Effect of the antitumoral alkylating agent 3-bromopyruvate on mitochondrial respiration: role of mitochondrially bound hexokinase

Succinate metabolism: a promising therapeutic target for inflammation, ischemia/reperfusion injury and cancer

Succinate serves as an essential circulating metabolite within the tricarboxylic acid (TCA) cycle and functions as a substrate for succinate dehydrogenase (SDH), thereby contributing to energy production in fundamental mitochondrial metabolic pathways. Aberrant changes in succinate concentrations have been associated with pathological states, including chronic inflammation, ischemia/reperfusion (IR) injury, and cancer, resulting from the exaggerated response of specific immune cells, thereby rendering it a central area of investigation. Recent studies have elucidated the pivotal involvement of succinate and SDH in immunity beyond metabolic processes, particularly in the context of cancer. Current scientific endeavors are concentrated on comprehending the functional repercussions of metabolic modifications, specifically pertaining to succinate and SDH, in immune cells operating within a hypoxic milieu. The efficacy of targeting succinate and SDH alterations to manipulate immune cell functions in hypoxia-related diseases have been demonstrated. Consequently, a comprehensive understanding of succinate's role in metabolism and the regulation of SDH is crucial for effectively targeting succinate and SDH as therapeutic interventions to influence the progression of specific diseases. This review provides a succinct overview of the latest advancements in comprehending the emerging functions of succinate and SDH in metabolic processes. Furthermore, it explores the involvement of succinate, an intermediary of the TCA cycle, in chronic inflammation, IR injury, and cancer, with particular emphasis on the mechanisms underlying succinate accumulation. This review critically assesses the potential of modulating succinate accumulation and metabolism within the hypoxic milieu as a means to combat various diseases. It explores potential targets for therapeutic interventions by focusing on succinate metabolism and the regulation of SDH in hypoxia-related disorders.

Mitochondria-targeted nanoplatforms for enhanced photodynamic therapy against hypoxia tumor

Background

Photodynamic therapy (PDT) is a promising therapeutic modality that can convert oxygen into cytotoxic reactive oxygen species (ROS) via photosensitizers to halt tumor growth. However, hypoxia and the unsatisfactory accumulation of photosensitizers in tumors severely diminish the therapeutic effect of PDT. In this study, a multistage nanoplatform is demonstrated to overcome these limitations by encapsulating photosensitizer IR780 and oxygen regulator 3-bromopyruvate (3BP) in poly (lactic-co-glycolic acid) (PLGA) nanocarriers.

Results

The as-synthesized nanoplatforms penetrated deeply into the interior region of tumors and preferentially remained in mitochondria due to the intrinsic characteristics of IR780. Meanwhile, 3BP could efficiently suppress oxygen consumption of tumor cells by inhibiting mitochondrial respiratory chain to further improve the generation of ROS. Furthermore, 3BP could abolish the excessive glycolytic capacity of tumor cells and lead to the collapse of ATP production, rendering tumor cells more susceptible to PDT. Successful tumor inhibition in animal models confirmed the therapeutic precision and efficiency. In addition, these nanoplatforms could act as fluorescence (FL) and photoacoustic (PA) imaging contrast agents, effectuating imaging-guided cancer treatment.

Conclusions

This study provides an ideal strategy for cancer therapy by concurrent oxygen consumption reduction, oxygen-augmented PDT, energy supply reduction, mitochondria-targeted/deep-penetrated nanoplatforms and PA/FL dual-modal imaging guidance/monitoring. It is expected that such strategy will provide a promising alternative to maximize the performance of PDT in preclinical/clinical cancer treatment.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01196-6.

Coupling of GABA Metabolism to Mitochondrial Glucose Phosphorylation

Glucose and oxygen (O₂) are vital to the brain. Glucose metabolism and mitochondria play a pivotal role in this process, culminating in the increase of reactive O₂ species. Hexokinase (HK) is a key enzyme on glucose metabolism and is coupled to the brain mitochondrial redox modulation by recycling ADP for oxidative phosphorylation (OXPHOS). GABA shunt is an alternative pathway to GABA metabolism that increases succinate levels, a Krebs cycle intermediate. Although glucose and GABA metabolisms are intrinsically connected, their interplay coordinating mitochondrial function is poorly understood. Here, we hypothesize that the HK and the GABA shunt interact to control mitochondrial metabolism differently in the cortex and the hypothalamus. The GABA shunt stimulated mitochondrial O₂ consumption and H₂O₂ production higher in hypothalamic synaptosomes (HSy) than cortical synaptosomes (CSy). The GABA shunt increased the HK coupled to OXPHOS activity in both population of synaptosomes, but the rate of activation was higher in HSy than CSy. Significantly, malonate and vigabatrin blocked the effects of the GABA shunt in the HK activity coupled to OXPHOS. It indicates that the glucose phosphorylation is linked to GABA and Krebs cycle reactions. Together, these data shed light on the HK and SDH role on the metabolism of each region fed by GABA turnover, which depends on the neurons' metabolic route.

