Mitochondria as subcellular targets for clinically useful anthracyclines

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.

The mitochondrial protein C1qbp promotes cell proliferation, migration and resistance to cell death

Complement 1q-Binding Protein (C1qbp) is a mitochondrial protein reported to be upregulated in cancer. However, whether C1qbp plays a tumor suppressive or tumorigenic role in the progression of cancer is controversial. Moreover, the exact effects of C1qbp on cell proliferation, migration, and death/survival have not been definitely proven. To this end, we comprehensively examined the effects of C1qbp on mitochondrial-dependent cell death, proliferation, and migration in both normal and breast cancer cells using genetic gain- and loss-of-function approaches. In normal fibroblasts, overexpression of C1qbp protected the cells against staurosporine-induce apoptosis, increased proliferation, decreased cellular ATP, and increased cell migration in a wound-healing assay. In contrast, the opposite effects were observed in fibroblasts depleted of C1qbp by RNA interference. C1qbp expression was found to be markedly elevated in 4 different human breast cancer cell lines as well as in ductal and adenocarcinoma tumors from breast cancer patients. Stable knockdown of C1qbp by shRNA in the aggressive MDA-MB-231 breast cancer cell line greatly reduced cell proliferation, increased ATP levels, and decreased cell migration compared to control shRNA-transfected cells. Moreover, C1qbp knockdown elicited a significant increase in doxorubicin-induced apoptosis in the MDA-MB-231 cells. Finally, C1qbp upregulation was not restricted to breast cancer cells and tumors, as levels of C1qbp were also found to be significantly elevated in both human lung and colon cancer cell lines and carcinomas. Together, these results establish a pro-tumor, rather than anti-tumor, role for C1qbp, and indicate that C1qbp could serve as a molecular target for cancer therapeutics.

Analysis of proteome changes in doxorubicin-treated adult rat cardiomyocyte

Doxorubicin-induced cardiomyopathy in cancer patients is well established. The proposed mechanism of cardiac damage includes generation of reactive oxygen species, mitochondrial dysfunction and cardiomyocyte apoptosis. Exposure of adult rat cardiomyocytes to low levels of DOX for 48h induced apoptosis. Analysis of protein expression showed a differential regulation of several key proteins including the voltage dependent anion selective channel protein 2 and methylmalonate semialdehyde dehydrogenase. In comparison, proteomic evaluation of DOX-treated rat heart showed a slightly different set of protein changes that suggests nuclear accumulation of DOX. Using a new solubilization technique, changes in low abundant protein profiles were monitored. Altered protein expression, modification and function related to oxidative stress response may play an important role in DOX cardiotoxicity.

Carotenoids in human skin

The interaction of free radicals with antioxidants is a topic of increasing interest in the development of prevention strategies against skin ageing. Carotenoids can serve as marker substances for the complete antioxidative network of human skin. Recently, it has become possible to measure the carotenoids non-invasively and online using resonance Raman spectroscopy. This method has been used in various studies to investigate the interaction of carotenoid antioxidants and free radicals in human skin. In this review, the results of the selected studies are summarized and compared. It could be demonstrated that the carotenoid concentration of the skin reflects the lifestyle of individuals. A high level of carotenoids can be achieved with a healthy diet rich, for instance, in fruit and vegetables. Stress factors such as illness, UV and IR radiation of the sun, and smoking and alcohol consumption reduce the concentration of the carotenoids in the skin. It could be demonstrated that premature skin ageing was less in people with a high level of antioxidants in their tissue. Consequently, the furrows and wrinkles were not so deep and dense as in the skin of individuals with a low antioxidant level. The measurements are highly suited for the development of anti-ageing strategies and can be efficiently used in the medical diagnostics and therapy control.

Global gene expression profiles of MT knockout and wild-type mice in the condition of doxorubicin-induced cardiomyopathy

Increasing evidence from in vivo and in vitro studies has indicated that MT exerts protective effects against DOX-induced cardiotoxicity; however the underlying precise mechanisms still remain an enigma. Therefore, the present study was designed using MT knockout mice in concert with genomic approaches to explore the possible molecular and cellular mechanisms in terms of the genetic network changes. MT-I/II null (MT⁻/⁻) mice and corresponding wild-type mice (MT+/+) were administrated with a single dose of DOX (15 mg/kg, i.p.) or equal volume of saline. Animals were sacrificed on the 4th day after DOX administration and samples were collected for further analyses. Global gene expression profiles of cardiac mRNA from two genotype mice revealed that 381 characteristically MT-responsive genes were identified between MT+/+ mice and MT⁻/⁻ mice in response to DOX, including fos, ucp3, car3, atf3, map3k6, etc. Functional analysis implied MAPK signaling pathway, p53 signaling pathway, Jak-STAT signaling pathway, PPAR signaling pathway, Wnt signaling pathway, etc. might be involved to mediate the protection of DOX cardiomyopathy by MT. Results from the present study not only validated the previously reported possible mechanisms of MT protection against DOX toxicity, but also provided new clues into the molecular mechanisms involved in this process.

Mitochondria as a target in treatment

Mitochondria are key organelles that perform essential cellular functions and play pivotal roles in cell death and survival signaling. Hence, they represent an attractive target for drugs to treat metabolic, degenerative, and hyperproliferative diseases. Targeting mitochondria with organelle-specific agents or prodrugs has proven to be an effective therapeutic strategy. More specifically, controlling the cellular ROS balance via selective delivery of an antioxidant "payload" into mitochondria is an elegant emerging therapeutic concept. Herein, we review the recent medicinal chemistry and clinical data of these exploratory strategies, which should point the way for future generations of therapeutics.

