Mitochondrial contributions to cancer cell physiology: potential for drug development

Mitochondria-Targeted Nanomedicine for Enhanced Efficacy of Cancer Therapy

Nanomedicines have been designed and developed to deliver anticancer drugs or exert anticancer therapy more selectively to tumor sites. Recent investigations have gone beyond delivering drugs to tumor tissues or cells, but to intracellular compartments for amplifying therapy efficacy. Mitochondria are attractive targets for cancer treatment due to their important functions for cells and close relationships to tumor occurrence and metastasis. Accordingly, multifunctional nanoplatforms have been constructed for cancer therapy with the modification of a variety of mitochondriotropic ligands, to trigger the mitochondria-mediated apoptosis of tumor cells. On this basis, various cancer therapeutic modalities based on mitochondria-targeted nanomedicines are developed by strategies of damaging mitochondria DNA (mtDNA), increasing reactive oxygen species (ROS), disturbing respiratory chain and redox balance. Herein, in this review, we highlight mitochondria-targeted cancer therapies enabled by nanoplatforms including chemotherapy, photothermal therapy (PTT), photodynamic therapy (PDT), chemodynamic therapy (CDT), sonodynamic therapy (SDT), radiodynamic therapy (RDT) and combined immunotherapy, and discussed the ongoing challenges.

Mitochondria autophagy: a potential target for cancer therapy

Mitophagy is a selective form of macroautophagy in which dysfunctional and damaged mitochondria can be efficiently degraded, removed and recycled through autophagy. Selective removal of damaged or fragmented mitochondria is critical to the functional integrity of the entire mitochondrial network and cells. In past decades, numerous studies have shown that mitophagy is involved in various diseases; however, since the dual role of mitophagy in tumour development, mitophagy role in tumour is controversial, and further elucidation is needed. That is, although mitophagy has been demonstrated to contribute to carcinogenesis, cell migration, ferroptosis inhibition, cancer stemness maintenance, tumour immune escape, drug resistance, etc. during cancer progression, many research also shows that to promote cancer cell death, mitophagy can be induced physiologically or pharmacologically to maintain normal cellular metabolism and prevent cell stress responses and genome damage by diminishing mitochondrial damage, thus suppressing tumour development accompanying these changes. Signalling pathway-specific molecular mechanisms are currently of great biological significance in the identification of potential therapeutic targets. Here, we review recent progress of molecular pathways mediating mitophagy including both canonical pathways (Parkin/PINK1- and FUNDC1-mediated mitophagy) and noncanonical pathways (FKBP8-, Nrf2-, and DRP1-mediated mitophagy); and the regulation of these pathways, and abovementioned pro-cancer and pro-death roles of mitophagy. Finally, we summarise the role of mitophagy in cancer therapy. Mitophagy can potentially be acted as the target for cancer therapy by promotion or inhibition.

Synthesis, Anticancer, and Antibacterial Activity of Betulinic and Betulonic Acid C-28-Triphenylphosphonium Conjugates with Variable Alkyl Linker Length

BACKGROUND

Conjugation of triterpenoids such as betulinic acid 1 with the Triphenylphosphonium (TPP) group is a powerful approach to generating medicinal compounds. Their development proposes structure optimization in respect of availability and activity towards target cells and organelles. Selection of 1 or its precursor betulonic acid 2 and the optimal linker is of particular importance for drug candidate identification among the TPP-triterpenoid conjugates.

OBJECTIVE

In this study, new C-28-TPP conjugated derivatives of 1 and 2 with the alkyl/alkoxyalkyl linkers of variable length were synthesized and compared regarding their anticancer, antibacterial, and mitochondriatargeted effects.

METHODS

The TPP conjugates of 1 and 2 [6a-f, 7a-f] were synthesized by the reaction of halogenalkyl esters [3a-f, 4a-f, 5] with triphenylphosphine in acetonitrile upon heating. Cytotoxicity (MTT assay), antibacterial activity (microdilution assay), and mitochondrial effects (flow cytofluorometry) were studied.

RESULTS

Conjugation with the TPP group greatly increased the cytotoxicity of the triterpenoids up to 30 times. The conjugates were up to 10-17 times more active against MCF-7 (IC50 = 0.17μM, 72h, 6c) and PC-3 (IC50 = 0.14μM, 72h, 6a) cancer cells than for human skin fibroblasts. The enhanced antibacterial (bactericidal) activity of the TPP-triterpenoid conjugates with MIC for Gram-positive bacteria as low as 2μM (6a, 7a) was for the first time revealed. The conjugates were found to effectively inhibit fluorescence of 2′,7′-dichlorofluorescin probe in the cytosol upon oxidation, decrease transmembrane potential, and increase superoxide radical level in mitochondria.

CONCLUSION

Relationships between the effects and structure of the TPP-triterpenoid conjugates were evaluated and discussed. Based on the results, 6a can be selected for further preclinical investigation as a potential anticancer compound.

Shikonin exerts antitumor activity by causing mitochondrial dysfunction in hepatocellular carcinoma through PKM2-AMPK-PGC1α signaling pathway

Shikonin, a naphthoquinone derivative isolated from the root of Lithospermum erythrorhizon, exhibits broad-spectrum antitumor activity via different molecular mechanisms. In this study, we investigated the effect of shikonin on mitochondrial dysfunction in hepatocellular carcinoma (HCC). Our results showed that shikonin inhibited the proliferation, migration, and invasiveness of HCCLM3 cells, and promoted cell apoptosis in a dose-dependent manner. More importantly, shikonin affected mitochondrial function by disrupting mitochondrial membrane potential and oxidative stress (OS) status. Furthermore, shikonin decreased the oxygen consumption rate of HCCLM3 cells, as well as the levels of ATP and metabolites involved in the tricarboxylic acid cycle (TCA cycle). We also investigated the molecular mechanisms underlying the regulation of mitochondrial function by shikonin as an inhibitor of PKM2. Shikonin decreased the expression of PKM2 in the mitochondria and affected other metabolic pathways (AMPK and PGC1α pathways), which aggravated the oxidative stress and nutrient deficiency. Our results indicate a novel role of shikonin in triggering mitochondria dysfunction via the PKM2-AMPK-PGC1α signaling pathway and provide a promising therapeutic approach for the treatment of HCC.

