Glutathione protects metastatic melanoma cells against oxidative stress in the murine hepatic microvasculature

Glutathione Depletion and Stalwart Anticancer Activity of Metallotherapeutics Inducing Programmed Cell Death: Opening a New Window for Cancer Therapy

The cellular defense system against exogenous substances makes therapeutics inefficient as intracellular glutathione (GSH) exhibits an astounding antioxidant activity in scavenging reactive oxygen species (ROS) or reactive nitrogen species (RNS) or other free radicals produced by the therapeutics. In the cancer cell microenvironment, the intracellular GSH level becomes exceptionally high to fight against oxidative stress created by the production of ROS/RNS or any free radicals, which are the byproducts of intracellular redox reactions or cellular respiration processes. Thus, in order to maintain redox homeostasis for survival of cancer cells and their rapid proliferation, the GSH level starts to escalate. In this circumstance, the administration of anticancer therapeutics is in vain, as the elevated GSH level reduces their potential by reduction or by scavenging the ROS/RNS they produce. Therefore, in order to augment the therapeutic potential of anticancer agents against elevated GSH condition, the GSH level must be depleted by hook or by crook. Hence, this Review aims to compile precisely the role of GSH in cancer cells, the importance of its depletion for cancer therapy and examples of anticancer activity of a few selected metal complexes which are able to trigger cancer cell death by depleting the GSH level.

Ferroptosis in cancer: From molecular mechanisms to therapeutic strategies

Ferroptosis is a non-apoptotic form of regulated cell death characterized by the lethal accumulation of iron-dependent membrane-localized lipid peroxides. It acts as an innate tumor suppressor mechanism and participates in the biological processes of tumors. Intriguingly, mesenchymal and dedifferentiated cancer cells, which are usually resistant to apoptosis and traditional therapies, are exquisitely vulnerable to ferroptosis, further underscoring its potential as a treatment approach for cancers, especially for refractory cancers. However, the impact of ferroptosis on cancer extends beyond its direct cytotoxic effect on tumor cells. Ferroptosis induction not only inhibits cancer but also promotes cancer development due to its potential negative impact on anticancer immunity. Thus, a comprehensive understanding of the role of ferroptosis in cancer is crucial for the successful translation of ferroptosis therapy from the laboratory to clinical applications. In this review, we provide an overview of the recent advancements in understanding ferroptosis in cancer, covering molecular mechanisms, biological functions, regulatory pathways, and interactions with the tumor microenvironment. We also summarize the potential applications of ferroptosis induction in immunotherapy, radiotherapy, and systemic therapy, as well as ferroptosis inhibition for cancer treatment in various conditions. We finally discuss ferroptosis markers, the current challenges and future directions of ferroptosis in the treatment of cancer.

Development of a mouse model expressing a bifunctional glutathione-synthesizing enzyme to study glutathione limitation in vivo

Glutathione (GSH) is a highly abundant tripeptide thiol that performs diverse protective and biosynthetic functions in cells. While changes in GSH availability are associated with inborn errors of metabolism, cancer, and neurodegenerative disorders, studying the limiting role of GSH in physiology and disease has been challenging due to its tight regulation. To address this, we generated cell and mouse models that express a bifunctional glutathione-synthesizing enzyme from Streptococcus thermophilus (GshF), which possesses both glutamate-cysteine ligase and glutathione synthase activities. GshF expression allows efficient production of GSH in the cytosol and mitochondria and prevents cell death in response to GSH depletion, but not ferroptosis induction, indicating that GSH is not a limiting factor under lipid peroxidation. CRISPR screens using engineered enzymes further revealed genes required for cell proliferation under cellular and mitochondrial GSH depletion. Among these, we identified the glutamate-cysteine ligase modifier subunit, GCLM, as a requirement for cellular sensitivity to buthionine sulfoximine, a glutathione synthesis inhibitor. Finally, GshF expression in mice is embryonically lethal but sustains postnatal viability when restricted to adulthood. Overall, our work identifies a conditional mouse model to investigate the limiting role of GSH in physiology and disease.

A mouse model to study glutathione limitation in vivo

Glutathione (GSH) is a highly abundant tripeptide thiol that performs diverse protective and biosynthetic functions in cells. While changes in GSH availability are linked to many diseases, including cancer and neurodegenerative disorders, determining the function of GSH in physiology and disease has been challenging due to its tight regulation. To address this, we generated cell and mouse models that express a bifunctional glutathione-synthesizing enzyme from Streptococcus Thermophilus (GshF). GshF expression allows efficient production of GSH in the cytosol and mitochondria and prevents cell death in response to GSH depletion, but not ferroptosis, indicating that GSH is not a limiting factor under lipid peroxidation. CRISPR screens using engineered enzymes revealed metabolic liabilities under compartmentalized GSH depletion. Finally, GshF expression in mice is embryonically lethal but sustains postnatal viability when restricted to adulthood. Overall, our work identifies a conditional mouse model to investigate the role of GSH availability in physiology and disease.

Nicotinamide riboside, pterostilbene and ibudilast protect motor neurons and extend survival in ALS mice

Oxidative stress and neuroinflammation are major contributors to the pathophysiology of ALS. Nicotinamide riboside (a NAD+ precursor) and pterostilbene (a natural antioxidant) were efficacious in a human pilot study of ALS patients and in ALS SOD1G93A transgenic mice. Ibudilast targets different phosphodiesterases and the macrophage migration inhibitory factor, reduces neuroinflammation, and in early-phase studies improved survival and slowed progression in ALS patients. Using two ALS murine models (SOD1G93A, FUSR521C) the effects of nicotinamide riboside, pterostilbene, and ibudilast on disease onset, progression and survival were studied. In both models ibudilast enhanced the effects of nicotinamide riboside and pterostilbene on survival and neuromotor functions. The triple combination reduced microgliosis and astrogliosis, and the levels of different proinflammatory cytokines in the CSF. TNFα, IFNγ and IL1β increased H2O2 and NO generation by motor neurons, astrocytes, microglia and endothelial cells isolated from ALS mice. Nicotinamide riboside and pterostilbene decreased H2O2 and NO generation in all these cells. Ibudilast specifically decreased TNFα levels and H2O2 generation by microglia and endothelial cells. Unexpectedly, pathophysiological concentrations of H2O2 or NO caused minimal motor neuron cytotoxicity. H2O2-induced cytotoxicity was increased by NO via a trace metal-dependent formation of potent oxidants (i.e. OH and -OONO radicals). In conclusion, our results show that the combination of nicotinamide riboside, pterostilbene and ibudilast improve neuromotor functions and survival in ALS murine models. Studies on the underlying mechanisms show that motor neuron protection involves the decrease of oxidative and nitrosative stress, the combination of which is highly damaging to motor neurons.

Lipids as mediators of cancer progression and metastasis

Metastasis formation is a complex process, involving multiple crucial steps, which are controlled by different regulatory mechanisms. In this context, the contribution of cancer metabolism to the metastatic cascade is being increasingly recognized. This Review focuses on changes in lipid metabolism that contribute to metastasis formation in solid tumors. We discuss the molecular mechanisms by which lipids induce a pro-metastatic phenotype and explore the role of lipids in response to oxidative stress and as signaling molecules. Finally, we reflect on potential avenues to target lipid metabolism to improve the treatment of metastatic cancers.