Photolabile ubiquinone analogues for identification and characterization of quinone binding sites in proteins

Quinones are essential components in most cell and organelle bioenergetic processes both for direct electron and/or proton transfer reactions but also as means to regulate various bioenergetic processes by sensing cell redox states. To understand how quinones interact with proteins, it is important to have tools for identifying and characterizing quinone binding sites. In this work three different photo-reactive azidoquinones were synthesized, two of which are novel compounds, and the methods of synthesis was improved. The reactivity of the azidoquinones was first tested with model peptides, and the adducts formed were analyzed by mass spectrometry. The added mass detected was that of the respective azidoquinone minus N(2). Subsequently, the biological activity of the three azidoquinones was assessed, using three enzyme systems of different complexity, and the ability of the compounds to inactivate the enzymes upon illumination with long wavelength UV light was investigated. The soluble flavodoxin-like protein WrbA could only use two of the azidoquinones as substrates, whereas respiratory chain Complexes I and II could utilize all three compounds as electron acceptors. Complex II, purified in detergent, was very sensitive to illumination also in the absence of azidoquinones, making the 'therapeutic window' in that enzyme rather narrow. In membrane bound Complex I, only two of the compounds inactivated the enzyme, whereas illumination in the presence of the third compound left enzyme activity essentially unchanged. Since unspecific labeling should be equally effective for all the compounds, this demonstrates that the observed inactivation is indeed caused by specific labeling.

Doxorubicin-mediated apoptosis in glioma cells requires NFAT3

Nuclear factor of activated T cells (NFAT), a family of transcription factors, has been implicated in many cellular processes, including some cancers. Here, we characterize, for the first time, the role of NFAT3 in doxorubicin (DOX)-mediated apoptosis, migration, and invasion in SNB19 and U87 glioma cells. This study demonstrates that the specific knockdown of NFAT3 results in a dramatic inhibition of the apoptotic effect induced by DOX and favors cell survival. Inhibition of NFAT3 activation by shNFAT3 (shNF3) significantly downregulated tumor necrosis factor (TNF)-alpha induction, its receptor TNFR1, caspase 10, caspase 3, and poly (ADP-ribose) polymerase, abrogating DOX-mediated apoptosis in glioma cells. DOX treatment resulted in NFAT3 translocation to the nucleus. Similarly, shNF3 treatment in SNB19 and U87 cells reversed DOX-induced inhibition of cell migration and invasion, as determined by wound healing and matrigel invasion assays. Taken together, these results indicate that NFAT3 is a prerequisite for the induction of DOX-mediated apoptosis in glioma cells.

Mitochondrial targeting of electron scavenging antioxidants: Regulation of selective oxidation vs random chain reactions

Effective regulation of highly compartmentalized production of reactive oxygen species and peroxidation reactions in mitochondria requires targeting of small molecule antioxidants and antioxidant enzymes into the organelles. This review describes recently developed approaches to mitochondrial targeting of small biologically active molecules based on: (i) preferential accumulation in mitochondria because of their hydrophobicity and positive charge (hydrophobic cations), (ii) binding with high affinity to an intra-mitochondrial constituent, and (iii) metabolic conversions by specific mitochondrial enzymes to reveal an active entity. In addition, targeted delivery of antioxidant enzymes via expression of leader sequences directing the proteins into mitochondria is considered. Examples of successful antioxidant and anti-apoptotic protection based on the ability of targeted cargoes to inhibit cytochrome c-catalyzed peroxidation of a mitochondria-specific phospholipid cardiolipin, in vitro and in vivo are presented. Particular emphasis is placed on the employment of triphenylphosphonium- and hemi-gramicidin S-moieties as two effective vehicles for mitochondrial delivery of antioxidants.

Anticancer DNA intercalators cause p53-dependent mitochondrial DNA nucleoid re-modelling

Many anticancer drugs, such as doxorubicin (DXR), intercalate into nuclear DNA of cancer cells, thereby inhibiting their growth. However, it is not well understood how such drugs interact with mitochondrial DNA (mtDNA). Using cell and molecular studies of cultured cells, we show that DXR and other DNA intercalators, such as ethidium bromide, can rapidly intercalate into mtDNA within living cells, causing aggregation of mtDNA nucleoids and altering the distribution of nucleoid proteins. Remodelled nucleoids excluded DXR and maintained mtDNA synthesis, whereas non-remodelled nucleoids became heavily intercalated with DXR, which inhibited their replication, thus leading to mtDNA depletion. Remodelling was accompanied by extensive mitochondrial elongation or interconnection, and was suppressed in cells lacking mitofusin 1 and optic atrophy 1 (OPA1), the key proteins for mitochondrial fusion. In contrast, remodelling was significantly increased by p53 or ataxia telangiectasia mutated inhibition (ATM), indicating a link between nucleoid dynamics and the genomic DNA damage response. Collectively, our results show that DNA intercalators can trigger a common mitochondrial response, which likely contributes to the marked clinical toxicity associated with these drugs.

Targeting of cancer energy metabolism

The main purpose of this review is to update and analyze the effect of several antineoplastic drugs (adriamycin, apoptodilin, casiopeinas, cisplatin, clotrimazole, cyclophosphamide, ditercalinium, NSAIDs, tamoxifen, taxol, 6-mercaptopurine, and alpha-tocopheryl succinate) and energy metabolism inhibitors (2-DOG, gossypol, delocalized lipophilic cations, and uncouplers) on tumor development and progression. The possibility that these antineoplastic drugs currently used in in vitro cancer models, in chemo-therapy, or under study in phase I to III clinical trials induce tumor cellular death by altering also metabolite concentration (i.e., ATP), enzyme activities, and/or energy metabolism fluxes is assessed. It is proposed that the use of energy metabolic therapy, as an alternative or complementary strategy, might be a promising novel approach in the treatment of cancer.

Mitochondrial DNA is a direct target of anti-cancer anthracycline drugs

The anthracyclines, such as doxorubicin (DXR), are potent anti-cancer drugs but they are limited by their clinical toxicity. The mechanisms involved remain poorly understood partly because of the difficulty in determining sub-cellular drug localisation. Using a novel method utilising the fluorescent DNA dye PicoGreen, we found that anthracyclines intercalated not only into nuclear DNA but also mitochondrial DNA (mtDNA). Intercalation of mtDNA by anthracyclines may thus contribute to the marked mitochondrial toxicity associated with these drugs. By contrast, ethidium bromide intercalated exclusively into mtDNA, without interacting with nuclear DNA, thereby explaining why mtDNA is the main target for ethidium. By exploiting PicoGreen quenching we also developed a novel assay for quantification of mtDNA levels by flow-cytometry, an approach which should be useful for studies of mitochondrial dysfunction. In summary our PicoGreen assay should be useful to study drug/DNA interactions within live cells, and facilitate therapeutic drug monitoring and kinetic studies in cancer patients.