Aryl- and alkyl-phosphorus-containing flame retardants induced mitochondrial impairment and cell death in Chinese hamster ovary (CHO-k1) cells

Phosphorus-containing flame retardants (PFRs) are increasingly in demand worldwide as replacements for brominated flame retardants (BFRs), but insufficient available toxicological information on PFRs makes assessing their health risks challenging. Mitochondria are important targets of various environmental pollutants, and mitochondrial dysfunction may lead to many common diseases. In the present study, mitochondria impairment-related endpoints were measured by a high content screening (HCS) assay for 11 selected non-halogen PFRs in Chinese hamster ovary (CHO-k1) cells. A cluster analysis was used to categorize these PFRs into three groups according to their structural characteristics and results from the HCS assay. Two groups, containing long-chain alkyl-PFRs and all aryl-PFRs, were found to cause mitochondrial impairment but showed different mechanisms of toxicity. Due to the high correlation between cell death and mitochondrial impairment, two PFRs with different structures, trihexyl phosphate (THP) and cresyl diphenyl phosphate (CDP), were selected and compared with chlorpyrifos (CPF) to elucidate their mechanism of inducing cell death. THP (an alkyl-PFR) was found to utilize a similar pathway as CPF to induce apoptosis. However, cell death induced by CDP (an aryl-PFR) was different from classical necrosis based on experiments to discriminate among the different modes of cell death. These results confirm that mitochondria might be important targets for some PFRs and that differently structured PFRs could function via distinct mechanisms of toxicity.

VDAC1 at the crossroads of cell metabolism, apoptosis and cell stress

This review presents current knowledge related to VDAC1 as a multi-functional mitochondrial protein acting on both sides of the coin, regulating cell life and death, and highlighting these functions in relation to disease. It is now recognized that VDAC1 plays a crucial role in regulating the metabolic and energetic functions of mitochondria. The location of VDAC1 at the outer mitochondrial membrane (OMM) allows the control of metabolic cross-talk between mitochondria and the rest of the cell and also enables interaction of VDAC1 with proteins involved in metabolic and survival pathways. Along with regulating cellular energy production and metabolism, VDAC1 is also involved in the process of mitochondria-mediated apoptosis by mediating the release of apoptotic proteins and interacting with anti-apoptotic proteins. VDAC1 functions in the release of apoptotic proteins located in the mitochondrial intermembrane space via oligomerization to form a large channel that allows passage of cytochrome c and AIF and their release to the cytosol, subsequently resulting in apoptotic cell death. VDAC1 also regulates apoptosis via interactions with apoptosis regulatory proteins, such as hexokinase, Bcl2 and Bcl-xL, some of which are also highly expressed in many cancers. This review also provides insight into VDAC1 function in Ca²⁺ homeostasis, oxidative stress, and presents VDAC1 as a hub protein interacting with over 100 proteins. Such interactions enable VDAC1 to mediate and regulate the integration of mitochondrial functions with cellular activities. VDAC1 can thus be considered as standing at the crossroads between mitochondrial metabolite transport and apoptosis and hence represents an emerging cancer drug target.

Clausenidin from Clausena excavata induces apoptosis in hepG2 cells via the mitochondrial pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Clausena excavata Burm.f. is used locally in folk medicine for the treatment of cancer in South East Asia.

AIM OF THE STUDY

To determine the mechanism of action of pure clausenidin crystals in the induction of hepatocellular carcinoma (hepG2) cells apoptosis.

MATERIALS AND METHODS

Pure clausenidin was isolated from Clausena excavata Burm.f. and characterized using ¹H and ¹³C NMR spectra. Clausenidin-induced cytotoxicity was determined by MTT assay. The morphology of hepG2 after treatment with clausenidin was determined by fluorescence and Scanning Electron Microscopy. The effect of clausenidin on the apoptotic genes and proteins were determined by real-time qPCR and protein array profiling, respectively. The involvement of the mitochondria in clausenidin-induced apoptosis was investigated using MMP, caspase 3 and 9 assays.

RESULTS

Clausenidin induced significant (p<0.05) and dose-dependent apoptosis of hepG2 cells. Cell cycle assay showed that clausenidin induced a G2/M phase arrest, caused mitochondrial membrane depolarization and significantly (p<0.05) increased expression of caspases 3 and 9, which suggest the involvement of the mitochondria in the apoptotic signals. In addition, clausenidin caused decreased expression of the anti-apoptotic protein, Bcl 2 and increased expression of the pro-apoptotic protein, Bax. This finding was confirmed by the downregulation of Bcl-2 gene and upregulation of the Bax gene in the treated hepG2 cells.

CONCLUSION

Clausenidin extracted from Clausena excavata Burm.f. is an anti-hepG2 cell compound as shown by its ability to induce apoptosis through the mitochondrial pathway of apoptosis. Clausenidin can potentially be developed into an anticancer compound.

Inhibition of glucose-6-phosphate dehydrogenase sensitizes cisplatin-resistant cells to death

The mechanisms of cisplatin resistance, one of the major limitations of current chemotherapy, has only partially been described. We previously demonstrated that cisplatin-resistant ovarian cancer cells (C13), are characterized by reduced mitochondrial activity and higher glucose-dependency when compared to the cisplatin-sensitive counterpart (2008). In this work we further characterized the role of metabolic transformation in cisplatin resistance. By using transmitochondrial hybrids we show that metabolic reprogramming of cisplatin-resistant cell is not caused by inherent mtDNA mutations. We also found that C13 cells not only present an increased glucose-uptake and consumption, but also exhibit increased expression and enzymatic activity of the Pentose Phosphate pathway (PPP) enzyme Glucose-6-Phosphate Dehydrogenase (G6PDH). Moreover, we show that cisplatin-resistant cells are more sensitive to G6PDH inhibition. Even if the metabolomic fingerprint of ovarian cancer cells remains to be further elucidated, these findings indicate that PPP offers innovative potential targets to overcome cisplatin resistance.

Design and synthesis of a mitochondria-targeting carrier for small molecule drugs

A novel mitochondria-targeting carrier QCy7HA was developed. QCy7HA transported the covalently attached doxorubicin (DOX) to mitochondria specifically. The conjugate limited the effects of P-glycoprotein (Pgp) efflux pumps of multidrug-resistant cells on DOX, indicating that diverting drugs to mitochondria is a potential promising method for treatment of drug-resistant cancers.

