Repurposed Biguanide Drugs in Glioblastoma Exert Antiproliferative Effects via the Inhibition of Intracellular Chloride Channel 1 Activity

The role of neurotransmitters in glioblastoma multiforme-associated seizures

GBM, or glioblastoma multiforme, is a brain tumor that poses a great threat to both children and adults, being the primary cause of death related to brain tumors. GBM is often associated with epilepsy, which can be debilitating. Seizures and the development of epilepsy are the primary symptoms that have a severe impact on the quality of life for GBM patients. It is increasingly apparent that the nervous system plays an essential role in the tumor microenvironment for all cancer types, including GBM. In recent years, there has been a growing understanding of how neurotransmitters control the progression of gliomas. Evidence suggests that neurotransmitters and neuromodulators found in the tumor microenvironment play crucial roles in the excitability, proliferation, quiescence, and differentiation of neurons, glial cells, and neural stem cells. The involvement of neurotransmitters appears to play a significant role in various stages of GBM. In this review, the focus is on presenting updated knowledge and emerging ideas regarding the interplay between neurotransmitters and neuromodulators, such as glutamate, GABA, norepinephrine, dopamine, serotonin, adenosine, and their relationship with GBM and the seizures induced by this condition. The review aims to explore the current understanding and provide new insights into the complex interactions between these neurotransmitters and neuromodulators in the context of GBM-related seizures.

Development and validation of a GC-MS method for determination of metformin in normal brain and in glioblastoma tissues

Metformin hydrochloride (MH) has recently been repurposed as an anticancer agent, showing antiproliferative activity in vitro and in vivo. In particular, experimental evidence has suggested its potential clinical efficacy in glioblastoma (GBM), a very aggressive tumor frequently characterized by gloomy prognosis. Unfortunately, the published literature concerning experimental applications of MH in glioblastoma animal models report no data on metformin levels reached in the brain, which, considering the high hydrophilicity of the drug, are likely very low. Therefore, new sensitive analytical methods to be applied on biological tissues are necessary to improve our knowledge of MH in vivo biodistribution and biological effects on tumors. In this research work, a GC-MS method for MH quantification in brain tissues is proposed. MH has been derivatized using N-methyl-bis(trifluoroacetamide), as already described in the literature, but the derivatization conditions have been optimized; moreover, deuterated MH has been selected as the best internal standard, after a comparative evaluation including other internal standards employed in published methods. After ascertaining method linearity, its accuracy, precision, specificity, repeatability, LOD and LOQ (0.373 µM and 1.242 µM, respectively, corresponding to 0.887 and 2.958 pmol/mg of wet tissue) have been evaluated on mouse brain tissue samples, obtained through a straightforward preparation procedure involving methanolic extraction from lyophilized brain homogenates and solid phase purification. The method has been validated on brain samples obtained from mice, either healthy or xenografted with GBM cells, receiving metformin dissolved in the drinking water. This analytical method can be usefully applied in preclinical studies aiming at clarifying MH mechanism of action in brain tumors.

Antitumor Potential of Antiepileptic Drugs in Human Glioblastoma: Pharmacological Targets and Clinical Benefits

Glioblastoma (GBM) is characterized by fast-growing cells, genetic and phenotypic heterogeneity, and radio-chemo-therapy resistance, contributing to its dismal prognosis. Various medical comorbidities are associated with the natural history of GBM. The most disabling and greatly affecting patients' quality of life are neurodegeneration, cognitive impairment, and GBM-related epilepsy (GRE). Hallmarks of GBM include molecular intrinsic mediators and pathways, but emerging evidence supports the key role of non-malignant cells within the tumor microenvironment in GBM aggressive behavior. In this context, hyper-excitability of neurons, mediated by glutamatergic and GABAergic imbalance, contributing to GBM growth strengthens the cancer-nervous system crosstalk. Pathogenic mechanisms, clinical features, and pharmacological management of GRE with antiepileptic drugs (AEDs) and their interactions are poorly explored, yet it is a potentially promising field of research in cancer neuroscience. The present review summarizes emerging cooperative mechanisms in oncogenesis and epileptogenesis, focusing on the neuron-to-glioma interface. The main effects and efficacy of selected AEDs used in the management of GRE are discussed in this paper, as well as their potential beneficial activity as antitumor treatment. Overall, although still many unclear processes overlapping in GBM growth and seizure onset need to be elucidated, this review focuses on the intriguing targeting of GBM-neuron mutual interactions to improve the outcome of the so challenging to treat GBM.

