Mitochondrial glutathione depletion by glutamine in growing tumor cells

Glutamine addiction in tumor cell: oncogene regulation and clinical treatment

After undergoing metabolic reprogramming, tumor cells consume additional glutamine to produce amino acids, nucleotides, fatty acids, and other substances to facilitate their unlimited proliferation. As such, the metabolism of glutamine is intricately linked to the survival and progression of cancer cells. Consequently, targeting the glutamine metabolism presents a promising strategy to inhibit growth of tumor cell and cancer development. This review describes glutamine uptake, metabolism, and transport in tumor cells and its pivotal role in biosynthesis of amino acids, fatty acids, nucleotides, and more. Furthermore, we have also summarized the impact of oncogenes like C-MYC, KRAS, HIF, and p53 on the regulation of glutamine metabolism and the mechanisms through which glutamine triggers mTORC1 activation. In addition, role of different anti-cancer agents in targeting glutamine metabolism has been described and their prospective applications are assessed.

Effect of Glutamine on Short-term Surgical Outcomes in Rectal Cancer Patients Receiving Neoadjuvant Therapy: A Propensity Score Matching Study

The effect of glutamine on postoperative complications and postoperative recovery in rectal cancer (RC) patients receiving neoadjuvant therapy (NT) is unclear. This study aimed to investigate the effects of intravenous glutamine supplementation on short-term postoperative outcomes in these patients. This retrospective study included patients with RC who received NT and underwent radical surgery between January 2013 and July 2022 and were either administered glutamine (glutamine group) or not administered glutamine (non-glutamine group). Propensity score matching method was used to analyze and compare postoperative complications and other outcome indicators. A total of 208 patients were reviewed, and 53 were included in each group post matching. While no significant difference in the time to first solid food intake between the two groups was observed, the glutamine group had a significantly reduced incidence of postoperative complications, shorter length of hospital stay, and shorter time to first defecation, first exhaust, and first fluid diet intake than those of the control group. Moreover, glutamine alleviated the reduction in albumin and prealbumin levels. Perioperative parenteral glutamine supplementation effectively reduces the incidence of postoperative complications, promotes postoperative recovery, and improves albumin levels in patients undergoing RC surgery and receiving NT.

Engineering nanomedicine for glutathione depletion-augmented cancer therapy

Glutathione (GSH), the main redox buffer, has long been recognized as a pivotal modulator of tumor initiation, progression and metastasis. It is also implicated in the resistance of platinum-based chemotherapy and radiation therapy. Therefore, depleting intracellular GSH was considered a potent solution to combating cancer. However, reducing GSH within cancer cells alone always failed to yield desirable therapeutic effects. In this regard, the convergence of GSH-scavenging agents with therapeutic drugs has thus been pursued in clinical practice. Unfortunately, the therapeutic outcomes are still unsatisfactory due to untargeted drug delivery. Advanced nanomedicine of synergistic GSH depletion and cancer treatment has attracted tremendous interest because they promise to deliver superior therapeutic benefits while alleviating life-threatening side effects. In the past five years, the authors and others have demonstrated that numerous nanomedicines, by simultaneously delivering GSH-depleting agents and therapeutic components, boost not only traditional chemotherapy and radiotherapy but also multifarious emerging treatment modalities, including photodynamic therapy, sonodynamic therapy, chemodynamic therapy, ferroptosis, and immunotherapy, to name a few, and achieved decent treatment outcomes in a large number of rodent tumor models. In this review, we summarize the most recent progress in engineering nanomedicine for GSH depletion-enhanced cancer therapies. Biosynthesis of GSH and various types of GSH-consuming strategies will be briefly introduced. The challenges and perspectives of leveraging nanomedicine for GSH consumption-augmented cancer therapies will be discussed at the end.

Oxidative Stress, Neuroinflammation and Mitochondria in the Pathophysiology of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron (MN) disease. Its primary cause remains elusive, although a combination of different causal factors cannot be ruled out. There is no cure, and prognosis is poor. Most patients with ALS die due to disease-related complications, such as respiratory failure, within three years of diagnosis. While the underlying mechanisms are unclear, different cell types (microglia, astrocytes, macrophages and T cell subsets) appear to play key roles in the pathophysiology of the disease. Neuroinflammation and oxidative stress pave the way leading to neurodegeneration and MN death. ALS-associated mitochondrial dysfunction occurs at different levels, and these organelles are involved in the mechanism of MN death. Molecular and cellular interactions are presented here as a sequential cascade of events. Based on our present knowledge, the discussion leads to the idea that feasible therapeutic strategies should focus in interfering with the pathophysiology of the disease at different steps.

