Enhancement of death-receptor induced caspase-8-activation in the death-inducing signalling complex by uncoupling of oxidative phosphorylation

In Vitro and In Silico Evaluation of Syzygium aromaticum Essential Oil: Effects on Mitochondrial Function and Cytotoxic Potential Against Cancer Cells

The current study proposes the in vitro and in silico anticancer evaluation of clove (Syzygium aromaticum L.) essential oil (CEO). The steam hydrodistillation method used yielded 10.7% (wt) CEO. GC-MS analysis revealed that the obtained oil is rich in eugenol (75%), β-caryophyllene (20%), and α- caryophyllene (2.8%) and also contains several other minor components accounting for approximately 1.5%. The DPPH-based scavenging antioxidant activity was assessed for the obtained CEO, exhibiting an IC50 value of 158 μg/mL. The cytotoxic effects of CEO, its major component eugenol, and CEO solubilized with Tween-20 and PEG-400 were tested against both noncancerous HaCaT cells and HT-29 human colorectal adenocarcinoma, RPMI-7951 melanoma, A431 skin carcinoma, and NCI-H460 non-small lung cancer cells, using the Alamar Blue and LDH assay after 48 h treatment. The Tween-20 and PEG-400 CEO formulations, at 200 μg/mL, recorded the highest cytotoxic and selective effects against RPMI-7951 (72.75% and 71.56%), HT-29 (71.51% and 45.43%), and A431 cells (61.62% and 59.65%). Furthermore, CEO disrupted mitochondrial function and uncoupled oxidative phosphorylation. This effect was more potent for the CEO against the RPMI-7951 and HT-29 cells, whereas for the other two tested cell lines, a more potent inhibition of mitochondrial function was attributed to eugenol. The present study is the first to specifically investigate the effects of CEO and Tween-20 and PEG-400 CEO formulations on the mitochondrial function of RPMI-7951, HT-29, A431, and NCI-H460 cancer cell lines using high-resolution respirometry, providing novel insights into their impact on mitochondrial respiration and bioenergetics in cancer cells. The results obtained may explain the increased ROS production observed in cancer cell lines treated with eugenol and CEO. Molecular docking identified potential protein targets, related to the CEO anticancer activity, in the form of PI3Kα, where the highest active theoretical inhibitor was calamenene (-7.5 kcal/mol). Docking results also showed that calamenene was the overall most active theoretical inhibitor for all docked proteins and indicated a potential presence of synergistic effects among all CEO constituents.

Targeting mitochondrial metabolism by the mitotoxin bromoxib in leukemia and lymphoma cells

Targeting mitochondrial metabolism represents a promising approach for cancer treatment. Here, we investigated the mitotoxic potential of the polybrominated diphenyl ether bromoxib, a natural compound isolated from the marine sponge Dysidea family. We could show that bromoxib comprised strong cytotoxicity in different leukemia and lymphoma cell lines (such as HL60, HPBALL, Jurkat, K562, KOPTK1, MOLT4, SUPB15 and Ramos), but also in solid tumor cell lines (such as glioblastoma cell lines SJ-GBM2 and TP365MG). Bromoxib activated the mitochondrial death pathway as evidenced by the rapid translocation of Bax to the mitochondria and the subsequent mitochondrial release of Smac. Accordingly, bromoxib-induced apoptosis was blocked in caspase 9 deficient Jurkat cells and Jurkat cells overexpressing the antiapoptotic protein Bcl-2. In addition, we could show that bromoxib functioned as an uncoupler of the electron transport chain with similar rapid kinetics as CCCP in terms of dissipation of the mitochondrial membrane potential (ΔΨm), processing of the dynamin-like GTPase OPA1 and subsequent fragmentation of mitochondria. Beyond that, bromoxib strongly abrogated ATP production via glycolysis as well as oxidative phosphorylation (OXPHOS) by targeting electron transport chain complexes II, III, and V (ATP-synthase) in Ramos lymphoma cells. Thus, bromoxib's potential to act on both cytosolic glycolysis and mitochondrial respiration renders it a promising agent for the treatment of leukemia and lymphoma.

