Mitochondria as targets for cancer chemotherapy

Mitochondrial respiratory chain complexes: apoptosis sensors mutated in cancer?

Mutations in cancer cells affecting subunits of the respiratory chain (RC) indicate a central role of oxidative phosphorylation for tumourigenesis. Recent studies have suggested that such mutations of RC complexes impact apoptosis induction. We review here the evidence for this hypothesis, which in particular emerged from work on how complex I and II mediate signals for apoptosis. Both protein aggregates are specifically inhibited for apoptosis induction through different means by exploiting with protease activation and pH change, two widespread but independent features of dying cells. Nevertheless, both converge on forming reactive oxygen species for the demise of the cell. Investigations into these mitochondrial processes will remain a rewarding area for unravelling the causes of tumourigenesis and for discovering interference options.

Sonodynamic action of pyropheophorbide-a methyl ester induces mitochondrial damage in liver cancer cells

Sonodynamic therapy with pyropheophorbide-a methyl ester (MPPa) presents a promising aspect in treating liver cancer. The present study aims to investigate the mitochondrial damage of liver cancer cells induced by MPPa-mediated sonodynamic action. Mouse hepatoma cell line H(22) cells were incubated with MPPa (2 μM) for 20 h and then exposed to ultrasound with an intensity of 0.97 W/cm(2) for 8 s. Cytotoxicity was investigated 24h after sonodynamic action using MTT assay and light microscopy. Mitochondrial membrane potential (ΔΨm) was analyzed using flow cytometry with rhodamine 123 staining and ultrastructural changes were observed using transmission electron microscopy (TEM). The cytotoxicity of MPPa-mediated SDT on H(22) cell line was 73.00±3.42%, greater than ultrasound treatment alone (28.12±5.19%) significantly while MPPa treatment alone had no significant effect on H(22) cells. Moreover, after MPPa-mediated SDT cancer cells showed swollen mitochondria under TEM and a significant collapse of mitochondrial membrane potential. Our findings demonstrated that MPPa-mediated SDT could remarkably induce cell death of H(22) cells, and highlighted that mitochondrial damage might be an important cause of cell death induced by MPPa-mediated SDT.

Lipophilic caffeic and ferulic acid derivatives presenting cytotoxicity against human breast cancer cells

In the present work, lipophilic caffeic and ferulic acid derivatives were synthesized, and their cytotoxicity on cultured breast cancer cells was compared. A total of six compounds were initially evaluated: caffeic acid (CA), hexyl caffeate (HC), caffeoylhexylamide (HCA), ferulic acid (FA), hexyl ferulate (HF), and feruloylhexylamide (HFA). Cell proliferation, cell cycle progression, and apoptotic signaling were investigated in three human breast cancer cell lines, including estrogen-sensitive (MCF-7) and insensitive (MDA-MB-231 and HS578T). Furthermore, direct mitochondrial effects of parent and modified compounds were investigated by using isolated liver mitochondria. The results indicated that although the parent compounds presented no cytotoxicity, the new compounds inhibited cell proliferation and induced cell cycle alterations and cell death, with a predominant effect on MCF-7 cells. Interestingly, cell cycle data indicates that effects on nontumor BJ fibroblasts were predominantly cytostatic and not cytotoxic. The parent compounds and derivatives also promoted direct alterations on hepatic mitochondrial bioenergetics, although the most unexpected and never before reported one was that FA induces the mitochondrial permeability transition. The results show that the new caffeic and ferulic acid lipophilic derivatives show increased cytotoxicity toward human breast cancer cell lines, although the magnitude and type of effects appear to be dependent on the cell type. Mitochondrial data had no direct correspondence with effects on intact cells suggesting that this organelle may not be a critical component of the cellular effects observed. The data provide a rational approach to the design of effective cytotoxic lipophilic hydroxycinnamic derivatives that in the future could be profitably applied for chemopreventive and/or chemotherapeutic purposes.

