NOV-002, a glutathione disulfide mimetic, as a modulator of cellular redox balance

Reactive Oxygen Species Modulation in the Current Landscape of Anticancer Therapies

Significance: Reactive oxygen species (ROS) are generated during mitochondrial oxidative metabolism, and are tightly controlled through homeostatic mechanisms to maintain intracellular redox, regulating growth and proliferation in healthy cells. However, ROS production is perturbed in cancers where abnormal accumulation of ROS leads to oxidative stress and genomic instability, triggering oncogenic signaling pathways on one hand, while increasing oxidative damage and triggering ROS-dependent death signaling on the other. Recent Advances: Our review illuminates how critical interactions between ROS and oncogenic signaling, the tumor microenvironment, and DNA damage response (DDR) pathways have led to interest in ROS modulation as a means of enhancing existing anticancer strategies and developing new therapeutic opportunities. Critical Issues: ROS equilibrium exists via a delicate balance of pro-oxidant and antioxidant species within cells. "Antioxidant" approaches have been explored mainly in the form of chemoprevention, but there is insufficient evidence to advocate its routine application. More progress has been made via the "pro-oxidant" approach of targeting cancer vulnerabilities and inducing oxidative stress. Various therapeutic modalities have employed this approach, including direct ROS-inducing agents, chemotherapy, targeted therapies, DDR therapies, radiotherapy, and immunotherapy. Finally, emerging delivery systems such as "nanosensitizers" as radiotherapy enhancers are currently in development. Future Directions: While approaches designed to induce ROS have shown considerable promise in selectively targeting cancer cells and dealing with resistance to conventional therapies, most are still in early phases of development and challenges remain. Further research should endeavor to refine treatment strategies, optimize drug combinations, and identify predictive biomarkers of ROS-based cancer therapies.

Dissecting the pleiotropic roles of reactive oxygen species (ROS) in lung cancer: From carcinogenesis toward therapy

Lung cancer is a major cause of morbidity and mortality. The specific pulmonary structure to directly connect with ambient air makes it more susceptible to damage from airborne toxins. External oxidative stimuli and endogenous reactive oxygen species (ROS) play a crucial role in promoting lung carcinogenesis and development. The biological properties of higher ROS levels in tumor cells than in normal cells make them more sensitive and vulnerable to ROS injury. Therefore, the strategy of targeting ROS has been proposed for cancer therapy for decades. However, it is embarrassing that countless attempts at ROS-based therapies have had very limited success, and no FDA approval in the anticancer list was mechanistically based on ROS manipulation. Even compared with the untargetable proteins, such as transcription factors, ROS are more difficult to be targeted due to their chemical properties. Thus, the pleiotropic roles of ROS provide therapeutic potential for anticancer drug discovery, while a better dissection of the mechanistic action and signaling pathways is a prerequisite for future breakthroughs. This review discusses the critical roles of ROS in cancer carcinogenesis, ROS-inspired signaling pathways, and ROS-based treatment, exemplified by lung cancer. In particular, an eight considerations rule is proposed for ROS-targeting strategies and drug design and development.

Energy metabolism as the hub of advanced non-small cell lung cancer management: a comprehensive view in the framework of predictive, preventive, and personalized medicine

Energy metabolism is a hub of governing all processes at cellular and organismal levels such as, on one hand, reparable vs. irreparable cell damage, cell fate (proliferation, survival, apoptosis, malignant transformation etc.), and, on the other hand, carcinogenesis, tumor development, progression and metastazing versus anti-cancer protection and cure. The orchestrator is the mitochondria who produce, store and invest energy, conduct intracellular and systemically relevant signals decisive for internal and environmental stress adaptation, and coordinate corresponding processes at cellular and organismal levels. Consequently, the quality of mitochondrial health and homeostasis is a reliable target for health risk assessment at the stage of reversible damage to the health followed by cost-effective personalized protection against health-to-disease transition as well as for targeted protection against the disease progression (secondary care of cancer patients against growing primary tumors and metastatic disease). The energy reprogramming of non-small cell lung cancer (NSCLC) attracts particular attention as clinically relevant and instrumental for the paradigm change from reactive medical services to predictive, preventive and personalized medicine (3PM). This article provides a detailed overview towards mechanisms and biological pathways involving metabolic reprogramming (MR) with respect to inhibiting the synthesis of biomolecules and blocking common NSCLC metabolic pathways as anti-NSCLC therapeutic strategies. For instance, mitophagy recycles macromolecules to yield mitochondrial substrates for energy homeostasis and nucleotide synthesis. Histone modification and DNA methylation can predict the onset of diseases, and plasma C7 analysis is an efficient medical service potentially resulting in an optimized healthcare economy in corresponding areas. The MEMP scoring provides the guidance for immunotherapy, prognostic assessment, and anti-cancer drug development. Metabolite sensing mechanisms of nutrients and their derivatives are potential MR-related therapy in NSCLC. Moreover, miR-495-3p reprogramming of sphingolipid rheostat by targeting Sphk1, 22/FOXM1 axis regulation, and A2 receptor antagonist are highly promising therapy strategies. TFEB as a biomarker in predicting immune checkpoint blockade and redox-related lncRNA prognostic signature (redox-LPS) are considered reliable predictive approaches. Finally, exemplified in this article metabolic phenotyping is instrumental for innovative population screening, health risk assessment, predictive multi-level diagnostics, targeted prevention, and treatment algorithms tailored to personalized patient profiles-all are essential pillars in the paradigm change from reactive medical services to 3PM approach in overall management of lung cancers. This article highlights the 3PM relevant innovation focused on energy metabolism as the hub to advance NSCLC management benefiting vulnerable subpopulations, affected patients, and healthcare at large.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13167-024-00357-5.

Microsomal glutathione transferase 1 controls metastasis and therapeutic response in melanoma

While recent targeted and immunotherapies in malignant melanoma are encouraging, most patients acquire resistance, implicating a need to identify additional drug targets to improve outcomes. Recently, attention has been given to pathways that regulate redox homeostasis, especially the lipid peroxidase pathway that protects cells against ferroptosis. Here we identify microsomal glutathione S-transferase 1 (MGST1), a non-selenium-dependent glutathione peroxidase, as highly expressed in malignant and drug resistant melanomas and as a specific determinant of metastatic spread and therapeutic sensitivity. Loss of MGST1 in mouse and human melanoma enhanced cellular oxidative stress, and diminished glycolysis, oxidative phosphorylation, and pentose phosphate pathway. Gp100 activated pmel-1 T cells killed more Mgst1 KD than control melanoma cells and KD cells were more sensitive to cytotoxic anticancer drugs and ferroptotic cell death. When compared to control, mice bearing Mgst1 KD B16 tumors had more CD8+ T cell infiltration with reduced expression of inhibitory receptors and increased cytokine response, large reduction of lung metastases and enhanced survival. Targeting MGST1 alters the redox balance and limits metastases in melanoma, enhancing the therapeutic index for chemo- and immunotherapies.

