Extracellular iron diminishes anticancer effects of vitamin C: an in vitro study

Interaction studies of biliverdin-Cu complex formation using XANES, XRF, and DFT analyses and its effect on cytotoxicity in glioblastoma cell line (U251)

Cu2+ and biliverdin build complex (BV-Cu) that is stable in water at physiological pH and may develop in living systems. However, the interactions of BV-Cu with cells and even its structure are not fully understood. Herein we showed that BV-Cu complex was significantly more cytotoxic to a human cell line than equimolar Cu2+ and biliverdin. Micro-XRF-generated maps of elements showed that in contrast to Cu2+-treated cells which exhibited physiological compartmentalization of Cu, cells treated with BV-Cu had almost even distribution of Cu throughout the cytosol. XANES showed that the complex contains Cu1+ with distorted tetrahedral or square planar geometry. This implicates that the formation of the complex includes redox reaction between the metal ion and the ligand. As a result, the complex is nominally made of Cu1+ and BV radical cation. The redistribution of charge and spin densities between Cu2+ and tetrapyrrole ring during complex formation was also corroborated by DFT modelling. Cells exposed to BV-Cu were loaded with Cu that remained in 1+ form with altered local geometry than the complex. The cytotoxicity of the BV-Cu complex may come as a result of its interference with regular Cu transport and storage routes.

High dose of ascorbic acid induces selective cell growth inhibition and cell death in human gastric signet-ring cell carcinoma-derived NUGC-4 cells

Anticancer effects of high-dose vitamin C (VC) have been evaluated on many cancer cell lines, and its efficacy in clinical trials and in combination with anticancer drugs or radiation have been reported; however, its effect on gastric cancer and its mechanisms remain unclear. In the present study, the cell growth inhibitory/lethal effects of high-dose ascorbic acid (AsA), a reduced form of VC was examined on three gastric cancer cell lines. Of these, signet ring cell carcinoma NUGC-4 cells were the most sensitive, but the effects were small and limited in normal cells. Second, high-dose AsA was effective in NUGC-4 cells, whereas dehydroascorbic acid, an oxidized form of VC, was less effective. Third, high-dose AsA showed stronger cell growth inhibitory/lethal effects on floating cells than on adherent cells, and was effective even under hypoxic microenvironment conditions. A single 1-h treatment of high-dose AsA strongly inhibited cell growth, causing apoptosis-like cell death over 72 h after treatment, triggered by hydrogen peroxide generation, actin abnormality, DNA synthesis suppression, DNA damage induction, and ATP level decrease. The effects of high-dose AsA were inhibited either by adding or chelating iron ions, but was not affected via inhibiting AsA transport. Inhibition of glutathione synthesis enhanced the anticancer effects of high-dose AsA. These results indicate that a single high-dose of AsA induces cancer cell-selective, sustained cell growth inhibition and cell death, and these effects may be regulated by iron ion and/or intracellular oxidative stress levels in human gastric signet-ring cell carcinoma-derived NUGC-4 cells.

Polyphenol stability and bioavailability in cell culture medium: Challenges, limitations and future directions

Polyphenols are abundant natural plant micronutrients that commonly contribute to human health due to their anti-inflammatory, antioxidant, antiviral, anti-carcinogenic, anti-aging, anti-allergic, and other biological activities. Their therapeutic benefits mainly depend on the structure, stability, chemical interactions, and absorption, which ultimately affect the bioavailability of these compounds. The bioactivity of polyphenols is evaluated by in vitro and in vivo studies, sometimes yielding inconsistent results due to numerous differences between used models. Among the main differences is the production of reactive oxygen species (ROS) in cultured cell models, potentially leading to misinterpretation of the effects of polyphenolic compounds. Little attention is paid to the polyphenol stability in cell culture medium and the potential generation of artifacts due to their chemical instability. Stability tests of polyphenols are strongly advised to be performed in parallel with cell culture, to help avoid misleading conclusions. This review highlights the existing challenges with cell-based research, focusing on polyphenols' stability in the cell culture media. We also emphasize that new methods analyzing the molecular interactions of compounds with cell culture media supplements are essential to provide a comprehensive understanding of the polyphenols in in vitro models.

Analysis of High-Dose Ascorbate-Induced Cytotoxicity in Human Glioblastoma Cells and the Role of Dehydroascorbic Acid and Iron

Several studies have demonstrated, both in vitro and in animal models, the anti-tumor efficacy of high-dose ascorbate treatment against a variety of tumor entities, including glioblastoma, the most common and aggressive primary malignant brain tumor. The aim of this study was to investigate the effects of high-dose ascorbate as well as dehydroascorbic acid on human glioblastoma cell lines and to evaluate different treatment conditions for the combined administration of ascorbate with magnesium (Mg2+) and iron (Fe3+). Intracellular levels of reactive oxygen species and the induction of cell death following ascorbate treatment were also investigated. We demonstrated high cytotoxicity and antiproliferative efficacy of high-dose ascorbate in human glioblastoma cells, whereas much weaker effects were observed for dehydroascorbic acid. Ascorbate-induced cell death was independent of apoptosis. Both the reduction in cell viability and the ascorbate-induced generation of intracellular reactive oxygen species could be significantly increased by incubating the cells with Fe3+ before ascorbate treatment. This work demonstrates, for the first time, an increase in ascorbate-induced intracellular ROS formation and cytotoxicity in human glioblastoma cells by pre-treatment of the tumor cells with ferric iron, as well as caspase-3 independence of cell death induced by high-dose ascorbate. Instead, the cell death mechanism caused by high-dose ascorbate in glioblastoma cells shows evidence of ferroptosis. The results of the present work provide insights into the efficacy and mode of action of pharmacological ascorbate for the therapy of glioblastoma, as well as indications for possible approaches to increase the effectiveness of ascorbate treatment.

Redox-active vitamin C suppresses human osteosarcoma growth by triggering intracellular ROS-iron-calcium signaling crosstalk and mitochondrial dysfunction

Pharmacological vitamin C (VC) has gained attention for its pro-oxidant characteristics and selective ability to induce cancer cell death. However, defining its role in cancer has been challenging due to its complex redox properties. In this study, using a human osteosarcoma (OS) model, we show that the redox-active property of VC is critical for inducing non-apoptotic cancer cell death via intracellular reactive oxygen species (ROS)-iron-calcium crosstalk and mitochondrial dysfunction. In both 2D and 3D OS cell culture models, only the oxidizable form of VC demonstrated potent dose-dependent cytotoxicity, while non-oxidizable and oxidized VC derivatives had minimal effects. Live-cell imaging showed that only oxidizable VC caused a surge in cytotoxic ROS, dependent on iron rather than copper. Inhibitors of ferroptosis, a form of iron-dependent cell death, along with classical apoptosis inhibitors, were unable to completely counteract the cytotoxic effects induced by VC. Further pharmacological and genetic inhibition analyses showed that VC triggers calcium release through inositol 1,4,5-trisphosphate receptors (IP3Rs), leading to mitochondrial ROS production and eventual cell death. RNA sequencing revealed down-regulation of genes involved in the mitochondrial electron transport chain and oxidative phosphorylation upon pharmacological VC treatment. Consistently, high-dose VC reduced mitochondrial membrane potential, oxidative phosphorylation, and ATP levels, with ATP reconstitution rescuing VC-induced cytotoxicity. In vivo OS xenograft studies demonstrated reduced tumor growth with high-dose VC administration, concomitant with the altered expression of mitochondrial ATP synthase (MT-ATP). These findings emphasize VC's potential clinical utility in osteosarcoma treatment by inducing mitochondrial metabolic dysfunction through a vicious intracellular ROS-iron-calcium cycle.

