L-S,R-buthionine sulfoximine: historical development and clinical issues

Roles of reactive oxygen species in inflammation and cancer

Reactive oxygen species (ROS) constitute a spectrum of oxygenic metabolites crucial in modulating pathological organism functions. Disruptions in ROS equilibrium span various diseases, and current insights suggest a dual role for ROS in tumorigenesis and the immune response within cancer. This review rigorously examines ROS production and its role in normal cells, elucidating the subsequent regulatory network in inflammation and cancer. Comprehensive synthesis details the documented impacts of ROS on diverse immune cells. Exploring the intricate relationship between ROS and cancer immunity, we highlight its influence on existing immunotherapies, including immune checkpoint blockade, chimeric antigen receptors, and cancer vaccines. Additionally, we underscore the promising prospects of utilizing ROS and targeting ROS modulators as novel immunotherapeutic interventions for cancer. This review discusses the complex interplay between ROS, inflammation, and tumorigenesis, emphasizing the multifaceted functions of ROS in both physiological and pathological conditions. It also underscores the potential implications of ROS in cancer immunotherapy and suggests future research directions, including the development of targeted therapies and precision oncology approaches. In summary, this review emphasizes the significance of understanding ROS-mediated mechanisms for advancing cancer therapy and developing personalized treatments.

Therapeutic Role of Synthetic Lethality in ARID1A-Deficient Malignancies

AT-rich interaction domain 1A (ARID1A), a mammalian switch/sucrose nonfermenting complex subunit, modulates several cellular processes by regulating chromatin accessibility. It is encoded by ARID1A, an immunosuppressive gene frequently disrupted in a many tumors, affecting the proliferation, migration, and invasion of cancer cells. Targeting molecular pathways and epigenetic regulation associated with ARID1A loss, such as inhibiting the PI3K/AKT pathway or modulating Wnt/β-catenin signaling, may help suppress tumor growth and progression. Developing epigenetic drugs like histone deacetylase or DNA methyltransferase inhibitors could restore normal chromatin structure and function in cells with ARID1A loss. As ARID1A deficiency correlates with enhanced tumor mutability, microsatellite instability, high tumor mutation burden, increased programmed death-ligand 1 expression, and T-lymphocyte infiltration, ARID1A-deficient cells can be a potential therapeutic target for immune checkpoint inhibitors that warrants further exploration. In this review, we discuss the role of ARID1A in carcinogenesis, its crosstalk with other signaling pathways, and strategies to make ARID1A-deficient cells a potential therapeutic target for patients with cancer.

Inhibition of the glutamate-cysteine ligase catalytic subunit with buthionine sulfoximine enhances the cytotoxic effect of doxorubicin and cyclophosphamide in Burkitt lymphoma cells

Burkitt lymphoma (BL) is a highly aggressive lymphoma that mainly affects children and young adults. Chemotherapy is effective in young BL patients but the outcome in adults is less satisfactory. Therefore, there is a need to enhance the cytotoxic effect of drugs used in BL treatment. Glutathione (GSH) is an important antioxidant involved in processes such as regulation of oxidative stress and drug detoxification. Elevated GSH levels have been observed in many cancers and were associated with chemoresistance. We previously identified GCLC, encoding an enzyme involved in GSH biosynthesis, as an essential gene in BL. We now confirm that knockout of GCLC decreases viability of BL cells and that the GCLC protein is overexpressed in BL tissues. Moreover, we demonstrate that buthionine sulfoximine (BSO), a known inhibitor of GCLC, decreases growth of BL cells but does not affect control B cells. Furthermore, we show for the first time that BSO enhances the cytotoxicity of compounds commonly used in BL treatment, doxorubicin, and cyclophosphamide. Given the fact that BSO itself was not toxic to control cells and well-tolerated in clinical trials, combination of chemotherapy with BSO may allow reduction of the doses of cytotoxic drugs required to obtain effective responses in BL patients.

EGFR promotes ALKBH5 nuclear retention to attenuate N6-methyladenosine and protect against ferroptosis in glioblastoma

Growth factor receptors rank among the most important oncogenic pathways, but pharmacologic inhibitors often demonstrate limited benefit as monotherapy. Here, we show that epidermal growth factor receptor (EGFR) signaling repressed N6-methyladenosine (m6A) levels in glioblastoma stem cells (GSCs), whereas genetic or pharmacologic EGFR targeting elevated m6A levels. Activated EGFR induced non-receptor tyrosine kinase SRC to phosphorylate the m6A demethylase, AlkB homolog 5 (ALKBH5), thereby inhibiting chromosomal maintenance 1 (CRM1)-mediated nuclear export of ALKBH5 to permit sustained mRNA m6A demethylation in the nucleus. ALKBH5 critically regulated ferroptosis through m6A modulation and YTH N6-methyladenosine RNA binding protein (YTHDF2)-mediated decay of the glutamate-cysteine ligase modifier subunit (GCLM). Pharmacologic targeting of ALKBH5 augmented the anti-tumor efficacy of EGFR and GCLM inhibitors, supporting an EGFR-ALKBH5-GCLM oncogenic axis. Collectively, EGFR reprograms the epitranscriptomic landscape through nuclear retention of the ALKBH5 demethylase to protect against ferroptosis, offering therapeutic paradigms for the treatment of lethal cancers.

Auranofin Induces Lethality Driven by Reactive Oxygen Species in High-Grade Serous Ovarian Cancer Cells

High-grade serous ovarian cancer (HGSOC) accounts for 70% of ovarian cancer cases, and the survival rate remains remarkably low due to the lack of effective long-term consolidation therapies. Clinical remission can be temporarily induced by platinum-based chemotherapy, but death subsequently results from the extensive growth of a platinum-resistant component of the tumor. This work explores a novel treatment against HGSOC using the gold complex auranofin (AF). AF primarily functions as a pro-oxidant by inhibiting thioredoxin reductase (TrxR), an antioxidant enzyme overexpressed in ovarian cancer. We investigated the effect of AF on TrxR activity and the various mechanisms of cytotoxicity using HGSOC cells that are clinically sensitive or resistant to platinum. In addition, we studied the interaction between AF and another pro-oxidant, L-buthionine sulfoximine (L-BSO), an anti-glutathione (GSH) compound. We demonstrated that AF potently inhibited TrxR activity and reduced the vitality and viability of HGSOC cells regardless of their sensitivities to platinum. We showed that AF induces the accumulation of reactive oxygen species (ROS), triggers the depolarization of the mitochondrial membrane, and kills HGSOC cells by inducing apoptosis. Notably, AF-induced cell death was abrogated by the ROS-scavenger N-acetyl cysteine (NAC). In addition, the lethality of AF was associated with the activation of caspases-3/7 and the generation of DNA damage, effects that were also prevented by the presence of NAC. Finally, when AF and L-BSO were combined, we observed synergistic lethality against HGSOC cells, which was mediated by a further increase in ROS and a decrease in the levels of the antioxidant GSH. In summary, our results support the concept that AF can be used alone or in combination with L-BSO to kill HGSOC cells regardless of their sensitivity to platinum, suggesting that the depletion of antioxidants is an efficient strategy to mitigate the course of this disease.