Glutathione and Glutaredoxin-Key Players in Cellular Redox Homeostasis and Signaling

This Special Issue of Antioxidants on Glutathione (GSH) and Glutaredoxin (Grx) was designed to collect review articles and original research studies focused on advancing the current understanding of the roles of the GSH/Grx system in cellular homeostasis and disease processes. The tripeptide glutathione (GSH) is the most abundant non-enzymatic antioxidant/nucleophilic molecule in cells. In addition to various metabolic reactions involving GSH and its oxidized counterpart GSSG, oxidative post-translational modification (PTM) of proteins has been a focal point of keen interest in the redox field over the last few decades. In particular, the S-glutathionylation of proteins (protein-SSG formation), i.e., mixed disulfides between GSH and protein thiols, has been studied extensively. This reversible PTM can act as a regulatory switch to interconvert inactive and active forms of proteins, thereby mediating cell signaling and redox homeostasis. The unique architecture of the GSH molecule enhances its relative abundance in cells and contributes to the glutathionyl specificity of the primary catalytic activity of the glutaredoxin enzymes, which play central roles in redox homeostasis and signaling, and in iron metabolism in eukaryotes and prokaryotes under physiological and pathophysiological conditions. The class-1 glutaredoxins are characterized as cytosolic GSH-dependent oxidoreductases that catalyze reversible protein S-glutathionylation specifically, thereby contributing to the regulation of redox signal transduction and/or the protection of protein thiols from irreversible oxidation. This Special Issue includes nine other articles: three original studies and six review papers. Together, these ten articles support the central theme that GSH/Grx is a unique system for regulating thiol-redox hemostasis and redox-signal transduction, and the dysregulation of the GSH/Grx system is implicated in the onset and progression of various diseases involving oxidative stress. Within this context, it is important to appreciate the complementary functions of the GSH/Grx and thioredoxin systems not only in thiol-disulfide regulation but also in reversible S-nitrosylation. Several potential clinical applications have emerged from a thorough understanding of the GSH/Grx redox regulatory system at the molecular level, and in various cell types in vitro and in vivo, including, among others, the concept that elevating Grx content/activity could serve as an anti-fibrotic intervention; and discovering small molecules that mimic the inhibitory effects of S-glutathionylation on dimer association could identify novel anti-viral agents that impact the key protease activities of the HIV and SARS-CoV-2 viruses. Thus, this Special Issue on Glutathione and Glutaredoxin has focused attention and advanced understanding of an important aspect of redox biology, as well as spawning questions worthy of future study.

A role for microsomal glutathione transferase 1 in melanin biosynthesis and melanoma progression

Recent advancements in the treatment of melanoma are encouraging, but there remains a need to identify additional therapeutic targets. We identify a role for microsomal glutathione transferase 1 (MGST1) in biosynthetic pathways for melanin and as a determinant of tumor progression. Knockdown (KD) of MGST1 depleted midline-localized, pigmented melanocytes in zebrafish embryos, while in both mouse and human melanoma cells, loss of MGST1 resulted in a catalytically dependent, quantitative, and linear depigmentation, associated with diminished conversion of L-dopa to dopachrome (eumelanin precursor). Melanin, especially eumelanin, has antioxidant properties, and MGST1 KD melanoma cells are under higher oxidative stress, with increased reactive oxygen species, decreased antioxidant capacities, reduced energy metabolism and ATP production, and lower proliferation rates in 3D culture. In mice, when compared to nontarget control, Mgst1 KD B16 cells had less melanin, more active CD8+ T cell infiltration, slower growing tumors, and enhanced animal survival. Thus, MGST1 is an integral enzyme in melanin synthesis and its inhibition adversely influences tumor growth.

Systematic identification of anticancer drug targets reveals a nucleus-to-mitochondria ROS-sensing pathway

Multiple anticancer drugs have been proposed to cause cell death, in part, by increasing the steady-state levels of cellular reactive oxygen species (ROS). However, for most of these drugs, exactly how the resultant ROS function and are sensed is poorly understood. It remains unclear which proteins the ROS modify and their roles in drug sensitivity/resistance. To answer these questions, we examined 11 anticancer drugs with an integrated proteogenomic approach identifying not only many unique targets but also shared ones-including ribosomal components, suggesting common mechanisms by which drugs regulate translation. We focus on CHK1 that we find is a nuclear H2O2 sensor that launches a cellular program to dampen ROS. CHK1 phosphorylates the mitochondrial DNA-binding protein SSBP1 to prevent its mitochondrial localization, which in turn decreases nuclear H2O2. Our results reveal a druggable nucleus-to-mitochondria ROS-sensing pathway-required to resolve nuclear H2O2 accumulation and mediate resistance to platinum-based agents in ovarian cancers.

Involvement of heat shock proteins HSP70 in the mechanisms of endogenous neuroprotection: the prospect of using HSP70 modulators

This analytical review summarizes literature data and our own research on HSP70-dependent mechanisms of neuroprotection and discusses potential pharmacological agents that can influence HSP70 expression to improve neurological outcomes and effective therapy. The authors formed a systemic concepts of the role of HSP70-dependent mechanisms of endogenous neuroprotection aimed at stopping the formation of mitochondrial dysfunction, activation of apoptosis, desensitization of estrogen receptors, reduction of oxidative and nitrosative stress, prevention of morpho-functional changes in brain cells during cerebral ischemia, and experimentally substantiated new target links for neuroprotection. Heat shock proteins (HSPs) are an evolutionarily integral part of the functioning of all cells acting as intracellular chaperones that support cell proteostasis under normal and various stress conditions (hyperthermia, hypoxia, oxidative stress, radiation, etc.). The greatest curiosity in conditions of ischemic brain damage is the HSP70 protein, as an important component of the endogenous neuroprotection system, which, first of all, performs the function of intracellular chaperones and ensures the processes of folding, holding and transport of synthesized proteins, as well as their degradation, both under normoxic conditions and stress-induced denaturation. A direct neuroprotective effect of HSP70 has been established, which is realized through the regulation the processes of apoptosis and cell necrosis due to a long-term effect on the synthesis of antioxidant enzymes, chaperone activity, and stabilization of active enzymes. An increase in the level of HSP70 leads to the normalization of the glutathione link of the thiol-disulfide system and an increase in the resistance of cells to ischemia. HSP 70 is able to activate and regulate compensatory ATP synthesis pathways during ischemia. It was found that in response to the cerebral ischemia formation, HIF-1a is expressed, which initiates the launch of compensatory mechanisms for energy production. Subsequently, the regulation of these processes switches to HSP70, which "prolongs" the action of HIF-1a, and also independently maintains the expression of mitochondrial NAD-dependent malate dehydrogenase activity, thereby maintaining the activity of the malate-aspartate shuttle mechanism for a long time. During ischemia of organs and tissues, HSP70 performs a protective function, which is realized through increased synthesis of antioxidant enzymes, stabilization of oxidatively damaged macromolecules, and direct anti-apoptotic and mitoprotective action. Such a role of these proteins in cellular reactions during ischemia raises the question of the development of new neuroprotective agents which are able to provide modulation/protection of the genes encoding the synthesis of HSP 70 and HIF-1a proteins. Numerous studies of recent years have noted the important role of HSP70 in the implementation of the mechanisms of metabolic adaptation, neuroplasticity and neuroprotection of brain cells, so the positive modulation of the HSP70 system is a perspective concept of neuroprotection, which can improve the efficiency of the treatment of ischemic-hypoxic brain damage and be the basis for substantiating of the feasibility of using of HSP70 modulators as promising neuroprotectors.