Therapy-induced DNA methylation inactivates MCT1 and renders tumor cells vulnerable to MCT4 inhibition

Metabolic plasticity in cancer cells makes use of metabolism-targeting agents very challenging. Drug-induced metabolic rewiring may, however, uncover vulnerabilities that can be exploited. We report that resistance to glycolysis inhibitor 3-bromopyruvate (3-BrPA) arises from DNA methylation in treated cancer cells and subsequent silencing of the monocarboxylate transporter MCT1. We observe that, unexpectedly, 3-BrPA-resistant cancer cells mostly rely on glycolysis to sustain their growth, with MCT4 as an essential player to support lactate flux. This shift makes cancer cells particularly suited to adapt to hypoxic conditions and resist OXPHOS inhibitors and anti-proliferative chemotherapy. In contrast, blockade of MCT4 activity in 3-BrPA-exposed cancer cells with diclofenac or genetic knockout, inhibits growth of derived spheroids and tumors in mice. This study supports a potential mode of collateral lethality according to which metabolic adaptation of tumor cells to a first-line therapy makes them more responsive to a second-line treatment.

Discovery of Halogenated Benzothiadiazine Derivatives with Anticancer Activity*

Mitochondrial respiratory complex II (CII), also known as succinate dehydrogenase, plays a critical role in mitochondrial metabolism. Known but low potency CII inhibitors are selectively cytotoxic to cancer cells including the benzothiadiazine-based anti-hypoglycemic diazoxide. Herein, we study the structure-activity relationship of benzothiadiazine derivatives for CII inhibition and their effect on cancer cells for the first time. A 15-fold increase in CII inhibition was achieved over diazoxide, albeit with micromolar IC₅₀ values. Cytotoxicity evaluation of the novel derivatives resulted in the identification of compounds with much greater antineoplastic effect than diazoxide, the most potent of which possesses an IC₅₀ of 2.93±0.07 μM in a cellular model of triple-negative breast cancer, with high selectivity over nonmalignant cells and more than double the potency of the clinical agent 5-fluorouracil. No correlation between cytotoxicity and CII inhibition was found, thus indicating an as-yet-undefined mechanism of action of this scaffold. The derivatives described herein represent valuable hit compounds for therapeutic discovery in triple-negative breast cancer.

The efficacy of the anticancer 3-bromopyruvate is potentiated by antimycin and menadione by unbalancing mitochondrial ROS production and disposal in U118 glioblastoma cells

Metabolic reprogramming of tumour cells sustains cancer progression. Similar to other cancer cells, glioblastoma cells exhibit an increased glycolytic flow, which encourages the use of antiglycolytics as an effective complementary therapy. We used the antiglycolytic 3-bromopyruvate (3BP) as a metabolic modifier to treat U118 glioblastoma cells and investigated the toxic effects and the conditions to increase drug effectiveness at the lowest concentration. Cellular vitality was not affected by 3BP concentrations lower than 40 μM, although p-Akt dephosphorylation, p53 degradation, and ATP reduction occurred already at 30 μM 3BP. ROS generated in mitochondria were enhanced at 30 μM 3BP, possibly by unbalancing their generation and their disposal because of glutathione peroxidase inhibition. ROS triggered JNK and ERK phosphorylation, and cyt c release outside mitochondria, not accompanied by caspases-9 and -3 activation, probably due to 3BP-dependent alkylation of cysteine residues at caspase-9 catalytic site. To explore the possibility of sensitizing cells to 3BP treatment, we exploited 3BP effects on mitochondria by using 30 μM 3BP in association with antimycin A or menadione concentrations that in themselves exhibit poor toxicity. 3BP effect on cyt c release and cell vitality loss was potentiated due the greater oxidative stress induced by antimycin or menadione association with 3BP, supporting a preeminent role of mitochondrial ROS in 3BP toxicity. Indeed, the scavenger of mitochondrial superoxide MitoTEMPO counteracted 3BP-induced cyt c release and weakened the potentiating effect of 3BP/antimycin association. In conclusion, the biochemical mechanisms leading U118 glioblastoma cells to viability loss following 3BP treatment rely on mitochondrial ROS-dependent pathways. Their potentiation at low 3BP concentrations is consistent with the goal to minimize the toxic effect of the drug towards non-cancer cells.