Structural basis of mammalian respiratory complex I inhibition by medicinal biguanides

The molecular mode of action of biguanides, including the drug metformin, which is widely used in the treatment of diabetes, is incompletely characterized. Here, we define the inhibitory drug-target interaction(s) of a model biguanide with mammalian respiratory complex I by combining cryo-electron microscopy and enzyme kinetics. We interpret these data to explain the selectivity of biguanide binding to different enzyme states. The primary inhibitory site is in an amphipathic region of the quinone-binding channel, and an additional binding site is in a pocket on the intermembrane-space side of the enzyme. An independent local chaotropic interaction, not previously described for any drug, displaces a portion of a key helix in the membrane domain. Our data provide a structural basis for biguanide action and enable the rational design of medicinal biguanides.

Proguanil and atovaquone use is associated with lower colorectal cancer risk: a nationwide cohort study

BACKGROUND

Individuals with a family history of colorectal cancer (CRC) are at a high risk of developing CRC. Preclinical studies suggest that the anti-malaria drug proguanil and atovaquone might play a role in preventing CRC, but population-based evidence is still lacking.

METHODS

By accessing a couple of nationwide Swedish registers, we performed a cohort study to explore whether using proguanil and atovaquone might associate with a lower risk of CRC by adopting a new-user study design. Adults who have 1 or more first-degree relatives (parents or siblings) diagnosed with CRC were identified and linked with the Prescribed Drug Register to evaluate their administration history of proguanil and atovaquone. Survival analysis of the time to CRC diagnosis with Cox proportional hazards regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

A total of 16,817 incident proguanil/atovaquone users were identified and matched with 168,170 comparisons, who did not use proguanil/atovaquone, on the ratio of 1:10. We found a significant negative association between proguanil/atovaquone use and risk of CRC (adjusted HR, 0.76; 95% CI, 0.62-0.93). Test for trend showed significant dose- and duration-response correlations (P < 0.001). The association was more pronounced in CRC diagnosed at an advanced stage than at an early stage (adjusted HR, 0.69 vs.0.81).

CONCLUSIONS

This national-wide population-based cohort study showed that the use of proguanil and atovaquone was associated with a reduced risk of CRC among individuals with a family history of CRC.

Chloride intracellular channel 1 activity is not required for glioblastoma development but its inhibition dictates glioma stem cell responsivity to novel biguanide derivatives

Background

Chloride intracellular channel-1 (CLIC1) activity controls glioblastoma proliferation. Metformin exerts antitumor effects in glioblastoma stem cells (GSCs) inhibiting CLIC1 activity, but its low potency hampers its translation in clinical settings.

Methods

We synthesized a small library of novel biguanide-based compounds that were tested as antiproliferative agents for GSCs derived from human glioblastomas, in vitro using 2D and 3D cultures and in vivo in the zebrafish model. Compounds were compared to metformin for both potency and efficacy in the inhibition of GSC proliferation in vitro (MTT, Trypan blue exclusion assays, and EdU labeling) and in vivo (zebrafish model), migration (Boyden chamber assay), invasiveness (Matrigel invasion assay), self-renewal (spherogenesis assay), and CLIC1 activity (electrophysiology recordings), as well as for the absence of off-target toxicity (effects on normal stem cells and toxicity for zebrafish and chick embryos).

Results

We identified Q48 and Q54 as two novel CLIC1 blockers, characterized by higher antiproliferative potency than metformin in vitro, in both GSC 2D cultures and 3D spheroids. Q48 and Q54 also impaired GSC self-renewal, migration and invasion, and displayed low systemic in vivo toxicity. Q54 reduced in vivo proliferation of GSCs xenotransplanted in zebrafish hindbrain. Target specificity was confirmed by recombinant CLIC1 binding experiments using microscale thermophoresis approach. Finally, we characterized GSCs from GBMs spontaneously expressing low CLIC1 protein, demonstrating their ability to grow in vivo and to retain stem-like phenotype and functional features in vitro. In these GSCs, Q48 and Q54 displayed reduced potency and efficacy as antiproliferative agents as compared to high CLIC1-expressing tumors. However, in 3D cultures, metformin and Q48 (but not Q54) inhibited proliferation, which was dependent on the inhibition dihydrofolate reductase activity.