Free radicals: Relationship to Human Diseases and Potential Therapeutic applications

Reactive species are highly-reactive enzymatically, or non-enzymatically produced compounds with important roles in physiological and pathophysiological cellular processes. Although reactive species represent an extensively researched topic in biomedical sciences, many aspects of their roles and functions remain unclear. This review aims to systematically summarize findings regarding the biochemical characteristics of various types of reactive species and specify the localization and mechanisms of their production in cells. In addition, we discuss the specific roles of free radicals in cellular physiology, focusing on the current lines of research that aim to identify the reactive oxygen species-initiated cascades of reactions resulting in adaptive or pathological cellular responses. Finally, we present recent findings regarding the therapeutic modulations of intracellular levels of reactive oxygen species, which may have substantial significance in developing novel agents for treating several diseases.

Harnessing redox signaling to overcome therapeutic-resistant cancer dormancy

Dormancy occurs when cells preserve viability but stop proliferating, which is considered an important cause of tumor relapse, which may occur many years after clinical remission. Since the life cycle of dormant cancer cells is affected by both intracellular and extracellular factors, gene mutation or epigenetic regulation of tumor cells may not fully explain the mechanisms involved. Recent studies have indicated that redox signaling regulates the formation, maintenance, and reactivation of dormant cancer cells by modulating intracellular signaling pathways and the extracellular environment, which provides a molecular explanation for the life cycle of dormant tumor cells. Indeed, redox signaling regulates the onset of dormancy by balancing the intrinsic pathways, the extrinsic environment, and the response to therapy. In addition, redox signaling sustains dormancy by managing stress homeostasis, maintaining stemness and immunogenic equilibrium. However, studies on dormancy reactivation are still limited, partly explained by redox-mediated activation of lipid metabolism and the transition from the tumor microenvironment to inflammation. Encouragingly, several drug combination strategies based on redox biology are currently under clinical evaluation. Continuing to gain an in-depth understanding of redox regulation and develop specific methods targeting redox modification holds the promise to accelerate the development of strategies to treat dormant tumors and benefit cancer patients.

Oxidative stress in cancer therapy: Friend or enemy?

Excessive cellular oxidative stress is widely perceived as a key factor in pathophysiological conditions and cancer development. Healthy cells use several mechanisms to maintain intracellular levels of reactive oxygen species (ROS) and overall redox homeostasis to avoid damage to DNA, proteins, and lipids. Cancer cells, in contrast, exhibit elevated ROS levels and upregulated protective antioxidant pathways. Counterintuitively, such elevated oxidative stress and enhanced antioxidant defence mechanisms in cancer cells provide a therapeutic opportunity for the development of drugs with different anticancer mechanisms of action (MoA). In this review, oxidative stress and the role of ROS in cells are described. The tumour-suppressive and tumour-promotive functions of ROS are discussed to compare these two different therapeutic strategies (increasing or decreasing ROS to fight cancer). Clinically approved drugs with demonstrated oxidative stress anticancer MoAs are highlighted before describing examples of metal-based anticancer drug candidates causing oxidative stress in cancer cells via novel MoAs.

Reactive oxygen species (ROS) in cancer pathogenesis and therapy: An update on the role of ROS in anticancer action of benzophenanthridine alkaloids

Reactive oxygen species play crucial role in biological homeostasis and pathogenesis of human diseases including cancer. In this line, now it has become evident that ROS level/concentration is a major factor in the growth, progression and stemness of cancer cells. Moreover, cancer cells maintain a delicate balance between ROS and antioxidants to promote pathogenesis and clinical challenges via targeting a battery of signaling pathways converging to cancer hallmarks. Recent findings also entail the therapeutic importance of ROS for the better clinical outcomes in cancer patients as they induce apoptosis and autophagy. Moreover, poor clinical outcomes associated with cancer therapies are the major challenge and use of natural products have been vital in attenuation of these challenges due to their multitargeting potential with less adverse effects. In fact, most available drugs are derived from natural resources, either directly or indirectly and available evidence show the clinical importance of natural products in the management of various diseases, including cancer. ROS play a critical role in the anticancer actions of natural products, particularly phytochemicals. Benzophenanthridine alkaloids of the benzyl isoquinoline family of alkaloids, such as sanguinarine, possess several pharmacological properties and are thus being studied for the treatment of different human diseases, including cancer. In this article, we review recent findings, on how benzophenanthridine alkaloid-induced ROS play a critical role in the attenuation of pathological changes and stemness features associated with human cancers. In addition, we highlight the role of ROS in benzophenanthridine alkaloid-mediated activation of the signaling pathway associated with cancer cell apoptosis and autophagy.

Cross-Talk between Oxidative Stress and m6A RNA Methylation in Cancer

Oxidative stress is a state of imbalance between oxidation and antioxidation. Excessive ROS levels are an important factor in tumor development. Damage stimulation and excessive activation of oncogenes cause elevated ROS production in cancer, accompanied by an increase in the antioxidant capacity to retain redox homeostasis in tumor cells at an increased level. Although moderate concentrations of ROS produced in cancer cells contribute to maintaining cell survival and cancer progression, massive ROS accumulation can exert toxicity, leading to cancer cell death. RNA modification is a posttranscriptional control mechanism that regulates gene expression and RNA metabolism, and m⁶A RNA methylation is the most common type of RNA modification in eukaryotes. m⁶A modifications can modulate cellular ROS levels through different mechanisms. It is worth noting that ROS signaling also plays a regulatory role in m⁶A modifications. In this review, we concluded the effects of m⁶A modification and oxidative stress on tumor biological functions. In particular, we discuss the interplay between oxidative stress and m⁶A modifications.

Moonlighting Metabolic Enzymes in Cancer: New Perspectives on the Redox Code

Significance: Metabolic reprogramming is considered to be a critical adaptive biological event that fulfills the energy and biomass demands for cancer cells. One hallmark of metabolic reprogramming is reduced oxidative phosphorylation and enhanced aerobic glycolysis. Such metabolic abnormalities contribute to the accumulation of reactive oxygen species (ROS), the by-products of metabolic pathways. Emerging evidence suggests that ROS can in turn directly or indirectly affect the expression, activity, or subcellular localization of metabolic enzymes, contributing to the moonlighting functions outside of their primary roles. This review summarizes the multifunctions of metabolic enzymes and the involved redox modification patterns, which further reveal the inherent connection between metabolism and cellular redox state. Recent Advances: These noncanonical functions of metabolic enzymes involve the regulation of epigenetic modifications, gene transcription, post-translational modification, cellular antioxidant capacity, and many other fundamental cellular events. The multifunctional properties of metabolic enzymes further expand the metabolic dependencies of cancer cells, and confer cancer cells with a means of adapting to diverse environmental stimuli. Critical Issues: Deciphering the redox-manipulated mechanisms with specific emphasis on the moonlighting function of metabolic enzymes is important for clarifying the pertinence between metabolism and redox processes. Future Directions: Investigation of the redox-regulated moonlighting functions of metabolic enzymes will shed new lights into the mechanism by which metabolic enzymes gain noncanonical functions, and yield new insights into the development of novel therapeutic strategies for cancer treatment by targeting metabolic-redox abnormalities. Antioxid. Redox Signal. 34, 979-1003.