Mitochondria in Cancer Stem Cells: From an Innocent Bystander to a Central Player in Therapy Resistance

Cancer continues to rank among the world's leading causes of mortality despite advancements in treatment. Cancer stem cells, which can self-renew, are present in low abundance and contribute significantly to tumor recurrence, tumorigenicity, and drug resistance to various therapies. The drug resistance observed in cancer stem cells is attributed to several factors, such as cellular quiescence, dormancy, elevated aldehyde dehydrogenase activity, apoptosis evasion mechanisms, high expression of drug efflux pumps, protective vascular niche, enhanced DNA damage response, scavenging of reactive oxygen species, hypoxic stability, and stemness-related signaling pathways. Multiple studies have shown that mitochondria play a pivotal role in conferring drug resistance to cancer stem cells, through mitochondrial biogenesis, metabolism, and dynamics. A better understanding of how mitochondria contribute to tumorigenesis, heterogeneity, and drug resistance could lead to the development of innovative cancer treatments.

Disturbing the Redox Balance Using Buthionine Sulfoximine Radiosensitized Somatostatin Receptor-2 Expressing Pre-Clinical Models to Peptide Receptor Radionuclide Therapy with 177Lu-DOTATATE

Peptide receptor radionuclide therapy with ¹⁷⁷Lu-DOTATATE improves the outcome of patients with somatostatin receptor (SSTR)-expressing neuroendocrine tumours. Nevertheless, stable disease has been the main response pattern observed, with some rare complete responses. Lu-177 exerts about two-thirds of its biological effects via the indirect effects of ionizing radiation that generate reactive oxygen species, eventually leading to oxidative damage and cell death. This provides a rationale for targeting the antioxidant defence system in combination with ¹⁷⁷Lu-DOTATATE. In the present study, the radiosensitizing potential and the safety of depleting glutathione (GSH) levels using buthionine sulfoximine (BSO) during ¹⁷⁷Lu-DOTATATE therapy were assessed in vitro and in vivo using a xenograft mouse model. In vitro, the combination resulted in a synergistic effect in cell lines exhibiting a BSO-mediated GSH decrease. In vivo, BSO neither influenced ¹⁷⁷Lu-DOTATATE biodistribution nor induced liver, kidney or bone marrow toxicity. In terms of efficacy, the combination resulted in reduced tumour growth and metabolic activity. Our results showed that disturbing the cell redox balance using a GSH synthesis inhibitor increased ¹⁷⁷Lu-DOTATATE efficacy without additional toxicity. Targeting the antioxidant defence system opens new safe treatment combination opportunities with ¹⁷⁷Lu-DOTATATE.

Targeting cancer lactate metabolism with synergistic combinations of synthetic catalysts and monocarboxylate transporter inhibitors

Synthetic anticancer catalysts offer potential for low-dose therapy and the targeting of biochemical pathways in novel ways. Chiral organo-osmium complexes, for example, can catalyse the asymmetric transfer hydrogenation of pyruvate, a key substrate for energy generation, in cells. However, small-molecule synthetic catalysts are readily poisoned and there is a need to optimise their activity before this occurs, or to avoid this occurring. We show that the activity of the synthetic organometallic redox catalyst [Os(p-cymene)(TsDPEN)] (1), which can reduce pyruvate to un-natural D-lactate in MCF7 breast cancer cells using formate as a hydride source, is significantly increased in combination with the monocarboxylate transporter (MCT) inhibitor AZD3965. AZD3965, a drug currently in clinical trials, also significantly lowers the intracellular level of glutathione and increases mitochondrial metabolism. These synergistic mechanisms of reductive stress induced by 1, blockade of lactate efflux, and oxidative stress induced by AZD3965 provide a strategy for low-dose combination therapy with novel mechanisms of action.

Molecular mechanisms of ferroptosis and their involvement in brain diseases

Ferroptosis is a type of regulated cell death characterized by intracellular accumulation of iron and reactive oxygen species, inhibition of system Xc-, glutathione depletion, nicotinamide adenine dinucleotide phosphate oxidation and lipid peroxidation. Since its discovery and characterization in 2012, many efforts have been made to reveal the underlying mechanisms, modulating compounds, and its involvement in disease pathways. Ferroptosis inducers include erastin, sorafenib, sulfasalazine and glutamate, which, by inhibiting system Xc-, prevent the import of cysteine into the cells. RSL3, statins, Ml162 and Ml210 induce ferroptosis by inhibiting glutathione peroxidase 4 (GPX4), which is responsible for preventing the formation of lipid peroxides, and FIN56 and withaferin trigger GPX4 degradation. On the other side, ferroptosis inhibitors include ferrostatin-1, liproxstatin-1, α-tocopherol, zileuton, FSP1, CoQ10 and BH4, which interrupt the lipid peroxidation cascade. Additionally, deferoxamine, deferiprone and N-acetylcysteine, by targeting other cellular pathways, have also been classified as ferroptosis inhibitors. Increased evidence has established the involvement of ferroptosis in distinct brain diseases, including Alzheimer's, Parkinson's and Huntington's diseases, amyotrophic lateral sclerosis, multiple sclerosis, and Friedreich's ataxia. Thus, a deep understanding of how ferroptosis contributes to these diseases, and how it can be modulated, can open a new window of opportunities for novel therapeutic strategies and targets. Other studies have shown a sensitivity of cancer cells with mutated RAS to ferroptosis induction and that chemotherapeutic agents and ferroptosis inducers synergize in tumor treatment. Thus, it is tempting to consider that ferroptosis may arise as a target mechanistic pathway for the treatment of brain tumors. Therefore, this work provides an up-to-date review on the molecular and cellular mechanisms of ferroptosis and their involvement in brain diseases. In addition, information on the main ferroptosis inducers and inhibitors and their molecular targets is also provided.

A platinum(IV) prodrug strategy to overcome glutathione-based oxaliplatin resistance

Clinical efficacy of oxaliplatin is frequently limited by severe adverse effects and therapy resistance. Acquired insensitivity to oxaliplatin is, at least in part, associated with elevated levels of glutathione (GSH). In this study we report on an oxaliplatin-based platinum(IV) prodrug, which releases L-buthionine-S,R-sulfoximine (BSO), an inhibitor of glutamate-cysteine ligase, the rate-limiting enzyme in GSH biosynthesis. Two complexes bearing either acetate (BSO-OxOAc) or an albumin-binding maleimide (BSO-OxMal) as second axial ligand were synthesized and characterized. The in vitro anticancer activity of BSO-OxOAc was massively reduced in comparison to oxaliplatin, proving its prodrug nature. Nevertheless, the markedly lower intracellular oxaliplatin uptake in resistant HCT116/OxR cells was widely overcome by BSO-OxOAc resulting in distinctly reduced resistance levels. Platinum accumulation in organs of a colorectal cancer mouse model revealed higher tumor selectivity of BSO-OxMal as compared to oxaliplatin. This corresponded with increased antitumor activity, resulting in significantly enhanced overall survival. BSO-OxMal-treated tumors exhibited reduced GSH levels, proliferative activity and enhanced DNA damage (pH2AX) compared to oxaliplatin. Conversely, pH2AX staining especially in kidney cells was distinctly increased by oxaliplatin but not by BSO-OxMal. Taken together, our data provide compelling evidence for enhanced tumor specificity of the oxaliplatin(IV)/BSO prodrug.