HDAC inhibitors activate lipid peroxidation and ferroptosis in gastric cancer

Gastric cancer remains among the deadliest neoplasms worldwide, with limited therapeutic options. Since efficacies of targeted therapies are unsatisfactory, drugs with broader mechanisms of action rather than a single oncogene inhibition are needed. Preclinical studies have identified histone deacetylases (HDAC) as potential therapeutic targets in gastric cancer. However, the mechanism(s) of action of HDAC inhibitors (HDACi) are only partially understood. This is particularly true with regard to ferroptosis as an emerging concept of cell death. In a panel of gastric cancer cell lines with different molecular characteristics, tumor cell inhibitory effects of different HDACi were studied. Lipid peroxidation levels were measured and proteome analysis was performed for the in-depth characterization of molecular alterations upon HDAC inhibition. HDACi effects on important ferroptosis genes were validated on the mRNA and protein level. Upon HDACi treatment, lipid peroxidation was found increased in all cell lines. Class I HDACi (VK1, entinostat) showed the same toxicity profile as the pan-HDACi vorinostat. Proteome analysis revealed significant and concordant alterations in the expression of proteins related to ferroptosis induction. Key enzymes like ACSL4, POR or SLC7A11 showed distinct alterations in their expression patterns, providing an explanation for the increased lipid peroxidation. Results were also confirmed in primary human gastric cancer tissue cultures as a relevant ex vivo model. We identify the induction of ferroptosis as new mechanism of action of class I HDACi in gastric cancer. Notably, these findings were independent of the genetic background of the cell lines, thus introducing HDAC inhibition as a more general therapeutic principle.

Iron promotes glycolysis to drive colon tumorigenesis

Colorectal cancer (CRC) is the third most common cancer and is also the third leading cause of cancer-related death in the USA. Understanding the mechanisms of growth and progression of CRC is essential to improve treatment. Macronutrients such as glucose are energy source for a cell. Many tumor cells exhibit increased aerobic glycolysis. Increased tissue micronutrient iron levels in both mice and humans are also associated with increased colon tumorigenesis. However, if iron drives colon carcinogenesis via affecting glucose metabolism is still not clear. Here we found the intracellular glucose levels in tumor colonoids were significantly increased after iron treatment. 13C-labeled glucose flux analysis indicated that the levels of several labeled glycolytic products were significantly increased, whereas several tricarboxylic acid cycle intermediates were significantly decreased in colonoids after iron treatment. Mechanistic studies showed that iron upregulated the expression of glucose transporter 1 (GLUT1) and mediated an inhibition of the pyruvate dehydrogenase (PDH) complex function via directly binding with tankyrase and/or pyruvate dehydrogenase kinase (PDHK) 3. Pharmacological inhibition of GLUT1 or PDHK reactivated PDH complex function and reduced high iron diet-enhanced tumor formation. In conclusion, excess iron promotes glycolysis and colon tumor growth at least partly through the inhibition of the PDH complex function.

Magnetite nanoparticles as a kinetically favorable source of iron to enhance GBM response to chemoradiosensitization with pharmacological ascorbate

Ferumoxytol (FMX) is an FDA-approved magnetite (Fe3O4) nanoparticle used to treat iron deficiency anemia that can also be used as an MR imaging agent in patients that can't receive gadolinium. Pharmacological ascorbate (P-AscH-; IV delivery; plasma levels ≈ 20 mM) has shown promise as an adjuvant to standard of care chemo-radiotherapy in glioblastoma (GBM). Since ascorbate toxicity mediated by H2O2 is enhanced by Fe redox cycling, the current study determined if ascorbate catalyzed the release of ferrous iron (Fe2+) from FMX for enhancing GBM responses to chemo-radiotherapy. Ascorbate interacted with Fe3O4 in FMX to produce redox-active Fe2+ while simultaneously generating increased H2O2 fluxes, that selectively enhanced GBM cell killing (relative to normal human astrocytes) as opposed to a more catalytically active Fe complex (EDTA-Fe3+) in an H2O2 - dependent manner. In vivo, FMX was able to improve GBM xenograft tumor control when combined with pharmacological ascorbate and chemoradiation in U251 tumors that were unresponsive to pharmacological ascorbate therapy. These data support the hypothesis that FMX combined with P-AscH- represents a novel combined modality therapeutic approach to enhance cancer cell selective chemoradiosentization in the management of glioblastoma.

Relevant Membrane Transport Proteins as Possible Gatekeepers for Effective Pharmacological Ascorbate Treatment in Cancer

Despite the increasing number of newly diagnosed malignancies worldwide, therapeutic options for some tumor diseases are unfortunately still limited. Interestingly, preclinical but also some clinical data suggest that the administration of pharmacological ascorbate seems to respond well, especially in some aggressively growing tumor entities. The membrane transport and channel proteins are highly relevant for the use of pharmacological ascorbate in cancer therapy and are involved in the transfer of active substances such as ascorbate, hydrogen peroxide, and iron that predominantly must enter malignant cells to induce antiproliferative effects and especially ferroptosis. In this review, the relevant conveying proteins from cellular surfaces are presented as an integral part of the efficacy of pharmacological ascorbate, considering the already known genetic and functional features in tumor tissues. Accordingly, candidates for diagnostic markers and therapeutic targets are mentioned.

Selenium Modulates Cancer Cell Response to Pharmacologic Ascorbate

High-dose ascorbate (vitamin C) has shown promising anticancer activity. Two redox mechanisms have been proposed: hydrogen peroxide generation by ascorbate itself or glutathione depletion by dehydroascorbate (formed by ascorbate oxidation). Here we show that the metabolic effects and cytotoxicity of high-dose ascorbate in vitro result from hydrogen peroxide independently of dehydroascorbate. These effects were suppressed by selenium through antioxidant selenoenzymes including glutathione peroxidase 1 (GPX1) but not the classic ferroptosis-inhibiting selenoenzyme GPX4. Selenium-mediated protection from ascorbate was powered by NADPH from the pentose phosphate pathway. In vivo, dietary selenium deficiency resulted in significant enhancement of ascorbate activity against glioblastoma xenografts. These data establish selenoproteins as key mediators of cancer redox homeostasis. Cancer sensitivity to free radical-inducing therapies, including ascorbate, may depend on selenium, providing a dietary approach for improving their anticancer efficacy.

SIGNIFICANCE

Selenium restriction augments ascorbate efficacy and extends lifespan in a mouse xenograft model of glioblastoma, suggesting that targeting selenium-mediated antioxidant defenses merits clinical evaluation in combination with ascorbate and other pro-oxidant therapies.

