Age-dependent kinetics and metabolism of dichloroacetate: possible relevance to toxicity

Effect and mechanism of Dichloroacetate in the treatment of stroke and the resolution strategy for side effect

Stroke is a serious disease that leads to high morbidity and mortality, and ischemic stroke accounts for more than 80% of strokes. At present, the only effective drug recombinant tissue plasminogen activator is limited by its indications, and its clinical application rate is not high. Therefore, it is urgent to develop effective new drugs according to the pathological mechanism. In the hypoxic state after ischemic stroke, anaerobic glycolysis has become the main way to provide energy to the brain. This process is essential for the maintenance of important brain functions and has important implications for recovery after stroke. However, acidosis caused by anaerobic glycolysis and lactic acid accumulation is an important pathological process after ischemic stroke. Dichloroacetate (DCA) is an orphan drug that has been used for decades to treat children with genetic mitochondrial diseases. Some studies have confirmed the role of DCA in stroke, but the conclusions are conflicting because some believe that DCA is not effective for ischemic stroke and may aggravate hemorrhagic stroke. This study reviews these studies and finds that DCA has a good effect on ischemic stroke. DCA can protect ischemic stroke by improving oxidative stress, reducing neuroinflammation, inhibiting apoptosis, protecting blood-brain barrier, and regulating metabolism. We also describe the differences in the outcomes of DCA in the treatment of ischemic stroke and the reasons why DCA aggravate hemorrhagic stroke. In addition, DCA, as a water disinfection byproduct, has been concerned about its toxicity. We describe the causes and solutions of peripheral neuropathy caused by DCA. In summary, this study analyzes the neuroprotective mechanism of DCA in ischemic stroke and the contradiction of the different research results, and discusses the causes and solutions of its adverse effects.

Glutathione S-transferase: A keystone in Parkinson's disease pathogenesis and therapy

Parkinson's disease is a progressive neurodegenerative disorder that predominantly affects motor function due to the loss of dopaminergic neurons in the substantia nigra. It presents significant challenges, impacting millions worldwide with symptoms such as tremors, rigidity, bradykinesia, and postural instability, leading to decreased quality of life and increased morbidity. The pathogenesis of Parkinson's disease is multifaceted, involving complex interactions between genetic susceptibility, environmental factors, and aging, with oxidative stress playing a central role in neuronal degeneration. Glutathione S-Transferase enzymes are critical in the cellular defense mechanism against oxidative stress, catalysing the conjugation of the antioxidant glutathione to various toxic compounds, thereby facilitating their detoxification. Recent research underscores the importance of Glutathione S-Transferase in the pathophysiology of Parkinson's disease, revealing that genetic polymorphisms in Glutathione S-Transferase genes influence the risk and progression of the disease. These genetic variations can affect the enzymatic activity of Glutathione S-Transferase, thereby modulating an individual's capacity to detoxify reactive oxygen species and xenobiotics, which are implicated in Parkinson's disease neuropathological processes. Moreover, biochemical studies have elucidated the role of Glutathione S-Transferase in not only maintaining cellular redox balance but also in modulating various cellular signalling pathways, highlighting its neuroprotective potential. From a therapeutic perspective, targeting Glutathione S-Transferase pathways offers promising avenues for the development of novel treatments aimed at enhancing neuroprotection and mitigating disease progression. This review explores the evident and hypothesized roles of Glutathione S-Transferase in Parkinson's disease, providing a comprehensive overview of its importance and potential as a target for therapeutic intervention.

Dichloroacetate for Cancer Treatment: Some Facts and Many Doubts

Rarely has a chemical elicited as much controversy as dichloroacetate (DCA). DCA was initially considered a dangerous toxic industrial waste product, then a potential treatment for lactic acidosis. However, the main controversies started in 2008 when DCA was found to have anti-cancer effects on experimental animals. These publications showed contradictory results in vivo and in vitro such that a thorough consideration of this compound's in cancer is merited. Despite 50 years of experimentation, DCA's future in therapeutics is uncertain. Without adequate clinical trials and health authorities' approval, DCA has been introduced in off-label cancer treatments in alternative medicine clinics in Canada, Germany, and other European countries. The lack of well-planned clinical trials and its use by people without medical training has discouraged consideration by the scientific community. There are few thorough clinical studies of DCA, and many publications are individual case reports. Case reports of DCA's benefits against cancer have been increasing recently. Furthermore, it has been shown that DCA synergizes with conventional treatments and other repurposable drugs. Beyond the classic DCA target, pyruvate dehydrogenase kinase, new target molecules have also been recently discovered. These findings have renewed interest in DCA. This paper explores whether existing evidence justifies further research on DCA for cancer treatment and it explores the role DCA may play in it.

Neuroprotective Effects and Therapeutic Potential of Dichloroacetate: Targeting Metabolic Disorders in Nervous System Diseases

Dichloroacetate (DCA) is an investigational drug used to treat lactic acidosis and malignant tumours. It works by inhibiting pyruvate dehydrogenase kinase and increasing the rate of glucose oxidation. Some studies have documented the neuroprotective benefits of DCA. By reviewing these studies, this paper shows that DCA has multiple pharmacological activities, including regulating metabolism, ameliorating oxidative stress, attenuating neuroinflammation, inhibiting apoptosis, decreasing autophagy, protecting the blood‒brain barrier, improving the function of endothelial progenitor cells, improving mitochondrial dynamics, and decreasing amyloid β-protein. In addition, DCA inhibits the enzyme that metabolizes it, which leads to peripheral neurotoxicity due to drug accumulation that may be solved by individualized drug delivery and nanovesicle delivery. In summary, in this review, we analyse the mechanisms of neuroprotection by DCA in different diseases and discuss the causes of and solutions to its adverse effects.

Clinical physiology and pharmacology of GSTZ1/MAAI

Herein I summarize the physiological chemistry and pharmacology of the bifunctional enzyme glutathione transferase zeta 1 (GSTZ1)/ maleylacetoacetate isomerase (MAAI) relevant to human physiology, drug metabolism and disease. MAAI is integral to the catabolism of the amino acids phenylalanine and tyrosine. Genetic or pharmacological inhibition of MAAI can be pathological in animals. However, to date, no clinical disease consequences are unequivocally attributable to inborn errors of this enzyme. MAAI is identical to the zeta 1 family isoform of GST, which biotransforms the investigational drug dichloroacetate (DCA) to the endogenous compound glyoxylate. DCA is a mechanism-based inhibitor of GSTZ1 that significantly reduces its rate of metabolism and increases accumulation of potentially harmful tyrosine intermediates and of the heme precursor δ-aminolevulinic acid (δ-ALA). GSTZ1 is most abundant in rodent and human liver, with its concentration several fold higher in cytoplasm than in mitochondria. Its activity and protein expression are dependent on the age of the host and the intracellular level of chloride ions. Gene association studies have linked GSTZ1 or its protein product to various physiological traits and pathologies. Haplotype variations in GSTZ1 influence the rate of DCA metabolism, enabling a genotyping strategy to allow potentially safe, precision-based drug dosing in clinical trials.

Regulating mitochondrial metabolism by targeting pyruvate dehydrogenase with dichloroacetate, a metabolic messenger

Dichloroacetate (DCA) is a naturally occurring xenobiotic that has been used as an investigational drug for over 50 years. Originally found to lower blood glucose levels and alter fat metabolism in diabetic rats, this small molecule was found to serve primarily as a pyruvate dehydrogenase kinase inhibitor. Pyruvate dehydrogenase kinase inhibits pyruvate dehydrogenase complex, the catalyst for oxidative decarboxylation of pyruvate to produce acetyl coenzyme A. Several congenital and acquired disease states share a similar pathobiology with respect to glucose homeostasis under distress that leads to a preferential shift from the more efficient oxidative phosphorylation to glycolysis. By reversing this process, DCA can increase available energy and reduce lactic acidosis. The purpose of this review is to examine the literature surrounding this metabolic messenger as it presents exciting opportunities for future investigation and clinical application in therapy including cancer, metabolic disorders, cerebral ischemia, trauma, and sepsis.

Lactic Acidosis in Patients with Solid Cancer

Significance: Cancer-associated tissue-specific lactic acidosis stimulates and mediates tumor invasion and metastasis and is druggable. Rarely, malignancy causes systemic lactic acidosis, the role of which is poorly understood. Recent Advances: The understanding of the role of lactate has shifted dramatically since its discovery. Long recognized as only a waste product, lactate has become known as an alternative metabolism substrate and a secreted nutrient that is exchanged between the tumor and the microenvironment. Tissue-specific lactic acidosis is targeted to improve the host body's anticancer defense and serves as a tool that allows the targeting of anticancer compounds. Systemic lactic acidosis is associated with poor survival. In patients with solid cancer, systemic lactic acidosis is associated with an extremely poor prognosis, as revealed by the analysis of 57 published cases in this study. Although it is considered a pathology worth treating, targeting systemic lactic acidosis in patients with solid cancer is usually inefficient. Critical Issues: Research gaps include simple questions, such as the unknown nuclear pH of the cancer cells and its effects on chemotherapy outcomes, pH sensitivity of glycosylation in cancer cells, in vivo mechanisms of response to acidosis in the absence of lactate, and overinterpretation of in vitro results that were obtained by using cells that were not preadapted to acidic environments. Future Directions: Numerous metabolism-targeting anticancer compounds induce lactatemia, lactic acidosis, or other types of acidosis. Their potential to induce acidic environments is largely overlooked, although the acidosis might contribute to a substantial portion of the observed clinical effects. Antioxid. Redox Signal. 37, 1130-1152.