Survival Mechanisms of Metastatic Melanoma Cells: The Link between Glucocorticoids and the Nrf2-Dependent Antioxidant Defense System

Circulating glucocorticoids increase during stress. Chronic stress, characterized by a sustained increase in serum levels of cortisol, has been associated in different cases with an increased risk of cancer and a worse prognosis. Glucocorticoids can promote gluconeogenesis, mobilization of amino acids, fat breakdown, and impair the body's immune response. Therefore, conditions that may favor cancer growth and the acquisition of radio- and chemo-resistance. We found that glucocorticoid receptor knockdown diminishes the antioxidant protection of murine B16-F10 (highly metastatic) melanoma cells, thus leading to a drastic decrease in their survival during interaction with the vascular endothelium. The BRAF^V600E mutation is the most commonly observed in melanoma patients. Recent studies revealed that VMF/PLX40-32 (vemurafenib, a selective inhibitor of mutant BRAF^V600E) increases mitochondrial respiration and reactive oxygen species (ROS) production in BRAF^V600E human melanoma cell lines. Early-stage cancer cells lacking Nrf2 generate high ROS levels and exhibit a senescence-like growth arrest. Thus, it is likely that a glucocorticoid receptor antagonist (RU486) could increase the efficacy of BRAF-related therapy in BRAF^V600E-mutated melanoma. In fact, during early progression of skin melanoma metastases, RU486 and VMF induced metastases regression. However, treatment at an advanced stage of growth found resistance to RU486 and VMF. This resistance was mechanistically linked to overexpression of proteins of the Bcl-2 family (Bcl-xL and Mcl-1 in different human models). Moreover, melanoma resistance was decreased if AKT and NF-κB signaling pathways were blocked. These findings highlight mechanisms by which metastatic melanoma cells adapt to survive and could help in the development of most effective therapeutic strategies.

N-Acetylcysteine Promotes Metastatic Spread of Melanoma in Mice

Simple Summary

Malignant melanoma is a cancer derived from melanocytes, the cells that produce pigment (melanin) in the skin. It develops on the skin, but can also appear on the mucous membranes and in other locations. Melanomas are responsible for 80% of deaths related to skin cancers. In recent years, the number of cases has increased alarmingly, likely in relation to sun exposure habits. Once melanoma spreads to distant parts of the body, the 5-year survival rate is about 10%. N-acetylcysteine (NAC) is a drug with antioxidant properties, and thereby could play a role in preventing cancer. NAC is commonly used as a mucolytic in different respiratory diseases, to treat acetaminophen (Tylenol) poisoning, and is also present in different nutritional supplements. Nevertheless, the use of NAC and other antioxidants in cancer has been questioned. Here, we show that high therapeutic doses of NAC may cause metastatic spread of a malignant melanoma.

Abstract

N-acetylcysteine (NAC) is a direct Cys donor and a promoter of glutathione (GSH) synthesis. GSH regulates melanoma growth and NAC has been suggested to increase melanoma metastases in mice. We found that high therapeutic doses of NAC do not increase the growth of melanoma xenografts, but can cause metastatic spread and distant metastases. Nevertheless, this is not due to an antioxidant effect since NAC, in fact, increases the generation of reactive oxygen species in the growing metastatic melanoma. Trolox, an antioxidant vitamin E derivative, administered in vivo, decreased metastatic growth. Metastatic cells isolated from NAC-treated mice showed an increase in the nuclear translocation of Nrf2, as compared to controls. Nrf2, a master regulator of the antioxidant response, controls the expression of different antioxidant enzymes and of the γ-glutamylcysteine ligase (the rate-limiting step in GSH synthesis). Cystine uptake through the xCT cystine-glutamate antiporter (generating intracellular Cys) and the γ-glutamylcysteine ligase activity are key to control metastatic growth. This is associated to an increase in the utilization of L-Gln by the metastatic cells, another metastases promoter. Our results demonstrate the potential of NAC as an inducer of melanoma metastases spread, and suggest that caution should be taken when administering GSH promoters to cancer patients.

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.

Drug Resistant Melanoma May Be Vulnerable to Inhibitors of Serine Synthesis

NRAS-driven melanomas frequently develop resistance to MAPK/extracellular signal-regulated kinase kinase inhibitors (MEKis), which limits their therapeutic utility. Nguyen et al. (2020) show that MEKi-resistant cells upregulate phosphoglycerate dehydrogenase (PHGDH), the rate-limiting enzyme in serine synthesis. Suppression of PHGDH rendered cells sensitive to MEKis, suggesting that PHGDH may be a therapeutic target for melanoma.

Liver prometastatic reaction: Stimulating factors and responsive cancer phenotypes

Cancer is first a localized tissue disorder, whose soluble and exosomal molecules and invasive cells induce a host response providing the stromal components of the primary tumor microenvironment (TME). Once the TME is developed, cancer-derived molecules and cells can more efficiently spread out and a whole-body response takes place, whose pathophysiological changes may result in a paraneoplastic syndrome. Remote organ-specific prometastatic reactions may also occur at this time, facilitating metastatic activities of circulating tumor cells (CTCs) through premetastatic niche development at targeted organs. However, additional signaling factors from the inter-organ communication network involved in the pathophysiology and comorbidities of cancer patients may also regulate prometastatic reaction-stimulating effects of cancer and non-cancer tissue factors. This article provides a conceptual overview of our ongoing clinical research on the liver prometastatic reaction (LPR) of patients with colorectal cancer (CRC), their portal vein- and hepatic artery-driven LPR-Stimulating Factors (LPR-SF), and their resulting LPR-derived Metastasis-Stimulating Factors (LPR-MSF) acting on liver-invading CRC cells. In addition, we also provide new insights on the molecular subtyping of LPR-responsive cancer phenotypes in patients with CRC and melanoma; and on how to investigate and interpret the prometastatic infrastructure in the real pathophysiological context of patients with cancer undergoing surgical procedures and receiving pharmacological treatments with multiple side effects, including those affecting the LPR, its stimulating factors and responsive cancer phenotypes.

Melanoma in the liver: Oxidative stress and the mechanisms of metastatic cell survival

Metastatic melanoma is a fatal disease with a rapid systemic dissemination. The most frequent target sites are the liver, bone, and brain. Melanoma metastases represent a heterogeneous cell population, which associates with genomic instability and resistance to therapy. Interaction of melanoma cells with the hepatic sinusoidal endothelium initiates a signaling cascade involving cytokines, growth factors, bioactive lipids, and reactive oxygen and nitrogen species produced by the cancer cell, the endothelium, and also by different immune cells. Endothelial cell-derived NO and H₂O₂ and the action of immune cells cause the death of most melanoma cells that reach the hepatic microvascularization. Surviving melanoma cells attached to the endothelium of pre-capillary arterioles or sinusoids may follow two mechanisms of extravasation: a) migration through vessel fenestrae or b) intravascular proliferation followed by vessel rupture and microinflammation. Invading melanoma cells first form micrometastases within the normal lobular hepatic architecture via a mechanism regulated by cross-talk with the stroma and multiple microenvironment-related molecular signals. In this review special emphasis is placed on neuroendocrine (systemic) mechanisms as potential promoters of liver metastatic growth. Growing metastatic cells undergo functional and metabolic changes that increase their capacity to withstand oxidative/nitrosative stress, which favors their survival. This adaptive process also involves upregulation of Bcl-2-related antideath mechanisms, which seems to lead to the generation of more resistant cell subclones.

