Dual inhibition of sodium-mediated proton and calcium efflux triggers non-apoptotic cell death in malignant gliomas

Brain multi-omic Mendelian randomisation to identify novel drug targets for gliomagenesis

BACKGROUND

Genetic variants associated with molecular traits that are also associated with liability to glioma can provide causal evidence for the identification and prioritisation of drug targets.

METHODS

We performed comprehensive two-sample Mendelian randomisation (Wald ratio and/or IVW) and colocalisation analyses of molecular traits on glioma. Instrumentable traits (QTLs P < 5 × 10-8) were identified amongst 11 985 gene expression measures, 13 285 splicing isoforms and 10 198 protein abundance measures, derived from 15 brain regions. Glioma summary-level data was extracted from a genome-wide association meta-analysis of 12 496 cases and 18 190 controls.

RESULTS

We found evidence for causal effect of 22 molecular traits (across 18 genes/proteins) on glioma risk. Thirteen molecular traits have been previously linked with glioma risk and five were novel; HBEGF (5q31.3) expression and all glioma [OR 1.36 (95%CI 1.19-1.55); P = 4.41 × 10-6]; a CEP192 (18p11.21) splice isoform and glioblastoma [OR 4.40 (95%CI 2.28-8.48); P = 9.78 × 10-4]; a FAIM (3q22.3) splice isoform and all glioma [OR 2.72-3.43; P = 1.03 × 10-5 to 1.09 × 10-5]; a SLC8A1 (2p22.1) splice isoform and all glioma [OR 0.37 (95%CI 0.24-0.56; P = 5.72 × 10-6]; D2HGDH (2q37.3) protein and all glioma [OR 0.86 (95%CI 0.80-0.92); P = 5.94 × 10-6)].

CONCLUSIONS

We provide robust causal evidence for prioritising genes and their protein products in glioma research. Our results highlight the importance of alternative splicing as a mechanism in gliomagenesis and as an avenue for exploration of drug targets.

Targeted Delivery to Dying Cells Through P-Selectin-PSGL-1 Axis: A Promising Strategy for Enhanced Drug Efficacy in Liver Injury Models

To minimize off-target adverse effects and improve drug efficacy, various tissue-specific drug delivery systems have been developed. However, even in diseased organs, both normal and stressed, dying cells coexist, and a targeted delivery system specifically for dying cells has yet to be explored to mitigate off-target effects within the same organ. This study aimed to establish such a system. By examining the surfaces of dying cells in vitro, we identified P-selectin glycoprotein ligand-1 (PSGL-1) as a universal marker for dying cells, positioning it as a potential target for selective drug delivery. We demonstrated that liposomes conjugated with the PSGL-1 binding protein P-selectin had significantly greater binding efficiency to dying cells compared to control proteins such as E-selectin, L-selectin, galectin-1, and C-type lectin-like receptor 2. Using thioacetamide (TAA) to induce hepatitis and hepatocyte damage in mice, we assessed the effectiveness of our P-selectin-based delivery system. In vivo, P-selectin-conjugated liposomes effectively delivered fluorescent dye and the apoptosis inhibitor z-DEVD to TAA-damaged livers in wild-type mice, but not in PSGL-1 knockout mice. In TAA-treated wild-type mice, unconjugated liposomes required a 100-fold higher z-DEVD dose compared to P-selectin-conjugated liposomes to achieve a comparable, albeit less effective, therapeutic outcome in lowering plasma alanine transaminase levels and alleviating thrombocytopenia. This emphasizes that P-selectin conjugation enhances drug delivery efficiency by approximately 100-fold in mice. These results suggest that P-selectin-based liposomes could be a promising strategy for targeted drug delivery, enabling both diagnosis and treatment by specifically delivering cell-labeling agents and rescue agents to dying cells via the P-selectin-PSGL-1 axis at the individual cell level.