Targeting Glucose Metabolism of Cancer Cells with Dichloroacetate to Radiosensitize High-Grade Gliomas

As the cornerstone of high-grade glioma (HGG) treatment, radiotherapy temporarily controls tumor cells via inducing oxidative stress and subsequent DNA breaks. However, almost all HGGs recur within months. Therefore, it is important to understand the underlying mechanisms of radioresistance, so that novel strategies can be developed to improve the effectiveness of radiotherapy. While currently poorly understood, radioresistance appears to be predominantly driven by altered metabolism and hypoxia. Glucose is a central macronutrient, and its metabolism is rewired in HGG cells, increasing glycolytic flux to produce energy and essential metabolic intermediates, known as the Warburg effect. This altered metabolism in HGG cells not only supports cell proliferation and invasiveness, but it also contributes significantly to radioresistance. Several metabolic drugs have been used as a novel approach to improve the radiosensitivity of HGGs, including dichloroacetate (DCA), a small molecule used to treat children with congenital mitochondrial disorders. DCA reverses the Warburg effect by inhibiting pyruvate dehydrogenase kinases, which subsequently activates mitochondrial oxidative phosphorylation at the expense of glycolysis. This effect is thought to block the growth advantage of HGGs and improve the radiosensitivity of HGG cells. This review highlights the main features of altered glucose metabolism in HGG cells as a contributor to radioresistance and describes the mechanism of action of DCA. Furthermore, we will summarize recent advances in DCA's pre-clinical and clinical studies as a radiosensitizer and address how these scientific findings can be translated into clinical practice to improve the management of HGG patients.

Targeting Glucose Metabolism of Cancer Cells with Dichloroacetate to Radiosensitize High-Grade Gliomas

As the cornerstone of high-grade glioma (HGG) treatment, radiotherapy temporarily controls tumor cells via inducing oxidative stress and subsequent DNA breaks. However, almost all HGGs recur within months. Therefore, it is important to understand the underlying mechanisms of radioresistance, so that novel strategies can be developed to improve the effectiveness of radiotherapy. While currently poorly understood, radioresistance appears to be predominantly driven by altered metabolism and hypoxia. Glucose is a central macronutrient, and its metabolism is rewired in HGG cells, increasing glycolytic flux to produce energy and essential metabolic intermediates, known as the Warburg effect. This altered metabolism in HGG cells not only supports cell proliferation and invasiveness, but it also contributes significantly to radioresistance. Several metabolic drugs have been used as a novel approach to improve the radiosensitivity of HGGs, including dichloroacetate (DCA), a small molecule used to treat children with congenital mitochondrial disorders. DCA reverses the Warburg effect by inhibiting pyruvate dehydrogenase kinases, which subsequently activates mitochondrial oxidative phosphorylation at the expense of glycolysis. This effect is thought to block the growth advantage of HGGs and improve the radiosensitivity of HGG cells. This review highlights the main features of altered glucose metabolism in HGG cells as a contributor to radioresistance and describes the mechanism of action of DCA. Furthermore, we will summarize recent advances in DCA’s pre-clinical and clinical studies as a radiosensitizer and address how these scientific findings can be translated into clinical practice to improve the management of HGG patients.

Targeting pyruvate dehydrogenase kinase signaling in the development of effective cancer therapy

Pyruvate is irreversibly decarboxylated to acetyl coenzyme A by mitochondrial pyruvate dehydrogenase complex (PDC). Decarboxylation of pyruvate is considered a crucial step in cell metabolism and energetics. The cancer cells prefer aerobic glycolysis rather than mitochondrial oxidation of pyruvate. This attribute of cancer cells allows them to sustain under indefinite proliferation and growth. Pyruvate dehydrogenase kinases (PDKs) play critical roles in many diseases because they regulate PDC activity. Recent findings suggest an altered metabolism of cancer cells is associated with impaired mitochondrial function due to PDC inhibition. PDKs inhibit the PDC activity via phosphorylation of the E1a subunit and subsequently cause a glycolytic shift. Thus, inhibition of PDK is an attractive strategy in anticancer therapy. This review highlights that PDC/PDK axis could be implicated in cancer's therapeutic management by developing potential small-molecule PDK inhibitors. In recent years, a dramatic increase in the targeting of the PDC/PDK axis for cancer treatment gained an attention from the scientific community. We further discuss breakthrough findings in the PDC-PDK axis. In addition, structural features, functional significance, mechanism of activation, involvement in various human pathologies, and expression of different forms of PDKs (PDK1-4) in different types of cancers are discussed in detail. We further emphasized the gene expression profiling of PDKs in cancer patients to prognosis and therapeutic manifestations. Additionally, inhibition of the PDK/PDC axis by small molecule inhibitors and natural compounds at different clinical evaluation stages has also been discussed comprehensively.

Exposure of Rats to Multiple Oral Doses of Dichloroacetate Results in Upregulation of Hepatic Glutathione Transferases and NAD(P)H Dehydrogenase [Quinone] 1

Dichloroacetate (DCA) is an investigational drug that is used in the treatment of various congenital and acquired disorders of energy metabolism. Although DCA is generally well tolerated, some patients experience peripheral neuropathy, a side effect more common in adults than children. Repetitive DCA dosing causes downregulation of its metabolizing enzyme, glutathione transferase zeta 1 (GSTZ1), which is also critical in the detoxification of maleylacetoacetate and maleylacetone. GSTZ1 (-/-) knockout mice show upregulation of glutathione transferases (GSTs) and antioxidant enzymes as well as an increase in the ratio of oxidized glutathione (GSSG) to reduced glutathione (GSH), suggesting GSTZ1 deficiency causes oxidative stress. We hypothesized that DCA-mediated depletion of GSTZ1 causes oxidative stress and used the rat to examine induction of GSTs and antioxidant enzymes after repeated DCA exposure. We determined the expression of alpha, mu, pi, and omega class GSTs, NAD(P)H dehydrogenase [quinone] 1 (NQO1), gamma-glutamylcysteine ligase complex (GCLC), and glutathione synthetase (GSS). GSH and GSSG levels were measured by liquid chromatography-tandem mass spectrometry. Enzyme activity was measured in hepatic cytosol using 1-chloro-2,4-dinitrobenzene, 1,2-dichloro-4-nitrobenzene, and 2,6-dichloroindophenol as substrates. In comparison with acetate-treated controls, DCA dosing increased the relative expression of GSTA1/A2 irrespective of rodent age, whereas only adults displayed higher levels of GSTM1 and GSTO1. NQO1 expression and activity were higher in juveniles after DCA dosing. GSH concentrations were increased by DCA in adults, but the GSH:GSSG ratio was not changed. Levels of GCLC and GSS were higher and lower, respectively, in adults treated with DCA. We conclude that DCA-mediated depletion of GSTZ1 causes oxidative stress and promotes the induction of antioxidant enzymes that may vary between age groups. SIGNIFICANCE STATEMENT: Treatment with the investigational drug, dichloroacetate (DCA), results in loss of glutathione transferase zeta 1 (GSTZ1) and subsequent increases in body burden of the electrophilic tyrosine metabolites, maleylacetoacetate and maleylacetone. Loss of GSTZ1 in genetically modified mice is associated with induction of glutathione transferases and alteration of the ratio of oxidized to reduced glutathione. Therefore, we determined whether pharmacological depletion of GSTZ1 through repeat administration of DCA produced similar changes in the liver, which could affect responses to other drugs and toxicants.

Effects of Multiple Doses of Dichloroacetate on GSTZ1 Expression and Activity in Liver and Extrahepatic Tissues of Young and Adult Rats

Glutathione transferase zeta 1 (GSTZ1), expressed in liver and several extrahepatic tissues, catalyzes dechlorination of dichloroacetate (DCA) to glyoxylate. DCA inactivates GSTZ1, leading to autoinhibition of its metabolism. DCA is an investigational drug for treating several congenital and acquired disorders of mitochondrial energy metabolism, including cancer. The main adverse effect of DCA, reversible peripheral neuropathy, is more common in adults treated long-term than in children, who metabolize DCA more quickly after multiple doses. One dose of DCA to Sprague Dawley rats reduced GSTZ1 expression and activity more in liver than in extrahepatic tissues; however, the effects of multiple doses of DCA that mimic its therapeutic use have not been studied. Here, we examined the expression and activity of GSTZ1 in cytosol and mitochondria of liver, kidney, heart, and brain 24 hours after completion of 8-day oral dosing of 100 mg/kg per day sodium DCA to juvenile and adult Sprague Dawley rats. Activity was measured with DCA and with 1,2-epoxy-3-(4-nitrophenoxy)propane (EPNPP), reported to be a GSTZ1-selective substrate. In DCA-treated rats, liver retained higher expression and activity of GSTZ1 with DCA than other tissues, irrespective of rodent age. DCA-treated juvenile rats retained more GSTZ1 activity with DCA than adults. Consistent with this finding, there was less measurable DCA in tissues of juvenile than adult rats. DCA-treated rats retained activity with EPNPP, despite losing over 98% of GSTZ1 protein. These data provide insight into the differences between children and adults in DCA elimination under a therapeutic regimen and confirm that the liver contributes more to DCA metabolism than other tissues. SIGNIFICANCE STATEMENT: Dichloroacetate (DCA) is one of few drugs exhibiting higher clearance from children than adults, after repeated doses, for reasons that are unclear. We hypothesized that juveniles retain more glutathione transferase zeta 1 (GSTZ1) than adults in tissues after multiple DCA doses and found this was the case for liver and kidney, with rat as a model to assess GSTZ1 protein expression and activity with DCA. Although 1,2-epoxy-3-(4-nitrophenoxy)propane was reported to be a selective GSTZ1 substrate, its activity was not reduced in concert with GSTZ1 protein.

