Inhibition of heme oxygenase-1 enhances anti-cancer effects of arsenic trioxide on glioma cells

Mechanisms of Cell Death Induced by Erastin in Human Ovarian Tumor Cells

Erastin (ER) induces cell death through the formation of reactive oxygen species (ROS), resulting in ferroptosis. Ferroptosis is characterized by an accumulation of ROS within the cell, leading to an iron-dependent oxidative damage-mediated cell death. ER-induced ferroptosis may have potential as an alternative for ovarian cancers that have become resistant due to the presence of Ras mutation or multi-drug resistance1 (MDR1) gene expression. We used K-Ras mutant human ovarian tumor OVCAR-8 and NCI/ADR-RES, P-glycoprotein-expressing cells, to study the mechanisms of ER-induced cell death. We used these cell lines as NCI/ADR-RES cells also overexpresses superoxide dismutase, catalase, glutathione peroxidase, and transferase compared to OVCAR-8 cells, leading to the detoxification of reactive oxygen species. We found that ER was similarly cytotoxic to both cells. Ferrostatin, an inhibitor of ferroptosis, reduced ER cytotoxicity. In contrast, RSL3 (RAS-Selective Ligand3), an inducer of ferroptosis, markedly enhanced ER cytotoxicity in both cells. More ROS was detected in OVCAR-8 cells than NCI/ADR-RES cells, causing more malondialdehyde (MDA) formation in OVCAR-8 cells than in NCI/ADR-RES cells. RSL3, which was more cytotoxic to NCI/ADR-RES cells, significantly enhanced MDA formation in both cells, suggesting that glutathione peroxidase 4 (GPX4) was involved in ER-mediated ferroptosis. ER treatment modulated several ferroptosis-related genes (e.g., CHAC1, GSR, and HMOX1/OX1) in both cells. Our study indicates that ER-induced ferroptotic cell death may be mediated similarly in both NCI/ADR-RES and OVCAR-8 cells. Additionally, our results indicate that ER is not a substrate of P-gp and that combinations of ER and RSL3 may hold promise as more effective treatment routes for ovarian cancers, including those that are resistant to other current therapeutic agents.

ROS regulation in gliomas: implications for treatment strategies

Gliomas are one of the most common primary malignant tumours of the central nervous system (CNS), of which glioblastomas (GBMs) are the most common and destructive type. The glioma tumour microenvironment (TME) has unique characteristics, such as hypoxia, the blood-brain barrier (BBB), reactive oxygen species (ROS) and tumour neovascularization. Therefore, the traditional treatment effect is limited. As cellular oxidative metabolites, ROS not only promote the occurrence and development of gliomas but also affect immune cells in the immune microenvironment. In contrast, either too high or too low ROS levels are detrimental to the survival of glioma cells, which indicates the threshold of ROS. Therefore, an in-depth understanding of the mechanisms of ROS production and scavenging, the threshold of ROS, and the role of ROS in the glioma TME can provide new methods and strategies for glioma treatment. Current methods to increase ROS include photodynamic therapy (PDT), sonodynamic therapy (SDT), and chemodynamic therapy (CDT), etc., and methods to eliminate ROS include the ingestion of antioxidants. Increasing/scavenging ROS is potentially applicable treatment, and further studies will help to provide more effective strategies for glioma treatment.

Ferroptosis-Mediated Cell Death Induced by NCX4040, The Non-Steroidal Nitric Oxide Donor, in Human Colorectal Cancer Cells: Implications in Therapy