Quantitative proteomics analysis identifies mitochondria as therapeutic targets of multidrug-resistance in ovarian cancer

Doxorubicin is a widely used chemotherapeutic agent for the treatment of a variety of solid tumors. However, resistance to this anticancer drug is a major obstacle to the effective treatment of tumors. As mitochondria play important roles in cell life and death, we anticipate that mitochondria may be related to drug resistance. Here, stable isotope labeling by amino acids in cell culture (SILAC)-based quantitative proteomic strategy was applied to compare mitochondrial protein expression in doxorubicin sensitive OVCAR8 cells and its doxorubicin-resistant variant NCI_ADR/RES cells. A total of 2085 proteins were quantified, of which 122 proteins displayed significant changes in the NCI_ADR/RES cells. These proteins participated in a variety of cell processes including cell apoptosis, substance metabolism, transport, detoxification and drug metabolism. Then qRT-PCR and western blot were applied to validate the differentially expressed proteins quantified by SILAC. Further functional studies with RNAi demonstrated TOP1MT, a mitochondrial protein participated in DNA repair, was involved in doxorubicin resistance in NCI_ADR/RES cells. Besides the proteomic study, electron microscopy and fluorescence analysis also observed that mitochondrial morphology and localization were greatly altered in NCI_ADR/RES cells. Mitochondrial membrane potential was also decreased in NCI_ADR/RES cells. All these results indicate that mitochondrial function is impaired in doxorubicin-resistant cells and mitochondria play an important role in doxorubicin resistance. This research provides some new information about doxorubicin resistance, indicating that mitochondria could be therapeutic targets of doxorubicin resistance in ovarian cancer cells.

Effect of magnetic modulation of mitochondrial voltage-dependent anion channel 2 against beta-amyloid induced neurotoxicity

The capture of VDAC2 channel with BMPs–VDAC2 antibody complexes significantly decreases the expressed intracellular calcium levels induced by Aβ.

Renoprotective effects of Moringa oleifera pods in 7,12-dimethylbenz [a] anthracene-exposed mice

OBJECTIVE

To investigate the potential of hydroethanolic extract of Moringa oleifera (MOHE) against 7, 12-dimethylbenz [a] anthracene (DMBA)-induced toxicity in male Swiss albino mice.

METHODS

Experimental mice were respectively pretreated with 200 and 400 mg/kg of MOHE, and 0.5% and 1% of butylated hydroxyanisole (BHA) for two weeks prior to the administration of 15 mg/kg of DMBA, respectively. Levels of xenobiotic metabolizing enzymes such as cytochrome (Cyt) P450 and Cyt b5, activities of reduced glutathione (GSH) and glutathione-S-transferase (GST) and renal aspartate amino transaminase (AST), alanine amino transaminase (ALT) and alkaline phosphatase (ALP), and content of protein and total cholesterol were measured to determine the nephrotoxicity caused by DMBA and to elucidate the ameliorating role of M. oleifera.

RESULTS

Single oral administration of 15 mg/kg of DMBA resulted in significant increases in Cyt P450 and Cyt b5 (P<0.01). The toxic effect of DMBA was justified by the significant decreases in the activities of GSH and GST in renal tissues (P<0.05). The levels of renal AST, ALT and ALP and protein content which are indicative of renocellular damage were also found decreased along with significant increase in total cholesterol content in DMBA-treated mice (P<0.01). The DMBA-induced alterations in the tissues were significantly reversed after pretreatment with 200 and 400 mg/kg of MOHE orally for 14 d (P<0.01).

CONCLUSION

The effects of MOHE in enhancing the levels of antioxidants and enhancing the levels of biochemical assays in DMBA-induced carcinogenesis are by reducing the formation of free radicals. This study rationalizes the ethnomedicinal use of M. oleifera for the protection against nephrotoxicity induced by chemical carcinogens.

A mitochondria-targeting gold-peptide nanoassembly for enhanced cancer-cell killing

Design and construction of multifunctional nanoparticles for effective delivery and therapeutic application remains a challenging task. It is desirable that nanoparticles can overcome multiple biological barriers and reach specific cellular locations to achieve maximum therapeutic effects. This aim often requires the fine tuning of nanoparticles' chemical and physical properties, as well as better understanding of their interaction with live cells. A peptide-modified gold-nanoparticle platform is designed, which consists of a 20-nm gold core stabilized with a layer of biotinylated CALNN-based peptides and a further layer of tetrameric streptavidins for functionalization with biotinylated molecules. The nanoassembly undergoes an efficient dynamin-dependent and caveolae-mediated endocytosis pathway, and displays highly specific localization to mitochondria, organelles of great therapeutic importance. When functionalized with a cytotoxic peptide (KLA: (KLAKLAK)2 ), the KLA-anchored nanoassembly exhibits dramatically enhanced anticancer activity, thousands of times stronger than that of the free KLA peptide, likely because of its improved cell entry efficiency, mitochondria-specific delivery, and the polyvalent effect of the nanoassembly. The study opens up the possibility of developing mitochondria-targeted nanomedicines.

Antitumor activity of a sulfated polysaccharide from Enteromorpha intestinalis targeted against hepatoma through mitochondrial pathway

A sulfated polysaccharide (EI-SP), extracted from Enteromorpha intestinalis that is a kind of algae, is found to have anticancer activity. This study was designed to investigate the anti-tumor effect of EI-SP on human hepatoma HepG2 cell line and its possible mechanisms. An MTT assay showed that EI-SP could specifically inhibit the growth of human hepatoma HepG2 cells in a dose-dependent manner. Analysis by flow cytometry indicated that the apoptosis of tumor cells increased after treatment with EI-SP in range of 100-400 μg/ml. Furthermore, Western blot analysis showed that EI-SP treatment led to decreased protein expression of Bcl-2 and an increase in Bax, cleaved caspase-3, cleaved caspase-9 and cleaved poly(ADP-ribose) polymerase (PARP). Moreover, it was found that EI-SP caused a loss of mitochondrial membrane potential (Δψ m) and the release of cytochrome c to the cytosol. Collectively, our results showed that the EI-SP induces apoptosis in HepG2 cells involving a caspases-mediated mitochondrial signalling pathway.

Modular design of redox-responsive stabilizers for nanocrystals

Many potent drugs are difficult to administer intravenously due to poor aqueous solubility. A common approach for addressing this issue is to process them into colloidal dispersions known as "nanocrystals" (NCs). However, NCs possess high-energy surfaces that must be stabilized with surfactants to prevent aggregation. An optimal surfactant should have high affinity for the nanocrystal's surface to stabilize it, but may also include a trigger mechanism that could offer the possibility of altering size distribution and uptake of the NC. This study presents a modular and systematic strategy for optimizing the affinity of polymeric stabilizers for drug nanocrystals both before and after oxidation (i.e., the selected trigger), thus allowing for the optimal responsiveness for a given application to be identified. A library of 10 redox-responsive polymer stabilizers was prepared by postpolymerization modification, using the thiol-yne reaction, of two parent block copolymers. The stabilizing potential of these polymers for paclitaxel NCs is presented as well as the influence of oxidation on size and dissolution following exposure to reactive oxygen species (ROS), which are strongly associated with chronic inflammation and cancer. Owing to the versatility of postpolymerization modification, this contribution provides general tools for preparing triggered-sheddable stabilizing coatings for nanoparticles.