Extracellular Matrix and Oxidative Stress Following Traumatic Spinal Cord Injury: Physiological and Pathophysiological Roles and Opportunities for Therapeutic Intervention

Significance: Traumatic spinal cord injury (SCI) causes significant disruption to neuronal, glial, vascular, and extracellular elements. The spinal cord extracellular matrix (ECM) comprises structural and communication proteins that are involved in reparative and regenerative processes after SCI. In the healthy spinal cord, the ECM helps maintain spinal cord homeostasis. After SCI, the damaged ECM limits plasticity and contributes to inflammation through the expression of damage-associated molecules such as proteoglycans. Recent Advances: Considerable insights have been gained by characterizing the origins of the gliotic and fibrotic scars, which not only reduce the spread of injury but also limit neuroregeneration. These properties likely limit the success of therapies used to treat patients with SCI. The ECM, which is a major contributor to the scars and normal physiological functions of the spinal cord, represents an exciting therapeutic target to enhance recovery post-SCI. Critical Issue: Various ECM-based preclinical therapies have been developed. These include disrupting scar components, inhibiting activity of ECM metalloproteinases, and maintaining iron homeostasis. Biomaterials have also been explored. However, the majority of these treatments have not experienced successful clinical translation. This could be due to the ECM and scars' polarizing roles. Future Directions: This review surveys the complexity involved in spinal ECM modifications, discusses new ECM-based combinatorial strategies, and explores the biomaterials evaluated in clinical trials, which hope to introduce new treatments that enhance recovery after SCI. These topics will incorporate oxidative species, which are both beneficial and harmful in reparative and regenerative processes after SCI, and not often assessed in pertinent literature. Antioxid. Redox Signal. 37, 184-207.

Exogenous iron impairs the anti-cancer effect of ascorbic acid both in vitro and in vivo

INTRODUCTION

The anti-cancer effect of high concentrations of ascorbic acid (AA) has been well established while its underlying mechanisms remain unclear. The association between iron and AA has attracted great attention but was still controversial due to the complicated roles of iron in tumors.

OBJECTIVES

Our study aims to explore the anti-cancer mechanisms of AA and the interaction between AA and iron in cancer.

METHODS

The MTT and ATP assays were used to evaluate the cytotoxicity of AA. Reactive oxygen species (ROS) generation, calcium (Ca²⁺), and lipid peroxidation were monitored with flow cytometry. Mitochondrial dysfunction was assessed by mitochondrial membrane potential (MMP) detection with JC-1 or tetramethylrhodamine methyl ester (TMRM) staining. Mitochondrial swelling was monitored with MitoTracker Green probe. FeSO₄ (Fe²⁺), FeCl₃ (Fe³⁺), Ferric ammonium citrate (Fe³⁺), hemin chloride (Fe³⁺) were used as an iron donor to investigate the effects of iron on AA's anti-tumor activity. The in vivo effects of AA and iron were analyzed in xenograft zebrafish and allograft mouse models.

RESULTS

High concentrations of AA exhibited cytotoxicity in a panel of cancer cells. AA triggered ROS-dependent non-apoptotic cell death. AA-induced cell death was essentially mediated by the accumulated intracellular Ca²⁺, which was partly originated from endoplasmic reticulum (ER). Surprisingly, exogenous iron could significantly reverse AA-induced ROS generation, Ca²⁺ overloaded, and cell death. Especially, the iron supplements significantly impaired the in vivo anti-tumor activity of AA.

CONCLUSIONS

Our study elucidated the protective roles of iron in ROS/Ca²⁺ mediated necrosis triggered by AA both in vitro and in vivo, which might shed novel insight into the anti-cancer mechanisms and provide clinical application strategies for AA in cancer treatment.

Starch-Based Carbon Dots for Nitrite and Sulfite Detection

Nitrite and sulfite play important roles in human health and environmental science, so it is desired to develop a facile and efficient method to evaluate NO2 - and SO3 2- concentrations. In this article, the use of green alternatives with the potential of multi-functionality has been synthesized to detect nitrite and sulfite based on fluorescent probe. The carbon dots (CDs) with starch as only raw materials show fluorescence turn "on-off-on" response towards NO2 - and SO3 2- with the limits of detection of 0.425 and 0.243 μМ, respectively. Once nitrite was present in the solution, the fluorescence of CDs was quenched rapidly due to the charge transfer. When sulfite was introduced, the quenching fluorescence of CDs was effectively recovered because of the redox reaction between NO2 - and SO3 2-, and thus providing a new way for NO2 - and SO3 2- detection. Owing to their excellent analytical characteristics and low cytotoxicity, the "on-off-on" sensor was successfully employed for intracellular bioimaging of NO2 - and SO3 2-.

Polymeric Iron Chelators Enhancing Pro-Oxidant Antitumor Efficacy of Vitamin C by Inhibiting the Extracellular Fenton Reaction

Intravenously injected high-dose vitamin C (VC) induces extracellular H₂O₂, which can penetrate into the tumor cells and suppress tumor growth. However, extracellular labile iron ions in the tumor decompose H₂O₂ via the Fenton reaction, limiting the therapeutic effect. In this regard, we recently developed a polymeric iron chelator that can inactivate the intratumoral labile iron ions. Here, we examined the effect of our polymeric iron chelator on the high-dose VC therapy in in vitro and in vivo. In the in vitro study, the polymeric iron chelator could inactivate the extracellular labile iron ions and prevent the unfavorable decomposition of VC-induced H₂O₂, augmenting pro-oxidative damage to DNA and inducing apoptosis in cultured cancer cells. Even in the in vivo study, the polymeric iron chelator significantly improved the antitumor effect of VC in subcutaneous DLD-1 and CT26 tumors in mice, while conventional iron chelators could not. This work indicates the importance of modulating tumor-associated iron ions in the high-dose VC therapy and should contribute to a better understanding of its mechanism.

High-dose intravenous vitamin C, a promising multi-targeting agent in the treatment of cancer

Mounting evidence indicates that vitamin C has the potential to be a potent anti-cancer agent when administered intravenously and in high doses (high-dose IVC). Early phase clinical trials have confirmed safety and indicated efficacy of IVC in eradicating tumour cells of various cancer types. In recent years, the multi-targeting effects of vitamin C were unravelled, demonstrating a role as cancer-specific, pro-oxidative cytotoxic agent, anti-cancer epigenetic regulator and immune modulator, reversing epithelial-to-mesenchymal transition, inhibiting hypoxia and oncogenic kinase signalling and boosting immune response. Moreover, high-dose IVC is powerful as an adjuvant treatment for cancer, acting synergistically with many standard (chemo-) therapies, as well as a method for mitigating the toxic side-effects of chemotherapy. Despite the rationale and ample evidence, strong clinical data and phase III studies are lacking. Therefore, there is a need for more extensive awareness of the use of this highly promising, non-toxic cancer treatment in the clinical setting. In this review, we provide an elaborate overview of pre-clinical and clinical studies using high-dose IVC as anti-cancer agent, as well as a detailed evaluation of the main known molecular mechanisms involved. A special focus is put on global molecular profiling studies in this respect. In addition, an outlook on future implications of high-dose vitamin C in cancer treatment is presented and recommendations for further research are discussed.