Regulation of succinate dehydrogenase and role of succinate in cancer

Succinate dehydrogenase (SDH) has been classically considered a mitochondrial enzyme with the unique property to participate in both the citric acid cycle and the electron transport chain. However, in recent years, several studies have highlighted the role of the SDH substrate, i.e. succinate, in biological processes other than metabolism, tumorigenesis being the most remarkable. For this reason, SDH has now been defined a tumor suppressor and succinate an oncometabolite. In this review, we discuss recent findings regarding alterations in SDH activity leading to succinate accumulation, which include SDH mutations, regulation of mRNA expression, post-translational modifications and endogenous SDH inhibitors. Further, we report an extensive examination of the role of succinate in cancer development through the induction of epigenetic and metabolic alterations and the effects on epithelial to mesenchymal transition, cell migration and invasion, and angiogenesis. Finally, we have focused on succinate and SDH as diagnostic markers for cancers having altered SDH expression/activity.

IL-8-induced O-GlcNAc modification via GLUT3 and GFAT regulates cancer stem cell-like properties in colon and lung cancer cells

Interleukin-8 (IL-8) is a pro-inflammatory chemokine that is associated with induction of chemotaxis and degranulation of neutrophils. IL-8 is overexpressed in many tumors, including colon and lung cancer, and recent studies demonstrated essential roles for IL-8 in tumor progression within the tumor microenvironment. However, the molecular mechanism underlying the functions of IL-8 in tumor progression is unclear. In this study, we found that IL-8 is overexpressed in colon and lung cancer cells with cancer stem cell (CSC)-like characteristics and is required for CSC properties, including tumor-initiating abilities. These findings suggest that IL-8 plays an essential role in the development of CSCs. We also showed that IL-8 stimulation of colon and lung cancer cells-induced glucose uptake and expressions of glucose transporter 3 (GLUT3) and glucosamine fructose-6-phosphate aminotransferase (GFAT), a regulator of glucose flux to the hexosamine biosynthetic pathway, resulting in enhancement of protein O-GlcNAcylation. We demonstrated that these events are required for the generation and maintenance CSC-like characteristics of colon and lung cancer cells. Moreover, an O-GlcNAcylation inhibitor, OSMI1, reduced CSC number and tumor development in vivo. Together, these results reveal that IL-8-induced O-GlcNAcylation is required for generation and maintenance of CSCs of colon and lung cancer cells and suggests this regulatory pathway as a candidate therapeutic target of CSCs.

Mitochondria-Bound Hexokinase (mt-HK) Activity Differ in Cortical and Hypothalamic Synaptosomes: Differential Role of mt-HK in H2O2 Depuration

Glucose and oxygen are vital for the brain, as these molecules provide energy and metabolic intermediates that are necessary for cell function. The glycolysis pathway and mitochondria play a pivotal role in cell energy metabolism, which is closely related to reactive oxygen species (ROS) production. Hexokinase (HK) is a key enzyme involved in glucose metabolism that modulates the level of brain mitochondrial ROS by recycling ADP for oxidative phosphorylation (OxPhos). Here, we hypothesize that the control of mitochondrial metabolism by hexokinase differs in distinct areas of the brain, such as the cortex and hypothalamus, in which ROS might function as signaling molecules. Thus, we investigated mitochondrial metabolism of synaptosomes derived from both brain regions. Cortical synaptosomes (CSy) show a predominance of glutamatergic synapses, while in the hypothalamic synaptosomes (HSy), the GABAergic synapses predominate. Significant differences of oxygen consumption and ROS production were related to higher mitochondrial complex II activity (succinate dehydrogenase-SDH) in CSy rather than to mitochondrial number. Mitochondrial HK (mt-HK) activity was higher in CSy than in HSy regardless the substrate added. Mitochondrial O₂ consumption related to mt-HK activation by 2-deoxyglucose was also higher in CSy. In the presence of substrate for complex II, the activation of synaptosomal mt-HK promoted depuration of ROS in both HSy and CSy, while ROS depuration did not occur in HSy when substrate for complex I was used. The impact of the mt-HK inhibition by glucose-6-phosphate (G6P) was the same in synaptosomes from both areas. Together, the differences found between CSy and HSy indicate specific roles of mt-HK and SDH on the metabolism of each brain region, what probably depends on the main metabolic route that is used by the neurons.

