

Conclusions

Altogether, our data identify a novel T-type calcium channel blocker with tight structure activity relationship (SAR) and relevant in vivo efficacy in inflammatory pain conditions.

Flunarizine prevents hepatitis C virus membrane fusion in a genotype-dependent manner by targeting the potential fusion peptide within E1

To explore mechanisms of hepatitis C viral (HCV) replication we screened a compound library including licensed drugs. Flunarizine, a diphenylmethylpiperazine used to treat migraine, inhibited HCV cell entry in vitro and in vivo in a genotype-dependent fashion. Analysis of mosaic viruses between susceptible and resistant strains revealed that E1 and E2 glycoproteins confer susceptibility to flunarizine. Time of addition experiments and single particle tracking of HCV demonstrated that flunarizine specifically prevents membrane fusion. Related phenothiazines and pimozide also inhibited HCV infection and preferentially targeted HCV genotype 2 viruses. However, phenothiazines and pimozide exhibited improved genotype coverage including the difficult to treat genotype 3. Flunarizine-resistant HCV carried mutations within the alleged fusion peptide and displayed cross-resistance to these compounds, indicating that these drugs have a common mode of action.

CONCLUSION

These observations reveal novel details about HCV membrane fusion; moreover, flunarizine and related compounds represent first-in-class HCV fusion inhibitors that merit consideration for repurposing as a cost-effective component of HCV combination therapies.

T-Type Calcium Channel: A Privileged Gate for Calcium Entry and Control of Adrenal Steroidogenesis

Intracellular calcium plays a crucial role in modulating a variety of functions such as muscle contraction, hormone secretion, gene expression, or cell growth. Calcium signaling has been however shown to be more complex than initially thought. Indeed, it is confined within cell microdomains, and different calcium channels are associated with different functions, as shown by various channelopathies. Sporadic mutations on voltage-operated L-type calcium channels in adrenal glomerulosa cells have been shown recently to be the second most prevalent genetic abnormalities present in human aldosterone-producing adenoma. The observed modification of the threshold of activation of the mutated channels not only provides an explanation for this gain of function but also reminds us on the importance of maintaining adequate electrophysiological characteristics to make channels able to exert specific cellular functions. Indeed, the contribution to steroid production of the various calcium channels expressed in adrenocortical cells is not equal, and the reason has been investigated for a long time. Given the very negative resting potential of these cells, and the small membrane depolarization induced by their physiological agonists, low threshold T-type calcium channels are particularly well suited for responding under these conditions and conveying calcium into the cell, at the right place for controlling steroidogenesis. In contrast, high threshold L-type channels are normally activated by much stronger cell depolarizations. The fact that dihydropyridine calcium antagonists, specific for L-type channels, are poorly efficient for reducing aldosterone secretion either in vivo or in vitro, strongly supports the view that these two types of channels differently affect steroid biosynthesis. Whether a similar analysis is transposable to fasciculata cells and cortisol secretion is one of the questions addressed in the present review. No similar mutations on L-type or T-type channels have been described yet to affect cortisol secretion or to be linked to the development of Cushing syndrome, but several evidences suggest that the function of T channels is also crucial in fasciculata cells. Putative molecular mechanisms and cellular structural organization making T channels a privileged entry for the "steroidogenic calcium" are also discussed.

The Physiology, Pathology, and Pharmacology of Voltage-Gated Calcium Channels and Their Future Therapeutic Potential

Voltage-gated calcium channels are required for many key functions in the body. In this review, the different subtypes of voltage-gated calcium channels are described and their physiologic roles and pharmacology are outlined. We describe the current uses of drugs interacting with the different calcium channel subtypes and subunits, as well as specific areas in which there is strong potential for future drug development. Current therapeutic agents include drugs targeting L-type Ca(V)1.2 calcium channels, particularly 1,4-dihydropyridines, which are widely used in the treatment of hypertension. T-type (Ca(V)3) channels are a target of ethosuximide, widely used in absence epilepsy. The auxiliary subunit α2δ-1 is the therapeutic target of the gabapentinoid drugs, which are of value in certain epilepsies and chronic neuropathic pain. The limited use of intrathecal ziconotide, a peptide blocker of N-type (Ca(V)2.2) calcium channels, as a treatment of intractable pain, gives an indication that these channels represent excellent drug targets for various pain conditions. We describe how selectivity for different subtypes of calcium channels (e.g., Ca(V)1.2 and Ca(V)1.3 L-type channels) may be achieved in the future by exploiting differences between channel isoforms in terms of sequence and biophysical properties, variation in splicing in different target tissues, and differences in the properties of the target tissues themselves in terms of membrane potential or firing frequency. Thus, use-dependent blockers of the different isoforms could selectively block calcium channels in particular pathologies, such as nociceptive neurons in pain states or in epileptic brain circuits. Of important future potential are selective Ca(V)1.3 blockers for neuropsychiatric diseases, neuroprotection in Parkinson's disease, and resistant hypertension. In addition, selective or nonselective T-type channel blockers are considered potential therapeutic targets in epilepsy, pain, obesity, sleep, and anxiety. Use-dependent N-type calcium channel blockers are likely to be of therapeutic use in chronic pain conditions. Thus, more selective calcium channel blockers hold promise for therapeutic intervention.

