Pharmacologically increased tumor hypoxia can be measured by 18F-Fluoroazomycin arabinoside positron emission tomography and enhances tumor response to hypoxic cytotoxin PR-104

Targeting Hypoxia: Hypoxia-Activated Prodrugs in Cancer Therapy

Hypoxia is an important characteristic of most solid malignancies, and is closely related to tumor prognosis and therapeutic resistance. Hypoxia is one of the most important factors associated with resistance to conventional radiotherapy and chemotherapy. Therapies targeting tumor hypoxia have attracted considerable attention. Hypoxia-activated prodrugs (HAPs) are bioreductive drugs that are selectively activated under hypoxic conditions and that can accurately target the hypoxic regions of solid tumors. Both single-agent and combined use with other drugs have shown promising antitumor effects. In this review, we discuss the mechanism of action and the current preclinical and clinical progress of several of the most widely used HAPs, summarize their existing problems and shortcomings, and discuss future research prospects.

Mechanism-Specific Pharmacodynamics of a Novel Complex-I Inhibitor Quantified by Imaging Reversal of Consumptive Hypoxia with [18F]FAZA PET In Vivo

Tumors lack a well-regulated vascular supply of O₂ and often fail to balance O₂ supply and demand. Net O₂ tension within many tumors may not only depend on O₂ delivery but also depend strongly on O₂ demand. Thus, tumor O₂ consumption rates may influence tumor hypoxia up to true anoxia. Recent reports have shown that many human tumors in vivo depend primarily on oxidative phosphorylation (OxPhos), not glycolysis, for energy generation, providing a driver for consumptive hypoxia and an exploitable vulnerability. In this regard, IACS-010759 is a novel high affinity inhibitor of OxPhos targeting mitochondrial complex-I that has recently completed a Phase-I clinical trial in leukemia. However, in solid tumors, the effective translation of OxPhos inhibitors requires methods to monitor pharmacodynamics in vivo. Herein, ¹⁸F-fluoroazomycin arabinoside ([¹⁸F]FAZA), a 2-nitroimidazole-based hypoxia PET imaging agent, was combined with a rigorous test-retest imaging method for non-invasive quantification of the reversal of consumptive hypoxia in vivo as a mechanism-specific pharmacodynamic (PD) biomarker of target engagement for IACS-010759. Neither cell death nor loss of perfusion could account for the IACS-010759-induced decrease in [¹⁸F]FAZA retention. Notably, in an OxPhos-reliant melanoma tumor, a titration curve using [¹⁸F]FAZA PET retention in vivo yielded an IC₅₀ for IACS-010759 (1.4 mg/kg) equivalent to analysis ex vivo. Pilot [¹⁸F]FAZA PET scans of a patient with grade IV glioblastoma yielded highly reproducible, high-contrast images of hypoxia in vivo as validated by CA-IX and GLUT-1 IHC ex vivo. Thus, [¹⁸F]FAZA PET imaging provided direct evidence for the presence of consumptive hypoxia in vivo, the capacity for targeted reversal of consumptive hypoxia through the inhibition of OxPhos, and a highly-coupled mechanism-specific PD biomarker ready for translation.

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.

Long-term stabilization of metastatic melanoma with sodium dichloroacetate

Sodium dichloroacetate (DCA) has been studied as a metabolic cancer therapy since 2007, based on a publication from Bonnet et al demonstrating that DCA can induce apoptosis (programmed cell death) in human breast, lung and brain cancer cells. Classically, the response of cancer to a medical therapy in human research is measured by Response Evaluation Criterial for Solid Tumours definitions, which define “response” by the degree of tumour reduction, or tumour disappearance on imaging, however disease stabilization is also a beneficial clinical outcome. It has been shown that DCA can function as a cytostatic agent in vitro and in vivo, without causing apoptosis. A case of a 32-year-old male is presented in which DCA therapy, with no concurrent conventional therapy, resulted in regression and stabilization of recurrent metastatic melanoma for over 4 years’ duration, with trivial side effects. This case demonstrates that DCA can be used to reduce disease volume and maintain long-term stability in patients with advanced melanoma.