Relationship between Porcine Sperm Motility and Sperm Enzymatic Activity using Paper-based Devices

Mammalian sperm motility has traditionally been analyzed to determine fertility using computer-assisted semen analysis (CASA) systems. To develop low-cost and robust male fertility diagnostics, we created a paper-based MTT assay and used it to estimate motile sperm concentration. When porcine sperm motility was inhibited using sperm enzyme inhibitors for sperm enzymes related to mitochondrial activity and glycolysis, we simultaneously recorded sperm motility and enzymatic reactivity using a portable motility analysis system (iSperm) and a paper-based MTT assay, respectively. When using our paper-based MTT-assay, we calculated the area mean value signal intensity (AMV) to evaluate enzymatic reactivity. Both sperm motility and AMV decreased following treatment with iodoacetamide (IODO) and 3-bromopyruvic acid (3BP), both of which are inhibitors of glycolytic enzymes including glyceraldehyde-3-phosphate dehydrogenase (GAPDH). We found a correlation between recorded motility using iSperm and AMV from our paper-based assay (P < 0.05), suggesting that a sperm-related enzymatic reaction is involved in sperm motility. Under this protocol, MTT reduction was coupled with catalysis of GAPDH and was promoted by electron transfer from NADH. Based on this inhibitor study, sperm motility can be estimated using our paper-based MTT-assay.

Cancer metabolism: the volatile signature of glycolysis-in vitro model in lung cancer cells

Discovering the volatile signature of cancer cells is an emerging approach in cancer research, as it may contribute to a fast and simple diagnosis of tumors in vivo and in vitro. One of the main contributors to such a volatile signature is hyperglycolysis, which characterizes the cancerous cell. The metabolic perturbation in cancer cells is known as the Warburg effect; glycolysis is preferred over oxidative phosphorylation (OXPHOS), even in the presence of oxygen. The precise mitochondrial alterations that underlie the increased dependence of cancer cells on aerobic glycolysis for energy generation have remained a mystery. We aimed to profile the volatile signature of the glycolysis activity in lung cancer cells. For that an in vitro model, using lung cancer cell line cultures (A549, H2030, H358, H322), was developed. The volatile signature was measured by proton transfer reaction mass spectrometry under normal conditions and glycolysis inhibition. Glycolysis inhibition and mitochondrial activity were also assessed by mitochondrial respiration capacity measurements. Cells were divided into two groups upon their glycolytic profile (PET positive and PET negative). Glycolysis blockade had a unique characteristic that was shared by all cells. Furthermore, each group had a characteristic volatile signature that enabled us to discriminate between those sub-groups of cells. In conclusion, lung cancer cells may have different subpopulations of cells upon low and high mitochondrial capacity. In both groups, glycolysis blockade induced a unique volatile signature.

Transport of haloacids across biological membranes

Haloacids are considered to be environmental pollutants, but some of them have also been tested in clinical research. The way that haloacids are transported across biological membranes is important for both biodegradation and drug delivery purposes. In this review, we will first summarize putative haloacids transporters and the information about haloacids transport when studying carboxylates transporters. We will then introduce MCT1 and SLC5A8, which are respective transporter for antitumor agent 3-bromopyruvic acid and dichloroacetic acid, and monochloroacetic acid transporters Deh4p and Dehp2 from a haloacids-degrading bacterium. Phylogenetic analysis of these haloacids transporters and other monocarboxylate transporters reveals their evolutionary relationships. Haloacids transporters are not studied to the extent that they deserve compared with their great application potentials, thus future inter-discipline research are desired to better characterize their transport mechanisms for potential applications in both environmental and clinical fields.