Machine Learning of Bacterial Transcriptomes Reveals Responses Underlying Differential Antibiotic Susceptibility

In vitro antibiotic susceptibility testing often fails to accurately predict in vivo drug efficacies, in part due to differences in the molecular composition between standardized bacteriologic media and physiological environments within the body. Here, we investigate the interrelationship between antibiotic susceptibility and medium composition in Escherichia coli K-12 MG1655 as contextualized through machine learning of transcriptomics data. Application of independent component analysis, a signal separation algorithm, shows that complex phenotypic changes induced by environmental conditions or antibiotic treatment are directly traced to the action of a few key transcriptional regulators, including RpoS, Fur, and Fnr. Integrating machine learning results with biochemical knowledge of transcription factor activation reveals medium-dependent shifts in respiration and iron availability that drive differential antibiotic susceptibility. By extension, the data generation and data analytics workflow used here can interrogate the regulatory state of a pathogen under any measured condition and can be applied to any strain or organism for which sufficient transcriptomics data are available.

IMPORTANCE Antibiotic resistance is an imminent threat to global health. Patient treatment regimens are often selected based on results from standardized antibiotic susceptibility testing (AST) in the clinical microbiology lab, but these in vitro tests frequently misclassify drug effectiveness due to their poor resemblance to actual host conditions. Prior attempts to understand the combined effects of drugs and media on antibiotic efficacy have focused on physiological measurements but have not linked treatment outcomes to transcriptional responses on a systems level. Here, application of machine learning to transcriptomics data identified medium-dependent responses in key regulators of bacterial iron uptake and respiratory activity. The analytical workflow presented here is scalable to additional organisms and conditions and could be used to improve clinical AST by identifying the key regulatory factors dictating antibiotic susceptibility.

New Insights into Red Blood Cell Microcytosis upon mTOR Inhibitor Administration

The aim of this study was to evaluate the effect of everolimus, a mammalian target of rapamycin (mTOR) inhibitor, on red blood cell parameters in the context of iron homeostasis in patients with tuberous sclerosis complex (TSC) and evaluate its effect on cell size in vitro. Everolimus has a significant impact on red blood cell parameters in patients with TSC. The most common alteration was microcytosis. The mean MCV value decreased by 9.2%, 12%, and 11.8% after 3, 6, and 12 months of everolimus treatment. The iron level declined during the first 3 months, and human soluble transferrin receptor concentration increased during 6 months of therapy. The size of K562 cells decreased when cultured in the presence of 5 μM everolimus by approximately 8%. The addition of hemin to the cell culture with 5 μM everolimus did not prevent any decrease in cell size. The stage of erythroid maturation did not affect the response to everolimus. Our results showed that the mTOR inhibitor everolimus caused red blood cell microcytosis in vivo and in vitro. This effect is not clearly related to a deficit of iron and erythroid maturation. This observation confirms that mTOR signaling plays a complex role in the control of cell size.

New promising developments for potential therapeutic applications of high-dose ascorbate as an anticancer drug

Vitamin C (ascorbate) is an essential dietary requirement, with fundamental redox, anti-oxidant functions at physiologic concentrations. Vitamin C is a cofactor for Fe²⁺ and 2-oxoglutarate-dependent dioxygenases, englobing large families of enzymes, including also epigenetic regulators of DNA and histone methylation. Importantly, vitamin C is involved in the control of the activity of TET (ten-eleven translocation) enzymes, key epigenetic regulators. For this spectrum of activities, often involving pathways deregulated in cancer cells, vitamin C possesses some pharmacologic activities that can be exploited in anticancer therapy. In particular, the capacity of pharmacological doses of vitamin C to target redox imbalance and to rescue deregulated epigenetic program observed in some cancer cells represents a consistent therapeutic potentiality. Several recent studies have identified some cancer subsets that could benefit from the pharmacological activities of vitamin C. The identification of these potentially responsive patients will help to carefully define controlled clinical trials aiming to evaluate the anticancer activity of Vitamin C.

Modulation of aminolevulinic acid-based photoinactivation efficacy by iron in vitro is cell type dependent

Iron availability to cells may be modified in the tumour microenvironment, which may be involved in treatment response. Iron availability affects the conversion of protoporphyrin IX to heme, which likely determines the efficacy of aminolevulinic acid-based photodynamic therapy (ALA-based PDT). We compared photoinactivation efficacy in three oesophageal cell lines in culture media differing in iron content, DMEM and RPMI 1640, and in RPMI 1640 supplemented with iron to understand the importance of iron presence for ALA-based PDT outcome. ALA-based PDT was more efficacious in DMEM than in RPMI 1640 in all tested cell lines. Consistently, the highest protoporphyrin IX fluorescence signals, indicating the highest level of protoporphyrin IX production, were detected from cell colonies incubated in DMEM compared to those incubated in RPMI 1640 irrespective of iron presence. Components in the culture media other than iron ions are likely to be responsible for the observed differences in two culture media. Nevertheless, iron supplementation to RPMI 1640 showed that the presence of ferric ions in the concentration range 0-8 mg/l affected ALA-based PDT efficacy in a cell type-dependent manner. In poorly differentiated carcinoma cells, the increased efficacy of ALA-induced photoinactivation in the presence of 0.1 mg/l of supplemented iron was found. At the same iron concentration, the slightly different mitochondrial potential at no modifications of the iron labile pool was observed. The efficacy of ALA-based PDT in vitro depends on the choice of culture medium and the presence of iron ions in culture medium depending on intrinsic properties of cells.

Labile iron affects pharmacological ascorbate-induced toxicity in osteosarcoma cell lines

Vitamin C and iron are both important nutrients for humans and involved in several physiological processes. The biological activities of vitamin C and iron are based on their abilities to accept or donate electrons. Although vitamin C is well known as an excellent electron donor in physiological conditions, it also has pro-oxidant properties, especially with catalytic metal iron. Cancer cells have a higher iron requirement than normal cells, which allows pharmacological ascorbate to kill cancer cells selectively. In this study, we demonstrated that the levels of H₂O₂ in cells were significantly raised after treated with pharmacological ascorbate, and intracellular labile iron could increase pharmacological ascorbate-mediated oxidative stress by Fenton reaction. Catalytic metal iron plays opposite roles in and outside cells. Intracellular excess labile iron improved ascorbate-induced toxicity, while the excess labile iron in the medium abolished ascorbate-induced toxicity. Fe³⁺ and Fe²⁺ have the same effect on ascorbate-induced toxicity, but Fe³⁺ chelator deferoxamine (DFO) has a profound inhibition effect than Fe²⁺ chelator 2,2'-bipyridyl (BIP) on ascorbate-induced toxicity. The influence of intracellular labile iron and ascorbate on the ferritin expression may cause selective sensitivity in osteosarcoma cell lines on pharmacological ascorbate. High iron requirement of many cancer cells facilitates pharmacological ascorbate on cancer treatment. In addition, increasing iron content in tumour tissue may be effective strategies to improve the effects of pharmacological ascorbate.

