Synergistic Anticancer Action of Lysosomal Membrane Permeabilization and Glycolysis Inhibition

Dissecting the Role of Autophagy-Related Proteins in Cancer Metabolism and Plasticity

Modulation of autophagy as an anticancer strategy has been widely studied and evaluated in several cell models. However, little attention has been paid to the metabolic changes that occur in a cancer cell when autophagy is inhibited or induced. In this review, we describe how the expression and regulation of various autophagy-related (ATGs) genes and proteins are associated with cancer progression and cancer plasticity. We present a comprehensive review of how deregulation of ATGs affects cancer cell metabolism, where inhibition of autophagy is mainly reflected in the enhancement of the Warburg effect. The importance of metabolic changes, which largely depend on the cancer type and form part of a cancer cell's escape strategy after autophagy modulation, is emphasized. Consequently, pharmacological strategies based on a dual inhibition of metabolic and autophagy pathways emerged and are reviewed critically here.

Combination of Ascorbic Acid and Menadione Induces Cytotoxic Autophagy in Human Glioblastoma Cells

We investigated the ability of the ascorbic acid (AA) and menadione (MD) combination, the well-known reactive oxidative species- (ROS-) generating system, to induce autophagy in human U251 glioblastoma cells. A combination of AA and MD (AA+MD), in contrast to single treatments, induced necrosis-like cell death mediated by mitochondrial membrane depolarization and extremely high oxidative stress. AA+MD, and to a lesser extent MD alone, prompted the appearance of autophagy markers such as autophagic vacuoles, autophagosome-associated LC3-II protein, degradation of p62, and increased expression of beclin-1. While both MD and AA+MD increased phosphorylation of AMP-activated protein kinase (AMPK), the well-known autophagy promotor, only the combined treatment affected its downstream targets, mechanistic target of rapamycin complex 1 (mTORC1), Unc 51-like kinase 1 (ULK1), and increased the expression of several autophagy-related genes. Antioxidant N-acetyl cysteine reduced both MD- and AA+MD-induced autophagy, as well as changes in AMPK/mTORC1/ULK1 activity and cell death triggered by the drug combination. Pharmacological and genetic autophagy silencing abolished the toxicity of AA+MD, while autophagy upregulation enhanced the toxicity of both AA+MD and MD. Therefore, by upregulating oxidative stress, inhibiting mTORC1, and activating ULK1, AA converts MD-induced AMPK-dependent autophagy from nontoxic to cytotoxic. These results suggest that AA+MD or MD treatment in combination with autophagy inducers could be further investigated as a novel approach for glioblastoma therapy.

Inhibition of PLA2G4E/cPLA2 promotes survival of random skin flaps by alleviating Lysosomal membrane permeabilization-Induced necroptosis

Necrosis that appears at the ischemic distal end of random-pattern skin flaps increases the pain and economic burden of patients. Necroptosis is thought to contribute to flap necrosis. Lysosomal membrane permeabilization (LMP) plays an indispensable role in the regulation of necroptosis. Nonetheless, the mechanisms by which lysosomal membranes become leaky and the relationship between necroptosis and lysosomes are still unclear in ischemic flaps. Based on Western blotting, immunofluorescence, enzyme-linked immunosorbent assay, and liquid chromatography-mass spectrometry (LC-MS) analysis results, we found that LMP was presented in the ischemic distal portion of random-pattern skin flaps, which leads to disruption of lysosomal function and macroautophagic/autophagic flux, increased necroptosis, and aggravated necrosis of the ischemic flaps. Moreover, bioinformatics analysis of the LC-MS results enabled us to focus on the role of PLA2G4E/cPLA2 (phospholipase A2, group IVE) in LMP of the ischemic flaps. In vivo inhibition of PLA2G4E with an adeno-associated virus vector attenuated LMP and necroptosis, and promoted flap survival. In addition, microRNA-seq helped us determine that Mir504-5p was differentially expressed in ischemic flaps. A string of in vitro and in vivo tests was employed to verify the inhibitory effect of Mir504-5p on PLA2G4E, LMP and necroptosis. Finally, we concluded that the inhibition of PLA2G4E by Mir504-5p reduced LMP-induced necroptosis, thereby promoting the survival of random-pattern skin flaps.

