Lysosomal membrane permeabilization is an early event in Sigma-2 receptor ligand mediated cell death in pancreatic cancer

Reactivation of nucleases with peroxidation damages induced by a menadione: ascorbate combination devastates human prostate carcinomas: ultrastructural aspects

INTRODUCTION

Xenografts of androgen-independent human DU145 prostate metastatic carcinomas implanted in nu/nu male mice have revealed a significant survival after a prooxidant anticancer treatment consisting of a combination of menadione bisulfite and sodium ascorbate (VK3:VC).

METHODS

Implanted samples of diaphragm carcinomas from longest survived mice from either oral, intraperitoneal (IP), or both oral and IP treatment groups were assessed with light, scanning, and transmission electron microscopy to analyze morphologic damages.

RESULTS

Compared with previous fine structure data of in vitro untreated carcinomas, the changes induced by oral, IP, and oral with IP VK3:VC treatment dismantled those xenografts with autoschizis, and necrotic atrophy was accomplished by cell's oxidative stress whose injuries were consequent to reactivated deoxyribonucleases and ribonucleases. Tumor destructions resulted from irreversible damages of nucleus components, endoplasmic reticulum, and mitochondria there. Other alterations included those of the cytoskeleton that resulted in characteristic self-excisions named " autoschizis." All these injuries lead resilient cancer cells to necrotic cell death.

CONCLUSION

The fine structure damages caused by VK3:VC prooxidant combination in the human DU145 prostate xenografts confirmed those shown in vitro and of other cell lines with histochemistry and biomolecular investigations. These devastations incurred without damage to normal tissues; thus, our data brought support for the above combination to assist in the treatment of prostate cancers and other cancers.

Thermal Proteome Profiling Strategy Identifies CNPY3 as a Cellular Target of Gambogic Acid for Inducing Prostate Cancer Pyroptosis

There is an urgent requirement to acquire a comprehensive comprehension of novel therapeutic targets for prostate cancer to facilitate the development of medications with innovative mechanisms. In this study, we identified gambogic acid (GBA) as a specific pyroptosis inducer in prostatic cancer cells. By using a thermal proteome profiling (TPP) strategy, we revealed that GBA induces pyroptosis by directly targeting the canopy FGF signaling regulator (CNPY3), which was previously considered "undruggable". Moreover, through the utilization of the APEX2-based proximity labeling method, we found that GBA recruited delactatease SIRT1, resulting in the elimination of lysine lactylation (Kla) on CNPY3. Of note, SIRT1-mediated delactylation influenced the cellular localization of CNPY3 to promote lysosome rupture for triggering pyroptosis. Taken together, our study identified CNPY3 as a distinctive cellular target for pyroptosis induction and its potential application in prostate cancer therapy.

Cytotoxic sigma-2 ligands trigger cancer cell death via cholesterol-induced-ER-stress

Sigma-2-ligands (S2L) are characterized by high binding affinities to their cognate sigma-2 receptor, overexpressed in rapidly proliferating tumor cells. As such, S2L were developed as imaging probes (ISO1) or as cancer therapeutics, alone (SV119 [C6], SW43 [C10]) and as delivery vehicles for cytotoxic drug cargoes (C6-Erastin, C10-SMAC). However, the exact mechanism of S2L-induced cytotoxicity remains to be fully elucidated. A series of high-affinity S2L were evaluated regarding their cytotoxicity profiles across cancer cell lines. While C6 and C10 displayed distinct cytotoxicities, C0 and ISO1 were essentially non-toxic. Confocal microscopy and lipidomics analysis in cellular and mouse models revealed that C10 induced increases in intralysosomal free cholesterol and in cholesterol esters, suggestive of unaltered intracellular cholesterol trafficking. Cytotoxicity was caused by cholesterol excess, a phenomenon that contrasts the effects of NPC1 inhibition. RNA-sequencing revealed gene clusters involved in cholesterol homeostasis and ER stress response exclusively by cytotoxic S2L. ER stress markers were confirmed by qPCR and their targeted modulation inhibited or enhanced cytotoxicity of C10 in a predicted manner. Moreover, C10 increased sterol regulatory element-binding protein 2 (SREBP2) and low-density lipoprotein receptor (LDLR), both found to be pro-survival factors activated by ER stress. Furthermore, inhibition of downstream processes of the adaptive response to S2L with simvastatin resulted in synergistic treatment outcomes in combination with C10. Of note, the S2L conjugates retained the ER stress response of the parental ligands, indicative of cholesterol homeostasis being involved in the overall cytotoxicity of the drug conjugates. Based on these findings, we conclude that S2L-mediated cell death is due to free cholesterol accumulation that leads to ER stress. Consequently, the cytotoxic profiles of S2L drug conjugates are proposed to be enhanced via concurrent ER stress inducers or simvastatin, strategies that could be instrumental on the path toward tumor eradication.

Harnessing ferroptosis for enhanced sarcoma treatment: mechanisms, progress and prospects

Sarcoma is a malignant tumor that originates from mesenchymal tissue. The common treatment for sarcoma is surgery supplemented with radiotherapy and chemotherapy. However, patients have a 5-year survival rate of only approximately 60%, and sarcoma cells are highly resistant to chemotherapy. Ferroptosis is an iron-dependent nonapoptotic type of regulated programmed cell death that is closely related to the pathophysiological processes underlying tumorigenesis, neurological diseases and other conditions. Moreover, ferroptosis is mediated via multiple regulatory pathways that may be targets for disease therapy. Recent studies have shown that the induction of ferroptosis is an effective way to kill sarcoma cells and reduce their resistance to chemotherapeutic drugs. Moreover, ferroptosis-related genes are related to the immune system, and their expression can be used to predict sarcoma prognosis. In this review, we describe the molecular mechanism underlying ferroptosis in detail, systematically summarize recent research progress with respect to ferroptosis application as a sarcoma treatment in various contexts, and point out gaps in the theoretical research on ferroptosis, challenges to its clinical application, potential resolutions of these challenges to promote ferroptosis as an efficient, reliable and novel method of clinical sarcoma treatment.

Copper nitroprusside: An innovative approach for targeted cancer therapy via ROS modulation

The clinical application of nanomaterials for chemodynamic therapy (CDT), which generate multiple reactive oxygen species (ROS), presents significant challenges. These challenges arise due to insufficient levels of endogenous hydrogen peroxide and catalytic ions necessary to initiate Fenton reactions. As a result, sophisticated additional delivery systems are required. In this study, a novel bimetallic copper (II) pentacyanonitrosylferrate (Cu(II)NP, Cu[Fe(CN) 5 NO]) material was developed to address these limitations. This material functions as a multiple ROS generator at tumoral sites by self-inducing hydrogen peroxide and producing peroxynitrite (ONOO-) species. The research findings demonstrate that this material exhibits low toxicity towards normal liver organoids, yet shows potent antitumoral effects on High Grade Serous Ovarian Cancer (HGSOC) organoid patients, regardless of platinum resistance. Significantly, this research introduces a promising therapeutic opportunity by proposing a single system capable of replacing the need for H2O2, additional catalysts, and NO-based delivery systems. This innovative system exhibits remarkable multiple therapeutic mechanisms, paving the way for potential advancements in clinical treatments.

Cytotoxic pathways activated by multifunctional thiosemicarbazones targeting sigma-2 receptors in breast and lung carcinoma cells

BACKGROUND

Multifunctional thiosemicarbazones (TSCs) able to bind sigma receptors and chelate metals are considered as a promising avenue for the treatment of pancreatic cancer due to the encouraging results obtained on in vitro and in vivo models. Here, we assessed the biochemical mechanism of these TSCs also on lung (A549) and breast (MCF7) cancer cells.

METHODS

The density of sigma-2 receptors in normal (BEAS-2B and MCF10A) and in lung and breast (A549 and MCF7) cancer cells was evaluated by flow cytometry. In these cells, cytotoxicity (MTT assay) and activation of ER- and mitochondria-dependent cell death pathways (by spectrofluorimetric assays to measure Caspases 3/7/9; qRT-PCR detection of GRP78, ATF6, IRE1, PERK; MitoSOX, DCFDA-AM and JC-1 staining), induced by the TSCs FA4, MLP44, PS3 and ACThio1, were evaluated.