Impaired mitochondrial functions contribute to 3-bromopyruvate toxicity in primary rat and mouse hepatocytes

A compound with promising anticancer properties, 3-bromopyruvate (3-BP) is a synthetic derivative of a pyruvate molecule; however, its toxicity in non-malignant cells has not yet been fully elucidated. Therefore, we elected to study the effects of 3-BP on primary hepatocytes in monolayer cultures, permeabilized hepatocytes and isolated mitochondria. After a 1-h treatment with 100 μM 3-BP cell viability of rat hepatocytes was decreased by 30 % as measured by the WST-1 test (p < 0.001); after 3-h exposure to ≥200 μM 3-BP lactate dehydrogenase leakage was increased (p < 0.001). Reactive oxygen species production was increased in the cell cultures after a 1-h treatment at concentrations ≥100 μmol/l (p < 0.01), and caspase 3 activity was increased after a 20-h incubation with 150 μM and 200 μM 3-BP (p < 0.001). This toxic effect of 3-BP was also proved using primary mouse hepatocytes. In isolated mitochondria, 3-BP induced a dose- and time-dependent decrease of mitochondrial membrane potential during a 10-min incubation both with Complex I substrates glutamate + malate or Complex II substrate succinate, although this decrease was more pronounced with the latter. We also measured the effect of 3-BP on respiration of isolated mitochondria. ADP-activated respiration was inhibited by 20 μM 3-BP within 10 min. Similar effects were also found in permeabilized hepatocytes of both species.

The anticancer agent 3-bromopyruvate: a simple but powerful molecule taken from the lab to the bedside

At the beginning of the twenty-first century, 3-bromopyruvate (3BP), a simple alkylating chemical compound was presented to the scientific community as a potent anticancer agent, able to cause rapid toxicity to cancer cells without bystander effects on normal tissues. The altered metabolism of cancers, an essential hallmark for their progression, also became their Achilles heel by facilitating 3BP's selective entry and specific targeting. Treatment with 3BP has been administered in several cancer type models both in vitro and in vivo, either alone or in combination with other anticancer therapeutic approaches. These studies clearly demonstrate 3BP's broad action against multiple cancer types. Clinical trials using 3BP are needed to further support its anticancer efficacy against multiple cancer types thus making it available to more than 30 million patients living with cancer worldwide. This review discusses current knowledge about 3BP related to cancer and discusses also the possibility of its use in future clinical applications as it relates to safety and treatment issues.

Killing multiple myeloma cells with the small molecule 3-bromopyruvate: implications for therapy

The small molecule 3-bromopyruvate (3-BP), which has emerged recently as the first member of a new class of potent anticancer agents, was tested for its capacity to kill multiple myeloma (MM) cancer cells. Human MM cells (RPMI 8226) begin to lose viability significantly within 8 h of incubation in the presence of 3-BP. The Km (0.3 mmol/l) for intracellular accumulation of 3-BP in MM cells is 24 times lower than that in control cells (7.2 mmol/l). Therefore, the uptake of 3-BP by MM cells is significantly higher than that by peripheral blood mononuclear cells. Further, the IC50 values for human MM cells and control peripheral blood mononuclear cells are 24 and 58 µmol/l, respectively. Therefore, specificity and selectivity of 3-BP toward MM cancer cells are evident on the basis of the above. In MM cells the transcription levels of the gene encoding the monocarboxylate transporter MCT1 is significantly amplified compared with control cells. The level of intracellular ATP in MM cells decreases by over 90% within 1 h after addition of 100 µmol/l 3-BP. The cytotoxicity of 3-BP, exemplified by a marked decrease in viability of MM cells, is potentiated by the inhibitor of glutathione synthesis buthionine sulfoximine. In addition, the lack of mutagenicity and its superior capacity relative to Glivec to kill MM cancer cells are presented in this study.

Primary clear cell renal carcinoma cells display minimal mitochondrial respiratory capacity resulting in pronounced sensitivity to glycolytic inhibition by 3-Bromopyruvate

Changes of cellular metabolism are an integral property of the malignant potential of most cancer cells. Already in the 1930s, Otto Warburg observed that tumor cells preferably utilize glycolysis and lactate fermentation for energy production, rather than the mitochondrial oxidative phosphorylation dominating in normal cells, a phenomenon today known as the Warburg effect. Even though many tumor types display a high degree of aerobic glycolysis, they still retain the activity of other energy-producing metabolic pathways. One exception seems to be the clear cell variant of renal cell carcinoma, ccRCC, where the activity of most other pathways than that of glycolysis has been shown to be reduced. This makes ccRCC a promising candidate for the use of glycolytic inhibitors in treatment of the disease. However, few studies have so far addressed this issue. In this report, we show a strikingly reduced mitochondrial respiratory capacity of primary human ccRCC cells, resulting in enhanced sensitivity to glycolytic inhibition by 3-Bromopyruvate (3BrPA). This effect was largely absent in established ccRCC cell lines, a finding that highlights the importance of using biologically relevant models in the search for new candidate cancer therapies. 3BrPA markedly reduced ATP production in primary ccRCC cells, followed by cell death. Our data suggest that glycolytic inhibitors such as 3BrPA, that has been shown to be well tolerated in vivo, should be further analyzed for the possible development of selective treatment strategies for patients with ccRCC.