The potential benefits of dinitrophenol combination with chemotherapy in the treatment of ovarian cancer

BACKGROUND

2,4-dinitrophenol (DNP), an uncoupling mitochondrial agent, has been identified as a source of oxidative stress and linked to the pathogenesis of ovarian cancer. In this study, we determine the cytotoxic effect of DNP alone or in combination with chemotherapies in ovarian cancer cells.

METHODS

We utilized human ovarian cancer cell lines SKOV-3 and MDAH-2774 with their chemoresistant counterparts. Cancer stem cells (CSCs) were isolated from SKOV-3 utilizing magnetic-activated cell sorting technique for CD44+/CD117+ cells. Human normal primary ovarian epithelial (NOEC) and HOSEpiC cell lines were used as a control. Cells were treated with and without chemotherapy (taxotere 0.3 µM or cisplatin 50 µM), with or without increasing doses of DNP (0.125, 0.25, or 0.5 mM) for 24 hours followed by evaluation of cell viability and IC50 utilizing MTT assay. For determination of synergism, Fa-combination Index plots were created using the CompuSyn software (ComboSyn, Inc., Paramus, NJ, USA). All data were run in triplicates and analyzed by t-test.

RESULTS

DNP treatment of ovarian cancer and chemoresistant ovarian cancer cell lines as well as CSCs resulted in decreased cell viability in a dose dependent manner with no effect on normal cells. Combination of DNP with chemotherapy synergistically enhances cytotoxicity of chemotherapeutics in all ovarian cancer cells as compared to chemotherapy alone.

CONCLUSIONS

Our data indicates the potential of the addition of DNP to the arsenal of drugs available to treat ovarian cancer, whether alone or in combination with chemotherapies. The synergistic effects of DNP in reducing the required amount of chemotherapy, is critical for the alleviation of harmful side effects.

Exploring the therapeutic potential of mitochondrial uncouplers in cancer

BACKGROUND

Mitochondrial uncouplers are well-known for their ability to treat a myriad of metabolic diseases, including obesity and fatty liver diseases. However, for many years now, mitochondrial uncouplers have also been evaluated in diverse models of cancer in vitro and in vivo. Furthermore, some mitochondrial uncouplers are now in clinical trials for cancer, although none have yet been approved for the treatment of cancer.

SCOPE OF REVIEW

In this review we summarise published studies in which mitochondrial uncouplers have been investigated as an anti-cancer therapy in preclinical models. In many cases, mitochondrial uncouplers show strong anti-cancer effects both as single agents, and in combination therapies, and some are more toxic to cancer cells than normal cells. Furthermore, the mitochondrial uncoupling mechanism of action in cancer cells has been described in detail, with consistencies and inconsistencies between different structural classes of uncouplers. For example, many mitochondrial uncouplers decrease ATP levels and disrupt key metabolic signalling pathways such as AMPK/mTOR but have different effects on reactive oxygen species (ROS) production. Many of these effects oppose aberrant phenotypes common in cancer cells that ultimately result in cell death. We also highlight several gaps in knowledge that need to be addressed before we have a clear direction and strategy for applying mitochondrial uncouplers as anti-cancer agents.

MAJOR CONCLUSIONS

There is a large body of evidence supporting the therapeutic use of mitochondrial uncouplers to treat cancer. However, the long-term safety of some uncouplers remains in question and it will be critical to identify which patients and cancer types would benefit most from these agents.