Ion Channel Drugs Suppress Cancer Phenotype in NG108-15 and U87 Cells: Toward Novel Electroceuticals for Glioblastoma

Glioblastoma is a lethal brain cancer that commonly recurs after tumor resection and chemotherapy treatment. Depolarized resting membrane potentials and an acidic intertumoral extracellular pH have been associated with a proliferative state and drug resistance, suggesting that forced hyperpolarization and disruption of proton pumps in the plasma membrane could be a successful strategy for targeting glioblastoma overgrowth. We screened 47 compounds and compound combinations, most of which were ion-modulating, at different concentrations in the NG108-15 rodent neuroblastoma/glioma cell line. A subset of these were tested in the U87 human glioblastoma cell line. A FUCCI cell cycle reporter was stably integrated into both cell lines to monitor proliferation and cell cycle response. Immunocytochemistry, electrophysiology, and a panel of physiological dyes reporting voltage, calcium, and pH were used to characterize responses. The most effective treatments on proliferation in U87 cells were combinations of NS1643 and pantoprazole; retigabine and pantoprazole; and pantoprazole or NS1643 with temozolomide. Marker analysis and physiological dye signatures suggest that exposure to bioelectric drugs significantly reduces proliferation, makes the cells senescent, and promotes differentiation. These results, along with the observed low toxicity in human neurons, show the high efficacy of electroceuticals utilizing combinations of repurposed FDA approved drugs.

Anticancer Effects and Mechanisms of OSW-1 Isolated From Ornithogalum saundersiae: A Review

For centuries, cancer has been a lingering dark cloud floating on people's heads. With rapid population growth and aging worldwide, cancer incidence and mortality are growing rapidly. Despite major advances in oncotherapy including surgery, radiation and chemical therapy, as well as immunotherapy and targeted therapy, cancer is expected be the leading cause of premature death in this century. Nowadays, natural compounds with potential anticancer effects have become an indispensable natural treasure for discovering clinically useful agents and made remarkable achievements in cancer chemotherapy. In this regards, OSW-1, which was isolated from the bulbs of Ornithogalum saundersiae in 1992, has exhibited powerful anticancer activities in various cancers. However, after almost three decades, OSW-1 is still far from becoming a real anticancer agent for its anticancer mechanisms remain unclear. Therefore, in this review we summarize the available evidence on the anticancer effects and mechanisms of OSW-1 in vitro and in vivo, and some insights for researchers who are interested in OSW-1 as a potential anticancer drug. We conclude that OSW-1 is a potential candidate for anticancer drugs and deserves further study.

Mechanisms of malignancy in glioblastoma cells are linked to mitochondrial Ca2 + uniporter upregulation and higher intracellular Ca2+ levels

Glioblastoma (GBM) is one of the most malignant brain tumours and, despite advances in treatment modalities, it remains largely incurable. Ca²⁺ regulation and dynamics play crucial roles in different aspects of cancer, but they have never been investigated in detail in GBM. Here, we report that spontaneous Ca²⁺ waves in GBM cells cause unusual intracellular Ca²⁺ ([Ca²⁺]_i) elevations (>1 μM), often propagating through tumour microtubes (TMs) connecting adjacent cells. This unusual [Ca²⁺]_i elevation is not associated with the induction of cell death and is concomitant with overexpression of mitochondrial Ca²⁺ uniporter (MCU). We show that MCU silencing decreases proliferation and alters [Ca²⁺]_i dynamics in U87 GBM cells, while MCU overexpression increases [Ca²⁺]_i elevation in human astrocytes (HAs). These results suggest that changes in the expression level of MCU, a protein involved in intracellular Ca²⁺ regulation, influences GBM cell proliferation, contributing to GBM malignancy.This article has an associated First Person interview with the first author of the paper.

Hydrogen Ion Dynamics of Cancer and a New Molecular, Biochemical and Metabolic Approach to the Etiopathogenesis and Treatment of Brain Malignancies

The treatment of cancer has been slowly but steadily progressing during the last fifty years. Some tumors with a high mortality in the past are curable nowadays. However, there is one striking exception: glioblastoma multiforme. No real breakthrough has been hitherto achieved with this tumor with ominous prognosis and very short survival. Glioblastomas, being highly glycolytic malignancies are strongly pH-dependent and driven by the sodium hydrogen exchanger 1 (NHE1) and other proton (H⁺) transporters. Therefore, this is one of those pathologies where the lessons recently learnt from the new pH-centered anticancer paradigm may soon bring a promising change to treatment. This contribution will discuss how the pH-centric molecular, biochemical and metabolic perspective may introduce some urgently needed and integral novel treatments. Such a prospective therapeutic approach for malignant brain tumors is developed here, either to be used alone or in combination with more standard therapies.