Glutaminases regulate glutathione and oxidative stress in cancer

Targeted therapies against cancer have improved both survival and quality of life of patients. However, metabolic rewiring evokes cellular mechanisms that reduce therapeutic mightiness. Resistant cells generate more glutathione, elicit nuclear factor erythroid 2-related factor 2 (NRF2) activation, and overexpress many anti-oxidative genes such as superoxide dismutase, catalase, glutathione peroxidase, and thioredoxin reductase, providing stronger antioxidant capacity to survive in a more oxidative environment due to the sharp rise in oxidative metabolism and reactive oxygen species generation. These changes dramatically alter tumour microenvironment and cellular metabolism itself. A rational design of therapeutic combination strategies is needed to flatten cellular homeostasis and accomplish a drop in cancer development. Context-dependent glutaminase isoenzymes show oncogenic and tumour suppressor properties, being mainly associated to MYC and p53, respectively. Glutaminases catalyze glutaminolysis in mitochondria, regulating oxidative phosphorylation, redox status and cell metabolism for tumour growth. In addition, the substrate and product of glutaminase reaction, glutamine and glutamate, respectively, can work as signalling molecules moderating redox and bioenergetic pathways in cancer. Novel synergistic approaches combining glutaminase inhibition and redox-dependent modulation are described in this review. Pharmacological or genetic glutaminase regulation along with oxidative chemotherapy can help to improve the design of combination strategies that escalate the rate of therapeutic success in cancer patients.

MicroRNAs in the regulation of cellular redox status and its implications in myocardial ischemia-reperfusion injury

MicroRNAs (miRNAs) are small RNAs that do not encode for proteins and play key roles in the regulation of gene expression. miRNAs are involved in a comprehensive range of biological processes such as cell cycle control, apoptosis, and several developmental and physiological processes. Oxidative stress can affect the expression levels of multiple miRNAs and, conversely, miRNAs may regulate the expression of redox sensors, alter critical components of the cellular antioxidants, interact with the proteasome, and affect DNA repair systems. The number of publications identifying redox-sensitive miRNAs has increased significantly over the last few years, and some miRNA targets such as Nrf2, SIRT1 and NF-κB have been identified. The complex interplay between miRNAs and ROS is discussed together with their role in myocardial ischemia-reperfusion injury and the potential use of circulating miRNAs as biomarkers of myocardial infarction. Detailed knowledge of redox-sensitive miRNAs is needed to be able to effectively use individual compounds or sets of miRNA-modulating compounds to improve the health-related outcomes associated with different diseases.

Oncogenes and tumor suppressors regulate glutamine metabolism in cancer cells

Several hallmarks of cancer cells are their display of metabolic changes and enhanced proliferation. Highly proliferating cells utilize glutamine as a source of nitrogen, and therefore, one of the commonly seen metabolic changes is increased glutaminolysis, or glutamine catabolism. In addition, glutamine is an important anaplerotic source by which cells support the pools of TCA cycle intermediates in Myc-expressing cancer cells. Glutamine is converted to aspartate, which forms oxaloacetate, malate, and pyruvate. These conversions increase the NADPH/NADP(+) ratio and maintain redox balance, which supports proliferation in K-ras-expressing cells. Therefore, glutamine is important for cancer cell proliferation and survival. On the other hand, glutamine stimulates the activation of the tumor suppressor p53, which induces apoptosis and tumor regression. The tumor suppressor SIRT4 inhibits glutamate dehydrogenase, which converts glutamic acid to α-ketoglutarate, an intermediate in the TCA cycle. Overall, the expression levels of oncogenes and tumor suppressors are critical to determine whether glutamine supports or suppresses proliferation and survival of cancer cells.

Influence of oral glutamine supplementation on survival outcomes of patients treated with concurrent chemoradiotherapy for locally advanced non-small cell lung cancer

Background

Glutamine (Gln) supplementation during concurrent chemoradiotherapy (C-CRT) effectively reduces the incidence and severity of acute radiation-induced esophagitis (RIE). However, there are concerns that Gln might stimulate tumor growth, and therefore negatively impact the outcomes of anticancer treatment. We retrospectively investigated the effect of co-administration of oral Gln during C-CRT on survival outcomes of patients with stage IIIB non-small cell lung carcinoma (NSCLC). We additionally evaluated role of oral Gln in preventing C-CRT-induced weight change, acute and late toxicities.