Beta-adrenergic receptor mediated protection against doxorubicin-induced apoptosis in cardiomyocytes: the impact of high ambient glucose

Recent studies have demonstrated that the beta2-adrenergic receptor (beta2AR)-Galphai signaling pathway exerts a cardiac antiapoptotic effect. The goals of this study were to determine the intracellular signaling factors involved in beta2AR-mediated protection against doxorubicin-induced apoptosis in H9c2 cardiomyocyte and explore the impact of high ambient glucose on the antiapoptotic effect. Under physiological glucose environment (100 mg/dl), beta2AR stimulation prevented doxorubicin-induced apoptosis, which was attenuated by cotreatment with wortmannin, a phosphoinositide 3-kinase (PI3K) inhibitor, or transfection of a dominant-negative Akt. Inhibition of Src kinase with 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d] pyrimidine or cSrc small interfering RNA 32 also attenuated the antiapoptotic effect. Inhibition of platelet-derived growth factor receptor (PDGFR) with AG1296 reversed the beta2AR-induced antiapoptotic effect. Transfection of an active Src cDNA (Y529F) alone was sufficient to render the cells resistant to apoptosis, and the resistance was blocked by wortmannin. Transfection of an active PI3K minigene (iSH2-p110) alone also induced resistance to apoptosis, and the resistance was reversed by an Akt-inhibitor but not by AG1296. High ambient glucose (450 mg/dl) caused two major effects: 1) it significantly reduced betaAR-induced PDGFR phosphorylation, Src kinase activity, and activation of PI3K signaling pathway; and 2) it partially attenuated beta2AR-induced antiapoptotic effect. These data provide in vitro evidence supporting a signaling cascade by which beta2AR exerts a protective effect against doxorubicin-induced apoptosis via sequential involvement of Galphai, Gbetagamma, Src, PDGFR, PI3K, and Akt. High ambient glucose significantly attenuates beta2AR-mediated cardioprotection by suppressing factors involved in this cascade including PDGFR, Src, and PI3K/Akt.

Nuclear factor-kappaB dependency of doxorubicin sensitivity in gastric cancer cells is determined by manganese superoxide dismutase expression

The role of nuclear factor-kappaB (NF-kappaB) activation in cancer cell apoptosis appears to be tailored specifically for each cell type and the type of NF-kappaB inducer. The present study aimed to determine whether or not NF-kappaB activation is associated with chemosensitivity to doxorubicin (DOX) using the DOX-sensitive SNU-601 and DOX-resistant SNU-216 gastric cancer cell lines. The effect of NF-kappaB activation on DOX (1 microg/mL) sensitivity was analyzed after the suppression of NF-kappaB activation using transfection of the super-suppressive mutant form of IkappaBalpha (mIkappaBalpha) or pretreatment with pyrrolidine dithiocarbamate. In addition, the association between NF-kappaB and manganese superoxide dismutase (MnSOD) in relation to DOX sensitivity was analyzed after the modulation of MnSOD expression. The NF-kappaB activity was much higher in DOX-resistant SNU-216 cells than in DOX-sensitive SNU-601 cells before and after DOX treatment. Overexpression of mIkappaBalpha or pyrrolidine dithiocarbamate pretreatment decreased the DOX resistance in SNU-601 cells with low MnSOD expression, but not in SNU-216 cells with high MnSOD expression. In comparison, the overexpression of MnSOD, which also suppressed NF-kappaB activation in both cell lines, increased DOX resistance in SNU-601 cells. Blocking of MnSOD expression using RNA interference techniques increased DOX sensitivity in SNU-216 cells, which was further augmented by the additional inhibition of NF-kappaB activity. Our results showed that whether NF-kappaB contributes to DOX sensitivity in gastric cancer cells is determined by the level of MnSOD expression. Thus, targeting both MnSOD and NF-kappaB may be helpful for increasing the efficacy of DOX treatment of DOX-resistant SNU gastric cancer cells.

Iron chelation by clinically relevant anthracyclines: alteration in expression of iron-regulated genes and atypical changes in intracellular iron distribution and trafficking

Anthracyclines are effective anticancer agents. However, their use is limited by cardiotoxicity, an effect linked to their ability to chelate iron and to perturb iron metabolism (Mol Pharmacol 68:261-271, 2005). These effects on iron-trafficking remain poorly understood, but they are important to decipher because treatment for anthracycline cardiotoxicity uses the chelator, dexrazoxane. Incubation of cells with doxorubicin (DOX) up-regulated mRNA levels of the iron-regulated genes transferrin receptor-1 (TfR1) and N-myc downstream-regulated gene-1 (Ndrg1). This effect was mediated by iron depletion, because it was reversed by adding iron and it was prevented by saturating the anthracycline metal binding site with iron. However, DOX did not act like a typical chelator, because it did not induce cellular iron mobilization. In the presence of DOX and (59)Fe-transferrin, iron-trafficking studies demonstrated ferritin-(59)Fe accumulation and decreased cytosolic-(59)Fe incorporation. This could induce cytosolic iron deficiency and increase TfR1 and Ndrg1 mRNA. Up-regulation of TfR1 and Ndrg1 by DOX was independent of anthracycline-mediated radical generation and occurred via hypoxia-inducible factor-1alpha-independent mechanisms. Despite increased TfR1 and Ndrg1 mRNA after DOX treatment, this agent decreased TfR1 and Ndrg1 protein expression. Hence, the effects of DOX on iron metabolism were complex because of its multiple effector mechanisms.