Mitochondrial approaches to protect against cardiac ischemia and reperfusion injury

The mitochondrion is a vital component in cellular energy metabolism and intracellular signaling processes. Mitochondria are involved in a myriad of complex signaling cascades regulating cell death vs. survival. Importantly, mitochondrial dysfunction and the resulting oxidative and nitrosative stress are central in the pathogenesis of numerous human maladies including cardiovascular diseases, neurodegenerative diseases, diabetes, and retinal diseases, many of which are related. This review will examine the emerging understanding of the role of mitochondria in the etiology and progression of cardiovascular diseases and will explore potential therapeutic benefits of targeting the organelle in attenuating the disease process. Indeed, recent advances in mitochondrial biology have led to selective targeting of drugs designed to modulate or manipulate mitochondrial function, to the use of light therapy directed to the mitochondrial function, and to modification of the mitochondrial genome for potential therapeutic benefit. The approach to rationally treat mitochondrial dysfunction could lead to more effective interventions in cardiovascular diseases that to date have remained elusive. The central premise of this review is that if mitochondrial abnormalities contribute to the etiology of cardiovascular diseases (e.g., ischemic heart disease), alleviating the mitochondrial dysfunction will contribute to mitigating the severity or progression of the disease. To this end, this review will provide an overview of our current understanding of mitochondria function in cardiovascular diseases as well as the potential role for targeting mitochondria with potential drugs or other interventions that lead to protection against cell injury.

Radiation response and regulation of apoptosis induced by a combination of TRAIL and CHX in cells lacking mitochondrial DNA: a role for NF-κB-STAT3-directed gene expression

Mitochondrial DNA depleted (ρ(0)) human skin fibroblasts (HSF) with suppressed oxidative phosphorylation were characterized by significant changes in the expression of 2100 nuclear genes, encoding numerous protein classes, in NF-κB and STAT3 signaling pathways, and by decreased activity of mitochondrial death pathway, compared to the parental ρ(+) HSF. In contrast, the extrinsic TRAIL/TRAIL-Receptor mediated death pathway remained highly active, and exogenous TRAIL in a combination with cycloheximide (CHX) induced higher levels of apoptosis in ρ(0) cells compared to ρ(+) HSF. Global gene expression analysis using microarray and qRT-PCR demonstrated that mRNA expression levels of many growth factors and their adaptor proteins (FGF13, HGF, IGFBP4, IGFBP6, and IGFL2), cytokines (IL6, ΙL17Β, ΙL18, ΙL19, and ΙL28Β) and cytokine receptors (IL1R1, IL21R, and IL31RA) were substantially decreased after mitochondrial DNA depletion. Some of these genes were targets of NF-κB and STAT3, and their protein products could regulate the STAT3 signaling pathway. Alpha-irradiation further induced expression of several NF-κB/STAT3 target genes, including IL1A, IL1B, IL6, PTGS2/COX2 and MMP12, in ρ(+) HSF, but this response was substantially decreased in ρ(0) HSF. Suppression of the IKK-NF-κB pathway by the small molecular inhibitor BMS-345541 and of the JAK2-STAT3 pathway by AG490 dramatically increased TRAIL-induced apoptosis in the control and irradiated ρ(+) HSF. Inhibitory antibodies against IL6, the main activator of JAK2-STAT3 pathway, added into the cell media, also increased TRAIL-induced apoptosis in HSF, especially after alpha-irradiation. Collectively, our results indicated that NF-κB activation was partially lost in ρ(0) HSF resulting in downregulation of the basal or radiation-induced expression of numerous NF-κB targets, further suppressing IL6-JAK2-STAT3 that in concert with NF-κB regulated protection against TRAIL-induced apoptosis.

Respiratory competent mitochondria in human ovarian and peritoneal cancer

Impaired respiration was proposed by Warburg to be responsible for aerobic glycolysis in cancer cells. However, intact mitochondria isolated from human ovarian and peritoneal cancer tissues exhibit substantive oxidative phosphorylating activities in terms of membrane potential, ATP biosynthesis and oxygen consumption. The specific activities of succinate, malate and glutamate dehydrogenases are comparable to reported values for human skeletal muscle, heart and liver but the rate of ATP production is one order of magnitude lower compared to human skeletal muscle. It was concluded that the TCA cycle is functional in these ovarian cancer tissues which contain OXPHOS competent mitochondria.

WJ9708012 exerts anticancer activity through PKC-α related crosstalk of mitochondrial and endoplasmic reticulum stresses in human hormone-refractory prostate cancer cells

AIM

To investigate the anticancer mechanism of a methoxyflavanone derivative, WJ9708012, highlighting its role on a crosstalk between endoplasmic reticulum (ER) and mitochondrial stress.