Synthesis and Transformations of NH-Sulfoximines

Recent years have seen a marked increase in the occurrence of sulfoximines in the chemical sciences, often presented as valuable motifs for medicinal chemistry. This has been prompted by both pioneering works taking sulfoximine containing compounds into clinical trials and the concurrent development of powerful synthetic methods. This review covers recent developments in the synthesis of sulfoximines concentrating on developments since 2015. This includes extensive developments in both S-N and S-C bond formations. Flow chemistry processes for sulfoximine synthesis are also covered. Finally, subsequent transformations of sulfoximines, particularly in N-functionalization are reviewed, including N-S, N-P, N-C bond forming processes and cyclization reactions.

IDO1 scavenges reactive oxygen species in myeloid-derived suppressor cells to prevent graft-versus-host disease

This study reveals that the tryptophan-degrading reaction catalyzed by indoleamine 2,3-dioxygenase 1 (IDO1) is linked to reactive oxygen species (ROS) scavenging in Gr-1⁺CD11b⁺ myeloid cells. The IDO1-mediated ROS scavenging promotes myeloid-derived suppressor cell characteristics in Gr-1⁺CD11b⁺ cells, suppressing their differentiation into proinflammatory neutrophils. These results could explain the increased lethality in graft-versus-host disease as well as the enhanced proinflammatory and reduced regulatory T cell responses after transplantation of IDO1-deficient bone marrow cells. Our findings provide a mechanistic insight into the immune-modulatory roles of IDO1.

Tryptophan-catabolizing enzyme indoleamine 2,3-dioxygenase 1 (IDO1) also has an immunological function to suppress T cell activation in inflammatory circumstances, including graft-versus-host disease (GVHD), a fatal complication after allogeneic bone marrow transplantation (allo-BMT). Although the mononuclear cell expression of IDO1 has been associated with improved outcomes in GVHD, the underlying mechanisms remain unclear. Herein, we used IDO-deficient (Ido1^−/−) BMT to understand why myeloid IDO limits the severity of GVHD. Hosts with Ido1^−/− BM exhibited increased lethality, with enhanced proinflammatory and reduced regulatory T cell responses compared with wild type (WT) allo-BMT controls. Despite the comparable expression of the myeloid-derived suppressor cell (MDSC) mediators, arginase-1, inducible nitric oxide synthase, and interleukin 10, Ido1^−/− Gr-1⁺CD11b⁺ cells from allo-BMT or in vitro BM culture showed compromised immune-suppressive functions and were skewed toward the Ly6C^lowLy6G^hi subset, compared with the WT counterparts. Importantly, Ido1^−/−Gr-1⁺CD11b⁺ cells exhibited elevated levels of reactive oxygen species (ROS) and neutrophil numbers. These characteristics were rescued by human IDO1 with intact heme-binding and catalytic activities and were recapitulated by the treatment of WT cells with the IDO1 inhibitor L1-methyl tryptophan. ROS scavenging by N-acetylcysteine reverted the Ido1^−/−Gr-1⁺CD11b⁺ composition and function to an MDSC state, as well as improved the survival of GVHD hosts with Ido1^−/− BM. In summary, myeloid-derived IDO1 enhances GVHD survival by regulating ROS levels and limiting the ability of Gr-1⁺CD11b⁺ MDSCs to differentiate into proinflammatory neutrophils. Our findings provide a mechanistic insight into the immune-regulatory roles of the metabolic enzyme IDO1.

Glutathione and its precursors in cancer

Buffering oxidative stress is as a crucial requirement for tumorigenesis. Antioxidant is a term reserved for molecules that quench reactive oxygen species (ROS) and alleviate oxidative stress. The details regarding antioxidant synthesis, their utilization to eliminate ROS, and their ability to promote different stages of tumorigenesis are unclear. Here, we focus on glutathione (GSH), the most abundant antioxidant in the cell, and its precursor amino acids (cysteine, glutamate, and glycine). Even though GSH was discovered more than a century ago, continued research into this antioxidant has provided answers to longstanding questions while also posing new ones.

2-Oxothiazolidine-4-carboxylic acid inhibits vascular calcification via induction of glutathione synthesis

Arterial medial calcification (AMC), the deposition of hydroxyapatite in the medial layer of the arteries, is a known risk factor for cardiovascular events. Oxidative stress is a known inducer of AMC and endogenous antioxidants, such as glutathione (GSH), may prevent calcification. GSH synthesis, however, can be limited by cysteine levels. Therefore, we assessed the effects of the cysteine prodrug 2-oxothiazolidine-4-carboxylic acid (OTC), on vascular smooth muscle cell (VSMC) calcification to ascertain its therapeutic potential. Human aortic VSMCs were cultured in basal or mineralising medium (1 mM calcium chloride/sodium phosphate) and treated with OTC (1-5 mM) for 7 days. Cell-based assays and western blot analysis were performed to assess cell differentiation and function. OTC inhibited calcification ≤90%, which was associated with increased ectonucleotide pyrophosphatase/phosphodiesterase activity, and reduced apoptosis. In calcifying cells, OTC downregulated protein expression of osteoblast markers (Runt-related transcription factor 2 and osteopontin), while maintaining expression of VSMC markers (smooth muscle protein 22α and α-smooth muscle actin). GSH levels were significantly reduced by 90% in VSMCs cultured in calcifying conditions, which was associated with declines in expression of gamma-glutamylcysteine synthetase and GSH synthetase. Treatment of calcifying cells with OTC blocked the reduction in expression of both enzymes and prevented the decline in GSH. This study shows OTC to be a potent and effective inhibitor of in vitro VSMC calcification. It appears to maintain GSH synthesis which may, in turn, prevent apoptosis and VSMCs gaining osteoblast-like characteristics. These findings may be of clinical relevance and raise the possibility that treatment with OTC could benefit patients susceptible to AMC.