Age and sex differences in microRNAs expression during the process of thymus aging

The gender-biased thymus involution and the importance of microRNAs (miRNAs, miRs) expression in modulating the thymus development have been reported in many studies. However, how males and females differ in so many ways in thymus involution remains unclear. To address this question, we investigated the miRNA expression profiles in both untreated 3- and 12-month-old female and male mice thymuses. The results showed that 7 and 18 miRNAs were defined as the sex- and age-specific miRNAs, respectively. The expression of miR-181c-5p, miR-20b-5p, miR-98b-5p, miR-329-3p, miR-341-5p, and miR-2137 showed significant age-difference in mice thymus by quantitative polymerase chain reaction. High expression levels of miR-2137 were detected in mice thymic epithelial cells and gradually increased during the process of thymus aging. MiR-27b-3p and miR-378a-3p of the female-biased miRNAs were confirmed as the sex- and estrogen-responsive miRNAs in mice thymus in vivo. Their potential target genes and the pathway were identified by the online software. Possible regulation roles of sex- and age-specific miRNA expression during the process of thymus aging were discussed. Our results suggested that these miRNAs may be potential biomarkers for the study of sex- and age-specific thymus aging and involution.

Comparative Evaluation of Nimesulide-Loaded Nanoparticles for Anticancer Activity Against Breast Cancer Cells

Recent clinical and epidemiological researches have declared that non-steroidal anti-inflammatory agents may display as antineoplastic agents and indicate pro-apoptotic and antiproliferative effects on cancer cells. The major purpose of this research was to develop a novel poly(ethyleneglycol)-block-poly(ε-caprolactone) (PEG-b-PCL) nano-sized particles encapsulated with nimesulide (NMS), a selective COX-2 inhibitor, and to evaluate its anticancer activity against MCF-7 breast cancer cells. NMS-encapsulated PEG-b-PCL nanoparticles were fabricated using three different production techniques: (i) by emulsion-solvent evaporation using a high shear homogenizer, (ii) by emulsion-solvent evaporation using an ultrasonicator, and (iii) by nanoprecipitation. Nanoparticles were evaluated with respect to the entrapment efficiency, size characteristics, drug release rates, thermal behavior, cell viability assays, and apoptosis. The resulting nanoparticles were found to be spherical shapes with negative surface charges. The average diameter of all nanoparticles ranged between 148.5 and 307.2 nm. In vitro release profiles showed that all nanoparticles exhibited a biphasic release pattern. NMS-loaded PEG-b-PCL nanoparticles demonstrated significant anticancer activity against MCF-7 breast cancer cells in a dose-dependent manner, and the effects of nanoparticles on cell proliferation were significantly affected by the preparation techniques. The nanoparticles developed in this work displayed higher potential for the NMS delivery against breast cancer treatment for the future.

Embelin prevents LMP1-induced TRAIL resistance via inhibition of XIAP in nasopharyngeal carcinoma cells

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selectively induces apoptosis in the majority of tumor cells, whilst sparing normal cells. However, the potential use of TRAIL in the treatment of cancer is limited by the inevitable emergence of drug resistance. The present study reports the upregulation of latent membrane protein 1 (LMP1)-induced TRAIL resistance via the enhanced expression of X-linked inhibitor of apoptosis protein (XIAP) in nasopharyngeal carcinoma (NPC) cells. LMP1-positive NPC cells were indicated to be more sensitive to TRAIL compared with LMP1-negative NPC cells in three NPC cell lines. CNE-1 is a LMP1-negative NPC cell line that was transfected with pGL6-LMP1; following which, sensitivity to TRAIL decreased. LMP1-induced TRAIL resistance was associated with the decreased cleavage of caspase-8,-3 and -9, BH3 interacting domain death agonist (Bid) and mitochondrial depolarization, without any effects on the expression of the death receptors, B-cell lymphoma (Bcl)-2 and Bcl-extra long. Knockdown of XIAP with small interfering RNA increased caspase-3 and -9 and Bid cleavage, and prevented LMP1-induced TRAIL resistance. Furthermore, embelin, the inhibitor of XIAP, prevented LMP1-induced TRAIL resistance in the Epstein-Barr virus (EBV)-positive CNE-1-LMP1 and C666-1 NPC cell lines. However, embelin did not enhance TRAIL-induced apoptosis in NP-69, which was used as a benign nasopharyngeal epithelial cell line. These data show that LMP1 inhibits TRAIL-mediated apoptosis by upregulation of XIAP. Embelin may be used in an efficacious and safe manner to prevent LMP1-induced TRAIL resistance. The present study may have implications for the development and validation of novel strategies to prevent TRAIL resistance in EBV-positive NPC.