Conclusions

These data highlight that, while CLIC1 is dispensable for the development of a subset of glioblastomas, it acts as a booster of proliferation in the majority of these tumors and its functional expression is required for biguanide antitumor class-effects. In particular, the biguanide-based derivatives Q48 and Q54, represent the leads to develop novel compounds endowed with better pharmacological profiles than metformin, to act as CLIC1-blockers for the treatment of CLIC1-expressing glioblastomas, in a precision medicine approach.

Targeting the metabolism of cancer stem cells by energy disruptor molecules

Cancer stem cells (CSCs) have been identified in various tumor types. CSCs are believed to contribute to tumor metastasis and resistance to conventional therapy. So targeting these cells could be an effective strategy to eliminate tumors and a promising new type of cancer treatment. Alterations in metabolism play an essential role in CSC biology and their resistance to treatment. The metabolic properties pathways in CSCs are different from normal cells, and to some extent, are different from regular tumor cells. Interestingly, CSCs can use other nutrients for their metabolism and growth. The different metabolism causes increased sensitivity of CSCs to agents that disrupt cellular homeostasis. Compounds that interfere with the central metabolic pathways are known as energy disruptors and can reduce CSC survival. This review highlights the differences between regular cancer cells and CSC metabolism and discusses the action mechanisms of energy disruptors at the cellular and molecular levels.

Liver Metastatic Colorectal Tumor Cells Change Their Phenotype During Consecutive Passages on Chick Embryo Chorioallantoic Membrane: Lessons from the Lab to the Clinic

BACKGROUND/AIM

Colon cancer liver metastases with desmoplastic growth pattern (dGP) have a highly heterogeneous therapy response. The aim of the study was to evaluate the dGP liver metastasis molecular profile from a chemo-naive patient by mimicking metastatic process on an experimental chick embryo chorioallantoic membrane (CAM) model.

MATERIALS AND METHODS

Three successive CAM passages of dGP human colorectal liver metastases were immunophenotyped for keratin (K) 8, and 20, CLIC1, VEGF, EGFR, CD34, podoplanin, Ki67, E-cadherin and vimentin.

RESULTS

Metastatic cells gradually lost K20 while K8, E-cadherin and vimentin heterogeneously increased during passages. VEGF, CLIC 1, EGFR expression increased in metastatic cells especially at the tumor graft periphery. Scattered proliferating and non-proliferating podoplanin-positive tumor cells, lymphatic and blood vessels were heterogeneously detected in tumor xenografts depending on passage stage.

CONCLUSION

By mimicking repetitive metastatic processes we proved that metastatic cells change their phenotype. This may explain why not all metastases have a similar response to therapy.

Study on Cancer Cell Invasiveness via Application of Mechanical Force to Induce Chloride Ion Efflux

Chloride channels regulate cell volume by an efflux of chloride ions in response to osmotic stresses. These have been shown to play a role in cancer invasion. However, their function in cancer metastasis remains unclear. As the internal environment of the human body is rarely exposed to osmotic stress, we presumed that Cl^- efflux in cancer cells is induced by mechanical stress caused by their crowded environment and invasion of their narrow interstitial spaces. In this study, we recruited atomic force microscopy to apply mechanical stress to mouse or human breast cancer cells with varying degrees of malignancy and examined their Cl^- efflux by N-ethoxycarbonylmethyl-6-methoxyquinolinium bromide (MQAE), which is quenched via collision with Cl^- ions. We found that intracellular MQAE fluorescence intensity increased immediately after cell compression, demonstrating induction of Cl^- efflux by mechanical force. Furthermore, Cl^- efflux ability showed correlation with the cancer metastatic potential. These results suggested that mechanical stress induced Cl^- efflux may serve as a potential reporter for estimating the invasion ability of cancer cells.