Cisplatin chemotherapy and renal function

Cisplatin has been a mainstay of cancer chemotherapy since the 1970s. Despite its broad anticancer potential, its clinical use has regularly been constrained by kidney toxicities. This review details those biochemical pathways and metabolic conversions that underlie the kidney toxicities. A wide range of redox events contribute to the eventual physiological consequences of drug activities.

Rediscovery of antimicrobial peptides as therapeutic agents

In recent years, the occurrence of antibiotic-resistant pathogens is increasing rapidly. There is growing concern as the development of antibiotics is slower than the increase in the resistance of pathogenic bacteria. Antimicrobial peptides (AMPs) are promising alternatives to antibiotics. Despite their name, which implies their antimicrobial activity, AMPs have recently been rediscovered as compounds having antifungal, antiviral, anticancer, antioxidant, and insecticidal effects. Moreover, many AMPs are relatively safe from toxic side effects and the generation of resistant microorganisms due to their target specificity and complexity of the mechanisms underlying their action. In this review, we summarize the history, classification, and mechanisms of action of AMPs, and provide descriptions of AMPs undergoing clinical trials. We also discuss the obstacles associated with the development of AMPs as therapeutic agents and recent strategies formulated to circumvent these obstacles.

Redox Regulation by Protein S-Glutathionylation: From Molecular Mechanisms to Implications in Health and Disease

S-glutathionylation, the post-translational modification forming mixed disulfides between protein reactive thiols and glutathione, regulates redox-based signaling events in the cell and serves as a protective mechanism against oxidative damage. S-glutathionylation alters protein function, interactions, and localization across physiological processes, and its aberrant function is implicated in various human diseases. In this review, we discuss the current understanding of the molecular mechanisms of S-glutathionylation and describe the changing levels of expression of S-glutathionylation in the context of aging, cancer, cardiovascular, and liver diseases.

Small molecules regulating reactive oxygen species homeostasis for cancer therapy

Elevated intracellular reactive oxygen species (ROS) and antioxidant defense systems have been recognized as one of the hallmarks of cancer cells. Compared with normal cells, cancer cells exhibit increased ROS to maintain their malignant phenotypes and are more dependent on the "redox adaptation" mechanism. Thus, there are two apparently contradictory but virtually complementary therapeutic strategies for the regulation of ROS to prevent or treat cancer. The first strategy, that is, chemoprevention, is to prevent or reduce intracellular ROS either by suppressing ROS production pathways or by employing antioxidants to enhance ROS clearance, which protects normal cells from malignant transformation and inhibits the early stage of tumorigenesis. The second strategy is the ROS-mediated anticancer therapy, which stimulates intracellular ROS to a toxicity threshold to activate ROS-induced cell death pathways. Therefore, targeting the regulation of intracellular ROS-related pathways by small-molecule candidates is considered to be a promising treatment for tumors. We herein first briefly introduce the source and regulation of ROS, and then focus on small molecules that regulate ROS-related pathways and show efficacy in cancer therapy from the perspective of pharmacophores. Finally, we discuss several challenges in developing cancer therapeutic agents based on ROS regulation and propose the direction of future development.

Oxidative Stress in Cancer

Contingent upon concentration, reactive oxygen species (ROS) influence cancer evolution in apparently contradictory ways, either initiating/stimulating tumorigenesis and supporting transformation/proliferation of cancer cells or causing cell death. To accommodate high ROS levels, tumor cells modify sulfur-based metabolism, NADPH generation, and the activity of antioxidant transcription factors. During initiation, genetic changes enable cell survival under high ROS levels by activating antioxidant transcription factors or increasing NADPH via the pentose phosphate pathway (PPP). During progression and metastasis, tumor cells adapt to oxidative stress by increasing NADPH in various ways, including activation of AMPK, the PPP, and reductive glutamine and folate metabolism.

Oxidative Stress in Cancer

Contingent upon concentration, reactive oxygen species (ROS) influence cancer evolution in apparently contradictory ways, either initiating/stimulating tumorigenesis and supporting transformation/proliferation of cancer cells or causing cell death. To accommodate high ROS levels, tumor cells modify sulfur-based metabolism, NADPH generation, and the activity of antioxidant transcription factors. During initiation, genetic changes enable cell survival under high ROS levels by activating antioxidant transcription factors or increasing NADPH via the pentose phosphate pathway (PPP). During progression and metastasis, tumor cells adapt to oxidative stress by increasing NADPH in various ways, including activation of AMPK, the PPP, and reductive glutamine and folate metabolism.

Mitochondrial Function in Enamel Development

Enamel is the most calcified tissue in vertebrates. Enamel formation and mineralization is a two-step process that is mediated by ameloblast cells during their secretory and maturation stages. In these two stages, ameloblasts are characterized by different morphology and function, which is fundamental for proper mineral growth in the extracellular space. Ultrastructural studies have shown that the mitochondria in these cells localize to different subcellular regions in both stages. However, limited knowledge is available on the role/s of mitochondria in enamel formation. To address this issue, we analyzed mitochondrial biogenesis and respiration, as well as the redox status of rat primary enamel cells isolated from the secretory and maturation stages. We show that maturation stage cells have an increased expression of PGC1α, a marker of mitochondrial biogenesis, and of components of the electron transport chain. Oxygen consumption rate (OCR), a proxy for mitochondrial function, showed a significant increase in oxidative phosphorylation during the maturation stage, promoting ATP production. The GSH/GSSG ratio was lower in the maturation stage, indicative of increased oxidation. Because higher oxidative phosphorylation can lead to higher ROS production, we tested if ROS affected the expression of AmelX and Enam genes that are essential for enamel formation. The ameloblast cell line LS8 treated with H₂O₂ to promote ROS elicited significant expression changes in AmelX and Enam. Our data highlight important metabolic and physiological differences across the two enamel stages, with higher ATP levels in the maturation stage indicative of a higher energy demand. Besides these metabolic shifts, it is likely that the enhanced ETC function results in ROS-mediated transcriptional changes.

ROS in cancer therapy: the bright side of the moon

Reactive oxygen species (ROS) constitute a group of highly reactive molecules that have evolved as regulators of important signaling pathways. It is now well accepted that moderate levels of ROS are required for several cellular functions, including gene expression. The production of ROS is elevated in tumor cells as a consequence of increased metabolic rate, gene mutation and relative hypoxia, and excess ROS are quenched by increased antioxidant enzymatic and nonenzymatic pathways in the same cells. Moderate increases of ROS contribute to several pathologic conditions, among which are tumor promotion and progression, as they are involved in different signaling pathways and induce DNA mutation. However, ROS are also able to trigger programmed cell death (PCD). Our review will emphasize the molecular mechanisms useful for the development of therapeutic strategies that are based on modulating ROS levels to treat cancer. Specifically, we will report on the growing data that highlight the role of ROS generated by different metabolic pathways as Trojan horses to eliminate cancer cells.