Metabolic reprogramming by the pyruvate dehydrogenase kinase-lactic acid axis: Linking metabolism and diverse neuropathophysiologies

Emerging evidence indicates that there is a complex interplay between metabolism and chronic disorders in the nervous system. In particular, the pyruvate dehydrogenase (PDH) kinase (PDK)-lactic acid axis is a critical link that connects metabolic reprogramming and the pathophysiology of neurological disorders. PDKs, via regulation of PDH complex activity, orchestrate the conversion of pyruvate either aerobically to acetyl-CoA, or anaerobically to lactate. The kinases are also involved in neurometabolic dysregulation under pathological conditions. Lactate, an energy substrate for neurons, is also a recently acknowledged signaling molecule involved in neuronal plasticity, neuron-glia interactions, neuroimmune communication, and nociception. More recently, the PDK-lactic acid axis has been recognized to modulate neuronal and glial phenotypes and activities, contributing to the pathophysiologies of diverse neurological disorders. This review covers the recent advances that implicate the PDK-lactic acid axis as a novel linker of metabolism and diverse neuropathophysiologies. We finally explore the possibilities of employing the PDK-lactic acid axis and its downstream mediators as putative future therapeutic strategies aimed at prevention or treatment of neurological disorders.

Targeting the hypoxic fraction of tumours using hypoxia-activated prodrugs

The presence of a microenvironment within most tumours containing regions of low oxygen tension or hypoxia has profound biological and therapeutic implications. Tumour hypoxia is known to promote the development of an aggressive phenotype, resistance to both chemotherapy and radiotherapy and is strongly associated with poor clinical outcome. Paradoxically, it is recognised as a high-priority target and one of the therapeutic strategies designed to eradicate hypoxic cells in tumours is a group of compounds known collectively as hypoxia-activated prodrugs (HAPs) or bioreductive drugs. These drugs are inactive prodrugs that require enzymatic activation (typically by 1 or 2 electron oxidoreductases) to generate cytotoxic species with selectivity for hypoxic cells being determined by (1) the ability of oxygen to either reverse or inhibit the activation process and (2) the presence of elevated expression of oxidoreductases in tumours. The concepts underpinning HAP development were established over 40 years ago and have been refined over the years to produce a new generation of HAPs that are under preclinical and clinical development. The purpose of this article is to describe current progress in the development of HAPs focusing on the mechanisms of action, preclinical properties and clinical progress of leading examples.

Targeting the hypoxic fraction of tumours using hypoxia-activated prodrugs

The presence of a microenvironment within most tumours containing regions of low oxygen tension or hypoxia has profound biological and therapeutic implications. Tumour hypoxia is known to promote the development of an aggressive phenotype, resistance to both chemotherapy and radiotherapy and is strongly associated with poor clinical outcome. Paradoxically, it is recognised as a high-priority target and one of the therapeutic strategies designed to eradicate hypoxic cells in tumours is a group of compounds known collectively as hypoxia-activated prodrugs (HAPs) or bioreductive drugs. These drugs are inactive prodrugs that require enzymatic activation (typically by 1 or 2 electron oxidoreductases) to generate cytotoxic species with selectivity for hypoxic cells being determined by (1) the ability of oxygen to either reverse or inhibit the activation process and (2) the presence of elevated expression of oxidoreductases in tumours. The concepts underpinning HAP development were established over 40 years ago and have been refined over the years to produce a new generation of HAPs that are under preclinical and clinical development. The purpose of this article is to describe current progress in the development of HAPs focusing on the mechanisms of action, preclinical properties and clinical progress of leading examples.

Overexpression of pyruvate dehydrogenase kinase supports dichloroacetate as a candidate for cutaneous melanoma therapy

OBJECTIVE

We aimed to verify if there is evidence to consider dichloroacetate (DCA), which inhibits the pyruvate dehydrogenase kinase (PDK) and reverts the metabolic shift of cancer cells from glycolysis to oxidative phosphorylation, as a promising drug for therapy of cutaneous melanoma (CM) patients.