New trends in glioma cancer therapy: Targeting Na+ /H + exchangers

Glioma is the oneof the most prevalent primarybrain tumors. There is a variety of oxidative stresses, inflammatory pathways, apoptosis signaling, and Na⁺ /H ⁺ exchangers (NHEs) involved in the pathophysiology of glioma. Previous studies have indicated a relationship between NHEs and some molecular pathways in glioma. NHEs, including NHE1, NHE5, and NHE9 affect apoptosis, tumor-associated macrophage inflammatory pathways, matrix metalloproteinases, cancer-cell growth, invasion, and migration of glioma. Also, inhibition of NHEs contributes to increased survival in animal models of glioma. Limited studies, however, have assessed the relationship between NHEs and molecular pathways in glioma. This review summarizes current knowledge and evidence regarding the relationship between NHEs and glioma, and the mechanisms involved.

Tumour acidosis: from the passenger to the driver's seat

The high metabolic demand of cancer cells leads to an accumulation of H⁺ ions in the tumour microenvironment. The disorganized tumour vasculature prevents an efficient wash-out of H⁺ ions released into the extracellular medium but also favours the development of tumour hypoxic regions associated with a shift towards glycolytic metabolism. Under hypoxia, the final balance of glycolysis, including breakdown of generated ATP, is the production of lactate and a stoichiometric amount of H⁺ ions. Another major source of H⁺ ions results from hydration of CO₂ produced in the more oxidative tumour areas. All of these events occur at high rates in tumours to fulfil bioenergetic and biosynthetic needs. This Review summarizes the current understanding of how H⁺-generating metabolic processes segregate within tumours according to the distance from blood vessels and inversely how ambient acidosis influences tumour metabolism, reducing glycolysis while promoting mitochondrial activity. The Review also presents novel insights supporting the participation of acidosis in cancer progression via stimulation of autophagy and immunosuppression. Finally, recent advances in the different therapeutic modalities aiming to either block pH-regulatory systems or exploit acidosis will be discussed.

Cellular acidification as a new approach to cancer treatment and to the understanding and therapeutics of neurodegenerative diseases

During the last few years, the understanding of the dysregulated hydrogen ion dynamics and reversed proton gradient of cancer cells has resulted in a new and integral pH-centric paradigm in oncology, a translational model embracing from cancer etiopathogenesis to treatment. The abnormalities of intracellular alkalinization along with extracellular acidification of all types of solid tumors and leukemic cells have never been described in any other disease and now appear to be a specific hallmark of malignancy. As a consequence of this intracellular acid-base homeostatic failure, the attempt to induce cellular acidification using proton transport inhibitors and other intracellular acidifiers of different origins is becoming a new therapeutic concept and selective target of cancer treatment, both as a metabolic mediator of apoptosis and in the overcoming of multiple drug resistance (MDR). Importantly, there is increasing data showing that different ion channels contribute to mediate significant aspects of cancer pH regulation and etiopathogenesis. Finally, we discuss the extension of this new pH-centric oncological paradigm into the opposite metabolic and homeostatic acid-base situation found in human neurodegenerative diseases (HNDDs), which opens novel concepts in the prevention and treatment of HNDDs through the utilization of a cohort of neural and non-neural derived hormones and human growth factors.

Value of pH regulators in the diagnosis, prognosis and treatment of cancer

Altered metabolism, associated with acidification of the extracellular milieu, is one of the major features of cancer. As pH regulation is crucial for the maintenance of all biological functions, cancer cells rely on the activity of lactate exporters and proton transporters to regulate their intracellular pH. The major players in cancer pH regulation are proton pump ATPases, sodium-proton exchangers (NHEs), monocarboxylate transporters (MCTs), carbonic anhydrases (CAs) and anion exchangers (AEs), which have been shown to be upregulated in several human malignancies. Thanks to the activity of the proton pumps and transporters, tumours acidify their microenvironment, becoming more aggressive and resistant to therapy. Thus, targeting tumour pH may contribute to more effective anticancer strategies for controlling tumour progression and therapeutic resistance. In the present study, we review the role of the main pH regulators expressed in human cancer cells, including their diagnostic and prognostic value, as well as their usefulness as therapeutic targets.