Targeting mitochondria

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are closely linked to degenerative diseases such as Alzheimer's disease, Parkinson's, neuronal death including ischemic and hemorrhagic stroke, acute and chronic degenerative cardiac myocyte death, and cancer. As a byproduct of oxidative phosphorylation, a steady stream of reactive species emerge from our cellular energy plants, the mitochondria. ROS and RNS potentially cause damage to all cellular components. Structure alteration, biomolecule fragmentation, and oxidation of side chains are trade-offs of cellular energy production. ROS and RNS escape results in the activation of cytosolic stress pathways, DNA damage, and the upregulation of JNK, p38, and p53. Incomplete scavenging of ROS and RNS particularly affects the mitochondrial lipid cardiolipin (CL), triggers the release of mitochondrial cytochrome c, and activates the intrinsic death pathway. Due to the active redox environment and the excess of NADH and ATP at the inner mitochondrial membrane, a broad range of agents including electron acceptors, electron donors, and hydride acceptors can be used to influence the biochemical pathways. The key to therapeutic value is to enrich selective redox modulators at the target sites. Our approach is based on conjugating nitroxides to segments of natural products with relatively high affinity for mitochondrial membranes. For example, a modified gramicidin S segment was successfully used for this purpose and proven to be effective in preventing superoxide production in cells and CL oxidation in mitochondria and in protecting cells against a range of pro-apoptotic triggers such as actinomycin D, radiation, and staurosporine. More importantly, these mitochondria-targeted nitroxide/gramicidin conjugates were able to protect against apoptosis in vivo by preventing CL oxidation induced by intestinal hemorrhagic shock. Optimization of nitroxide carriers could lead to a new generation of effective antiapoptotic agents acting at an early mitochondrial stage. Alternative chemistry-based approaches to targeting mitochondria include the use of proteins and peptides, as well as the attachment of payloads to lipophilic cationic compounds, sulfonylureas, anthracyclines, and other agents with proven or hypothetical affinities for mitochondria. Manganese superoxide dismutase (MnSOD), SS tetrapeptides with 2',6'-dimethyltyrosine (Dmt) residues, rhodamine, triphenylphosphonium salts, nonopioid analgesics, adriamycin, and diverse electron-rich aromatics and stilbenes were used to influence mitochondrial biochemistry and the biology of aging. Some general structural principles for effective therapeutic agents are now emerging. Among these are the presence of basic or positively charged functional groups, hydrophobic substructures, and, most promising for future selective strategies, classes of compounds that are actively shuttled into mitochondria, bind to mitochondria-specific proteins, or show preferential affinity to mitochondria-specific lipids.

Persistent alterations to the gene expression profile of the heart subsequent to chronic Doxorubicin treatment

Doxorubicin (DOX, Adriamycin) is a potent antineoplastic agent used to treat a number of cancers. Despite its utility, DOX causes a cumulative, irreversible cardiomyopathy that may become apparent shortly after treatment or years subsequent to therapy. Numerous studies have been conducted to elucidate the basis of DOX cardiotoxicity, but the precise mechanism responsible remains elusive. This investigation was designed to assess global gene expression using microarrays in order to identify the full spectrum of potential molecular targets of DOX cardiotoxicity to further delineate the underlying pathological mechanism(s) responsible for this dose-limiting cardiomyopathy. Male, Sprague-Dawley rats received 6 weekly injections of 2 mg/kg (s.c.) DOX followed by a 5 week drug-free period prior to analysis of cardiac tissue transcripts. Ontological evaluation in terms of subcellular targets identified gene products involved in mitochondrial processes are significantly suppressed, consistent with the well-established persistent mitochondrial dysfunction. Further classification of genes into biochemical networks revealed several pathways modulated by DOX, including glycolysis and fatty acid metabolism, supporting the notion that mitochondria are key targets in DOX toxicity. In conclusion, this comprehensive transcript profile provides important insights into critical targets and molecular adaptations that characterize the persistent cardiomyopathy associated with long-term exposure to DOX.

Existence of a distinct concentration window governing daunorubicin-induced mammalian liver mitotoxicity—implication for determining therapeutic window

Daunorubicin (DNR) is a well known anticancer drug believed to act mainly by topoisomerase II inhibition and mitochondria-mediated free radical generation. Though several studies were dedicated to elucidate the mechanism of action of DNR, however the mechanism still remains illusive. DNR is reported to affect mitochondrial respiration. However, there are contradictory reports regarding DNR effect on oxygen consumption. Interestingly, DNR at low concentration (<10 microM) dose-dependently augments respiration but at higher concentration inhibits respiration. To investigate, if a concentration window exists in which the effect of DNR on mitochondria is optimum, dose-dependent effect of DNR on mitochondria was studied. DNR inhibited electron transfer and generates reactive oxygen species (ROS) at complex I and III but not at complex II. DNR-induced ROS generation was found instrumental in mitochondrial membrane potential collapse and mitochondrial permeability transition (MPT) opening. MPT closure reduced the observed respiratory burst. Thus, at lower DNR concentration, MPT opening leads to a sudden burst of respiration while at higher concentration electron transfer gets inhibited, therefore respiration gets repressed. We for the first time, provide a possible explanation for the reports regarding the differential regulation of respiration by DNR. Thus, further establishing the concept of concentration window and justifying the need for dose optimization for maximal therapeutic effect.

Signaling of Mitochondrial Biogenesis following Oxidant Injury

Mitochondrial dysfunction is a common consequence of ischemia-reperfusion and drug injuries. For example, sublethal injury of renal proximal tubular cells (RPTCs) with the model oxidant tert-butylhydroperoxide (TBHP) causes mitochondrial injury that recovers over the course of six days. Although regeneration of mitochondrial function is integral to cell repair and function, the signaling pathway of mitochondrial biogenesis following oxidant injury has not been examined. A 10-fold overexpression of the mitochondrial biogenesis regulator PPAR-gamma cofactor-1alpha (PGC-1alpha) in control RPTCs resulted in a 52% increase in mitochondrial number, a 27% increase in respiratory capacity, and a 30% increase in mitochondrial protein markers, demonstrating that PGC-1alpha mediates mitochondrial biogenesis in RPTCs. RPTCs sublethally injured with TBHP exhibited a 50% decrease in mitochondrial function and increased mitochondrial autophagy. Compared with the controls, PGC-1alpha levels increased 12-fold on days 1, 2, and 3 post-injury and returned to base line on day 4 as mitochondrial function returned. Inhibition p38 MAPK blocked the up-regulation of PGC-1alpha following oxidant injury, whereas inhibition of calcium-calmodulin-dependent protein kinase, calcineurin A, nitric-oxide synthase, and phosphoinositol 3-kinase had no effect. The epidermal growth factor receptor (EGFR) was activated following TBHP exposure, and the EGFR inhibitor AG1478 blocked the up-regulation of PGC-1alpha. Additional inhibitor studies revealed that the sequential activation of Src, p38 MAPK, EGFR, and p38 MAPK regulate the expression of PGC-1alpha following oxidant injury. In contrast, although Akt was activated following oxidant injury, it did not play a role in PGC-1alpha expression. We suggest that mitochondrial biogenesis following oxidant injury is mediated by p38 and EGFR activation of PGC-1alpha.