Displacing hexokinase from mitochondrial voltage-dependent anion channel impairs GLT-1-mediated glutamate uptake but does not disrupt interactions between GLT-1 and mitochondrial proteins

The glutamate transporter GLT-1 is the major route for the clearance of extracellular glutamate in the forebrain, and most GLT-1 protein is found in astrocytes. This protein is coupled to the Na(+) electrochemical gradient, supporting the active intracellular accumulation of glutamate. We recently used a proteomic approach to identify proteins that may interact with GLT-1 in rat cortex, including the Na(+)/K(+) -ATPase, most glycolytic enzymes, and several mitochondrial proteins. We also showed that most GLT-1 puncta (∼ 70%) are overlapped by mitochondria in astroglial processes in organotypic slices. From this analysis, we proposed that the glycolytic enzyme hexokinase (HK)-1 might physically form a scaffold to link GLT-1 and mitochondria because HK1 is known to interact with the outer mitochondrial membrane protein voltage-dependent anion channel (VDAC). The current study validates the interactions among HK-1, VDAC, and GLT-1 by using forward and reverse immunoprecipitations and provides evidence that a subfraction of HK1 colocalizes with GLT-1 in vivo. A peptide known to disrupt the interaction between HK and VDAC did not disrupt interactions between GLT-1 and several mitochondrial proteins. In parallel experiments, displacement of HK from VDAC reduced GLT-1-mediated glutamate uptake. These results suggest that, although HK1 forms coimmunoprecipitatable complexes with both VDAC and GLT-1, it does not physically link GLT-1 to mitochondrial proteins. However, the interaction of HK1 with VDAC supports GLT-1-mediated transport activity.

Energy metabolism targeted drugs synergize with photodynamic therapy to potentiate breast cancer cell death

Malignant cells are highly dependent on aerobic glycolysis, which differs significantly from normal cells (the Warburg effect). Interference of this metabolic process has been considered as an innovative method for developing selective cancer therapy. A recent study demonstrated that the glycolysis inhibitor 2-deoxyglucose (2-DG) can potentiate PDT efficacy, whereas the possible mechanisms have not been carefully investigated. This study firstly proved the general potentiation of PDT efficacy by 2-DG and 3-bromopyruvate (3-BP) in human breast cancer MDA-MB-231 cells, and carefully elucidated the underlying mechanism in the process. Our results showed that both 2-DG and 3-BP could significantly promote a PDT-induced cell cytotoxic effect when compared with either monotherapy. Synergistic potentiation of mitochondria- and caspase-dependent cell apoptosis was observed, including a mitochondrial membrane potential (MMP) drop, Bax translocation, and caspase-3 activation. Besides, ROS generation and the expression of oxidative stress related proteins such as P38 MAPK phosphorylation and JNK phosphorylation were notably increased after the combined treatments. Moreover, when pretreated with the ROS scavenger N-acetylcysteine (NAC), the ROS generation, the MMP drop, cell apoptosis and cytotoxicity were differently inhibited, suggesting that ROS was vertical in the pro-apoptotic process induced by 2-DG/3-BP combined with PDT treatment. These results indicate that the combination of glycolytic antagonists and PDT may be a promising therapeutic strategy to effectively kill cancer cells.

The energy blockers 3-bromopyruvate and lonidamine: effects on bioenergetics of brain mitochondria