METHODS

Cell proliferation was examined using sulforhodamine B assay. Cell-cycle progression, Ca(2+) mobilization and mitochondrial membrane potential (ΔΨ(m)) were detected using flow cytometric analysis. Protein expression was detected using Western blot.

RESULTS

WJ9708012 displayed an antiproliferative and apoptotic activity in human hormone-refractory prostate cancer cells with IC(50) values of 6.4 and 5.3 μmol/L in PC-3 and DU-145 cells. WJ9708012 induced a prompt increase of cytosolic Ca(2+) level and activation of protein kinase C (PKC)-α. The cleavage of μ-calpain was also induced by WJ9708012. Furthermore, WJ9708012 induced cell-cycle arrest at G(1)-phase associated with down-regulation of cyclin D1, cyclin E and cyclin-dependent kinase-4 expressions. It also caused a rapid and time-dependent decrease of phosphorylation level of mTOR (Ser(2448)), 4E-BP1 (Thr(37)/Thr(46)/Thr(70)) and p70S6K (Thr(389)), indicating the inhibition of mTOR-mediated translational pathways. The ER stress was activated by the identification of up-regulated GADD153 and glucose-regulated protein-78 protein levels. The subsequent mitochondrial stress was also identified by the observation of a decreased Bcl-2 and Bcl-xL expressions, an increased truncated Bid and Bad and a loss of ΔΨ(m).

CONCLUSION

WJ9708012 induces an increase of cytosolic Ca(2+) concentration and activation of PKC-α. Subsequently, a crosstalk between ER stress and mitochondrial insult is induced, leading to the inhibition of mTOR pathways and arrest of the cell-cycle at G(1) phase. The apoptosis is ultimately induced by a severe damage of mitochondrial function.

Effect of Brazilian propolis on human umbilical vein endothelial cell apoptosis

Brazilian propolis has been widely studied in recent years. Considering the lack of data concerning the effects of Brazilian propolis on human umbilical vein endothelial cells (HUVECs), we examined the effects of ethanol-extracted Brazilian propolis (EEBP) at 12.5, 25 and 50 μg/ml on apoptosis of HUVECs deprived of basic fibroblast growth factor (FGF-2) and serum. A high concentration of the extract induced HUVEC apoptosis at 24h. Furthermore, we investigated the molecular mechanisms of HUVEC apoptosis induced by EEBP by testing the levels of integrin β4, p53, reactive oxygen species (ROS) and mitochondrial membrane potential. A low concentration of EEBP (12.5 μg/ml) could decrease the expression of integrin β4, p53 and ROS levels, whereas high concentrations (25 and 50 μg/ml) could increase the levels of integrin β4, p53 and ROS at 24h and depress mitochondrial membrane potential level at all times. Considering the doses and the results obtained in this study, Brazilian propolis at high concentrations may be an apoptosis-inducing agent associated with the signal pathway mediated by integrin β4, p53, ROS and mitochondrial membrane potential, thus, propolis should be used in safer levels for human health.

Methoxychalcone induces cell-cycle arrest and apoptosis in human hormone-resistant prostate cancer cells through PI 3-kinase-independent inhibition of mTOR pathways

BACKGROUND

Chalcones are contained in fruits and vegetables, and have been suggested to display anticancer activities. In this study, the anticancer mechanism of WJ9708011 (a methoxychalcone derivative) was delineated in human prostate cancer cells.

METHOD

Cell proliferation was examined by sulforhodamine B and clonogenic assays. Cell-cycle progression and mitochondrial membrane potential (DeltaPsi(m)) were detected by flow cytometric analysis. Expressions of protein and mRNA were detected by Western blot and RT-PCR technique, respectively. The protein synthesis was examined by [(3)H]leucine incorporation assay. The overexpression or knockdown techniques for specific target protein were also used in this study.