Methods

The study included 104 patients: 56 (53.8%) received prophylactic powdered Gln (Gln+) orally at a dose of 10 g/8 h and 48 (46.2%) did not receive Gln (Gln-) and served as controls. The prescribed radiation dose to the planning target volume was 66 Gy in 2-Gy fractions. Primary endpoints of progression-free survival (PFS), local/regional progression-free survival (LRPFS), and overall survival (OS) were correlated with status of Gln supplementation.

Results

Oral Gln was well tolerated except for mild nausea/vomiting in 14 (25.0%) patients. There was no C-CRT-related acute or late grade 4–5 toxicity. Administration of Gln was associated with a decrease in the incidence of grade 3 acute radiation-induced esophagitis (RIE) (7.2% vs. 16.7% for Gln+ vs. Gln-; p=0.02) and late-RIE (0% vs. 6.3%; p=0.06), a reduced need for unplanned treatment breaks (7.1% vs. 20.8%; p=0.04), and reduced incidence of weight loss (44.6% vs. 72.9%; p=0.002). At a median follow-up of 24.2 months (range 9.2-34.4) the median OS, LRPFS, and PFS for Gln+ vs. Gln- cohorts were 21.4 vs. 20.4 (p=0.35), 14.2 vs.11.3 (p=0.16), and 10.2 vs. 9.0 months (p=0.11), respectively.

Conclusion

In our study, supplementation with Gln during C-CRT had no detectable negative impact on tumor control and survival outcomes in patients with Stage IIIB NSCLC. Furthermore, Gln appeared to have a beneficial effect with respect to prevention of weight loss and unplanned treatment delays, and reduced the severity and incidence of acute- and late-RIE.

Strategic role for mitochondria in Alzheimer's disease and cancer

SIGNIFICANCE

Detailed knowledge about cell death and cell survival mechanisms and how these pathways are impaired in neurodegenerative disorders and cancer forms the basis for future drug development for these diseases that affect millions of people around the world.

RECENT ADVANCES

In neurodegenerative disorders such as Alzheimer's disease (AD), cell death pathways are inappropriately activated, resulting in neuronal cell death. In contrast, cancer cells develop resistance to apoptosis by regulating anti-apoptotic proteins signaling via mitochondria. Mounting evidence shows that mitochondrial function is central in both cancer and AD. Cancer cells typically shut down oxidative phosphorylation (OXPHOS) in mitochondria and switch to glycolysis for ATP production, making them resistant to hypoxia. In AD, for example, amyloid-β peptide (Aβ) and reactive oxygen species impair mitochondrial function. Neurons therefore also switch to glycolysis to maintain ATP production and to produce molecules involved in antioxidant metabolism in an attempt to survive.

CRITICAL ISSUES

One critical difference between cancer cells and neurons is that cancer cells can survive without OXPHOS, while neurons are dependent on OXPHOS for long-term survival.

FUTURE DIRECTIONS

This review will focus on these abnormalities of mitochondrial function shared in AD and cancer and discuss the potential mechanisms underlying links that may be key steps in the development of therapeutic strategies.

Glutathione in cancer cell death

Glutathione (L-γ-glutamyl-L-cysteinyl-glycine; GSH) in cancer cells is particularly relevant in the regulation of carcinogenic mechanisms; sensitivity against cytotoxic drugs, ionizing radiations, and some cytokines; DNA synthesis; and cell proliferation and death. The intracellular thiol redox state (controlled by GSH) is one of the endogenous effectors involved in regulating the mitochondrial permeability transition pore complex and, in consequence, thiol oxidation can be a causal factor in the mitochondrion-based mechanism that leads to cell death. Nevertheless GSH depletion is a common feature not only of apoptosis but also of other types of cell death. Indeed rates of GSH synthesis and fluxes regulate its levels in cellular compartments, and potentially influence switches among different mechanisms of death. How changes in gene expression, post-translational modifications of proteins, and signaling cascades are implicated will be discussed. Furthermore, this review will finally analyze whether GSH depletion may facilitate cancer cell death under in vivo conditions, and how this can be applied to cancer therapy.

Glutamine targeting inhibits systemic metastasis in the VM-M3 murine tumor model

Metastatic cancer is a major cause of morbidity and mortality. Current therapeutic options consist of chemotherapy, radiation or targeted therapies. However, these therapies are often toxic, effective over a small range of cancer types or result in drug resistance. Therefore, a more global, less toxic strategy for the management of metastatic cancer is required. Although most cancers display increased glucose metabolism, glutamine is also a major energy substrate for many cancers. We evaluated the antimetastatic potential of 6-diazo-5-oxo-L-norleucine (DON), a glutamine analog, using the new VM mouse model of systemic metastasis. We found that primary tumor growth was ∼20-fold less in DON-treated mice than in untreated control mice. We also found that DON treatment inhibited metastasis to liver, lung and kidney as detected by bioluminescence imaging and histology. Our findings provide proof of concept that metabolic therapies targeting glutamine metabolism can manage systemic metastatic cancer.