Graphene quantum dot antioxidant and proautophagic actions protect SH-SY5Y neuroblastoma cells from oxidative stress-mediated apoptotic death

We investigated the ability of graphene quantum dot (GQD) nanoparticles to protect SH-SY5Y human neuroblastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP). GQD reduced SNP cytotoxicity by preventing mitochondrial depolarization, caspase-2 activation, and subsequent apoptotic death. Although GQD diminished the levels of nitric oxide (NO) in SNP-exposed cells, NO scavengers displayed only a slight protective effect, suggesting that NO quenching was not the main protective mechanism of GQD. GQD also reduced SNP-triggered increase in the intracellular levels of hydroxyl radical (^•OH), superoxide anion (O₂^•-), and lipid peroxidation. Nonselective antioxidants, ^•OH scavenging, and iron chelators, but not superoxide dismutase, mimicked GQD cytoprotective activity, indicating that GQD protect cells by neutralizing ^•OH generated in the presence of SNP-released iron. Cellular internalization of GQD was required for optimal protection, since a removal of extracellular GQD by extensive washing only partly diminished their protective effect. Moreover, GQD cooperated with SNP to induce autophagy, as confirmed by the inhibition of autophagy-limiting Akt/PRAS40/mTOR signaling and increase in autophagy gene transcription, protein levels of proautophagic beclin-1 and LC3-II, formation of autophagic vesicles, and degradation of autophagic target p62. The antioxidant activity of GQD was not involved in autophagy induction, as antioxidants N-acetylcysteine and dimethyl sulfoxide failed to stimulate autophagy in SNP-exposed cells. Pharmacological inhibitors of early (wortmannin, 3-methyladenine) or late stages of autophagy (NH₄Cl) efficiently reduced the protective effect of GQD. Therefore, the ability of GQD to prevent the in vitro neurotoxicity of SNP depends on both ^•OH/NO scavenging and induction of cytoprotective autophagy.

Natural Products Induce Lysosomal Membrane Permeabilization as an Anticancer Strategy

Cancer is a global health and economic issue. The majority of anticancer therapies become ineffective due to frequent genomic turnover and chemoresistance. Furthermore, chemotherapy and radiation are non-specific, killing all rapidly dividing cells including healthy cells. In this review, we examine the ability of some natural products to induce lysosomal-mediated cell death in neoplastic cells as a way to kill them more specifically than conventional therapies. This list is by no means exhaustive. We postulate mechanisms to explain lysosomal membrane permeabilization and its role in triggering cell death in cancer cells.

3-Methyladenine prevents energy stress-induced necrotic death of melanoma cells through autophagy-independent mechanisms

We investigated the effect of 3-methyladenine (3MA), a class III phosphatidylinositol 3-kinase (PI3K)-blocking autophagy inhibitor, on cancer cell death induced by simultaneous inhibition of glycolysis by 2-deoxyglucose (2DG) and mitochondrial respiration by rotenone. 2DG/rotenone reduced ATP levels and increased mitochondrial superoxide production, causing mitochondrial swelling and necrotic death in various cancer cell lines. 2DG/rotenone failed to increase proautophagic beclin-1 and autophagic flux in melanoma cells despite the activation of AMP-activated protein kinase (AMPK) and inhibition of mechanistic target of rapamycin complex 1 (mTORC1). 3MA, but not autophagy inhibition with other PI3K and lysosomal inhibitors, attenuated 2DG/rotenone-induced mitochondrial damage, oxidative stress, ATP depletion, and cell death, while antioxidant treatment mimicked its protective action. The protection was not mediated by autophagy upregulation via class I PI3K/Akt inhibition, as it was preserved in cells with genetically inhibited autophagy. 3MA increased AMPK and mTORC1 activation in energy-stressed cells, but neither AMPK nor mTORC1 inhibition reduced its cytoprotective effect. 3MA reduced JNK activation, and JNK pharmacological/genetic suppression mimicked its mitochondria-preserving and cytoprotective activity. Therefore, 3MA prevents energy stress-triggered cancer cell death through autophagy-independent mechanisms possibly involving JNK suppression and decrease of oxidative stress. Our results warrant caution when using 3MA as an autophagy inhibitor.