A synthetic lethal drug combination mimics glucose deprivation-induced cancer cell death in the presence of glucose

Metabolic reprogramming in cancer cells can increase their dependence on metabolic substrates such as glucose. As such, the vulnerability of cancer cells to glucose deprivation creates an attractive opportunity for therapeutic intervention. Because it is not possible to starve tumors of glucose in vivo, here we sought to identify the mechanisms in glucose deprivation-induced cancer cell death and then designed inhibitor combinations to mimic glucose deprivation-induced cell death. Using metabolomic profiling, we found that cells undergoing glucose deprivation-induced cell death exhibited dramatic accumulation of intracellular l-cysteine and its oxidized dimer, l-cystine, and depletion of the antioxidant GSH. Building on this observation, we show that glucose deprivation-induced cell death is driven not by the lack of glucose, but rather by l-cystine import. Following glucose deprivation, the import of l-cystine and its subsequent reduction to l-cysteine depleted both NADPH and GSH pools, thereby allowing toxic accumulation of reactive oxygen species. Consistent with this model, we found that the glutamate/cystine antiporter (xCT) is required for increased sensitivity to glucose deprivation. We searched for glycolytic enzymes whose expression is essential for the survival of cancer cells with high xCT expression and identified glucose transporter type 1 (GLUT1). Testing a drug combination that co-targeted GLUT1 and GSH synthesis, we found that this combination induces synthetic lethal cell death in high xCT-expressing cell lines susceptible to glucose deprivation. These results indicate that co-targeting GLUT1 and GSH synthesis may offer a potential therapeutic approach for targeting tumors dependent on glucose for survival.

Overcoming Cancer Cell Drug Resistance by a Folic Acid Targeted Polymeric Conjugate of Buthionine Sulfoximine

Background:

Glutathione (GSH), which is the predominant low molecular weight intracellular thiol in mammals, has multiple functions, such as those of protecting against oxidative stress and detoxifying endogenous and exogenous electrophiles. High GSH levels, which have been observed in various types of tumors, have been thought to contribute to the resistance of neoplastic cells to apoptotic stimuli triggered by pro-oxidant therapy. Although L-(S,R)-Buthionine Sulfoximine (BSO), a selective irreversible inhibitor of glutamate cysteine ligase, depletes GSH in vitro and in in vivo and sensitizes tumor cells to radiation and some cancer chemotherapeutics, its toxicity and short in vivo half-life have limited its application to combination anticancer therapies.

Objective:

To demonstrate that a folate-targeted PEGylated BSO conjugate can sensitize cancer cells to a Reactive Oxygen Species (ROS)-generating anticancer agent by depleting GSH.

Methods:

A novel folate-targeted PEGylated-BSO conjugate was synthesized and tested in combination with gemcitabine in human cell lines that over-express (HeLa) or do not express (A549) the folate receptor.

Results:

The prepared folate-PEG-GFLG-BSO conjugate proved to be efficacious in reducing GSH levels and, when used in combination with the pro-oxidant drug gemcitabine, it enhanced drug activity in the cell line overexpressing the folate receptor.

Conclusion:

The folate-PEG-GFLG-BSO conjugate studied was found to be effective in sensitizing folatereceptor positive cancer cells to the ROS-generating drug gemcitabine.

l-Serine protects mouse hippocampal neuronal HT22 cells against oxidative stress-mediated mitochondrial damage and apoptotic cell death

The cytoprotective mechanism of l-serine against oxidative stress-mediated neuronal apoptosis was investigated in mouse hippocampal neuronal HT22 cells. Treatment with the reactive oxygen species (ROS) inducer 2,3-dimethoxy-1,4-naphthoquinone (DMNQ) increased cytosolic and mitochondrial ROS and apoptosis, without necrosis, in HT22 cells. ROS-mediated apoptosis was accompanied by the induction of the endoplasmic reticulum (ER) stress-mediated apoptotic pathway, involving CHOP/GADD153 upregulation, JNK and p38 MAPK activation, and caspase-12 and caspase-8 activation, and subsequent induction of the mitochondrial apoptotic pathway through BAK and BAX activation, mitochondrial membrane potential (Δψm) loss, caspase-9 and caspase-3 activation, PARP cleavage, and nucleosomal DNA fragmentation. However, the DMNQ-caused ROS elevation and ER stress- and mitochondrial damage-induced apoptotic events were dose-dependently suppressed by co-treatment with l-serine (7.5-20 mM). Although DMNQ reduced both the intracellular glutathione (GSH) level and the ratios of reduced GSH to oxidized GSH (GSSG), the reduction was restored by co-treatment with l-serine. Co-treatment with GSH or N-acetylcysteine also blocked DMNQ-caused ROS elevation and apoptosis; however, co-treatment with the GSH synthesis inhibitor buthionine sulfoximine significantly promoted ROS-mediated apoptosis and counteracted the protection by l-serine. In HT22 cells, DMNQ treatment appeared to tilt the mitochondrial fusion-fission balance toward fission by down-regulating the levels of profusion proteins (MFN1/2 and OPA1) and inhibitory phosphorylation of profission protein DRP1 at Ser-637, resulting in mitochondrial fragmentation. These DMNQ-caused alterations were prevented by l-serine. A comparison of mitochondrial energetic function between DMNQ- and DMNQ/l-serine-treated HT22 cells showed that the DMNQ-caused impairment of the mitochondrial energy generation capacity was restored by l-serine. These results demonstrate that l-serine can protect neuronal cells against oxidative stress-mediated apoptotic cell death by contributing to intracellular antioxidant GSH synthesis and maintaining the mitochondrial fusion-fission balance.

Glutathione Metabolism in Renal Cell Carcinoma Progression and Implications for Therapies

A significantly increased level of the reactive oxygen species (ROS) scavenger glutathione (GSH) has been identified as a hallmark of renal cell carcinoma (RCC). The proposed mechanism for increased GSH levels is to counteract damaging ROS to sustain the viability and growth of the malignancy. Here, we review the current knowledge about the three main RCC subtypes, namely clear cell RCC (ccRCC), papillary RCC (pRCC), and chromophobe RCC (chRCC), at the genetic, transcript, protein, and metabolite level and highlight their mutual influence on GSH metabolism. A further discussion addresses the question of how the manipulation of GSH levels can be exploited as a potential treatment strategy for RCC.

Arsenic Disulfide Combined with L-Buthionine-(S, R)-Sulfoximine Induces Synergistic Antitumor Effects in Two-Dimensional and Three-Dimensional Models of MCF-7 Breast Carcinoma Cells

Three-dimensionally (3D) cultured tumor cells (spheroids) exhibit more resistance to therapeutic agents than the cells cultured in traditional two-dimensional (2D) system (monolayers). We previously demonstrated that arsenic disulfide (As₂S2) exerted significant anticancer efficacies in both 2D- and 3D-cultured MCF-7 cells, whereas 3D spheroids were shown to be resistant to the As₂S₂ treatment. L-buthionine-(S, R)-sulfoximine (BSO), an inhibitor of glutathione (GSH) synthesis, has been regarded to be a potent candidate for combinatorial treatment due to its GSH modulation function. In the present study, we introduced BSO in combination with As₂S₂ at a low concentration to investigate the possible enhancing anticancer efficacy by the combinatorial treatment on 2D- and 3D-cultured MCF-7 cells. Our results presented for the first time that the combination of As₂S₂ and BSO exerted potent anticancer synergism in both MCF-7 monolayers and spheroids. The IC50 values of As₂S₂ in combinatorial treatment were significantly lower than those in treatment of As₂S₂ alone in both 2D- and 3D-cultured MCF-7 cells (P<0.01, respectively). In addition, augmented induction of apoptosis and enhanced cell cycle arrest along with the regulation of apoptosis- and cell cycle-related proteins, as well as synergistic inhibitions of PI3K/Akt signals, were also observed following co-treatment of As₂S₂ and BSO. Notably, the combinatorial treatment significantly decreased the cellular GSH levels in both 2D- and 3D-cultured MCF-7 cells in comparison with each agent alone (P<0.05 in each). Our results suggest that the combinatorial treatment with As₂S₂ and BSO could be a promising novel strategy to reverse arsenic resistance in human breast cancer.