An Understudied Dimension: Why Age Needs to Be Considered When Studying Epigenetic-Environment Interactions

We live in a complex chemical environment where there are an estimated 350 000 chemical compounds or mixtures commercially produced. A strong body of literature shows that there are time points during early development when an organism’s epigenome is particularly sensitive to chemicals in its environment. What is less understood is how gene-environment and epigenetic-environment interactions change with age. This question is bidirectional: (1) how do chemicals in the environment affect the aging process and (2) how does aging affect an organism’s response to its chemical environment? The study of gene-environment interactions with age is especially important because, in many parts of the world, older individuals are a large and rapidly growing proportion of the population and because aging is a process universal to most of the animal kingdom. Epigenetics has emerged as a crucial framework for studying aging as epigenetic pathways, often triggered by environmental stimuli, have been shown to be essential regulators of the aging process. In this perspective article, we delineate the connection between aging, epigenetics, and environmental exposures. We discuss why it is essential to consider age when researching how an organism interacts with its environment. We describe recent advances in understanding how the chemical environment affects aging and the gap in research on how age affects an organism’s response to the environment. Finally, we highlight how model organisms and network approaches can help fill this crucial gap. Taken together, systemic changes that occur in the epigenome with age indicate that adult organisms cannot be treated as a homogeneous population and that there are discrete mechanisms modulating the aging epigenome that we do not yet understand.

Melatonin inhibits Warburg-dependent cancer by redirecting glucose oxidation to the mitochondria: a mechanistic hypothesis

Melatonin has the ability to intervene in the initiation, progression and metastasis of some experimental cancers. A large variety of potential mechanisms have been advanced to describe the metabolic and molecular events associated with melatonin's interactions with cancer cells. There is one metabolic perturbation that is common to a large number of solid tumors and accounts for the ability of cancer cells to actively proliferate, avoid apoptosis, and readily metastasize, i.e., they use cytosolic aerobic glycolysis (the Warburg effect) to rapidly generate the necessary ATP required for the high metabolic demands of the cancer cells. There are several drugs, referred to as glycolytic agents, that cause cancer cells to abandon aerobic glycolysis and shift to the more conventional mitochondrial oxidative phosphorylation for ATP synthesis as in normal cells. In doing so, glycolytic agents also inhibit cancer growth. Herein, we hypothesize that melatonin also functions as an inhibitor of cytosolic glycolysis in cancer cells using mechanisms, i.e., downregulation of the enzyme (pyruvate dehydrogenase kinase) that interferes with the conversion of pyruvate to acetyl CoA in the mitochondria, as do other glycolytic drugs. In doing so, melatonin halts the proliferative activity of cancer cells, reduces their metastatic potential and causes them to more readily undergo apoptosis. This hypothesis is discussed in relation to the previously published reports. Whereas melatonin is synthesized in the mitochondria of normal cells, we hypothesize that this synthetic capability is not present in cancer cell mitochondria because of the depressed acetyl CoA; acetyl CoA is necessary for the rate limiting enzyme in melatonin synthesis, arylalkylamine-N-acetyltransferase. Finally, the ability of melatonin to switch glucose oxidation from the cytosol to the mitochondria also explains how tumors that become resistant to conventional chemotherapies are re-sensitized to the same treatment when melatonin is applied.

Pharmacokinetic and Biochemical Profiling of Sodium Dichloroacetate in Pregnant Ewes and Fetuses

Sodium dichloroacetate (DCA) is an investigational drug that shows promise in the treatment of acquired and congenital mitochondrial diseases, including myocardial ischemia and failure. DCA increases glucose utilization and decreases lactate production, so it may also have clinical utility in reducing lactic acidosis during labor. In the current study, we tested the ability of DCA to cross the placenta and be measured in fetal blood after intravenous administration to pregnant ewes during late gestation and labor. Sustained administration of DCA to the mother over 72 hours achieved pharmacologically active levels of DCA in the fetus and decreased fetal plasma lactate concentrations. Multicompartmental pharmacokinetics modeling indicated that drug metabolism in the fetal and maternal compartments is best described by the DCA inhibiting lactate production in both compartments, consistent with our finding that the hepatic expression of the DCA-metabolizing enzyme glutathione transferase zeta1 was decreased in the ewes and their fetuses exposed to the drug. We provide the first evidence that DCA can cross the placental compartment to enter the fetal circulation and inhibit its own hepatic metabolism in the fetus, leading to increased DCA concentrations and decreased fetal plasma lactate concentrations during its parenteral administration to the mother. SIGNIFICANCE STATEMENT: This study was the first to administer sodium dichloroacetate (DCA) to pregnant animals (sheep). It showed that DCA administered to the mother can cross the placental barrier and achieve concentrations in fetus sufficient to decrease fetal lactate concentrations. Consistent with findings reported in other species, DCA-mediated inhibition of glutathione transferase zeta1 was also observed in ewes, resulting in reduced metabolism of DCA after prolonged administration.

Structural basis for the inhibition of PDK2 by novel ATP- and lipoyl-binding site targeting compounds

Pyruvate dehydrogenase kinase (PDK) controls the activity of pyruvate decarboxylase complex (PDC) by phosphorylating key serine residues on the E1 subunit, which leads to a decreased oxidative phosphorylation in mitochondria. Inhibition of PDK activity by natural/synthetic compounds has been shown to reverse the Warburg effect, a characteristic metabolism in cancer cells. PDK-PDC axis also has been associated with diabetes and heart disease. Therefore, regulation of PDK activity has been considered as a promising strategy to treat related diseases. Here we present the X-ray crystal structure of PDK2 complexed with a recently identified PDK4 inhibitor, compound 8c, which has been predicted to bind at the lipoyl-binding site and interrupt intermolecular interactions with the E2-E3bp subunits of PDC. The co-crystal structure confirmed the specific binding location of compound 8c and revealed the remote conformational change in the ATP-binding pocket. In addition, two novel 4,5-diarylisoxazole derivatives, GM10030 and GM67520, were synthesized and used for structural studies, which target the ATP-binding site of PDK2. These compounds bind to PDK2 with a sub-100nM affinity as determined by isothermal titration calorimetry experiments. Notably, the crystal structure of the PDK2-GM10030 complex displays unprecedented asymmetric conformation of human PDK2 dimer, especially in the ATP-lids and C-terminal tails.

Cancer cachexia has many symptoms but only one cause: anoxia

During nearly 100 years of research on cancer cachexia (CC), science has been reciting the same mantra: it is a multifactorial syndrome. The aim of this paper is to show that the symptoms are many, but they have a single cause: anoxia. CC is a complex and devastating condition that affects a high proportion of advanced cancer patients. Unfortunately, it cannot be reversed by traditional nutritional support and it generally reduces survival time. It is characterized by significant weight loss, mainly from fat deposits and skeletal muscles. The occurrence of cachexia in cancer patients is usually a late phenomenon. The conundrum is why do similar patients with similar tumors, develop cachexia and others do not? Even if cachexia is mainly a metabolic dysfunction, there are other issues involved such as the activation of inflammatory responses and crosstalk between different cell types.  The exact mechanism leading to a wasting syndrome is not known, however there are some factors that are surely involved, such as anorexia with lower calorie intake, increased glycolytic flux, gluconeogenesis, increased lipolysis and severe tumor hypoxia. Based on this incomplete knowledge we put together a scheme explaining the molecular mechanisms behind cancer cachexia, and surprisingly, there is one cause that explains all of its characteristics: anoxia.  With this different view of CC we propose a treatment based on the physiopathology that leads from anoxia to the symptoms of CC.  The fundamentals of this hypothesis are based on the idea that CC is the result of anoxia causing intracellular lactic acidosis. This is a dangerous situation for cell survival which can be solved by activating energy consuming gluconeogenesis. The process is conducted by the hypoxia inducible factor-1α. This hypothesis was built by putting together pieces of evidence produced by authors working on related topics.