Protective effect of Cordyceps polysaccharide on hydrogen peroxide-induced mitochondrial dysfunction in HL-7702 cells

Multiple reports have suggested that reactive oxygen species (ROS) are implicated in hepatic fibrosis and that they are capable of causing hepatocyte apoptosis in hepatic fibrosis by causing oxidative damage to the liver. Thus, the study of antioxidant compounds may shed light on the treatment of hepatic fibrosis. The aim of the current study was to investigate the protective effects of Cordyceps polysaccharide (CPS), a major antioxidative component of Cordyceps militaris, on hydrogen peroxide (H2O2)-induced cell apoptosis. The data showed that CPS markedly inhibited H2O2-induced mitochondrial dysfunction, lowered cell viability, increased the apoptotic rate, boosted ROS production, decreased mitochondrial membrane potential (MMP), reduced the intracellular adenosine triphosphate (ATP) level, increased the Bax/Bcl-2 ratio and promoted cytochrome C (Cyt C) release. These results indicated that CPS protected HL-7702 cells, which are used as the main model of hepatic fibrosis, against H2O2-induced mitochondrial dysfunction by decreasing ROS production and regulating mitochondrial apoptotic signaling through the Cyt C, Bax and Bcl-2 apoptosis-related proteins.

The novel resveratrol analogue HS-1793 induces apoptosis via the mitochondrial pathway in murine breast cancer cells

Resveratrol (3,4',5 tri-hydroxystilbene), a natural plant polyphenol, has gained interest as a non-toxic chemopreventive agent capable of inducing tumor cell death in a variety of cancer types. Several studies were undertaken to obtain synthetic analogues of resveratrol with potent anticancer activity. The aim of the present study was to investigate the effect of HS-1793 as a new resveratrol analog on apoptosis via the mitochondrial pathway in murine breast cancer cells. A pharmacological dose (1.3-20 µM) of HS-1793 exerted a cytotoxic effect on murine breast cancer cells resulting in apoptosis. HS-1793-mediated cytotoxicity in FM3A cells by several apoptotic events including mitochondrial cytochrome c release, activation of caspase-3 and PARP occurred. In addition, HS-1793 induced collapse of ∆Ψm and enhanced AIF and Endo G release from mitochondria while undergoing apoptosis. These results demonstrate that the cytotoxicity by HS-1793 in FM3A cells can mainly be attributed to apoptosis via a mitochondrial pathway by caspase activation or contributions of AIF and Endo G.

Differential transcriptomic analysis of spontaneous lung tumors in B6C3F1 mice: comparison to human non-small cell lung cancer

Lung cancer is the leading cause of cancer-related death in people and is mainly due to environmental factors such as smoking and radon. The National Toxicology Program (NTP) tests various chemicals and mixtures for their carcinogenic hazard potential. In the NTP chronic bioassay using B6C3F1 mice, the incidence of lung tumors in treated and control animals is second only to the liver tumors. In order to study the molecular mechanisms of chemically induced lung tumors, an understanding of the genetic changes that occur in spontaneous lung (SL) tumors from untreated control animals is needed. The authors have evaluated the differential transcriptomic changes within SL tumors compared to normal lungs from untreated age-matched animals. Within SL tumors, several canonical pathways associated with cancer (eukaryotic initiation factor 2 signaling, RhoA signaling, PTEN signaling, and mammalian target of rapamycin signaling), metabolism (Inositol phosphate metabolism, mitochondrial dysfunction, and purine and pyramidine metabolism), and immune responses (FcγR-mediated phagocytosis, clathrin-mediated endocytosis, interleukin 8 signaling, and CXCR4 signaling) were altered. Meta-analysis of murine SL tumors and human non-small cell lung cancer transcriptomic data sets revealed a high concordance. These data provide important information on the differential transcriptomic changes in murine SL tumors that will be critical to our understanding of chemically induced lung tumors and will aid in hazard analysis in the NTP 2-year carcinogenicity bioassays.

Intracellular delivery of redox cycler-doxorubicin to the mitochondria of cancer cell by folate receptor targeted mitocancerotropic liposomes

Cancer cells reflect higher level of ROS in comparison to the normal cell, so they become more vulnerable to further oxidative stress induced by exogenous ROS-generating agents. Through this a novel therapeutic strategy has evolved, which involves the delivery of redox cycler-doxorubicin (DOX) to the mitochondria of cancer cell where it acts as a source of exogenous ROS production. The purpose of this study is to develop a liposomal preparation which exhibits a propensity to selectively target cancer cell along with the potential of delivering drug to mitochondria of cell. We have rendered liposomes mitocancerotropic (FA-MTLs) by their surface modification with dual ligands, folic acid (FA) for cancer cell targeting and triphenylphosphonium (TPP) cations for mitochondria targeting. The cytotoxicity, ROS production and cell uptake of doxorubicin loaded liposomes were evaluated in FR (+) KB cells and found to be increased considerably with FA-MTLs in comparison to folic acid appended, mitochondria targeted and non-targeted liposomes. As confirmed by confocal microscopy, the STPP appended liposomes delivered DOX to mitochondria of cancer cell and also showed higher ROS production and cytotoxicity in comparison to folic acid appended and non-targeted liposomes. Most importantly, mitocancerotropic liposomes showed superior activity over mitochondria targeted liposomes which confirm the synergistic effect imparted by the presence of dual ligands - folic acid and TPP on the enhancement of cellular and mitochondrial delivery of doxorubicin in KB cells.

Scutellaria litwinowii induces apoptosis through both extrinsic and intrinsic apoptotic pathways in human promyelocytic leukemia cells

Scutellaria is a genus of Lamiaceae with known antiproliferative potentials. Scutellaria litwinowii Bornm. & Sint. ex Bornm. is one of the Iranian species of Scutellaria. Although there are widespread reports about the cytotoxic and antitumor effects of some species of this genus, research on the molecular mechanism responsible for the anticancer effects of S. litwinowii has not yet been conducted. In the current study, the apoptotic effects of S. litwinowii on 2 myeloid cell lines, apoptosis-proficient HL60 cells and apoptosis-resistant K562 cells, were analyzed. An increase in the activity of caspases-3, -8, and -9, poly (ADP ribose) polymerase (PARP) cleavage, detection of phosphatidylserine on the outer layer of cell membrane and sub-G1 peak in the flow cytometry histogram of treated cells, suggested the induction of apoptosis. S. litwinowii also increased the Bax/Bcl-2 ratio. It could be concluded that S. litwinowii induced apoptosis in both apoptosis-proficient and apoptosis-resistant leukemic cells and it might be considered as a novel candidate in the treatment of hematological malignancies.