The abundance of metabolites related to protein methylation correlates with the metastatic capacity of human melanoma xenografts

Metabolic reprogramming is a major factor in transformation, and particular metabolic phenotypes correlate with oncogenotype, tumor progression, and metastasis. By profiling metabolites in 17 patient-derived xenograft melanoma models, we identified durable metabolomic signatures that correlate with biological features of the tumors. BRAF mutant tumors had metabolomic and metabolic flux features of enhanced glycolysis compared to BRAF wild-type tumors. Tumors that metastasized efficiently from their primary sites had elevated levels of metabolites related to protein methylation, including trimethyllysine (TML). TML levels correlated with histone H3 trimethylation at Lys⁹ and Lys²⁷, and methylation at these sites was also enhanced in efficiently metastasizing tumors. Erasing either of these marks by genetically or pharmacologically silencing the histone methyltransferase SETDB1 or EZH2 had no effect on primary tumor growth but reduced cellular invasiveness and metastatic spread. Thus, metabolite profiling can uncover targetable epigenetic requirements for the metastasis of human melanoma cells.

Opposite Effects of Mechanical Action of Fluid Flow on Proangiogenic Factor Secretion From Human Adipose-Derived Stem Cells With and Without Oxidative Stress

Mechanical forces, hypoxia, and oxidative stress contribute to skin renewal, perfusion, and wound healing, but how are they regulating subcutaneous adipose-derived stem cells (ASCs) in the inflammatory microenvironment associated to skin repair and disorders is unknown. In this study, ASCs were isolated from lipoaspirate samples from plastic surgery patients, primary cultured and their differentiation and secretion of a panel of cytokines with pronounced effects on skin repair and angiogenesis were studied under mechanical stimulation by intermittent fluid flow, 1% hypoxia and oxidative stress by glutathione (GSH) depletion with buthionine sulfoximine (BSO) treatment. Mechanical action of fluid flow did not alter mesenchymal phenotype of CD90⁺ /CD29⁺ /CD44⁺ /CD34^- /CD106^- /CD45^- ASCs; however, it remarkably induced ASC secretion of human umbilical vein endothelial cell (HUVEC) migration-stimulating factors. Multiplex Luminex assay further confirmed an increased secretion of VEGF, G-CSF, HGF, Leptin, IL-8, PDGF-BB, Angiopoietin-2, and Follistatin from mechanically-stimulated ASCs via cyclooxygenase-2. Consistent with this mechanism, GSH depletion and hypoxia also increased ASC secretion of VEGF, IL-8, leptin, Angiopoitein-2, and PDGF-BB. However, mechanical action of fluid flow abrogated VEGF and HUVEC migration-stimulating activity from GSH-depleted and hypoxic ASCs. Conversely, GSH depletion and hypoxia abrogated VEGF and HUVEC migration-stimulating activity from mechano-stimulated ASCs. Although mechanical action of fluid flow, hypoxia, and GSH-depletion had independent proangiogenic-stimulating activity on ASCs, mechanical stimulation had opposite effects on proangiogenic factor secretion from ASCs with and without oxidative stress. These data uncover the role of hypoxia and endogenous redox balance during the proangiogenic response of ASCs and other mesenchymal-derived cell types to mechanical action of interstitial fluid flow. J. Cell. Physiol. 232: 2158-2167, 2017. © 2016 Wiley Periodicals, Inc.

Glucocorticoid receptor knockdown decreases the antioxidant protection of B16 melanoma cells: an endocrine system-related mechanism that compromises metastatic cell resistance to vascular endothelium-induced tumor cytotoxicity

We previously reported an interorgan system in which stress-related hormones (corticosterone and noradrenaline), interleukin-6, and glutathione (GSH) coordinately regulate metastatic growth of highly aggressive B16-F10 melanoma cells. Corticosterone, at levels measured in tumor-bearing mice, also induces apoptotic cell death in metastatic cells with low GSH content. In the present study we explored the potential role of glucocorticoids in the regulation of metastatic cell death/survival during the early stages of organ invasion. Glucocorticoid receptor (GCR) knockdown decreased the expression and activity of γ-glutamylcysteine synthetase (γ-GCS), the rate-limiting step in GSH synthesis, in metastatic cells in vivo independent of the tumor location (liver, lung, or subcutaneous). The decrease in γ-GCS activity was associated with lower intracellular GSH levels. Nrf2- and p53-dependent down-regulation of γ-GCS was associated with a decrease in the activities of superoxide dismutase 1 and 2, catalase, glutathione peroxidase, and glutathione reductase, but not of the O₂⁻-generating NADPH oxidase. The GCR knockdown-induced decrease in antioxidant protection caused a drastic decrease in the survival of metastatic cells during their interaction with endothelial cells, both in vitro and in vivo; only 10% of cancer cells attached to the endothelium survived compared to 90% survival observed in the controls. This very low rate of metastatic cell survival was partially increased (up to 52%) in vivo by inoculating B16-F10 cells preloaded with GSH ester, which enters the cell and delivers free GSH. Taken together, our results indicate that glucocorticoid signaling influences the survival of metastatic cells during their interaction with the vascular endothelium.

The role of a Schiff base scaffold, N-(2-hydroxy acetophenone) glycinate-in overcoming multidrug resistance in cancer

Drug resistance is a problem that hinders the numerous successes of chemotherapeutic intervention of cancer and continues to be a major obstacle for cures. Till date, several attempts have been made to develop suitable multidrug resistance (MDR) reversing agents. But, throughout the clinical development of MDR reversing agents, patients repeatedly suffer from toxicities. So far, some anticancer activity of Schiff bases which are the condensation products of carbonyl compounds and primary amines and their metal complexes has been described. But, overcoming multidrug resistance, by the use of such small molecules still remain unexplored. Under this backdrop, in search of less toxic and more effective MDR reversing agents our laboratory has developed the different metal chelates of Schiff base N-(2-hydroxy acetophenone)glycinate (NG) which is structurally similar to azatyrosine [L-β-(5-hydroxy-2-pyridyl)-alanine] that inhibits tumor formation by deactivating the c-Raf-1 kinase and c-Ha-ras signalling pathway. A decade-long research proposes possible strategies to overcome MDR by exploiting the chemical nature of such metal chelates. In this review we have catalogued the success of metal chelates of NG to overcome MDR in cancer. The review depict that the problem of MDR can be circumvent by synchronized activation of immunogenic cell death pathways that utilize the components of a host's immune system to kill cancer cells in combination with other conventional strategies. The current wealth of preclinical information promises better understanding of the cellular processes underlying MDR reversing activity of metal derivatives of NG and thus exposes several cellular targets for rational designing of new generation of Schiff base metal chelates as MDR reversing agents.