Dichloroacetate Overcomes Oxaliplatin Chemoresistance in Colorectal Cancer through the miR-543/PTEN/Akt/mTOR Pathway

Chemoresistance is responsible for most colorectal cancer (CRC) related deaths. In this study, we found that dichloroacetate (DCA), a pyruvate dehydrogenase kinase (PDK) inhibitor, can be used as a sensitizer for oxaliplatin (L-OHP) chemoresistant CRC cells. The aim of this study was to explore the ability of DCA to overcome L-OHP resistance in CRC cells and to identify the underlying molecular mechanisms. We found that DCA sensitizes chemoresistant CRC cells to L-OHP-induced cytotoxic effects by inhibiting clone formation capacity and promoting cell apoptosis. A microRNA (miRNA) array was used for screen, and miR-543 was identified and shown to be downregulated after DCA treatment. The expression of miR-543 was higher in chemoresistant CRC cells than in chemosensitive CRC cells. Overexpression of miR-543 increased chemoresistance in CRC cells. The validated target gene, PTEN, was negatively regulated by miR-543 both in vitro and in vivo, and PTEN was upregulated by DCA through miR-543. In addition, overexpression of miR-543 reversed the inhibition of colony formation after DCA treatment. Furthermore, the Akt/mTOR pathway is activated by miR-543 and is involved in the miR-543 induced chemoresistance. There was a significant inverse relationship between miR-543 expression and PTEN level in CRC patients, and high miR-543 expression was associated with worse prognosis. In conclusion, DCA restored chemosensitivity through miR-543/PTEN/Akt/mTOR pathway, and miR-543 may be a potential marker or therapeutic target for chemoresistance in CRC.

Dichloroacetate restores colorectal cancer chemosensitivity through the p53/miR-149-3p/PDK2-mediated glucose metabolic pathway

The development of chemoresistance remains a major challenge that accounts for colorectal cancer (CRC) lethality. Dichloroacetate (DCA) was originally used as a metabolic regulator in the treatment of metabolic diseases; here, DCA was assayed to identify the mechanisms underlying the chemoresistance of CRC. We found that DCA markedly enhanced chemosensitivity of CRC cells to fluorouracil (5-FU), and reduced the colony formation due to high levels of apoptosis. Using the microarray assay, we noted that miR-149-3p was involved in the chemoresistance of CRC, which was modulated by wild-type p53 after DCA treatment. In addition, PDK2 was identified as a direct target of miR-149-3p. Mechanistic analyses showed that overexpression of miR-149-3p enhanced 5-FU-induced apoptosis and reduced glucose metabolism, similar to the effects of PDK2 knockdown. In addition, overexpression of PDK2 partially reversed the inhibitory effect of miR-149-3p on glucose metabolism. Finally, both DCA treatment and miR-149-3p overexpression in 5-FU-resistant CRC cells were found to markedly sensitize the chemotherapeutic effect of 5-FU in vivo, and this effect was also validated in a small retrospective cohort of CRC patients. Taken together, we determined that the p53/miR-149-3p/PDK2 signaling pathway can potentially be targeted with DCA treatment to overcome chemoresistant CRC.

Mitochondrial Glutathione Transferase Zeta 1 Is Inactivated More Rapidly by Dichloroacetate than the Cytosolic Enzyme in Adult and Juvenile Rat Liver

Dichloroacetate (DCA) has potential for treating mitochondrial disorders and cancer by activating the mitochondrial pyruvate dehydrogenase complex. Repeated dosing of DCA results in reduced drug clearance due to inactivation of glutathione transferase ζ1 (GSTZ1), its metabolizing enzyme. We investigated the time-course of inactivation of GSTZ1 in hepatic cytosol and mitochondria after one oral dose of 100 mg/kg DCA to female Sprague-Dawley rats aged 4 weeks (young) and 52 weeks (adult) as models for children and adults, respectively. GSTZ1 activity with both DCA and an endogenous substrate, maleylacetone (MA), as well as GSTZ1 protein expression were rapidly reduced in cytosol from both ages following DCA treatment. In mitochondria, loss of GSTZ1 protein and activity with DCA were even more rapid. The cytosolic in vivo half-lives of the loss of GSTZ1 activity with DCA were 1.05 ± 0.03 and 0.82 ± 0.02 h (mean ± S.D., n = 6) for young and adult rats, respectively, with inactivation significantly more rapid in adult rats, p < 0.001. The mitochondrial inactivation half-lives were similar in young (0.57 ± 0.02 h) and adult rats (0.54 ± 0.02 h) and were significantly (p < 0.0001) shorter than cytosolic inactivation half-lives. By 24 h after DCA administration, activity and expression remained at 10% or less than control values. The in vitro GSTZ1 inactivation half-lives following incubation with 2 mM DCA in the presence of physiological chloride (Cl^-) concentrations (cytosol = 44 mM, mitochondria = 1-2 mM) exhibited marked differences between subcellular fractions, being 3 times longer in the cytosol than in the mitochondria, regardless of age, suggesting that the lower Cl^- concentration in mitochondria explained the faster degradation of GSTZ1. These results demonstrate for the first time that rat mitochondrial GSTZ1 is more readily inactivated by DCA than cytosolic GSTZ1, and cytosolic GSTZ1 is inactivated more rapidly in adult than young rats.

The Importance of Gender-Related Anticancer Research on Mitochondrial Regulator Sodium Dichloroacetate in Preclinical Studies In Vivo

Sodium dichloroacetate (DCA) is an investigational medicinal product which has a potential anticancer preparation as a metabolic regulator in cancer cells’ mitochondria. Inhibition of pyruvate dehydrogenase kinases by DCA keeps the pyruvate dehydrogenase complex in the active form, resulting in decreased lactic acid in the tumor microenvironment. This literature review displays the preclinical research data on DCA’s effects on the cell pyruvate dehydrogenase deficiency, pyruvate mitochondrial oxidative phosphorylation, reactive oxygen species generation, and the Na⁺–K⁺–2Cl⁻ cotransporter expression regulation in relation to gender. It presents DCA pharmacokinetics and the hepatocarcinogenic effect, and the safety data covers the DCA monotherapy efficacy for various human cancer xenografts in vivo in male and female animals. Preclinical cancer researchers report the synergistic effects of DCA combined with different drugs on cancer by reversing resistance to chemotherapy and promoting cell apoptosis. Researchers note that female and male animals differ in the mechanisms of cancerogenesis but often ignore studying DCA’s effects in relation to gender. Preclinical gender-related differences in DCA pharmacology, pharmacological mechanisms, and the elucidation of treatment efficacy in gonad hormone dependency could be relevant for individualized therapy approaches so that gender-related differences in treatment response and safety can be proposed.

Gender-Related Effect of Sodium Dichloroacetate on the Number of Hassall's Corpuscles and RNA NKCC1 Expression in Rat Thymus

The aim was to investigate the effect of dichloroacetate (DCA) on thymus weight, Hassall's corpuscle number (HCs), and NKCC1 RNA expression in Wistar rats aged 4–5 weeks. They were investigated in the controls and DCA-treated gonad-intact and castrated males and females. The treatment lasted 4 weeks with DCA 200 mg/kg/day. At the end of the experiment, rat thymus was weighted, and its lobe was taken for the expression of NKCC1 RNA determined by the PCR method and of Hassall's corpuscles by immunohistochemistry. DCA caused a thymus weight decrease in DCA-treated gonad-intact rats of both genders as compared with their controls (p < 0.05), and no such impact was found in castrated DCA-treated males and females. DCA caused an increase of the HCs in gonad-intact males (p < 0.05), and no such increase in the DCA-treated gonad-intact females was found. There was gender-related difference in the HCs when comparing DCA-treated gonad-intact males and females: males showed significantly higher HCs (p < 0.05); no gender-related differences were found in the castrated DCA-treated groups. The Slc12a2 gene RNA expression level was found to be significantly decreased only in gonad-intact and in castrated DCA-treated males. The authors discuss the gender-related DCA effects on the thymus.

Dichloroacetate-induced peripheral neuropathy

Dichloroacetate (DCA) has been the focus of research by both environmental toxicologists and biomedical scientists for over 50 years. As a product of water chlorination and a metabolite of certain industrial chemicals, DCA is ubiquitous in our biosphere at low μg/kg body weight daily exposure levels without obvious adverse effects in humans. As an investigational drug for numerous congenital and acquired diseases, DCA is administered orally or parenterally, usually at doses of 10-50mg/kg per day. As a therapeutic, its principal mechanism of action is to inhibit pyruvate dehydrogenase kinase (PDK). In turn, PDK inhibits the key mitochondrial energy homeostat, pyruvate dehydrogenase complex (PDC), by reversible phosphorylation. By blocking PDK, DCA activates PDC and, consequently, the mitochondrial respiratory chain and ATP synthesis. A reversible sensory/motor peripheral neuropathy is the clinically limiting adverse effect of chronic DCA exposure and experimental data implicate the Schwann cell as a toxicological target. It has been postulated that stimulation of PDC and respiratory chain activity by DCA in normally glycolytic Schwann cells causes uncompensated oxidative stress from increased reactive oxygen species production. Additionally, the metabolism of DCA interferes with the catabolism of the amino acids phenylalanine and tyrosine and with heme synthesis, resulting in accumulation of reactive molecules capable of forming adducts with DNA and proteins and also resulting in oxidative stress. Preliminary evidence in rodent models of peripheral neuropathy suggest that DCA-induced neurotoxicity may be mitigated by naturally occurring antioxidants and by a specific class of muscarinic receptor antagonists. These findings generate a number of testable hypotheses regarding the etiology and treatment of DCA peripheral neuropathy.