Our recent studies show that the treatment of human ovarian tumor cells with NCX4040 results in significant depletions of cellular glutathione, the formation of reactive oxygen/nitrogen species and cell death. NCX4040 is also cytotoxic to several human colorectal cancer (CRC) cells in vitro and in vivo. Here, we examined the ferroptosis-dependent mechanism(s) of cytotoxicity of NCX4040 in HT-29 and K-RAS mutant HCT 116 colon cell lines. Ferroptosis is characterized by the accumulation of reactive oxygen species (ROS) within the cell, leading to an iron-dependent oxidative stress-mediated cell death. However, its relevance in the mechanism of NCX4040 cytotoxicity in CRCs is not known. We found that NCX4040 generates ROS in CRC cells without any depletion of cellular GSH. Combinations of NCX4040 with erastin (ER) or RSL3 (RAS-selective lethal 3), known inducers of ferroptosis, enhanced CRC death. In contrast, ferrostatin-1, an inhibitor of ferroptosis, significantly inhibited NCX4040-induced cell death. Treatment of CRC cells with NCX4040 resulted in the induction of lipid peroxidation in a dose- and time-dependent manner. NCX4040 treatment induced several genes related to ferroptosis (e.g., CHAC1, GPX4 and NOX4) in both cell lines. Metabolomic studies also indicated significant increases in both lipid and energy metabolism following the drug treatment in HT-29 and HCT 116 cells. These observations strongly suggest that NCX4040 causes the ferroptosis-mediated cell death of CRC cells. Furthermore, combinations of NCX4040 and ER or RSL3 may contribute significantly to the treatment of CRC, including those that are difficult to treat due to the presence of Ras mutations in the clinic. NCX4040-induced ferroptosis may also be a dynamic form of cell death for the treatment of other cancers.

Gene Expression Profiling Elucidates Cellular Responses to NCX4040 in Human Ovarian Tumor Cells: Implications in the Mechanisms of Action of NCX4040

The nitric oxide donor, NCX4040 is a non-steroidal anti-inflammatory-NO donor and has been shown to be extremely cytotoxic to a number of human tumors, including ovarian tumors cells. We have found that NCX4040 is cytotoxic against both OVCAR-8 and its adriamycin-selected OVCAR-8 variant (NCI/ADR-RES) tumor cell lines. While the mechanism of action of NCX4040 is not entirely clear, we as well as others have shown that NCX4040 generates reactive oxygen species (ROS) and induces DNA damage in tumor cells. Recently, we have reported that NCX4040 treatment resulted in a significant depletion of cellular glutathione, and formation of both reactive oxygen and nitrogen species (ROS/RNS), resulting in oxidative stress in these tumor cells. Furthermore, our results indicated that more ROS/RNS were generated in OVCAR-8 cells than in NCI/ADR-RES cells due to increased activities of superoxide dismutase (SOD), glutathione peroxidase and transferases expressed in NCI/ADR-RES cells. Further studies suggested that NCX4040-induced cell death may be mediated by peroxynitrite formed from NCX4040 in cells. In this study we used microarray analysis following NCX4040 treatment of both OVCAR-8 and its ADR-resistant variant to identify various molecular pathways involved in NCX4040-induced cell death. Here, we report that NCX4040 treatment resulted in the differential induction of oxidative stress genes, inflammatory response genes (TNF, IL-1, IL-6 and COX2), DNA damage response and MAP kinase response genes. A mechanism of tumor cell death is proposed based on our findings where oxidative stress is induced by NCX4040 from simultaneous induction of NOX4, TNF-α and CHAC1 in tumor cell death.

Molecular Mechanisms of Cytotoxicty of NCX4040, the Non-Steroidal Anti-Inflammatory NO-Donor, in Human Ovarian Cancer Cells

NCX4040, the non-steroidal anti-inflammatory-NO donor, is cytotoxic to several human tumors, including ovarian tumor cells. We have found that NCX4040 is also cytotoxic against both OVCAR-8 and its adriamycin resistant (NCI/ADR-RES) tumor cell lines. Here, we have examined mechanism(s) for the cytotoxicity of NCX4040 in OVCAR-8 and NCI/ADR-RES cell lines. We found that NCX4040 induced significant apoptosis in both cell lines. Furthermore, NCX4040 treatment caused significant depletion of cellular glutathione, causing oxidative stress due to the formation of reactive oxygen/nitrogen species (ROS/RNS). Significantly more ROS/RNS were detected in OVCAR-8 cells than in NCI/ADR-RES cells which may have resulted from increased activities of SOD, glutathione peroxidase and transferases expressed in NCI/ADR-RES cells. NCX4040 treatment resulted in the formation of double-strand DNA breaks in both cells; however, more of these DNA breaks were detected in OVCAR-8 cells. RT-PCR studies indicated that NCX4040-induced DNA damage was not repaired as efficiently in NCI/ADR-RES cells as in OVCAR-8 cells which may lead to a differential cell death. Pretreatment of OVCAR-8 cells with N-acetylcysteine (NAC) significantly decreased cytotoxicity of NCX4040 in OVCAR-8 cells; however, NAC had no effects on NCX4040 cytotoxicity in NCI/ADR-RES cells. In contrast, FeTPPS, a peroxynitrite scavenger, completely blocked NCX4040-induced cell death in both cells, suggesting that NCX4040-induced cell death could be mediated by peroxynitrite formed from NCX4040 following cellular metabolism.