Redox regulation in stem-like cancer cells by CD44 variant isoforms

Increasing evidence indicates that several types of solid tumor are hierarchically organized and sustained by a distinct population of cancer stem cells (CSCs). CSCs possess enhanced mechanisms of protection from stress induced by reactive oxygen species (ROS) that render them resistant to chemo- and radiotherapy. Expression of CD44, especially variant isoforms (CD44v) of this major CSC marker, contributes to ROS defense through upregulation of the synthesis of reduced glutathione (GSH), the primary intracellular antioxidant. CD44v interacts with and stabilizes xCT, a subunit of the cystine-glutamate transporter xc(-), and thereby promotes cystine uptake for GSH synthesis. Given that cancer cells are often exposed to high levels of ROS during tumor progression, the ability to avoid the consequences of such exposure is required for cancer cell survival and propagation in vivo. CSCs, in which defense against ROS is enhanced by CD44v are thus thought to drive tumor growth, chemoresistance and metastasis. Therapy targeted to the CD44v-xCT system may therefore impair the ROS defense ability of CSCs and thereby sensitize them to currently available treatments.

Stress associated gene expression in blood cells is related to outcome in radiotherapy treated head and neck cancer patients

Background

We previously observed that a radiotherapy-induced biochemical response in plasma was associated with favourable outcome in head and neck squamous carcinoma cancer (HNSCC) patients. The aim of the present study was to compare stress associated blood cell gene expression between two sub-groups of HNSCC patients with different biochemical responses to radiotherapy.

Methods

Out of 87 patients (histologically verified), 10 biochemical ‘responders’ having a high relative increase in plasma oxidative damage and a concomitant decrease in plasma antioxidants during radiotherapy and 10 ‘poor-responders’ were selected for gene-expression analysis and compared using gene set enrichment analysis.

Results

There was a significant induction of stress-relevant gene-sets in the responders following radiotherapy compared to the poor-responders. The relevance of the involvement of similar stress associated gene expression for HNSCC cancer and radioresistance was verified using two publicly available data sets of 42 HNSCC cases and 14 controls (GEO GSE6791), and radiation resistant and radiation sensitive HNSCC xenografts (E-GEOD-9716).

Conclusions

Radiotherapy induces a systemic stress response, as revealed by induction of stress relevant gene expression in blood cells, which is associated to favourable outcome in a cohort of 87 HNSCC patients. Whether these changes in gene expression reflects a systemic effect or are biomarkers of the tumour micro-environmental status needs further study.

Trial registration

Raw data are available at ArrayExpress under accession number E-MEXP-2460.

Glutathione and Bcl-2 targeting facilitates elimination by chemoradiotherapy of human A375 melanoma xenografts overexpressing bcl-xl, bcl-2, and mcl-1

BACKGROUND

Bcl-2 is believed to contribute to melanoma chemoresistance. However, expression of Bcl-2 proteins may be different among melanomas. Thus correlations among expression of Bcl-2-related proteins and in vivo melanoma progression, and resistance to combination therapies, was investigated.

METHODS

Human A375 melanoma was injected s.c. into immunodeficient nude mice. Protein expression was studied in tumor samples obtained by laser microdisection. Transfection of siRNA or ectopic overexpression were applied to manipulate proteins which are up- or down-regulated, preferentially, during melanoma progression. Anti-bcl-2 antisense oligonucleotides and chemoradiotherapy (glutathione-depleting agents, paclitaxel protein-binding particles, daunorubicin, X rays) were administered in combination.

RESULTS

In vivo A375 cells down-regulated pro-apoptotic bax expression; and up-regulated anti-apoptotic bcl-2, bcl-xl, and mcl-1, however only Bcl-2 appeared critical for long-term tumor cell survival and progression in vivo. Reduction of Bcl-2, combined with partial therapies, decreased melanoma growth. But only Bcl-2 targeting plus the full combination of chemoradiotherapy eradicated A375 melanoma, and led to long-term survival (> 120 days) without recurrence in 80% of mice. Tumor regression was not due to immune stimulation. Hematology and clinical chemistry data were within accepted clinical toxicities.

CONCLUSION

Strategies to target Bcl-2, may increase the effectiveness of antitumor therapies against melanomas overexpressing Bcl-2 and likely other Bcl-2-related antiapoptotic proteins.

Intertissue flow of glutathione (GSH) as a tumor growth-promoting mechanism: interleukin 6 induces GSH release from hepatocytes in metastatic B16 melanoma-bearing mice

B16 melanoma F10 (B16-F10) cells with high glutathione (GSH) content show high metastatic activity in vivo. An intertissue flow of GSH, where the liver is the main reservoir, can increase GSH content in metastatic cells and promote their growth. We have studied here possible tumor-derived molecular signals that could activate GSH release from hepatocytes. GSH efflux increases in hepatocytes isolated from mice bearing liver or lung metastases, thus suggesting a systemic mechanism. Fractionation of serum-free conditioned medium from cultured B16-F10 cells and monoclonal antibody-induced neutralization techniques facilitated identification of interleukin (IL)-6 as a tumor-derived molecule promoting GSH efflux in hepatocytes. IL-6 activates GSH release through a methionine-sensitive/organic anion transporter polypeptide 1- and multidrug resistance protein 1-independent channel located on the sinusoidal site of hepatocytes. Specific siRNAs were used to knock down key factors in the main signaling pathways activated by IL-6, which revealed a STAT3-dependent mechanism. Our results show that IL-6 (mainly of tumor origin in B16-F10-bearing mice) may facilitate GSH release from hepatocytes and its interorgan transport to metastatic growing foci.

Sodium nitroprusside induces autophagic cell death in glutathione-depleted osteoblasts

Previous studies reported that high levels of nitric oxide (NO) induce apoptotic cell death in osteoblasts. We examined molecular mechanisms of cytotoxic injury induced by sodium nitroprusside (SNP), a NO donor, in both glutathione (GSH)-depleted and control U2-OS osteoblasts. Cell viability was reduced by much lower effective concentrations of SNP in GSH-depleted cells compared to normal cells. The data suggest that the level of intracellular GSH is critical in SNP-induced cell death processes of osteoblasts. The level of oxidative stress due to SNP treatments doubled in GSH-depleted cells when measured with fluorochrome H2DCFDA. Pretreatment with the NO scavenger PTIO preserved the viability of cells treated with SNP. Viability of cells treated with SNP was recovered by pretreatment with Wortmannin, an autophagy inhibitor, but not by pretreatment with zVAD-fmk, a pan-specific caspase inhibitor. Large increases of LC3-II were shown by immunoblot analysis of the SNP-treated cells, and the increase was blocked by pretreatment with PTIO or Wortmannin; this implies that under GSH-depleted conditions SNP induces different molecular signaling that lead to autophagic cell death. The ultrastructural morphology of SNP-treated cells in transmission electron microscopy showed numerous autophagic vacuoles. These data suggest NO produces oxidative stress and cellular damage that culminate in autophagic cell death of GSH-depleted osteoblasts.