Age-associated changes in GSH S-transferase gene/proteins in livers of rats

OBJECTIVES

Glutathione S-transferases (GSTs) are phase-II metabolic enzymes playing important roles in drug metabolism, anti-oxidative stress and anti-aging. Age is a key factor influencing GSTs expression. Thus, age-related changes of 10 GSTs were examined.

METHODS

Livers from male Sprague-Dawley rats at fetus (-2 d), neonates (1, 7, 14 and 21 d), puberty (28 and 35 d), adulthood (60 and 180 d), and aging (540 and 800 d), were collected and subjected to qPCR analysis. Liver proteins from 14, 28, 60, 180, 540 and 800 d were also extracted for selected protein analysis by Western-blot.

RESULTS

The expression of GSTA1 and GSTP1 increased over the life span and the expression of GSTA4, GSTO1 and GSTZ1 gradually increased until adulthood, and slightly decreased at 800 days. The expression of GSTM1, GSTM3, GSTT1, GSTT2 and GSTK1 gradually increased until adulthood, but significantly decreased during aging of 540 and 800 days. There is a small peak at 7-14 d for GSTA1, GSTP1 and GSTZ1. The protein expression of GSTA1, GSTM1 and GSTP1 followed the trend of mRNA changes.

DISCUSSION

This study characterized three expression patterns of 10 GSTs during development and aging in rat liver, adding to our understanding of anti-aging role of GSTs.

Age-Related Changes in Expression and Activity of Human Hepatic Mitochondrial Glutathione Transferase Zeta1

Glutathione transferase zeta1 (GSTZ1) catalyzes glutathione (GSH)-dependent dechlorination of dichloroacetate (DCA), an investigational drug with therapeutic potential in metabolic disorders and cancer. GSTZ1 is expressed in both hepatic cytosol and mitochondria. Here, we examined the ontogeny and characterized the properties of human mitochondrial GSTZ1. GSTZ1 expression and activity with DCA were determined in 103 human hepatic mitochondrial samples prepared from livers of donors aged 1 day to 84 years. DNA from each sample was genotyped for three common GSTZ1 functional single nucleotide polymorphisms. Expression of mitochondrial GSTZ1 protein increased in an age-dependent manner to a plateau after age 21 years. Activity with DCA correlated with expression, after taking into account the somewhat higher activity of samples that were homo- or heterozygous for GSTZ1A. In samples from livers with the GSTZ1C variant, apparent enzyme kinetic constants for DCA and GSH were similar for mitochondria and cytosol after correcting for the loss of GSH observed in mitochondrial incubations. In the presence of 38 mM chloride, mitochondrial GSTZ1 exhibited shorter half-lives of inactivation compared with the cytosolic enzyme (P = 0.017). GSTZ1 protein isolated from mitochondria was shown by mass spectrometry to be identical to cytosolic GSTZ1 protein in the covered primary protein sequence. In summary, we report age-related development in the expression and activity of human hepatic mitochondrial GSTZ1 does not have the same pattern as that reported for cytosolic GSTZ1. Some properties of cytosolic and mitochondrial GSTZ1 differed, but these were not related to differences in amino acid sequence or post-translationally modified residues.

Regulation of dichloroacetate biotransformation in rat liver and extrahepatic tissues by GSTZ1 expression and chloride concentration

Biotransformation of dichloroacetate (DCA) to glyoxylate by hepatic glutathione transferase zeta 1 (GSTZ1) is considered the principal determinant of the rate of plasma clearance of the drug. However, several other organismal and subcellular factors are also known to influence DCA metabolism. We utilized a female rat model to study these poorly understood processes. Rats aged 4 weeks (young) and 42-52 weeks (adult) were used to model children and adults, respectively. Hepatic chloride concentrations, which influence the rate of GSTZ1 inactivation by DCA, were lower in rat than in human tissues and rats did not show the age dependence previously seen in humans. We found GSTZ1 expression and activity in rat brain, heart, and kidney cell-free homogenates that were age-dependent. GSTZ1 expression in brain was higher in young rats than adult rats, whereas cardiac and renal GSTZ1 expression levels were higher in adult than young rats. GSTZ1 activity with DCA could not be measured accurately in kidney cell-free homogenates due to rapid depletion of glutathione by γ-glutamyl transpeptidase. Following oral administration of DCA, 100 mg/kg, to rats, GSTZ1 expression and activity were reduced in all rat tissues, but chloride concentrations were not affected. Together, these data extend our understanding of factors that determine the in vivo kinetics of DCA.

Treating patients suffering from myalgic encephalopathy/chronic fatigue syndrome (ME/CFS) with sodium dichloroacetate: An open-label, proof-of-principle pilot trial

Twenty-two consecutive patients suffering from refractory myalgic encephalitis/chronic fatigue syndrome (ME/CFS) were treated with an innovative nutriceutical containing sodium dichloroacetate in a proof-of-principle, pilot, open-label prospective cohort trial. Ten patients experienced significant improvement of their health condition with reduction to almost half of their score in the fatigue severity scale. In twelve patients treatment failed to exert any beneficial effect. In the latter patients several other diseases have commonly been revealed by extensive biological and imaging investigations. These preliminary findings sustain the hypothetical role of mitochondrial hypo-metabolism due to inhibition of the activity of the pyruvate dehydrogenase in the pathogenesis of primary ME/CFS, and suggest a possible benefit of nutriceutical treatment by sodium dichloroacetate.

Therapeutic Targeting of the Pyruvate Dehydrogenase Complex/Pyruvate Dehydrogenase Kinase (PDC/PDK) Axis in Cancer

The mitochondrial pyruvate dehydrogenase complex (PDC) irreversibly decarboxylates pyruvate to acetyl coenzyme A, thereby linking glycolysis to the tricarboxylic acid cycle and defining a critical step in cellular bioenergetics. Inhibition of PDC activity by pyruvate dehydrogenase kinase (PDK)-mediated phosphorylation has been associated with the pathobiology of many disorders of metabolic integration, including cancer. Consequently, the PDC/PDK axis has long been a therapeutic target. The most common underlying mechanism accounting for PDC inhibition in these conditions is post-transcriptional upregulation of one or more PDK isoforms, leading to phosphorylation of the E1α subunit of PDC. Such perturbations of the PDC/PDK axis induce a "glycolytic shift," whereby affected cells favor adenosine triphosphate production by glycolysis over mitochondrial oxidative phosphorylation and cellular proliferation over cellular quiescence. Dichloroacetate is the prototypic xenobiotic inhibitor of PDK, thereby maintaining PDC in its unphosphorylated, catalytically active form. However, recent interest in the therapeutic targeting of the PDC/PDK axis for the treatment of cancer has yielded a new generation of small molecule PDK inhibitors. Ongoing investigations of the central role of PDC in cellular energy metabolism and its regulation by pharmacological effectors of PDKs promise to open multiple exciting vistas into the biochemical understanding and treatment of cancer and other diseases.

Model Informed Dose Optimization of Dichloroacetate for the Treatment of Congenital Lactic Acidosis in Children

Dichloroacetate (DCA) is an investigational drug used to treat congenital lactic acidosis and other mitochondrial disorders. Response to DCA therapy in young children may be suboptimal following body weight-based dosing. This is because of autoinhibition of its metabolism, age-dependent changes in pharmacokinetics, and polymorphisms in glutathione transferase zeta 1 (GSTZ1), its primary metabolizing enzyme. Our objective was to predict optimal DCA doses for the treatment of congenital lactic acidosis in children. Accordingly, a semimechanistic pharmacokinetic-enzyme turnover model was developed in a step-wise approach: (1) a population pharmacokinetic model for adults was developed; (2) the adult model was scaled to children using allometry and physiology-based scaling; and (3) the scaled model was externally qualified, updated with clinical data, and optimal doses were projected. A 2-compartment model accounting for saturable clearance and GSTZ1 enzyme turnover successfully characterized the DCA PK in adults and children. DCA-induced inactivation of GSTZ1 resulted in phenoconversion of all subjects into slow metabolizers after repeated dosing. However, rate and extent of inactivation was 2-fold higher in subjects without the wild-type EGT allelic variant of GSTZ1, resulting in further phenoconversion into ultraslow metabolizers after repeated DCA administration. Furthermore, DCA-induced GSTZ1 inactivation rate and extent was found to be 25- to 30-fold lower in children than in adults, potentially accounting for the observed age-dependent changes in PK. Finally, a 12.5 and 10.6 mg/kg twice-daily DCA dose was optimal in achieving the target steady-state trough concentrations (5-25 mg/L) for EGT carrier and EGT noncarrier children, respectively.