RESULTS

FA4 and PS3 exerted more potent cytotoxicity than MLP44 and ACThio1 in all cancer cell lines, where the density of sigma-2 receptors was higher than in normal cells. Remarkably, FA4 promoted ER- and mitochondria-dependent cell death pathways in both cell models, whereas the other TSCs had variable, cell-dependent effects on the activation of the two proapoptotic pathways.

CONCLUSIONS

Our data suggest that FA4 is a promising compound that deserves to be further studied for lung and breast cancer treatment. However, the other multifunctional TSCs also hold promise for the development of therapies towards a personalized medicine approach. Indeed, the presence of the sigma-2 receptor-targeting moiety would lead to a more specific tumor delivery embracing the characteristics of individual tumor types.

Lysosomes as a Target of Anticancer Therapy

Lysosomes are organelles containing acidic hydrolases that are responsible for lysosomal degradation and the maintenance of cellular homeostasis. They play an important role in autophagy, as well as in various cell death pathways, such as lysosomal and apoptotic death. Various agents, including drugs, can induce lysosomal membrane permeability, resulting in the translocation of acidic hydrolases into the cytoplasm, which promotes lysosomal-mediated death. This type of death may be of great importance in anti-cancer therapy, as both cancer cells with disturbed pathways leading to apoptosis and drug-resistant cells can undergo it. Important compounds that damage the lysosomal membrane include lysosomotropic compounds, antihistamines, immunosuppressants, DNA-damaging drugs, chemotherapeutics, photosensitizers and various plant compounds. An interesting approach in the treatment of cancer and the search for ways to overcome the chemoresistance of cancer cells may also be combining lysosomotropic compounds with targeted modulators of autophagy to induce cell death. These compounds may be an alternative in oncological treatment, and lysosomes may become a promising therapeutic target for many diseases, including cancer. Understanding the functional relationships between autophagy and apoptosis and the possibilities of their regulation, both in relation to normal and cancer cells, can be used to develop new and more effective anticancer therapies.

Malic Enzyme 1 Absence in Synovial Sarcoma Shifts Antioxidant System Dependence and Increases Sensitivity to Ferroptosis Induction with ACXT-3102

PURPOSE

To investigate the metabolism of synovial sarcoma (SS) and elucidate the effect of malic enzyme 1 absence on SS redox homeostasis.

EXPERIMENTAL DESIGN

ME1 expression was measured in SS clinical samples, SS cell lines, and tumors from an SS mouse model. The effect of ME1 absence on glucose metabolism was evaluated utilizing Seahorse assays, metabolomics, and C13 tracings. The impact of ME1 absence on SS redox homeostasis was evaluated by metabolomics, cell death assays with inhibitors of antioxidant systems, and measurements of intracellular reactive oxygen species (ROS). The susceptibility of ME1-null SS to ferroptosis induction was interrogated in vitro and in vivo.

RESULTS

ME1 absence in SS was confirmed in clinical samples, SS cell lines, and an SS tumor model. Investigation of SS glucose metabolism revealed that ME1-null cells exhibit higher rates of glycolysis and higher flux of glucose into the pentose phosphate pathway (PPP), which is necessary to produce NADPH. Evaluation of cellular redox homeostasis demonstrated that ME1 absence shifts dependence from the glutathione system to the thioredoxin system. Concomitantly, ME1 absence drives the accumulation of ROS and labile iron. ROS and iron accumulation enhances the susceptibility of ME1-null cells to ferroptosis induction with inhibitors of xCT (erastin and ACXT-3102). In vivo xenograft models of ME1-null SS demonstrate significantly increased tumor response to ACXT-3102 compared with ME1-expressing controls.

CONCLUSIONS

These findings demonstrate the translational potential of targeting redox homeostasis in ME1-null cancers and establish the preclinical rationale for a phase I trial of ACXT-3102 in SS patients. See related commentary by Subbiah and Gan, p. 3408.

Lysosomal membrane permeabilization mediated apoptosis involve in perphenazine-induced hepatotoxicity in vitro and in vivo

Antipsychotic drugs represent a class of lysosomotropic drugs widely used in clinical practice. However, the hepatotoxicity of these drugs has been reported in recent years. Therefore, understanding the changes in cellular homeostasis mediated by these drugs is of great significance for revealing the true mechanisms underlying hepatotoxicity. Perphenazine is a classical antipsychotic drug that can reportedly induce extrapyramidal and sympatholytic side effects. The present research focuses on the toxicity effect of perphenazine on normal human hepatocytes. To assess the hepatotoxicity of continuous administration of perphenazine and investigate potential mechanisms related to apoptosis, human normal L02 hepatocytes were exposed to 10-40μM perphenazine in vitro. The results showed that perphenazine inhibited cell viability in a concentration and time-dependent manner. Furthermore, 30μM perphenazine induced intense lysosome vacuolation, impaired lysosomal membrane, and induced lysosomal membrane permeabilization (LMP), ultimately triggering lysosomal cell death in L02 cells. Knockdown cathepsin D(CTSD) also ameliorated perphenazine-induced liver injury via the inhibition of LMP. In vivo, ICR mice received intragastric administration of 10-180mg/kg B.W. perphenazine every other day for 21 days. 180mg/kg perphenazine significantly increased histological injury and aminotransferases compared with control. Taken together, our findings suggest that perphenazine can trigger hepatotoxicity through lysosome disruption both in vitro and in vivo.

Brain-derived neurotrophic factor for high-throughput evaluation of selective Sigma-1 receptor ligands

The Sigma-1 receptor (S1R) is an endoplasmic reticulum (ER) chaperone protein that has been implicated in attenuating inflammatory stress-mediated brain injuries. Selective S1R agonists represent a new class of therapeutic agent for treating neuropsychiatric and neurodegenerative disorders, however, to date, no S1R ligand has been approved for therapeutic purposes. We used three potential methods on known and potential S1R ligands to develop an unambiguous high-throughput cell screen for S1R activity. We screened known and potential S1R ligands using radioligand binding and previously reported markers of S1R activity including BDNF release, modulation of IP3 mediated calcium release, and modulation of NGF-induced neurite sprouting. Here, we present results several prototypical S1R compounds and some compounds with the potential for drug repurposing. Using an in-situ ELISA approach we demonstrated that these compounds could stimulate S1R-mediated BDNF release, which is a valuable therapeutic property since BDNF plays a critical role in neuronal support. These compounds were classified as S1R agonists because the BDNF response was comparable to the prototypical agonist 4-PPBP and because it could be reversed by a S1R selective concentration of the antagonist BD1063. When modulation of IP3 mediated calcium response and NGF-induced neurite sprouting were used as a measure of S1R activation, we were unable to reproduce the published results and determined that they are not reliable measures for evaluating functional properties of S1R ligands.

Multifunctional thiosemicarbazones targeting sigma receptors: in vitro and in vivo antitumor activities in pancreatic cancer models

PURPOSE

Association of the metal chelating portion of thiosemicarbazone with the cytotoxic activity of sigma-2 receptors appears a promising strategy for the treatment of pancreatic tumors. Here, we developed a novel sigma-2 receptor targeting thiosemicarbazone (FA4) that incorporates a moiety associated with lysosome destabilization and ROS increase in order to design more efficient antitumor agents.

METHODS

The density of sigma receptors in pancreatic cancer cells was evaluated by flow cytometry. In these cells, cytotoxicity (MTT assay) and activation of ER- and mitochondria-dependent cell death pathways (mRNA expression of GRP78, ATF6, IRE1, PERK; ROS levels by MitoSOX and DCFDA-AM; JC-1 staining) induced by the thiosemicarbazones FA4, MLP44, PS3 and ACthio-1, were evaluated. The expression of autophagic proteins (ATG5, ATG7, ATG12, beclin, p62 and LC3-I) was also studied. In addition, the in vivo effect of FA4 in xenograft models with and without gemcitabine challenge was investigated.