L-Glutamine Use in the Treatment and Prevention of Mucositis and Cachexia: A Naturopathic Perspective

L-Glutamine (L-GLN) is considered a nonessential amino acid that has a variety of applications in naturopathic medicine. It has been postulated that in the critically ill patient, GLN becomes an essential amino acid for recovery, restoration, and repair at a cellular level. Mucositis is an intestinal mucosal damage of the gastrointestinal tract—mouth, throat, stomach, intestines, rectum, and anus—that is caused directly by chemotherapies and radiotherapies. Cancer cachexia is a significant biochemical event, which is characterized by weight loss, fatigue, and indicative of depletion of skeletal muscle GLN—a hypercatabolic state. There has been some question as to the use of GLN in this patient population because of its role as a preferred energy source not only for enterocytes and lymphocytes but for malignant cells as well.This article will address the questions of safety, efficacy, dosing, and toxicity of GLN used as an integrative therapeutic in ongoing integrative cancer treatment.

Mitochondria and energetic depression in cell pathophysiology

Mitochondrial dysfunction is a hallmark of almost all diseases. Acquired or inherited mutations of the mitochondrial genome DNA may give rise to mitochondrial diseases. Another class of disorders, in which mitochondrial impairments are initiated by extramitochondrial factors, includes neurodegenerative diseases and syndromes resulting from typical pathological processes, such as hypoxia/ischemia, inflammation, intoxications, and carcinogenesis. Both classes of diseases lead to cellular energetic depression (CED), which is characterized by decreased cytosolic phosphorylation potential that suppresses the cell's ability to do work and control the intracellular Ca(2+) homeostasis and its redox state. If progressing, CED leads to cell death, whose type is linked to the functional status of the mitochondria. In the case of limited deterioration, when some amounts of ATP can still be generated due to oxidative phosphorylation (OXPHOS), mitochondria launch the apoptotic cell death program by release of cytochrome c. Following pronounced CED, cytoplasmic ATP levels fall below the thresholds required for processing the ATP-dependent apoptotic cascade and the cell dies from necrosis. Both types of death can be grouped together as a mitochondrial cell death (MCD). However, there exist multiple adaptive reactions aimed at protecting cells against CED. In this context, a metabolic shift characterized by suppression of OXPHOS combined with activation of aerobic glycolysis as the main pathway for ATP synthesis (Warburg effect) is of central importance. Whereas this type of adaptation is sufficiently effective to avoid CED and to control the cellular redox state, thereby ensuring the cell survival, it also favors the avoidance of apoptotic cell death. This scenario may underlie uncontrolled cellular proliferation and growth, eventually resulting in carcinogenesis.

Glutathione in Cancer Biology and Therapy

The glutathione (GSH) content of cancer cells is particularly relevant in regulating mutagenic mechanisms, DNA synthesis, growth, and multidrug and radiation resistance. In malignant tumors, as compared with normal tissues, that resistance associates in most cases with higher GSH levels within these cancer cells. Thus, approaches to cancer treatment based on modulation of GSH should control possible growth-associated changes in GSH content and synthesis in these cells. Despite the potential benefits for cancer therapy of a selective GSH-depleting strategy, such a methodology has remained elusive up to now. Metastatic spread, not primary tumor burden, is the leading cause of cancer death. For patient prognosis to improve, new systemic therapies capable of effectively inhibiting the outgrowth of seeded tumor cells are needed. Interaction of metastatic cells with the vascular endothelium activates local release of proinflammatory cytokines, which act as signals promoting cancer cell adhesion, extravasation, and proliferation. Recent work shows that a high percentage of metastatic cells with high GSH levels survive the combined nitrosative and oxidative stresses elicited by the vascular endothelium and possibly by macrophages and granulocytes. ?-Glutamyl transpeptidase overexpression and an inter-organ flow of GSH (where the liver plays a central role), by increasing cysteine availability for tumor GSH synthesis, function in combination as a metastatic-growth promoting mechanism. The present review focuses on an analysis of links among GSH, adaptive responses to stress, molecular mechanisms of invasive cancer cell survival and death, and sensitization of metastatic cells to therapy. Experimental evidence shows that acceleration of GSH efflux facilitates selective GSH depletion in metastatic cells.