Superoxide Anions Are Involved in Doxorubicin-Induced ERK Activation in Hepatocyte Cultures

Doxorubicin (DOX), an antineoplastic agent widely used for the treatment of cancer, belongs to the anthracycline family of antitumor antibiotics. DOX may undergo one-electron reduction to the corresponding semiquinone free radical by flavin-containing reductases. Under aerobic conditions, the semiquinone radical reacts rapidly with oxygen to generate superoxide anion, undergoing redox cycling. At moderate concentrations, reactive oxygen species (ROS) play an important role as regulatory mediators in signaling processes. We have shown that DOX increased phosphorylation of enzymes comprising mitogen-activated protein (MAP) kinase cascades in primary hepatocyte cultures, and that this action was independent of oxidant damage. In particular, extracellular signal-regulated kinase (ERK) was phosphorylated by the drug treatment. In this work, we have determined the possible involvement of particular free radicals in DOX-induced ERK phosphorylation in hepatocyte cultures by using specific free radical scavengers. The levels of ERK phosphorylation were measured by Western blot analysis with an anti-Thr202/Tyr204-phosphorylated p44/p42 MAPK antibody. Deferoxamine (DFO; iron chelator), catalase (hydrogen peroxide-removing enzyme), or alpha-tocopherol (peroxyl-radical scavenger) did not affect DOX-increased ERK phosphorylation levels. However, the cell-permeable superoxide dismutase mimetic MnTBAP and the flavin-containing enzyme inhibitor diphenyleneiodonium reverted DOX-induced effects. These results suggest that superoxide anions, probably generated by DOX metabolism, are involved in the effects of the anthracycline on the MAP kinase cascade activation.

Calcineurin activation is not necessary for Doxorubicin-induced hypertrophy in H9c2 embryonic rat cardiac cells: involvement of the phosphoinositide 3-kinase-Akt pathway

The calcium/calmodulin-dependent phosphatase calcineurin has been shown to be both necessary and sufficient to induce cardiac hypertrophy in vivo and in vitro. Treatment with the antineoplastic agent doxorubicin (DOX) was shown to activate calcineurin signaling in H9c2 rat cardiac muscle cells; however, the effect of this activation on hypertrophy was not investigated. Therefore, the present study was undertaken to examine the involvement of calcineurin activation in DOX-induced cardiac cell hypertrophy. H9c2 cells were treated with 1 microM DOX for 2 h following pretreatment with and in the presence of calcineurin inhibitors cyclosporine A (CsA) or FK506 (tacrolimus). Subsequent analysis of calcineurin signaling and cellular hypertrophy was performed 8 to 48 h after the treatment. DOX treatment activated calcineurin signaling and resulted in cellular hypertrophy as assessed by an increase in cell volume and protein content per cell. Inhibition of calcineurin with CsA or FK506 blocked DOX-induced calcineurin signaling. However, this inhibition did not prevent the DOX-induced hypertrophic response in H9c2 cells. Further evaluation of the possible signaling pathways involved in DOX-induced H9c2 cellular hypertrophy revealed that DOX treatment resulted in phosphorylation of the serine/threonine protein kinase Akt, a downstream effector of phosphoinositide 3-kinase (PI3K). Moreover, the DOX-induced hypertrophic response was blunted by LY294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one], a specific inhibitor for PI3K. These results demonstrate that, although calcineurin is activated by DOX treatment, it is not necessary for DOX-induced hypertrophy in H9c2 cells. Rather, the PI3K-Akt signaling pathway seems to be more critically involved in DOX-induced hypertrophy.

New insights into doxorubicin-induced cardiotoxicity: the critical role of cellular energetics

Cardiotoxic side-effects represent a serious complication of anticancer therapy with anthracyclines, in particular with doxorubicin (DXR) being the leading drug of the group. Different hypotheses, accentuating various mechanisms and/or targets, have been proposed to explain DXR-induced cardiotoxicity. This review focuses on the myocardial energetic network as a target of DXR toxic action in heart and highlights the recent advances in understanding its role in development of the DXR related cardiac dysfunction. We present a survey of DXR-induced defects in different steps of cardiac energy metabolism, including reduction of oxidative capacity of mitochondria, changes in the profile of energy substrate utilization, disturbance of energy transfer between sites of energy production and consumption, as well as defects in energy signaling. Considering the wide spectrum and diversity of the changes reported, we attempt to integrate these facts into a common framework and to discuss important functional and temporal relationships between DXR-induced events and the possible underlying molecular mechanisms.

Alterations in myocardial energy metabolism induced by the anti-cancer drug doxorubicin

Doxorubicin and other anthracyclines are among the most potent chemotherapeutic drugs for the treatment of acute leukaemia, lymphomas and different types of solid tumours such as breast, liver and lung cancers. Their clinical use is, however, limited by the risk of severe cardiotoxicity, which can lead to irreversible congestive heart failure. There is increasing evidence that essential components of myocardial energy metabolism are among the highly sensitive and early targets of doxorubicin-induced damage. Here we review doxorubicin-induced detrimental changes in cardiac energetics, with an emphasis on the emerging importance of defects in energy-transferring and -signalling systems, like creatine kinase and AMP-activated protein kinase.