RESULTS

We found that FA4 exerted a more potent cytotoxicity than previously studied thiosemicarbazones (MLP44, PS3 and ACthio-1), which were found to display variable effects on the ER or the mitochondria-dependent pro-apoptotic axis. By contrast, FA4 activated pro-apoptotic pathways and decreased autophagy, except in MiaPaCa2 cells, in which autophagic proteins were expressed at lower levels and remained unmodified by FA4. FA4 treatment of PANC-1 xenografted mouse models, poorly responsive to conventional chemotherapy, significantly reduced tumor volumes and increased intratumor apoptosis compared to gemcitabine, with no signs of toxicity.

CONCLUSIONS

Our data indicate that FA4 exhibits encouraging activity in pancreatic cancer cells unresponsive to gemcitabine. These results warrant further investigation in patient-derived pancreatic cancers, and hold promise for the development of therapies that can more efficiently target the specific characteristics of individual tumor types.

Hepatic small extracellular vesicles promote microvascular endothelial hyperpermeability during NAFLD via novel-miRNA-7

BACKGROUND

A recent study has reported that patients with nonalcoholic fatty liver disease (NAFLD) are more susceptible to coronary microvascular dysfunction (CMD), which may predict major adverse cardiac events. However, little is known regarding the causes of CMD during NAFLD. In this study, we aimed to explore the role of hepatic small extracellular vesicles (sEVs) in regulating the endothelial dysfunction of coronary microvessels during NAFLD.

RESULTS

We established two murine NAFLD models by feeding mice a methionine-choline-deficient (MCD) diet for 4 weeks or a high-fat diet (HFD) for 16 weeks. We found that the NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome-dependent endothelial hyperpermeability occurred in coronary microvessels during both MCD diet and HFD-induced NAFLD. The in vivo and in vitro experiments proved that novel-microRNA(miR)-7-abundant hepatic sEVs were responsible for NLRP3 inflammasome-dependent endothelial barrier dysfunction. Mechanistically, novel-miR-7 directly targeted lysosomal associated membrane protein 1 (LAMP1) and promotes lysosomal membrane permeability (LMP), which in turn induced Cathepsin B-dependent NLRP3 inflammasome activation and microvascular endothelial hyperpermeability. Conversely, a specific novel-miR-7 inhibitor markedly improved endothelial barrier integrity. Finally, we proved that steatotic hepatocyte was a significant source of novel-miR-7-contained hepatic sEVs, and steatotic hepatocyte-derived sEVs were able to promote NLRP3 inflammasome-dependent microvascular endothelial hyperpermeability through novel-miR-7.

CONCLUSIONS

Hepatic sEVs contribute to endothelial hyperpermeability in coronary microvessels by delivering novel-miR-7 and targeting the LAMP1/Cathepsin B/NLRP3 inflammasome axis during NAFLD. Our study brings new insights into the liver-to-microvessel cross-talk and may provide a new diagnostic biomarker and treatment target for microvascular complications of NAFLD.

QSAR-Based Computational Approaches to Accelerate the Discovery of Sigma-2 Receptor (S2R) Ligands as Therapeutic Drugs

S2R overexpression is associated with various forms of cancer as well as both neuropsychiatric disorders (e.g., schizophrenia) and neurodegenerative diseases (Alzheimer’s disease: AD). In the present study, three ligand-based methods (QSAR modeling, pharmacophore mapping, and shape-based screening) were implemented to select putative S2R ligands from the DrugBank library comprising 2000+ entries. Four separate optimization algorithms (i.e., stepwise regression, Lasso, genetic algorithm (GA), and a customized extension of GA called GreedGene) were adapted to select descriptors for the QSAR models. The subsequent biological evaluation of selected compounds revealed that three FDA-approved drugs for unrelated therapeutic indications exhibited sub-1 uM binding affinity for S2R. In particular, the antidepressant drug nefazodone elicited a S2R binding affinity Ki = 140 nM. A total of 159 unique S2R ligands were retrieved from 16 publications for model building, validation, and testing. To our best knowledge, the present report represents the first case to develop comprehensive QSAR models sourced by pooling and curating a large assemblage of structurally diverse S2R ligands, which should prove useful for identifying new drug leads and predicting their S2R binding affinity prior to the resource-demanding tasks of chemical synthesis and biological evaluation.

Current development of sigma-2 receptor radioligands as potential tumor imaging agents

Sigma receptors are transmembrane proteins with two different subtypes: σ₁ and σ₂. Because of its overexpression in tumors, the σ₂ receptor (σ₂R) is a well-known biomarker for cancer cells. A large number of small-molecule ligands for the σ₂Rs have been identified and tested for imaging the proliferative status of tumors using single photon emission computed tomography (SPECT) and positron emission tomography (PET). These small molecules include derivatives of bicyclic amines, indoles, cyclohexylpiperazines and tetrahydroisoquinolines. This review discusses various aspects of small molecule ligands, such as chemical composition, labeling strategy, affinity for σ₂Rs, and in vitro/in vivo investigations. The recent studies described here could be useful for the development of σ₂R radioligands as potential tumor imaging agents.

σ2 Receptor and Its Role in Cancer with Focus on a MultiTarget Directed Ligand (MTDL) Approach

Sigma-2 (σ2) is an endoplasmic receptor identified as the Endoplasmic Reticulum (ER) transmembrane protein TMEM97. Despite its controversial identity, which was only recently solved, this protein has gained scientific interest because of its role in the proliferative status of cells; many tumor cells from different organs overexpress the σ2 receptor, and many σ2 ligands display cytotoxic actions in (resistant) cancer cells. These properties have shed light on the σ2 receptor as a potential druggable target to be bound/activated for the diagnosis or therapy of tumors. Additionally, diverse groups have shown how the σ2 receptor can be exploited for the targeted delivery of the anticancer drugs to tumors. As the cancer disease is a multifactorial pathology with multiple cell populations, a polypharmacological approach is very often needed. Instead of the simultaneous administration of different classes of drugs, the use of one molecule that interacts with diverse pharmacological targets, namely MultiTarget Directed Ligand (MTDL), is a promising and currently pursued strategy, that may overcome the pharmacokinetic problems associated with the administration of multiple molecules. This review aims to point out the progress regarding the σ2 ligands in the oncology field, with a focus on MTDLs directed towards σ2 receptors as promising weapons against (resistant) cancer diseases.

1,2,3,4-Tetrahydroisoquinoline (THIQ) as privileged scaffold for anticancer de novo drug design

Introduction: Cancer is a dreadful disorder that is emerging as one of the leading causes of mortality across the globe. The complex tumor environment, supplemented with drawbacks of the existing drugs, has made it a global health concern. The Tetrahydroisoquinoline (THIQ) ring holds an important position in medicinal chemistry due to its wide range of pharmacological properties. Several THIQ based natural products have been previously explored for their antitumor properties, making it a vital scaffold for anticancer drug design.Areas covered: This review article addresses the potential of THIQ as anticancer agents. Various medicinal chemistry strategies employed for the design and development of THIQ analogs as inhibitors or modulators of relevant anticancer targets have been discussed in detail. Moreover, the common strategies employed for the synthesis of the core scaffold are also highlighted.Expert opinion: Evidently, THIQs have tremendous potential in anticancer drug design. Some of these analogs exhibited potent activity against various cancer molecular targets. However, there are some drawbacks, such as selectivity that need addressing. The synthetic ease for constructing the core scaffold complimented with its reactivity makes it ideal for further structure-activity relationship studies. For these reasons, THIQ is a privileged scaffold for the design and development of novel anticancer agents.