Prevention of acute radiation-induced esophagitis with glutamine in non-small cell lung cancer patients treated with radiotherapy: evaluation of clinical and dosimetric parameters

BACKGROUND

The purpose of this study was to evaluate the efficacy of oral glutamine in the prevention of acute radiation-induced esophagitis (ARIE) and weight loss in lung carcinoma patients, and to determine the clinical/dosimetric predictors of ARIE.

PATIENTS AND METHODS

Data from 41 patients with stage III lung carcinoma treated with thoracic irradiation were retrospectively analyzed. Twenty-two patients (53.6%) received prophylactic powdered glutamine in doses of 10g/8h. Prescribed radiation dose to planning target volume was 60Gy, in 30 fractions, 5 days/week. The primary endpoint included the ARIE incidence and its correlation with clinical/dosimetric factors relative to treatment with glutamine.

RESULTS

Glutamine was well tolerated. Grade 2 or 3 ARIE occurred in 20 (48.8%) of 41 patients: seven in the glutamine-supplemented group, and 13 in the glutamine-free group (p=0.002). All seven patients with grade 3 esophagitis were in the glutamine-free group (36.8% vs. 0%). Glutamine supplementation appeared to significantly delay ARIE onset for six days (22 days vs. 16 days; p=0.002). Glutamine-supplemented patients demonstrated a lower incidence of grade 2 or 3 ARIE (27.2%), and gained weight during radiotherapy (p=0.04). V55 was the only dosimetric parameter that correlated with the severity of ARIE in glutamine-free patients: a V55 of <35% had a 31% risk of ARIE grade 2 or 3, and the risk increased to 76% with a V55 of >or=35% (p=0.01).

CONCLUSION

This schedule and dosage of glutamine may be beneficial in the prevention of ARIE and weight loss in lung cancer patients undergoing thoracic irradiation.

Increased chemosensitivity and elevated reactive oxygen species are mediated by glutathione reduction in glutamine deprived neuroblastoma cells

PURPOSE

Glutamine is an essential amino acid for the synthesis of glutathione (GSH), the major endogenous antioxidant which protects cells from oxidative injury. To evaluate the effects of glutamine concentrations, cell growth, GSH levels, oxidative stress, and chemosensitivity were evaluated in neuroblastoma cell lines.

METHODS

Three human neuroblastoma cell lines (SMS-KCNR, SMS-KANR, SMS-LHN) were cultured with different concentrations of glutamine (2, 0.2 and 0 mM) under hypoxic (5% O(2)) or normoxic (20% O(2)) condition. Cell proliferation and chemosensitivity were determined by MTT assay, and the levels of intracellular GSH were measured by DTNB-GSSG reductase method. Cellular reactive oxidative species (ROS) were quantified by flow cytometry.

RESULTS

There was a significant decrease of cell growth in low glutamine (0.2 and 0 mM) compared with control (2 mM) in all three cell lines (P < 0.01), while adding GSH partially restored the reduced cell proliferation by low glutamine. The levels of GSH in neuroblastoma cells decreased significantly in low glutamine compared with the levels of control cells cultured in 2 mM glutamine (P < 0.05), and the accumulation of cellular ROS was significantly higher in 0 mM glutamine compared to the control. Moreover, glutamine deprivation significantly enhanced cytotoxicity of L-PAM in all three cell lines, which was abolished after addition of GSH.

CONCLUSION

Glutamine deprivation decreased cell proliferation and enhances cell chemosensitivity in neuroblastoma, which is presumably associated with GSH depletion.

Bcl-2 and glutathione depletion sensitizes B16 melanoma to combination therapy and eliminates metastatic disease

PURPOSE

Advanced melanoma resists all current therapies, and metastases in the liver are particularly problematic. Prevalent resistance factors include elevated glutathione (GSH) and increased expression of bcl-2 in melanoma cells. GSH has pleiotropic effects promoting cell growth and broad resistance to therapy, whereas Bcl-2 inhibits the activation of apoptosis and contributes to elevation of GSH. This study determined the in vivo efficacy of combination therapies administered while GSH and Bcl-2 were individually and simultaneously decreased in metastatic melanoma lesions.

EXPERIMENTAL DESIGN

Highly metastatic murine B16 melanoma (B16M-F10) cells have elevated levels of both GSH and Bcl-2. B16M-F10 cells were injected i.v. to establish metastatic lesions in vivo. GSH was decreased using an L-glutamine--enriched diet and administration of verapamil and acivicin, whereas Bcl-2 was reduced using oligodeoxynucleotide G3139. Paclitaxel, X-rays, tumor necrosis factor-alpha, and IFN-gamma were administered as a combination therapy.