CLIC1 recruits PIP5K1A/C to induce cell-matrix adhesions for tumor metastasis

Membrane protrusion and adhesion to the extracellular matrix, which involves the extension of actin filaments and formation of adhesion complexes, are the fundamental processes for cell migration, tumor invasion, and metastasis. How cancer cells efficiently coordinate these processes remains unclear. Here, we showed that membrane-targeted chloride intracellular channel 1 (CLIC1) spatiotemporally regulates the formation of cell-matrix adhesions and membrane protrusions through the recruitment of PIP5Ks to the plasma membrane. Comparative proteomics identified CLIC1 upregulated in human hepatocellular carcinoma (HCC) and associated with tumor invasiveness, metastasis, and poor prognosis. In response to migration-related stimuli, CLIC1 recruited PIP5K1A and PIP5K1C from the cytoplasm to the leading edge of the plasma membrane, where PIP5Ks generate a phosphatidylinositol 4,5-bisphosphate-rich (PIP2-rich) microdomain to induce the formation of integrin-mediated cell-matrix adhesions and the signaling for cytoskeleon extension. CLIC1 silencing inhibited the attachment of tumor cells to culture plates and the adherence and extravasation in the lung alveoli, resulting in suppressed lung metastasis in mice. This study reveals what we believe is an unrecognized mechanism that spatiotemporally coordinates the formation of both lamellipodium/invadopodia and nascent cell-matrix adhesions for directional migration and tumor invasion/metastasis. The unique traits of upregulation and membrane targeting of CLIC1 in cancer cells make it an excellent therapeutic target for tumor metastasis.

Effect of metformin on stem cells: Molecular mechanism and clinical prospect

Metformin is a first-line medication for type II diabetes. Numerous studies have shown that metformin not only has hypoglycemic effects, but also modulates many physiological and pathological processes ranging from aging and cancer to fracture healing. During these different physiological activities and pathological changes, stem cells usually play a core role. Thus, many studies have investigated the effects of metformin on stem cells. Metformin affects cell differentiation and has promising applications in stem cell medicine. It exerts anti-aging effects and can be applied to gerontology and regenerative medicine. The potential anti-cancer stem cell effect of metformin indicates that it can be an adjuvant therapy for cancers. Furthermore, metformin has beneficial effects against many other diseases including cardiovascular and autoimmune diseases. In this review, we summarize the effects of metformin on stem cells and provide an overview of its molecular mechanisms and clinical prospects.

Ion channels and transporters in microglial function in physiology and brain diseases

Microglial cells interact with all components of the central nervous system (CNS) and are increasingly recognized to play essential roles during brain development, homeostasis and disease pathologies. Functions of microglia include maintaining tissue integrity, clearing cellular debris and dead neurons through the process of phagocytosis, and providing tissue repair by releasing anti-inflammatory cytokines and neurotrophic factors. Changes of microglial ionic homeostasis (Na⁺, Ca²⁺, K⁺, H⁺, Cl^-) are important for microglial activation, including proliferation, migration, cytokine release and reactive oxygen species production, etc. These are mediated by ion channels and ion transporters in microglial cells. Here, we review the current knowledge about the role of major microglial ion channels and transporters, including several types of Ca²⁺ channels (store-operated Ca²⁺ entry (SOCE) channels, transient receptor potential (TRP) channels and voltage-gated Ca²⁺ channels (VGCCs)) and Na⁺ channels (voltage-gated Na⁺ channels (Nav) and acid-sensing ion channels (ASICs)), K⁺ channels (inward rectifier K⁺ channels (K_ir), voltage-gated K⁺ channels (K_V) and calcium-activated K⁺ channels (K_Ca)), proton channels (voltage-gated proton channel (Hv1)), and Cl^- channels (volume (or swelling)-regulated Cl^- channels (VRCCs) and chloride intracellular channels (CLICs)). In addition, ion transporter proteins such as Na⁺/Ca²⁺ exchanger (NCX), Na⁺-K⁺-Cl^- cotransporter (NKCC1), and Na⁺/H⁺ exchanger (NHE1) are also involved in microglial function in physiology and brain diseases. We discussed microglial activation and neuroinflammation in relation to the ion channel/transporter stimulation under brain disease conditions and therapeutic aspects of targeting microglial ion channels/transporters for neurodegenerative disease, ischemic stroke, traumatic brain injury and neuropathic pain.