Redox modulation by plant polyphenols targeting vitagenes for chemoprevention and therapy: Relevance to novel anti-cancer interventions and mini-brain organoid technology

The scientific community, recently, has focused notable attention on the chemopreventive and therapeutic effects of dietary polyphenols for human health. Emerging evidence demonstrates that polyphenols, flavonoids and vitamins counteract and neutralize genetic and environmental stressors, particularly oxidative stress and inflammatory process closely connected to cancer initiation, promotion and progression. Interestingly, polyphenols can exert antioxidant or pro-oxidant cytotoxic effects depending on their endogenous concentration. Notably, polyphenols at high dose act as pro-oxidants in a wide type of cancer cells by inhibiting Nrf2 pathway and the expression of antioxidant vitagenes, such as NAD(P)H-quinone oxidoreductase (NQO1), glutathione transferase (GT), GPx, heme oxygenase-1 (HO-1), sirtuin-1 (Sirt1) and thioredoxin (Trx) system which play an essential role in the metabolism of reactive oxygen species (ROS), detoxification of xenobiotics and inhibition of cancer progression, by inducing apoptosis and cell cycle arrest according to the hormesis approach. Importantly, mutagenesis of Nrf2 pathway can exacerbate its "dark side" role, representing a crucial event in the initiation stage of carcinogenesis. Herein, we review the hormetic effects of polyphenols and nanoincapsulated-polyphenols in chemoprevention and treatment of brain tumors via activation or inhibition of Nrf2/vitagenes to suppress carcinogenesis in the early stages, and thus inhibit its progression. Lastly, we discuss innovative preclinical approaches through mini-brain tumor organoids to study human carcinogenesis, from basic cancer research to clinical practice, as promising tools to recapitulate the arrangement of structural neuronal tissues and biological functions of the human brain, as well as test drug toxicity and drive personalized and precision medicine in brain cancer.

Arsenic trioxide as a novel anti-glioma drug: a review

Arsenic trioxide has shown a strong anti-tumor effect with little toxicity when used in the treatment of acute promyelocytic leukemia (APL). An effect on glioma has also been shown. Its mechanisms include regulation of apoptosis and autophagy; promotion of the intracellular production of reactive oxygen species, causing oxidative damage; and inhibition of tumor stem cells. However, glioma cells and tissues from other sources show different responses to arsenic trioxide. Researchers are working to enhance its efficacy in anti-glioma treatments and reducing any adverse reactions. Here, we review recent research on the efficacy and mechanisms of action of arsenic trioxide in the treatment of gliomas to provide guidance for future studies.

Heme Oxygenase-1 in Central Nervous System Malignancies

Central nervous system tumors are the most common pediatric solid tumors and account for 20–25% of all childhood malignancies. Several lines of evidence suggest that brain tumors show altered redox homeostasis that triggers the activation of various survival pathways, leading to disease progression and chemoresistance. Among these pathways, heme oxygenase-1 (HO-1) plays an important role. HO-1 catalyzes the enzymatic degradation of heme with the simultaneous release of carbon monoxide (CO), ferrous iron (Fe²⁺), and biliverdin. The biological effects of HO-1 in tumor cells have been shown to be cell-specific since, in some tumors, its upregulation promotes cell cycle arrest and cellular death, whereas, in other neoplasms, it is associated with tumor survival and progression. This review focuses on the role of HO-1 in central nervous system malignancies and the possibility of exploiting such a target to improve the outcome of well-established therapeutic regimens. Finally, several studies show that HO-1 overexpression is involved in the development and resistance of brain tumors to chemotherapy and radiotherapy, suggesting the use of HO-1 as an innovative therapeutic target to overcome drug resistance. The following keywords were used to search the literature related to this topic: nuclear factor erythroid 2 p45-related factor 2, heme oxygenase, neuroblastoma, medulloblastoma, meningioma, astrocytoma, oligodendroglioma, glioblastoma multiforme, and gliomas.