RESULTS

Metastatic cells were isolated from liver to confirm the depletion of GSH and Bcl-2 in vivo. Reduction of Bcl-2 and GSH, combined with partial therapies, decreased the number and volume of invasive B16M-F10 foci in liver by up to 99% (P<0.01). The full combination of paclitaxel, X-rays, and cytokines eliminated B16M-F10 cells from liver and all other systemic disease, leading to long-term survival (>120 days) without recurrence in 90% of mice receiving the full therapy. Toxicity was manageable; the mice recovered quickly, and hematology and clinical chemistry data were representative of accepted clinical toxicities.

CONCLUSIONS

Our results suggest a new strategy to induce regression of late-stage metastatic melanoma.

Modulation of p53 and c-myc in DMBA-Induced Mammary Tumors by Oral Glutamine

Previous studies established that oral glutamine (GLN) reduced tumor development in implantable and 7,12-dimethylbenz(a)anthracene (DMBA)-induced breast cancer models. This finding was associated with a decrease in tumor glutathione (GSH) levels, while maintaining normal gut, blood, and breast GSH. Alterations in GSH levels contribute to the control of apoptotic and cell cycle-regulating signaling. The aim of this study was to examine the role of dietary GLN on activation of p53 and c-myc, which play critical roles in cancer development and sensitivity to radiation and chemotherapy. Mammary gland carcinomas were induced in rats by DMBA. The rats were gavaged daily with GLN or water (controls), starting 1 wk prior DMBA-application and throughout the duration of the experiment (11 wk after DMBA). Tumor DNA was examined for mutations in p53 exons 5 and 6. Protein and mRNA levels of p53, p21(WAF1/CIP1), PTEN, IGF-IR, mdm2, and c-myc in tumors of GLN-supplemented rats were compared with those of the control rats (received water). The sequencing of p53 showed that it was wild type. Increased phosphorylation of p53, as well as higher mRNA and protein levels of p21(WAF1/CIP1), PTEN, and mdm2, and lower levels of IGF-IR were detected in tumors of GLN-supplemented rats vs. controls. Both phosphorylated c-myc and c-myc mRNA levels were reduced by GLN. The up-regulation of tumor p53 signaling and down-regulation of c-myc, in addition to previously established inhibition of Akt signaling in DMBA-breast cancer model, suggest that dietary GLN could be a useful approach for increasing the effectiveness of cancer treatment.

Bcl-2 and Mn-SOD antisense oligodeoxynucleotides and a glutamine-enriched diet facilitate elimination of highly resistant B16 melanoma cells by tumor necrosis factor-alpha and chemotherapy

Mitochondrial glutathione (mtGSH) depletion increases sensitivity of Bcl-2-overexpressing B16 melanoma (B16M)-F10 cells (high metastatic potential) to tumor necrosis factor-alpha (TNF-alpha)-induced oxidative stress and death in vitro. In vivo, mtGSH depletion in B16M-F10 cells was achieved by feeding mice (where the B16M-F10 grew as a solid tumor in the footpad) with an L-glutamine (L-Gln)-enriched diet, which promoted in the tumor cells an increase in glutaminase activity, accumulation of cytosolic L-glutamate, and competitive inhibition of GSH transport into mitochondria. L-Gln-adapted B16M-F10 cells, isolated using anti-Met-72 monoclonal antibodies and flow cytometry-coupled cell sorting, were injected into the portal vein to produce hepatic metastases. In l-Gln-adapted invasive (iB16M-Gln+) cells, isolated from the liver by the same methodology and treated with TNF-alpha and an antisense Bcl-2 oligodeoxynucleotide, viability decreased to approximately 12%. iB16M-Gln+ cell death associated with increased generation of O2*- and H2O2, opening of the mitochondrial permeability transition pore complex, and release of proapoptotic molecular signals. Activation of cell death mechanisms was prevented by GSH ester-induced mtGSH replenishment. The oxidative stress-resistant survivors showed an adaptive response that includes overexpression of manganese-containing superoxide dismutase (Mn-SOD) and catalase activities. By treating iB16M-Gln+ cells with a double anti- antisense therapy (Bcl-2 and SOD2 antisense oligodeoxynucleotides) and TNF-alpha, metastatic cell survival decreased to approximately 1%. Chemotherapy (taxol plus daunorubicin) easily removed this minimum percentage of survivors. This contribution identifies critical molecules that can be sequentially targeted to facilitate elimination of highly resistant metastatic cells.