Deubiquitinases Maintain Protein Homeostasis and Survival of Cancer Cells upon Glutathione Depletion

Cells are subjected to oxidative stress during the initiation and progression of tumors, and this imposes selective pressure for cancer cells to adapt mechanisms to tolerate these conditions. Here, we examined the dependency of cancer cells on glutathione (GSH), the most abundant cellular antioxidant. While cancer cell lines displayed a broad range of sensitivities to inhibition of GSH synthesis, the majority were resistant to GSH depletion. To identify cellular pathways required for this resistance, we carried out genetic and pharmacologic screens. Both approaches revealed that inhibition of deubiquitinating enzymes (DUBs) sensitizes cancer cells to GSH depletion. Inhibition of GSH synthesis, in combination with DUB inhibition, led to an accumulation of polyubiquitinated proteins, induction of proteotoxic stress, and cell death. These results indicate that depletion of GSH renders cancer cells dependent on DUB activity to maintain protein homeostasis and cell viability and reveal a potentially exploitable vulnerability for cancer therapy.

Combinatorial Synthesis to Identify a Potent, Necrosis-Inducing Rhenium Anticancer Agent

Combinatorial synthesis can be applied for developing a library of compounds that can be rapidly screened for biological activity. Here, we report the application of microwave-assisted combinatorial chemistry for the synthesis of 80 rhenium(I) tricarbonyl complexes bearing diimine ligands. This library was evaluated for anticancer activity in three different cancer cell lines, enabling the identification of three lead compounds with cancer cell growth-inhibitory activities of less than 10 μM. These three lead structures, Re-9B, Re-9C, and Re-9D, were synthesized independently and fully characterized by NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray crystallography. The most potent of these three complexes, Re-9D, was further explored to understand its mechanism of action. Complex Re-9D is equally effective in both wild-type and cisplatin-resistant A2780 ovarian cancer cells, indicating that it circumvents cisplatin resistance. This compound was also shown to possess promising activity against ovarian cancer tumor spheroids. Additionally, flow cytometry showed that Re-9D does not induce cell cycle arrest or flipping of phosphatidylserine to the outer cell membrane. Analysis of the morphological changes of cancer cells treated with Re-9D revealed that this compound gives rise to rapid plasma membrane rupture. Collectively, these data suggest that Re-9D induces necrosis in cancer cells. To assess the in vivo biodistribution and stability of this compound, a radioactive ^99mTc analogue of Re-9D, ^99mTc-9D(H₂O), was synthesized and administered to naı̈ve BALB/c mice. Results of these studies indicate that ^99mTc-9D(H₂O) exhibits high metabolic stability and a distinct biodistribution profile. This research demonstrates that combinatorial synthesis is an effective approach for the development of new rhenium anticancer agents with advantageous biological properties.

Nicotinamide Nucleotide Transhydrogenase as a Novel Treatment Target in Adrenocortical Carcinoma

Adrenocortical carcinoma (ACC) is an aggressive malignancy with poor response to chemotherapy. In this study, we evaluated a potential new treatment target for ACC, focusing on the mitochondrial reduced form of NAD phosphate (NADPH) generator nicotinamide nucleotide transhydrogenase (NNT). NNT has a central role within mitochondrial antioxidant pathways, protecting cells from oxidative stress. Inactivating human NNT mutations result in congenital adrenal insufficiency. We hypothesized that NNT silencing in ACC cells will induce toxic levels of oxidative stress. To explore this, we transiently knocked down NNT in NCI-H295R ACC cells. As predicted, this manipulation increased intracellular levels of oxidative stress; this resulted in a pronounced suppression of cell proliferation and higher apoptotic rates, as well as sensitization of cells to chemically induced oxidative stress. Steroidogenesis was paradoxically stimulated by NNT loss, as demonstrated by mass spectrometry-based steroid profiling. Next, we generated a stable NNT knockdown model in the same cell line to investigate the longer lasting effects of NNT silencing. After long-term culture, cells adapted metabolically to chronic NNT knockdown, restoring their redox balance and resilience to oxidative stress, although their proliferation remained suppressed. This was associated with higher rates of oxygen consumption. The molecular pathways underpinning these responses were explored in detail by RNA sequencing and nontargeted metabolome analysis, revealing major alterations in nucleotide synthesis, protein folding, and polyamine metabolism. This study provides preclinical evidence of the therapeutic merit of antioxidant targeting in ACC as well as illuminating the long-term adaptive response of cells to oxidative stress.

Intracellular glutathione-depleting polymeric micelles for cisplatin prodrug delivery to overcome cisplatin resistance of cancers

The intrinsic or acquired cisplatin resistance of cancer cells frequently limits the final therapeutic efficacy. Detoxification by the high level of intracellular glutathione (GSH) plays critical roles in the majority of cisplatin-resistant cancers. In this report, we designed an amphiphilic diblock copolymer composed of poly(ethylene glycol) (PEG) and polymerized phenylboronic ester-functionalized methacrylate (PBEMA), PEG-b-PBEMA, which can self-assemble into micelles in aqueous solutions to load hydrophobic cisplatin prodrug (Pt(IV)). Pt(IV)-loaded PEG-b-PBEMA micelles (PtBE-Micelle) reverse cisplatin-resistance of cancer cells through improving cellular uptake efficiency and reducing intracellular GSH level. We found that the cellular uptake amount of platinum from PtBE-Micelle was 6.1 times higher than that of free cisplatin in cisplatin-resistant human lung cancer cells (A549R). Meanwhile, GSH concentration of A549R cells was decreased to 32% upon treatment by PEG-b-PBEMA micelle at the phenyl borate-equivalent concentration of 100μM. PtBE-Micelle displayed significantly higher cytotoxicity toward A549R cells with half maximal inhibitory concentration (IC₅₀) of cisplatin-equivalent 0.20μM compared with free cisplatin of 33.15μM and Pt(IV)-loaded PEG-b-poly(ε-caprolactone) micelles of cisplatin-equivalent 0.75μM. PtBE-Micelle can inhibit the growth of A549R xenograft tumors effectively. Accordingly, PEG-b-PBEMA micelles show great potentials as drug delivery nanocarriers for platinum-based chemotherapy toward cisplatin-resistant cancers.

