Lysosomes as Oxidative Targets for Cancer Therapy

Iron Promotes Dihydroartemisinin Cytotoxicity via ROS Production and Blockade of Autophagic Flux via Lysosomal Damage in Osteosarcoma

Osteosarcoma cellular iron concentration is higher than that in normal bone cells and other cell types. High levels of cellular iron help catalyze the Fenton reaction to produce reactive oxygen species (ROS), which promotes cancer cell proliferation. Dihydroartemisinin (DHA), a classic anti-malarial drug, kills plasmodium through iron-dependent ROS generation. In this research, we observed the anti-osteosarcoma effects and mechanisms of DHA. We found that DHA induced ROS production, caused mitochondrial damage, and activated autophagy via stimulation of the ROS/Erk1/2 pathway. As the storage site for a pool of ferrous iron, lysosomes are often the key organelles affected by drugs targeting iron. In this study, we observed that DHA induced lysosomal superoxide production, leading lysosomal membrane permeabilization (LMP), and autophagic flux blockage. By reducing or increasing cellular iron using deferoxamine (DFO) or ferric ammonium citrate (FAC), respectively, we found that DHA inhibited osteosarcoma in an iron-dependent manner. Therefore, iron may be a potential adjuvant for DHA in osteosarcoma treatment.

Arylquin 1, a potent Par-4 secretagogue, induces lysosomal membrane permeabilization-mediated non-apoptotic cell death in cancer cells

Arylquin 1, a small-molecule prostate-apoptosis-response-4 (Par-4) secretagogue, targets vimentin to induce Par-4 secretion. Secreted Par-4 binds to its receptor, 78-kDa glucose-regulated protein (GRP78), on the cancer cell surface and induces apoptosis. In the present study, we investigated the molecular mechanisms of arylquin 1 in cancer cell death. Arylquin 1 induces morphological changes (cell body shrinkage and cell detachment) and decreases cell viability in various cancer cells. Arylquin 1-induced cell death is not inhibited by apoptosis inhibitors (z-VAD-fmk, a pan-caspase inhibitor), necroptosis inhibitors (necrostatin-1), and paraptosis inhibitors. Furthermore, arylquin 1 significantly induces reactive oxygen species levels, but antioxidants [N-acetyl-l-cysteine and glutathione ethyl ester] do not inhibit arylquin 1-induced cell death. Furthermore, Par-4 knock-down by small interfering RNA confers no effect on cytotoxicity in arylquin 1-treated cells. Interestingly, arylquin 1 induces lysosomal membrane permeabilization (LMP), and cathepsin inhibitors and overexpression of 70-kDa heat shock protein (HSP70) markedly prevent arylquin 1-induced cell death. Therefore, our results suggest that arylquin 1 induces non-apoptotic cell death in cancer cells through the induction of LMP.

Targeting Super-Enhancers via Nanoparticle-Facilitated BRD4 and CDK7 Inhibitors Synergistically Suppresses Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignant cancer with complex genomic variations, and no targetable genomic lesions have been found yet. Super-enhancers (SEs) have been found to contribute to the continuous and robust oncogenic transcription. Here, histone H3 lysine 27 acetylation (H3K27ac) is profiled in PDAC cell lines to establish SE landscapes. Concurrently, it is also shown that PDAC is vulnerable to the perturbation of the SE complex using bromodomain-containing protein 4 (BRD4) inhibitor, JQ1, synergized with cyclin-dependent kinase 7 (CDK7) inhibitor, THZ1. Formulations of hydrophobic l-phenylalanine-poly (ester amide) nanoparticles (NPs) with high drug loading of JQ1 and THZ1 (J/T@8P4s) are further designed and developed. J/T@8P4s is assessed for size, encapsulation efficiency, morphology, drug release profiles, and drug uptake in vitro. Compared to conventional free drug formulation, the nanodelivery system dramatically reduces the hepatotoxicity while significantly enhancing the tumor inhibition effects and the bioavailability of incorporated JQ1 and THZ1 at equal doses in a Gemcitabine-resistant PDAC patient-derived xenograft (PDX) model. Overall, the present study demonstrates that the J/T@8P4s can be a promising therapeutic treatment against the PDAC via suppression of SE-associated oncogenic transcription, and provides a strategy utilizing NPs to assist the drug delivery targeting SEs.