Fasting to enhance Cancer treatment in models: the next steps

Short-term fasting (STF) is a technique to reduce nutrient intake for a specific period. Since metabolism plays a pivotal role in tumor progression, it can be hypothesized that STF can improve the efficacy of chemotherapy. Recent studies have demonstrated the efficacy of STF in cell and animal tumor models. However, large-scale clinical trials must be conducted to verify the safety and effectiveness of these diets. In this review, we re-examine the concept of how metabolism affects pathophysiological pathways. Next, we provided a comprehensive discussion of the specific mechanisms of STF on tumor progression, derived through studies carried out with tumor models. There are currently at least four active clinical trials on fasting and cancer treatment. Based on these studies, we highlight the potential caveats of fasting in clinical applications, including the onset of metabolic syndrome and other metabolic complications during chemotherapy, with a particular focus on the regulation of the epithelial to mesenchymal pathway and cancer heterogeneity. We further discuss the advantages and disadvantages of the current state-of-art tumor models for assessing the impact of STF on cancer treatment. Finally, we explored upcoming fasting strategies that could complement existing chemotherapy and immunotherapy strategies to enable personalized medicine. Overall, these studies have the potential for breakthroughs in cancer management.

Heme Oxygenase-1 and Carbon Monoxide Regulate Growth and Progression in Glioblastoma Cells

In human glioma tumours, heme oxygenase-1 (HO-1) is overexpressed when compared with normal brain tissues and during oligodendroglioma progression. However, the molecular mechanisms mediated by HO-1 to promote glioblastoma remain unknown. We therefore aimed at investigating the effect of HO-1 expression and its selective enzymatic inhibition in two different cell lines (i.e. A172 and U87-MG). HO-1 was induced by hemin treatment (10 μM), and VP13/47 (100 μM) was used as a specific non-competitive inhibitor of HO-1 activity. Cell proliferation was measured by cell index measurement (xCelligence technology) and clonogenic assay, whereas cell migration was assessed by wound healing assay. Carbon monoxide-releasing molecules (CORMs) (i.e. CORM-3 and CORM-A1) were also used in a separate set of experiments to confirm the effect of HO-1 by-product in glioblastoma progression further. Our results were further validated using GSE4412 microarray dataset analysis and comparing biopsies overexpressing HO-1 with the rest of the cases. Our results showed that hemin was able to induce both HO-1 gene and protein expression in a cell-dependent manner being A172 more responsive to pharmacological upregulation of HO-1. Hemin, but not CORMs treatment, resulted in a significant increase of cell proliferation following 24 h of treatment as measured by increased cell index and colony formation capacity and such effect was abolished by VP13/47. Interestingly, both hemin and CORMs showed a significant effect on the wound healing assay also exhibiting cell specificity. Finally, our dataset analysis showed a positive correlation of HO-1 gene expression with ITGBI and ITGBII which are membrane receptors involved in cell adhesion, embryogenesis, tissue repair, immune response and metastatic diffusion of tumour cells. In conclusion, our data suggest that HO-1 and its by-product CO exhibit a cell-specific effect on various aspects of disease progression and are associated with a complex series of molecular mechanisms driving cell proliferation, survival and metastasis.

The Roles of NRF2 in Modulating Cellular Iron Homeostasis

SIGNIFICANCE

Iron and oxygen are intimately linked: iron is an essential nutrient utilized as a cofactor in enzymes for oxygen transport, oxidative phosphorylation, and metabolite oxidation. However, excess labile iron facilitates the formation of oxygen-derived free radicals capable of damaging biomolecules. Therefore, biological utilization of iron is a tightly regulated process. The nuclear factor (erythroid-derived 2)-like 2 (NRF2) transcription factor, which can respond to oxidative and electrophilic stress, regulates several genes involved in iron metabolism. Recent Advances: The bulk of NRF2 transcription factor research has focused on its roles in detoxification and cancer prevention. Recent works have identified that several genes involved in heme synthesis, hemoglobin catabolism, iron storage, and iron export are under the control of NRF2. Constitutive NRF2 activation and subsequent deregulation of iron metabolism have been implicated in cancer development: NRF2-mediated upregulation of the iron storage protein ferritin or heme oxygenase 1 can lead to enhanced proliferation and therapy resistance. Of note, NRF2 activation and alterations to iron signaling in cancers may hinder efforts to induce the iron-dependent cell death process known as ferroptosis.