Lipophilic phosphonium-lanthanide compounds with magnetic, luminescent, and tumor targeting properties

Multifunctional phosphonium-lanthanide compounds that simultaneously possess paramagnetism, luminescence, and tumor mitochondrial targeting properties were prepared by use of a facile method. These compounds were fully characterized by use of (1)H, (13)C, (31)P NMR, FT-IR, and elemental analyses. The thermal properties of these compounds including melting points and decomposition temperatures were investigated using DSC and TGA analyses. In addition, the paramagnetism, luminescence, and tumor targeting properties of these multifunctional compounds were confirmed by respective use of SQUID, fluorescence, and cell cytotoxicity studies. All compounds exhibited paramagnetism at room temperature, which could provide target delivery of these compounds to parts of the body containing tumor cells using a strong external magnetic field. In addition, these compounds display two major characteristic emissions originating from Dy(3+), which can be utilized for imaging tumor cells. The IC(50) values of these compounds measured against normal breast cell line (Hs578Bst) are significantly greater than those measured against the corresponding carcinoma breast cell line (Hs578T), clearly indicating the selective tumor targeting properties of these compounds. Confocal fluorescence microscopy studies were used to confirm the yellowish-green fluorescence corresponding to the emission of dysprosium thiocyanate anion within cancer cells upon exposure of cancer cell lines such as human pancreatic carcinoma cell line (MIAPaCa-2) and human breast carcinoma (MDA-MB-231) to a solution of these phosphonium-dysprosium compounds.

Attenuating sevoflurane-induced cellular injury of human peripheral lymphocytes by propofol in a concentration-dependent manner

Sevoflurane, one of the most commonly used inhalation anesthetics, induces apoptosis and oxidative stress in lymphocytes. Propofol, an intravenous anesthetic, exhibits antiapoptotic and antioxidative activities. Therefore, the present study aimed to investigate whether propofol attenuates sevoflurane-induced cellular injury in human peripheral lymphocytes. Lymphocytes harvested from healthy volunteers were assigned to treatments with different concentrations of propofol, or 8% sevoflurane, or their combination. Propofol at concentrations of 5, 10 or 25 μg/mL had little effect, but 50 μg/mL propofol or 8% sevoflurane significantly reduced cell viability and mitochondrial membrane potential (ΔΦm), and increased cell apoptosis, activation of caspase-3 and the production of intracellular reactive oxygen species, compared with untreated cells. Five and ten μg/mL propofol attenuated the impact of sevoflurane on cell viability, apoptosis and ΔΦm, and 5, 10 and 25 μg/mL propofol inhibited the production of intracellular reactive oxygen species stimulated by sevoflurane. However, a combination of 50 μg/mL propofol and 8% sevoflurane led to more severe cellular injury than sevoflurane alone. The results suggest that propofol can attenuate sevoflurane-induced cellular injury of human peripheral lymphocytes in a concentration-dependent manner, providing a rational for the clinical use of sevoflurane combined with appropriate doses of propofol.

SFE-CO2 extract from Typhonium giganteum Engl. tubers, induces apoptosis in human hepatoma SMMC-7721 cells involvement of a ROS-mediated mitochondrial pathway

Typhonium giganteum Engl. (BaiFuzi) is one of the herbs commonly used in traditional Chinese medicine against cancer. In our previous studies, 37 compounds were identified the SFE-CO₂ (supercritical fluid extraction with CO₂) extract by GC-MS, including the four major components [β-sitosterol (40.22%), campesterol (18.45%), n-hexadecanoic acid (9.52%) and (Z,Z)-9,12-octadecadienoic acid (8.15%)]. The anti-cancer mechanisms of the SFE-CO₂ extract from T. giganteum Engl. tubers have not been reported as yet. In this paper, the molecular mechanisms of the SFE-CO₂ extract-mediated apoptosis in SMMC-7721 cells were further examined. SFE-CO₂ extract inhibited the growth of SMMC-7721 cells in a time- and dose-dependent manner, arrested the cell cycle in the S phase and G2/M phase, and induced apoptosis. In addition, reactive oxygen species (ROS) increase, reduction of mitochondrial membrane potential, a rise in intracellular calcium levels were found in SMMC-7721 cells after treated with the extract. Western blot analysis showed that the extract caused down-regulation of Bcl-2 expression, and up-regulation of Bax expression. Moreover, caspase-3 and caspase-9 protease activity significantly increased in a dose-dependent manner. Collectively, our results showed that the SFE-CO₂ extract from T. giganteum Engl. tubers induces apoptosis in SMMC-7721 cells involving a ROS-mediated mitochondrial signalling pathway.

Endoplasmic reticulum stress-induced JNK activation is a critical event leading to mitochondria-mediated cell death caused by β-lapachone treatment

Background

β-lapachone (β-lap) is a bioreductive agent that is activated by the two-electron reductase NAD(P)H quinone oxidoreductase 1 (NQO1). Although β-lap has been reported to induce apoptosis in various cancer types in an NQO1-dependent manner, the signaling pathways by which β-lap causes apoptosis are poorly understood.

Methodology/Principal Findings

β-lap-induced apoptosis and related molecular signaling pathways in NQO1-negative and NQO1-overexpressing MDA-MB-231 cells were investigated. Pharmacological inhibitors or siRNAs against factors involved in β-lap-induced apoptosis were used to clarify the roles played by such factors in β-lap-activated apoptotic signaling pathways. β-lap leads to clonogenic cell death and apoptosis in an NQO1- dependent manner. Treatment of NQO1-overexpressing MDA-MB-231 cells with β-lap causes rapid disruption of mitochondrial membrane potential, nuclear translocation of AIF and Endo G from mitochondria, and subsequent caspase-independent apoptotic cell death. siRNAs targeting AIF and Endo G effectively attenuate β-lap-induced clonogenic and apoptotic cell death. Moreover, β-lap induces cleavage of Bax, which accumulates in mitochondria, coinciding with the observed changes in mitochondria membrane potential. Pretreatment with Salubrinal (Sal), an endoplasmic reticulum (ER) stress inhibitor, efficiently attenuates JNK activation caused by β-lap, and subsequent mitochondria-mediated cell death. In addition, β-lap-induced generation and mitochondrial translocation of cleaved Bax are efficiently blocked by JNK inhibition.