Time-dependent activity of Na+/H+ exchanger isoform 1 and homeostasis of intracellular pH in astrocytes exposed to CoCl2 treatment

Hypoxia causes injury to the central nervous system during stroke and has significant effects on pH homeostasis. Na+/H+ exchanger isoform 1 (NHE1) is important in the mechanisms of hypoxia and intracellular pH (pHi) homeostasis. As a well-established hypoxia-mimetic agent, CoCl2 stabilizes and increases the expression of hypoxia inducible factor‑1α (HIF-1α), which regulates several genes involved in pH balance, including NHE1. However, it is not fully understood whether NHE1 is activated in astrocytes under CoCl2 treatment. In the current study, pHi and NHE activity were analyzed using the pHi‑sensitive dye BCECF‑AM. Using cariporide (an NHE1‑specific inhibitor) and EIPA (an NHE nonspecific inhibitor), the current study demonstrated that it was NHE1, not the other NHE isoforms, that was important in regulating pHi homeostasis in astrocytes during CoCl2 treatment. Additionally, the present study observed that, during the early period of CoCl2 treatment (the first 2 h), NHE1 activity and pHi dropped immediately, and NHE1 mRNA expression was reduced compared with control levels, whereas expression levels of the NHE1 protein had not yet changed. In the later period of CoCl2 treatment, NHE1 activity and pHi significantly increased compared with the control levels, as did the mRNA and protein expression levels of NHE1. Furthermore, the cell viability and injury of astrocytes was not changed during the initial 8 h of CoCl2 treatment; their deterioration was associated with the higher levels of pHi and NHE1 activity. The current study concluded that NHE1 activity and pHi homeostasis are regulated by CoCl2 treatment in a time-dependent manner in astrocytes, and may be responsible for the changes in cell viability and injury observed under hypoxia-mimetic conditions induced by CoCl2 treatment.

The Na⁺/H⁺ exchanger (NHE1) as a novel co-adjuvant target in paclitaxel therapy of triple-negative breast cancer cells

Dysregulation of Na⁺ /H⁺ exchanger isoform one (NHE1) activity is a hallmark of cells undergoing tumorigenesis and metastasis, the leading cause of patient mortality. The acidic tumor microenvironment is thought to facilitate the development of resistance to chemotherapy drugs and to promote extracellular matrix remodeling leading to metastasis. Here, we investigated NHE1 as a co-adjuvant target in paclitaxel chemotherapy of metastatic breast cancer. We generated a stable NHE1-knockout of the highly invasive, triple-negative, MDA-MB-231 breast cancer cells. The NHE1-knockout cells proliferated comparably to parental cells, but had markedly lower rates of migration and invasion in vitro. In vivo xenograft tumor growth in athymic nude mice was also dramatically decreased compared to parental MDA-MB-231 cells. Loss of NHE1 expression also increased the susceptibility of knockout cells to paclitaxel-mediated cell death. NHE1 inhibition, in combination with paclitaxel, resulted in a dramatic decrease in viability, and migratory and invasive potential of triple-negative breast cancer cells, but not in hormone receptor-positive, luminal MCF7 cells. Our data suggest that NHE1 is critical in triple-negative breast cancer metastasis, and its chemical inhibition boosts the efficacy of paclitaxel in vitro, highlighting NHE1 as a novel, potential co-adjuvant target in breast cancer chemotherapy.

Microenvironmental acidosis in carcinogenesis and metastases: new strategies in prevention and therapy

Much effort is currently devoted to developing patient-specific cancer therapy based on molecular characterization of tumors. In particular, this approach seeks to identify driver mutations that can be blocked through small molecular inhibitors. However, this approach is limited by extensive intratumoral genetic heterogeneity, and, not surprisingly, even dramatic initial responses are typically of limited duration as resistant tumor clones rapidly emerge and proliferate. We propose an alternative approach based on observations that while tumor evolution produces genetic divergence, it is also associated with striking phenotypic convergence that loosely correspond to the well-known cancer “hallmarks”. These convergent properties can be described as driver phenotypes and may be more consistently and robustly expressed than genetic targets. To this purpose, it is necessary to identify strategies that are critical for cancer progression and metastases, and it is likely that these driver phenotypes will be closely related to cancer “hallmarks”. It appears that an antiacidic approach, by targetting a driver phenotype in tumors, may be thought as a future strategy against tumors in either preventing the occurrence of cancer or treating tumor patients with multiple aims, including the improvement of efficacy of existing therapies, possibly reducing their systemic side effects, and controlling tumor growth, progression, and metastasis. This may be achieved with existing molecules such as proton pump inhibitors (PPIs) and buffers such as sodium bicarbonate, citrate, or TRIS.