HPMA copolymer-bound doxorubicin induces apoptosis in ovarian carcinoma cells by the disruption of mitochondrial function

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymer-bound doxorubicin has showed greater potency than free doxorubicin in the treatment of ovarian cancer in vivo and in vitro. The promising activity of the conjugate demonstrated in clinical trials has generated considerable interest in understanding the mechanism of action of this macromolecular therapeutic. In this study, the involvement of the mitochondrial pathway in HPMA copolymer-bound doxorubicin-induced apoptosis in the human ovarian cancer cell line A2780 was investigated. Through a series of in vitro assays, including confocal microscopy, flow cytometry, and spectrofluorimetry, a significant decrease in mitochondrial membrane potential in A2780 cells treated with HPMA copolymer-bound doxorubicin was found. The most dramatic changes in mitochondrial membrane potential were observed between 2 and 12 h of continuous drug exposure. The potential of the mitochondrial membrane remained collapsed when drug treatment continued up to 24 h. For the first time, it was shown that HPMA copolymer-bound doxorubicin induces apoptosis in ovarian cancer cells by simultaneous activation of both caspase-dependent and caspase-independent pathways of DNA damage. This was determined by monitoring the translocation of the mitochondrial proteins cytochrome c and apoptosis-inducing factor to cytosol. The altered balance between anti-apoptotic and pro-apoptotic members of the Bcl-2 family of proteins was responsible for the mitochondrial function distraction. HPMA copolymer-bound doxorubicin induced a time-dependent decrease in the expression of the anti-apoptotic Bcl-2 and Bcl-xL proteins, which control cell survival. At the same time, the expression level of pro-apoptotic members (Bax, Bad) of the Bcl-2 family was increased under the chosen experimental conditions. Altogether, these results indicate that HPMA copolymer-bound doxorubicin induced apoptosis in ovarian cancer cells through the mitochondrial pathway.

Mitochondrial localization and activity of P-glycoprotein in doxorubicin-resistant K562 cells

It is now well-established that P-glycoprotein 170 (P-gp), an efflux pump involved in multidrug resistance (MDR) is overexpressed at the plasma membrane of doxorubicin-resistant K562 leukemia cells. Nevertheless, several results suggested: (i) that P-gp-mediated drug efflux was not the only mechanism involved in resistance; (ii) that intracellular compartments could accumulate the drug, preventing it from reaching its nuclear targets; (iii) that agents able to reverse multidrug resistance may lead to intracellular drug redistribution. We have studied the localization of P-gp in mitochondria as well as its functional properties in this compartment. Using several monoclonal antibodies (MoAbs) directed against different P-gp epitopes, a protein was detected in the cytoplasm of two doxorubicin-resistant K562 sublines and, by confocal laser scanning microscopy, this protein was shown to co-localize in the Golgi apparatus and in mitochondria, in equivalent proportions. Purified mitochondria were isolated from K562 cell variants; the presence of a protein of about 170 kDa and reacting with several anti-P-gp antibodies was assessed in MDR cells by Western blotting and flow cytometry. Functional assays have shown that mitochondrial P-gp was involved in doxorubicin accumulation inside the organelle but not in its efflux, suggesting an orientation of P-gp in the mitochondrial membrane inverse to that observed in the plasma membrane. A potential role for mitochondrial P-gp in MDR cells would be to protect the nucleus from doxorubicin. This is the first demonstration of the presence and functional activity of P-gp in mitochondria of MDR cells.

Effects of permeability transition inhibition and decrease in cytochrome c content on doxorubicin toxicity in K562 cells

As mitochondria play a key role in the commitment to cell death, we have investigated the mitochondrial consequences of resistance to doxorubicin (DOX) in K562 cells. We found that the permeability transition pore (PTP) inhibitor cyclosporine A (CsA) failed to inhibit PTP opening in the resistant clone. Moreover, the Ca2+ loading capacity in the resistant clone was identical to that observed in the parent cells in the presence of CsA, suggesting that the PTP was already inhibited in a CsA-like manner in the resistant cells. In agreement with this proposal, the mitochondrial target of CsA cyclophilin D (CyD) decreased by half in the resistant cells. The levels of adenine nucleotide translocator, voltage anion-dependent channel, Bax, Bcl-2, Bcl-xL, AIF and Smac/Diablo, were similar in both cell lines, whereas cytochrome c content was divided by three in the resistant cells. Since P-glycoprotein inhibition did not restore DOX toxicity in the resistant cells, while DOX-induced cell death in the parent cells was prevented by either PTP inhibition or siRNA-induced decrease in cytochrome c content, we conclude that the inhibition of PTP opening and the decrease in cytochrome c content participate in the mechanism that makes K562 cells resistant to DOX.

Modulation of cytochrome C oxidase-va is possibly involved in metallothionein protection from doxorubicin cardiotoxicity

Previous studies using a cardiac-specific metallothionein (MT)-overexpressing transgenic (MT-TG) mouse model have demonstrated that MT protects from doxorubicin (DOX)-induced oxidative heart injury. The molecular mechanisms that underlie this cardioprotection, however, have yet to be defined. In the present study, we tested the hypothesis that MT overexpression activates cytoprotective mechanisms, leading to cardiac protection from DOX toxicity. MT-TG mice and nontransgenic wild-type (WT) controls were treated i.p. with DOX at a single dose of 20 mg/kg and sacrificed on the third day after the treatment. An expression proteomic analysis involving two-dimensional gel electrophoresis and matrix-assisted laser desorption ionization time-of-flight mass spectrometry was used to identify MT-induced changes in cytoprotection-related proteins. We identified 18 proteins that were modified by DOX treatment in the heart. These proteins included those involved in cellular antioxidant defense, enzymes of the mitochondrial electron transport chain, enzymes involved in beta-oxidation of fatty acids and glycolysis, and proteins involved in regulation of cardiac muscle contraction. However, the most dominant modification by MT is the cytochrome c oxidase subunit Va (CCO-Va). In response to DOX treatment, a specific isoform of CCO-Va was enhanced in the MT-TG but not in the WT mouse hearts. Because CCO-Va is a critical component in the mitochondrial electron transport chain, the results suggest that the cardioprotective effect of MT may be related to an increased expression or a differential modification of CCO-Va.