A Mechanism-Based Pharmacokinetic Enzyme Turnover Model for Dichloroacetic Acid Autoinhibition in Rats

Dichloroacetic acid (DCA), a halogenated organic acid, is a pyruvate dehydrogenase kinase inhibitor that has been used to treat congenital or acquired lactic acidosis and is currently in early-phase clinical trials for cancer treatment. DCA was found to inhibit its own metabolism by irreversibly inactivating glutathione transferase zeta 1 (GSTZ1-1), resulting in nonlinear kinetics and abnormally high accumulation ratio after repeated dosing. In this analysis, a semi-mechanistic pharmacokinetic enzyme turnover model was developed for the first time to capture DCA autoinhibition, gastrointestinal region-dependent absorption, and time-dependent change in bioavailability in rats. The maximum rate constant for DCA-induced GSTZ1-1 inactivation is estimated to be 0.96/h, which is 110 times that of the rate constant for GSTZ1-1 natural degradation (0.00875/h). The model-predicted DCA concentration that corresponds to 50% of maximum enzyme inhibition (EC₅₀) is 4.32 mg/L. The constructed pharmacokinetic enzyme turnover model, when applied to human data, could be used to predict the accumulation of DCA after repeated oral dosing, guide selection of dosing regimens in clinical studies, and facilitate clinical development of DCA.

Therapeutic applications of dichloroacetate and the role of glutathione transferase zeta-1

Dichloroacetate (DCA) has several therapeutic applications based on its pharmacological property of inhibiting pyruvate dehydrogenase kinase. DCA has been used to treat inherited mitochondrial disorders that result in lactic acidosis, as well as pulmonary hypertension and several different solid tumors, the latter through its ability to reverse the Warburg effect in cancer cells and restore aerobic glycolysis. The main clinically limiting toxicity is reversible peripheral neuropathy. Although administration of high doses to rodents can result in liver cancer, there is no evidence that DCA is a human carcinogen. In all studied species, including humans, DCA has the interesting property of inhibiting its own metabolism upon repeat dosing, resulting in alteration of its pharmacokinetics. The first step in DCA metabolism is conversion to glyoxylate catalyzed by glutathione transferase zeta 1 (GSTZ1), for which DCA is a mechanism-based inactivator. The rate of GSTZ1 inactivation by DCA is influenced by age, GSTZ1 haplotype and cellular concentrations of chloride. The effect of DCA on its own metabolism complicates the selection of an effective dose with minimal side effects.

Hypoxic repression of pyruvate dehydrogenase activity is necessary for metabolic reprogramming and growth of model tumours

Tumour cells fulfil the bioenergetic and biosynthetic needs of proliferation using the available environmental metabolites. Metabolic adaptation to hypoxia causes decreased mitochondrial function and increased lactate production. This work examines the biological importance of the hypoxia-inducible inhibitory phosphorylations on the pyruvate dehydrogenase E1α subunit. Pancreatic cancer cell lines were genetically manipulated to alter the net phosphorylation of PDH E1α through reduced kinase expression or enhanced phosphatase expression. The modified cells were tested for hypoxic changes in phosphorylated E1α, mitochondrial metabolism and growth as xenografted tumours. Even though there are four PDHK genes, PDHK1 is essential for inhibitory PDH phosphorylation of E1α at serine 232, is partially responsible for modification of serines 293 and 300, and these phosphorylations are necessary for model tumour growth. In order to determine the clinical relevance, a cohort of head and neck cancer patient biopsies was examined for phosphorylated E1α and expression of PDHK1. Patients with detectable 232 phosphorylation or expression of PDHK1 tend to have worse clinical outcome. These data show that PDHK1 activity is unique and non-redundant in the family of PHDK enzymes and a PDHK1 specific inhibitor would therefore have anti-cancer activity with reduced chance of side effects from inhibition of other PDHKs.

Mitochondria dysfunction: A novel therapeutic target in pathological lung remodeling or bystander?

The renascence in mitochondrial research has fueled breakthroughs in our understanding of mitochondrial biology identifying major roles in biological processes ranging from cellular oxygen sensing and regulation of intracellular calcium levels through to initiation of apoptosis or a shift in cell phenotype. Chronic respiratory diseases are no exception to the resurgent interest in mitochondrial biology. Microscopic observations of lungs from patients with chronic respiratory diseases such as pulmonary arterial hypertension, asthma and COPD show accumulation of dysmorphic mitochondria and provide the first evidence of mitochondrial dysfunction in diseased lungs. Recent mechanistic insights have established links between mitochondrial dysfunction or aberrant biogenesis and the pathogenesis of chronic respiratory diseases through playing a causative role in structural remodeling of the lung. The aim here is to discuss the case for a mitochondrial basis of lung remodeling in patients with chronic respiratory diseases. The present article will focus on the question of whether currently available data supports mitochondrial mechanisms as a viable point of therapeutic intervention in respiratory diseases and suggestions for future avenues of research in this rapidly evolving field.

Pharmacogenetic considerations with dichloroacetate dosing

The investigational drug dichloroacetate (DCA) is a metabolic regulator that has been successfully used to treat acquired and congenital metabolic diseases and, recently, solid tumors. Its clinical use has revealed challenges in selecting appropriate doses. Chronic administration of DCA leads to inhibition of DCA metabolism and potential accumulation to levels that result in side effects. This is because conversion of DCA to glyoxylate is catalyzed by one enzyme, glutathione transferase zeta 1 (GSTZ1-1), which is inactivated by DCA. SNPs in the GSTZ1 gene result in expression of polymorphic variants of the enzyme that differ in activity and rates of inactivation by DCA under physiological conditions: these properties lead to considerable variation between people in the pharmacokinetics of DCA.

Chloral hydrate, through biotransformation to dichloroacetate, inhibits maleylacetoacetate isomerase and tyrosine catabolism in humans

BACKGROUND

Chloral hydrate (CH), a sedative and metabolite of the environmental contaminant trichloroethylene, is metabolized to trichloroacetic acid, trichloroethanol, and possibly dichloroacetate (DCA). DCA is further metabolized by glutathione transferase zeta 1 (GSTZ1), which is identical to maleylacetoacetate isomerase (MAAI), the penultimate enzyme in tyrosine catabolism. DCA inhibits its own metabolism through depletion/inactivation of GSTZ1/MAAI with repeated exposure, resulting in lower plasma clearance of the drug and the accumulation of the urinary biomarker maleylacetone (MA), a metabolite of tyrosine. It is unknown if GSTZ1/MAAI may participate in the metabolism of CH or any of its metabolites and, therefore, affect tyrosine catabolism. Stable isotopes were utilized to determine the biotransformation of CH, the kinetics of its major metabolites, and the influence, if any, of GSTZ1/MAAI.

METHODS

Eight healthy volunteers (ages 21-40 years) received a dose of 1 g of CH (clinical dose) or 1.5 μg/kg (environmental) for five consecutive days. Plasma and urinary samples were analyzed by gas chromatography-mass spectrometry.

RESULTS

Plasma DCA (1.2-2.4 μg/mL), metabolized from CH, was measured on the fifth day of the 1 g/day CH dosage but was undetectable in plasma at environmentally relevant doses. Pharmacokinetic measurements from CH metabolites did not differ between slow and fast GSTZ1 haplotypes. Urinary MA levels increased from undetectable to 0.2-0.7 μg/g creatinine with repeated CH clinical dose exposure. Kinetic modeling of a clinical dose of 25 mg/kg DCA administered after 5 days of 1 g/day CH closely resembled DCA kinetics obtained in previously naïve individuals.

CONCLUSIONS

These data indicate that the amount of DCA produced from clinically relevant doses of CH, although insufficient to alter DCA kinetics, is sufficient to inhibit MAAI and tyrosine catabolism, as evidenced by the accumulation of urinary MA.

Chloride concentrations in human hepatic cytosol and mitochondria are a function of age

We recently reported that, in a concentration-dependent manner, chloride protects hepatic glutathione transferase zeta 1 from inactivation by dichloroacetate, an investigational drug used in treating various acquired and congenital metabolic diseases. Despite the importance of chloride ions in normal physiology, and decades of study of chloride transport across membranes, the literature lacks information on chloride concentrations in animal tissues other than blood. In this study we measured chloride concentrations in human liver samples from male and female donors aged 1 day to 84 years (n = 97). Because glutathione transferase zeta 1 is present in cytosol and, to a lesser extent, in mitochondria, we measured chloride in these fractions by high-performance liquid chromatography analysis following conversion of the free chloride to pentafluorobenzylchloride. We found that chloride concentration decreased with age in hepatic cytosol but increased in liver mitochondria. In addition, chloride concentrations in cytosol, (105.2 ± 62.4 mM; range: 24.7-365.7 mM) were strikingly higher than those in mitochondria (4.2 ± 3.8 mM; range 0.9-22.2 mM). These results suggest a possible explanation for clinical observations seen in patients treated with dichloroacetate, whereby children metabolize the drug more rapidly than adults following repeated doses, and also provide information that may influence our understanding of normal liver physiology.