Anti-invasion effect of rosmarinic acid via the extracellular signal-regulated kinase and oxidation-reduction pathway in Ls174-T cells

Rosmarinic acid is a major phenylpropanoid isolated from Prunella vulgaris L., which is a composition of herbal tea for centuries in China. However, the anti-invasion activity on Ls174-T human colon carcinoma cells has not been studied. In this study, we investigated the anti-metastasis functions according to wound healing assay, adhesion assay, and Transwell assay and found that rosmarinic acid could inhibit migration, adhesion, and invasion dose-dependently. Rosmarinic acid also could decrease the level of reactive oxygen species by enhancing the level of reduced glutathione hormone. In addition, rosmarinic acid repressed the activity and expression of matrix metalloproteinase-2,9. According to Western blot and quantitative real-time PCR assay, rosmarinic acid may inhibit metastasis from colorectal carcinoma mainly via the pathway of extracellular signal-regulated kinase. In animal experiment, intraperitoneal administration of 2 mg of rosmarinic acid reduced weight of tumors and the number of lung nodules significantly compared with those of control group. Therefore, these results demonstrated that rosmarinic acid can effectively inhibit tumor metastasis in vitro and in vivo.

Oxidative and nitrosative stress in the metastatic microenvironment

Metastases that are resistant to conventional therapies are the main cause of most cancer-related deaths in humans. Tumor cell heterogeneity, which associates with genomic and phenotypic instability, represents a major problem for cancer therapy. Additional factors, such as the attack of immune cells or organ-specific microenvironments, also influence metastatic cell behavior and the response to therapy. Interaction of cancer and endothelial cells in capillary beds, involving mechanical contact and transient adhesion, is a critical step in the initiation of metastasis. This interaction initiates a cascade of activation pathways that involves cytokines, growth factors, bioactive lipids and reactive oxygen and nitrogen species (ROS and RNS) produced by either the cancer cell or the endothelium. Vascular endothelium-derived NO and H₂O₂ are cytotoxic for the cancer cells, but also help to identify some critical molecular targets that appear essential for survival of invasive metastatic cell subsets. Surviving cancer cells that extravasate and start colonization of an organ or tissue can still be attacked by macrophages and be influenced by specific intraorgan microenvironment conditions. At all steps; from the primary tumor until colonization of a distant organ; metastatic cells undergo a dynamic process of constant adaptations that may lead to the survival of highly resistant malignant cell subsets. In this sequence of molecular events both ROS and RNS play key roles.

Biochemical mechanism of acetaminophen (APAP) induced toxicity in melanoma cell lines

In this work, we investigated the biochemical mechanism of acetaminophen (APAP) induced toxicity in SK-MEL-28 melanoma cells using tyrosinase enzyme as a molecular cancer therapeutic target. Our results showed that APAP was metabolized 87% by tyrosinase at 2 h incubation. AA and NADH, quinone reducing agents, were significantly depleted during APAP oxidation by tyrosinase. The IC(50) (48 h) of APAP towards SK-MEL-28, MeWo, SK-MEL-5, B16-F0, and B16-F10 melanoma cells was 100 microM whereas it showed no significant toxicity towards BJ, Saos-2, SW-620, and PC-3 nonmelanoma cells, demonstrating selective toxicity towards melanoma cells. Dicoumarol, a diaphorase inhibitor, and 1-bromoheptane, a GSH depleting agent, enhanced APAP toxicity towards SK-MEL-28 cells. AA and GSH were effective in preventing APAP induced melanoma cell toxicity. Trifluoperazine and cyclosporin A, inhibitors of permeability transition pore in mitochondria, significantly prevented APAP melanoma cell toxicity. APAP caused time and dose-dependent decline in intracellular GSH content in SK-MEL-28, which preceded cell toxicity. APAP led to ROS formation in SK-MEL-28 cells which was exacerbated by dicoumarol and 1-bromoheptane whereas cyslosporin A and trifluoperazine prevented it. Our investigation suggests that APAP is a tyrosinase substrate, and that intracellular GSH depletion, ROS formation and induced mitochondrial toxicity contributed towards APAP's selective toxicity in SK-MEL-28 cells.

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.

Gamma-glutamyltransferase is upregulated after oxidative stress through the Ras signal transduction pathway in rat colon carcinoma cells

Gamma-glutamyltransferase (GGT) plays a central role in the homeostasis of the antioxidant glutathione (GSH). The expression of GGT has been shown to be upregulated after oxidative stress, but the signalling pathways implicated remain poorly characterized. The results here show that acute exposure of CC531 cells to oxidative stress resulted in activation of Ras and augmented GGT enzyme activity, both at the transcriptional and at the translation level. Moreover, an involvement of the GGT promoter II was detected after RT-PCR and transient transfection studies. Ectopic expression of activated Ras, but not dominant negative Ras, also resulted in increased GGT promoter II transcriptional activity, an effect that was attenuated by over-expression of dominant negative mutants of Akt, p38 MAPK and MEK1. Addition of specific inhibitors of these kinases during oxidative stress diminished the activation of GGT. In conclusion, oxidative stress-induced activation of GGT involves Ras and several downstream signalling pathways.

The prometastatic microenvironment of the liver

The liver is a major metastasis-susceptible site and majority of patients with hepatic metastasis die from the disease in the absence of efficient treatments. The intrahepatic circulation and microvascular arrest of cancer cells trigger a local inflammatory reaction leading to cancer cell apoptosis and cytotoxicity via oxidative stress mediators (mainly nitric oxide and hydrogen peroxide) and hepatic natural killer cells. However, certain cancer cells that resist or even deactivate these anti-tumoral defense mechanisms still can adhere to endothelial cells of the hepatic microvasculature through proinflammatory cytokine-mediated mechanisms. During their temporary residence, some of these cancer cells ignore growth-inhibitory factors while respond to proliferation-stimulating factors released from tumor-activated hepatocytes and sinusoidal cells. This leads to avascular micrometastasis generation in periportal areas of hepatic lobules. Hepatocytes and myofibroblasts derived from portal tracts and activated hepatic stellate cells are next recruited into some of these avascular micrometastases. These create a private microenvironment that supports their development through the specific release of both proangiogenic factors and cancer cell invasion- and proliferation-stimulating factors. Moreover, both soluble factors from tumor-activated hepatocytes and myofibroblasts also contribute to the regulation of metastatic cancer cell genes. Therefore, the liver offers a prometastatic microenvironment to circulating cancer cells that supports metastasis development. The ability to resist anti-tumor hepatic defense and to take advantage of hepatic cell-derived factors are key phenotypic properties of liver-metastasizing cancer cells. Knowledge on hepatic metastasis regulation by microenvironment opens multiple opportunities for metastasis inhibition at both subclinical and advanced stages. In addition, together with metastasis-related gene profiles revealing the existence of liver metastasis potential in primary tumors, new biomarkers on the prometastatic microenvironment of the liver may be helpful for the individual assessment of hepatic metastasis risk in cancer patients.