CRITICAL ISSUES

Despite growing recognition of NRF2 as a modulator of iron signaling, exactly how iron metabolism is altered due to NRF2 activation in normal physiology and in pathologic conditions remains imprecise; moreover, the roles of NRF2-mediated iron signaling changes in disease progression are only beginning to be uncovered.

FUTURE DIRECTIONS

Further studies are necessary to connect NRF2 activation with physiological and pathological changes to iron signaling and oxidative stress. Antioxid. Redox Signal. 00, 000-000.

Gene expression profile induced by arsenic trioxide in chronic lymphocytic leukemia cells reveals a central role for heme oxygenase-1 in apoptosis and regulation of matrix metalloproteinase-9

CLL remains an incurable disease in spite of the many new compounds being tested. Arsenic trioxide (ATO) induces apoptosis in all CLL cell types and could constitute an efficient therapy. To further explore this, we have studied the gene expression profile induced by ATO in CLL cells. ATO modulated many genes, largely involved in oxidative stress, being HMOX1 the most upregulated gene, also induced at the protein level. ATO also increased MMP-9, as we previously observed, both at the mRNA and protein level. Using specific inhibitors, qPCR analyses, and gene silencing approaches we demonstrate that upregulation of MMP-9 by ATO involved activation of the p38 MAPK/AP-1 signaling pathway. Moreover, gene silencing HMOX1 or inhibiting HMOX1 activity enhanced p38 MAPK phosphorylation and c-jun expression/activation, resulting in transcriptional upregulation of MMP-9. Overexpression of HMOX1 or enhancement of its activity, had the opposite effect. Cell viability analyses upon modulation of HMOX1 expression or activity demonstrated that HMOX1 had a pro-apoptotic role and enhanced the cytotoxic effect of ATO in CLL cells. We have therefore identified a new mechanism in which HMOX1 plays a central role in the response of CLL cells to ATO and in the regulation of the anti-apoptotic protein MMP-9. Thus, HMOX1 arises as a new therapeutic target in CLL and the combination of HMOX1 modulators with ATO may constitute an efficient therapeutic strategy in CLL.

HO-1 Induction in Cancer Progression: A Matter of Cell Adaptation

The upregulation of heme oxygenase-1 (HO-1) is one of the most important mechanisms of cell adaptation to stress. Indeed, the redox sensitive transcription factor Nrf2 is the pivotal regulator of HO-1 induction. Through the antioxidant, antiapoptotic, and antinflammatory properties of its metabolic products, HO-1 plays a key role in healthy cells in maintaining redox homeostasis and in preventing carcinogenesis. Nevertheless, several lines of evidence have highlighted the role of HO-1 in cancer progression and its expression correlates with tumor growth, aggressiveness, metastatic and angiogenetic potential, resistance to therapy, tumor escape, and poor prognosis, even though a tumor- and tissue-specific activity has been observed. In this review, we summarize the current literature regarding the pro-tumorigenic role of HO-1 dependent tumor progression as a promising target in anticancer strategy.

Genetic Factors Affecting Intraoperative 5-aminolevulinic Acid-induced Fluorescence of Diffuse Gliomas

Background

In patients operated for malignant glioma, 5-aminolevulinic acid (5-ALA)-induced fluorescence guidance is useful. However, we occasionally experience instances of non-visible fluorescence despite a histopathological diagnosis of high-grade glioma. We sought to identify factors that influence the intraoperative visualization of gliomas by their 5-ALA-induced fluorescence.

Patients and methods

We reviewed data from 60 patients with astrocytic or oligodendroglial tumors who underwent tumor removal under 5-ALA-induced fluorescence guidance between January 2014 and December 2015. Their characteristics, preoperative magnetic resonance imaging (MRI) findings, histological diagnosis, and genetic profile were analyzed and univariate and multivariate statistical analyses were performed.

Results

In 42 patients (70%) we intraoperatively observed tumor 5-ALA fluorescence. They were 2 of 8 (25%) patients with World Health Organization (WHO) grade II, 9 of 17 (53%) with grade III, and 31 of 35 (89%) patients with grade IV gliomas. Univariate analysis revealed a statistically significant association between 5-ALA fluorescence and the isocitrate dehydrogenase 1 (IDH1) status, 1p19q loss of heterozygosity (LOH), the MIB-1 labeling index, and the tumor margin, -heterogeneity, and -contrast enhancement on MRI scans (p < 0.001, p = 0.003, p = 0.007, p = 0.046, p = 0.021, and p = 0.002, respectively). Multivariate analysis showed that the IDH1 status was the only independent, statistically significant factor related to 5-ALA fluorescence (p = 0.009).