Tumor cells favor abnormal energy production via aerobic glycolysis and show resistance to apoptosis, suggesting the involvement of mitochondrial dysfunction. The differences between normal and cancer cells in their energy metabolism provide a biochemical basis for developing new therapeutic strategies. The energy blocker 3-bromopyruvate (3BP) can eradicate liver cancer in animals without associated toxicity, and is a potent anticancer towards glioblastoma cells. Since mitochondria are 3BP targets, in this work the effects of 3BP on the bioenergetics of normal rat brain mitochondria were investigated in vitro, in comparison with the anticancer agent lonidamine (LND). Whereas LND impaired oxygen consumption dependent on any complex of the respiratory chain, 3BP was inhibitory to malate/pyruvate and succinate (Complexes I and II), but preserved respiration from glycerol-3-phosphate and ascorbate (Complex IV). Accordingly, although electron flow along the respiratory chain and ATP levels were decreased by 3BP in malate/pyruvate- and succinate-fed mitochondria, they were not significantly influenced from glycerol-3-phosphate- or ascorbate-fed mitochondria. LND produced a decrease in electron flow from all substrates tested. No ROS were produced from any substrate, with the exception of 3BP-induced H(2)O(2) release from succinate, which suggests an antimycin-like action of 3BP as an inhibitor of Complex III. We can conclude that 3BP does not abolish completely respiration and ATP synthesis in brain mitochondria, and has a limited effect on ROS production, confirming that this drug may have limited harmful effects on normal cells.

Mitochondria: 3-bromopyruvate vs. mitochondria? A small molecule that attacks tumors by targeting their bioenergetic diversity

Enhanced glycolysis, the classic bioenergetic phenotype of cancer cells was described by Otto Warburg approximately 90 years ago. However, the Warburg hypothesis does not necessarily imply mitochondrial dysfunction. The alkyl-halogen, 3-bromopyruvate (3BP), would not be expected to have selective targets for cancer therapy due to its high potential reactivity toward many SH side groups. Contrary to predictions, 3BP interferes with glycolysis and oxidative phosphorylation in cancer cells without side effects in normal tissues. The mitochondrial hexokinase II has been claimed as the main target. This "Organelle in focus" article presents a historical view of the use of 3BP in biochemistry and its effects on ATP-producing pathways of cancer cells. I will discuss how the alkylated enzymes contribute to the cooperative collapse of mitochondria and apoptosis. Perspectives for targeting 3BP to bioenergetics enzymes for cancer treatment will be considered.

How does the metabolism of tumour cells differ from that of normal cells

Tumour cells thrive in environments that would be hostile to their normal cell counterparts. Survival depends on the selection of cell lines that harbour modifications of both, gene regulation that shifts the balance between the cell cycle and apoptosis and those that involve the plasticity of the metabolic machinery. With regards to metabolism, the selected phenotypes usually display enhanced anaerobic glycolysis even in the presence of oxygen, the so-called Warburg effect, and anabolic pathways that provide precursors for the synthesis of lipids, proteins and DNA. The review will discuss the original ideas of Otto Warburg and how they initially led to the notion that mitochondria of tumour cells were dysfunctional. Data will be presented to show that not only the organelles are viable and respiring, but that they are key players in tumorigenesis and metastasis. Likewise, interconnecting pathways that stand out in the tumour phenotype and that require intact mitochondria such as glutaminolysis will be addressed. Furthermore, comments will be made as to how the peculiarities of the biochemistry of tumour cells renders them amenable to new forms of treatment by highlighting possible targets for inhibitors. In this respect, a case study describing the effect of a metabolite analogue, the alkylating agent 3BP (3-bromopyruvate), on glycolytic enzyme targets will be presented.

Emerging metabolic targets in the therapy of hematological malignancies

During the last decade, the development of anticancer therapies has focused on targeting neoplastic-related metabolism. Cancer cells display a variety of changes in their metabolism, which enable them to satisfy the high bioenergetic and biosynthetic demands for rapid cell division. One of the crucial alterations is referred to as the "Warburg effect", which involves a metabolic shift from oxidative phosphorylation towards the less efficient glycolysis, independent of the presence of oxygen. Although there are many examples of solid tumors having altered metabolism with high rates of glucose uptake and glycolysis, it was only recently reported that this phenomenon occurs in hematological malignancies. This review presents evidence that targeting the glycolytic pathway at different levels in hematological malignancies can inhibit cancer cell proliferation by restoring normal metabolic conditions. However, to achieve cancer regression, high concentrations of glycolytic inhibitors are used due to limited solubility and biodistribution, which may result in toxicity. Besides using these inhibitors as monotherapies, combinatorial approaches using standard chemotherapeutic agents could display enhanced efficacy at eradicating malignant cells. The identification of the metabolic enzymes critical for hematological cancer cell proliferation and survival appears to be an interesting new approach for the targeted therapy of hematological malignancies.