Metabolic Bioactivation and Toxicity of Ethyl 4-Hydroxybenzoate in Human SK-MEL-28 Melanoma Cells

The metabolism and toxicity of ethyl 4-hydroxybenzoate (4-HEB) were investigated in vitro using tyrosinase enzyme, a melanoma molecular target, and CYP2E1 induced rat liver microsomes, and in human SK-MEL-28 melanoma cells. The results were compared to 4-hydroxyanisole (4-HA). At 90 min, 4-HEB was metabolized 48% by tyrosinase and 26% by liver microsomes while the extent of 4-HA metabolism was 196% and 88%, respectively. The IC50 (day 2) of 4-HEB and 4-HA towards SK-MEL-28 cells were 75 and 50 microM, respectively. Dicoumarol, a diaphorase inhibitor, and 1-bromoheptane, a GSH depleting agent, increased 4-HEB toxicity towards SK-MEL-28 cells indicating o-quinone formation played an important role in 4-HEB induced cell toxicity. Addition of ascorbic acid and GSH to the media was effective in preventing 4-HEB cell toxicity. Cyclosporin A and trifluoperazine, inhibitors of permeability transition pore in mitochondria, were significantly potent in inhibiting 4-HEB cell toxicity. 4-HEB caused time-dependent decline in intracellular GSH concentration which preceded cell death. 4-HEB also led to reactive oxygen species (ROS) formation in melanoma cells which exacerbated by dicoumarol and 1-bromoheptane whereas cyclosporin A and trifluoperazine prevented it. Our findings suggest that the mechanisms of 4-HEB toxicity in SK-MEL-28 were o-quinone formation, intracellular GSH depletion, ROS formation and mitochondrial toxicity.

Oxidative stress in endometrial hyperplasia

OBJECTIVE

Reactive oxygen species seem to be involved in the onset and promotion of carcinogenesis. In 80% of cases of endometrial adenocarcinoma type I, a clear association exists with endometrial hyperplasia, which is considered a key factor in the endometrial oncological spectrum. The presence or absence of atypical cells determines oncological potential. This study explored the behavior of oxidative stress (catalase and malondialdehyde) in endometrial hyperplasia (with or without atypical cells) by comparing it with the oxidative stress existing in both the proliferative and secretory phases.

DESIGN

Endometrial specimens from 55 women were used, 32 of which were histologically diagnosed as physiological (17 proliferative and 15 secretory endometria) and 23 as endometrial hyperplasia (18 nonatypical and 5 atypical endometrial hyperplasia).

RESULTS

Significant differences were found in the malondialdehyde variable between the proliferative endometrium and the endometrium with atypical hyperplasia (P = 0.0208) and between both types of endometrial hyperplasia (P = 0.0441). The other comparisons were not statistically significant. No changes in catalase activity were observed.

CONCLUSION

Our findings seem to suggest that the presence of atypical cells in endometrial hyperplasia induces a reduction in lipid peroxidation, which could permit survival and growth of these cells. This possible decrease in lipid peroxidation does not seem to be mediated by an increase in endometrial catalase activity.

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.

Nitric oxide mediates natural polyphenol-induced Bcl-2 down-regulation and activation of cell death in metastatic B16 melanoma

Intravenous administration to mice of trans-pterostilbene (t-PTER; 3,5-dimethoxy-4'-hydroxystilbene) and quercetin (QUER; 3,3',4',5,6-pentahydroxyflavone), two structurally related and naturally occurring small polyphenols, inhibits metastatic growth of highly malignant B16 melanoma F10 (B16M-F10) cells. t-PTER and QUER inhibit bcl-2 expression in metastatic cells, which sensitizes them to vascular endothelium-induced cytotoxicity. However, the molecular mechanism(s) linking polyphenol signaling and bcl-2 expression are unknown. NO is a potential bioregulator of apoptosis with controversial effects on Bcl-2 regulation. Polyphenols may affect NO generation. Short-term exposure (60 min/day) to t-PTER (40 microM) and QUER (20 microM) (approximate mean values of the plasma concentrations measured within the first hour after intravenous administration of 20 mg of each polyphenol/kg) down-regulated inducible NO synthetase in B16M-F10 cells and up-regulated endothelial NO synthetase in the vascular endothelium and thereby facilitated endothelium-induced tumor cytotoxicity. Very low and high NO levels down-regulated bcl-2 expression in B16M-F10 cells. t-PTER and QUER induced a NO shortage-dependent decrease in cAMP-response element-binding protein phosphorylation, a positive regulator of bcl-2 expression, in B16M-F10 cells. On the other hand, during cancer and endothelial cell interaction, t-PTER- and QUER-induced NO release from the vascular endothelium up-regulated neutral sphingomyelinase activity and ceramide generation in B16M-F10 cells. Direct NO-induced cytotoxicity and ceramide-induced mitochondrial permeability transition and apoptosis activation can explain the increased endothelium-induced death of Bcl-2-depleted B16M-F10 cells.

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.

Repressions of MMP-9 expression and NF-kappa B localization are involved in inhibition of lung carcinoma 95-D cell invasion by (-)-epigallocatechin-3-gallate

Epigallocatechin-3-gallate (EGCG) repressed the invasion of lung carcinoma 95-D cells in invasion assay. RT-PCR analysis illuminated that 40 microM EGCG down-regulated the expression of MMP-9 by 45.7% and the result of Western blot analysis provided further evidence. NF-kappa B localized in the nucleus of the 95-D cells was diminished in a dose-dependent manner in EGCG-treated cells as shown by Western blot. Intracellular oxidants were more abundant in invasive cells than in invasion-suppressed cells fed with EGCG for 18 h. Thus, the inhibition of tumor invasion by EGCG was shown to be attributed to decreases of the expression of MMP-9 and NF-kappa B, which may result from decrease of intracellular oxidants.

Association between pterostilbene and quercetin inhibits metastatic activity of B16 melanoma

Inhibition of cancer growth by resveratrol (trans-3,5,4'-trihydroxystilbene; RESV), a phytoalexin present in many plant species, is limited by its low bioavailability. Pterostilbene (3,5-dimethoxy-4'-hydroxystilbene; PTER) and quercetin (3,3',4',5,6-pentahydroxyflavone; QUER), two structurally related and naturally occurring small polyphenols, show longer half-life in vivo. In vitro growth of highly malignant B16 melanoma F10 cells (B16M-F10) is inhibited (56%) by short-time exposure (60 min/day) to PTER (40 microm) and QUER (20 microm) (approximate mean values of plasma concentrations measured within the first hour after intravenous administration of 20 mg/kg each polyphenol). Intravenous administration of PTER and QUER (20 mg/kg per day) to mice inhibits (73%) metastatic growth of B16M-F10 cell in the liver, a common site for metastasis development. The anti-metastatic mechanism involves: 1) a PTER-induced inhibition of vascular adhesion molecule 1 expression in the hepatic sinusoidal endothelium, which consequently decreases B16M-F10 cell adhesion to the endothelium through very late activation antigen 4; and 2) a QUER- and PTER-induced inhibition of Bcl-2 expression in metastatic cells, which sensitizes them to vascular endothelium-induced cytotoxicity. Our findings demonstrate that the association of PTER and QUER inhibits metastatic melanoma growth and extends host survival.