A novel thiol oxidation-based mechanism for adriamycin-induced cell injury in human macrophages

Adriamycin is a widely used antitumor antibiotic, but its use has been limited by its cytotoxicity in both cardiomyocytes and non-cardiac tissues. While adriamycin's ability to redox cycle via one-electron transfer reactions and generate ROS is thought to promote cardiotoxicity, the mechanisms involved in non-cardiac tissue injury are not clear. Here we show that prolonged exposure (48 h) of human monocyte-derived macrophages to adriamycin at concentrations as low as 1 microM promotes caspase-independent cell death. Treatment of cells with scavengers of superoxide and peroxyl radicals blocked adriamycin-induced oxidation of dichlorodihydrofluorescein (DCFH) but did not prevent macrophage injury. Macrophages treated with either adriamycin or the thiol oxidant diamide showed elevated levels of glutathione disulfide and increased protein-S-glutathionylation prior to cell injury, indicating that thiol oxidation is involved in adriamycin-induced macrophage death. Furthermore, inhibition of glutathione reductase (GR) with 1,3-bis[2-chloroethyl]-1-nitrosourea or transfection of macrophages with small inhibitory RNA (siRNA) directed against GR or glutaredoxin (Grx) potentiated adriamycin-induced macrophage injury. Thus, both GR and Grx appear to play a crucial role in protecting macrophages from adriamycin-induced cell injury. These findings suggest a new mechanism for adriamycin-induced tissue injury whereby thiol oxidation, rather than one-electron redox cycling and ROS generation, mediates adriamycin-induced cell damage.

Synthesis and cytotoxicity of new aminoterpenylquinones

Several 6(7)-alkyl-1,4-naphthoquinones (NQ) have been prepared by cycloaddition reactions between the monoterpene alpha-myrcene and p-benzoquinones and halogen and nitrogen-containing functional groups have been introduced at the C-2 position of the naphthoquinone ring via nucleophilic addition or substitution reactions. These substituents at positions 2/3 of the NQ clearly influence the cytotoxic potency of this type of compound. Of particular interest is substitution by arylamino, specifically p-oxyarylamino, groups, which considerably enhance their bioactivity and selectivity.

Molecular pharmacology of the interaction of anthracyclines with iron

Although anthracyclines such as doxorubicin are widely used antitumor agents, a major limitation for their use is the development of cardiomyopathy at high cumulative doses. This severe adverse side effect may be due to interactions with cellular iron metabolism, because iron loading promotes anthracycline-induced cell damage. On the other hand, anthracycline-induced cardiotoxicity is significantly alleviated by iron chelators (e.g., desferrioxamine and dexrazoxane). The molecular mechanisms by which anthracyclines interfere with cellular iron trafficking are complex and still unclear. Doxorubicin can directly bind iron and can perturb iron metabolism by interacting with multiple molecular targets, including the iron regulatory proteins (IRP) 1 and 2. The RNA-binding activity of these molecules regulates synthesis of the transferrin receptor 1 and ferritin, which are crucial proteins involved in iron uptake and storage, respectively. At present, it is not clear whether doxorubicin affects IRP1-RNA-binding activity by intracellular formation of doxorubicinol and/or by generation of the doxorubicin-iron(III) complex. Furthermore, doxorubicin prevents the mobilization of iron from ferritin by a mechanism that may involve lysosomal degradation of this protein. Prevention of iron mobilization from ferritin would probably disturb vital cellular functions as a result of inhibition of essential iron-dependent proteins, such as ribonucleotide reductase. This review discusses the molecular interactions of anthracyclines with iron metabolism and the development of cardioprotective strategies such as iron chelators.

Lipoic acid ameliorates adriamycin-induced testicular mitochondriopathy

Adriamycin (ADR), an anthracycline antibiotic, which is widely used as an antineoplastic drug in the treatment of various solid tumors, has been shown to induce reproductive abnormalities in males. In the present study, the effect of lipoic acid (LA), a universal antioxidant was investigated on ADR-induced testicular toxicity in rats. Adult male albino rats of Wistar strain were administered ADR (1 mg/kg body weight, i.v.), once a week for 10 weeks. Mitochondrial fractions of the testis were obtained by differential centrifugation. The activities of mitochondrial antioxidant enzymes such as superoxide dismutase, glutathione peroxidase and glutathione reductase were decreased significantly in the animals treated with ADR. The levels of mitochondrial lipid peroxides and hydrogen peroxide were increased in ADR-treated rats. ADR-treated rats also showed decline in the activities of mitochondrial enzymes such as succinate dehydrogenase (SDH), malate dehydrogenase (MDH) and isocitrate dehydrogenase (ICDH). Treatment with lipoic acid (35 mg/kg body weight, i.p.) 1 day prior to ADR administration, maintained near normal activities of the enzymes, thereby proving to be an effective cytoprotectant.

Chronic progressive cardiac dysfunction years after doxorubicin therapy for childhood acute lymphoblastic leukemia

PURPOSE

Cross-sectional studies show that cardiac abnormalities are common in long-term survivors of doxorubicin-treated childhood malignancies. Longitudinal data, however, are rare.

METHODS

Serial echocardiograms (N = 499) were obtained from 115 doxorubicin-treated long-term survivors of childhood acute lymphoblastic leukemia (median age at diagnosis, 4.8 years; median follow-up after completion of doxorubicin, 11.8 years). Results were expressed as z scores to indicate the number of standard deviations (SDs) above (+) or below (-) the normal predicted value. Median individual and cumulative doxorubicin doses were 30 mg/m2 per dose and 352 mg/m2, respectively.

RESULTS

Left ventricular fractional shortening was significantly reduced after doxorubicin therapy, and the reduction was related to cumulative dose. z scores for fractional shortening transiently improved before falling to -2.76 more than 12 years after diagnosis. Reduced fractional shortening was related to impaired contractility and increasing afterload, consequences of a progressive reduction of ventricular mass, and wall thickness relative to body-surface area. Left ventricular contractility fell significantly over time and was depressed at last follow-up in patients receiving more than 300 mg/m2 of doxorubicin. Systolic and diastolic blood pressures were below normal more than 9 years after diagnosis. Even patients receiving lower cumulative doxorubicin doses experienced reduced mass and dimension. Fractional shortening and dimension at the end of therapy predicted these parameters 11.8 years later.

CONCLUSION

Cardiac abnormalities were persistent and progressive after doxorubicin therapy. Inadequate ventricular mass with chronic afterload excess was associated with progressive contractile deficit and possibly reduced cardiac output and restrictive cardiomyopathy. The deficits were worst after highest cumulative doses of doxorubicin, but appeared even after low doses.