RESEARCH DESIGN AND METHODS

We assessed the expression profile of PDK 1, 2 and 3 in a series of melanoma samples, to verify if melanoma tumors express the DCA targets, if this expression correlates with the activation of important signaling cascades for melanomagenesis and also with the prognosis of melanoma patients. We also established the sensitivity of melanoma cell lines to DCA treatment, by assessing their metabolic alterations, proliferation and survival.

RESULTS

We observed that both PDK 1 and 2 isoforms are overexpressed in CM compared to nevi, this expression being associated with the expression of the mTOR pathway effectors and independent of the BRAF mutational status. Melanoma cell lines treated with DCA showed a shift in metabolism, that is, a decrease in glucose consumption and lactate production, downregulation of proliferation, an increase of apoptosis and a decrease in mTOR pathway activation.

CONCLUSION

Our results suggest that PDK expression may play a role in melanoma development and that DCA can be useful for CM therapy, alone or in combination with mTOR inhibitors.

Adipose tissue dysfunction and its effects on tumor metabolism

Growing by an alarming rate in the Western world, obesity has become a condition associated with a multitude of diseases such as diabetes, metabolic syndrome and various cancers. Generally viewed as an abnormal accumulation of hypertrophied adipocytes, obesity is also a poor prognostic factor for recurrence and chemoresistance in cancer patients. With more than two-thirds of the adult population in the United States considered clinically overweight or obese, it is critical that the relationship between obesity and cancer is further emphasized and elucidated. Adipocytes are highly metabolically active cells, which, through release of adipokines and cytokines and activation of endocrine and paracrine pathways, affect processes in neighboring and distant cells, altering their normal homeostasis. This work will examine specifically how adipocyte-derived factors regulate the cellular metabolism of malignant cells within the tumor niche. Briefly, tumor cells undergo metabolic pressure towards a more glycolytic and hypoxic state through a variety of metabolic regulators and signaling pathways, i.e., phosphoinositol-3 kinase (PI3K), hypoxia-inducible factor-1 alpha (HIF-1α), and c-MYC signaling. Enhanced glycolysis and high lactate production are hallmarks of tumor progression largely because of a process known as the Warburg effect. Herein, we review the latest literature pertaining to the body of work on the interactions between adipose and tumor cells, and underlining the changes in cancer cell metabolism that have been targeted by the currently available treatments.

18F-EF5 PET Is Predictive of Response to Fractionated Radiotherapy in Preclinical Tumor Models

We evaluated the relationship between pre-treatment positron emission tomography (PET) using the hypoxic tracer ¹⁸F-[2-(2-nitro-1-H-imidazol-1-yl)-N-(2,2,3,3,3- pentafluoropropyl) acetamide] (¹⁸F-EF5) and the response of preclinical tumor models to a range of fractionated radiotherapies. Subcutaneous HT29, A549 and RKO tumors grown in nude mice were imaged using ¹⁸F-EF5 positron emission tomography (PET) in order to characterize the extent and heterogeneity of hypoxia in these systems. Based on these results, 80 A549 tumors were subsequently grown and imaged using ¹⁸F-EF5 PET, and then treated with one, two, or four fraction radiation treatments to a total dose of 10–40 Gy. Response was monitored by serial caliper measurements of tumor volume. Longitudinal post-treatment ¹⁸F-EF5 PET imaging was performed on a subset of tumors. Terminal histologic analysis was performed to validate ¹⁸F-EF5 PET measures of hypoxia. EF5-positive tumors responded more poorly to low dose single fraction irradiation relative to EF5-negative tumors, however both groups responded similarly to larger single fraction doses. Irradiated tumors exhibited reduced ¹⁸F-EF5 uptake one month after treatment compared to control tumors. These findings indicate that pre- treatment ¹⁸F-EF5 PET can predict the response of tumors to single fraction radiation treatment. However, increasing the number of fractions delivered abrogates the difference in response between tumors with high and low EF5 uptake pre-treatment, in agreement with traditional radiobiology.