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.

Up-regulation of CLIC1 activates MYC signaling and forms a positive feedback regulatory loop with MYC in Hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is leading cause of tumor-related deaths worldwide. The intracellular chloride channel protein (CLIC1) plays a role in the occurrence and progression of HCC, although the underlying mechanisms are still unclear. We evaluated the CLIC1 mRNA and protein levels in both patient tissues and HCC cell lines, and analyzed the correlation between CLIC1 expression and clinical features. The biological function of CLIC1 in HCC was examined in vivo and in vitro. The upstream regulatory factors were identified by bioinformatics programs, and downstream mechanisms affecting HCC behavior have also been explored and validated. CLIC1 was up-regulated in HCC tissues and cell lines, and promoted the proliferation, invasion and migration of HCC cells in vivo and in vitro. TP53 was identified as the upstream transcription factor of CLIC1. MiR-122-5p also regulated CLIC1 levels by degrading the transcripts. More importantly, we found that the increased CLIC1 was significantly related to the activation of MYC signaling. By binding with MYC, CLIC1 enhanced the transcription activity of MYC to downstream genes, rather than by altering its expression. Finally, a positive feedback regulatory loop between CLIC1 and MYC was established. CLIC1 is closely related to the occurrence, progression and prognosis of HCC, and a promising novel therapeutic target.

Intracellular Chloride Channels: Novel Biomarkers in Diseases

Ion channels are integral membrane proteins present on the plasma membrane as well as intracellular membranes. In the human genome, there are more than 400 known genes encoding ion channel proteins. Ion channels are known to regulate several cellular, organellar, and physiological processes. Any mutation or disruption in their function can result in pathological disorders, both common or rare. Ion channels present on the plasma membrane are widely acknowledged for their role in various biological processes, but in recent years, several studies have pointed out the importance of ion channels located in intracellular organelles. However, ion channels located in intracellular organelles are not well-understood in the context of physiological conditions, such as the generation of cellular excitability and ionic homeostasis. Due to the lack of information regarding their molecular identity and technical limitations of studying them, intracellular organelle ion channels have thus far been overlooked as potential therapeutic targets. In this review, we focus on a novel class of intracellular organelle ion channels, Chloride Intracellular Ion Channels (CLICs), mainly documented for their role in cardiovascular, neurophysiology, and tumor biology. CLICs have a single transmembrane domain, and in cells, they exist in cytosolic as well as membranous forms. They are predominantly present in intracellular organelles and have recently been shown to be localized to cardiomyocyte mitochondria as well as exosomes. In fact, a member of this family, CLIC5, is the first mitochondrial chloride channel to be identified on the molecular level in the inner mitochondrial membrane, while another member, CLIC4, is located predominantly in the outer mitochondrial membrane. In this review, we discuss this unique class of intracellular chloride channels, their role in pathologies, such as cardiovascular, cancer, and neurodegenerative diseases, and the recent developments concerning their usage as theraputic targets.

Neuromodulatory effects of anti-diabetes medications: A mechanistic review

Diabetes mellitus is a potent upstream event in the molecular pathophysiology which gives rise to various diabetes-related complications. There are several classes of anti-diabetic medications that have been developed to normalize blood glucose concentrations through a variety of molecular mechanisms. Beyond glucose-lowering effects, these agents may also provide further therapeutic potential. For instance, there is a high incidence of diabetes-induced neuronal disorders among patients with diabetes, who may also develop neurodegenerative and psychological complications. If anti-diabetic agents can modify the molecular mechanisms involved in the pathophysiology of neuronal comorbidities, this could potentially be translated to reducing the risk of other neurological conditions such as Alzheimer's disease, Parkinson's disease, depression, memory deficits and cognition impairments among patients with diabetes. This review aimed to shed light on some of the potentially beneficial aspects of anti-diabetic agents in lowering the risk or treating neuronal disorders by reviewing the molecular mechanisms by which these agents can potentially modulate neuronal behaviors.