Conclusions

This study identified the IDH1 status as the factor with the most influence on the 5-ALA fluorescence of diffuse gliomas.

Inhibition of heme oxygenase-1 enhances the chemosensitivity of laryngeal squamous cell cancer Hep-2 cells to cisplatin

It has been previously reported that cisplatin is a well-known anticancer drug being used against a wide range of malignancies including head and neck, ovarian and non-small cell lung carcinoma, and demonstrated its anticancer activity by reacting with DNA or changing cell structure, immune response, reactive oxygen species level (ROS). In this research we proved that cisplatin induced cell injuries and heme oxygenase-1 (HO-1) expression in laryngeal squamous cell cancer Hep-2 cells through ROS generation. The induction of HO-1 clearly protected Hep-2 cells from cisplatin-induced cell death and ROS reaction, and the inhibitor of HO-1 enhanced the cell death and ROS generation induced by cisplatin. Furthermore, the HO-1 expression induced by cisplatin was strongly inhibited by the knockdown of nuclear factor-erythroid-2-related factor-2 (Nrf-2), and the oxidative damages induced by cisplatin were significantly enhanced. Therefore, it may be concluded that the inhibition of HO-1 or the knockdown of Nrf-2 significantly enhanced cisplatin's anticancer effects on Hep-2 cells. In clinic, with the overexpression of HO-1 in laryngeal squamous cancer tissues, the combination of cisplatin with the inhibitor of HO-1 or Nrf-2 siRNA may act as a new method to the treatment of laryngeal squamous cancer.

Fasting-Mimicking Diet Reduces HO-1 to Promote T Cell-Mediated Tumor Cytotoxicity

Immune-based interventions are promising strategies to achieve long-term cancer-free survival. Fasting was previously shown to differentially sensitize tumors to chemotherapy while protecting normal cells, including hematopoietic stem and immune cells, from its toxic side effects. Here, we show that the combination of chemotherapy and a fasting-mimicking diet (FMD) increases the levels of bone marrow common lymphoid progenitor cells and cytotoxic CD8(+) tumor-infiltrating lymphocytes (TILs), leading to a major delay in breast cancer and melanoma progression. In breast tumors, this effect is partially mediated by the downregulation of the stress-responsive enzyme heme oxygenase-1 (HO-1). These data indicate that FMD cycles combined with chemotherapy can enhance T cell-dependent targeted killing of cancer cells both by stimulating the hematopoietic system and by enhancing CD8(+)-dependent tumor cytotoxicity.

Oncogenic potential of Nrf2 and its principal target protein heme oxygenase-1

Nuclear factor erythroid 2-related factor 2 (Nrf2) is an essential component of cellular defense against a vast variety of endogenous and exogenous insults, including oxidative stress. Nrf2 acts as a master switch in the circuits upregulating the expression of various stress-response proteins, especially heme oxygenase-1 (HO-1). Paradoxically, however, recent studies have demonstrated oncogenic functions of Nrf2 and its major target protein HO-1. Levels of Nrf2 and HO-1 are elevated in many different types of human malignancies, which may facilitate the remodeling of the tumor microenvironment making it advantageous for the autonomic growth of cancer cells, metastasis, angiogenesis, and tolerance to chemotherapeutic agents and radiation and photodynamic therapy. In this context, the cellular stress response or cytoprotective signaling mediated via the Nrf2-HO-1 axis is hijacked by cancer cells for their growth advantage and survival of anticancer treatment. Therefore, Nrf2 and HO-1 may represent potential therapeutic targets in the management of cancer. This review highlights the roles of Nrf2 and HO-1 in proliferation of cancer cells, their tolerance/resistance to anticancer treatments, and metastasis or angiogenesis in tumor progression.