Targeting ion channels for cancer therapy by repurposing the approved drugs

Ion channels have been shown to be involved in oncogenesis and efforts are being poured in to target the ion channels. There are many clinically approved drugs with ion channels as "off" targets. The question is, can these drugs be repurposed to inhibit ion channels for cancer treatment? Repurposing of drugs will not only save investors' money but also result in safer drugs for cancer patients. Advanced bioinformatics techniques and availability of a plethora of open access data on FDA approved drugs for various indications and omics data of large number of cancer types give a ray of hope to look for possibility of repurposing those drugs for cancer treatment. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Microglial intracellular Ca(2+) signaling as a target of antipsychotic actions for the treatment of schizophrenia

Microglia are resident innate immune cells which release many factors including proinflammatory cytokines, nitric oxide (NO) and neurotrophic factors when they are activated in response to immunological stimuli. Recent reports show that pathophysiology of schizophrenia is related to the inflammatory responses mediated by microglia. Intracellular Ca²⁺ signaling, which is mainly controlled by the endoplasmic reticulum (ER), is important for microglial functions such as release of NO and cytokines, migration, ramification and deramification. In addition, alteration of intracellular Ca²⁺ signaling underlies the pathophysiology of schizophrenia, while it remains unclear how typical or atypical antipsychotics affect intracellular Ca²⁺ mobilization in microglial cells. This mini-review article summarizes recent findings on cellular mechanisms underlying the characteristic differences in the actions of antipsychotics on microglial intracellular Ca²⁺ signaling and reinforces the importance of the ER of microglial cells as a target of antipsychotics for the treatment of schizophrenia.

Chronic haloperidol increases voltage-gated Na+ currents in mouse cortical neurons

Typical antipsychotics are characterized by extrapyramidal syndrome (EPS). Previous studies demonstrated that typical antipsychotics could inhibit neuronal voltage-gated sodium channel (VGSC). However, EPS typically emerge only upon prolonged exposure. As a result, we examined effects of haloperidol, a prototype typical antipsychotic, on neuronal VGSC upon incubation for varying duration. Briefly, VGSC currents were activated and recorded using a whole-cell patch-clamp technique in primary culture of mouse cortical neurons. VGSC activity was inhibited by acute haloperidol exposure (for minutes), but enhanced in a time- and concentration-dependent manner by chronic haloperidol exposure (for hours). The effects of chronic haloperidol were associated with increased expression of VGSC subunits as well as corresponding electrophysiological channel properties. In summary, we found enhanced VGSC currents upon chronic haloperidol exposure in cortical neurons in contrast to inhibition by acute haloperidol exposure. Such a results may contribute to EPS of typical antipsychotics.

T-type calcium channel Cav3.2 deficient mice show elevated anxiety, impaired memory and reduced sensitivity to psychostimulants

The fine-tuning of neuronal excitability relies on a tight control of Ca²⁺ homeostasis. The low voltage-activated (LVA) T-type calcium channels (Ca_v3.1, Ca_v3.2 and Ca_v3.3 isoforms) play a critical role in regulating these processes. Despite their wide expression throughout the central nervous system, the implication of T-type Ca_v3.2 isoform in brain functions is still poorly characterized. Here, we investigate the effect of genetic ablation of this isoform in affective disorders, including anxiety, cognitive functions as well as sensitivity to drugs of abuse. Using a wide range of behavioral assays we show that genetic ablation of the cacna1h gene results in an anxiety-like phenotype, whereas novelty-induced locomotor activity is unaffected. Deletion of the T-type channel Ca_v3.2 also triggers impairment of hippocampus-dependent recognition memories. Acute and sensitized hyperlocomotion induced by d-amphetamine and cocaine are dramatically reduced in T-type Ca_v3.2 deficient mice. In addition, the administration of the T-type blocker TTA-A2 prevented the expression of locomotor sensitization observed in wildtype mice. In conclusion, our data reveal that physiological activity of this specific Ca²⁺ channel is required for affective and cognitive behaviors. Moreover, our work highlights the interest of T-type channel blockers as therapeutic strategies to reverse drug-associated alterations.