Mechanism of apoptosis induced by doxorubicin through the generation of hydrogen peroxide

The main anticancer action of doxorubicin (DOX) is believed to be due to topoisomerase II inhibition and free radical generation. Our previous study has demonstrated that TAS-103, a topoisomerase inhibitor, induces apoptosis through DNA cleavage and subsequent H(2)O(2) generation mediated by NAD(P)H oxidase activation [H. Mizutani et al. J. Biol. Chem. 277 (2002) 30684-30689]. Therefore, to clarify whether DOX functions as an anticancer drug through the same mechanism or not, we investigated the mechanism of apoptosis induced by DOX in the human leukemia cell line HL-60 and the H(2)O(2)-resistant sub-clone, HP100. DOX-induced DNA ladder formation could be detected in HL-60 cells after a 7 h incubation, whereas it could not be detected under the same condition in HP100 cells, suggesting the involvement of H(2)O(2)-mediated pathways in apoptosis. Flow cytometry revealed that H(2)O(2) formation preceded the increase in Delta Psi m and caspase-3 activation. Poly(ADP-ribose) polymerase (PARP) and NAD(P)H oxidase inhibitors prevented DOX-induced DNA ladder formation in HL-60 cells. Moreover, DOX significantly induced formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine, an indicator of oxidative DNA damage, in HL-60 cells at 1 h, but not in HP100 cells. DOX-induced apoptosis was mainly initiated by oxidative DNA damage in comparison with the ability of other topoisomerase inhibitors (TAS-103, amrubicin and amrubicinol) to cause DNA cleavage and apoptosis. These results suggest that the critical apoptotic trigger of DOX is considered to be oxidative DNA damage by the DOX-induced direct H(2)O(2) generation, although DOX-induced apoptosis may involve topoisomerase II inhibition. This oxidative DNA damage causes indirect H(2)O(2) generation through PARP and NAD(P)H oxidase activation, leading to the Delta Psi m increase and subsequent caspase-3 activation in DOX-induced apoptosis.

Acetaminophen stimulates the peroxidative metabolism of anthracyclines

Acetaminophen, a common analgesic and antipyretic drug, is frequently administered to individuals undergoing anthracycline chemotherapy. Here, the effect of acetaminophen on the metabolism of daunorubicin and doxorubicin by isolated enzymes lactoperoxidase and myeloperoxidase, and by myeloperoxidase-containing human leukemia HL-60 cells was investigated using spectrophotometric and EPR techniques. We report that at pharmacological concentrations acetaminophen strongly stimulates oxidation of the anthracyclines by lactoperoxidase and myeloperoxidase systems, which results in irreversibly altered (colorless) products. The initial rate and efficacy of daunorubicin oxidation depends on pH. While at pH approximately 7 the oxidation is rapid and extensive, almost no oxidation occurs at pH approximately 5. In the absence of daunorubicin, oxidation of acetaminophen by lactoperoxidase/hydrogen peroxide is only weakly dependent on pH, however, at pH 7.4 it strongly depends on [daunorubicin]. Ascorbate and reduced glutathione strongly inhibited oxidation of anthracyclines by lactoperoxidase and HL-60 systems. Using EPR, a daunorubicin-derived radical was detected in a daunorubicin/acetaminophen/peroxidase/hydrogen peroxide system as a narrow single line (0.175 mT) with g = 2.0047. When daunorubicin was omitted, only an acetaminophen-melanin EPR signal was detected (g = 2.0043, line width approximately 0.5 mT). Similar results were obtained with doxorubicin. We suggest that the stimulation by acetaminophen is primarily due to its preferential oxidation by peroxidases to the corresponding phenoxyl radical, which subsequently reacts with daunorubicin (doxorubicin). Because biological properties of oxidatively transformed anthracyclines will certainly be different from those of their parent compounds, the possible acetaminophen-enhanced degradation of the anthracyclines in vivo is likely to interfere with anticancer and/or cardiotoxic activities of these agents.

Mitochondria in tumor cells studied by laser scanning confocal microscopy

We present here a confocal fluorescence microscopy study of mitochondria in sensitive and resistant carcinoma cells by using two potentiometric probes of mitochondria, rhodamine 123 (R123) and dimethylaminostyryl-methylpyridiniumiodine. We have found that active mitochondria in sensitive MCF-7 and multidrug resistant MCF-7/DX carcinoma cells are very different in localization and morphology. In sensitive cells active mitochondria are found in the perinuclear region, whereas in the multidrug resistance (MDR) subline they are confined to the cell periphery. Interestingly, the MDR revertant verapamil has been found to restore in MCF-7/DX cells the same pattern of active mitochondria seen in sensitive cells. We have also studied R123 in human lung carcinoma A549 cells, which display a low responsivity to doxorubicin, and overexpress the lung resistance-related protein. In addition to perinuclear mitochondria, peripheral mitochondria with weaker fluorescence can be seen in this cell line. Interestingly, in the two examined carcinoma lines we have been able to recognize by image analysis a common new star-lobed morphology. Our results indicate that in resistant carcinoma cells two populations of mitochondria coexist with different localization, morphology, and activity.

Structure and function of "metalloantibiotics"

Although most antibiotics do not need metal ions for their biological activities, there are a number of antibiotics that require metal ions to function properly, such as bleomycin (BLM), streptonigrin (SN), and bacitracin. The coordinated metal ions in these antibiotics play an important role in maintaining proper structure and/or function of these antibiotics. Removal of the metal ions from these antibiotics can cause changes in structure and/or function of these antibiotics. Similar to the case of "metalloproteins," these antibiotics are dubbed "metalloantibiotics" which are the title subjects of this review. Metalloantibiotics can interact with several different kinds of biomolecules, including DNA, RNA, proteins, receptors, and lipids, rendering their unique and specific bioactivities. In addition to the microbial-originated metalloantibiotics, many metalloantibiotic derivatives and metal complexes of synthetic ligands also show antibacterial, antiviral, and anti-neoplastic activities which are also briefly discussed to provide a broad sense of the term "metalloantibiotics."