Mis-trafficking of endosomal urokinase proteins triggers drug-induced glioma nonapoptotic cell death

5-Benzylglycinyl-amiloride (UCD38B) is the parent molecule of a class of anticancer small molecules that kill proliferative and nonproliferative high-grade glioma cells by programmed necrosis. UCD38B intracellularly triggers endocytosis, causing 40-50% of endosomes containing proteins of the urokinase plasminogen activator system (uPAS) to relocate to perinuclear mitochondrial regions. Endosomal "mis-trafficking" caused by UCD38B in human glioma cells corresponds to mitochondrial depolarization with the release and nuclear translocation of apoptotis-inducing factor (AIF) followed by irreversible caspase-independent cell demise. High-content quantification of immunocytochemical colocalization studies identified that UCD38B treatment increased endocytosis of the urokinase plasminogen activator (uPA), its receptor (uPAR), and plasminogen activator inhibitor-1 (PAI-1) into the early and late endosomes by 4- to 5-fold prior to AIF nuclear translocation and subsequent glioma demise. PAI-1 was found to comparably relocate with a subset of early and late endosomes in four different human glioma cell lines after UCD38B treatment, followed by caspase-independent, nonapoptotic cell death. Following UCD38B treatment, the receptor guidance protein LRP-1, which is required for endosomal recycling of the uPA receptor to the plasmalemma, remained abnormally associated with PAI-1 in early and late endosomes. The resultant aberrant endosomal recycling increased the total cellular content of the uPA-PAI-1 protein complex. Reversible inhibition of cellular endocytosis demonstrated that UCD38B bypasses the plasmalemmal uPAS complex and directly acts intracellularly to alter uPAS endocytotic trafficking. UCD38B represents a class of small molecules whose anticancer cytotoxicity is a consequence of causing the mis-trafficking of early and late endosomes containing uPAS cargo and leading to AIF-mediated necrotic cell death.

Malignancy-associated metabolic profiling of human glioma cell lines using 1H NMR spectroscopy

BACKGROUND

Ambiguity in malignant transformation of glioma has made prognostic diagnosis very challenging. Tumor malignant transformation is closely correlated with specific alterations of the metabolic profile. Exploration of the underlying metabolic alterations in glioma cells of different malignant degree is therefore vital to develop metabolic biomarkers for prognosis monitoring.

METHODS

We conducted (1)H nuclear magnetic resonance (NMR)-based metabolic analysis on cell lines (CHG5, SHG44, U87, U118, U251) developed from gliomas of different malignant grades (WHO II and WHO IV). Several methods were applied to analyze the (1)H-NMR spectral data of polar extracts of cell lines and to identify characteristic metabolites, including principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA), fuzzy c-means clustering (FCM) analysis and orthogonal projection to latent structure with discriminant analysis (OPLS-DA). The expression analyses of glial fibrillary acidic protein (GFAP) and matrix metal proteinases (MMP-9) were used to assess malignant behaviors of cell lines. GeneGo pathway analysis was used to associate characteristic metabolites with malignant behavior protein markers GFAP and MMP-9.

RESULTS

Stable and distinct metabolic profiles of the five cell lines were obtained. The metabolic profiles of the low malignancy grade group (CHG5, SHG44) were clearly distinguished from those of the high malignancy grade group (U87, U118, U251). Seventeen characteristic metabolites were identified that could distinguish the metabolic profiles of the two groups, nine of which were mapped to processes related to GFAP and MMP-9. Furthermore, the results from both quantitative comparison and metabolic correlation analysis indicated that the significantly altered metabolites were primarily involved in perturbation of metabolic pathways of tricarboxylic acid (TCA) cycle anaplerotic flux, amino acid metabolism, anti-oxidant mechanism and choline metabolism, which could be correlated with the changes in the glioma cells' malignant behaviors.

CONCLUSIONS

Our results reveal the metabolic heterogeneity of glioma cell lines with different degrees of malignancy. The obtained metabolic profiles and characteristic metabolites are closely associated with the malignant features of glioma cells, which may lay the basis for both determining the molecular mechanisms underlying glioma malignant transformation and exploiting non-invasive biomarkers for prognosis monitoring.