Amorfrutin C Induces Apoptosis and Inhibits Proliferation in Colon Cancer Cells through Targeting Mitochondria

A known (1) and a structurally related new natural product (2), both belonging to the amorfrutin benzoic acid class, were isolated from the roots of Glycyrrhiza foetida. Compound 1 (amorfrutin B) is an efficient agonist of the nuclear peroxisome proliferator activated receptor (PPAR) gamma and of other PPAR subtypes. Compound 2 (amorfrutin C) showed comparably lower PPAR activation potential. Amorfrutin C exhibited striking antiproliferative effects for human colorectal cancer cells (HT-29 and T84), prostate cancer (PC-3), and breast cancer (MCF7) cells (IC50 values ranging from 8 to 16 μM in these cancer cell lines). Notably, amorfrutin C (2) showed less potent antiproliferative effects in primary colon cells. For HT-29 cells, compound 2 induced G0/G1 cell cycle arrest and modulated protein expression of key cell cycle modulators. Amorfrutin C further induced apoptotic events in HT-29 cells, including caspase activation, DNA fragmentation, PARP cleavage, phosphatidylserine externalization, and formation of reactive oxygen species. Mechanistic studies revealed that 2 disrupts the mitochondrial integrity by depolarization of the mitochondrial membrane (IC50 0.6 μM) and permanent opening of the mitochondrial permeability transition pore, leading to increased mitochondrial oxygen consumption and extracellular acidification. Structure-activity-relationship experiments revealed the carboxylic acid and the hydroxy group residues of 2 as fundamental structural requirements for inducing these apoptotic effects. Synergy analyses demonstrated stimulation of the death receptor signaling pathway. Taken together, amorfrutin C (2) represents a promising lead for the development of anticancer drugs.

Hydroxycamptothecin-loaded Fe3O4 nanoparticles induce human lung cancer cell apoptosis through caspase-8 pathway activation and disrupt tight junctions

10-Hydroxycamptothecin (HCPT) elicits strong anti-cancer effects and is less toxic than camptothecin (CPT), making it widely used in recent clinical trials. However, its low solubility limits its application as an effective anti-cancer therapy. In the present study we investigate the hypothesis that the unique water dispersible oleic acid-Triton X-100-coated Fe3O4 nanoparticles loaded with HCPT disrupt epithelial cell-cell junctions and induce human lung cancer cell apoptosis through the caspase-8 pathway. We characterized the HCPT-loaded nanoparticles and determined their effects on lung cancer cell viability and apoptosis by using immunofluorescence light microscopy and SDS-PAGE/immunoblots. We found that HCPT-loaded nanoparticles elicited an anti-proliferative effect in a dose-dependent manner. HCPT-loaded nanoparticles reduced the expression of cell-cell junction protein claudins, E-cadherin and ZO-1, and transmission electron microcopy demonstrated a disrupted tight junction ultrastructure. Transepithelial electric resistance was also reduced, indicating the reduction of tight junction functions. The HCPT-loaded nanoparticles increased phosphorylation of p38 and SAPK/JNK while it showed no effects on p42/44 MAP kinase. Compared with void Fe3O4 nanoparticles or HCPT drug alone, HCPT drug-loaded nanoparticles evoked synergistic effects by increasing cell apoptosis with enhanced activation of the caspase-8 pathway. Therefore, our current study highlights the potential of HCPT drug-loaded nanoparticles as a chemotherapeutic agent for increasing anti-cancer drug efficacy.