Stressing out over survival: glutamine as an apoptotic modulator

INTRODUCTION

The amino acid glutamine (GLN) has received considerable attention as a potential therapeutic adjuvant in critical illness and in improving postoperative clinical outcomes. Most studies on the role of GLN in cellular physiology have historically focused on its anabolic roles in specific cell types and its contribution to growth in cancer cells. However, an emerging body of work that examines the consequences of GLN deprivation on cellular survival and gene expression has constructed a new paradigm for this amino acid, namely, that limited extracellular GLN supplies modulate stress and apoptotic responses.

METHODS

A survey of the scientific literature was conducted on GLN in cell survival signaling and apoptosis. Work from our laboratory in liver cancer cells also was included in this review.

RESULTS

Most studies on this topic have used mammalian cell lines derived from the gut, immune system (including hybridomas), and various cancers. GLN limitation, even in the presence of an adequate glucose supply, impacts stress-related gene expression, differentially modulates receptor-mediated apoptosis, and directly elicits apoptosis through signaling mechanisms and caspase cascades that are specific to cell type. To date, GLN transporters, cellular hydration, glutaminyl-tRNA synthetase, ATP levels, mRNA stability, and glutathione economy have been variably implicated in GLN-dependent survival signaling.

CONCLUSION

The cell type-specific mechanisms underlying the regulatory role of GLN in cell survival continue to unfold at a steady pace through in vitro studies. These results have collectively provided testable hypotheses for further in vivo studies into their physiological relevance during GLN "nutritional pharmacology."

Glutathione Redox State Regulates Mitochondrial Reactive OxygenProduction

Oxidative stress induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin) is poorly understood. Following one dose of TCDD (5 microg/kg body weight), mitochondrial succinate-dependent production of superoxide and H2O2 in mouse liver doubled at 7-28 days, then subsided by day 56; concomitantly, levels of GSH and GSSG increased in both cytosol and mitochondria. Cytosol displayed a typical oxidative stress response, consisting of diminished GSH relative to GSSG, decreased potential to reduce protein-SSG mixed disulfide bonds (type 1 thiol redox switch) or protein-SS-protein disulfide bonds (type 2 thiol redox switch), and a +10 mV change in GSSG/2GSH reduction potential. In contrast, mitochondria showed a rise in reduction state, consisting of increased GSH relative to GSSG, increases in type 1 and type 2 thiol redox switches, and a -25 mV change in GSSG/2GSH reduction potential. Comparing Ahr(-/-) knock-out and wild-type mice, we found that TCDD-induced thiol changes in both cytosol and mitochondria were dependent on the aromatic hydrocarbon receptor (AHR). GSH was rapidly taken up by mitochondria and stimulated succinate-dependent H2O2 production. A linear dependence of H2O2 production on the reduction potential for GSSG/2GSH exists between -150 and -300 mV. The TCDD-stimulated increase in succinate-dependent and thiol-stimulated production of reactive oxygen paralleled a four-fold increase in formamidopyrimidine DNA N-glycosylase (FPG)-sensitive cleavage sites in mitochondrial DNA, compared with a two-fold increase in nuclear DNA. These results suggest that TCDD produces an AHR-dependent oxidative stress in mitochondria, with concomitant mitochondrial DNA damage mediated, at least in part, by an increase in the mitochondrial thiol reduction state.

Prevention of chemotherapy and radiation toxicity with glutamine

GOALS OF THE WORK

Malignancy produces a state of physiologic stress that is characterized by a relative deficiency of glutamine, a condition that is further exacerbated by the effects of cancer treatment. Glutamine deficiency may impact on normal tissue tolerance to antitumor treatment, and may lead to dose reductions and compromised treatment outcome. Providing supplemental glutamine during cancer treatment has the potential to abrogate treatment-related toxicity. We reviewed the available data on the use of glutamine to decrease the incidence and severity of adverse effects due to chemotherapy and/or radiation in cancer patients.

METHODS

We performed a search of the MEDLINE database during the time period 1980-2003, and reviewed the English language literature of both human and animal studies pertaining to the use of glutamine in subjects with cancer. We also manually searched the bibliographies of published articles for relevant references.

MAIN RESULTS

The available evidence suggests that glutamine supplementation may decrease the incidence and/or severity of chemotherapy-associated mucositis, irinotecan-associated diarrhea, paclitaxel-induced neuropathy, hepatic veno-occlusive disease in the setting of high dose chemotherapy and stem cell transplantation, and the cardiotoxicity that accompanies anthracycline use. Oral glutamine supplementation may enhance the therapeutic index by protecting normal tissues from, and sensitizing tumor cells to chemotherapy and radiation-related injury.

