Mitochondrial Targeting of Vitamin E Succinate Enhances Its Pro-apoptotic and Anti-cancer Activity via Mitochondrial Complex II (original) (raw)
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Journal of Bioenergetics and Biomembranes, 2007
Recently mitochondria in cancer cells have emerged as the Achilles heel for tumour destruction. Anticancer agents specifically targeting cancer cell mitochondria are referred to as 'mitocans'. These compounds act by destabilising these organelles, unleashing their apoptogenic potential, resulting in the efficient death of malignant cells and Lubomir Prochazka is a visiting student suppression of tumour growth. Importantly, at least some mitocans are selective for cancer cells, and these are represented by the group of redox-silent vitamin E analogues, epitomised by α-tocopheryl succinate (α-TOS). This compound has proven itself in pre-clinical models to be an efficient anti-cancer agent, targeting complex II of the respiratory chain to displace ubiquinone binding. We propose that disrupting the electron flow of mitochondrial complex II results in generation of superoxide, triggering mitochondrial destabilisation and initiation of apoptotic pathways. Moreover, α-TOS is selective for cancer cells with their reduced antioxidant defenses and lower esterase activity than the normal (non-malignant) counterparts. In this mini-review we discuss the emerging significance of mitocans, as exemplified by α-TOS.
PLOS ONE, 2019
To determine the target of the recently identified lead compound NSC130362 that is responsible for its selective anti-cancer efficacy and safety in normal cells, structure-activity relationship (SAR) studies were conducted. First, NSC13062 was validated as a starting compound for the described SAR studies in a variety of cell-based viability assays. Then, a small library of 1,4-naphthoquinines (1,4-NQs) and quinoline-5,8-diones was tested in cell viability assays using pancreatic cancer MIA PaCa-2 cells and normal human hepatocytes. The obtained data allowed us to select a set of both non-toxic compounds that preferentially induced apoptosis in cancer cells and toxic compounds that induced apoptosis in both cancer and normal cells. Anti-cancer activity of the selected non-toxic compounds was confirmed in viability assays using breast cancer HCC1187 cells. Consequently, the two sets of compounds were tested in multiple cell-based and in vitro activity assays to identify key factors responsible for the observed activity. Inhibition of the mitochondrial electron transfer chain (ETC) is a key distinguishing activity between the non-toxic and toxic compounds. Finally, we developed a mathematical model that was able to distinguish these two sets of compounds. The development of this model supports our conclusion that appropriate quantitative SAR (QSAR) models have the potential to be employed to develop anti-cancer compounds with improved potency while maintaining non-toxicity to normal cells.
Recent Patents on Anti-Cancer Drug Discovery, 2006
Mitochondria are proving to be worthy targets for activating specific killing of cancer cells in tumors and a diverse range of mitochondrial targeted drugs are currently in clinical trial to determine their effectiveness as anti-cancer therapies. The mechanism of action of mitochondrial targeted anti-cancer drugs relies on their ability to disrupt the energy producing systems of cancer cell mitochondria, leading to increased reactive oxygen species and activation of the mitochondrial dependent cell death signaling pathways inside cancer cells. We propose that this emerging class of drugs be called "mitocans", a term that reflects their mitochondrial targeting and anti-cancer roles. They are discussed in this review in the context of their mode of action whereby they target the functional differences and altered properties of the mitochondria inside cancerous but not normal cells. Hence, mitocans include drugs affecting the following mitochondrial associated activities: hexokinase inhibitors; electron transport/respiratory chain blockers; activators of the mitochondrial membrane permeability transition pore targeting constituent protein subunits, either the voltage dependent anion-selective channel (VDAC) or adenine nucleotide transporter (ANT); inhibitors of Bcl-2 anti-apoptotic family proteins and Bax/Bid pro-apoptotic mimetics. In particular, a recent surge has occurred in the number of patent documents describing small molecule inhibitors and BH3 mimetic blockers of Bcl-2/Bcl-x L function as obvious and important targets for promoting mitochondrial induced cancer cell death and for enhancing the actions of other chemotherapeutic agents. One of the other highly significant results to emerge from clinical applications of mitochondrial targeted drugs as cancer therapies to date is that they have shown limited side-effects on the normal "healthy" cell populations in vivo. It is still too early to judge the clinical impact that mitocans will make in treating cancer. Further clinical studies will be required before these novel drugs become established as single modality anti-cancer therapies or are used in conjunction with existing chemotherapies. However, it is clear from the present studies that mitocans offer great potential as effective and exciting new developments in cancer therapy, providing direct activation of cancer cell death by mitochondrial mediated apoptosis and that this complements the other pathways by which existing treatments kill cancer cells. Undoubtedly, mitocans will become an integral part of modern weaponry in the fight to eliminate cancer.