The Double-Faced Role of Nitric Oxide and Reactive Oxygen Species in Solid Tumors

Disturbed redox homeostasis represents a hallmark of cancer phenotypes, affecting cellular metabolism and redox signaling. Since reactive oxygen and nitrogen species (ROS/RNS) are involved in regulation of proliferation and apoptosis, they may play a double-faced role in cancer, entailing protumorigenic and tumor-suppressing effects in early and later stages, respectively. In addition, ROS and RNS impact the activity and communication of all tumor constituents, mediating their reprogramming from anti- to protumorigenic phenotypes, and vice versa. An important role in this dichotomic action is played by the variable amounts of O₂ in the tumor microenvironment, which dictates the ultimate outcome of the influence of ROS/RNS on carcinogenesis. Moreover, ROS/RNS levels remarkably influence the cancer response to therapy. The relevance of ROS/RNS signaling in solid tumors is witnessed by the emergence of novel targeted treatments of solid tumors with compounds that target ROS/RNS action and production, such as tyrosine kinase inhibitors and monoclonal antibodies, which might contribute to the complexity of redox regulation in cancer. Prospectively, the dual role of ROS/RNS in the different stages of tumorigenesis through different impact on oxidation and nitrosylation may also allow development of tailored diagnostic and therapeutic approaches.

Ferrous iron binding to epinephrine promotes the oxidation of iron and impedes activation of adrenergic receptors

Upon release in response to stress, epinephrine (Epi) may interact with labile iron pool in human plasma with potentially important (patho)physiological consequences. We have shown that Epi and Fe³⁺ build stable 1:1 high-spin bidentate complex at physiological pH, and that Epi does not undergo degradation in the presence of iron. However, the interactions of Epi with the more soluble Fe²⁺, and the impact of iron on biological activity of Epi are still not known. Herein we showed that Epi and Fe²⁺ build colorless complex which is stable under anaerobic conditions. In the presence of O₂, Epi promoted the oxidation of Fe²⁺ and the formation of Epi-Fe³⁺ complex. Cyclic voltammetry showed that mid-point potential of Epi-Fe²⁺ complex is very low (-582 mV vs. standard hydrogen electrode), which explains catalyzed oxidation of Fe²⁺. Next, we examined the impact of iron binding on biological performance of Epi using patch clamping in cell culture with constitutive expression of adrenergic receptors. Epi alone evoked an increase of outward currents, whereas Epi in the complex with Fe³⁺ did not. This implies that the binding of Epi to adrenergic receptors and their activation is prevented by the formation of complex with iron. Pro-oxidative activity of Epi-Fe²⁺ complex may represent a link between chronic stress and cardiovascular problems. On the other hand, labile iron could serve as a modulator of biological activity of ligands. Such interactions may be important in human pathologies that are related to iron overload or deficiency.

Pro- and Antioxidant Effects of Vitamin C in Cancer in correspondence to Its Dietary and Pharmacological Concentrations

Vitamin C is an antioxidant that may scavenge reactive oxygen species preventing DNA damage and other effects important in cancer transformation. Dietary vitamin C from natural sources is taken with other compounds affecting its bioavailability and biological effects. High pharmacological doses of vitamin C may induce prooxidant effects, detrimental for cancer cells. An oxidized form of vitamin C, dehydroascorbate, is transported through glucose transporters, and cancer cells switch from oxidative phosphorylation to glycolysis in energy production so an excess of vitamin C may limit glucose transport and ATP production resulting in energetic crisis and cell death. Vitamin C may change the metabolomic and epigenetic profiles of cancer cells, and activation of ten-eleven translocation (TET) proteins and downregulation of pluripotency factors by the vitamin may eradicate cancer stem cells. Metastasis, the main reason of cancer-related deaths, requires breakage of anatomical barriers containing collagen, whose synthesis is promoted by vitamin C. Vitamin C induces degradation of hypoxia-inducible factor, HIF-1, essential for the survival of tumor cells in hypoxic conditions. Dietary vitamin C may stimulate the immune system through activation of NK and T cells and monocytes. Pharmacological doses of vitamin C may inhibit cancer transformation in several pathways, but further studies are needed to address both mechanistic and clinical aspects of this effect.

18F-fluoromisonidazole positron emission tomography may be applicable in the evaluation of colorectal cancer liver metastasis

BACKGROUND

Positron emission tomography (PET) imaging is a non-invasive functional imaging method used to reflect tumor spatial information, and to provide biological characteristics of tumor progression. The aim of this study was to focus on the application of ¹⁸F-fluoromisonidazole (FMISO) PET quantitative parameter of maximum standardized uptake value (SUVmax) ratio to detect the liver metastatic potential of human colorectal cancer (CRC) in mice.

METHODS

Colorectal liver metastases (CRLM) xenograft models were established by injecting tumor cells (LoVo, HT29 and HCT116) into spleen of mice, tumor-bearing xenograft models were established by subcutaneously injecting tumor cells in the right left flank of mice. Wound healing assays were performed to examine the ability of cell migration in vitro. ¹⁸F-FMISO uptake in CRC cell lines was measured by cellular uptake assay. ¹⁸F-FMISO-based micro-PET imaging of CRLM and tumor-bearing mice was performed and quantified by tumor-to-liver SUVmax ratio. The correlation between the ¹⁸F-FMISO SUVmax ratio, liver metastases number, hypoxia-induced factor 1α (HIF-1α) and serum starvation-induced glucose transporter 1 (GLUT-1) was evaluated using Pearson correlation analysis.

RESULTS

Compared with HT29 and HCT116, LoVo-CRLM mice had significantly higher liver metastases ratio and shorter median survival time. LoVo cells exhibited stronger migration capacity and higher radiotracer uptake compared with HT29 and HCT116 in in vitro. Moreover, ¹⁸F-FMISO SUVmax ratio was significantly higher in both LoVo-CRLM model and LoVo-bearing tumor model compared to models established using HT29 and HCT116. In addition, Pearson correlation analysis revealed a significant correlation between ¹⁸F-FMISO SUVmax ratio of CRLM mice and number of liver metastases larger than 0.5 cm, as well as between ¹⁸F-FMISO SUVmax ratio and HIF-1α or GLUT-1 expression in tumor-bearing tissues.

CONCLUSIONS

¹⁸F-FMISO parameter of SUVmax ratio may provide useful tumor biological information in mice with CRLM, thus allowing for better prediction of CRLM and yielding useful radioactive markers for predicting liver metastasis potential in CRC.