Deferasirox protects against hydrogen peroxide-induced cell apoptosis by inhibiting ubiquitination and degradation of p21WAF1/CIP1

Deferasirox (DFX) is an iron chelator approved for the treatment of iron overload diseases. However, the role of DFX in oxidative stress-induced cell apoptosis and the exact molecular mechanisms underlying these processes remain poorly understood and require further investigation. In this study, we found that DFX rendered resistant to H₂O₂-induced apoptosis in HEK293T cells, reduced the intracellular levels of the labile iron pool (LIP) and oxidative stress induced by H₂O₂. Furthermore, DFX inhibited the ubiquitination and degradation of the cyclin-dependent kinase inhibitor p21^WAF1/CIP1 (p21) via modulation of the interaction of p21 with SCF-Skp2. DFX also showed the inhibition effect on the activation of c-Jun N-terminal kinase (JNK), pro-caspase-3 and related mitochondrial apoptosis pathway induced by H₂O₂. These results provide novel insights into the molecular mechanism underpinning iron-mediated oxidative stress and apoptosis, and they may represent a promising target for therapeutic interventions in related pathological conditions.

In vitro cytogenotoxic evaluation of sertraline

Sertraline (SRT) is an antidepressant agent used as a neuronal selective serotonin-reuptake inhibitor (SSRI). SRT blocks serotonin reuptake and increases serotonin stimulation of somatodendritic serotonin 1A receptor (5-HT1AR) and terminal autoreceptors in the brain. In the present study, the genotoxic potential of SRT was evaluated using cytokinesis-block micronucleus (CBMN) cytome assay in peripheral blood lymphocytes of healthy human subjects. DNA cleavage-protective effects of SRT were analyzed on plasmid pBR322. In addition, biochemical parameters of total oxidant status (TOS) and total antioxidant status (TAS) in blood plasma were measured to quantitate oxidative stress. Human peripheral blood lymphocytes were exposed to four different concentrations (1.25, 2.5, 3.75 and 5 μg/mL) of SRT for 24- or 48-h treatment periods. In this study, SRT was not found to induce MN formation either in 24- or 48-h treatment periods. In contrast, SRT concentration-dependently decreased the percentage of MN and MNBN (r=-0.979, p<0.01; r=-0.930, p<0.05, respectively) when it was present for the last 48 hr (48-h treatment) of the culture period. SRT neither demonstrated a cleavage activity on plasmid DNA nor conferred DNA protection against H₂O₂. The application of various concentrations of SRT significantly increased the TOS and oxidative stress index (OSI) in human peripheral blood lymphocytes for both the 24- and 48-h treatment periods. Morover, the increase in TOS was potent as the positive control MMC at both treatment times. However, SRT did not alter the TAS levels in either 24- or 48-h treatment periods when compared to control. In addition, exposing cells to SRT caused significant decreases in the nuclear division index at 1.25, 2.50 and 3.75 μg/mL in the 24-h and at the highest concentration (5 μg/mL) in the 48-h treatment periods. Our results suggest that SRT may have cytotoxic effect via oxidative stress on cultured human peripheral blood lymphocytes.

Design, Synthesis, and Characterization of Bis(7-(N-(2-morpholinoethyl)sulfamoyl)benzo[c][1,2,5]oxadiazol-5-yl)sulfane for Nonprotein Thiol Imaging in Lysosomes in Live Cells