Free Radical Biology and Medicine, 2011
Malignant mesothelioma (MM) is a fatal neoplastic disease with no therapeutic option. Therefore, the search for novel therapies is of paramount importance. Methods: Since mitochondrial targeting of α-tocopheryl succinate (α-TOS) by its tagging with triphenylphosphonium enhances its cytotoxic effects to cancer cells, we tested its effect on MM cells and experimental mesotheliomas. Results: Mitochondrially targeted vitamin E succinate (MitoVES) was more efficient in killing MM cells than α-TOS with IC 50 lower by up to two orders of magnitude. Mitochondrial association of MitoVES in MM cells was documented using its fluorescently tagged analogue. MitoVES caused apoptosis in MM cells by mitochondrial destabilization, resulting in the loss of mitochondrial membrane potential, generation of reactive oxygen species, and destabilization of respiratory supercomplexes. The role of the mitochondrial complex II in the activity of MitoVES was confirmed by the finding that MM cells with suppressed succinate quinone reductase were resistant to MitoVES. MitoVES suppressed mesothelioma growth in nude mice with high efficacy. Discussion: MitoVES is more efficient in killing MM cells and suppressing experimental mesotheliomas compared with the non-targeted α-TOS, giving it a potential clinical benefit.
Anticancer Drugs Targeting the Mitochondrial Electron Transport Chain
Antioxidants & Redox Signaling, 2011
Treatment of cancer is by no means universally successful and often manifests harmful side effects. The best way to improve the success rate and reduce the side effects would be to develop compounds that are able to kill cancer cells while leaving normal cells unaffected. In this respect, mitocans (an acronym from 'mitochondria' and 'cancer'), a summary term we proposed for compounds that induce cell death by targeting mitochondria, show an encouraging trend.
Molecular Aspects of Medicine, 2007
Mitochondria have recently emerged as new and promising targets for cancer prevention and therapy. One of the reasons for this is that mitochondria are instrumental to many types of cell death and often lie downstream from the initial actions of anti-cancer drugs. Unlike the tumour suppressor gene encoding p53 that is notoriously prone to inactivating 0098-2997/$ -see front matter Ó Molecular Aspects of Medicine 28 mutations but whose function is essential for induction of apoptosis by DNA-targeting agents (such as doxorubicin or 5-fluorouracil), mitochondria present targets that are not so compromised by genetic mutation and whose targeting overcomes problems with mutations of upstream targets such as p53. We have recently proposed a novel class of anticancer agents, mitocans that exert their anti-cancer activity by destabilising mitochondria, promoting the selective induction of apoptotic death in tumour cells. In this communication, we review recent findings on mitocans and propose a common basis for their mode of action in inducing apoptosis of cancer cells. We use as an example the analogues of vitamin E that are proving to be cancer cell-specific and may soon be developed into efficient anti-cancer drugs.
Advanced Drug Delivery Reviews, 2009
Warburg effect Aerobic glycolysis Glycolytic inhibitors Targeted drug delivery to cancer Delocalized lipophilic cations Inhibitors of mitochondrial electron transport chain Biosynthetic alterations in cancer cells Mitochondrial redox system Mitochondrial apoptotic machinery Triphenylphosphonium compounds Cancer cells are characterized by self-sufficiency in the absence of growth signals, their ability to evade apoptosis, resistance to anti-growth signals, sustained angiogenesis, uncontrolled proliferation, and invasion and metastasis. Alterations in cellular bioenergetics are an emerging hallmark of cancer. The mitochondrion is the major organelle implicated in the cellular bioenergetic and biosynthetic changes accompanying cancer. These bioenergetic modifications contribute to the invasive, metastatic and adaptive properties typical in most tumors. Moreover, mitochondrial DNA mutations complement the bioenergetic changes in cancer. Several cancer management therapies have been proposed that target tumor cell metabolism and mitochondria. Glycolytic inhibitors serve as a classical example of cancer metabolism targeting agents. Several TCA cycle and OXPHOS inhibitors are being tested for their anticancer potential. Moreover, agents targeting the PDC/PDK (pyruvate dehydrogenase complex/pyruvate dehydrogenase kinase) interaction are being studied for reversal of Warburg effect. Targeting of the apoptotic regulatory machinery of mitochondria is another potential anticancer field in need of exploration. Additionally, oxidative phosphorylation uncouplers, potassium channel modulators, and mitochondrial redox are under investigation for their anticancer potential. To this end there is an increased demand for agents that specifically hit their target. Delocalized lipophilic cations have shown tremendous potential in delivering anticancer agents selectively to tumor cells. This review provides an overview of the potential anticancer agents that act by targeting cancer cell metabolism and mitochondria, and also brings us face to face with the emerging opportunities in cancer therapy. permeability transition; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; 99 m-Tc-MIBI, 99 m-Tc-Sestamibi; MTD, maximum tolerated dose; mTOR, mammalian target of rapamycin; NAD + , nicotinamide adenine dinucleotide (oxidized); NADH, nicotinamide adenine dinucleotide (reduced); NADPH, nicotinamide adenine dinucleotide phosphate (reduced); NCI, National Cancer Institute; NFAT, nuclear factor of activated T cells; NO, nitric oxide; OXPHOS, oxidative phosphorylation; PCD, programmed cell death; PDC, pyruvate dehydrogenase