Association of elevated reactive oxygen species and hyperthermia induced radiosensitivity in cancer stem-like cells

Cancer stem-like cells (CSCs) are the principal causes of tumor radio-resistance, dormancy and recurrence after radiotherapy. Clinical trials show hyperthermia (HT) might be a potent radiation sensitizer. In this study, CSCs were found to be more susceptible to radiation when combined with HT treatment. Treated cells showed significantly reduced self-renewal, cell survival and proliferation in vitro, as well as significant reduced tumor formation in vivo. Further study demonstrated that the radiosensitization effect was associated with increased intracellular reactive oxygen species (ROS) level in CSCs, confirmed by modifying redox status in CSCs bidirectionally. Pharmacologic depletion of glutathione by buthionine sulphoximine mimicked HT induced radiosensitivity in CSCs. Antioxidant N-acetylcysteine could efficiently rescue HT induced radiosensitivity in CSCs. To our knowledge, this may be the first report suggesting the association between elevated intracellular ROS level and HT induced radiosensitization in human breast CSCs and pancreatic CSCs, which might provide new strategy for improving CSCs radiosensitivity.

Metabolic characterization of invaded cells of the pancreatic cancer cell line, PANC-1

We previously reported that about 0.4% of cells in the cultured human pancreatic cancer cell line, PANC-1, can invade matrigel during the transwell invasion assay, suggesting that these invaded PANC-1 cells may have specific characteristics to keep their invasive potential. To identify the metabolic characterization specific in the invaded PANC-1 cells, metabolome analysis of the invaded PANC-1 compared with the whole cultured PANC-1 was performed using CE-TOFMS, and concentrations of 110 metabolites were measured. In contrast to the whole cultured cells, the invaded PANC-1 was characterized as a population with reduced levels of amino acids and TCA cycle intermediates, and decreased and increased intermediates in glycolysis and nucleic acid metabolism. In particular, the ratio of both adenosine and guanosine energy charge was reduced in the invaded cells, revealing that the consumption of ATP and GTP was high in the invaded cells, and thus suggesting that ATP- or GTP-generating pathways are stimulated. In addition, the GSH/GSSG ratio was low in the invaded cells, but these cells had a higher surviving fraction after exposure to hydrogen peroxide. Thus, the invaded cells were the population resistant to oxidative stress. Furthermore, reduction in intracellular GSH content inhibited PANC-1 invasiveness, indicated that GSH has an important role in PANC-1 invasiveness. Overall, we propose the invaded cells have several unique metabolic profiles.

Enhancement of Radiation Response in Breast Cancer Stem Cells by Inhibition of Thioredoxin- and Glutathione-Dependent Metabolism

The goal of this study was to determine if depletion of glutathione (GSH) and inhibition of thioredoxin (Trx) reductase (TrxR) activity could enhance radiation responses in human breast cancer stem cells by a mechanism involving thiol-dependent oxidative stress. The following were used to inhibit GSH and Trx metabolism: buthionine sulfoximine (BSO), a GSH synthesis inhibitor; sulfasalazine (SSZ), an inhibitor of x_c^- cysteine/glutamate antiporter; auranofin (Au), a thioredoxin reductase inhibitor; or 2-AAPA, a GSH-reductase inhibitor. Clonogenic survival, Matrigel assays, flow cytometry cancer stem cell assays (CD44⁺CD24^-ESA⁺ or ALDH1) and human tumor xenograft models were used to determine the antitumor activity of drug and radiation combinations. Combined inhibition of GSH and Trx metabolism enhanced cancer cell clonogenic killing and radiation responses in human breast and pancreatic cancer cells via a mechanism that could be inhibited by N-acetylcysteine (NAC). Au, BSO and radiation also significantly decreased breast cancer cell migration and invasion in a thiol-dependent manner that could be inhibited by NAC. In addition, pretreating cells with Au sensitized breast cancer stem cell populations to radiation in vitro as determined by CD44⁺CD24^-ESA⁺ or ALDH1. Combined administration of Au and BSO, given prior to irradiation, significantly increased the survival of mice with human breast cancer xenografts, and decreased the number of ALDH1⁺ cancer stem cells. These results indicate that combined inhibition of GSH- and Trx-dependent thiol metabolism using pharmacologically relevant agents can enhance responses of human breast cancer stem cells to radiation both in vitro and in vivo.

Selected polyphenols potentiate the apoptotic efficacy of glycolytic inhibitors in human acute myeloid leukemia cell lines. Regulation by protein kinase activities

Background

The glycolysis inhibitor 2-deoxy-d-glucose (2-DG) is a safe, potentially useful anti-tumour drug, but its efficacy is normally low when used alone. Recent studies indicated that 2-DG stimulates the PI3K/Akt and MEK/ERK defensive pathways, which limits the apoptotic efficacy in tumour cell lines. We hypothesized that co-treatment with selected polyphenols could improve 2-DG-provoked apoptosis by preventing defensive kinase activation.

Methods

Cell proliferation was measured by cell counting or the MTT assay. Cell cycle, apoptosis and necrosis were determined by propidium iodide staining and/or annexin V labeling followed by flow cytometry. Mitochondria pore transition and depolarization were determined by calcein-ATM or rhodamine 123 labeling followed flow cytometry. Intracellular reactive oxygen species and GSH were determined by dichlorodihydrofluorescein diacetate or monochlorobimane labeling followed by flow cytometry or fluorimetry. Expression and phosphorylation of protein kinases were analyzed by the Western blot.

Results

(i) 2-DG-provoked apoptosis was greatly potentiated by co-treatment with the sub-lethal concentrations of the flavonoid quercetin in human HL60 acute myeloblastic leukemia cells. Allowing for quantitative differences, apoptosis potentiation was also obtained using NB4 promyelocytic and THP-1 promonocytic cells, using curcumin or genistein instead of quercetin, and using lonidamine instead of 2-DG, but not when 2-DG was substituted by incubation in glucose-free medium. (ii) Quercetin and 2-DG rapidly elicited the opening of mitochondria pore transition, which preceded the trigger of apoptosis. (iii) Treatments did not affect GSH levels, and caused disparate effects on reactive oxygen species generation, which did not match the changes in lethality. (iv) 2-DG and lonidamine stimulated defensive Akt and ERK phosphorylation/activation, while glucose starvation was ineffective. Polyphenols prevented the stimulation of Akt phosphorylation, and in some cases also ERK phosphorylation. In addition, quercetin and 2-DG stimulated GSK-3α,β phosphorylation/inactivation, although with different isoform specificity. The use of pharmacologic inhibitors confirmed the importance of these kinase modifications for apoptosis.

Conclusions

The present in vitro observations suggest that co-treatment with low concentrations of selected polyphenols might represent a manner of improving the poor anti-tumour efficacy of some glycolytic inhibitors, and that apoptosis potentiation may be at least in part explained by the regulation of defensive protein kinase activities.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-016-0345-y) contains supplementary material, which is available to authorized users.