Highly reactive molecules called reactive oxygen species (ROS), which at low levels are natural regulators of important signaling pathways in cells, might be recruited to act as “Trojan horses” to kill cancer cells. Researchers in Italy led by Bruno Perillo of the Institute of Food Sciences in Avelllino review the growing evidence suggesting that stimulating production of natural ROS species could become useful in treating cancer. Although ROS production is elevated in cancer cells it can also promote a natural process called programmed cell death. This normally regulates cell turnover, but could be selectively activated to target diseased cells. The authors discuss molecular mechanisms underlying the potential anti-cancer activity of various ROS-producing strategies, including drugs and light-stimulated therapies. They expect modifying the production of ROS to have potential for developing new treatments.

3-ketodihydrosphingosine reductase mutation induces steatosis and hepatic injury in zebrafish

3-ketodihydrosphingosine reductase (KDSR) is the key enzyme in the de novo sphingolipid synthesis. We identified a novel missense kdsr^I105R mutation in zebrafish that led to a loss of function, and resulted in progression of hepatomegaly to steatosis, then hepatic injury phenotype. Lipidomics analysis of the kdsr^I105R mutant revealed compensatory activation of the sphingolipid salvage pathway, resulting in significant accumulation of sphingolipids including ceramides, sphingosine and sphingosine 1-phosphate (S1P). Ultrastructural analysis revealed swollen mitochondria with cristae damage in the kdsr^I105R mutant hepatocytes, which can be a cause of hepatic injury in the mutant. We found elevated sphingosine kinase 2 (sphk2) expression in the kdsr^I105R mutant. Genetic interaction analysis with the kdsr^I105R and the sphk2^wc1 mutants showed that sphk2 depletion suppressed liver defects observed in the kdsr^I105R mutant, suggesting that liver defects were mediated by S1P accumulation. Further, both oxidative stress and ER stress were completely suppressed by deletion of sphk2 in kdsr^I105R mutants, linking these two processes mechanistically to hepatic injury in the kdsr^I105R mutants. Importantly, we found that the heterozygous mutation in kdsr induced predisposed liver injury in adult zebrafish. These data point to kdsr as a novel genetic risk factor for hepatic injury.

Targeting Metabolic-Redox Circuits for Cancer Therapy

Metabolic alterations and elevated levels of reactive oxygen species (ROS) are two characteristics of cancer. The metabolic patterns of cancer cells are elaborately reprogrammed to fulfill the high biomass demands of rapid propagation. ROS, the byproducts of metabolic processes, are accumulated in cancer cells partially due to metabolic abnormalities or oncogenic mutations. To prevent oxidative damage, cancer cells can orchestrate metabolic adaptation to maintain reduction-oxidation (redox) balance by producing reducing equivalents. ROS, acting as second messengers, can in turn manipulate metabolic pathways by directly or indirectly affecting the function of metabolic enzymes. In this review we discuss how cancer cell metabolism and redox signaling are intertwined, with an emphasis on the perspective of targeting metabolic-redox circuits for cancer therapy.

S-Glutathionylation of estrogen receptor α affects dendritic cell function

Glutathione S-transferase Pi (GSTP) is a thiolase that catalyzes the addition of glutathione (GSH) to receptive cysteines in target proteins, producing an S-glutathionylated residue. Accordingly, previous studies have reported that S-glutathionylation is constitutively decreased in cells from mice lacking GSTP (Gstp1/p2^-/-). Here, we found that bone marrow-derived dendritic cells (BMDDCs) from Gstp1/p2^-/- mice have proliferation rates that are greater than those in their WT counterparts (Gstp1/p2^+/+). Moreover, Gstp1/p2^-/- BMDDCs had increased reactive oxygen species (ROS) levels and decreased GSH:glutathione disulfide (GSSG) ratios. Estrogen receptor α (ERα) is linked to myeloproliferation and differentiation, and we observed that its steady-state levels are elevated in Gstp1/p2^-/- BMDDCs, indicating a link between GSTP and ERα activities. BMDDCs differentiated by granulocyte-macrophage colony-stimulating factor had elevated ERα levels, which were more pronounced in Gstp1/p2^-/- than WT mice. When stimulated with lipopolysaccharide for maturation, Gstp1/p2^-/- BMDDCs exhibited augmented endocytosis, maturation rate, cytokine secretion, and T-cell activation; heightened glucose uptake and glycolysis; increased Akt signaling (in the mTOR pathway); and decreased AMPK-mediated phosphorylation of proteins. Of note, GSTP formed a complex with ERα, stimulating ERα S-glutathionylation at cysteines 221, 245, 417, and 447; altering ERα's binding affinity for estradiol; and reducing overall binding potential (receptor density and affinity) 3-fold. Moreover, in Gstp1/p2^-/- BMDDCs, ERα S-glutathionylation was constitutively decreased. Taken together, these findings suggest that GSTP-mediated S-glutathionylation of ERα controls BMDDC differentiation and affects metabolic function in dendritic cells.

Multifaceted Roles of Glutathione and Glutathione-Based Systems in Carcinogenesis and Anticancer Drug Resistance

SIGNIFICANCE

Glutathione is the most abundant antioxidant molecule in living organisms and has multiple functions. Intracellular glutathione homeostasis, through its synthesis, consumption, and degradation, is an intricately balanced process. Glutathione levels are often high in tumor cells before treatment, and there is a strong correlation between elevated levels of intracellular glutathione/sustained glutathione-mediated redox activity and resistance to pro-oxidant anticancer therapy. Recent Advances: Ample evidence demonstrates that glutathione and glutathione-based systems are particularly relevant in cancer initiation, progression, and the development of anticancer drug resistance.

CRITICAL ISSUES

This review highlights the multifaceted roles of glutathione and glutathione-based systems in carcinogenesis, anticancer drug resistance, and clinical applications.

FUTURE DIRECTIONS

The evidence summarized here underscores the important role played by glutathione and the glutathione-based systems in carcinogenesis and anticancer drug resistance. Future studies should address mechanistic questions regarding the distinct roles of glutathione in different stages of cancer development and cancer cell death. It will be important to study how metabolic alterations in cancer cells can influence glutathione homeostasis. Sensitive approaches to monitor glutathione dynamics in subcellular compartments will be an indispensible step. Therapeutic perspectives should focus on mechanism-based rational drug combinations that are directed against multiple redox targets using effective, specific, and clinically safe inhibitors. This new strategy is expected to produce a synergistic effect, prevent drug resistance, and diminish doses of single drugs. Antioxid. Redox Signal. 27, 1217-1234.

Anti-cancer agents and reactive oxygen species modulators that target cancer cell metabolism

Traditionally the perspective on reactive oxygen species (ROS) has centered on the role they play as carcinogenic or cancer-causing radicals. Over the years, characterization and functional studies have revealed the complexity of ROS as signaling molecules that regulate various physiological cellular responses or whose levels are altered in various diseases. Cancer cells often maintain high basal level of ROS and are vulnerable to any further increase in ROS levels beyond a certain protective threshold. Consequently, ROS-modulation has emerged as an anticancer strategy with synthesis of various ROS-inducing or responsive agents that target cancer cells. Of note, an increased carbohydrate uptake and/or induction of death receptors of cancer cells was exploited to develop glycoconjugates that potentially induce cellular stress, ROS and apoptosis. This mini review highlights the development of compounds that target cancer cells by taking advantage of redox or metabolic alteration in cancer cells.