Structural and functional remodeling of mitochondria as an adaptive response to energy deprivation

Cancer cells bioenergetics is more dependent on glycolysis than mitochondrial oxidative phosphorylation, a phenomenon known as the Warburg Effect. It has been proposed that inhibition of glycolysis may selectively affect cancer cells. However, the effects of glycolysis inhibition on mitochondrial function and structure in cancer cells are not completely understood. Here, we investigated the comparative effects of 2-deoxy-d-glucose (2-DG, a glucose analogue, which suppresses cellular glycolysis) on cellular bioenergetics in human colon cancer DLD-1 cells, smooth muscle cells, human umbilical vein endothelial cells and HL-1 cardiomyocytes. In all cells, 2-DG treatment resulted in significant ATP depletion, however, the cell viability remained unchanged. Also, we did not observe the synergistic effects of 2-DG with anticancer drugs doxorubicin and 5-fluorouracil. Instead, after 2-DG treatment and ATP depletion, mitochondrial respiration and membrane potential were significantly enhanced and mitochondrial morphology changed in the direction of more network organization. Analysis of protein expression demonstrated that 2-DG treatment induced an activation of AMPK (elevated pAMPK/AMPK ratio), increased mitochondrial fusion (mitofusins 1 and 2) and decreased fission (Drp1) proteins. In conclusion, this study suggests a strong link between respiratory function and structural organization of mitochondria in the cell. We propose that the functionality of the mitochondrial network is enhanced compared to disconnected mitochondria.

Dual targeting of tumor cell energy metabolism and lysosomes as an anticancer strategy

To sustain their proliferative and metastatic capacity, tumor cells increase the activity of energy-producing pathways and lysosomal compartment, resorting to autophagolysosomal degradation when nutrients are scarce. Consequently, large fragile lysosomes and enhanced energy metabolism may serve as targets for anticancer therapy. A simultaneous induction of energy stress (by caloric restriction and inhibition of glycolysis, oxidative phosphorylation, Krebs cycle, or amino acid/fatty acid metabolism) and lysosomal stress (by lysosomotropic detergents, vacuolar ATPase inhibitors, or cationic amphiphilic drugs) is an efficient anti-cancer strategy demonstrated in a number of studies. However, the mechanisms of lysosomal/energy stress co-amplification, apart from the protective autophagy inhibition, are poorly understood. We here summarize the established and suggest potential mechanisms and candidates for anticancer therapy based on the dual targeting of lysosomes and energy metabolism.

Decreased Hepatocyte Autophagy Leads to Synergistic IL-1β and TNF Mouse Liver Injury and Inflammation

BACKGROUND AND AIMS

The proinflammatory cytokine IL-1β has been implicated in the pathophysiology of nonalcoholic and alcoholic steatohepatitis. How IL-1β promotes liver injury in these diseases is unclear, as no IL-1β receptor-linked death pathway has been identified. Autophagy functions in hepatocyte resistance to injury and death, and findings of decreased hepatic autophagy in many liver diseases suggest a role for impaired autophagy in disease pathogenesis. Recent findings that autophagy blocks mouse liver injury from lipopolysaccharide led to an examination of autophagy's function in hepatotoxicity from proinflammatory cytokines.