Upregulation of NHE1 protein expression enables glioblastoma cells to escape TMZ-mediated toxicity via increased H⁺ extrusion, cell migration and survival

Sodium-hydrogen exchanger isoform 1 (NHE1) plays a role in survival and migration/invasion of several cancers and is an emerging new therapeutic target. However, the role of NHE1 in glioblastoma and the interaction of NHE1 expression and function in glioblastoma cells with cytotoxic temozolomide (TMZ) therapy remain unknown. In this study, we detected high levels of NHE1 protein only in primary human glioma cells (GC), glioma xenografts and glioblastoma, but not in human neural stem cells or astrocytes. GC exhibited an alkaline resting pHi (7.46±0.04) maintained by robust NHE1-mediated H(+) extrusion. GC treatment with TMZ for 2-24h triggered a transient decrease in pHi, which recovered by 48h and correlated with concurrent upregulation of NHE1 protein expression. NHE1 protein was colocalized with ezrin at lamellipodia and probably involved in GC migration. The TMZ-treated GC exhibited increased migration and invasion, which was attenuated by addition of NHE1 inhibitor HOE-642. Most importantly, NHE1 inhibition prevented prosurvival extracellular signal-regulated kinase activation and accelerated TMZ-induced apoptosis. Taken together, our study provides the first evidence that GC upregulate NHE1 protein to maintain alkaline pHi. Combining TMZ therapy with NHE1 inhibition suppresses GC migration and invasion, and also augments TMZ-induced apoptosis. These findings strongly suggest that NHE1 is an important cytoprotective mechanism in GC and presents a new therapeutic strategy of combining NHE1 inhibition and TMZ chemotherapy.

Disrupting proton dynamics and energy metabolism for cancer therapy

Intense interest in the 'Warburg effect' has been revived by the discovery that hypoxia-inducible factor 1 (HIF1) reprogrammes pyruvate oxidation to lactic acid conversion; lactic acid is the end product of fermentative glycolysis. The most aggressive and invasive cancers, which are often hypoxic, rely on exacerbated glycolysis to meet the increased demand for ATP and biosynthetic precursors and also rely on robust pH-regulating systems to combat the excessive generation of lactic and carbonic acids. In this Review, we present the key pH-regulating systems and synthesize recent advances in strategies that combine the disruption of pH control with bioenergetic mechanisms. We discuss the possibility of exploiting, in rapidly growing tumours, acute cell death by 'metabolic catastrophe'.

A cell-permeant amiloride derivative induces caspase-independent, AIF-mediated programmed necrotic death of breast cancer cells

Amiloride is a potassium-sparing diuretic that has been used as an anti-kaliuretic for the chronic management of hypertension and heart failure. Several studies have identified a potential anti-cancer role for amiloride, however the mechanisms underlying its anti-tumor effects remain to be fully delineated. Our group previously demonstrated that amiloride triggers caspase-independent cytotoxic cell death in human glioblastoma cell lines but not in primary astrocytes. To delineate the cellular mechanisms underlying amiloride’s anti-cancer cytotoxicity, cell permeant and cell impermeant derivatives of amiloride were synthesized that exhibit markedly different potencies in cancer cell death assays. Here we compare the cytotoxicities of 5-benzylglycinyl amiloride (UCD38B) and its free acid 5-glycinyl amiloride (UCD74A) toward human breast cancer cells. UCD74A exhibits poor cell permeability and has very little cytotoxic activity, while UCD38B is cell permeant and induces the caspase-independent death of proliferating and non-proliferating breast cancer cells. UCD38B treatment of human breast cancer cells promotes autophagy reflected in LC3 conversion, and induces the dramatic swelling of the endoplasmic reticulum, however these events do not appear to be the cause of cell death. Surprisingly, UCD38B but not UCD74A induces efficient AIF translocation from the mitochondria to the nucleus, and AIF function is necessary for the efficient induction of cancer cell death. Our observations indicate that UCD38B induces programmed necrosis through AIF translocation, and suggest that its cytosolic accessibility may facilitate drug action.