Transcriptome analysis of murine thymocytes reveals age-associated changes in thymic gene expression

The decline in adaptive immunity, naïve T-cell output and a contraction in the peripheral T cell receptor (TCR) repertoire with age are largely attributable to thymic involution and the loss of critical cytokines and hormones within the thymic microenvironment. To assess the molecular changes associated with this loss of thymic function, we used cDNA microarray analyses to examine the transcriptomes of thymocytes from mice of various ages ranging from very young (1 month) to very old (24 months). Genes associated with various biological and molecular processes including oxidative phosphorylation, T- and B- cell receptor signaling and antigen presentation were observed to significantly change with thymocyte age. These include several immunoglobulin chains, chemokine and ribosomal proteins, annexin A2, vav 1 and several S100 signaling proteins. The increased expression of immunoglobulin genes in aged thymocytes could be attributed to the thymic B cells which were found to be actively producing IgG and IgM antibodies. Upon further examination, we found that purified thymic T cells derived from aged but not young thymi also exhibited IgM on their cell surface suggesting the possible presence of auto-antibodies on the surface thymocytes with advancing age. These studies provide valuable insight into the cellular and molecular mechanisms associated with thymic aging.

Caspase-8 dependent trail-induced apoptosis in cancer cell lines is inhibited by vitamin C and catalase

TNF-related apoptosis-inducing ligand (TRAIL/ Apo-2L) is a member of the TNF family of apoptosis-inducing proteins that initiates apoptosis in a variety of neoplastic cells while displaying minimal or absent cytotoxicity to most normal cells. Therefore, TRAIL is currently considered a promising target to develop anti-cancer therapies. TRAIL-receptor ligation recruits and activates pro-caspase-8, which in turn activates proteins that mediate disruption of the mitochondrial membranes. These events lead to the nuclear and cytosolic damage characteristic of apoptosis. Here we report that TRAIL-induced apoptosis is mediated by oxidative stress and that vitamin C (ascorbic acid), a potent nutritional antioxidant, protects cancer cell lines from apoptosis induced by TRAIL. Vitamin C impedes the elevation of reactive oxygen species (ROS) levels induced by TRAIL and impairs caspase-8 activation. We found that the removal of hydrogen peroxide by extracellular catalase during TRAIL-induced apoptosis also impairs caspase-8 activation. These data suggest that hydrogen peroxide is produced during TRAIL-receptor ligation, and that the increase of intracellular ROS regulates the activation of caspase-8 during apoptosis. Additionally we propose a mechanism by which cancer cells might resist apoptosis via TRAIL, by the intake of the nutritional antioxidant vitamin C.

Vitamin D sensitizes breast cancer cells to the action of H2O2: mitochondria as a convergence point in the death pathway

Calcitriol, the hormonal form of vitamin D3, sensitizes breast cancer cells to reactive oxygen species (ROS)-dependent cytotoxicity induced by various anticancer modalities. This effect could be due to increased generation of ROS and/ or to increased sensitivity of the target cells to ROS. This work examined the effect of calcitriol on the damage inflicted on breast cancer cells by the direct action of ROS represented by H2O2. Treatment of MCF-7 cells with H2O2 resulted in activation of caspase 7 as well as induction of caspase-independent cell death. Both were enhanced by 48-72 h of pretreatment with calcitriol. This effect was not due to modulation of H2O2 degradation or to a specific effect on *OH-mediated cytotoxicity. The H2O2-induced drop in mitochondrial membrane potential and release of cytochrome c were enhanced by calcitriol. These findings indicate that calcitriol sensitizes breast cancer cells to ROS-induced death by affecting event(s) common to both caspase-dependent and -independent modes of cell death upstream to mitochondrial damage.