PB28, the Sigma-1 and Sigma-2 Receptors Modulator With Potent Anti-SARS-CoV-2 Activity: A Review About Its Pharmacological Properties and Structure Affinity Relationships

These unprecedented times have forced the scientific community to gather to face the COVID-19 pandemic. Efforts in diverse directions have been made. A multi-university team has focused on the identification of the host (human) proteins interacting with SARS-CoV-2 viral proteins, with the aim of hampering these interactions that may cause severe COVID-19 symptoms. Sigma-1 and sigma-2 receptors surprisingly belong to the “druggable” host proteins found, with the pan-sigma receptor modulator PB28 displaying the most potent anti–SARS-CoV-2 activity in in vitro assays. Being 20-fold more active than hydroxychloroquine, without cardiac side effects, PB28 is a promising antiviral candidate worthy of further investigation. Our research group developed PB28 in 1996 and have thoroughly characterized its biological properties since then. Structure–affinity relationship (SAfiR) studies at the sigma receptor subtypes were also undertaken with PB28 as the lead compound. We herein report our knowledge of PB28 to share information that may help to gain insight into the antiviral action of this compound and sigma receptors, while providing structural hints that may speed up the translation into therapeutics of this class of ligands.

Sigma-2 Receptor-A Potential Target for Cancer/Alzheimer's Disease Treatment via Its Regulation of Cholesterol Homeostasis

The sigma receptors were classified into sigma-1 and sigma-2 receptor based on their different pharmacological profiles. In the past two decades, our understanding of the biological and pharmacological properties of the sigma-1 receptor is increasing; however, little is known about the sigma-2 receptor. Recently, the molecular identity of the sigma-2 receptor has been identified as TMEM97. Although more and more evidence has showed that sigma-2 ligands have the ability to treat cancer and Alzheimer’s disease (AD), the mechanisms connecting these two diseases are unknown. Data obtained over the past few years from human and animal models indicate that cholesterol homeostasis is altered in AD and cancer, underscoring the importance of cholesterol homeostasis in AD and cancer. In this review, based on accumulated evidence, we proposed that the beneficial roles of sigma-2 ligands in cancer and AD might be mediated by their regulation of cholesterol homeostasis.

Induction of Lysosomal Membrane Permeabilization Is a Major Event of FTY720-Mediated Non-Apoptotic Cell Death in Human Glioma Cells

Simple Summary

FTY720, a sphingosine-1-phosphate (S1P) analog, is a potent immunosuppressant for the treatment of multiple sclerosis. In addition to being an immune modulator, FTY720 also features antitumor activity in several cancer models, but the molecular mechanisms are unclear. Here, we extended our research to analyze the signaling pathways mediating FTY720-induced cell death. FTY720 did not induce apoptotic cell death, autophagy, paraptosis, or necroptosis in glioma cells. Interestingly, FTY720 accumulated in lysosomes, resulting in the induction of lysosomal membrane permeabilization (LMP). Inhibition of LMP by overexpression of HSP70 and cathepsin inhibitors blocked FTY720-induced cell death. These data suggest that FTY720 induces cell death induced by LMP in glioma cells.

Abstract

FTY720, a sphingosine-1-phosphate (S1P) receptor modulator, is a synthetic compound produced by the modification of a metabolite from I. sinclairii. Here, we found that FTY720 induced non-apoptotic cell death in human glioma cells (U251MG, U87MG, and U118MG). FTY720 (10 µM) dramatically induced cytoplasmic vacuolation in glioma cells. However, FTY720-mediated vacuolation and cell death are not associated with autophagy. Genetic or pharmacological inhibition of autophagy did not inhibit FTY720-induced cell death. Herein, we detected that FTY720-induced cytoplasmic vacuoles were stained with lysotracker red, and FTY720 induced lysosomal membrane permeabilization (LMP). Interestingly, cathepsin inhibitors (E64D and pepstatin A) and ectopic expression of heat shock protein 70 (HSP70), which is an endogenous inhibitor of LMP, markedly inhibited FTY720-induced cell death. Our results demonstrated that FTY720 induced non-apoptotic cell death via the induction of LMP in human glioma cells.

Computational screening of natural and natural-like compounds to identify novel ligands for sigma-2 receptor

Sigma-2 (σ₂) receptor is a transmembrane protein shown to be linked with neurodegenerative diseases and cancer development. Thus, it emerges as a potential biological target for the advancement of anticancer and anti-Alzheimer's agents. The current study was aimed to identify potential σ₂ receptor ligands using integrated computational approaches including homology modelling, combined pharmacophore- and docking-based virtual screening, and molecular dynamics (MD) simulation. Pharmacophore-based screening was conducted against a database composed of 20,523 small natural and natural-like products. In total, 1200 structures were found to satisfy the required pharmacophore features and were then exposed to docking-based screening against the generated homology model of σ₂ receptor. On the basis of the pharmacophore fit scores, docking scores, and mechanism of binding interaction, 20 potential hits were retained. Five promising candidates were selected (SR84, SR823, SR300, SR413, and SR530) on the basis of their binding score and interaction. Further, in silico ADMET profiling of these compounds showed that the selected compounds possess favourable ADME properties with low toxicity risk. The mechanism of interaction of these compounds with σ₂ receptor as well as their binding stability were characterized by MD simulation.

Synthesis and Pharmacological Evaluation of σ2 Receptor Ligands Based on a 3-Alkoxyisoxazole Scaffold: Potential Antitumor Effects against Osteosarcoma

Since its initial discovery as the basis for nicotinic acetylcholine receptor ligands, the 3-alkoxyisoxazole scaffold has been shown to be a versatile platform for the development of potent σ1 and σ2 receptor ligands. Herein we report a further SAR exploration of the 3-alkoxyisoxazole scaffold with the aim of obtaining potent σ2 receptor ligands. Various substitutions on the benzene ring and at the basic amino regions resulted in a total of 21 compounds that were tested for their binding affinities for the σ2 receptor. In particular, compound 51 [(2S)-1-(4-ammoniobutyl)-2-(((5-((3,4-dichlorophenoxy)methyl)isoxazol-3-yl)oxy)methyl)pyrrolidin-1-ium chloride] was identified as one of the most potent σ2 ligands within the series, with a K_i value of 7.9 nM. It demonstrated potent antiproliferative effects on both osteosarcoma cell lines 143B and MOS-J (IC₅₀ values of 0.89 and 0.71 μM, respectively), relative to siramesine (IC₅₀ values of 1.81 and 2.01 μM). Moreover, compound 51 inhibited clonal formation of osteosarcoma 143B cells at 1 μM, corresponding to half the dose required of siramesine for similar effects. The general cytotoxicity profile of compound 51 was assessed in a number of normal cell lines, including HaCaT, HAF, and LO2 cells. Furthermore, FACS analysis showed that compound 51 likely inhibits osteosarcoma cell growth by disruption of the cell cycle and promotion of apoptosis.

Small-Molecule Modulators of Sigma1 and Sigma2/TMEM97 in the Context of Cancer: Foundational Concepts and Emerging Themes

There are two known subtypes of the so-called sigma receptors, Sigma1 and Sigma2. Sigma1 (encoded by the SIGMAR1 gene and also known as Sigma-1 receptor, S1R) is a unique pharmacologically regulated integral membrane chaperone or scaffolding protein that allosterically modulates the activity of its associated proteins. Sigma2, recently identified as transmembrane protein 97 (TMEM97), is an integral membrane protein implicated in cellular cholesterol homeostasis. A number of publications over the past two decades have suggested a role for both sigma proteins in tumor biology. Although there is currently no clinically used anti-cancer drug that targets Sigma1 or Sigma2/TMEM97, a growing body of evidence supports the potential of small-molecule compounds with affinity for these proteins, putative sigma ligands, as therapeutic agents to treat cancer. In preclinical models, these compounds have been reported to inhibit cancer cell proliferation, survival, adhesion, and migration; furthermore, they have been demonstrated to suppress tumor growth, to alleviate cancer-associated pain, and to exert immunomodulatory properties. Here, we will address the known knowns and the known unknowns of Sigma1 and Sigma2/TMEM97 ligand actions in the context of cancer. This review will highlight key discoveries and published evidence in support of a role for sigma proteins in cancer and will discuss several fundamental questions regarding the physiological roles of sigma proteins in cancer and sigma ligand mechanism of action.