RESULTS

WJ9708011 induced time- and concentration-dependent G1 arrest of the cell cycle and subsequent apoptosis in human prostate cancer cells. The G1-arrest effect was confirmed by down-regulated expressions of several G1-phase regulators, including cyclin D1, cyclin E, cyclin-dependent kinase (Cdk)-4, Cdk2, phospho-RB, E2F-1, and Cdc25A. The mRNA expressions of cyclin D1 and cyclin E were also inhibited through the suppression of NF-kappaB. WJ9708011 blocked the protein synthesis and inhibited mammalian target of rapamycin (mTOR) signaling pathways. The suppression of mTOR pathways were irrespective of Akt- and AMPK-activated protein kinase (AMPK), but were attributed to mitochondrial stress, in which the down-regulation of survivin protein level may play a crucial role.

CONCLUSIONS

The data suggest that WJ9708011 induces transcriptional and translational suppression of cell-cycle regulators that might be through Akt- and AMPK-independent loss of DeltaPsi(m) and inhibition of mTOR signaling pathway, leading to G1 arrest of the cell cycle and subsequent apoptotic cell death.

Hypoxia-induced metabolic shifts in cancer cells: moving beyond the Warburg effect

Hypoxia has been recognized to play a role in promoting the invasive and metastatic behaviour of cancer cells. Largely via the transcription factor, hypoxia-induced factor 1, hypoxia exerts significant effects on cellular metabolism, with numerous downstream consequences. Energetically there is a significant shift away from oxidative phosphorylation in mitochondria towards glycolysis, a state also involved in the 'Warburg effect'. The proteins involved in mediating the altered metabolic pathways seen in tumour cells thus represent new targets for potential therapeutic intervention. Hypoxia has been associated with the development of aggressive phenotypes in cancer cells, and can be accompanied by changes in carbohydrate and lipid metabolism that impact tumour cell proliferation, adhesion, and angiogenesis. Herein, we examine glycolytic and other less investigated metabolic pathways in relation to cancer and hypoxia, with a focus on emerging tools for large-scale metabolite profiling ('metabolomics'). Metabolomic technologies permit the measurement of a wide range of metabolites in an untargeted manner, however, to date, this technology has been relatively under utilized for studying cellular responses to hypoxia. We detail some of the common experimental approaches employed in metabolomics experiments, including nuclear magnetic resonance and new mass spectrometry-based methods of analysis. Selected examples of the application of these technologies to the study of metabolic alterations brought about by hypoxia are provided, particularly as they relate to energy, carbohydrate, and lipid metabolism. Finally, the potential for therapeutic targeting of metabolic processes activated by hypoxia is presented.

The neem limonoids azadirachtin and nimbolide induce cell cycle arrest and mitochondria-mediated apoptosis in human cervical cancer (HeLa) cells

Limonoids from the neem tree (Azadirachta indica) have attracted considerable research attention in recent years owing to their potent antioxidant and anti-proliferative effects. The present study was designed to investigate the cellular and molecular mechanisms by which azadirachtin and nimbolide exert cytotoxic effects in the human cervical cancer (HeLa) cell line. Both azadirachtin and nimbolide significantly suppressed the viability of HeLa cells in a dose-dependent manner by inducing cell cycle arrest at G0/G1 phase accompanied by p53-dependent p21 accumulation and down-regulation of the cell cycle regulatory proteins cyclin B, cyclin D1 and PCNA. Characteristic changes in nuclear morphology, presence of a subdiploid peak and annexin-V staining pointed to apoptosis as the mode of cell death. Increased generation of reactive oxygen species with decline in the mitochondrial transmembrane potential and release of cytochrome c confirmed that the neem limonoids transduced the apoptotic signal via the mitochondrial pathway. Altered expression of the Bcl-2 family of proteins, inhibition of NF-kappaB activation and over-expression of caspases and survivin provide compelling evidence that azadirachtin and nimbolide induce a shift of balance toward a pro-apoptotic phenotype. Antioxidants such as azadirachtin and nimbolide that can simultaneously arrest the cell cycle and target multiple molecules involved in mitochondrial apoptosis offer immense potential as anti-cancer therapeutic drugs.