Thiols are critical to cellular structures and functions. Disturbance of cellular thiols has been found to affect cell functions and cause various diseases. Intracellularly, thiols were found unevenly distributed in subcellular organelles. Probes capable of detecting subcellular thiol density in live cells are valuable tools in determining thiols' roles at the subcellular level. The subcellular organelle lysosome is the place where unwanted macromolecules are removed through degradation by hydrolytic enzymes. The degradation also serves as a regulation of a variety of cellular functions such as autophagy, endocytosis, and phagocytosis to maintain cellular homeostasis. Thiols are found to be involved in the lysosomal degradation process. A probe that can detect lysosomal thiols in live cells will be a valuable tool in unveiling the roles of thiols in lysosomes. We would like to report bis(7-(N-(2-morpholinoethyl)sulfamoyl)benzo[c][1,2,5]-oxadiazol-5-yl)sulfane (BISMORX) as a thiol specific fluorogenic agent for live cell nonprotein thiol (NPSH) imaging in lysosomes through fluorescence microscopy. BISMORX itself shows no fluorescence and reacts readily with a NPSH to form a fluorescent thiol adduct with excitation and emission wavelengths of 380 and 540 nm, respectively. BISMORX does not react with compounds containing nucleophilic functional groups other than thiols such as -OH, -NH₂, and -COOH. No reaction was observed either when BISMORX was mixed with protein thiols. BISMORX was able to image, quantify, and detect the change of NPSH in lysosomes in live cells. A colocalization experiment with LysoTracker Red DND-99 confirmed that the thiols imaged by BISMORX were indeed lysosomal thiols.

Dual lysosomal-mitochondrial targeting by antihistamines to eradicate leukaemic cells

Background

Despite great efforts to identify druggable molecular targets for AML, there remains an unmet need for more effective therapies.

Methods

An in silico screening was performed using Connectivity Maps to identify FDA-approved drugs that may revert an early leukaemic transformation gene signature. Hit compounds were validated in AML cell lines. Cytotoxic effects were assessed both in primary AML patient samples and healthy donor blood cells. Xenotransplantation assays were undertaken to determine the effect on engraftment of hit compounds. The mechanism of action responsible for the antileukaemic effect was studied focussing on lysosomes and mitochondria.

Findings

We identified a group of antihistamines (termed ANHAs) with distinct physicochemical properties associated with their cationic-amphiphilic nature, that selectively killed leukaemic cells. ANHAs behaved as antileukaemic agents against primary AML samples ex vivo, sparing healthy cells. Moreover, ANHAs severely impaired the in vivo leukaemia regeneration capacity. ANHAs' cytotoxicity relied on simultaneous mitochondrial and lysosomal disruption and induction of autophagy and apoptosis. The pharmacological effect was exerted based on their physicochemical properties that permitted the passive targeting of both organelles, without the involvement of active molecular recognition.

Interpretation

Dual targeting of lysosomes and mitochondria constitutes a new promising therapeutic approach for leukaemia treatment, supporting the further clinical development.

Fund

This work was funded by the Fundación Mutua Madrileña (RMR), CaixaImpulse (RMR), the Spanish Ministry of Economy (RMR), the Josep Carreras International Leukaemia Foundation (RMR), l'Obra Social “La Caixa” (RMR), and Generalitat de Catalunya (IJC).

Thiol-specific fluorogenic agent for live cell non-protein thiol imaging in lysosomes

Thiol molecules play a significant role in cellular structures and functions. These molecules are distributed in cells unevenly at the subcellular level. Disturbance of cellular thiols has been associated with various diseases and disorders. Probes that are able to detect subcellular thiol density in live cells are valuable tools in determining thiols' roles at the subcellular level. Lysosomes are a subcellular organelle involved in the degradation of macromolecules through the action of proteolytic enzymes. The degradation not only serves as a way to dispose of unwanted macromolecules but also a way to regulate a variety of cellular functions such as autophagy, endocytosis, and phagocytosis to maintain cell homeostasis. A probe that can detect lysosomal thiols in live cells will be useful in unveiling the roles of thiols in lysosomes. Currently, limited probes are available to detect lysosomal thiols in live cells. We would like to report 4,4'-{[7,7'-thiobis(benzo[c][1,2,5]oxadiazole-4,4'-sulfonyl)]bis(oxy))bis(naphthalene-2,7-disulfonicacid) (TBONES) as a thiol-specific fluorogenic agent for lysosomal thiol imaging in live cells through fluorescence microscopy. TBONES exhibits no fluorescence and readily reacts with non-protein thiols to form fluorescent thiol adducts with λ_ex = 400 nm and λ_em = 540 nm. No reaction was observed when TBONES was mixed with compounds containing nucleophilic functional groups other than thiols such as -OH, -NH₂, and -COOH. No reaction was observed either when TBONES was mixed with protein thiols. When incubated with cells, TBONES selectively and effectively imaged lysosomal thiols in live cells. Imaging of lysosomal thiols was confirmed by a co-localization experiment with LysoTracker™ Blue DND-22.