Sigma-2 receptor/TMEM97 agonist PB221 as an alternative drug for brain tumor

Background

There are limited effective drugs that can reach the brain to target brain tumors, in particular glioblastoma, which is one of the most difficult cancers to be cured from. Because the overexpression of the sigma-2 receptor is frequently reported in glioma clinical samples and associated with poor prognosis and malignancy, we herein studied the anti-tumor effect of the sigma-2 receptor agonist PB221 (4-cyclohexyl-1-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl]piperidine) on an anaplastic astrocytoma tumor model based on previous encouraging results in pancreatic cancer and neuroblastoma SK-N-SH cells.

Methods

The expression of the sigma-2 receptor, transmembrane protein 97 (TMEM97), in ALTS1C1 and UN-KC6141 cell lines was measured by RT-PCR and quantitative RT-PCR. The binding of sigma-2 receptor fluorescent ligands PB385 (6-[5-[3-(4-cyclohexylpiperazin-1-yl)propyl]-5,6,7,8-tetrahydronaphthalen-5-yloxy]-N-(7-nitro-2,1,3-benzoxadiazol-4-yl)hexanamine) and NO1 (2-{6-[2-(3-(6,7-dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl)propyl)-3,4-dihydroisoquinolin-1(2H)-one-5-yloxy]hexyl}-5-(dimethylamino)isoindoline-1,3-dione) was examined by flow cytometry and the fluorescent plate reader. The antitumor activity of PB221 was initially examined in the murine brain tumor cell line ALTS1C1 and then in the murine pancreatic cell line UN-KC6141. The potential therapeutic efficacy of PB221 for murine brain tumors was examined by in vitro migration and invasion assays and in vivo ectopic and orthotopic ALTS1C1 tumor models.

Results: The IC₅₀ of PB221 for ALTS1C1 and UN-KC6141 cell lines was 10.61 ± 0.96 and 13.13 ± 1.15 μM, respectively. A low dose of PB221 (1 μM) significantly repressed the migration and invasion of ALTS1C1 cells, and a high dose of PB221 (20 μM) resulted in the apoptotic cell death of ALTS1C1 cells. These effects were reduced by the lipid antioxidant α-tocopherol, but not by the hydrophilic N-acetylcysteine, suggesting mitochondrial oxidative stress is involved. The in vivo study revealed that PB221 effectively retarded tumor growth to 36% of the control tumor volume in the ectopic intramuscular tumor model and increased the overall survival time by 20% (from 26 to 31 days) in the orthotopic intracerebral tumor model.

Conclusions

This study demonstrates that the sigma-2 receptor agonist PB221 has the potential to be an alternative chemotherapeutic drug for brain tumors with comparable side effects as the current standard-of-care drug, temozolomide.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5700-7) contains supplementary material, which is available to authorized users.

Bicycloheptylamine-Doxorubicin Conjugate: Synthesis and Anticancer Activities in σ2 Receptor-Expressing Cell Lines

BACKGROUND

Novel bicycloheptylamines were designed and synthesized. These compounds were found to be selective for sigma-2 receptors. These receptors have been found to be up to 10 fold over-expressed in certain cancer cell lines, leading to investigation of possible uses as a biomarker in diagnosis and/or treatment especially in cancers with poor prognosis.

OBJECTIVES

The aim was to conjugate a novel sigma-2 receptor ligand to doxorubicin to examine anticancer activities, with and without conjugation, and therefore possibilities in drug delivery.

METHODS

Conjugation was conducted using N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide HCl as a coupling agent. Affinity towards the sigma-2 receptor was tested using ligand-receptor binding studies. Anticancer activities against cancer cell lines were carried out using cell viability assays. Caspase dependency was tested using Z-VAD-FMK, a pan-caspase inhibitor, to begin to investigate mechanisms of action.

RESULTS

The target compound retained affinity towards the sigma-2 receptor and exhibited potent anticancer activities on cancer cell lines expressing the sigma-2 receptor. The potencies exceeded those of doxorubicin, the lead sigma-2 receptor ligand, as well as non-covalent combination of both drugs. The activity was also found to be caspase-dependent.

CONCLUSION

The conjugation of target bicycloheptylamines with cytotoxic moieties may yield potent and selective molecules for detection and/or treatment of certain cancers.

Effectiveness of ZnPc and of an amine derivative to inactivate Glioblastoma cells by Photodynamic Therapy: an in vitro comparative study

Glioblastoma multiforme is considered to be one of the most aggressive types of tumors of the central nervous system, with a poor prognosis and short survival periods of ~ one year. The current protocol for glioblastoma treatment includes the surgical excision of the primary tumor followed by radio and chemotherapy. Photodynamic therapy (PDT) is considered a promising strategy for the treatment of several types of tumors. Phthalocyanines (Pcs) are good photosensitizers (PSs) for PDT because they induce cell death in several cellular models. ZnPc (Zn(II)phthalocyanine) is a well-known Pc, extensively tested in different cells and tumor models, but its evaluation on a glioblastoma model has been poorly studied. Herein, we compare the capacity of ZnPc and one of its derivatives, Zn(II)tetraminephthalocyanine (TAZnPc), to photoinactivate glioblastoma cells (T98G, MO59, LN229 and U87-MG) in culture. We measured the cellular uptake, the toxicity in the dark and the subcellular localization of the different Pcs, as well as the clonogenic capacity of surviving cells after PDT. The mechanism of cell death induced after PDT was determined by measuring caspase 3 activation, DNA fragmentation, phosphatidylserine externalization, mitochondrial morphological changes and loss of mitochondrial membrane potential as well as lysosomal membrane integrity. Overall, ZnPc and TAZnPc present good properties to be used as PSs with photoinactivation capacity on glioblastoma cells.

TMEM97 and PGRMC1 do not mediate sigma-2 ligand-induced cell death

Sigma-2 receptors have been implicated in both tumor proliferation and neurodegenerative diseases. Recently the sigma-2 receptor was identified as transmembrane protein 97 (TMEM97). Progesterone receptor membrane component 1 (PGRMC1) was also recently reported to form a complex with TMEM97 and the low density lipoprotein (LDL) receptor, and this trimeric complex is responsible for the rapid internalization of LDL. Sigma-2 receptor ligands with various structures have been shown to induce cell death in cancer cells. In the current study, we examined the role of TMEM97 and PGRMC1 in mediating sigma-2 ligand-induced cell death. Cell viability and caspase-3 assays were performed in control, TMEM97 knockout (KO), PGRMC1 KO, and TMEM97/PGRMC1 double KO cell lines treated with several sigma-2 ligands. The data showed that knockout of TMEM97, PGRMC1, or both did not affect the concentrations of sigma-2 ligands that induced 50% of cell death (EC₅₀), suggesting that cytotoxic effects of these compounds are not mediated by TMEM97 or PGRMC1. Sigma-1 receptor ligands, (+)-pentazocine and NE-100, did not block sigma-2 ligand cytotoxicity, suggesting that sigma-1 receptor was not responsible for sigma-2 ligand cytotoxicity. We also examined whether the alternative, residual binding site (RBS) of 1,3-Di-o-tolylguanidine (DTG) could be responsible for sigma-2 ligand cytotoxicity. Our data showed that the binding affinities (K_i) of sigma-2 ligands on the DTG RBS did not correlate with the cytotoxicity potency (EC₅₀) of these ligands, suggesting that the DTG RBS was not fully responsible for sigma-2 ligand cytotoxicity. In addition, we showed that knocking out TMEM97, PGRMC1, or both reduced the initial internalization rate of a sigma-2 fluorescent ligand, SW120. However, concentrations of internalized SW120 became identical later in the control and knockout cells. These data suggest that the initial internalization process of sigma-2 ligands does not appear to mediate the cell-killing effect of sigma-2 ligands. In summary, we have provided evidence that sigma-2 receptor/TMEM97 and PGRMC1 do not mediate sigma-2 ligand cytotoxicity. Our work will facilitate elucidating mechanisms of sigma-2 ligand cytotoxicity.