Conclusions/Significance

Our results indicate that β-lap triggers induction of endoplasmic reticulum (ER) stress, thereby leading to JNK activation and mitochondria-mediated apoptosis. The signaling pathways that we revealed in this study may significantly contribute to an improvement of NQO1-directed tumor therapies.

Chromene induces apoptosis via caspase-3 activation in human leukemia HL-60 cells

In this study, the potent anti-tumor effects of brown algae on human leukemia HL-60 cells were investigated. The Sargassum siliquastrum extract among the 14 species of brown algae exhibited profound growth inhibitory effect on HL-60 cells in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, therefore, S. siliquastrum was selected for use in further experiments. The highest inhibitory activity of S. siliquastrum on HL-60 cells was detected in the chloroform fraction, and the active compound was identified as a kind of chromene, sargachromanol E (SE). SE treatment showed significant growth inhibitory effects on HL-60 cells in a dose-dependent manner by inducing apoptosis, as evidenced by the formation of apoptotic bodies, fragmented DNA ladder, and the accumulation of DNA in the sub-G(1) phase of cell cycle. SE induced apoptosis was accompanied by downregulation of Bcl-xL, upregulation of Bax, activation of caspase-3, and cleavage of poly (ADP-ribose) polymerase (PARP). Moreover, z-DEVD-fmk, a caspase-3 inhibitor, significantly inhibited cell cytotoxicity, apoptotic characteristics such as apoptotic bodies, sub-G(1) DNA content, and cleavage of PARP induced by SE. These results suggest that SE exerts its growth inhibitory effects on HL-60 cells through caspase-3-mediated induction of apoptosis. Therefore, SE offers promising chemotherapeuric potential to prevent cancers such as human leukemia.

Stem cells in squamous head and neck cancer

The initiation and metastasis of head and neck squamous cell carcinomas (HNSCC) and other cancers have recently been related to the presence of cancer stem cells (CSC). CSC are cancer initiating, sustaining and are mostly quiescent. Specific markers that vary considerably depending on tumor type or tissue of origin characterize putative CSC. Compared to the bulk tumor mass, CSC are less sensitive to chemo- and radiotherapy and may also have low immunogenicity. Therapeutic targeting of CSC may improve clinical outcome of HNSCC which has two distinct etiologies: infection of epithelial stem cells by high-risk types of the human papillomavirus, or long-term tobacco and alcohol abuse. Recent knowledge on the role of CSC in HNSCC is reviewed and where necessary parallels to CSC of other origin are drawn to give a more comprehensive picture.

Essential oil from rhizomes of Ligusticum chuanxiong induces apoptosis in hypertrophic scar fibroblasts

CONTEXT

Hypertrophic scarring following surgical procedures, trauma and especially burns can lead to severe functional and cosmetic impairment, causing a decrease in the quality of life. Although a wide choice of treatments is offered, few therapeutic methods are universally accepted because of their side effects.

OBJECTIVE

The effects of the essential oil (EO) extracted from rhizomes of Ligusticum chuanxiong Hort. (Umbelliferae) in human hypertrophic scar fibroblasts (HSFs) are investigated for the first time.

MATERIALS AND METHODS

Chemical composition of hydrodistilled EO obtained from rhizomes of Ligusticum chuanxiong was analyzed by gas chromatography-mass spectrometry (GC-MS). The effects of EO on cell viability, apoptosis rate, mitochondrial membrane potential (MMP), lactate dehydrogenase (LDH), reactive oxygen species (ROS) and caspase-3 in HSFs were investigated.

RESULTS

The experimental results showed that EO significantly inhibited cell viability, elicited morphological changes and induced apoptosis in HSFs. EO also evidently increased the loss of MMP, the levels of LDH release and cellular ROS production, and the activity of caspase-3.

DISCUSSION AND CONCLUSION

EO-induced apoptosis was at least partially carried out via destruction of the intracellular antioxidant system and elicitation of excessive ROS accumulation in HSFs, which impaired mitochondrial membranes and elicited caspase-3 activation. EO could be an effective cure for human hypertrophic scar.

The iron-chelating drug triapine causes pronounced mitochondrial thiol redox stress

Triapine (Tp) is an iron chelator with activity against several types of cancer. Iron-Tp [Fe(III)(Tp)(2)] can be redox-cycled to generate reactive oxygen species that may contribute to its cytotoxicity. However, evidence for this mechanism in cells is limited. The cytosolic and mitochondrial thioredoxins (Trx1 and Trx2, respectively) are essential for cell survival. They are normally maintained in the reduced state, and support the function of many intracellular proteins including the peroxiredoxins (Prxs). Their redox status can indicate oxidant stress in their respective subcellular compartments. Tp treatment of human lung A549 cells caused almost complete oxidation of Trx2 and its dependent peroxiredoxin (Prx3), but there was no effect on Trx1 redox status. Significant inhibition of total TrxR activity did not occur until Tp levels were 4-fold above those needed to cause Trx2 oxidation. While Tp caused a 36-45% decline in reduced glutathione (GSH) levels, GSH accounted for >99% of the total glutathione in the absence and presence of Tp. In vitro studies demonstrated that cysteine reduces Fe(III)(Tp)(2) to Fe(II)(Tp)(2), and cysteine was faster and more efficient than reduced glutathione (GSH) in this regard. Fe(III)(Tp)(2) also mediated the oxidation of purified Trx2 in vitro. Thus, Fe(III)(Tp)(2) itself, and/or various reactive species that may result from its redox cycling, could account for Trx2 and Prx3 oxidation in Tp-treated cells. The striking difference between the effects on Trx2 and Trx1 implies a pronounced thiol redox stress that is largely directed at the mitochondria. These previously unrecognized effects of Tp could contribute to its overall cytotoxicity.

Reactive oxygen species-mitochondria pathway involved in LYG-202-induced apoptosis in human hepatocellular carcinoma HepG(2) cells

Previously, we demonstrated that LYG-202, a newly synthesized flavonoid with a piperazine substitution, exhibited obvious antitumor activity in vivo and in vitro. The exact mechanism of this new compound remains unclear. In the present study, we examined the effects of LYG-202 on reactive oxygen species (ROS) production and the downstream signaling pathway in the apoptosis of human hepatocellular carcinoma HepG(2) cells. Pretreatment with NAC (N-acetylcysteine), a ROS production inhibitor, partly inhibited the apoptosis induced by LYG-202 via blocking the ROS generation. Further data revealed that LYG-202 induced ROS accumulation followed by a decrease in mitochondrial membrane potential (MMP), release of cytochrome c (Cyt c) and apoptosis-inducing factor (AIF) to cytosol, which induced apoptosis of the cells. Moreover, the mitogen-activated protein kinases (MAPK), the downstream effect of ROS accumulation including c-Jun N-terminal kinase (JNK) and p38 MAPK, could be activated by LYG-202. Taken together, the generation of ROS might play an important role in LYG-202-induced mitochondrial apoptosis pathway, which provided further support for LYG-202 as a novel anticancer therapeutic candidate.