Lysosomal dysfunction disturbs porcine oocyte maturation and developmental capacity by disorganizing chromosome/cytoskeleton and activating autophagy/apoptosis

Lysosome, an important organelle in eukaryotes, can sequester macromolecules submitted by the endocytosis and autophagy pathways for degradation and recycling. Massive macromolecular turnover is also vital to the growth and development of mammalian oocytes. However, the functional role of lysosomes in the meiotic maturation of mammalian oocytes remains largely unexplored. Here, by treating in vitro matured porcine cumulus-oocyte complexes (COCs) with chloroquine (CQ), a lysosome inhibitor, we showed that regardless of CQ concentration, lysosomal inhibition affected neither the extrusion of the first polar body (PB1), nor the ROS levels. However, CQ treatment dramatically decreased the rates of oocytes with normal chromosome alignment and cytoskeleton organization (P < 0.05), but boosted the rates of oocytes with apoptosis (P < 0.05). Subsequently, after pathenogenetic activation or in vitro fertilization, the death or fragmentation rates of oocytes treated by CQ (both 35 μM and 45 μM) were significantly higher (P < 0.05), whereas the rates of embryo cleavage, embryos developed to blastocysts, and average blastomere number per blastocyst, were all significantly lower (P < 0.05), respectively. Furthermore, CQ (35 μM) treatment activated the autophagy pathway by elevating the LC3 II/I ratio. Taken together, lysosomes could affect porcine oocyte maturation and subsequent developmental capacity partially through the chromosome organization/cytoskeleton assembly and autophagy/apoptosis pathways.

The Role of Cysteine Cathepsins in Cancer Progression and Drug Resistance

Cysteine cathepsins are lysosomal enzymes belonging to the papain family. Their expression is misregulated in a wide variety of tumors, and ample data prove their involvement in cancer progression, angiogenesis, metastasis, and in the occurrence of drug resistance. However, while their overexpression is usually associated with highly aggressive tumor phenotypes, their mechanistic role in cancer progression is still to be determined to develop new therapeutic strategies. In this review, we highlight the literature related to the role of the cysteine cathepsins in cancer biology, with particular emphasis on their input into tumor biology.

Lysosome Inhibition by Mefloquine Preferentially Enhances the Cytotoxic Effects of Tyrosine Kinase Inhibitors in Blast Phase Chronic Myeloid Leukemia

Despite the efficacy of BCR-ABL tyrosine kinase inhibitors (TKIs) in chronic phase-chronic myeloid leukemia, the management of blast phase-chronic myeloid leukemia (BP-CML) remains a challenge. Therefore, there is an urgent need to identify alternative agents that act synergistically with BCR-ABL TKIs in BP-CML. Our results show that the anti-malarial agent, mefloquine augments the efficacy of TKIs in CML cell lines and primary CML cells in vitro, including those with the T315I mutation. This effect is selective as mefloquine is more effective in inducing apoptosis, inhibiting colony formation and self-renewal capacity of CD34⁺ cells derived from TKI-resistant BP-CML patients than normal cord blood (CB) CD34⁺ stem/progenitor cells. Notably, the combination of mefloquine and TKIs at sublethal concentrations leads to synergistic effects in CML CD34⁺ cells, while sparing normal CB CD34⁺ cells. We further demonstrate that the initial action of mefloquine in CML cells is to increase lysosomal biogenesis and activation, followed by oxidative stress, lysosomal lipid damage and functional impairment. Taken together, our work elucidates that mefloquine selectively augments the effects of TKIs in CML stem/progenitor cells by inducing lysosomal dysfunction.