Autophagic effects and mechanisms of silver nanoparticles in renal cells under low dose exposure

With the advancement of nanotechnology and unique properties, silver nanoparticles (AgNPs) have been generally used in our work and life. However, the concerns on nanosafety have not been thoroughly understood. Although mounting studies have documented AgNPs-mediated autophagy under toxic dose, very few studies have been made to reveal the mechanisms of AgNPs-induced autophagy at non-toxic concentrations. Here, we investigated AgNPs-mediated biological effects on autophagy in renal cells under sublethal exposure. Sublethal AgNPs resulted in increase of LC3II level and accumulation of autophagy related genes in HEK293T and A498 cells, which demonstrated AgNPs could activate autophagy at lower concentrations. Mechanistic investigation manifested that AMPK-mTOR signaling was enrolled in AgNPs-induced autophagy process rather than PI3K/AKT/mTOR signaling. In addition, P62 was elevated in AgNPs-treated cells in an mTOR-independent manner. We further uncovered that sublethal AgNPs exposure impaired the integrity and protease activities of lysosome. Together, our results revealed the mechanism by which AgNPs induced autophagy in renal cells under sublethal concentration.

Sigma-2 receptor: past, present and perspectives on multiple therapeutic exploitations

Identification of sigma-2 receptor (sig-2R) has been controversial. Nevertheless, interest in sig-2R is high for its overexpression in tumors and potentials in oncology. Additionally, sig-2R antagonists inhibit Aβ binding at neurons, blocking the cognitive impairments of Alzheimer's disease. The most representative classes of sig-2R ligands are herein treated with focus on compounds that served to study sig-2R biology and to produce sig-2R: fluorescent ligands; multifunctional anticancer agents; and targeting nanoparticles. Although fluorescent ligands serve as ‘green’ pharmacological tools, sig-2R-multifunctional conjugates and sig-2R-targeted nanoparticles show how sig-2R targeting increases the activity of anticancer drugs in tumors with reduced toxicity. Altogether, this review draws a picture of the multiple approaches of sig-2R ligands in cancer therapy and as Alzheimer's disease modifying disease agents.

The Outcome of the Cryptococcus neoformans-Macrophage Interaction Depends on Phagolysosomal Membrane Integrity

Cryptococcus neoformans is a fungal pathogen with worldwide distribution. C. neoformans resides within mature phagolysosomes where it often evades killing and replicates. C. neoformans induces phagolysosomal membrane permeabilization (PMP), but the mechanism for this phenomenon and its consequences for macrophage viability are unknown. In this study, we used flow cytometry methodology in combination with cell viability markers and LysoTracker to measure PMP in J774.16 and murine bone marrow-derived macrophages infected with C. neoformans Our results showed that cells manifesting PMP were positive for apoptotic markers, indicating an association between PMP and apoptosis. We investigated the role of phospholipase B1 in C. neoformans induction of PMP. Macrophages infected with a C. neoformans Δplb1 mutant had reduced PMP compared with those infected with wild-type and phospholipase B1-complemented strains, suggesting a mechanism of action for this virulence factor. Capsular enlargement inside macrophages was identified as an additional likely mechanism for phagolysosomal membrane damage. Macrophages undergoing apoptosis did not maintain an acidic phagolysosomal pH. Induction of PMP with ciprofloxacin enhanced macrophages to trigger lytic exocytosis whereas nonlytic exocytosis was common in those without PMP. Our results suggest that modulation of PMP is a critical event in determining the outcome of C. neoformans-macrophage interaction.

Multifunctional thiosemicarbazones and deconstructed analogues as a strategy to study the involvement of metal chelation, Sigma-2 (σ2) receptor and P-gp protein in the cytotoxic action: In vitro and in vivo activity in pancreatic tumors

The aggressiveness of pancreatic cancer urgently requires more efficient treatment options. Because the sigma-2 (σ2) receptor was recently proposed as a promising target for pancreatic cancer therapy, we explored our previously developed multifunctional thiosemicarbazones, designed to synergistically impair cell energy levels, by targeting σ2 and P-gp proteins and chelating Iron. A deconstruction approach was herein applied by removing one function at a time from the potent multifunctional thiosemicarbazones 1 and 2, to investigate the contribution to cytotoxicity of each target involved. The results from in vitro (panel of pancreatic tumor cells) and in vivo experiments (C57BL/6 bearing KP02 tumor), suggest that while the multifunctional activity was not required for the antitumor activity of these thiosemicarbazones, σ2-targeting appeared to allow alternative tumor cell death mechanisms, leading to potent and less toxic off-targets toxicities compared to other thiosemicarbazones devoid of σ2-targeting.

Salvianolic acid B protects hepatocytes from H2O2 injury by stabilizing the lysosomal membrane

AIM

To investigate the capability of salvianolic acid B (Sal B) to protect hepatocytes from hydrogen peroxide (H2O2)/carbon tetrachloride (CCl4)-induced lysosomal membrane permeabilization.

METHODS

Cell Counting Kit-8 assay was used to measure cell viability. Apoptosis and death were assayed through flow cytometry. BrdU incorporation was used to detect cell proliferation. Serum alanine aminotransferase activity and liver malondialdehyde (MDA) content were measured. Liver histopathological changes were evaluated using hematoxylin-eosin staining. Lysosomal membrane permeability was detected with LysoTracker Green-labeled probes and acridine orange staining. The levels of protein carbonyl content (PCC), cathepsins (Cat)B/D, and lysosome-associated membrane protein 1 (LAMP1) were evaluated through western blotting. Cytosol CatB activity analysis was performed with chemiluminescence detection. The mRNA level of LAMP1 was evaluated through quantitative real-time polymerase chain reaction.

RESULTS

Results indicated that H2O2 induced cell injury/death. Sal B attenuated H2O2-induced cell apoptosis and death, restored the inhibition of proliferation, decreased the amount of PCC, and stabilized the lysosome membrane by increasing the LAMP1 protein level and antagonizing CatB/D leakage into the cytosol. CCl4 also triggered hepatocyte death. Furthermore, Sal B effectively rescued hepatocytes by increasing LAMP1 expression and by reducing lysosomal enzyme translocation to the cytosol.

CONCLUSION

Sal B protected mouse embryonic hepatocytes from H2O2/CCl4-induced injury/death by stabilizing the lysosomal membrane.

Sigma-2 ligands and PARP inhibitors synergistically trigger cell death in breast cancer cells

The sigma-2 receptor is overexpressed in proliferating cells compared to quiescent cells and has been used as a target for imaging solid tumors by positron emission tomography. Recent work has suggested that the sigma-2 receptor may also be an effective therapeutic target for cancer therapy. Poly (ADP-ribose) polymerase (PARP) is a family of enzymes involved in DNA damage response. In this study, we looked for potential synergy of cytotoxicity between PARP inhibitors and sigma-2 receptor ligands in breast cancer cell lines. We showed that the PARP inhibitor, YUN3-6, sensitized mouse breast cancer cell line, EMT6, to sigma-2 receptor ligand (SV119, WC-26, and RHM-138) induced cell death determined by cell viability assay and colony forming assay. The PARP inhibitor, olaparib, sensitized tumor cells to a different sigma-2 receptor ligand SW43-induced apoptosis and cell death in human triple negative cell line, MDA-MB-231. Olaparib inhibited PARP activity and cell proliferation, and arrested cells in G2/M phase of the cell cycle in MDA-MB-231 cells. Subsequently cells became sensitized to SW43 induced cell death. In conclusion, the combination of sigma-2 receptor ligands and PARP inhibitors appears to hold promise for synergistically triggering cell death in certain types of breast cancer cells and merits further investigation.

Sigma-2 receptor agonist derivatives of 1-Cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl]piperazine (PB28) induce cell death via mitochondrial superoxide production and caspase activation in pancreatic cancer

Background

Despite considerable efforts by scientific research, pancreatic cancer is the fourth leading cause of cancer related mortalities. Sigma-2 receptors, which are overexpressed in several tumors, represent promising targets for triggering selective pancreatic cancer cells death.