Dichloroacetate restores drug sensitivity in paclitaxel-resistant cells by inducing citric acid accumulation

BACKGROUND

The Warburg effect describes the increased reliance of tumor cells on glycolysis for ATP generation. Mitochondrial respiratory defect is thought to be an important factor leading to the Warburg effect in some types of tumor cells. Consequently, there is growing interest in developing anti-cancer drugs that target mitochondria. One example is dichloroacetate (DCA) that stimulates mitochondria through inhibition of pyruvate dehydrogenase kinase.

METHODS

We investigated the anti-cancer activity of DCA using biochemical and isotopic tracing methods.

RESULTS

We observed that paclitaxel-resistant cells contained decreased levels of citric acid and sustained mitochondrial respiratory defect. DCA specifically acted on cells with mitochondrial respiratory defect to reverse paclitaxel resistance. DCA could not effectively activate oxidative respiration in drug-resistant cells, but induced higher levels of citrate accumulation, which led to inhibition of glycolysis and inactivation of P-glycoprotein.

CONCLUSIONS

The abilityof DCA to target cells with mitochondrial respiratory defect and restore paclitaxel sensitivity by inducing citrate accumulation supports further preclinical development.

Pyruvate induces transient tumor hypoxia by enhancing mitochondrial oxygen consumption and potentiates the anti-tumor effect of a hypoxia-activated prodrug TH-302

Background

TH-302 is a hypoxia-activated prodrug (HAP) of bromo isophosphoramide mustard that is selectively activated within hypoxic regions in solid tumors. Our recent study showed that intravenously administered bolus pyruvate can transiently induce hypoxia in tumors. We investigated the mechanism underlying the induction of transient hypoxia and the combination use of pyruvate to potentiate the anti-tumor effect of TH-302.

Methodology/Results

The hypoxia-dependent cytotoxicity of TH-302 was evaluated by a viability assay in murine SCCVII and human HT29 cells. Modulation in cellular oxygen consumption and invivo tumor oxygenation by the pyruvate treatment was monitored by extracellular flux analysis and electron paramagnetic resonance (EPR) oxygen imaging, respectively. The enhancement of the anti-tumor effect of TH-302 by pyruvate treatment was evaluated by monitoring the growth suppression of the tumor xenografts inoculated subcutaneously in mice. TH-302 preferentially inhibited the growth of both SCCVII and HT29 cells under hypoxic conditions (0.1% O₂), with minimal effect under aerobic conditions (21% O₂). Basal oxygen consumption rates increased after the pyruvate treatment in SCCVII cells in a concentration-dependent manner, suggesting that pyruvate enhances the mitochondrial respiration to consume excess cellular oxygen. In vivo EPR oxygen imaging showed that the intravenous administration of pyruvate globally induced the transient hypoxia 30 min after the injection in SCCVII and HT29 tumors at the size of 500–1500 mm³. Pretreatment of SCCVII tumor bearing mice with pyruvate 30 min prior to TH-302 administration, initiated with small tumors (∼550 mm³), significantly delayed tumor growth.

Conclusions/Significance

Our invitro and invivo studies showed that pyruvate induces transient hypoxia by enhancing mitochondrial oxygen consumption in tumor cells. TH-302 therapy can be potentiated by pyruvate pretreatment if started at the appropriate tumor size and oxygen concentration.

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.

5'-AMP-activated protein kinase (AMPK) supports the growth of aggressive experimental human breast cancer tumors

Rapid tumor growth can establish metabolically stressed microenvironments that activate 5'-AMP-activated protein kinase (AMPK), a ubiquitous regulator of ATP homeostasis. Previously, we investigated the importance of AMPK for the growth of experimental tumors prepared from HRAS-transformed mouse embryo fibroblasts and for primary brain tumor development in a rat model of neurocarcinogenesis. Here, we used triple-negative human breast cancer cells in which AMPK activity had been knocked down to investigate the contribution of AMPK to experimental tumor growth and core glucose metabolism. We found that AMPK supports the growth of fast-growing orthotopic tumors prepared from MDA-MB-231 and DU4475 breast cancer cells but had no effect on the proliferation or survival of these cells in culture. We used in vitro and in vivo metabolic profiling with [(13)C]glucose tracers to investigate the contribution of AMPK to core glucose metabolism in MDA-MB-231 cells, which have a Warburg metabolic phenotype; these experiments indicated that AMPK supports tumor glucose metabolism in part through positive regulation of glycolysis and the nonoxidative pentose phosphate cycle. We also found that AMPK activity in the MDA-MB-231 tumors could systemically perturb glucose homeostasis in sensitive normal tissues (liver and pancreas). Overall, our findings suggest that the contribution of AMPK to the growth of aggressive experimental tumors has a critical microenvironmental component that involves specific regulation of core glucose metabolism.