5-Benzylglycinyl-amiloride kills proliferating and nonproliferating malignant glioma cells through caspase-independent necroptosis mediated by apoptosis-inducing factor

5'-Βenzylglycinyl-amiloride (UCD38B) and glycinyl-amiloride (UCD74A) are cell-permeant and cell-impermeant derivatives of amiloride, respectively, and used here to identify the cellular mechanisms of action underlying their antiglioma effects. UCD38B comparably kills proliferating and nonproliferating gliomas cells when cell cycle progression is arrested either by cyclin D1 siRNA or by acidification. Cell impermeant UCD74A inhibits plasmalemmal urokinase plasminogen activator (uPA) and the type 1 sodium-proton exchanger with potencies analogous to UCD38B, but is cytostatic. In contrast, UCD38B targets intracellular uPA causing mistrafficking of uPA into perinuclear mitochondria, reducing the mitochondrial membrane potential, and followed by the release of apoptotic inducible factor (AIF). AIF nuclear translocation is followed by a caspase-independent necroptotic cell death. Reduction in AIF expression by siRNA reduces the antiglioma cytotoxic effects of UCD38B, while not activating the caspase pathway. Ultrastructural changes shortly following treatment with UCD38B demonstrate dilation of endoplasmic reticulum (ER) and mitochondrial swelling followed by nuclear condensation within hours consistent with a necroptotic cell death differing from apoptosis and from autophagy. These drug mechanism of action studies demonstrate that UCD38B induces a cell cycle-independent, caspase-independent necroptotic glioma cell death that is mediated by AIF and independent of poly (ADP-ribose) polymerase and H2AX activation.

Effective killing of leukemia cells by the natural product OSW-1 through disruption of cellular calcium homeostasis

3β,16β,17α-Trihydroxycholest-5-en-22-one 16-O-(2-O-4-methoxybenzoyl-β-D-xylopyranosyl)-(1→3)-2-O-acetyl-α-L-arabinopyranoside (OSW-1) is a natural product with potent antitumor activity against various types of cancer cells, but the exact mechanisms of action remain to be defined. In this study, we showed that OSW-1 effectively killed leukemia cells at subnanomolar concentrations through a unique mechanism by causing a time-dependent elevation of cytosolic Ca(2+) prior to induction of apoptosis. A mechanistic study revealed that this compound inhibited the sodium-calcium exchanger 1 on the plasma membrane, leading to an increase in cytosolic Ca(2+) and a decrease in cytosolic Na(+). The elevated cytosolic Ca(2+) caused mitochondrial calcium overload and resulted in a loss of mitochondrial membrane potential, release of cytochrome c, and activation of caspase-3. Furthermore, OSW-1 also caused a Ca(2+)-dependent cleavage of the survival factor GRP78. Inhibition of Ca(2+) entry into the mitochondria by the uniporter inhibitor RU360 or by cyclosporin A significantly prevented the OSW-1-induced cell death, indicating the important role of mitochondria in mediating the cytotoxic activity. The extremely potent activity of OSW-1 against leukemia cells and its unique mechanism of action suggest that this compound may be potentially useful in the treatment of leukemia.

2-Amidino analogs of glycine-amiloride conjugates: inhibitors of urokinase-type plasminogen activator

The relative non-toxicity of the diuretic amiloride, coupled with its selective inhibition of the protease urokinase plasminogen activator (uPA), makes this compound class attractive for structure-activity studies. Herein we substituted the C(2)-acylguanidine of C(5)-glycyl-amiloride with amidine and amidoxime groups. The data show the importance of maintaining C(5)-hydrophobicity. The C(5)-benzylglycine analogs containing either C(2)-acylguanidine or amidine inhibited uPA with an IC(50) ranging from 3 to 7 μM and were cytotoxic to human U87 malignant glioma cells.

Interfering with pH regulation in tumours as a therapeutic strategy

The high metabolic rate of tumours often leads to acidosis and hypoxia in poorly perfused regions. Tumour cells have thus evolved the ability to function in a more acidic environment than normal cells. Key pH regulators in tumour cells include: isoforms 2, 9 and 12 of carbonic anhydrase, isoforms of anion exchangers, Na+/HCO3- co-transporters, Na+/H+ exchangers, monocarboxylate transporters and the vacuolar ATPase. Both small molecules and antibodies targeting these pH regulators are currently at various stages of clinical development. These antitumour mechanisms are not exploited by the classical cancer drugs and therefore represent a new anticancer drug discovery strategy.