The impact of arsenic trioxide and all-trans retinoic acid on p53 R273H-codon mutant glioblastoma

Glioblastoma (GBM) is the most common primary brain tumor in adults and demonstrates a 1-year median survival time. Codon-specific hotspot mutations of p53 result in constitutively active mutant p53, which promotes aberrant proliferation, anti-apoptosis, and cell cycle checkpoint failure in GBM. Recently identified CD133(+) cancer stem cell populations (CSC) within GBM also confer therapeutic resistance. We studied targeted therapy in a codon-specific p53 mutant (R273H) created by site-directed mutagenesis in U87MG. The effects of arsenic trioxide (ATO, 1 μM) and all-trans retinoic acid (ATRA, 10 μM), possible targeted treatments of CSCs, were investigated in U87MG neurospheres. The results showed that U87-p53(R273H) cells generated more rapid neurosphere growth than U87-p53(wt) but inhibition of neurosphere proliferation was seen with both ATO and ATRA. U87-p53(R273H) neurospheres showed resistance to differentiation into glial cells and neuronal cells with ATO and ATRA exposure. ATO was able to generate apoptosis at high doses and proliferation of U87-p53(wt) and U87-p53(R273H) cells was reduced with ATO and ATRA in a dose-dependent manner. Elevated pERK1/2 and p53 expression was seen in U87-p53(R273H) neurospheres, which could be reduced with ATO and ATRA treatment. Additionally, differential responses in pERK1/2 were seen with ATO treatment in neurospheres and non-neurosphere cells. In conclusion, codon-specific mutant p53 conferred a more aggressive phenotype to our CSC model. However, ATO and ATRA could potently suppress CSC properties in vitro and may support further clinical investigation of these agents.

Redox control of leukemia: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species (ROS) play both positive and negative roles in the proliferation and survival of a cell. This dual nature has been exploited by leukemia cells to promote growth, survival, and genomic instability-some of the hallmarks of the cancer phenotype. In addition to altered ROS levels, many antioxidants are dysregulated in leukemia cells. Together, the production of ROS and the expression and activity of antioxidant enzymes make up the primary redox control of leukemia cells. By manipulating this system, leukemia cells gain proliferative and survival advantages, even in the face of therapeutic insults. Standard treatment options have improved leukemia patient survival rates in recent years, although relapse and the development of resistance are persistent challenges. Therapies targeting the redox environment show promise for these cases. This review highlights the molecular mechanisms that control the redox milieu of leukemia cells. In particular, ROS production by the mitochondrial electron transport chain, NADPH oxidase, xanthine oxidoreductase, and cytochrome P450 will be addressed. Expression and activation of antioxidant enzymes such as superoxide dismutase, catalase, heme oxygenase, glutathione, thioredoxin, and peroxiredoxin are perturbed in leukemia cells, and the functional consequences of these molecular alterations will be described. Lastly, we delve into how these pathways can be potentially exploited therapeutically to improve treatment regimens and promote better outcomes for leukemia patients.

Arsenic trioxide depletes cancer stem-like cells and inhibits repopulation of neurosphere derived from glioblastoma by downregulation of Notch pathway

Notch signaling has been demonstrated to have a central role in cancer stem-like cells (CSLCs) in glioblastoma multiforme (GBM). We have recently demonstrated the inhibitory effect of arsenic trioxide (ATO) on CSLCs in glioblastoma cell lines. In this study we used neurosphere recovery assay that measured neurosphere formation at three time points to assess the capacity of the culture to repopulate after ATO treatment. Our results provided strong evidence that ATO depleted CSLCs in GBM, and inhibited neurosphere recovery and secondary neurosphere formation. ATO inhibited the phosphorylation and activation of AKT and STAT3 through Notch signaling blockade. These data show that the ATO is a promising new approach to decrease glioblastoma proliferation and recurrence by downregulation of Notch pathway.

A phase I trial of arsenic trioxide chemoradiotherapy for infiltrating astrocytomas of childhood

BACKGROUND

Arsenic trioxide (ATO) has demonstrated preclinical evidence of activity in the treatment of infiltrating astrocytomas.

METHODS

We conducted a phase I trial of ATO given concomitantly with radiation therapy in children with newly diagnosed anaplastic astrocytoma, glioblastoma, or diffuse intrinsic pontine glioma. Eligible patients received a fixed daily dose of 0.15 mg/kg of ATO once a week, with each subsequent cohort of patients receiving an additional dose per week up to a planned frequency of ATO administration 5 days per week as tolerated. Twenty-four children were enrolled and 21 children were evaluable.

RESULTS

ATO was well tolerated throughout the entire dose escalation, resulting in confirmation of safety when administered 5 days per week during irradiation.

CONCLUSIONS

The recommended dose of ATO during conventional irradiation is 0.15 mg/kg given on a daily basis with each fraction of radiation therapy administered.