'Patchiness' and basic cancer research: unravelling the proteases

The recent developments in Cathepsin protease research have unveiled a number of key observations which are fundamental to further our understanding of normal cellular homeostasis and disease. By far, the most interesting and promising area of Cathepsin biology stems from how these proteins are linked to the fate of living cells through the phenomenon of Lysosomal Leakage and Lysosomal Membrane Permeabilisation. While extracellular Cathepsins are generally believed to be of central importance in tumour progression, through their ability to modulate the architecture of the Extracellular Matrix, intracellular Cathepsins have been established as being of extreme significance in mediating cell death through Apoptosis. With these two juxtaposed key research areas in mind, the focus of this review highlights recent advancements in how this fast-paced area of Cathepsin research has recently evolved in the context of their mechanistic regulation in cancer research. Abbreviations : ECM, Extracellular Matrix; MMP, Matrix Metalloproteases; LL, Lysosomal Leakage; LMP, Lysosomal Membrane Permeabilisation; LMA, Lysosomorphic Agents; BC, Breast Cancer; ASM, Acid Sphingomyelinase; TNF-α, Tumor Necrosis Factor-alpha; LAMP, Lysosomal Associated membrane Protein; PCD, Programmed Cell Death; PDAC, Pancreatic Ductal Adenocarcinoma; ROS, Reactive Oxygen Species; aa, amino acids.

Membrane Lipid Composition: Effect on Membrane and Organelle Structure, Function and Compartmentalization and Therapeutic Avenues

Biological membranes are key elements for the maintenance of cell architecture and physiology. Beyond a pure barrier separating the inner space of the cell from the outer, the plasma membrane is a scaffold and player in cell-to-cell communication and the initiation of intracellular signals among other functions. Critical to this function is the plasma membrane compartmentalization in lipid microdomains that control the localization and productive interactions of proteins involved in cell signal propagation. In addition, cells are divided into compartments limited by other membranes whose integrity and homeostasis are finely controlled, and which determine the identity and function of the different organelles. Here, we review current knowledge on membrane lipid composition in the plasma membrane and endomembrane compartments, emphasizing its role in sustaining organelle structure and function. The correct composition and structure of cell membranes define key pathophysiological aspects of cells. Therefore, we explore the therapeutic potential of manipulating membrane lipid composition with approaches like membrane lipid therapy, aiming to normalize cell functions through the modification of membrane lipid bilayers.

Targeting prostate cancer cell proliferation, stemness and metastatic potential using Costus speciosus derived phytochemicals

Prostate cancer is still at the forefront causes of cancer-related morbidity and mortality in men throughout the globe. The disease is initiated and fostered by a subset of cancer stem cells (CSCs). Costus speciosus is an oriental herb used in traditional medicine and is a source of bioactive compounds with known pharmacological activities. The present study aims to evaluate the anticancer property of varied extracts isolated from C. speciosus against the human prostate cancer PC-3 cells. Extracts derived from C. speciosus were analyzed by chromatography-mass spectrometry and their effects on the proliferation, migration, invasion, apoptosis and cell cycle distribution of PC-3 cells were investigated. Results showed that crude hexane extract of C. speciosus (CHECS) inhibited proliferation, clonogenic and metastatic potential of PC-3 cells. It induced apoptosis in PC-3 cells associated with generation of reactive oxygen species (ROS), reduction of GSH and permeabilization of mitochondrial and lysosomal membranes, induction of caspase-9/-3 activity and PARP-1 cleavage, DNA damage and an increase in ratio of Bax/Bcl-2 proteins. CHECS induced G0/G1 and G2/M arrest in PC-3 cells and targeted PC-3 prostaspheres. These findings indicate that phytochemicals of CHECS exhibit potential for natural therapeutic product development for prostate cancer.

Iron metabolism and its contribution to cancer (Review)

Iron is an essential element for biological processes. Iron homeostasis is regulated through several mechanisms, from absorption by enterocytes to recycling by macrophages and storage in hepatocytes. Iron has dual properties, which may facilitate tumor growth or cell death. Cancer cells exhibit an increased dependence on iron compared with normal cells. Macrophages potentially deliver iron to cancer cells, resulting in tumor promotion. Mitochondria utilize cellular iron to synthesize cofactors, including heme and iron sulfur clusters. The latter is composed of essential enzymes involved in DNA synthesis and repair, oxidation‑reduction reactions, and other cellular processes. However, highly increased iron concentrations result in cell death through membrane lipid peroxidation, termed ferroptosis. Ferroptosis, an emerging pathway for cancer treatment, is similar to pyroptosis, apoptosis and necroptosis. In the present review, previous studies on the physiology of iron metabolism and its role in cancer are summarized. Additionally, the significance of iron regulation, and the association between iron homeostasis and carcinogenic mechanisms are discussed.