Potential therapeutic benefits of strategies directed to mitochondria

The mitochondrion is the most important organelle in determining continued cell survival and cell death. Mitochondrial dysfunction leads to many human maladies, including cardiovascular diseases, neurodegenerative disease, and cancer. These mitochondria-related pathologies range from early infancy to senescence. The central premise of this review is that if mitochondrial abnormalities contribute to the pathological state, alleviating the mitochondrial dysfunction would contribute to attenuating the severity or progression of the disease. Therefore, this review will examine the role of mitochondria in the etiology and progression of several diseases and explore potential therapeutic benefits of targeting mitochondria in mitigating the disease processes. Indeed, recent advances in mitochondrial biology have led to selective targeting of drugs designed to modulate and manipulate mitochondrial function and genomics for therapeutic benefit. These approaches to treat mitochondrial dysfunction rationally could lead to selective protection of cells in different tissues and various disease states. However, most of these approaches are in their infancy.

Targeting mitochondria for cancer therapy

Mitochondria are the cells' powerhouse, but also their suicidal weapon store. Dozens of lethal signal transduction pathways converge on mitochondria to cause the permeabilization of the mitochondrial outer membrane, leading to the cytosolic release of pro-apoptotic proteins and to the impairment of the bioenergetic functions of mitochondria. The mitochondrial metabolism of cancer cells is deregulated owing to the use of glycolytic intermediates, which are normally destined for oxidative phosphorylation, in anabolic reactions. Activation of the cell death machinery in cancer cells by inhibiting tumour-specific alterations of the mitochondrial metabolism or by stimulating mitochondrial membrane permeabilization could therefore be promising therapeutic approaches.

Lipids, mitochondria and cell death: implications in neuro-oncology

Polyunsaturated fatty acids (PUFAs) are known to inhibit cell proliferation of many tumour types both in vitro and in vivo. Their capacity to interfere with cell proliferation has been linked to their induction of reactive oxygen species (ROS) production in tumour tissues leading to cell death through apoptosis. However, the exact mechanisms of action of PUFAs are far from clear, particularly in brain tumours. The loss of bound hexokinase from the mitochondrial voltage-dependent anion channel has been directly related to loss of protection from apoptosis, and PUFAs can induce this loss of bound hexokinase in tumour cells. Tumour cells overexpressing Akt activity, including gliomas, are sensitised to ROS damage by the Akt protein and may be good targets for chemotherapeutic agents, which produce ROS, such as PUFAs. Cardiolipin peroxidation may be an initial event in the release of cytochrome c from the mitochondria, and enriching cardiolipin with PUFA acyl chains may lead to increased peroxidation and therefore an increase in apoptosis. A better understanding of the metabolism of fatty acids and eicosanoids in primary brain tumours such as gliomas and their influence on energy balance will be fundamental to the possible targeting of mitochondria in tumour treatment.

Molecular oncology focus - is carcinogenesis a 'mitochondriopathy'?

Mitochondria are sub-cellular organelles that produce adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS). As suggested over 70 years ago by Otto Warburg and recently confirmed with molecular techniques, alterations in respiratory activity and in mitochondrial DNA (mtDNA) appear to be common features of malignant cells. Somatic mtDNA mutations have been reported in many types of cancer cells, and some reports document the prevalence of inherited mitochondrial DNA polymorphisms in cancer patients. Nevertheless, a careful reanalysis of methodological criteria and methodology applied in those reports has shown that numerous papers can't be used as relevant sources of data for systematic review, meta-analysis, or finally for establishment of clinically applicable markers. In this review technical and conceptual errors commonly occurring in the literature are summarized. In the first place we discuss, why many of the published papers cannot be used as a valid and clinically useful sources of evidence in the biomedical and healthcare contexts. The reasons for introduction of noise in data and in consequence - bias for the interpretation of the role of mitochondrial DNA in the complex process of tumorigenesis are listed. In the second part of the text practical aspects of mtDNA research and requirements necessary to fulfill in order to use mtDNA analysis in clinics are shown. Stringent methodological criteria of a case-controlled experiment in molecular medicine are indicated. In the third part we suggest, what lessons can be learned for the future and propose guidelines for mtDNA analysis in oncology. Finally we conclude that, although several conceptual and methodological difficulties hinder the research on mitochondrial patho-physiology in cancer cells, this area of molecular medicine should be considered of high importance for future clinical practice.

Mitochondrial damage in nasopharyngeal carcinoma cells induced by ultrasound radiation in the presence of hypocrellin B

OBJECTIVE

The mitochondrion is an important target of ultrasound-induced cell death. This study aimed to investigate the mitochondrial damage in nasopharyngeal carcinoma (NPC) cells induced by ultrasound radiation in the presence of hypocrellin B (HB).