Butyrate reduces liver metastasis of rat colon carcinoma cells in vivo and resistance to oxidative stress in vitro

Injection of the rat colon carcinoma cell line CC531 into spleen of syngeneic rats results in considerable amounts of liver metastases within 14 days. We investigated whether preincubation of the cells with butyrate reduced their metastatic ability in vivo and whether this was accompanied by reduction in related properties such as secretion of metalloproteinases and their ability to withstand oxidative stress. Butyrate incubation reduced cell growth rate and initiated apoptosis in a dose- and time-related manner, but proliferation was retrieved when cultivation was continued in medium without butyrate. Splenic injection of butyrate treated, proliferating cells resulted in significantly reduced amounts of tumor mass compared to untreated cells. The butyrate treated cells were more susceptible to oxidative stress than control cells, as demonstrated by increased number of apoptotic cells and reduced cell growth after exposure to menadione. A reduction in cellular glutathione was found after prolonged incubation with butyrate. Butyrate appeared not to alter the secretion of active metalloproteinases from the cells although an apparent increase in proforms was demonstrated. Neither did butyrate alter the synthesis of metalloproteinase inhibitors. Lastly, a reduced adhesion of the tumor cells to collagen coated matrix was found after butyrate treatment. Thus, the inhibitory effects of butyrate on tumor malignancy are caused by a diversity of mechanisms.

Acceleration of glutathione efflux and inhibition of gamma-glutamyltranspeptidase sensitize metastatic B16 melanoma cells to endothelium-induced cytotoxicity

Highly metastatic B16 melanoma (B16M)-F10 cells, as compared with the low metastatic B16M-F1 line, have higher GSH content and preferentially overexpress BCL-2. In addition to its anti-apoptotic properties, BCL-2 inhibits efflux of GSH from B16M-F10 cells and thereby may facilitate metastatic cell resistance against endothelium-induced oxidative/nitrosative stress. Thus, we investigated in B16M-F10 cells which molecular mechanisms channel GSH release and whether their modulation may influence metastatic activity. GSH efflux was abolished in multidrug resistance protein 1 knock-out (MRP-/-1) B16M-F10 transfected with the Bcl-2 gene or in MRP-/-1 B16M-F10 cells incubated with l-methionine, which indicates that GSH release from B16M-F10 cells is channeled through MRP1 and a BCL-2-dependent system (likely related to an l-methionine-sensitive GSH carrier previously detected in hepatocytes). The BCL-2-dependent system was identified as the cystic fibrosis transmembrane conductance regulator, since monoclonal antibodies against this ion channel or H-89 (a protein kinase A-selective inhibitor)-induced inhibition of cystic fibrosis transmembrane conductance regulator gene expression completely blocked the BCL-2-sensitive GSH release. By using a perifusion system that mimics in vivo conditions, we found that GSH depletion in metastatic cells can be achieved by using Bcl-2 antisense oligodeoxynucleotide- and verapamil (an MRP1 activator)-induced acceleration of GSH efflux, in combination with acivicin-induced inhibition of gamma-glutamyltranspeptidase (which limits GSH synthesis by preventing cysteine generation from extracellular GSH). When applied under in vivo conditions, this strategy increased tumor cytotoxicity (up to approximately 90%) during B16M-F10 cell adhesion to the hepatic sinusoidal endothelium.

Down-regulation of glutathione and Bcl-2 synthesis in mouse B16 melanoma cells avoids their survival during interaction with the vascular endothelium

B16 melanoma (B16M) cells with high GSH content show high metastatic activity. However, the molecular mechanisms linking GSH to metastatic cell survival are unclear. The possible relationship between GSH and the ability of Bcl-2 to prevent cell death was studied in B16M cells with high (F10) and low (F1) metastatic potential. Analysis of a Bcl-2 family of genes revealed that B16M-F10 cells, as compared with B16M-F1 cells, overexpressed preferentially Bcl-2 (approximately 5.7-fold). Hepatic sinusoidal endothelium-induced B16M-F10 cytotoxicity in vitro increased from approximately 19% (controls) to approximately 97% in GSH-depleted B16M-F10 cells treated with an antisense Bcl-2 oligodeoxynucleotide (Bcl-2-AS). l-Buthionine (S,R)-sulfoximine-induced GSH depletion or Bcl-2-AS decreased the metastatic growth of B16M-F10 cells in the liver. However, the combination of l-buthionine (S,R)-sulfoximine and Bcl-2-AS abolished metastatic invasion. Bcl-2-overexpressing B16M-F1/Tet-Bcl-2 and B16M-F10/Tet-Bcl-2 cells, as compared with controls, showed an increase in GSH content, no change in the rate of GSH synthesis, and a decrease in GSH efflux. Thus, Bcl-2 overexpression may increase metastatic cell resistance against oxidative/nitrosative stress by inhibiting release of GSH. In addition, Bcl-2 availability regulates the mitochondrial GSH (mtGSH)-dependent opening of the permeability transition pore complex. Death in B16M-F10 cells was sharply activated at mtGSH levels below 30% of controls values. However, this critical threshold increased to approximately 60% of control values in Bcl-2-AS-treated B16M-F10 cells. GSH ester-induced replenishment of mtGSH levels (even under conditions of cytosolic GSH depletion) prevented cell death. Our results indicate that survival of B16M cells with high metastatic potential can be challenged by inhibiting their GSH and Bcl-2 synthesis.

CC531s colon carcinoma cells induce apoptosis in rat hepatic endothelial cells by the Fas/FasL-mediated pathway

The mechanisms involved in colorectal carcinoma with liver metastasis are not well known. Metastasizing colon carcinoma cells express more FasL than primary colon carcinoma cells and cancer cells induce apoptosis in hepatocytes by the Fas/FasL pathway. Therefore, this study focused on Fas/FasL expression and functionality in rat liver sinusoidal endothelial cells (LSECs) and CC531s colon carcinoma cells in vitro and in vivo. RT-PCR and immunochemistry revealed Fas and FasL in LSECs and CC531s, respectively. Functionality of Fas was assessed in vitro by incubation with human recombinant FasL (1-100 ng/ml) with or without enhancer. At concentrations of 10 and 100 ng/ml with enhancer, respectively 21% and 44% of endothelial cells showed signs of apoptosis using Hoechst 33342/propidium iodide staining and electron microscopy. In co-cultures, apoptosis could be detected in endothelial cells neighboring the CC531s and could be inhibited by an antagonistic FasL antibody. Moreover, 18 h after mesenteric injection of CC531s, the sinusoidal endothelium revealed disruption. In conclusion, (i). CC531s cells induce apoptosis in LSECs in vitro by using Fas/FasL; (ii). CC531s cells damage the sinusoidal endothelial lining in vivo; and (iii). this might provide FasL-positive tumor cells a gateway towards the hepatocytes.

Tumor cytotoxicity by endothelial cells. Impairment of the mitochondrial system for glutathione uptake in mouse B16 melanoma cells that survive after in vitro interaction with the hepatic sinusoidal endothelium

High GSH content associates with high metastatic activity in B16-F10 melanoma cells cultured to low density (LD B16M). GSH homeostasis was investigated in LD B16M cells that survive after adhesion to the hepatic sinusoidal endothelium (HSE). Invasive B16M (iB16M) cells were isolated using anti-Met-72 monoclonal antibodies and flow cytometry-coupled cell sorting. HSE-derived NO and H(2)O(2) caused GSH depletion and a decrease in gamma-glutamylcysteine synthetase activity in iB16M cells. Overexpression of gamma-glutamylcysteine synthetase heavy and light subunits led to a rapid recovery of cytosolic GSH, whereas mitochondrial GSH (mtGSH) further decreased during the first 18 h of culture. NO and H(2)O(2) damaged the mitochondrial system for GSH uptake (rates in iB16M were approximately 75% lower than in LD B16M cells). iB16M cells also showed a decreased activity of mitochondrial complexes II, III, and IV, less O(2) consumption, lower ATP levels, higher O(2) and H(2)O(2) production, and lower mitochondrial membrane potential. In vitro growing iB16M cells maintained high viability (>98%) and repaired HSE-induced mitochondrial damages within 48 h. However, iB16M cells with low mtGSH levels were highly susceptible to TNF-alpha-induced oxidative stress and death. Therefore depletion of mtGSH levels may represent a critical target to challenge survival of invasive cancer cells.