In Vitro and In Vivo Antimetastatic Effect of Glutathione Disulfide Liposomes

Cancer metastasis is the major cause of cancer mortality. Despite extensive research efforts, effective treatment for cancer metastasis is still lacking. Cancer metastasis involves 4 essential steps: cell detachment, migration, invasion, and adhesion. Detachment is the first and required step for metastasis. Glutathione disulfide (GSSG) is derived from the oxidation of glutathione (GSH), which is present in biological systems in millimolar concentration. Although GSSG is commercially available, the impact of GSSG on cell functions/dysfunctions has not been fully explored due to the fact that GSSG is not cell membrane permeable and a lack of method to specifically increase GSSG in cells. We have developed GSSG liposomes that effectively deliver GSSG to cells. Unexpectedly, cells treated with GSSG liposomes were resistant to detachment by trypsinization. This observation led to the investigation of the antimetastatic effect of GSSG liposomes. Our data demonstrate that GSSG liposomes at 1 mg/mL completely blocked cell detachment and migration, and significantly inhibited cancer cell invasion. Aqueous GSSG showed no such effect, confirming that the effects on cell detachment, migration, and invasion were caused by the intracellular delivery of GSSG. An in vivo experiment with a murine melanoma experimental metastasis model showed that GSSG liposomes prevented melanoma lung metastasis. The unique antimetastatic mechanism through the effects on detachment and migration, and effective in vitro and in vivo metastasis inhibition, warrants further investigation of the GSSG liposomes as a potential treatment for cancer metastasis.

Clinically Evaluated Cancer Drugs Inhibiting Redox Signaling

SIGNIFICANCE

There are a number of redox-active anticancer agents currently in development based on the premise that altered redox homeostasis is necessary for cancer cell's survival. Recent Advances: This review focuses on the relatively few agents that target cellular redox homeostasis to have entered clinical trial as anticancer drugs.

CRITICAL ISSUES

The success rate of redox anticancer drugs has been disappointing compared to other classes of anticancer agents. This is due, in part, to our incomplete understanding of the functions of the redox targets in normal and cancer tissues, leading to off-target toxicities and low therapeutic indexes of the drugs. The field also lags behind in the use biomarkers and other means to select patients who are most likely to respond to redox-targeted therapy.

FUTURE DIRECTIONS

If we wish to derive clinical benefit from agents that attack redox targets, then the future will require a more sophisticated understanding of the role of redox targets in cancer and the increased application of personalized medicine principles for their use. Antioxid. Redox Signal. 26, 262-273.

Inhibition of interleukin-3- and interferon- α-induced JAK/STAT signaling by the synthetic α-X-2′,3,4,4′-tetramethoxychalcones α-Br-TMC and α-CF3-TMC

The JAK/STAT pathway is an essential mediator of cytokine signaling, often upregulated in human diseases and therefore recognized as a relevant therapeutic target. We previously identified the synthetic chalcone α-bromo-2′,3,4,4′-tetramethoxychalcone (α-Br-TMC) as a novel JAK2/STAT5 inhibitor. We also found that treatment with α-Br-TMC resulted in a downward shift of STAT5 proteins in SDS-PAGE, suggesting a post-translational modification that might affect STAT5 function. In the present study, we show that a single cysteine within STAT5 is responsible for the α-Br-TMC-induced protein shift, and that this modification does not alter STAT5 transcriptional activity. We also compared the inhibitory activity of α-Br-TMC to that of another synthetic chalcone, α-trifluoromethyl-2′,3,4,4′-tetramethoxychalcone (α-CF3-TMC). We found that, like α-Br-TMC, α-CF3-TMC inhibits JAK2 and STAT5 phosphorylation in response to interleukin-3, however without altering STAT5 mobility in SDS-PAGE. Moreover, we demonstrate that both α-Br-TMC and α-CF3-TMC inhibit interferon-α-induced activation of STAT1 and STAT2, by inhibiting their phosphorylation and the expression of downstream interferon-stimulated genes. Together with the previous finding that α-Br-TMC and α-CF3-TMC inhibit the response to inflammation by inducing Nrf2 and blocking NF-κB activities, our data suggest that synthetic chalcones might be useful as anti-inflammatory, anti-cancer and immunomodulatory agents in the treatment of human diseases.

The Hallmarks of Cancer from a Redox Perspective

SIGNIFICANCE

For a healthy cell to turn into a cancer cell and grow out to become a tumor, it needs to undergo a series of complex changes and acquire certain traits, summarized as "The Hallmarks of Cancer." These hallmarks can all be regarded as the result of altered signal transduction cascades and an understanding of these cascades is essential for cancer treatment.

RECENT ADVANCES

Redox signaling is a long overlooked form of signal transduction that proceeds through the reversible oxidation of cysteines in proteins and that uses hydrogen peroxide as a second messenger.

CRITICAL ISSUES

In this article, we provide examples that show that redox signaling is involved in the regulation of proteins and signaling cascades that play roles in every hallmark of cancer.

FUTURE DIRECTIONS

An understanding of how redox signaling and "classical" signal transduction are intertwined could hold promising strategies for cancer therapy in the future. Antioxid. Redox Signal. 25, 300-325.

Pro-Oxidant Activity of Amine-Pyridine-Based Iron Complexes Efficiently Kills Cancer and Cancer Stem-Like Cells

Differential redox homeostasis in normal and malignant cells suggests that pro-oxidant-induced upregulation of cellular reactive oxygen species (ROS) should selectively target cancer cells without compromising the viability of untransformed cells. Consequently, a pro-oxidant deviation well-tolerated by nonmalignant cells might rapidly reach a cell-death threshold in malignant cells already at a high setpoint of constitutive oxidative stress. To test this hypothesis, we took advantage of a selected number of amine-pyridine-based Fe(II) complexes that operate as efficient and robust oxidation catalysts of organic substrates upon reaction with peroxides. Five of these Fe(II)-complexes and the corresponding aminopyridine ligands were selected to evaluate their anticancer properties. We found that the iron complexes failed to display any relevant activity, while the corresponding ligands exhibited significant antiproliferative activity. Among the ligands, none of which were hemolytic, compounds 1, 2 and 5 were cytotoxic in the low micromolar range against a panel of molecularly diverse human cancer cell lines. Importantly, the cytotoxic activity profile of some compounds remained unaltered in epithelial-to-mesenchymal (EMT)-induced stable populations of cancer stem-like cells, which acquired resistance to the well-known ROS inducer doxorubicin. Compounds 1, 2 and 5 inhibited the clonogenicity of cancer cells and induced apoptotic cell death accompanied by caspase 3/7 activation. Flow cytometry analyses indicated that ligands were strong inducers of oxidative stress, leading to a 7-fold increase in intracellular ROS levels. ROS induction was associated with their ability to bind intracellular iron and generate active coordination complexes inside of cells. In contrast, extracellular complexation of iron inhibited the activity of the ligands. Iron complexes showed a high proficiency to cleave DNA through oxidative-dependent mechanisms, suggesting a likely mechanism of cytotoxicity. In summary, we report that, upon chelation of intracellular iron, the pro-oxidant activity of amine-pyrimidine-based iron complexes efficiently kills cancer and cancer stem-like cells, thus providing functional evidence for an efficient family of redox-directed anti-cancer metallodrugs.