CONCLUSIONS

The role of glutamine in the prevention of chemotherapy and radiation-induced toxicity is evolving. Glutamine supplementation is inexpensive and it may reduce the incidence of gastrointestinal, neurologic, and possibly cardiac complications of cancer therapy. Further studies, particularly placebo-controlled phase III trials, are needed to define its role in chemotherapy-induced toxicity.

Natural products for cancer prevention: a global perspective

The control of cancer, the second leading cause of death worldwide, may benefit from the potential that resides in alternative therapies. The primary carcinogens stem from a variety of agricultural, industrial, and dietary factors. Conventional therapies cause serious side effects and, at best, merely extend the patient's lifespan by a few years. There is thus the need to utilise alternative concepts or approaches to the prevention of cancer. This review focuses on the many natural products that have been implicated in cancer prevention and that promote human health without recognisable side effects. These molecules originate from vegetables, fruits, plant extracts, and herbs.

Enhanced antioxidant defenses and resistance to TNF-alpha in a glycolysis-depleted lung epithelial cell line

Glycolysis-depleted cells, obtained by stable transfection of fructose 2,6-bisphosphatase in mink lung epithelial cells (Mv1Lu), were less sensitive to serum withdrawal- and TNF-alpha-induced apoptosis than cells transfected with the empty vector pcDNA3 (control cells). We compared the differences in the redox status of the two transfectants and the changes produced by TNF-alpha treatment. The activities of the antioxidant enzymes catalase and glutathione peroxidase, as well as the content of reduced glutathione (GSH) and the activity of the nuclear transcription factor kappa B (NF-kappa B), were higher in pFBPase-2 clones than in control cells in all the conditions tested. TNF-alpha challenge sharpened the differences in glutathione peroxidase activity, GSH/GSSG ratios, and NF-kappa B activation between transfectants. These data indicate that glycolysis restriction at the PFK step protects cells against apoptotic stimuli by increasing the GSH content and NF-kappa B activity. This acquired feature may compromise antineoplastic treatments based on glycolytic depletion.

Glutamine and its relationship with intracellular redox status, oxidative stress and cell proliferation/death

Glutamine is a multifaceted amino acid used for hepatic urea synthesis, renal ammoniagenesis, gluconeogenesis in both liver and kidney, and as a major respiratory fuel for many cells. Decreased glutamine concentrations are found during catabolic stress and are related to susceptibility to infections. Besides, glutamine is not only an important energy source in mitochondria, but is also a precursor of the brain neurotransmitter glutamate, which is likewise used for biosynthesis of the cellular antioxidant glutathione. Reactive oxygen species, such as superoxide anions and hydrogen peroxide, function as intracellular second messengers activating, among others, apoptosis, whereas glutamine is an apoptosis suppressor. In fact, it could contribute to block apoptosis induced by exogenous agents or by intracellular stimuli. In conclusion, this article shows evidences for the important role of glutamine in the regulation of the cellular redox balance, including brain oxidative metabolism, apoptosis and tumour cell proliferation.

Glutamine potentiates TNF-alpha-induced tumor cytotoxicity

L-glutamine (Gln) sensitizes tumor cells to tumor necrosis factor (TNF)-alpha-induced cytotoxicity. The type and mechanism of cell death induced by TNF-alpha was studied in Ehrlich ascites tumor (EAT)-bearing mice fed a Gln-enriched diet (GED; where 30% of the total dietary nitrogen was from Gln). A high rate of Gln oxidation promotes a selective depletion of mitochondrial glutathione (mtGSH) content to approximately 58% of the level found in tumor mitochondria of mice fed a nutritionally complete elemental diet (standard diet, SD). The mechanism of mtGSH depletion involves a glutamate-induced inhibition of GSH transport from the cytosol into mitochondria. The increase in reactive oxygen intermediates (ROIs) production induced by TNF-alpha further depletes mtGSH to approximately 35% of control values, which associates with a decrease in the mitochondrial transmembrane potential (MMP), and elicits mitochondrial membrane permeabilization and release of cytochrome c. Mitochondrial membrane permeabilization was also found in intact tumor cells cultured with a Gln-enriched medium under conditions of buthionine sulfoximine (BSO)-induced selective GSH synthesis inhibition. Enforced expression of the bcl-2 gene in tumor cells could not avoid the glutamine- and TNF-alpha-induced cell death under conditions of mtGSH depletion. However, addition of GSH ester, which delivers free intracellular GSH and increases mtGSH levels, preserved cell viability. These findings show that glutamine oxidation and TNF-alpha, by causing a change in the glutathione redox status within tumor mitochondria, activates the molecular mechanism of apoptotic cell death.