Emodin enhances cisplatin-induced cytotoxicity in human bladder cancer cells through ROS elevation and MRP1 downregulation

Background

Chemoresistance is one of the most leading causes for tumor progression and recurrence of bladder cancer. Reactive oxygen species (ROS) plays a key role in the chemosensitivity of cancer cells. In the present study, emodin (1,3,8-trihydroxy-6-methylanthraquinone) was applied as a ROS generator in combination with cisplatin in T24 and J82 human bladder cancer cells.

Methods

Cell viability and apoptosis rate of different treatment groups were detected by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) and flow cytometry (FCM). The expression of transporters was measured at both the transcription and translation levels using PCR and western blotting. In vitro findings were confirmed by in vivo experiments using tumor-bearing mice. The expression of multidrug resistance-associated protein 1 (MRP1) in tumour tissue was measured using immunohistochemistry and side effects of the emodin/cisplatin co-treatment were investigated by histological examination.

Results

Emodin increased the cellular ROS level and effectively enhanced the cisplatin-induced cytotoxicity of T24 and J82 human bladder cancer cells through decreasing glutathione-cisplatin (GSH-cisplatin) conjugates. It blocked the chemoresistance of T24 and J82 cells to cisplatin through suppressing the expression of MRP1. This effect was specific in T24 and J82 cells but not in HCV-29 normal bladder epithelial cells. Consistent with in vitro experiments, emodin/cisplatin co-treatment increased the cell apoptosis and repressed the MRP1 expression in xenograft tumors, and without obvious systemic toxicity.

Conclusions

This study revealed that emodin could increase the cisplatin-induced cytotoxicity against T24 and J82 cells via elevating the cellular ROS level and downregulating MRP1 expression. We suggest that emodin could serve as an effective adjuvant agent for the cisplatin-based chemotherapy of bladder cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2640-3) contains supplementary material, which is available to authorized users.

Magnetic Resonance Imaging Identifies Differential Response to Pro-Oxidant Chemotherapy in a Xenograft Model

Induction of oxidative stress is a key component of cancer therapy. Pro-oxidant drugs have been demonstrated to enhance the efficacy of radiotherapy and chemotherapy. An emerging concept is that therapeutic outcomes are dictated by the differential redox buffering reserve in subpopulations of malignant cells, indicating the need for noninvasive biomarkers of tumor redox that can be used for dose identification and response assessment in a longitudinal setting. Magnetic resonance imaging (MRI) enhanced with the thiol-binding contrast agent Gd-LC6-SH, and hemodynamic response imaging (HRI) in combination with hypercapnia and hyperoxia were investigated as biomarkers of the pharmacodynamics of the small molecule pro-oxidant imexon (IMX). Human multiple myeloma cell lines 8226/S and an IMX-resistant variant, 8226/IM10, were established as contralateral tumors in SCID mice. T1slope, an MRI measure of the washout rate of Gd-LC6-SH, was significantly lower post-IMX therapy in 8226/S tumors compared with vehicle controls, indicating treatment-related oxidization of the tumor microenvironment, which was confirmed by analysis of tumor tissue for thiols. T1slope and ex vivo assays for thiols both indicated a more reduced microenvironment in 8226/IM10 tumors following IMX therapy. HRI with hypercapnia challenge revealed IMX inhibition of vascular dilation in 8226/S tumors but not 8226/IM10 tumors, consistent with decreased immunohistochemical staining for smooth muscle actin in treated 8226/S tumors. MRI enhanced with Gd-LC6-SH, and HRI coupled with a hypercapnic challenge provide noninvasive biomarkers of tumor response to the redox modulator imexon.

Oxidative stress, cell cycle arrest and differentiation contribute toward the antiproliferative action of BSO and calcitriol on Caco-2 cells

The prognosis and incidence of colon cancer are linked to vitamin D3 serum levels. To evaluate the effects of D,L-buthionine-S,R-sulfoximine (BSO), 1,25(OH)2D3 and their combination on intestinal Caco-2 cell growth, to elucidate the possible cellular mechanisms involved in their antiproliferative action, and to determine whether BSO acts as a sensitizer to 1,25(OH)2D3 treatment, enabling minimization of the toxic effects caused by high doses of the steroid. Human colon cancer Caco-2 cells were treated with 1,25(OH)2D3, BSO, both, or vehicle. Cell proliferation was evaluated by crystal violet staining. Cell cycle and mitochondrial membrane potential were measured by flow cytometry. Total glutathione, catalase, superoxide dismutase, superoxide anion levels, and alkaline phosphatase activities were analyzed by spectrophotometry. DNA fragmentation was evaluated using the terminal dUTP nick end labeling assay. BSO and 1,25(OH)2D3 inhibited Caco-2 cell growth, an effect that was higher with the combined treatment. The antiproliferative effect produced by the combination could be protected by ascorbic acid. BSO plus 1,25(OH)2D3 induced cell cycle arrest and suppressed cell division. Total glutathione decreased and superoxide anion increased with BSO and BSO plus 1,25(OH)2D3. Catalase activity increased with the combined treatment. Mitochondrial membrane potential and alkaline phosphatase activity were altered by 1,25(OH)2D3 alone or plus BSO. The percentage of terminal dUTP nick end labeling-positive cells was increased. BSO increases the antiproliferative effect of 1,25(OH)2D3 on Caco-2 cells through induction of oxidative stress, which occurs simultaneously with DNA breakage. The antioxidant system can partially compensate the damage induced by BSO plus 1,25(OH)2D3. Cell differentiation induction is also involved in the response to the combined treatment.

The glutathione synthesis inhibitor buthionine sulfoximine synergistically enhanced melphalan activity against preclinical models of multiple myeloma

Melphalan (L-PAM) has been an integral part of multiple myeloma (MM) treatment as a conditioning regimen before stem cell transplant (SCT). After initial response, most treated patients experience relapse with an aggressive phenotype. Increased glutathione (GSH) in MM may mediate resistance to L-PAM. We demonstrated that the GSH synthesis inhibitor buthionine sulfoximine (BSO) synergistically enhanced L-PAM activity (inducing 2–4 logs of cell kill) against nine MM cell lines (also in the presence of marrow stroma or cytokines) and in seven primary MM samples (combination indices <1.0). In MM cell lines, BSO significantly (P<0.05) depleted GSH, increased L-PAM-induced single-strand DNA breaks, mitochondrial depolarization, caspase cleavage and apoptosis. L-PAM depleted GSH, but GSH rapidly recovered in a L-PAM-resistant MM cell line unless also treated with BSO. Treatment with N-acetylcysteine antagonized BSO+L-PAM cytotoxicity without increasing GSH. In human MM xenografted into beige-nude-xid mice, BSO significantly depleted MM intracellular GSH and significantly increased apoptosis compared with L-PAM alone. BSO+L-PAM achieved complete responses (CRs) in three MM xenograft models including maintained CRs >100 days, and significantly increased the median event-free survival relative to L-PAM alone. Combining BSO with L-PAM warrants clinical testing in advanced MM.