Co-expression of HIF-1α, MDR1 and LAPTM4B in peripheral blood of solid tumors

The hypoxic tumor microenvironment is the major contributor of chemotherapy resistance in solid tumors. One of the key regulators of hypoxic responses within the cell is the hypoxia inducible factor-1α (HIF-1α) that is involved in transcription of genes promoting cell survival and chemotherapy resistance. Multidrug resistance gene-1 (MDR1) and Lysosome-associated protein transmembrane 4B-35 (LAPTM4B-35) are among those notable players which augment their responses to cellular hypoxia. MDR1 is the hypoxia responsive gene involved in multidrug resistance phenotype while LAPTM4B-35 is involved in chemotherapy resistance by stabilizing HIF-1α and overexpressing MDR1. Overexpression of HIF-1α, MDR1 and LAPTM4B has been associated with poor disease outcome in many cancers when studied individually at tissue level. However, accessibility of the tissues following the course of chemotherapy for ascertaining chemotherapy resistance is difficult and sometimes not clinically feasible. Therefore, indication of hypoxic biomarkers in patient’s blood can significantly alter the clinical outcome. Hence there is a need to identify a blood based marker to understand the disease progression. In the current study the expression of hypoxia associated chemotherapy resistance genes were studied in the peripheral blood lymphocytes of solid tumor patients and any potential correlation with disease progression were explored. The expression of HIF-1α, MDR1 and LAPTM4B was studied in blood of 72 breast, 42 ovarian, 32 colon and 21 prostate cancer patients through real time PCR analysis using delta cycle threshold method. The statistical scrutiny was executed through Fisher’s Exact test and the Spearman correlation method. There was 12–13 fold increased in expression of HIF-1α, two fold increased in MDR1 and 13–14 fold increased in LAPTM4B mRNA level in peripheral blood of breast, ovarian, prostate and colon cancer patients. In the current study there was an association of HIF-1α, MDR1 and LAPTM4B expression with advanced tumor stage, metastasis and chemotherapy treated group in breast, ovarian, prostate and colon cancer patients. The Spearman analysis also revealed a positive linear association among HIF-1α, MDR1 and LAPTM4B in all the studied cancer patients. The elevated expression of HIF-1α, MDR1 and LAPTM4B in peripheral blood of solid tumor patients can be a predictor of metastasis, disease progression and treatment response in these cancers. However, larger studies are needed to further strengthen their role as a potential biomarker for cancer prognosis.

Mobilization of iron from ferritin: new steps and details

Much evidence indicates that iron stored in ferritin is mobilized through protein degradation in lysosomes, but concerns about this process have lingered, and the mechanistic details of its aspects are lacking. In the studies presented here, ⁵⁹Fe-labeled ferritin was induced by preloading hepatic (HepG2) cells with radiolabeled Fe. Placing these cells in a medium containing desferrioxamine resulted in the loss of ferritin-⁵⁹Fe, but adding high concentrations of reducing agents or modulating the internal GSH concentration failed to alter the rates of ferritin-⁵⁹Fe release. Confocal microscopy showed that Fe deprivation increased the movement of ferritin into lysosomes and hyperaccumulation was observed when lysosomal proteolysis was inhibited. It also resulted in the rapid movement of DMT1 to lysosomes, which was inhibited by bafilomycin. Ferrihydrite crystals isolated from purified rat liver/spleen ferritin were solubilized at pH 5 and 7 by GSH, ascorbate, citrate and lysosomal fluids obtained from livers and J774a.1 macrophages. The inhibition of DMT1/Nramp2 and siRNA knockdown of Nramp1 each reduced the transfer of ⁵⁹Fe from lysosomes to the cytosol; and hepatocyte-specific knockout of DMT1 in mice prevented the release of Fe from the liver responding to EPO treatment, but did not inhibit lysosomal ferritin degradation. We conclude that ferritin-Fe mobilization does not occur through changes in cellular concentrations of reducing/chelating agents but by the coordinated movement of ferritin and DMT1 to lysosomes, where the ferrihydrite crystals exposed by ferritin degradation dissolve in the lysosomal fluid, and the reduced iron is transported back to the cytosol via DMT1 in hepatocytes, and by both DMT1 and Nramp1 in macrophages, prior to release into the blood or storage in ferritin.