Noninvasive evaluation of 18F-FDG/18F-FMISO-based Micro PET in monitoring hepatic metastasis of colorectal cancer

This study aimed to explore the application of two radiotracers (¹⁸F-fluorodeoxyglucose (FDG) and ¹⁸F-fluoromisonidazole (FMISO)) in monitoring hepatic metastases of human colorectal cancer (CRC). Mouse models of CRC hepatic metastases were established by implantation of the human CRC cell lines LoVo and HT29 by intrasplenic injection. Wound healing and Transwell assays were performed to examine cell migration and invasion abilities. Radiotracer-based cellular uptake in vitro and micro-positron emission tomography imaging of liver metastases in vivo were performed. The incidence of liver metastases in LoVo-xenografted mice was significantly higher than that in HT29-xenografted ones. The SUVmax/mean values of ¹⁸F-FMISO, but not ¹⁸F-FDG, in LoVo xenografts were significantly greater than in HT29 xenografts. In vitro, LoVo cells exhibited stronger metastatic potential and higher radiotracer uptake than HT29 cells. Mechanistically, the expression of HIF-1α and GLUT-1 in LoVo cells and LoVo tumor tissues was remarkably higher than in HT29 cells and tissues. Linear regression analysis demonstrated correlations between cellular ¹⁸F-FDG/¹⁸F-FMISO uptake and HIF-1α/GLUT-1 expression in vitro, as well as between ¹⁸F-FMISO SUVmax and GLUT-1 expression in vivo. ¹⁸F-FMISO uptake may serve as a potential biomarker for the detection of liver metastases in CRC, whereas its clinical use warrants validation.

Iron removal enhances vitamin C-induced apoptosis and growth inhibition of K-562 leukemic cells

Although vitamin C (VC) has recently garnered interest as an alternative cancer therapy, its clinical effects remain controversial. It was recently reported using in vitro prostate cancer cell lines that excess extracellular iron (EEI) diminishes anti-cancer effects of VC, promoting the decomposition of hydrogen peroxide (H₂O₂) generated by VC. Here we demonstrated that EEI diminished the inhibitory effect of VC on the survival of K562 human leukemic cells in vitro, by reducing the amount of H₂O₂ and abrogating the apoptosis pathways induced by VC. In vivo, in the presence of EEI, the growth inhibitory effect of VC on K562 cells was completely abrogated; in fact, VC enhanced K562 cell growth. Reduction of EEI restored the apoptosis-inducing effect of VC in vitro and enhanced the growth inhibitory effect of VC in vivo. Further studies are warranted to investigate whether the combination of VC and iron depletion has similar effects in various other leukemic or cancer cells against which VC has been effective in previous experimental studies.

GPx3 supports ovarian cancer progression by manipulating the extracellular redox environment

Ovarian cancer remains the most lethal gynecologic malignancy, and is primarily diagnosed at late stage when considerable metastasis has occurred in the peritoneal cavity. At late stage abdominal cavity ascites accumulation provides a tumor-supporting medium in which cancer cells gain access to growth factors and cytokines that promote survival and metastasis. However, little is known about the redox status of ascites, or whether antioxidant enzymes are required to support ovarian cancer survival during transcoelomic metastasis in this medium. Gene expression cluster analysis of antioxidant enzymes identified two distinct populations of high-grade serous adenocarcinomas (HGSA), the most common ovarian cancer subtype, which specifically separated into clusters based on glutathione peroxidase 3 (GPx3) expression. High GPx3 expression was associated with poorer overall patient survival and increased tumor stage. GPx3 is an extracellular glutathione peroxidase with reported dichotomous roles in cancer. To further examine a potential pro-tumorigenic role of GPx3 in HGSA, stable OVCAR3 GPx3 knock-down cell lines were generated using lentiviral shRNA constructs. Decreased GPx3 expression inhibited clonogenicity and anchorage-independent cell survival. Moreover, GPx3 was necessary for protecting cells from exogenous oxidant insult, as demonstrated by treatment with high dose ascorbate. This cytoprotective effect was shown to be due to GPx3-dependent removal of extracellular H₂O₂. Importantly, GPx3 was necessary for clonogenic survival when cells were cultured in patient-derived ascites fluid. While oxidation reduction potential (ORP) of malignant ascites was heterogeneous in our patient cohort, and correlated positively with ascites iron content, GPx3 was required for optimal survival regardless of ORP or iron content. Collectively, our data suggest that HGSA ovarian cancers cluster into distinct groups of high and low GPx3 expression. GPx3 is necessary for HGSA ovarian cancer cellular survival in the ascites tumor environment and protects against extracellular sources of oxidative stress, implicating GPx3 as an important adaptation for transcoelomic metastasis.

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High grade serous ovarian cancers cluster into distinct groups of antioxidant enzyme expression.

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High GPx3 expression is associated with decreased overall patient survival.

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GPx3 promotes cell viability by protecting cells from extracellular sources of oxidative stress.

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GPx3 enhances cell survival in ovarian cancer patient ascites fluid.

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Malignant ascites oxidation-reduction potential correlates with iron content.

Coordinate and redox interactions of epinephrine with ferric and ferrous iron at physiological pH

Coordinate and redox interactions of epinephrine (Epi) with iron at physiological pH are essential for understanding two very different phenomena – the detrimental effects of chronic stress on the cardiovascular system and the cross-linking of catecholamine-rich biopolymers and frameworks. Here we show that Epi and Fe³⁺ form stable high-spin complexes in the 1:1 or 3:1 stoichiometry, depending on the Epi/Fe³⁺ concentration ratio (low or high). Oxygen atoms on the catechol ring represent the sites of coordinate bond formation within physiologically relevant bidentate 1:1 complex. Redox properties of Epi are slightly impacted by Fe³⁺. On the other hand, Epi and Fe²⁺ form a complex that acts as a strong reducing agent, which leads to the production of hydrogen peroxide via O₂ reduction, and to a facilitated formation of the Epi–Fe³⁺ complexes. Epi is not oxidized in this process, i.e. Fe²⁺ is not an electron shuttle, but the electron donor. Epi-catalyzed oxidation of Fe²⁺ represents a plausible chemical basis of stress-related damage to heart cells. In addition, our results support the previous findings on the interactions of catecholamine moieties in polymers with iron and provide a novel strategy for improving the efficiency of cross-linking.

Mechanisms of redox interactions of bilirubin with copper and the effects of penicillamine

Toxic effects of unconjugated bilirubin (BR) in neonatal hyperbilirubinemia have been related to redox and/or coordinate interactions with Cu²⁺. However, the development and mechanisms of such interactions at physiological pH have not been resolved. This study shows that BR reduces Cu²⁺ to Cu¹⁺ in 1:1 stoichiometry. Apparently, BR undergoes degradation, i.e. BR and Cu²⁺ do not form stable complexes. The binding of Cu²⁺ to inorganic phosphates, liposomal phosphate groups, or to chelating drug penicillamine, impedes redox interactions with BR. Cu¹⁺ undergoes spontaneous oxidation by O₂ resulting in hydrogen peroxide accumulation and hydroxyl radical production. In relation to this, copper and BR induced synergistic oxidative/damaging effects on erythrocytes membrane, which were alleviated by penicillamine. The production of reactive oxygen species by BR and copper represents a plausible cause of BR toxic effects and cell damage in hyperbilirubinemia. Further examination of therapeutic potentials of copper chelators in the treatment of severe neonatal hyperbilirubinemia is needed.