Autophagy interplays with apoptosis and cell cycle regulation in the growth inhibiting effect of Trisenox in HEP-2, a laryngeal squamous cancer

Laryngeal squamous cell carcinoma (LSCC) is the most common among several types of head and neck cancers. Current treatments have a poor effect on early and advanced cases, and further investigations for novel agents against LSCCs are desirable. In this study, we elucidate the cytotoxic enhancing effect of arsenic trioxide (As2O3) combined with L-buthionine sulfoximine (BSO) in LSCC. The effect of BSO with As2O3 or Cisplatin (CDDP) on cell viability was examined using 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). The reactive oxygen species (ROS) levels, cell cycle, and apoptosis were measured by flow cytometry using 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), propidium iodide (PI) and annexin V/PI. The acidic vacuolar organelles were visualized by fluorescence microscope and quantified using flow cytometry. Neither CDDP nor As2O3 when used alone reduced the cell viability. BSO was found to enhance only As2O3 sensitivity, leading to G2/M arrest and autophagy with no correlation of ROS induction. This result suggests that modulation of glutathione enhances autophagy, which interplays with apoptosis. In this study, we obtained initial preclinical evidence for the potential efficacy of these drugs in a combined therapy protocol.

The pro-oxidant buthionine sulfoximine (BSO) reduces tumor growth of implanted Lewis lung carcinoma in mice associated with increased protein carbonyl, tubulin abundance, and aminopeptidase activity

This study evaluated the effects of the pro-oxidant buthionine sulfoximine (BSO) and of the interaction between BSO and TETRAC, an antagonist of αvß3 integrin, on tumor development and aminopeptidase (AP) activity in a murine model of implanted Lewis's carcinoma. Male CBA-C57 mice were untreated (controls) or treated with BSO (222 mg/100 mL in drinking water), TETRAC (10 mg/kg/day, i.p.), or BSO + TETRAC. BSO for 28 days and TETRAC were given for the last 20 days. Mice were subcutaneously inoculated with 1 × 10(6) Lewis carcinoma 3LL cells into the dorsum. Study variables were tumor weight (TW); Hb, as index of tumor-mediated angiogenesis; vascular endothelial growth factor (VEGF) protein abundance; protein carbonyl content; α-tubulin abundance; and GluAp, AlaAp, and AspAp activities. BSO produced a major decrease in TW (203 ± 18 mg) with respect to controls (365 ± 26) and a reduction in Hb content. The TETRAC group also showed marked reductions in TW (129 ± 15) and Hb concentration associated with a reduced VEGF content. The BSO + TETRAC group showed a major TW reduction (125 ± 13); although, the difference with the TETRAC group was not significant. BSO treatment increased protein carbonyl and tubulin abundance in comparison to controls. The activity of all APs was increased in the three experimental groups and was strongly and negatively correlated with TW. In conclusion, administration of BSO reduced the TW, which inversely correlated with protein carbonyl content, suggesting a loss of microtubule polymerization. The finding of a negative correlation between TW and AP activity opens up new perspectives for the study of APs as tumor growth modulators.

A paradoxical chemoresistance and tumor suppressive role of antioxidant in solid cancer cells: a strange case of Dr. Jekyll and Mr. Hyde

Modulation of intracellular antioxidant concentration is a double-edged sword, with both sides exploited for potential therapeutic benefits. While antioxidants may hamper the efficacy of chemotherapy by scavenging reactive oxygen species and free radicals, it is also possible that antioxidants alleviate unwanted chemotherapy-induced toxicity, thus allowing for increased chemotherapy doses. Under normoxic environment, antioxidants neutralize toxic oxidants, such as reactive oxygen species (ROS), maintaining them within narrow boundaries level. This redox balance is achieved by various scavenging systems such as enzymatic system (e.g., superoxide dismutases, catalase, and peroxiredoxins), nonenzymatic systems (e.g., glutathione, cysteine, and thioredoxin), and metal-binding proteins (e.g., ferritin, metallothionein, and ceruloplasmin) that sequester prooxidant metals inhibiting their participation in redox reactions. On the other hand, therapeutic strategies that promote oxidative stress and eventually tumor cells apoptosis have been explored based on availability of chemotherapy agents that inhibit ROS-scavenging systems. These contradictory assertions suggest that antioxidant supplementation during chemotherapy treatment can have varied outcomes depending on the tumor cellular context. Therefore, understanding the antioxidant-driven molecular pathways might be crucial to design new therapeutic strategies to fight cancer progression.

Pivotal role for ROS activation of p38 MAPK in the control of differentiation and tumor-initiating capacity of glioma-initiating cells

Reactive oxygen species (ROS) are involved in various aspects of cancer cell biology, yet their role in cancer stem cells (CSCs) has been poorly understood. In particular, it still remains unclear whether and how ROS control the self-renewal/differentiation process and the tumor-initiating capacity of CSCs. Here we show that ROS-mediated activation of p38 MAPK plays a pivotal role in the control of differentiation and tumor-initiating capacity of glioma-initiating cells (GICs) derived from human glioblastomas. Mechanistically, ROS triggered p38-dependent Bmi1 protein degradation and FoxO3 activation in GICs, which were shown to be responsible for the loss of their self-renewal capacity and differentiation, respectively. Thus, the results suggest that Bmi1 and FoxO3 govern distinct phases of transition from undifferentiated to fully differentiated cells. Furthermore, we also demonstrate in this study that oxidative stress deprives GICs of their tumor-initiating capacity through the activation of the ROS-p38 axis. As such, this is the first study to the best of our knowledge to delineate how ROS control self-renewal/differentiation and the tumor-initiating capacity of stem-like cancer cells. This study also suggests that targeting of the ROS-p38 axis could be a novel approach in the development of therapeutic strategies against gliomas, represented by glioblastoma.

NRF2 and p53: Januses in cancer?

The transcription factor nuclear factor (erythroid-derived 2)-like 2, also known as NFE2L2 or NRF2, is a master regulator of the anti-oxidative stress response and positively controls the expression of a battery of anti-oxidative stress response proteins and enzymes implicated in detoxification and glutathione generation. Although its detoxifying activity is important in cancer prevention, it has recently been shown that cancer cells also exploit its protective functions to thrive and resist chemotherapy. NRF2 was also shown to the pentose phosphate pathway and glutaminolysis, which promotes purine synthesis for supporting rapid proliferation and glutathione for providing anti-oxidative stress protection. Evidence obtained from cancer patients and cell lines suggest that NRF2 is highly active in a variety of human cancers and is associated with aggressiveness. p53 is a tumor suppressor that also promotes an anti-oxidative stress metabolic program and glutaminolysis. Here we will discuss the similarities between NRF2 and p53 and review evidence that p53 might be exploited by cancer cells to gain protection against oxidative stress, as is the case for NRF2. We discuss findings of co-regulation between these transcription factors and propose possible therapeutic strategies that can be used for treatment of cancers that harbor WT p53 and express high levels of NRF2.