METHODS

The NPC cell line CNE2 was used to investigate the effect of HB on ultrasonic action with an HB concentration of 2.5 mumol/L and ultrasound exposure for 15 seconds at an intensity of 0.65 W/cm(2). Cytotoxicity was investigated 24 hours after ultrasound exposure. Mitochondrial structure changes were observed by transmission electron microscopy. The mitochondrial membrane potential was evaluated by confocal laser-scanning microscopy with rhodamine 123 staining.

RESULTS

The mean death rates of the CNE2 cells +/- SD were 25.14% +/- 1.50% after ultrasound radiation alone and 76.72% +/- 1.13% after ultrasound radiation in the presence of HB. Transmission electron microscopy showed that slightly enlarging mitochondria were found in the ultrasound-treated cells. After treatment with ultrasound and HB together, some cells had seriously damaged mitochondria, namely, obvious swollen mitochondria and mitochondria in which cristae had almost completely disappeared. The mitochondrial membrane potential was more significantly collapsed when the CNE2 cells were exposed to HB for 5 hours and then ultrasound at 0.65 mW/cm(2) than with ultrasound radiation alone (P < .05).

CONCLUSIONS

Hypocrellin B significantly enhanced the cytotoxicity of ultrasound radiation in the CNE2 cells. The damage to the mitochondrial structure and function might be an important cause of death in the CNE2 cells induced by treatment with ultrasound radiation and HB together.

Akt and c-Myc differentially activate cellular metabolic programs and prime cells to bioenergetic inhibition

The high glucose consumption of tumor cells even in an oxygen-rich environment, referred to as the Warburg effect, has been noted as a nearly universal biochemical characteristic of cancer cells. Targeting the glycolysis pathway has been explored as an anti-cancer therapeutic strategy to eradicate cancer based on this fundamental biochemical property of cancer cells. Oncoproteins such as Akt and c-Myc regulate cell metabolism. Accumulating studies have uncovered various molecular mechanisms by which oncoproteins affect cellular metabolism, raising a concern as to whether targeting glycolysis will be equally effective in treating cancers arising from different oncogenic activities. Here, we established a dual-regulatable FL5.12 pre-B cell line in which myristoylated Akt is expressed under the control of doxycycline, and c-Myc, fused to the hormone-binding domain of the human estrogen receptor, is activated by 4-hydroxytamoxifen. Using this system, we directly compared the effect of these oncoproteins on cell metabolism in an isogenic background. Activation of either Akt or c-Myc leads to the Warburg effect as indicated by increased cellular glucose uptake, glycolysis, and lactate generation. When cells are treated with glycolysis inhibitors, Akt sensitizes cells to apoptosis, whereas c-Myc does not. In contrast, c-Myc but not Akt sensitizes cells to the inhibition of mitochondrial function. This is correlated with enhanced mitochondrial activities in c-Myc cells. Hence, although both Akt and c-Myc promote aerobic glycolysis, they differentially affect mitochondrial functions and render cells susceptible to the perturbation of cellular metabolic programs.

Mitochondrial Complex I decrease is responsible for bioenergetic dysfunction in K-ras transformed cells

Many cancer cells are characterized by high rate of glycolysis and reduced rate of aerobic respiration, whose mechanism is still elusive. Here we investigate the down-regulation of oxidative phosphorylation (OXPHOS) in K-ras transformed mouse fibroblasts as compared to a control counterpart. Transcriptional analysis showed different expression levels of several OXPHOS nuclear genes in the two cell lines. In particular, during the exponential growth phase most genes encoding proteins of Complex I were expressed at lower levels in transformed cells. Consistently, a significant decrease of Complex I content was found in transformed cells. Moreover, analysis of NAD-dependent respiration and ATP synthesis indicated a strong decrease of Complex I activity in the mitochondria from neoplastic cells, that was confirmed by direct assay of the enzyme redox activity. At variance, succinate-dependent respiration and ATP synthesis were not significantly affected. Taken together, our results provide the new insight that the reduction of respiration observed in K-ras transformed cells is specifically due to a Complex I activity decrease.