Gambogic acid induces autophagy and combines synergistically with chloroquine to suppress pancreatic cancer by increasing the accumulation of reactive oxygen species

Background

Gambogic acid is a natural component isolated from gamboge that possesses anticancer properties. Our previous study suggested that gambogic acid might be involved in autophagy; however, its role in pancreatic cancer remained unclear.

Methods

Cell viability and apoptosis of pancreatic cancer cell lines were determined using (4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan and flow cytometry. The effects of gambogic acid on autophagy was assessed by western blot, acridine orange staining, transmission electron microscopy, and measurement of autophagic flux through RFP-GFP-LC3 lentiviral transfection. The mitochondrial membrane potential was assessed by JC-1 staining. The production of reactive oxygen species was measured using CM-H2DCFDA staining. A xenograft tumor model of pancreatic cancer was created to determine the efficacy of gambogic acid and chloroquine.

Results

Gambogic acid induced the expression of LC3-II and Beclin-1 proteins in pancreatic cancer cells, whereas the expression of P62 showed a decline. Gambogic acid also increased the formation of both acidic vesicular organelles and autophagosomes, and increased autophagic flux. These findings indicated that gambogic acid induced the autophagic process. Furthermore, inhibition of autophagy by chloroquine or 3-methyladenine, or knockdown of Atg-7 all enhanced the cytotoxicity of gambogic acid, suggesting that gambogic acid-induced autophagy improves the survival of pancreatic cancer cells. Moreover, gambogic acid reduced the mitochondrial membrane potential and promoted ROS production, which contributed to the activation of autophagy. The inhibition of autophagy by chloroquine further reduced the mitochondrial membrane potential and increased the accumulation of ROS. This indicated that the inhibition of autophagy could mitigate the cellular protective effects induced by gambogic acid. The treatment combination of gambogic acid and chloroquine synergistically inhibited tumor growth in the xenograft tumor model.

Conclusions

These results demonstrate that gambogic acid induces cytoprotective autophagy in pancreatic cancer cells. The inhibition of autophagy promotes the cytotoxicity of gambogic acid by increasing the accumulation of ROS in pancreatic cancer cells. Combining chloroquine and gambogic acid may be a promising treatment for pancreatic cancer.

Electronic supplementary material

The online version of this article (10.1186/s12935-018-0705-x) contains supplementary material, which is available to authorized users.

Tubeimoside I induces accumulation of impaired autophagolysosome against cervical cancer cells by both initiating autophagy and inhibiting lysosomal function

Cervical cancer is one of the most aggressive human cancers with poor prognosis due to constant chemoresistance and repeated relapse. Tubeimoside I (TBM) has been identified as a potent antitumor agent that inhibits cancer cell proliferation by triggering apoptosis and inducing cell cycle arrest. Nevertheless, the detailed mechanism remains unclear and needs to be further elucidated, especially in cervical cancer. In this study, we found that TBM could induce proliferation inhibition and cell death in cervical cancer cells both in vitro and in vivo. Further results demonstrated that treatment with TBM could induce autophagosome accumulation, which was important to TBM against cervical cancer cells. Mechanism studies showed that TBM increased autophagosome by two pathways: First, TBM could initiate autophagy by activating AMPK that would lead to stabilization of the Beclin1-Vps34 complex via dissociating Bcl-2 from Beclin1; Second, TBM could impair lysosomal cathepsin activity and block autophagic flux, leading to accumulation of impaired autophagolysosomes. In line with this, inhibition of autophagy initiation attenuated TBM-induced cell death, whereas autophagic flux inhibition could exacerbated the cytotoxic activity of TBM in cervical cancer cells. Strikingly, as a novel lethal impaired autophagolysosome inducer, TBM might enhance the therapeutic effects of chemotherapeutic drugs towards cervical cancer, such as cisplatin and paclitaxel. Together, our study provides new insights into the molecular mechanisms of TBM in the antitumor therapy, and establishes potential applications of TBM for cervical cancer treatment in clinic.

Genomic landscape and mutational impacts of recurrently mutated genes in cancers

BACKGROUND

Cancer genes tend to be highly mutated under positive selection. Better understanding the recurrently mutated genes (RMGs) in cancer is critical for explicating the mechanisms of tumorigenesis and providing vital clues for therapy. Although some studies have investigated functional impacts of RMGs in specific cancer types, a comprehensive analysis of RMGs and their mutational impacts across cancers is still needed.