Evaluating state dependence and subtype selectivity of calcium channel modulators in automated electrophysiology assays

Voltage-gated Ca2+ channels play essential roles in control of neurosecretion and muscle contraction. The pharmacological significance of Cav channels stem from their identification as the molecular targets of calcium blockers used in the treatment of cardiovascular diseases, such as hypertension, angina, and arrhythmia, and neurologic diseases, such as pain and seizure. It has been proposed that state-dependent Cav inhibitors, that is, those that preferentially bind to channels in open or inactivated states, may improve the therapeutic window over relatively state-independent Cav inhibitors. High-throughput fluorescent-based functional assays have been useful in screening chemical libraries to identify Cav inhibitors. However, hit confirmation, mechanism of action, and subtype selectivity are better suited to automated patch clamp assays that have sufficient capacity to handle the volume of compounds identified during screening, even of modest sized libraries (≤500,000 compounds), and the flexible voltage control that allows evaluation of state-dependent drug blocks. IonWorks Barracuda (IWB), the newest generation of IonWorks instruments, provides the opportunity to accelerate the Cav drug discovery studies in an automated patch clamp platform in 384-well format capable of medium throughput screening and profiling studies. We have validated hCav1.2, hCav2.1, hCav2.2, and hCav3.2 channels assays on the IWB platform (population patch clamp mode) and demonstrated that the biophysical characteristics of the channels (activation, inactivation, and steady-state inactivation) obtained with the IWB system are consistent with known subtype-specific characteristics. Using standard reference compounds (nifedipine, BAY K8644, verapamil, mibefradil, and pimozide), we demonstrated subtype-selective and state- and use-dependent characteristics of drug-channel interactions. Here we describe the design and validation of novel robust high-throughput Cav channel assays on the IWB platform. The assays can be used to screen focused compound libraries for state-dependent Cav channel antagonists, to prioritize compounds for potency or to counterscreen for Cav subtype selectivity.

T-type calcium channel blockers as neuroprotective agents

T-type calcium channels are expressed in many diverse tissues, including neuronal, cardiovascular, and endocrine. T-type calcium channels are known to play roles in the development, maintenance, and repair of these tissues but have also been implicated in disease when not properly regulated. Calcium channel blockers have been developed to treat various diseases and their use clinically is widespread due to both their efficacy as well as their safety. Aside from their established clinical applications, recent studies have suggested neuroprotective effects of T-type calcium channel blockers. Many of the current T-type calcium channel blockers could act on other molecular targets besides T-type calcium channels making it uncertain whether their neuroprotective effects are solely due to blocking of T-type calcium channels. In this review, we discuss these drugs as well as newly developed chemical compounds that are designed to be more selective for T-type calcium channels. We review in vitro and in vivo evidence of neuroprotective effects by these T-type calcium channel blockers. We conclude by discussing possible molecular mechanisms underlying the neuroprotective effects by T-type calcium channel blockers.

Isolation, synthesis and characterization of ω-TRTX-Cc1a, a novel tarantula venom peptide that selectively targets L-type Cav channels

Spider venoms are replete with peptidic ion channel modulators, often with novel subtype selectivity, making them a rich source of pharmacological tools and drug leads. In a search for subtype-selective blockers of voltage-gated calcium (CaV) channels, we isolated and characterized a novel 39-residue peptide, ω-TRTX-Cc1a (Cc1a), from the venom of the tarantula Citharischius crawshayi (now Pelinobius muticus). Cc1a is 67% identical to the spider toxin ω-TRTX-Hg1a, an inhibitor of CaV2.3 channels. We assembled Cc1a using a combination of Boc solid-phase peptide synthesis and native chemical ligation. Oxidative folding yielded two stable, slowly interconverting isomers. Cc1a preferentially inhibited Ba(2+) currents (IBa) mediated by L-type (CaV1.2 and CaV1.3) CaV channels heterologously expressed in Xenopus oocytes, with half-maximal inhibitory concentration (IC50) values of 825nM and 2.24μM, respectively. In rat dorsal root ganglion neurons, Cc1a inhibited IBa mediated by high voltage-activated CaV channels but did not affect low voltage-activated T-type CaV channels. Cc1a exhibited weak activity at NaV1.5 and NaV1.7 voltage-gated sodium (NaV) channels stably expressed in mammalian HEK or CHO cells, respectively. Experiments with modified Cc1a peptides, truncated at the N-terminus (ΔG1-E5) or C-terminus (ΔW35-V39), demonstrated that the N- and C-termini are important for voltage-gated ion channel modulation. We conclude that Cc1a represents a novel pharmacological tool for probing the structure and function of L-type CaV channels.