Metabolism targeting therapy of dichloroacetate-loaded electrospun mats on colorectal cancer

Differences in energy metabolism between tumor cells and normal cells offer an attractive avenue of research into drug targets for tumor therapy. The use of a metabolic modulator (sodium dichloroacetate, DCA), administered in situ, to reverse the "Warburg effect" of tumor cells has been demonstrated as an effective tumor therapy. Herein, DCA and diisopropylamine dichloroacetate (DADA) were incorporated separately into polylactide (PLA) electrospun mats and applied to C26 tumor-bearing mice via in situ administration. After 12 d of treatment, the tumor suppression rates of 75% and 84% were achieved in the DC group (treated with a DCA-loaded mat) and the DA group (treated with a DADA-loaded mat), respectively. With tolerable physiologic toxicity under high local concentration, the DA group showed a 95% tumor suppression rate without any recurrence after 15 d of therapy. The desirable therapeutic effects of these metabolic modulators should ascribe to the energy-central metabolism-targeting effects of DCA and DADA, which were demonstrated both in vitro and in vivo. Therefore, DCA- and DADA-loaded mats are the effective anti-cancer drugs dosages to discriminate between tumor cells and normal cells for minimizing systemic toxicity.

Pyruvate dehydrogenase kinase as a potential therapeutic target for malignant gliomas

Metabolic aberrations in the form of altered flux through key metabolic pathways are the major hallmarks of several life-threatening malignancies including malignant gliomas. These adaptations play an important role in the enhancement of the survival and proliferation of gliomas at the expense of the surrounding normal/healthy tissues. Recent studies in the field of neurooncology have directly targeted the altered metabolic pathways of malignant tumor cells for the development of anti-cancer drugs. Aerobic glycolysis due to elevated production of lactate from pyruvate regardless of oxygen availability is a common metabolic alteration in most malignancies. Aerobic glycolysis offers survival advantages in addition to generating substrates such as fatty acids, amino acids and nucleotides required for the rapid proliferation of cells. This review outlines the role of pyruvate dehydrogenase kinase (PDK) in gliomas as an inhibitor of pyruvate dehydrogenase that catalyzes the oxidative decarboxylation of pyruvate. An in-depth investigation on the key metabolic enzyme PDK may provide a novel therapeutic approach for the treatment of malignant gliomas.

PGC-1-related coactivator (PRC) negatively regulates endothelial adhesion of monocytes via inhibition of NF κB activity

PGC-1-related coactivator (PRC) is a growth-regulated transcriptional cofactor known to activate many of the nuclear genes specifying mitochondrial respiratory function. Endothelial dysfunction is a prominent feature found in many inflammatory diseases. Adhesion molecules, such as VCAM-1, mediate the attachment of monocytes to endothelial cells, thereby playing an important role in endothelial inflammation. The effects of PRC in regards to endothelial inflammation remain unknown. In this study, our findings show that PRC can be inhibited by the inflammatory cytokine LPS in cultured human umbilical vein endothelial cells (HUVECs). In the presence of LPS, the expression of endothelial cell adhesion molecular, such as VCAM1 and E-selectin, is found to be increased. These effects can be negated by overexpression of PRC. Importantly, monocyte adhesion to endothelial cells caused by LPS is significantly attenuated by PRC. In addition, overexpression of PRC protects mitochondrial metabolic function and suppresses the rate of glycolysis against LPS. It is also found that overexpression of PRC decreases the transcriptional activity of NF-κB. These findings suggest that PRC is a negative regulator of endothelial inflammation.