MCT1-mediated transport of a toxic molecule is an effective strategy for targeting glycolytic tumors

There is increasing evidence that oncogenic transformation modifies the metabolic program of cells. A common alteration is the upregulation of glycolysis, and efforts to target glycolytic enzymes for anti-cancer therapy are underway. Here, we performed a genome-wide haploid genetic screen to identify resistance mechanisms to 3-bromopyruvate (3-BrPA), a drug candidate that inhibits glycolysis in a poorly understood fashion. We identified the SLC16A1 gene product, MCT1, as the main determinant of 3-BrPA sensitivity. MCT1 is necessary and sufficient for 3-BrPA uptake by cancer cells. Additionally, MCT1 mRNA levels are the best predictor of 3-BrPA sensitivity and are most elevated in glycolytic cancer cells. Lastly, forced MCT1 expression in 3-BrPA resistant cancer cells sensitizes tumor xenografts to 3-BrPA treatment in vivo. Our results identify a potential biomarker for 3-BrPA sensitivity and provide proof of concept that the selectivity of cancer-expressed transporters can be exploited for delivering toxic molecules to tumors.

Mitochondrial complex II, a novel target for anti-cancer agents

With the arrival of the third millennium, in spite of unprecedented progress in molecular medicine, cancer remains as untamed as ever. The complexity of tumours, dictating the potential response of cancer cells to anti-cancer agents, has been recently highlighted in a landmark paper by Weinberg and Hanahan on hallmarks of cancer [1]. Together with the recently published papers on the complexity of tumours in patients and even within the same tumour (see below), the cure for this pathology seems to be an elusive goal. Indisputably, the strategy ought to be changed, searching for targets that are generally invariant across the landscape of neoplastic diseases. One such target appears to be the mitochondrial complex II (CII) of the electron transfer chain, a recent focus of research. We document and highlight this particularly intriguing target in this review paper and give examples of drugs that use CII as their molecular target. This article is part of a Special Issue entitled: Respiratory complex II: Role in cellular physiology and disease.

3-Bromopyruvate (3BP) a fast acting, promising, powerful, specific, and effective "small molecule" anti-cancer agent taken from labside to bedside: introduction to a special issue

Although the "Warburg effect", i.e., elevated glucose metabolism to lactic acid (glycolysis) even in the presence of oxygen, has been recognized as the most common biochemical phenotype of cancer for over 80 years, its biochemical and genetic basis remained unknown for over 50 years. Work focused on elucidating the underlying mechanism(s) of the "Warburg effect" commenced in the author's laboratory in 1969. By 1985 among the novel findings made two related most directly to the basis of the "Warburg effect", the first that the mitochondrial content of tumors exhibiting this phenotype is markedly decreased relative to the tissue of origin, and the second that such mitochondria have markedly elevated amounts of the enzyme hexokinase-2 (HK2) bound to their outer membrane. HK2 is the first of a number of enzymes in cancer cells involved in metabolizing the sugar glucose to lactic acid. At its mitochondrial location HK2 binds at/near the protein VDAC (voltage dependent anion channel), escapes inhibition by its product glucose-6-phosphate, and gains access to mitochondrial produced ATP. As shown by others, it also helps immortalize cancer cells, i.e., prevents cell death. Based on these studies, the author's laboratory commenced experiments to elucidate the gene basis for the overexpression of HK2 in cancer. These studies led to both the discovery of a unique HK2 promoter region markedly activated by both hypoxic conditions and moderately activated by several metabolites (e.g., glucose), Also discovered was the promoter's regulation by epigenetic events (i.e., methylation, demethylation). Finally, the author's laboratory turned to the most important objective. Could they selectively and completely destroy cancerous tumors in animals? This led to the discovery in an experiment conceived, designed, and conducted by Young Ko that the small molecule 3-bromopyruvate (3BP), the subject of this mini-review series, is an incredibly powerful and swift acting anticancer agent. Significantly, in subsequent experiments with rodents (19 animals with advanced cancer) Ko led a project in which 3BP was shown in a short treatment period to eradicate all (100%). Ko's and co-author's findings once published attracted global attention leading world-wide to many other studies and publications related to 3BP and its potent anti-cancer effect. This Issue of the Journal of Bioenergetics and Biomembranes (JOBB 44-1) captures only a sampling of research conducted to date on 3BP as an anticancer agent, and includes also a Case Report on the first human patient known to the author to be treated with specially formulated 3BP. Suffice it to say in this bottom line, "3BP, a small molecule, results in a remarkable therapeutic effect when it comes to treating cancers exhibiting a "Warburg effect". This includes most cancer types.