APPROACH AND RESULTS

AML12 cells with decreased autophagy from a lentiviral autophagy-related 5 (Atg5) knockdown were resistant to toxicity from TNF, but sensitized to death from IL-1β, which was markedly amplified by TNF co-treatment. IL-1β/TNF death was necrosis by trypan blue and propidium iodide positivity, absence of mitochondrial death pathway and caspase activation, and failure of a caspase inhibitor or necrostatin-1s to prevent death. IL-1β/TNF depleted autophagy-deficient cells of ATP, and ATP depletion and cell death were prevented by supplementation with the energy substrate pyruvate or oleate. Pharmacological inhibitors and genetic knockdown studies demonstrated that IL-1β/TNF-induced necrosis resulted from lysosomal permeabilization and release of cathepsins B and L in autophagy-deficient cells. Mice with a tamoxifen-inducible, hepatocyte-specific Atg5 knockout were similarly sensitized to cathepsin-dependent hepatocellular injury and death from IL-1β/TNF in combination, but neither IL-1β nor TNF alone. Knockout mice had increased hepatic inflammation, and IL-1β/TNF-treated, autophagy-deficient AML12 cells secreted exosomes with proinflammatory damage-associated molecular patterns.

CONCLUSIONS

The findings delineate mechanisms by which decreased hepatocyte autophagy promotes IL-1β/TNF-induced necrosis from impaired energy homeostasis and lysosomal permeabilization and inflammation through the secretion of exosomal damage-associated molecular patterns.

Subcellular drug distribution: mechanisms and roles in drug efficacy, toxicity, resistance, and targeted delivery

After administration, drug molecules usually enter target cells to access their intracellular targets. In eukaryotic cells, these targets are often located in organelles, including the nucleus, endoplasmic reticulum, mitochondria, lysosomes, Golgi apparatus, and peroxisomes. Each organelle type possesses unique biological features. For example, mitochondria possess a negative transmembrane potential, while lysosomes have an intraluminal delta pH. Other properties are common to several organelle types, such as the presence of ATP-binding cassette (ABC) or solute carrier-type (SLC) transporters that sequester or pump out xenobiotic drugs. Studies on subcellular drug distribution are critical to understand the efficacy and toxicity of drugs along with the body's resistance to them and to potentially offer hints for targeted subcellular drug delivery. This review summarizes the results of studies from 1990 to 2017 that examined the subcellular distribution of small molecular drugs. We hope this review will aid in the understanding of drug distribution within cells.

Xanthone-rich extract from Gentiana dinarica transformed roots and its active component norswertianin induce autophagy and ROS-dependent differentiation of human glioblastoma cell line

BACKGROUND

Glioblastoma multiforme (GMB) is the most malignant of all brain tumors with poor prognosis. Anticancer potential of xanthones, bioactive compounds found in Gentiana dinarica, is well-documented. Transformation of G. dinarica roots with Agrobacterium rhizogenes provides higher xanthones accumulation, which enables better exploitation of these anticancer compounds.

HYPOTHESIS/PURPOSE

The aim of this study was to investigate antiglioma effect of three different G. dinarica extracts: E1-derived from untransformed roots, E2-derived from roots transformed using A. rhizogenes strain A4M70GUS, and E3-derived from roots transformed using A. rhizogenes strain 15834/PI. Further, mechanisms involved in anticancer potential of the most potent extract were examined in detail, and its active component was determined.

METHODS

The cell viability was assessed using MTT and crystal violet test. Cell cycle analysis, the expression of differentiation markers, the levels of autophagy, and oxidative stress were analyzed by flow cytometry. Autophagy and related signaling pathways were assessed by immunoblotting.

RESULTS

E3, in contrast to E1 and E2, strongly reduced growth of U251 human glioblastoma cells, triggered cell cycle arrest in G₂/M phase, changed cellular morphology, and increased expression of markers of differentiated astrocytes (glial fibrillary acidic protein) and neurons (β-tubulin). E3 stimulated autophagy, as demonstrated by enhanced intracellular acidification, increased microtubule-associated light chain 3B (LC3-I) conversion to autophagosome associated LC3-II, and decreased level of selective autophagy target p62. Induction of autophagy was associated with Akt-dependent inhibition of main autophagy suppressor mammalian target of rapamycin (mTOR). Both genetic and pharmacological inhibition of autophagy suppressed the expression of differentiation markers, but had no effect on cell cycle arrest in E3-treated cells. E3 stimulated oxidative stress, and antioxidants vitamin E and N-acetyl cysteine inhibited autophagy and differentiation of E3-treated U251 cells. The most prevalent compound of E3, xanthone aglycone norswertianin, also arrested glioblastoma cell proliferation in G₂/M phase and induced glioblastoma cell differentiation through induction of autophagy and oxidative stress.