Vitamin C-Conjugated Nanoparticle Protects Cells from Oxidative Stress at Low Doses but Induces Oxidative Stress and Cell Death at High Doses

Although the antioxidant property of vitamin C is well-known for protecting cells from oxidative stress, a recent study shows that it can also generate oxidative stress under a high intracellular concentration and induce cell death. However, poor chemical stability and low biological concentration (micromolar) of vitamin C restrict its function primarily as an antioxidant. Here, we report two different nanoparticle forms of vitamin C with its intact chemical stability, glucose-responsive release from nanoparticle, and efficient cell delivery in micro to millimolar concentrations. Nanoparticles are composed of silica-coated Au nanoparticles or lipophilic polyaspartic acid-based polymer micelles which are conjugated with vitamin C via phenylboronic acid. Surface chemistry of nanoparticles is optimized for an efficient cellular interaction/uptake and for cell delivery of vitamin C. We found that vitamin C protects cells from oxidative stress at micromolar concentrations, but at millimolar concentrations, it induces cell death by generating oxidative stress. In particular, high-dose vitamin C produces H₂O₂, disrupts the cellular redox balance, and induces cell death. This study highlights the concentration-dependent biological performance of vitamin C and the requirement of a high-dose cell delivery approach for enhanced therapeutic benefit.

Redox active metals and H2O2 mediate the increased efficacy of pharmacological ascorbate in combination with gemcitabine or radiation in pre-clinical sarcoma models

Soft tissue sarcomas are a histologically heterogeneous group of rare mesenchymal cancers for which treatment options leading to increased overall survival have not improved in over two decades. The current study shows that pharmacological ascorbate (systemic high dose vitamin C achieving ≥ 20 mM plasma levels) is a potentially efficacious and easily integrable addition to current standard of care treatment strategies in preclinical models of fibrosarcoma and liposarcoma both in vitro and in vivo. Furthermore, enhanced ascorbate-mediated toxicity and DNA damage in these sarcoma models were found to be dependent upon H₂O₂ and intracellular labile iron. Together, these data support the hypothesis that pharmacological ascorbate may represent an easily implementable and non-toxic addition to conventional sarcoma therapies based on taking advantage of fundamental differences in cancer cell oxidative metabolism.

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Ascorbate sensitizes sarcoma cells to radiation- or chemo-therapy by a mechanism involving redox active metal ions and H₂O₂.

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Pharmacological ascorbate in combination with radio-chemo-therapy decreases sarcoma disease burden in murine xenografts.

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Ascorbate-mediated DNA damage is dependent on intracellular redox active iron.

Mechanisms of anti-cancer effects of ascorbate: Cytotoxic activity and epigenetic modulation

Vitamin C (Vit C or Ascorbate) is essential for many fundamental biochemical processes. Vit C is an essential nutrient with redox functions at normal physiologic concentrations. The main physiologic function of this vitamin is related to its capacity to act as a co-factor for a large family of enzymes, collectively known as Fe and 2-oxoglutarate-dependent dioxygenases. It also modulates epigenetic gene expression through the control of TET enzymes activity. Vit C also has several biological properties allowing to restore the deregulated epigenetic response observed in many tumors. High-dose Vit C has been investigated as a treatment for cancer patients since the 1969. Pharmacologic ascorbate acts as a pro-drug for hydrogen peroxide formation (H₂O₂) and, through this mechanism, kills cancer cells. To achieve high in vivo concentrations, Ascorbate must be injected by i.v. route. Initial clinical studies of Ascorbate cancer treatment have provided encouraging results, not confirmed in subsequent studies. Recent clinical studies using i.v. injection of high-dose Ascorbate have renewed the interest in the field, showing that significant anti-tumor activity. Pre-clinical studies have led to identify tumors sensitive to Ascorbate that could potentially benefit from this treatment either through an epigenetic modulator effect or through tumor killing by oxidative stress.

Augmentation of intracellular iron using iron sucrose enhances the toxicity of pharmacological ascorbate in colon cancer cells

Pharmacological doses (> 1 mM) of ascorbate (a.k.a., vitamin C) have been shown to selectively kill cancer cells through a mechanism that is dependent on the generation of H₂O₂ at doses that are safely achievable in humans using intravenous administration. The process by which ascorbate oxidizes to form H₂O₂ is thought to be mediated catalytically by redox active metal ions such as iron (Fe). Because intravenous iron sucrose is often administered to colon cancer patients to help mitigate anemia, the current study assessed the ability of pharmacological ascorbate to kill colon cancer cells in the presence and absence of iron sucrose.

In vitro survival assays showed that 10 mM ascorbate exposure (2 h) clonogenically inactivated 40–80% of exponentially growing colon cancer cell lines (HCT116 and HT29). When the H₂O₂ scavenging enzyme, catalase, was added to the media, or conditionally over-expressed using a doxycycline inducible vector, the toxicity of pharmacological ascorbate was significantly blunted. When colon cancer cells were treated in the presence or absence of 250 µM iron sucrose, then rinsed, and treated with 10 mM ascorbate, the cells demonstrated increased levels of labile iron that resulted in significantly increased clonogenic cell killing, compared to pharmacological ascorbate alone. Interestingly, when colon cancer cells were treated with iron sucrose for 1 h and then 10 mM ascorbate was added to the media in the continued presence of iron sucrose, there was no enhancement of toxicity despite similar increases in intracellular labile iron. The combination of iron chelators, deferoxamine and diethylenetriaminepentaacetic acid, significantly inhibited the toxicity of either ascorbate alone or ascorbate following iron sucrose. These observations support the hypothesis that increasing intracellular labile iron pools, using iron sucrose, can be used to increase the toxicity of pharmacological ascorbate in human colon cancer cells by a mechanism involving increased generation of H₂O₂.

Apple pectin-derived oligosaccharides produce carbon dioxide radical anion in Fenton reaction and prevent growth of Escherichia coli and Staphylococcus aureus

Pectin is the main soluble fiber in apples or citruses. It may be fermented by gut microbiota to metabolites showing local intestinal and systemic effects. A wide range of beneficial effects of dietary pectin includes impacts on the redox milieu and microbiota profile. We prepared pectin-derived oligosaccharides (apple (APDO) and citrus) and polygalacturonic acid-derived oligosaccharides, using alkaline hydrolysis by hydrogen peroxide, and analyzed them by Fourier Transform Infrared spectrometry. Furthermore, we analyzed the effects of pectin-derived oligosaccharides on hydroxyl radical (HO)-generating Fenton reaction using electron paramagnetic resonance spin-trapping spectroscopy, and the effects on the growth of Escherichia coli and Staphylococcus aureus in the presence of dietary-relevant HO-generating system (iron+ascorbate). The oligosaccharides react with HO radical to produce carbon dioxide radical anion (CO₂^-). A comparative analysis showed that APDO has the most prominent bacteriostatic effect. This might be at least partially related to the higher capacity of APDO to produce CO₂^-, which specifically targets proteins and appears to have a longer lifetime and larger diffusion radius in biological systems compared to HO.