Arsenic-mediated activation of the Nrf2-Keap1 antioxidant pathway

Arsenic is present in the environment and has become a worldwide health concern due to its toxicity and carcinogenicity. However, the specific mechanism(s) by which arsenic elicits its toxic effects has yet to be fully elucidated. The transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) has been recognized as the master regulator of a cellular defense mechanism against toxic insults. This review highlights studies demonstrating that arsenic activates the Nrf2-Keap1 antioxidant pathway by a distinct mechanism from that of natural compounds such as sulforaphane (SF) found in broccoli sprouts or tert-butylhyrdoquinone (tBHQ), a natural antioxidant commonly used as a food preservative. Evidence also suggests that arsenic prolongs Nrf2 activation and may mimic constitutive activation of Nrf2, which has been found in several human cancers due to disruption of the Nrf2-Keap1 axis. The current literature strongly suggests that activation of Nrf2 by arsenic potentially contributes to, rather than protects against, arsenic toxicity and carcinogenicity. The mechanism(s) by which known Nrf2 activators, such as the natural chemopreventive compounds SF and lipoic acid, protect against the deleterious effects caused by arsenic will also be discussed. These findings will provide insight to further understand how arsenic promotes a prolonged Nrf2 response, which will lead to the identification of novel molecular markers and development of rational therapies for the prevention or intervention of arsenic-induced diseases. The National Institute of Environmental Health Science (NIEHS) Outstanding New Environmental Scientist (ONES) award has provided the opportunity to review the progress both in the fields of arsenic toxicology and Nrf2 biology. Much of the funding has led to (1) the novel discovery that arsenic activates the Nrf2 pathway by a mechanism different to that of other Nrf2 activators, such as sulforaphane and tert-butylhydroquinone, (2) activation of Nrf2 by chemopreventive compounds protects against arsenic toxicity and carcinogenicity both in vitro and in vivo, (3) constitutive activation of Nrf2 by disrupting Keap1-mediated negative regulation contributes to cancer and chemoresistance, (4) p62-mediated sequestration of Keap1 activates the Nrf2 pathway, and (5) arsenic-mediated Nrf2 activation may be through a p62-dependent mechanism. All of these findings have been published and are discussed in this review. This award has laid the foundation for my laboratory to further investigate the molecular mechanism(s) that regulate the Nrf2 pathway and how it may play an integral role in arsenic toxicity. Moreover, understanding the biology behind arsenic toxicity and carcinogenicity will help in the discovery of potential strategies to prevent or control arsenic-mediated adverse effects.

An effective strategy for increasing the radiosensitivity of Human lung Cancer cells by blocking Nrf2-dependent antioxidant responses

Radiotherapy and chemotherapeutic agents can effectively induce apoptosis through generation of reactive oxygen species (ROS). Cancer cells frequently express high levels of ROS-scavenging enzymes, which confer resistance to ROS-mediated cell death. Keap1 (Kelch-like ECH-associated protein 1) sequesters and promotes the degradation of the antioxidant response element-binding transcription factor Nrf2 (nuclear factor erythroid-2-related factor 2). In non-small-cell lung cancer (NSCLC) cell lines and NSCLC patients, Keap1 is often present as a biallelic mutant that results in constitutive activation of Nrf2 function, which contributes to cytoprotection against oxidative stress and xenobiotics. To identify small molecules that inhibit antioxidant responses and increase apoptotic death after radiotherapy, we screened a chemical library containing 8000 synthetic compounds using a cell-based luciferase assay system. 4-(2-Cyclohexylethoxy)aniline (IM3829) inhibited the increase in Nrf2-binding activity and expression of the Nrf2 target genes induced by treatment with tertiary butylhydroquinone or radiation. Combined treatment with IM3829 and radiation significantly inhibited clonogenic survival of H1299, A549, and H460 lung cancer cells. IM3829 significantly increased ROS accumulation in irradiated cells compared with cells exposed to radiation alone and led to apoptotic cell death, as confirmed by caspase-3 and PARP cleavage. In mice bearing H1299 or A549 lung cancer xenografts, IM3829 together with radiation inhibited tumor growth more effectively than radiation alone. Our findings suggest that IM3829 could be a promising radiosensitizer in lung cancer patients, particularly those with high expression of Nrf2.