CONCLUSION

These results indicate that E3 and its main active component norswertianin may serve as a potential candidate for differentiation therapy of glioblastoma.

Tumor metabolism regulating chemosensitivity in ovarian cancer

Elevated metabolism is a key hallmark of multiple cancers, serving to fulfill high anabolic demands. Ovarian cancer (OVCA) is the fifth leading cause of cancer deaths in women with a high mortality rate (45%). Chemoresistance is a major hurdle for OVCA treatment. Although substantial evidence suggests that metabolic reprogramming contributes to anti-apoptosis and the metastasis of multiple cancers, the link between tumor metabolism and chemoresistance in OVCA remains unknown. While clinical trials targeting metabolic reprogramming alone have been met with limited success, the synergistic effect of inhibiting tumor-specific metabolism with traditional chemotherapy warrants further examination, particularly in OVCA. This review summarizes the role of key glycolytic enzymes and other metabolic synthesis pathways in the progression of cancer and chemoresistance in OVCA. Within this context, mitochondrial dynamics (fission, fusion and cristae structure) are addressed regarding their roles in controlling metabolism and apoptosis, closely associated with chemosensitivity. The roles of multiple key oncogenes (Akt, HIF-1α) and tumor suppressors (p53, PTEN) in metabolic regulation are also described. Next, this review summarizes recent research of metabolism and future direction. Finally, we examine clinical drugs and inhibitors to target glycolytic metabolism, as well as the rationale for such strategies as potential therapeutics to overcome chemoresistant OVCA.

Pharmacologic ascorbate induces neuroblastoma cell death by hydrogen peroxide mediated DNA damage and reduction in cancer cell glycolysis

An ascorbate-mediated production of oxidative stress has been shown to retard tumor growth. Subsequent glycolysis inhibition has been suggested. Here, we further define the mechanisms relevant to this observation. Ascorbate was cytotoxic to human neuroblastoma cells through the production of H₂O₂, which led to ATP depletion, inhibited GAPDH, and non-apoptotic and non-autophagic cell death. The mechanism of cytotoxicity is different when PARP-dependent DNA repair machinery is active or inhibited. Ascorbate-generated H₂O₂ damaged DNA, activated PARP, depleted NAD+, and reduced glycolysis flux. NAD+ supplementation prevented ATP depletion and cell death, while treatment with a PARP inhibitor, olaparib, preserved NAD+ and ATP levels but led to increased DNA double-strand breakage and did not prevent ascorbate-induced cell death. These data indicate that in cells with an intact PARP-associated DNA repair system, ascorbate-induced cell death is caused by NAD+ and ATP depletion, while in the absence of PARP activation ascorbate-induced cell death still occurs but is a consequence of ROS-induced DNA damage. In a mouse xenograft model, intraperitoneal ascorbate inhibited neuroblastoma tumor growth and prolonged survival. Collectively, these data suggest that ascorbate could be effective in the treatment of glycolysis-dependent tumors. Also, in cancers that use alternative energy metabolism pathways, combining a PARP inhibitor with ascorbate treatment could be useful.

Iron granules in plasma cells

Resistance of cancer cells to chemotherapy is the first cause of cancer-associated death. Thus, new strategies to deal with the evasion of drug response and to improve clinical outcomes are needed. Genetic and epigenetic mechanisms associated with uncontrolled cell growth result in metabolism reprogramming. Cancer cells enhance anabolic pathways and acquire the ability to use different carbon sources besides glucose. An oxygen and nutrient-poor tumor microenvironment determines metabolic interactions among normal cells, cancer cells and the immune system giving rise to metabolically heterogeneous tumors which will partially respond to metabolic therapy. Here we go into the best-known cancer metabolic profiles and discuss several studies that reported tumors sensitization to chemotherapy by modulating metabolic pathways. Uncovering metabolic dependencies across different chemotherapy treatments could help to rationalize the use of metabolic modulators to overcome therapy resistance.