METHODS

We obtained data from The Cancer Genome Atlas (TCGA) and calculated mutation rate of each gene in 31 cancer types. Functional analysis was performed to identify the important signaling pathways and enriched protein types of RMGs. In order to evaluate functional impacts of RMGs, differential expression, survival, and pairwise mutation patterns analyses were performed.

RESULTS

Totally, we identified 897 RMGs and 624 of them were specifically mutant in only a single cancer type. Functional analysis demonstrated that these RMGs were enriched in hydrolases, cytoskeletal protein, and pathways like MAPK, cell cycle, PI3K-Akt, ECM receptor interaction, and energy metabolism. The differentially expressed genes potentially affected by the same common RMG showed a relatively low overlap across different cancer types. For the 19 Mucin (MUC) family genes, nine of them were RMGs and four of them (MUC17, MUC5B, MUC4, and MUC16) were common RMGs shared in 8 to 17 cancer types. The results showed that recurrent mutations in MUC genes were significantly associated with better survival prognosis. Only a small part of RMGs was differentially expressed due to their own mutations and most of them were downregulated. In addition, pairwise mutation pattern analysis revealed the high frequency of co-occurred mutations among RMGs in STAD.

CONCLUSION

Through the functional analysis of RMGs, we found that six signaling pathways were disrupted in most cancer types and that energy metabolism was abnormal in tumors. The results also revealed a strong correlation between recurrently mutated genes from MUC family and human survival. In addition, gene expression and survival prognosis were associated with different mutation types of RMGs.

Antimalarial drugs trigger lysosome-mediated cell death in chronic lymphocytic leukemia (CLL) cells

Lysosomes are the most acidic vesicles within mammalian cells and are promising targets for the treatment of breast cancer, glioblastomas and acute myeloid leukemia (AML). Our previous studies have shown that chronic lymphocytic leukemia (CLL) cells are also sensitive to lysosome disruption and cell death, by siramesine or chemotherapy. In the present study, we screened the antimalarial drugs, mefloquine, atovaquone, primaquine, and tafenoquine, for their effects on lysosome disruption and cytotoxicity in primary CLL cells. We found that mefloquine and tafenoquine could permeabilize lysosome membranes and induce cell death at doses that are clinically achievable. In contrast, these agents had less effect on normal B cells. Tafenoquine was most effective at inducing cell death, and this was associated with increased formation of reactive oxygen species (ROS) and lipid peroxidation. Addition of ROS scavengers blocked both tafenoquine- and mefloquine-induced cell death. Moreover, blocking the activity of cathepsins released from the lysosomes decreased tafenoquine-induced cell death. Taken together, lysosome disruption using antimalarial drugs is a novel approach for the treatment of CLL.

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field.

Monitoring of hydrogen peroxide production under photodynamic treatment using protein sensor HyPer

An interest to H₂O₂ accumulation under photodynamic treatment can be explained by its participation in intracellular signal cascades. It is important not only to detect H₂O₂ generation, but also to trace the dynamics of its intracellular content. In the present study the dynamics of cellular H₂O₂ content under photodynamic treatment was analyzed using genetically encoded reversible H₂O₂-sensitive sensor HyPer. Real-time detecting of H₂O₂ production after photodynamic treatment was performed using the protein sensor and individual features of action of different photosensitizers were revealed. Photodynamic treatment with a number of chlorin and phthalocyanine photosensitizers was found to induce secondary production of H₂O₂ in the cells. Three types of dynamic responses were registered: monotonous increase of H₂O₂ level during the entire observation time in the presence of Fotoditazin and Holosens; transient short-term accumulation in the presence of Radachlorin and Phthalosens; and relatively low-level stable increase in the presence of Photosens. The listed photosensitizers differ significantly in intracellular localization and physicochemical properties, which can determine the differences in the response of H₂O₂ after the photodynamic treatment. In general, it has been shown that the rapid transient H₂O₂ response is typical for hydrophobic compounds localized in membrane cell structures, whereas in the presence of more hydrophilic dyes a prolonged monotonous H₂O₂ accumulation occurs.