Oxidative stress, redox regulation and diseases of cellular differentiation

BACKGROUND

Within cells, there is a narrow concentration threshold that governs whether reactive oxygen species (ROS) induce toxicity or act as second messengers.

SCOPE OF REVIEW

We discuss current understanding of how ROS arise, facilitate cell signaling, cause toxicities and disease related to abnormal cell differentiation and those (primarily) sulfur based pathways that provide nucleophilicity to offset these effects.

PRIMARY CONCLUSIONS

Cellular redox homeostasis mediates a plethora of cellular pathways that determine life and death events. For example, ROS intersect with GSH based enzyme pathways to influence cell differentiation, a process integral to normal hematopoiesis, but also affecting a number of diverse cell differentiation related human diseases. Recent attempts to manage such pathologies have focused on intervening in some of these pathways, with the consequence that differentiation therapy targeting redox homeostasis has provided a platform for drug discovery and development.

GENERAL SIGNIFICANCE

The balance between electrophilic oxidative stress and protective biomolecular nucleophiles predisposes the evolution of modern life forms. Imbalances of the two can produce aberrant redox homeostasis with resultant pathologies. Understanding the pathways involved provides opportunities to consider interventional strategies. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Glutathione S-transferase P influences redox and migration pathways in bone marrow

To interrogate why redox homeostasis and glutathione S-transferase P (GSTP) are important in regulating bone marrow cell proliferation and migration, we isolated crude bone marrow, lineage negative and bone marrow derived-dendritic cells (BMDDCs) from both wild type (WT) and knockout (Gstp1/p2(-/-)) mice. Comparison of the two strains showed distinct thiol expression patterns. WT had higher baseline and reactive oxygen species-induced levels of S-glutathionylated proteins, some of which (sarco-endoplasmic reticulum Ca2(+)-ATPase) regulate Ca(2+) fluxes and subsequently influence proliferation and migration. Redox status is also a crucial determinant in the regulation of the chemokine system. CXCL12 chemotactic response was stronger in WT cells, with commensurate alterations in plasma membrane polarization/permeability and intracellular calcium fluxes; activities of the downstream kinases, ERK and Akt were also higher in WT. In addition, expression levels of the chemokine receptor CXCR4 and its associated phosphatase, SHP-2, were higher in WT. Inhibition of CXCR4 or SHP2 decreased the extent of CXCL12-induced migration in WT BMDDCs. The differential surface densities of CXCR4, SHP-2 and inositol trisphosphate receptor in WT and Gstp1/p2(-/-) cells correlated with the differential CXCR4 functional activities, as measured by the extent of chemokine-induced directional migration and differences in intracellular signaling. These observed differences contribute to our understanding of how genetic ablation of GSTP causes different levels of myeloproliferation and migration [corrected]

Possible modulating impact of glutathione disulfide mimetic on physiological changes in irradiated rats

Glutathione disulfide mimetic (NOV-002) is a complex of oxidized glutathione (GSSG) formulated with cisplatin at approximately 1000:1 molar ratio. Cisplatin serves to stabilize GSSG but does not assert any therapeutic effect. The objective of this study is to evaluate the impact of NOV-002 on hematological suppression, excessive free radical damage and DNA fragmentation in splenocytes, and metabolite disorders in whole-body γ-irradiated rats. The obtained data revealed that rats treated with 25 mg kg(-1) NOV-002 injected intraperitoneally (i.p.) for 5 days after whole-body γ-irradiation (IR) at 6.5 Gy attenuated the decrease of red blood cells, platelets, total white blood cells, absolute lymphocytes and neutrophils counts, hematocrit value, and hemoglobin content. NOV-002 treatment inhibits serum advanced oxidation protein products, malondialdehyde concentrations as well as cholesterol, triglycerides, urea, and creatinine levels, while enhances glutathione content and superoxide dismutase activity and improves DNA fragmentation in splenocytes. These findings provide a better understanding of the NOV-002 modulating impact in whole-body γ-rays-induced hematological toxicities, oxidative stress, and biological disturbances in γ-irradiated rats and could enhance the tolerance to high doses of ionizing IR utilized in radiotherapy.

The synthetic α-bromo-2',3,4,4'-tetramethoxychalcone (α-Br-TMC) inhibits the JAK/STAT signaling pathway

Signal transducer and activator of transcription STAT5 and its upstream activating kinase JAK2 are essential mediators of cytokine signaling. Their activity is normally tightly regulated and transient. However, constitutive activation of STAT5 is found in numerous cancers and a driving force for malignant transformation. We describe here the identification of the synthetic chalcone α-Br-2′,3,4,4′-tetramethoxychalcone (α-Br-TMC) as a novel JAK/STAT inhibitor. Using the non-transformed IL-3-dependent B cell line Ba/F3 and its oncogenic derivative Ba/F3-1*6 expressing constitutively activated STAT5, we show that α-Br-TMC targets the JAK/STAT pathway at multiple levels, inhibiting both JAK2 and STAT5 phosphorylation. Moreover, α-Br-TMC alters the mobility of STAT5A/B proteins in SDS-PAGE, indicating a change in their post-translational modification state. These alterations correlate with a decreased association of STAT5 and RNA polymerase II with STAT5 target genes in chromatin immunoprecipitation assays. Interestingly, expression of STAT5 target genes such as Cis and c-Myc was differentially regulated by α-Br-TMC in normal and cancer cells. While both genes were inhibited in IL-3-stimulated Ba/F3 cells, expression of the oncogene c-Myc was down-regulated and that of the tumor suppressor gene Cis was up-regulated in transformed Ba/F3-1*6 cells. The synthetic chalcone α-Br-TMC might therefore represent a promising novel anticancer agent for therapeutic intervention in STAT5-associated malignancies.

Modulation of oxidative stress as an anticancer strategy

The regulation of oxidative stress is an important factor in both tumour development and responses to anticancer therapies. Many signalling pathways that are linked to tumorigenesis can also regulate the metabolism of reactive oxygen species (ROS) through direct or indirect mechanisms. High ROS levels are generally detrimental to cells, and the redox status of cancer cells usually differs from that of normal cells. Because of metabolic and signalling aberrations, cancer cells exhibit elevated ROS levels. The observation that this is balanced by an increased antioxidant capacity suggests that high ROS levels may constitute a barrier to tumorigenesis. However, ROS can also promote tumour formation by inducing DNA mutations and pro-oncogenic signalling pathways. These contradictory effects have important implications for potential anticancer strategies that aim to modulate levels of ROS. In this Review, we address the controversial role of ROS in tumour development and in responses to anticancer therapies, and elaborate on the idea that targeting the antioxidant capacity of tumour cells can have a positive therapeutic impact.