VDAC, a multi-functional mitochondrial protein regulating cell life and death

Research over the past decade has extended the prevailing view of the mitochondrion to include functions well beyond the generation of cellular energy. It is now recognized that mitochondria play a crucial role in cell signaling events, inter-organellar communication, aging, cell proliferation, diseases and cell death. Thus, mitochondria play a central role in the regulation of apoptosis (programmed cell death) and serve as the venue for cellular decisions leading to cell life or death. One of the mitochondrial proteins controlling cell life and death is the voltage-dependent anion channel (VDAC), also known as mitochondrial porin. VDAC, located in the mitochondrial outer membrane, functions as gatekeeper for the entry and exit of mitochondrial metabolites, thereby controlling cross-talk between mitochondria and the rest of the cell. VDAC is also a key player in mitochondria-mediated apoptosis. Thus, in addition to regulating the metabolic and energetic functions of mitochondria, VDAC appears to be a convergence point for a variety of cell survival and cell death signals mediated by its association with various ligands and proteins. In this article, we review what is known about the VDAC channel in terms of its structure, relevance to ATP rationing, Ca(2+) homeostasis, protection against oxidative stress, regulation of apoptosis, involvement in several diseases and its role in the action of different drugs. In light of our recent findings and the recently solved NMR- and crystallography-based 3D structures of VDAC1, the focus of this review will be on the central role of VDAC in cell life and death, addressing VDAC function in the regulation of mitochondria-mediated apoptosis with an emphasis on structure-function relations. Understanding structure-function relationships of VDAC is critical for deciphering how this channel can perform such a variety of functions, all important for cell life and death. This review also provides insight into the potential of VDAC1 as a rational target for new therapeutics.

Implications of mitochondrial DNA mutations and mitochondrial dysfunction in tumorigenesis

Alterations in oxidative phosphorylation resulting from mitochondrial dysfunction have long been hypothesized to be involved in tumorigenesis. Mitochondria have recently been shown to play an important role in regulating both programmed cell death and cell proliferation. Furthermore, mitochondrial DNA (mtDNA) mutations have been found in various cancer cells. However, the role of these mtDNA mutations in tumorigenesis remains largely unknown. This review focuses on basic mitochondrial genetics, mtDNA mutations and consequential mitochondrial dysfunction associated with cancer. The potential molecular mechanisms, mediating the pathogenesis from mtDNA mutations and mitochondrial dysfunction to tumorigenesis are also discussed.

Early alterations in protein and gene expression in rat kidney following bromate exposure

Bromate, a common disinfectant byproduct of drinking water ozonation, has been linked to human and animal renal toxicity, including renal cell carcinomas in multiple animal species. Here, we evaluate changes in protein and gene expression through two-dimensional difference gel electrophoresis (2D-DIGE) and Affymetrix arrays to identify potential modes of action involved in potassium bromate carcinogenicity. Male rats were exposed to potassium bromate in drinking water at concentrations of 0, 1, 20 and 400 ppm for two weeks. Differential expression of glycolytic proteins including enolase 1 (Eno1), triosephosphate isomerase 1 (Tpi1) and glyceraldehyde-3-phosphate dehydrogenase (Gapdh) suggests that bromate toxicity is associated with changes in energy consumption and utilization in renal cells involving up-regulation of glycolytic processes that may be the result of altered mitochondrial function. Several alterations in glycolysis and mitochondrial gene transcripts were also observed to be consistent with this mode of action. These studies provide insight into early events in renal cell physiology altered by bromate exposure.

Reactive oxygen species accumulation contributes to gambogic acid-induced apoptosis in human hepatoma SMMC-7721 cells

It is reported that gambogic acid (GA), the main active compound of gamboge which is a dry resin extracted from Garcinia hanburyi tree, has potent antitumor activity both in vivo and in vitro. Activation of mitochondrial apoptotic pathway in cancer cells is one effective therapy for cancer treatment. In the present study, we focus on the effect of GA on induction of reactive oxygen species (ROS) accumulation and triggering the mitochondrial signaling pathway in human hepatoma SMMC-7721 cells. The results indicated that GA induced ROS accumulation and collapse of mitochondrial membrane potential in SMMC-7721 cells in a concentration-dependent manner and subsequently induced that release of Cytochrome c and apoptosis-inducing factor from mitochondria to cytosol, which inhibited ATP generation and induced apoptosis in the cells. Moreover, GA elevated the phosphorylation of c-Jun-N-terminal protein kinase (JNK) and p38, which was the downstream effect of ROS accumulation. Furthermore, N-acetylcysteine, a ROS production inhibitor, partly reversed the activation of JNK and p38 and the induction of apoptosis in GA-treated cells. Collectively, our study demonstrated that accumulation of ROS played an important role in GA-induced mitochondrial signaling pathway, which provided further theoretical support for the application of GA as a promising anticancer agent.

Crosstalk between calcium and redox signaling: from molecular mechanisms to health implications

Studies done many years ago established unequivocally the key role of calcium as a universal second messenger. In contrast, the second messenger roles of reactive oxygen and nitrogen species have emerged only recently. Therefore, their contributions to physiological cell signaling pathways have not yet become universally accepted, and many biological researchers still regard them only as cellular noxious agents. Furthermore, it is becoming increasingly apparent that there are significant interactions between calcium and redox species, and that these interactions modify a variety of proteins that participate in signaling transduction pathways and in other fundamental cellular functions that determine cell life or death. This review article addresses first the central aspects of calcium and redox signaling pathways in animal cells, and continues with the molecular mechanisms that underlie crosstalk between calcium and redox signals under a number of physiological or pathological conditions. To conclude, the review focuses on conditions that, by promoting cellular oxidative stress, lead to the generation of abnormal calcium signals, and how this calcium imbalance may cause a variety of human diseases including, in particular, degenerative diseases of the central nervous system and cardiac pathologies.