Trichloroethylene biotransformation and its role in mutagenicity, carcinogenicity and target organ toxicity

Metabolism is critical for the mutagenicity, carcinogenicity, and other adverse health effects of trichloroethylene (TCE). Despite the relatively small size and simple chemical structure of TCE, its metabolism is quite complex, yielding multiple intermediates and end-products. Experimental animal and human data indicate that TCE metabolism occurs through two major pathways: cytochrome P450 (CYP)-dependent oxidation and glutathione (GSH) conjugation catalyzed by GSH S-transferases (GSTs). Herein we review recent data characterizing TCE processing and flux through these pathways. We describe the catalytic enzymes, their regulation and tissue localization, as well as the evidence for transport and inter-organ processing of metabolites. We address the chemical reactivity of TCE metabolites, highlighting data on mutagenicity of these end-products. Identification in urine of key metabolites, particularly trichloroacetate (TCA), dichloroacetate (DCA), trichloroethanol and its glucuronide (TCOH and TCOG), and N-acetyl-S-(1,2-dichlorovinyl)-L-cysteine (NAcDCVC), in exposed humans and other species (mostly rats and mice) demonstrates function of the two metabolic pathways in vivo. The CYP pathway primarily yields chemically stable end-products. However, the GST pathway conjugate S-(1,2-dichlorovinyl)glutathione (DCVG) is further processed to multiple highly reactive species that are known to be mutagenic, especially in kidney where in situ metabolism occurs. TCE metabolism is highly variable across sexes, species, tissues and individuals. Genetic polymorphisms in several of the key enzymes metabolizing TCE and its intermediates contribute to variability in metabolic profiles and rates. In all, the evidence characterizing the complex metabolism of TCE can inform predictions of adverse responses including mutagenesis, carcinogenesis, and acute and chronic organ-specific toxicity.

Dichloroacetate and cancer: new home for an orphan drug?

We reviewed the anti-cancer effects of DCA, an orphan drug long used as an investigational treatment for various acquired and congenital disorders of mitochondrial intermediary metabolism. Inhibition by DCA of mitochondrial pyruvate dehydrogenase kinases and subsequent reactivation of the pyruvate dehydrogenase complex and oxidative phosphorylation is the common mechanism accounting for the drug's anti-neoplastic effects. At least two fundamental changes in tumor metabolism are induced by DCA that antagonize tumor growth, metastases and survival: the first is the redirection of glucose metabolism from glycolysis to oxidation (reversal of the Warburg effect), leading to inhibition of proliferation and induction of caspase-mediated apoptosis. These effects have been replicated in both human cancer cell lines and in tumor implants of diverse germ line origin. The second fundamental change is the oxidative removal of lactate, via pyruvate, and the co-incident buffering of hydrogen ions by dehydrogenases located in the mitochondrial matrix. Preclinical studies demonstrate that DCA has additive or synergistic effects when used in combination with standard agents designed to modify tumor oxidative stress, vascular remodeling, DNA integrity or immunity. These findings and limited clinical results suggest that potentially fruitful areas for additional clinical trials include 1) adult and pediatric high grade astrocytomas; 2) BRAF-mutant cancers, such as melanoma, perhaps combined with other pro-oxidants; 3) tumors in which resistance to standard platinum-class drugs alone may be overcome with combination therapy; and 4) tumors of endodermal origin, in which extensive experimental research has demonstrated significant anti-proliferative, pro-apoptotic effects of DCA, leading to improved host survival.

Chloride and other anions inhibit dichloroacetate-induced inactivation of human liver GSTZ1 in a haplotype-dependent manner

The in vivo elimination rate of dichloroacetate (DCA), an investigational drug; is determined by the rate of its biotransformation to glyoxylate, catalyzed by glutathione transferase ζ1 (GSTZ1). DCA is a mechanism-based inactivator of GSTZ1, thus elimination of DCA is slowed with repeated dosing. We observed that chloride, a physiologically important anion, attenuated DCA-induced GSTZ1 inactivation in human liver cytosol in a concentration and GSTZ1 haplotype-dependent way. In the absence of chloride, incubation with 0.5mM DCA resulted in inactivation of GSTZ1 with a half-life of 0.4h (samples with the KRT haplotype) to 0.5h (EGT haplotype). At the hepatic physiological chloride concentration, 38mM, samples with the EGT haplotype retained more activity (80%) following a 2-h incubation with 0.5mM DCA than those possessing the KRT haplotype (55%). The chloride concentration that protected 50% of the GSTZ1 activity following 2-h incubation with 0.5mM DCA (EC50) was 15.0±3.1mM (mean±S.D., n=3) for EGT samples and 36.2±2.2mM for KRT samples. Bromide, iodide and sulfite also protected GSTZ1 from inactivation by DCA, however fluoride, sulfate, carbonate, acetate, cyanide did not. Protection by bromide varied by GSTZ1 haplotype: EC50 was 1.3±0.3mM for the EGT haplotype and 5.0±0.60mM for the KRT haplotype. The EC50 values for iodide and sulfite in liver cytosol samples with EGT haplotype were respectively 0.14±0.06mM and 9.6±1.1mM (mean±S.D., n=3). Because the in vivo half-life of DCA is determined by the fraction of active GSTZ1 in the liver, identifying factors that regulate GSTZ1 activity is important in determining appropriate DCA dosing in humans.

Preliminary X-ray crystallographic analysis of glutathione transferase zeta 1 (GSTZ1a-1a)

Glutathione transferase zeta 1 (GSTZ1-1) is a homodimeric enzyme found in the cytosol and mitochondrial matrix of the liver and other tissues. It catalyzes the glutathione-dependent isomerization of maleylacetoacetate to fumarylacetoacetate in the tyrosine catabolic pathway and can metabolize small halogenated carboxylic acids. GSTZ1a-1a crystals diffracted to a resolution of 3.1 Å and belonged to space group P1, with unit-cell parameters a = 42.0, b = 49.6, c = 54.6 Å, α = 82.9, β = 69.9, γ = 73.4°, with a calculated Matthews coefficient of 2.1 Å(3) Da(-1) assuming a dimer in the crystallographic asymmetric unit. Refinement of the structure is currently in progress.

Phase 1 trial of dichloroacetate (DCA) in adults with recurrent malignant brain tumors

BACKGROUND

Recurrent malignant brain tumors (RMBTs) carry a poor prognosis. Dichloroacetate (DCA) activates mitochondrial oxidative metabolism and has shown activity against several human cancers.

DESIGN

We conducted an open-label study of oral DCA in 15 adults with recurrent WHO grade III - IV gliomas or metastases from a primary cancer outside the central nervous system. The primary objective was detection of a dose limiting toxicity for RMBTs at 4 weeks of treatment, defined as any grade 4 or 5 toxicity, or grade 3 toxicity directly attributable to DCA, based on the National Cancer Institute's Common Toxicity Criteria for Adverse Events, version 4.0. Secondary objectives involved safety, tolerability and hypothesis-generating data on disease status. Dosing was based on haplotype variation in glutathione transferase zeta 1/maleylacetoacetate isomerase (GSTZ1/MAAI), which participates in DCA and tyrosine catabolism.

RESULTS

Eight patients completed at least 1 four week cycle. During this time, no dose-limiting toxicities occurred. No patient withdrew because of lack of tolerance to DCA, although 2 subjects experienced grade 0-1 distal parasthesias that led to elective withdrawal and/or dose-adjustment. All subjects completing at least 1 four week cycle remained clinically stable during this time and remained on DCA for an average of 75.5 days (range 26-312).

CONCLUSIONS

Chronic, oral DCA is feasible and well-tolerated in patients with recurrent malignant gliomas and other tumors metastatic to the brain using the dose range established for metabolic diseases. The importance of genetic-based dosing is confirmed and should be incorporated into future trials of chronic DCA administration.

Long-term safety of dichloroacetate in congenital lactic acidosis

We followed 8 patients (4 males) with biochemically and/or molecular genetically proven deficiencies of the E1α subunit of the pyruvate dehydrogenase complex (PDC; 3 patients) or respiratory chain complexes I (1 patient), IV (3 patients) or I+IV (1 patient) who received oral dichloroacetate (DCA; 12.5 mg/kg/12 h) for 9.7 to 16.5 years. All subjects originally participated in randomized controlled trials of DCA and were continued on an open-label chronic safety study. Patients (1 adult) ranged in age from 3.5 to 40.2 years at the start of DCA administration and are currently aged 16.9 to 49.9 years (mean ± SD: 23.5 ± 10.9 years). Subjects were either normal or below normal body weight for age and gender. The 3 PDC deficient patients did not consume high fat (ketogenic) diets. DCA maintained normal blood lactate concentrations, even in PDC deficient children on essentially unrestricted diets. Hematological, electrolyte, renal and hepatic status remained stable. Nerve conduction either did not change or decreased modestly and led to reduction or temporary discontinuation of DCA in 3 patients, although symptomatic worsening of peripheral neuropathy did not occur. We conclude that chronic DCA administration is generally well-tolerated in patients with congenital causes of lactic acidosis and is effective in maintaining normal blood lactate levels, even in PDC-deficient children not consuming strict ketogenic diets.