Protein Disulfide Isomerase Superfamily in Disease and the Regulation of Apoptosis

Cellular homeostasis requires the balance of a multitude of signaling cascades that are contingent upon the essential proteins being properly synthesized, folded and delivered to appropriate subcellular locations. In eukaryotic cells the endoplasmic reticulum (ER) is a specialized organelle that is the central site of synthesis and folding of secretory, membrane and a number of organelletargeted proteins. The integrity of protein folding is enabled by the presence of ATP, Ca++, molecular chaperones, as well as an oxidizing redox environment. The imbalance between the load and capacity of protein folding results in a cellular condition known as ER stress. Failure of these pathways to restore ER homeostasis results in the activation of apoptotic pathways. Protein disulfide isomerases (PDI) compose a superfamily of oxidoreductases that have diverse sequences and are localized in the ER, nucleus, cytosol, mitochondria and cell membrane. The PDI superfamily has multiple functions including, acting as molecular chaperones, protein-binding partners, and hormone reservoirs. Recently, PDI family members have been implicated in the regulation of apoptotic signaling events. The complexities underlying the molecular mechanisms that define the switch from pro-survival to pro-death response are evidenced by recent studies that reveal the roles of specific chaperone proteins as integration points in signaling pathways that determine cell fate. The following review discusses the dual role of PDI in cell death and survival during ER stress.

NOV-002, A Glutathione Disulfide Mimetic, Suppresses Tumor Cell Invasion and Metastasis

Metastasis is the major cause of death in cancer. Most therapies currently in the clinic aim to eradicate primary tumor, but do not have ideal effects on metastasis. The lack of effective therapy in metastasis prevention and treatment results in high mortality rate in cancer patients with advanced diseases. Here we report the oxidized glutathione small molecule compound NOV-002 reduces cancer cell invasion in vitro and metastasis in an animal model in combination with chemotherapy drug gemcitabine. NOV-002 regulates cell signaling pathways by suppressing ErbB2 and PI3K phosphorylation and subsequent inhibition of Akt and RhoA activation. Our results suggest that NOV-002 affects cell signaling pathways that are critical for invasion and metastasis and can potentially be effective in metastasis treatment in combination of other chemotherapies.

Glutathionylation of UCP2 sensitizes drug resistant leukemia cells to chemotherapeutics

Uncoupling protein-2 (UCP2) is used by cells to control reactive oxygen species (ROS) production by mitochondria. This ability depends on the glutathionylation state of UCP2. UCP2 is often overexpressed in drug resistant cancer cells and therein controls cell ROS levels and limits drug toxicity. With our recent observation that glutathionylation deactivates proton leak through UCP2, we decided to test if diamide, a glutathionylation catalyst, can sensitize drug resistant cells to chemotherapeutic agents. Using drug sensitive HL-60 cells and the drug resistant HL-60 subline, Mx2, we show that chemical induction of glutathionylation selectively deactivates proton leak through UCP2 in Mx2 cells. Chemical glutathionylation of UCP2 disables chemoresistance in the Mx2 cells. Exposure to 200μM diamide led to a significant increase in Mx2 cell death that was augmented when cells were exposed to either menadione or the anthracycline doxorubicin. Diamide also sensitized Mx2 cells to a number of other chemotherapeutics. Proton leak through UCP2 contributed significantly to the energetics of the Mx2 cells. Knockdown of UCP2 led to a significant decrease in both resting and state 4 (i.e., proton leak-dependent) respiration (~43% and 62%, respectively) in Mx2 cells. Similarly diamide inhibited proton leak-dependent respiration by ~64%. In contrast, diamide had very little effect on proton leak in HL-60 cells. Collectively, our observations indicate that manipulation of UCP2 glutathionylation status can serve as a therapeutic strategy for cancer treatment.

Thiol-based posttranslational modifications in parasites

SIGNIFICANCE

Cysteine residues of proteins participate in the catalysis of biochemical reactions, are crucial for redox reactions, and influence protein structure by the formation of disulfide bonds. Covalent posttranslational modifications (PTMs) of cysteine residues are important mediators of redox regulation and signaling by coupling protein activity to the cellular redox state, and moreover influence stability, function, and localization of proteins. A diverse group of protozoan and metazoan parasites are a major cause of diseases in humans, such as malaria, African trypanosomiasis, leishmaniasis, toxoplasmosis, filariasis, and schistosomiasis.

RECENT ADVANCES

Human parasites undergo dramatic morphological and metabolic changes while they pass complex life cycles and adapt to changing environments in host and vector. These processes are in part regulated by PTMs of parasitic proteins. In human parasites, posttranslational cysteine modifications are involved in crucial cellular events such as signal transduction (S-glutathionylation and S-nitrosylation), redox regulation of proteins (S-glutathionylation and S-nitrosylation), protein trafficking and subcellular localization (palmitoylation and prenylation), as well as invasion into and egress from host cells (palmitoylation). This review focuses on the occurrence and mechanisms of these cysteine modifications in parasites.

CRITICAL ISSUES

Studies on cysteine modifications in human parasites are so far largely based on in vitro experiments.

FUTURE DIRECTIONS

The in vivo regulation of cysteine modifications and their role in parasite development will be of great interest in order to understand redox signaling in parasites.

The glutathione disulfide mimetic NOV-002 inhibits cyclophosphamide-induced hematopoietic and immune suppression by reducing oxidative stress

The oxidized glutathione mimetic NOV-002 is a unique anti-tumor agent that not only has the ability to inhibit tumor cell proliferation, survival, and invasion, but in some settings can also ameliorate cytotoxic chemotherapy-induced hematopoietic and immune suppression. However, the mechanisms by which NOV-002 protects the hematopoietic and immune systems against the cytotoxic effects of chemotherapy are not known. Therefore, in this study we investigated the mechanisms of action of NOV-002 using a mouse model in which hematopoietic and immune suppression was induced by cyclophosphamide (CTX) treatment. We found that NOV-002 treatment in a clinically comparable dose regimen attenuated CTX-induced reduction in bone marrow hematopoietic stem and progenitor cells (HSPCs) and reversed the immunosuppressive activity of myeloid-derived suppressor cells (MDSCs), which led to a significant improvement in hematopoietic and immune functions. These effects of NOV-002 may be attributable to its ability to modulate cellular redox. This suggestion is supported by the finding that NOV-002 treatment upregulated the expression of superoxide dismutase 3 and glutathione peroxidase 2 in HSPCs, inhibited CTX-induced increases in reactive oxygen species production in HSPCs and MDSCs, and attenuated CTX-induced reduction of the ratio of reduced glutathione to oxidized glutathione in splenocytes. These findings provide a better understanding of the mechanisms whereby NOV-002 modulates chemotherapy-induced myelosuppression and immune dysfunction and a stronger rationale for clinical utilization of NOV-002 to reduce chemotherapy-induced hematopoietic and immune suppression.

S-glutathionylated serine proteinase inhibitors as plasma biomarkers in assessing response to redox-modulating drugs

Many cancer drugs impact cancer cell redox regulatory mechanisms and disrupt redox homeostasis. Pharmacodynamic biomarkers that measure therapeutic efficacy or toxicity could improve patient management. Using immunoblot analyses and mass spectrometry, we identified that serpins A1 and A3 were S-glutathionylated in a dose- and time-dependent manner following treatment of mice with drugs that alter reactive oxygen or nitrogen species. Tandem mass spectrometry analyses identified Cys(256) of serpin A1 and Cys(263) of serpin A3 as the S-glutathionylated residues. In human plasma from cancer patients, there were higher levels of unmodified serpin A1 and A3, but following treatments with redox active drugs, relative S-glutathionylation of these serpins was higher in plasma from normal individuals. There is potential for S-glutathionylated serpins A1 and A3 to act as pharmacodynamic biomarkers for evaluation of patient response to drugs that target redox pathways.