Dichloroacetate induces tumor-specific radiosensitivity in vitro but attenuates radiation-induced tumor growth delay in vivo

BACKGROUND

Inhibition of pyruvate dehydrogenase kinase (PDK) by dichloroacetate (DCA) can shift tumor cell metabolism from anaerobic glycolysis to glucose oxidation, with activation of mitochondrial activity and chemotherapy-dependent apoptosis. In radiotherapy, DCA could thus potentially enhance the frequently moderate apoptotic response of cancer cells that results from their mitochondrial dysfunction. The aim of this study was to investigate tumor-specific radiosensitization by DCA in vitro and in a human tumor xenograft mouse model in vivo.

MATERIALS AND METHODS

The interaction of DCA with photon beam radiation was investigated in the human tumor cell lines WIDR (colorectal) and LN18 (glioma), as well as in the human normal tissue cell lines HUVEC (endothelial), MRC5 (lung fibroblasts) and TK6 (lymphoblastoid). Apoptosis induction in vitro was assessed by DAPI staining and sub-G1 flow cytometry; cell survival was quantified by clonogenic assay. The effect of DCA in vivo was investigated in WIDR xenograft tumors growing subcutaneously on BALB/c-nu/nu mice, with and without fractionated irradiation. Histological examination included TUNEL and Ki67 staining for apoptosis and proliferation, respectively, as well as pinomidazole labeling for hypoxia.

RESULTS

DCA treatment led to decreased clonogenic survival and increased specific apoptosis rates in tumor cell lines (LN18, WIDR) but not in normal tissue cells (HUVEC, MRC5, TK6). However, this significant tumor-specific radiosensitization by DCA in vitro was not reflected by the situation in vivo: The growth suppression of WIDR xenograft tumors after irradiation was reduced upon additional DCA treatment (reflected by Ki67 expression levels), although early tumor cell apoptosis rates were significantly increased by DCA. This apparently paradoxical effect was accompanied by a marked DCA-dependent induction of hypoxia in tumor-tissue.

CONCLUSION

DCA induced tumor-specific radiosensitization in vitro but not in vivo. DCA also induced development of hypoxia in tumor tissue in vivo. Further investigations relating to the interplay between tumor cell metabolism and tumor microenvironment are necessary to explain the limited success of metabolic targeting in radiotherapy.

Dichloroacetate inhibits aerobic glycolysis in multiple myeloma cells and increases sensitivity to bortezomib

Background:

Dichloroacetate (DCA), through the inhibition of aerobic glycolysis (the ‘Warburg effect') and promotion of pyruvate oxidation, induces growth reduction in many tumours and is now undergoing several clinical trials. If aerobic glycolysis is active in multiple myeloma (MM) cells, it can be potentially targeted by DCA to induce myeloma growth inhibition.

Methods:

Representative multiple myeloma cell lines and a myeloma-bearing mice were treated with DCA, alone and in combination with bortezomib.

Results:

We found that aerobic glycolysis occurs in approximately half of MM cell lines examined, producing on average 1.86-fold more lactate than phorbol myristate acetate stimulated-peripheral blood mononuclear cells and is associated with low-oxidative capacity. Lower doses of DCA (5–10 mℳ) suppressed aerobic glycolysis and improved cellular respiration that was associated with activation of the pyruvate dehydrogenase complex. Higher doses of DCA (10–25 mℳ) induced superoxide production, apoptosis, suppressed proliferation with a G_0/1 and G₂M phase arrest in MM cell lines. In addition, DCA increased MM cell line sensitivity to bortezomib, and combinatorial treatment of both agents improved the survival of myeloma-bearing mice.

Conclusion:

Myeloma cells display aerobic glycolysis and DCA may complement clinically used MM therapies to inhibit disease progression.