Methods

We selected five differently structured high-affinity sigma-2 ligands (PB28, PB183, PB221, F281 and PB282) to study how they affect the viability of diverse pancreatic cancer cells (human cell lines BxPC3, AsPC1, Mia PaCa-2, and Panc1 and mouse Panc-02, KCKO and KP-02) and how this is reflected in vivo in a tumor model.

Results

Important cytotoxicity was shown by the compounds in the aggressive Panc02 cells, where cytotoxic activity was caspase-3 independent for four of the five compounds. However, both cytotoxicity and caspase-3 activation involved generation of Reactive Oxygen Species (ROS), which could be partially reverted by the lipid antioxidant α-tocopherol, but not by the hydrophilic N-acetylcysteine (NAC) indicating crucial differences in the intracellular sites exposed to oxidative stress induced by sigma-2 receptor ligands. Importantly, all the compounds strongly increased the production of mitochondrial superoxide radicals except for PB282. Despite a poor match between in vitro and the in vivo efficacy, daily treatment of C57BL/6 mice bearing Panc02 tumors resulted in promising effects with PB28 and PB282 which were similar compared to the current standard-of-care chemotherapeutic gemcitabine without showing signs of systemic toxicities.

Conclusions

Overall, this study identified differential sensitivities of pancreatic cancer cells to structurally diverse sigma-2 receptor ligands. Of note, we identified the mitochondrial superoxide pathway as a previously unrecognized sigma-2 receptor-activated process, which encourages further studies on sigma-2 ligand-mediated cancer cell death for the targeted treatment of pancreatic tumors.

The Evolution of the Sigma-2 (σ2) Receptor from Obscure Binding Site to Bona Fide Therapeutic Target

The sigma-2 (σ₂) receptor represents one of the most poorly understood proteins in cell biology. Although this receptor was identified through in vitro binding studies over 25 years ago, the molecular identity of this protein is currently not unambiguously known, and the results from recent attempts to identify the σ₂ receptor through protein purification and mass spectral analysis have been the subject of debate in the literature. However, there is overwhelming data demonstrating that the σ₂ receptor is an important biomarker of tumor cell proliferation . The observation that σ₂ receptor agonists are potent anticancer agents whereas σ₂ antagonists block Aβ1-42 oligomer synaptic dysfunction in transgenic mouse models of Alzheimer's disease have clearly identified this protein as an important therapeutic target for the treatment of a variety of pathological conditions.

Sigma1 Pharmacology in the Context of Cancer

Sigma1 (also known as sigma-1 receptor, Sig1R, σ1 receptor) is a unique pharmacologically regulated integral membrane chaperone or scaffolding protein. The majority of publications on the subject have focused on the neuropharmacology of Sigma1. However, a number of publications have also suggested a role for Sigma1 in cancer. Although there is currently no clinically used anti-cancer drug that targets Sigma1, a growing body of evidence supports the potential of Sigma1 ligands as therapeutic agents to treat cancer. In preclinical models, compounds with affinity for Sigma1 have been reported to inhibit cancer cell proliferation and survival, cell adhesion and migration, tumor growth, to alleviate cancer-associated pain, and to have immunomodulatory properties. This review will highlight that although the literature supports a role for Sigma1 in cancer, several fundamental questions regarding drug mechanism of action and the physiological relevance of aberrant SIGMAR1 transcript and Sigma1 protein expression in certain cancers remain unanswered or only partially answered. However, emerging lines of evidence suggest that Sigma1 is a component of the cancer cell support machinery, that it facilitates protein interaction networks, that it allosterically modulates the activity of its associated proteins, and that Sigma1 is a selectively multifunctional drug target.

Lysosomal cell death mechanisms in aging

Lysosomes are degradative organelles essential for cell homeostasis that regulate a variety of processes, from calcium signaling and nutrient responses to autophagic degradation of intracellular components. Lysosomal cell death is mediated by the lethal effects of cathepsins, which are released into the cytoplasm following lysosomal damage. This process of lysosomal membrane permeabilization and cathepsin release is observed in several physiopathological conditions and plays a role in tissue remodeling, the immune response to intracellular pathogens and neurodegenerative diseases. Many evidences indicate that aging strongly influences lysosomal activity by altering the physical and chemical properties of these organelles, rendering them more sensitive to stress. In this review we focus on how aging alters lysosomal function and increases cell sensitivity to lysosomal membrane permeabilization and lysosomal cell death, both in physiological conditions and age-related pathologies.

58-F, a flavanone from Ophiopogon japonicus, prevents hepatocyte death by decreasing lysosomal membrane permeability

Lysosome membrane permeabilization (LMP) has been implicated in cell death. In the present study, we investigated the relationship between cell death and H₂O₂-/CCl₄-induced LMP in hepatocytes in vitro and following acute liver injury in vivo. The key finding was that H₂O₂ triggered LMP by oxidative stress, as evidenced by a suppression of LAMP1 expression, a reduction in LysoTracker Green and AO staining, and the leakage of proton and cathepsin B/D from the lysosome to the cytoplasm, resulting in cell death. CCl₄ also triggered hepatocyte death by decreasing lysosome LAMP1 expression and by inducing the accumulation of products of peroxidative lipids and oxidized proteins. Furthermore, a novel compound 5,8-dimethoxy-6-methyl-7-hydroxy-3-3(2-hydroxy-4-methoxybenzyl) chroman-4-one (58-F) was extracted from Ophiopogon japonicus and served as a potential therapeutic drug. In vivo and in vitro results showed that 58-F effectively rescued hepatocytes by decreasing LMP and by inducing lysosomal enzyme translocation to the cytosol.

SW43-DOX ± loading onto drug-eluting bead, a potential new targeted drug delivery platform for systemic and locoregional cancer treatment - An in vitro evaluation

Treatment of unresectable primary cancer and their distant metastases, with the liver representing one of the most frequent location, is still plagued by insufficient treatment success and poor survival rates. The Sigma-2 receptor is preferentially expressed on many tumor cells making it an appealing target for therapy. Thus, we developed a potential targeted drug conjugate consisting of the Sigma-2 receptor ligand SW43 and Doxorubicin (SW43-DOX) for systemic cancer therapy and for locoregional treatment of primary and secondary liver malignancies when loaded onto drug-eluting bead (DEB) which was compared in vitro to the treatment with Doxorubicin alone. SW43-DOX binds specifically to the Sigma-2 receptor expressed on hepatocellular (Hep G2, Hep 3B), pancreatic (Panc-1) and colorectal (HT-29) carcinoma cell lines with high affinity and subsequent early specific internalization. Free SW43-DOX showed superior concentration and time depended cancer toxicity than treatment with Doxorubicin alone. Action mechanisms analysis revealed an apoptotic cell death with increased caspase 3/7 activation and reactive oxygen species (ROS) production. Only ROS scavenging with α-Tocopherol, but not the caspase inhibition (Z-VAD-FMK), partly reverted the effect. SW43-DOX could successfully be loaded onto DEB and showed prolonged eluting kinetics compared to Doxorubicin. SW43-DOX loaded DEB vs. Doxorubicin loaded DEB showed a significantly greater time dependent toxicity in all cell lines. In conclusion, the novel conjugate SW43-DOX ± loading onto DEB is a promising drug delivery platform for targeted systemic and locoregional cancer therapy.

Development of sigma-1 (σ1) receptor fluorescent ligands as versatile tools to study σ1 receptors

Despite their controversial physiology, sigma-1 (σ1) receptors are intriguing targets for the development of therapeutic agents for central nervous system diseases. With the aim of providing versatile pharmacological tools to study σ1 receptors, we developed three σ1 fluorescent tracers by functionalizing three well characterized σ1 ligands with a fluorescent tag. A good compromise between σ1 binding affinity and fluorescent properties was reached, and the σ1 specific targeting of the novel tracers was demonstrated by confocal microscopy and flow cytometry. These novel ligands were also successfully used in competition binding studies by flow cytometry, showing their utility in nonradioactive binding assays as an alternative strategy to the more classical radioligand binding assays. To the best of our knowledge these are the first σ1 fluorescent ligands to be developed and successfully employed in living cells, representing promising tools to strengthen σ1 receptors related studies.