Hexokinase-I protection against apoptotic cell death is mediated via interaction with the voltage-dependent anion channel-1: mapping the site of binding

In brain and tumor cells, the hexokinase isoforms HK-I and HK-II bind to the voltage-dependent anion channel (VDAC) in the outer mitochondrial membrane. We have previously shown that HK-I decreases murine VDAC1 (mVDAC1) channel conductance, inhibits cytochrome c release, and protects against apoptotic cell death. Now, we define mVDAC1 residues, found in two cytoplasmic domains, involved in the interaction with HK-I. Protection against cell death by HK-I, as induced by overexpression of native or mutated mVDAC1, served to identify the mVDAC1 amino acids required for interaction with HK-I. HK-I binding to mVDAC1 either in isolated mitochondria or reconstituted in a bilayer was inhibited upon mutation of specific VDAC1 residues. HK-I anti-apoptotic activity was also diminished upon mutation of these amino acids. HK-I-mediated inhibition of cytochrome c release induced by staurosporine was also diminished in cells expressing VDAC1 mutants. Our results thus offer new insights into the mechanism by which HK-I promotes tumor cell survival via inhibition of cytochrome c release through HK-I binding to VDAC1. These results, moreover, point to VDAC1 as a key player in mitochondrially mediated apoptosis and implicate an HK-I-VDAC1 interaction in the regulation of apoptosis. Finally, these findings suggest that interference with the binding of HK-I to mitochondria by VDAC1-derived peptides may offer a novel strategy by which to potentiate the efficacy of conventional chemotherapeutic agents.

Kinetin riboside preferentially induces apoptosis by modulating Bcl-2 family proteins and caspase-3 in cancer cells

Here, we demonstrate that kinetin riboside (KR), a cytokinin analog, induces apoptosis in HeLa and mouse melanoma B16F-10 cells. KR disrupted the mitochondrial membrane potential and induced the release of cytochrome c and activation of caspase-3. Bad were upregulated while Bcl-2 was down-regulated under KR exposure. A tumor growth in mice was dramatically suppressed by KR. In contrast, human skin fibroblast CCL-116 and bovine primary fibroblast cells show resistances to KR and no significant changes in Bad, Bcl-X(L,) and cleaved PARP were observed. Our data suggest that KR selectively induces apoptosis in cancer cells through the classical mitochondria dependent apoptosis pathway.

Mitochondria as a critical target of the chemotheraputic agent cisplatin in head and neck cancer

Cisplatin is among the most important chemotherapeutic agents ever developed. It is a critical component of therapeutic regimens in a broad range of malignancies. However, more than a generation after its clinical introduction, the exact mechanism of cisplatin action on tumor cells is not fully defined. The preponderance of research over the last three decades has focused on cisplatin interactions with nuclear DNA which are felt to lead to apoptotic cell death in sensitive cells. However, recent data have shown that cisplatin may have important direct interactions with mitochondria which can induce apoptosis and may account for a significant portion of the clinical activity associated with this drug. These direct interactions between cisplatin and mitochondria may have critical implications for our understanding of this class of drugs and the development of new therapeutic agents.

Alteration of DMBA-induced oxidative stress by additive action of a modified indigenous preparation--Kalpaamruthaa

The present study investigated the protective efficacy of the novel preparation named as Kalpaamruthaa (KA, includes Semecarpus anacardium Linn nut milk extract (SA), dried powder of Phyllanthus emblica fruit and honey) on the peroxidative damage and abnormal antioxidant levels in the hepatic mitochondrial fraction of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinoma rats. Female Sprague-Dawley rats of weight 180+/-10 g were categorized into six groups. Three groups were administered DMBA (25 mg/rat dissolved in olive oil, orally) to induce mammary carcinoma. One of these groups received KA treatment (300 mg/kg b.wt., orally) and other group received SA (200 mg/kg b.wt., orally) for 14 days after 90 days of DMBA induction. Vehicle-treated control and drug control groups were also included. The hepatic mitochondrial fraction of untreated DMBA rats showed 2.96-fold increase in MDA content when compared to control rats and abnormal changes in the activities/levels of mitochondrial enzymic (superoxide dismutase, glutathione peroxidase and glutathione reductase) and non-enzymic (glutathione, vitamin C and vitamin E) antioxidants were observed. DMBA-treated rats also showed decline in the activities of mitochondrial enzymes such as succinate dehydrogenase, alpha-ketoglutarate dehydrogenase, malate dehydrogenase and isocitrate dehydrogenase. In contrast, rats treated with SA and KA showed normal lipid peroxidation antioxidant defenses and mitochondrial enzymes, thereby showing the protection rendered by SA and KA. Although, KA treatment exhibited more profound effect in inhibiting DMBA-induced oxidative stress than sole SA treatment. Results of the study indicate that the anticarcinogenic activity of KA during DMBA-initiated mammary carcinogenesis is mediated through alteration of hepatic antioxidant status as well as modulation of TCA cycle enzymes. On the basis of the observed results, KA can be considered as a readily accessible, promising and novel cancer chemopreventive agent.

Cisplatin preferentially binds mitochondrial DNA and voltage-dependent anion channel protein in the mitochondrial membrane of head and neck squamous cell carcinoma: possible role in apoptosis

PURPOSE

Cisplatin adducts to nuclear DNA (nDNA) are felt to be the molecular lesions that trigger apoptosis, but the mechanism linking nDNA adduct formation and cell death is unclear. Some literature in the last decade has suggested a possible direct effect of cisplatin on mitochondria independent of nDNA interaction. In this study, we define separately the sequelae of cisplatin interactions with nDNA and with mitochondria in head and neck squamous cell carcinoma (HNSCC) cell lines.

EXPERIMENTAL DESIGN

Cisplatin binding to mitochondrial DNA (mtDNA) and proteins was analyzed by atomic absorption spectroscopy and other methods.

RESULTS

Following 1 hour of exposure to cisplatin, platinum adducts to mtDNA were 300- to 500-fold more abundant than adducts to nDNA; these differences were not due to differences in rates of adduct repair. Whereas HNSCC cell cytoplasts free of nDNA retained the same dose-dependent cisplatin sensitivity as parental cells, HNSCC rho(0) cells free of mtDNA were 4- to 5-fold more resistant to cisplatin than parental cells. Isolated mitochondria released cytochrome c within minutes of exposure to cisplatin, and ultrastructural analysis of intact HNSCC cells by electron microscopy showed marked mitochondrial disruption after 4 hours of cisplatin treatment, whereas the nucleus and other cellular structures remain intact. The very prompt release of cytochrome c from isolated mitochondria implies that apoptosis does not require alteration in mitochondrial gene transcription. Further, cisplatin binds preferentially to mitochondrial membrane proteins, particularly the voltage-dependent anion channel.

CONCLUSIONS

Cisplatin binding to nDNA is not necessary for induction of apoptosis in HNSCC, which can result from direct action of cisplatin on mitochondria.