Inflammatory response of microglial BV-2 cells includes a glycolytic shift and is modulated by mitochondrial glucose-regulated protein 75/mortalin

Recent studies suggest a link between mitochondria and proinflammatory cytokine generation. We previously demonstrated that overexpression of mitochondrial chaperone glucose-regulated protein75 (Grp75/mortalin) protects mitochondria. In this study we investigated the modulation of the lipopolisaccharide (LPS)-induced inflammatory response of microglial BV-2 cells by Grp75. We demonstrate that LPS-induced activation promotes significant metabolic changes suppressing mitochondrial function and increasing glycolysis. Overexpression of Grp75 attenuates the LPS-induced oxidative and metabolic responses, and suppresses proinflammatory activation, which depends on both NF-κB activation and lactate. Thus overexpression of Grp75 provides a novel strategy to modulate proinflammatory cytokine production of relevance to inflammation-associated pathologies.

Effects of three modifiers of glycolysis on ATP, lactate, hypoxia, and growth in human tumor cell lines in vivo

BACKGROUND

High pretreatment tumor lactate content is associated with poor outcome after fractionated irradiation in human squamous cell carcinoma (hSCC) xenografts. Therefore, decreasing lactate content might be a promising approach for increasing tumor radiosensitivity. As the basis for such experiments, the effects of the biochemical inhibitors pyruvate dehydrogenase kinase dichloroacetate (DCA), lactate dehydrogenase oxamate, and monocarboxylic acid transporter-1 α-cyano-4-hydroxycinnamate (CHC) on tumor micromilieu and growth were investigated.

MATERIALS AND METHODS

Oxygen consumption (OCR) and extracellular acidification rates (ECAR) were measured in FaDu and UT-SCC-5 hSCC in response to DCA in vitro. Mice bearing FaDu, UT-SCC-5, and WiDr colorectal adenocarcinoma received either DCA in drinking water or DCA injected twice a day, or CHC injected daily. WiDr was also treated daily with oxamate. FaDu and UT-SCC-5 were either excised 8 days after treatment for histology or tumor growth was monitored. WiDr tumors were excised at 8 mm. Effect of inhibitors on ATP, lactate, hypoxia, and Ki67 labeling index (LI) was evaluated.

RESULTS

DCA increased OCR and decreased ECAR in vitro. None of the treatments with inhibitors significantly changed lactate content, hypoxia levels, and Ki67 LI in the three tumor lines in vivo. ATP concentration significantly decreased after only daily twice injections of DCA in FaDu accompanied by a significant increase in necrotic fraction. Tumor growth was not affected by any of the treatments.

CONCLUSION

Overall, tumor micromilieu and tumor growth could not be changed by glycolysis modifiers in the three tumor cell lines in vivo. Further studies are necessary to explore the impact of metabolic targets on radiation response.

Dichloroacetate Induces Different Rates of Cell Death in Cancer and Noncancer Cell Lines in Vitro

Aims and Background

The pyruvate mimetic dichloroacetate (DCA) has been shown to induce cell death in cancer cells. A number of studies in vitro and in vivo have suggested this molecule may serve as an anticancer agent, but some cells are resistant. Here we wanted to examine the effects of DCA on cancerous and noncancerous cells grown in culture for a prolonged period of exposure and at increasing concentrations.

Methods

Six cancer cell lines (A549, SK-HEP-1, HCT116, UPCI:SCC070, HeLa and MES-SA) and three noncancerous lines (RPE, GM03349B and HEK293) were exposed to 0.5 mM DCA for seven days and cell counts were taken every day to determine viability and cell cycle progression. The same cell lines were also exposed to higher doses of DCA up to 10 mM and viability was scored.

Results

Five cancer cell lines showed high levels of cell death early in the trial, but three of the lines showed a second delayed increase in cell death at later stages. HCT116 cells were unaffected by 0.5 mM DCA. GM03349B and RPE cells also died when treated with DCA. At high concentrations, all cell lines exhibited high rates of death. No specific cell cycle arrest of the cells was observed.

Conclusion

We found that there is considerable difference in the way cancer cells are affected by DCA. Some have populations that are highly resistant to treatment, while others have stronger rates of death only after prolonged exposure. We also found noncancerous cells are not all resistant to DCA, a significant finding that has not previously been observed in other in vitro DCA trials.