Potential applications for sigma receptor ligands in cancer diagnosis and therapy

Sigma receptors (sigma-1 and sigma-2) represent two independent classes of proteins. Their endogenous ligands may include the hallucinogen N,N-dimethyltryptamine (DMT) and sphingolipid-derived amines which interact with sigma-1 receptors, besides steroid hormones (e.g., progesterone) which bind to both sigma receptor subpopulations. The sigma-1 receptor is a ligand-regulated molecular chaperone with various ion channels and G-protein-coupled membrane receptors as clients. The sigma-2 receptor was identified as the progesterone receptor membrane component 1 (PGRMC1). Although sigma receptors are over-expressed in tumors and up-regulated in rapidly dividing normal tissue, their ligands induce significant cell death only in tumor tissue. Sigma ligands may therefore be used to selectively eradicate tumors. Multiple mechanisms appear to underlie cell killing after administration of sigma ligands, and the signaling pathways are dependent both on the type of ligand and the type of tumor cell. Recent evidence suggests that the sigma-2 receptor is a potential tumor and serum biomarker for human lung cancer and an important target for inhibiting tumor invasion and cancer progression. Current radiochemical efforts are focused on the development of subtype-selective radioligands for positron emission tomography (PET) imaging. Right now, the mostpromising tracers are [18F]fluspidine and [18F]FTC-146 for sigma-1 receptors and [11C]RHM-1 and [18F]ISO-1 for the sigma-2 subtype. Nanoparticles coupled to sigma ligands have shown considerable potential for targeted delivery of antitumor drugs in animal models of cancer, but clinical studies exploring this strategy in cancer patients have not yet been reported. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Proton pump inhibitors for the treatment of cancer in companion animals

The treatment of cancer presents a clinical challenge both in human and veterinary medicine. Chemotherapy protocols require the use of toxic drugs that are not always specific, do not selectively target cancerous cells thus resulting in many side effects. A recent therapeutic approach takes advantage of the altered acidity of the tumour microenvironment by using proton pump inhibitors (PPIs) to block the hydrogen transport out of the cell. The alteration of the extracellular pH kills tumour cells, reverses drug resistance, and reduces cancer metastasis. Human clinical trials have prompted to consider this as a viable and safe option for the treatment of cancer in companion animals. Preliminary animal studies suggest that the same positive outcome could be achievable. The purpose of this review is to support investigations into the use of PPIs for cancer treatment cancer in companion animals by considering the evidence available in both human and veterinary medicine.

Isoquercitrin inhibits the progression of pancreatic cancer in vivo and in vitro by regulating opioid receptors and the mitogen-activated protein kinase signalling pathway

Pancreatic cancer is a common malignant tumour that affects individuals worldwide. In recent years, the incidence and mortality rates of pancreatic cancer have continuously increased. Currently, the primary clinical treatment methods for pancreatic cancer include surgical resection, chemotherapy and radiotherapy. However, these treatment methods rarely produce satisfactory therapeutic outcomes. Extensive research has also proven that the effective components of several traditional Chinese medicines, particularly flavonoids extracted from plants, have significant antitumour effects. Isoquercitrin, which is one of the flavonoids found in Bidens pilosa extracts, has a significant antitumour effect. However, the antitumour effect of isoquercitrin and its mechanism of action remain unclear. The objective of the present study was to investigate the effect of isoquercitrin on the progression of pancreatic cancer and to further understand the biological characteristics of the participation of isoquercitrin in the progression of pancreatic cancer. In vitro, we found that a therapeutic dose of isoquercitrin significantly inhibited proliferation, promoted apoptosis and induced cell cycle arrest within the G1 phase in pancreatic cancer cells. Isoquercitrin activated caspase-3, -8 and -9 and reduced the mitochondrial membrane potential. In addition, isoquercitrin inhibited the expression level of the δ opioid receptor; however, isoquercitrin had no effect on the κ and µ opioid receptors. Furthermore, isoquercitrin inhibited extracellular signal-regulated kinase (ERK) phosphorylation and promoted c-Jun N-terminal kinase (JNK) phosphorylation. In vivo, we found that a therapeutic dose of isoquercitrin significantly inhibited xenograft growth in nude mice. In summary, the present study demonstrated that isoquercitrin inhibits human pancreatic cancer progression in vivo and in vitro and that its molecular mechanism may be closely related to opioid receptors and to the activation of the mitogen-activated protein kinase (MAPK) signalling pathway.

Novel metal chelators thiosemicarbazones with activity at the σ2receptors and P-glycoprotein: an innovative strategy for resistant tumor treatment

Novel multitarget thiosemicarbazones that bind simultaneously σ₂receptors and P-glycoprotein efflux pump and chelate metals were designed for resistant tumors treatment.

Deconstruction of 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline moiety to separate P-glycoprotein (P-gp) activity from σ2 receptor affinity in mixed P-gp/σ2 receptor agents

6,7-Dimethoxytetrahydroisoquinoline is widely used as basic moiety in σ2 receptor ligands, in order to provide σ2versus σ1 selectivity. This same moiety is also widely exploited in modulators of P-glycoprotein (P-gp) efflux pump, so that mixed σ2/P-gp agents are often obtained. Deconstruction of 6,7-dimethoxytetrahydroisoquinoline moiety present in the potent mixed σ2/P-gp agent 6,7-dimethoxy-2-[4-[1-(4-fluorophenyl)-1H-indol-3-yl]butyl]-1,2,3,4-tetrahydroisoquinoline (1) could lead to the separation of σ2 affinity from P-gp activity. Therefore, phenethylamino-, benzylamino- and indanamine series were obtained. The NH group was also methylated in the N-phenethylamino series, and ethylated in the benzylamino series, to better match 6,7-dimethoxytetrahydroisoquinoline. The σ2 affinity drastically decreased with the increase of conformational freedom, whereas alkylation of the NH-group was beneficial for σ2 receptor interaction. By contrast, deconstruction of 6,7-dimethoxytetrahydroisoquinoline slightly reduced P-gp activity, with dimethoxy-substituted derivatives displaying potent P-gp interaction. Therefore, 'ring-opened' 6,7-dimethoxytetrahydroisoquinoline derivatives represent a promising strategy to obtain P-gp selective agents devoid of σ2 receptor affinity.

Critical roles for nitric oxide and ERK in the completion of prosurvival autophagy in 4OHTAM-treated estrogen receptor-positive breast cancer cells

Autophagy is a mechanism of tamoxifen (TAM) resistance in ER-positive (ER+) breast cancer cells. In this study, we showed in ER+ MCF7 cells that 4-hydroxytamoxifen (4OHTAM) induced cellular nitric oxide (NO) that negatively regulates cellular superoxide (O2-) and cytotoxicity. 4OHTAM stimulated LC3 lipidation and formation of monodansylcadaverine (MDC)-labeled autophagic vesicles dependent on O2-. Depletion of NO increased O2- and LC3 lipidation, yet reduced formation of MDC-labeled autophagic vesicles. Instead, NO-depleted cells formed remarkably large vacuoles with rims decorated by LC3. The vacuoles were not labeled by MDC or the acidic lysosome-specific fluorescence dye acridine orange (AO). The vacuoles were increased by the late stage autophagy inhibitor chloroquine, which also increased LC3 lipidation. These results suggest NO is required for proper autophagic vesicle formation or maturation at a step after LC3 lipidation. In addition, 4OHTAM induced O2--dependent activation of ERK, inhibition of which destabilized lysosomes/autolysosomes upon 4OHTAM treatment and together with depletion of NO led to necrotic cell death. These results suggest an essential role for endogenous NO and ERK activation in the completion of pro-survival autophagy.