Prenatal and postnatal expression of glutathione transferase ζ 1 in human liver and the roles of haplotype and subject age in determining activity with dichloroacetate

Glutathione transferase ζ 1 (GSTZ1), also known as maleylacetoacetate isomerase, catalyzes the penultimate step of tyrosine catabolism and metabolizes several α-halocarboxylic acids, including dichloroacetic acid (DCA), an investigational drug used for lactic acidosis and, recently, solid tumors. Age-related differences have been suggested in DCA pharmacotoxicology, but no information is available on GSTZ1 ontogeny in humans. Here, we investigated the cytosolic GSTZ1 developmental expression pattern and the influence of haplotype on GSTZ1 activity with DCA by using human livers from donors between 10 weeks gestation and 74 years. GSTZ1 expression was very low in fetal livers (<2 pmol of GSTZ1/mg cytosol). The expression began to increase after birth in an age-dependent manner until age 7 years. GSTZ1 was then sustained at stable, yet variable, levels (median, 20.0 pmol/mg cytosol; range, 4.8-47.3 pmol/mg cytosol) until age 74 years. GSTZ1 activity with DCA was strongly associated with haplotype and expression level. Samples homozygous or heterozygous for GSTZ1A exhibited ∼3-fold higher DCA dechlorinating activity than samples carrying other alleles at a given level of expression. The correlations (r²) between activity and expression were 0.90 and 0.68, respectively, for GSTZ1A carriers (n = 11) and noncarriers (n = 61). GSTZ1 is expressed in mitochondria in addition to cytosol. The GSTZ1A allele exhibited similar effects in the mitochondrial fraction by conferring a higher activity with DCA. In summary, we report a neonatal onset and an age-related increase in GSTZ1 protein expression during human liver development. Haplotype influenced GSTZ1 activity with DCA but not protein expression.

Cotreatment with dichloroacetate and omeprazole exhibits a synergistic antiproliferative effect on malignant tumors

It has been reported that treating cancer cells with dichloroacetate (DCA), an approved treatment for congenital lactic acidosis, reverses the Warburg effect and inhibits tumor growth). Furthermore, omeprazole (OMP) is a well-known agent that enhances the effects of anticancer drugs. The aim of this study was to find clinically-used drugs that enhance the effects of DCA. The combination of DCA and OMP exhibited a more potent antitumor activity than DCA alone in HT1080 fibrosarcoma cells and RKO colon cancer cells, while the drugs did not affect the proliferation of WI-38 human fibroblasts. The inhibitory effect of DCA combined with OMP was reversed with vitamin E and Z-VAD-FMK; therefore conventional caspase-dependent cell growth inhibition through superoxide production was suggested as the mechanism for inhibition. The combination of these drugs also had an effect on HT1080 fibrosarcoma cells inoculated into mice. Since OMP and DCA may be administered orally and have been used clinically for several years without major side effects, we believe that this combination therapy could be readily translated to treat malignant tumors.

Human polymorphisms in the glutathione transferase zeta 1/maleylacetoacetate isomerase gene influence the toxicokinetics of dichloroacetate

Dichloroacetate (DCA), a chemical relevant to environmental science and allopathic medicine, is dehalogenated by the bifunctional enzyme glutathione transferase zeta (GSTz1)/maleylacetoacetate isomerase (MAAI), the penultimate enzyme in the phenylalanine/tyrosine catabolic pathway. The authors postulated that polymorphisms in GSTz1/MAAI modify the toxicokinetics of DCA. GSTz1/MAAI haplotype significantly affected the kinetics and biotransformation of 1,2-¹³C-DCA when it was administered at either environmentally (µg/kg/d) or clinically (mg/kg/d) relevant doses. GSTz1/MAAI haplotype also influenced the urinary accumulation of potentially toxic tyrosine metabolites. Atomic modeling revealed that GSTz1/MAAI variants associated with the slowest rates of DCA metabolism induced structural changes in the enzyme homodimer, predicting protein instability or abnormal protein-protein interactions. Knowledge of the GSTz1/MAAI haplotype can be used prospectively to identify individuals at potential risk of DCA's adverse side effects from environmental or clinical exposure or who may exhibit aberrant amino acid metabolism in response to dietary protein.

Why are there no proven therapies for genetic mitochondrial diseases?

Although mitochondrial disease research in general is robust, adequate treatment of these life-threatening conditions has lagged, partly because of a persistence of clinical anecdotes as substitutes for scientifically and ethically rigorous clinical trials. Here I summarize the key lessons learned from some of the "first generation" of randomized controlled trials for genetic mitochondrial diseases and suggest how future trials may benefit from both past experience and exciting new resources available for patient-oriented research and training in this field.

The dichloroacetate dilemma: environmental hazard versus therapeutic goldmine--both or neither?

BACKGROUND

Dichloroacetate (DCA) is known to environmental scientists as a by-product of water chlorination and as a metabolite of industrial solvents, including Superfund chemicals. In contrast, DCA is studied by clinical investigators for its therapeutic potential in several life-threatening conditions, including genetic mitochondrial diseases, pulmonary arterial hypertension, and cancer. Thus, DCA holds an almost unique position at the interface between environmental science and allopathic medicine.

OBJECTIVE

I critically reviewed laboratory and clinical pharmacological research on DCA to address questions about the current and future status of DCA in relation to human health.

DISCUSSION

Recent information on the clinical toxicogenetics of DCA is interpreted particularly in light of its use as an investigational drug. Adverse effects from chronic DCA exposure have been identified in several target organs in animals. However, in humans, toxicity has so far been limited to reversible effects on the nervous system and liver. DCA is primarily biotransformed to glyoxylate by the bifunctional enzyme glutathione transferase zeta1 and maleylacetoacetate isomerase (GSTz1/MAAI), which also catalyzes the penultimate step in the phenylalanine and tyrosine catabolic pathway. DCA is a suicide inhibitor of GSTz1/MAAI, which can result in delayed plasma clearance of DCA and the accumulation of potentially toxic tyrosine intermediates. Age and GSTz1/MAAI haplotype can markedly affect the toxicokinetics of DCA in humans and rodents.

CONCLUSIONS

I have defined new potential avenues of research that focus on discrete human populations that may be at increased health risk or that may receive increased health benefit from chronic exposure to DCA at both environmentally and clinically relevant concentrations.

Mitochondrion as a novel site of dichloroacetate biotransformation by glutathione transferase zeta 1

Dichloroacetate (DCA) is a potential environmental hazard and an investigational drug. Repeated doses of DCA result in reduced drug clearance, probably through inhibition of glutathione transferase ζ1 (GSTZ1), a cytosolic enzyme that converts DCA to glyoxylate. DCA is known to be taken up by mitochondria, where it inhibits pyruvate dehydrogenase kinase, its major pharmacodynamic target. We tested the hypothesis that the mitochondrion was also a site of DCA biotransformation. Immunoreactive GSTZ1 was detected in liver mitochondria from humans and rats, and its identity was confirmed by liquid chromatography/tandem mass spectrometry analysis of the tryptic peptides. Study of rat submitochondrial fractions revealed GSTZ1 to be localized in the mitochondrial matrix. The specific activity of GSTZ1-catalyzed dechlorination of DCA was 2.5- to 3-fold higher in cytosol than in whole mitochondria and was directly proportional to GSTZ1 protein expression in the two compartments. Rat mitochondrial GSTZ1 had a 2.5-fold higher (App)K(m) for glutathione than cytosolic GSTZ1, whereas the (App)K(m) values for DCA were identical. Rats administered DCA at a dose of 500 mg/kg/day for 8 weeks showed reduced hepatic GSTZ1 activity and expression of ∼10% of control levels in both cytosol and mitochondria. We conclude that the mitochondrion is a novel site of DCA biotransformation catalyzed by GSTZ1, an enzyme colocalized in cytosol and mitochondrial matrix.

The effect of dichloroacetate on health- and lifespan in C. elegans

Aging is associated with increased vulnerability to chronic, degenerative diseases and death. Strategies for promoting healthspan without necessarily affecting lifespan or aging rate have gained much interest. The mitochondrial free radical theory of aging suggests that mitochondria and, in particular, age-dependent mitochondrial decline play a central role in aging, making compounds that affect mitochondrial function a possible strategy for the modulation of healthspan and possibly the aging rate. Here we tested such a "metabolic tuning" approach in nematodes using the mitochondrial modulator dichloroacetate (DCA). We explored DCA as a proof-of-principle compound to alter mitochondrial parameters in wild-type animals and tested whether this approach is suitable for reducing reactive oxygen species (ROS) production and for improving organismal health- and lifespan. In parallel, we addressed the potential problem of operator bias by running both unblinded and blinded lifespan studies. We found that DCA treatment (1) increased ATP levels without elevating oxidative protein damage and (2) reduced ROS production in adult C. elegans. DCA treatment also significantly prolonged nematode health- and lifespan, but did not strongly impact mortality doubling time. Operator blinding resulted in considerably smaller lifespan-extending effects of DCA. Our data illustrate the promise of a "metabolic tuning" intervention strategy, emphasize the importance of mitochondria in nematode aging and highlight operator bias as a potential confounder in lifespan studies.