Proangiogenic role of tumor-activated hepatic stellate cells in experimental melanoma metastasis

Myofibroblasts infiltrate malignant liver tumors, although their pathogenic implications are unclear. Immunohistochemical detection of alpha-smooth muscle actin, glial fibrillary acidic protein (GFAP), and CD31 and CD34 expression was used to analyze the contribution of myofibroblasts to angiogenesis in hepatic metastasis produced by intrasplenically-injected B16 melanoma (B16M). Because activated hepatic stellate cells (HSCs) are oxygen-sensing myofibroblasts producing vascular endothelial growth factor (VEGF), the effect of B16M and human A375 melanoma supernatants on VEGF production by immortalized rat HSC line T6 and primary cultured human HSCs also was studied under an hypoxic atmosphere mimicking a tumor microenvironment. Myofibroblast infiltration preceded endothelium recruitment in avascular micrometastasis and generated specific stroma for sinusoidal-type and portal-type angiogeneses. Thereafter, myofibroblasts and endothelial cells colocalized within both angiogenic patterns and their numerical densities correlated with metastasis development. Myofibroblasts often were GFAP-positive, suggesting an HSC origin. Melanoma supernatants stimulated VEGF messenger RNA and protein synthesis by HSCs. These effects were potentiated by hypoxia. VEGF up-regulation was accompanied by increased expression of cyclooxygenase type 2 (COX-2) and PGE2 synthesis. HSC production of VEGF decreased under COX-2 inhibition, whereas it was increased by exogenous PGE2. The high VEGF expression in HSCs induced by melanoma factors and hypoxia resulted in mitogenic, antiapoptotic, and motogenic stimulation of both murine hepatic sinusoidal endothelium and human umbilical vein endothelium. In conclusion, temporal and positional relationships evolve between myofibroblast and endothelium recruitment during metastasis development. Mechanistically, hypoxic induction of VEGF in tumor-activated HSCs may create a proangiogenic microenvironment, facilitating endothelial cell recruitment and survival during hepatic metastasis transition from an avascular to a vascular stage.

Increased resistance towards oxidative stress accompanies enhancement of metastatic potential obtained by repeated in vivo passage of colon carcinoma cells in syngeneic rats

The colon carcinoma cell line CC531 is metastatic to liver after splenic injection in syngeneic rats. After repeated in vivo passages, a subline was selected that produced liver metastases at a considerably higher rate than the original cell line. These cells were characterized by increased intracellular glutathione, proliferation and ability to restore glutathione after exposure to oxidative stress, thus indicating an elevated resistance to oxidative stress. Furthermore, the increased metastatic ability was also accompanied by increased proliferation rate, adhesion to extracellular matrix proteins and endothelial cells, and secretion of a 60 kD matrix metalloproteinase. When cultured in vitro for a prolonged time (more than 30 trypsinizations), the cells showed a reduced in vivo metastatic ability, reduced secretion of three metalloproteinases including the 60 kD proteinase, and reduced intracellular glutathione. These results indicate that metastatic ability can be influenced through several adaptive mechanisms, and that the cell's ability to resist oxidative stress and maintain intracellular glutathione are of central importance.

Inhibition of cancer growth by resveratrol is related to its low bioavailability

The relationship between resveratrol (RES) bioavalability and its effect on tumor growth was investigated. Tissue levels of RES were studied after i.v. and oral administration of trans-resveratrol (t-RES) to rabbits, rats, and mice. Half-life of RES in plasma, after i.v. administration of 20 mg t-RES/kg b.wt., was very short (e.g., 14.4 min in rabbits). The highest concentration of RES in plasma, either after i.v. or oral administration (e.g., 2.6 +/- 1.0 microM in mice 2.5 min after receiving 20 mg t-RES/kg orally), was reached within the first 5 min in all animals studied. Extravascular levels (brain, lung, liver, and kidney) of RES, which paralleled those in plasma, were always < 1 nmol/g fresh tissue. RES measured in plasma or tissues was in the trans form (at least 99%). Hepatocytes metabolized t-RES in a dose-dependent fashion (e.g., 43 nmol of t-RES/g x min in the presence of 20 microM tRES), which means that the liver can remove circulating RES very rapidly. In vitro B16 melanoma (B16M) cell proliferation and generation of reactive oxygen species (ROS) was inhibited by t-RES in a concentration-dependent fashion (100% inhibition of tumor growth was found in the presence of 5 microM t-RES). Addition of 10 microM H(2)O(2) to B16M cells, cultured in the presence of 5 microM t-RES, reactivated cell growth. Oral administration of t-RES (20 mg/kg twice per day; or included in the drinking water at 23 mg/l) did not inhibit growth of B16M inoculated into the footpad of mice (solid growth). However, oral administration of t-RES (as above) decreased hepatic metastatic invasion of B16M cells inoculated intrasplenically. The antimetastatic mechanism involves a t-RES (1 microM)-induced inhibition of vascular adhesion molecule 1 (VCAM-1) expression in the hepatic sinusoidal endothelium (HSE), which consequently decreased in vitro B16M cell adhesion to the endothelium via very late activation antigen 4 (VLA-4).

Modeling of the anticancer action for radical derivatives of nitroazoles: quantitative structure-activity relationship (QSAR) study

A QSAR analysis of the anti-tumor, anti-metastasis and anti-colony formation (for metastatic colonies) activities of eighteen nitroazoles (including metronidazole and hypoxic radiosensitizers RP-170, KU-2285 and sanazole (drug AK-2123)) and their nitro and nitroso anion radical derivatives against melanoma B16 in mice has been performed. The QSAR models were built with the use of the frontal polygon method. This approach has features of different 3D QSAR methodologies and belongs to the group of "indirect" methods. The procedure allows to build robust models with high predictive ability even in series of diverse and conformationally flexible compounds. Key atomic characteristics accompany the geometrical requirements in the analysis of local 3D molecular similarity. By variation of weight coefficients for hydrophobicity, refraction increments, and partial charge it is possible to achieve better quality of QSAR and evaluate the importance of each characteristic for biological activity under consideration. It was found that hydrophobicity, molar refraction and charge characteristics of nitro anion radical derivatives are more significant for interaction with molecular targets than those of the parent compounds and of the nitroso anion radical derivatives. Size and hydrophobic properties of substituents in nitro anion radicals play significant role for ligand-target interaction in the processes of inhibition of metastatic spreading and growth of metastatic colonies by nitroazoles. A scheme of competitive interaction of parent nitroazoles and their anion radicals with a target in organism is suggested. It can be concluded that the step of one-electron reduction of nitroazoles can be important for anticancer activity of these drugs.