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.

Synthesis of 68Ga-labeled DOTA-nitroimidazole derivatives and their feasibilities as hypoxia imaging PET tracers

The imaging of hypoxia is important for therapeutic decision making in various diseases. (68)Ga is an important radionuclide for positron emission tomography (PET), and its usage is increasing, due to the development of the (68)Ge/(68)Ga-generator. In the present study, the authors synthesized two nitroimidazole derivatives by conjugating nitroimidazole and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) via an amide bond (4) and a thiourea bond (5). Both derivatives were labeled with (68)Ga with high labeling efficiency and were stable after labeling. The low partition coefficients (logP) of (68)Ga-4 (-4.6) and (68)Ga-5 (-4.5) demonstrated the hydrophilic natures of the derivatives, and both showed higher uptake in cancer cell lines cultured under hypoxic condition than under normoxic condition. However, (68)Ga-5 showed higher liver uptake than (68)Ga-4 in a biodistribution study due to higher lipophilicity. In an animal PET study, (68)Ga-4 showed higher standard uptake values (SUV) in tumors than (68)Ga-5 in mice xenografted with CT-26 mouse colon cancer cells.

Regulation of cancer cell metabolism

Interest in the topic of tumour metabolism has waxed and waned over the past century of cancer research. The early observations of Warburg and his contemporaries established that there are fundamental differences in the central metabolic pathways operating in malignant tissue. However, the initial hypotheses that were based on these observations proved inadequate to explain tumorigenesis, and the oncogene revolution pushed tumour metabolism to the margins of cancer research. In recent years, interest has been renewed as it has become clear that many of the signalling pathways that are affected by genetic mutations and the tumour microenvironment have a profound effect on core metabolism, making this topic once again one of the most intense areas of research in cancer biology.

Anticancer drugs that target metabolism: Is dichloroacetate the new paradigm?

Recent findings in the fields of oncogenic regulation of metabolism, mitochondrial function and macromolecular synthesis have brought tumor metabolism and the Warburg effect back into the scientific limelight. A number of metabolic pathways that seem to be important for tumor growth are being touted as novel targets for anticancer drug development. One of the candidates in this class of drugs being investigated is dichloroacetate (DCA), a molecule used for over 25 years in the treatment of children with inborn errors in mitochondrial function. This pyruvate mimetic compound stimulates mitochondrial function by inhibiting the family of regulatory pyruvate dehydrogenase kinases (PDK1-4). The stimulation of mitochondrial function, at the expense of glycolysis, reverses the Warburg effect and is thought to block the growth advantage of highly glycolytic tumors. Interestingly, some of the recent in vitro findings have shown very modest "antitumor cell activity" of DCA when cells are treated in a dish. However, several studies have reported "antitumor activity" in model tumors. This apparent paradox raises the question, how do we evaluate cancer drugs designed to target tumor metabolism? Traditional approaches in cancer drug development have used in vitro assays as a first pass to evaluate potential lead compounds. The fact that DCA has better in vivo activity than in vitro activity suggests that there are unique aspects of solid tumor growth and metabolism that are difficult to recapitulate in vitro and may be important in determining the effectiveness of this class of drugs.

Sodium dichloroacetate (DCA) reduces apoptosis in colorectal tumor hypoxia

We examined the effect of hypoxia on apoptosis of human colorectal cancer (CRC) cells in vitro and in vivo. All cell lines tested were susceptible to hypoxia-induced apoptosis. DCA treatment caused significant apoptosis under normoxia in SW480 and Caco-2 cells, but these cells displayed decreased apoptosis when treated with DCA combined with hypoxia, possibly through HIF-1alpha dependent pathways. DCA treatment also induced significantly increased growth of SW480 tumor xenografts, and a decrease in TUNEL positive nuclei in hypoxic but not normoxic regions of treated tumors. Thus DCA is cytoprotective to some CRC cells under hypoxic conditions, highlighting the need for further investigation before DCA can be used as a reliable apoptosis-inducing agent in cancer therapy.