International Journal of Molecular Sciences, 2015
Nearly a century has passed since Otto Warburg first observed high rates of aerobic glycolysis in a variety of tumor cell types and suggested that this phenomenon might be due to an impaired mitochondrial respiratory capacity in these cells. Subsequently, much has been written about the role of mitochondria in the initiation and/or progression of various forms of cancer, and the possibility of exploiting differences in mitochondrial structure and function between normal and malignant cells as targets for cancer chemotherapy. A number of mitochondria-targeted compounds have shown efficacy in selective cancer cell killing in pre-clinical and early clinical testing, including those that induce mitochondria permeability transition and apoptosis, metabolic inhibitors, and ROS regulators. To date, however, none has exhibited the standards for high selectivity and efficacy and low toxicity necessary to progress beyond phase III clinical trials and be used as a viable, single modality treatment option for human cancers. This review explores alternative treatment strategies that have been shown to enhance the efficacy and selectivity of mitochondria-targeted anticancer agents in vitro and in vivo, and may yet fulfill the clinical promise of exploiting the mitochondrion as a target for cancer chemotherapy.
2007
The search for a selective and efficient anti-cancer agent for treating all neoplastic disease has yet to deliver a universally suitable compound(s). Majority of established anti-cancer drugs are either non-selective or lose their efficacy due to the constant mutational changes of malignant cells. Until recently, a largely neglected target for potential anti-cancer agents was the mitochondrion, showing a considerable promise for future clinical applications. Vitamin E (VE) analogs, epitomized by α-tocopheryl succinate, belong to the group of 'mitocans' (mitochondrially targeted anti-cancer drugs). They are selective for malignant cells, cause destabilization of their mitochondria and suppress cancer in pre-clinical models. This review focuses on our current understanding of VE analogs in the context of their pro-apoptotic/anticancer efficacy and suggests that their effect on mitochondria may be amplified by modulation of alternative pathways operating in parallel. We show here that the analogs of VE that cause apoptosis (which translates into their anti-cancer efficacy) generally do not possess anti-oxidant (redox) activity and are prototypic of the mitocan group of anti-cancer compounds. Therefore, by analogy to Oscar Wilde's play 'The Importance of Being Earnest', we use the motto in the title 'The importance of being redox-silent' to emphasize an essentially novel paradigm for cancer therapy, where redox-silence is a prerequisite property for most of the anti-cancer activities described in this communication.
The mitochondrial uncoupling as a promising pharmacological target against cancer
Journal of Pharmacy & Pharmacognosy, 2019
Context: Mitochondria represent a key intracellular signalling hub that is emerging as important determinants of numerous aspects of cancer development and progression. In this sense, the organelle constitutes a promising target for the development of novel anticancer agents. Despite the negative history, mitochondrial uncoupling has recently proposed as a pharmacological target against cancer, but little is known about the mechanisms involved. Aims: To demonstrate the role of mitochondria in tumor formation and to describe how targeting of mitochondria uncoupling can be beneficial in the therapy of these diseases, which affect a large human population. Methods: The data for this systematic review were collected from three popular databases including PubMed, Google Scholar, and Scopus and included in the search terms the words “mitochondrial uncoupling” and “cancer”. The influence of mitochondrial uncoupling on cells physiology that could lead to cancer cells death, invasion and metastasis was critically appraised from relevant researches. The anticancer effects of small molecules mitochondrial uncouplers and their anticancer mechanisms were also discussed. The present dataset finally included 201 published articles. Results: It was found that the mitochondrial uncoupling-mediated responses possibly involved in the anti-cancer/anti-metastatic effects include Ca2+ homeostasis and bioenergetics disruption, mitochondrial membrane potential dissipation, reactive oxygen species generation, mitochondrial dynamics alteration, and gene expression modulation. Conclusions: Overall, this critical review suggests that mitochondrial uncoupling could be an interesting pharmacological target to be considered in the design and synthesis of novel anti-cancer compounds with optimal physic-chemical and biopharmaceutical properties and improved safety profiles.