Impact of elemental iron on human spermatozoa and mouse embryonic development in a defined synthetic culture medium

There is a paucity of studies on effect of iron in embryo culture procedures. This study aims to ascertain the optimal, tolerance and toxic levels of iron in a protein-free embryo culture medium (PFM) to determine the effect of iron on embryonic development. The application of PFM in assisted reproductive technologies (ART) is intended to eliminate disease transmission and improve ART treatment outcome. The optimal, tolerance and toxic levels of iron on human spermatozoa and mouse embryos were determined by challenging them with different levels of iron (ferric iron; Fe⁺³). Human normozoospermic semen samples (n=24) and days 1-4 Quakenbush Special (Qs) mouse embryos (n=1160) were incubated in PFM supplemented with different concentrations of Fe⁺³ over different periods of time. 2.0μg/mL (35.8μM) of Fe⁺³ was the optimal level of Fe⁺³ for human spermatozoa with a tolerance range of 0.5-2μg/mL; whereas a level of 0.11μg/mL (2μM) of Fe⁺³ was the optimum for day 2 embryos. Levels of ferric iron at 0.11 to 2.8μg/mL appear to enhance spermatozoa motility, preserve its DNA integrity and possibly increase percentage of blastocysts developed but levels of ferric iron >16μg/mL is hazardous for both spermatozoa and embryos. In spite of beneficial effects of iron it is premature to recommend its supplementation in embryo culture media because of the known deleterious nature of iron and the paucity of toxicological data. Toxicological studies must be performed following which it can be decided whether it is safe to consider iron as a supplement in human embryo and spermatozoa culture media.

O2⋅- and H2O2-Mediated Disruption of Fe Metabolism Causes the Differential Susceptibility of NSCLC and GBM Cancer Cells to Pharmacological Ascorbate

Pharmacological ascorbate has been proposed as a potential anti-cancer agent when combined with radiation and chemotherapy. The anti-cancer effects of ascorbate are hypothesized to involve the autoxidation of ascorbate leading to increased steady-state levels of H2O2; however, the mechanism(s) for cancer cell-selective toxicity remain unknown. The current study shows that alterations in cancer cell mitochondrial oxidative metabolism resulting in increased levels of O2⋅- and H2O2 are capable of disrupting intracellular iron metabolism, thereby selectively sensitizing non-small-cell lung cancer (NSCLC) and glioblastoma (GBM) cells to ascorbate through pro-oxidant chemistry involving redox-active labile iron and H2O2. In addition, preclinical studies and clinical trials demonstrate the feasibility, selective toxicity, tolerability, and potential efficacy of pharmacological ascorbate in GBM and NSCLC therapy.

Ascorbic acid does not reduce the anticancer effect of radiotherapy

The present study hypothesized that the therapeutic use of ascorbic acid (AsA) in combination with radiation may reduce therapy-related side effects and increase the antitumor effects. The aim of the study was to examine the association between the scavenged activity of AsA and the biological anticancer effect of hydroxyl (OH) radicals generated by X-ray irradiation. Cell survival, DNA fragmentation of human leukemia HL60 cells and the amount of OH radicals were investigated following X-ray irradiation and AsA treatment. The number of living cells decreased, and DNA fragmentation increased at AsA concentrations >1 mM. Electron spin resonance spectra revealed that X-ray irradiation generated OH radicals, which were scavenged by AsA at concentrations >75 µM. The AsA concentration inside the cell was 75 µM when cells underwent extracellular treatment with 5 mM AsA, which significantly induced HL60 cell death even without irradiation. No increase in the number of viable HL60 cells was observed following AsA treatment with irradiation when compared to irradiation alone. In conclusion, the disappearance of the radiation anticancer effects with AsA treatment in combination with radiotherapy for cancer treatment is not a cause for concern.

Tumor cells have decreased ability to metabolize H2O2: Implications for pharmacological ascorbate in cancer therapy

Ascorbate (AscH⁻) functions as a versatile reducing agent. At pharmacological doses (P-AscH⁻; [plasma AscH⁻] ≥≈20 mM), achievable through intravenous delivery, oxidation of P-AscH⁻ can produce a high flux of H₂O₂ in tumors. Catalase is the major enzyme for detoxifying high concentrations of H₂O₂. We hypothesize that sensitivity of tumor cells to P-AscH⁻ compared to normal cells is due to their lower capacity to metabolize H₂O₂. Rate constants for removal of H₂O₂ (k_cell) and catalase activities were determined for 15 tumor and 10 normal cell lines of various tissue types. A differential in the capacity of cells to remove H₂O₂ was revealed, with the average k_cell for normal cells being twice that of tumor cells. The ED₅₀ (50% clonogenic survival) of P-AscH⁻ correlated directly with k_cell and catalase activity. Catalase activity could present a promising indicator of which tumors may respond to P-AscH⁻.

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Ascorbate oxidizes in cell culture medium to generate a flux of H₂O₂.

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The rate constants for removal of extracellular H₂O₂ are on average 2-fold higher in normal cells than in cancer cells.

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The ED₅₀ of high-dose ascorbate correlated with the ability of tumor cells to remove extracellular H₂O₂.

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The response to pharmacological ascorbate in murine-models of pancreatic cancer paralleled the in vitro results.

Disulfiram anti-cancer efficacy without copper overload is enhanced by extracellular H2O2 generation: antagonism by tetrathiomolybdate

Highlights

Background

Cu/Zn superoxide dismutases (SODs) like the extracellular SOD3 and cytoplasmic SOD1 regulate cell proliferation by generating hydrogen peroxide (H₂O₂). This pro-oxidant inactivates essential cysteine residues in protein tyrosine phosphatases (PTP) helping receptor tyrosine kinase activation by growth factor signaling, and further promoting downstream MEK/ERK linked cell proliferation. Disulfiram (DSF), currently in clinical cancer trials is activated by copper chelation, being potentially capable of diminishing the copper dependent activation of MEK1/2 and SOD1/SOD3 and promoting reactive oxygen species (ROS) toxicity. However, copper (Cu) overload may occur when co-administered with DSF, resulting in toxicity and mutagenicity against normal tissue, through generation of the hydroxyl radical (•OH) by the Fenton reaction.

Purpose

To investigate: a) whether sub-toxic DSF efficacy can be increased without Cu overload against human melanoma cells with unequal BRAF(V600E) mutant status and Her2-overexpressing SKBR3 breast cancer cells, by increasing H₂O₂from exogenous SOD; b) to compare the anti-tumor efficacy of DSF with that of another clinically used copper chelator, tetrathiomolybdate (TTM)

Results

a) without copper supplementation, exogenous SOD potentiated sub-toxic DSF toxicity antagonized by sub-toxic TTM or by the anti-oxidant N-acetylcysteine; b) exogenous glucose oxidase, another H₂O₂ generator resembled exogenous SOD in potentiating sub-toxic DSF.

Conclusions

potentiation of sub-lethal DSF toxicity by extracellular H₂O₂ against the human tumor cell lines investigated, only requires basal Cu and increased ROS production, being unrelated to non-specific or TTM copper chelator sequestration.

Significance

These findings emphasize the relevance of extracellular H₂O₂ as a novel mechanism to improve disulfiram anticancer effects minimizing copper toxicity.

Effect of cobalt(II) chloride hexahydrate on some human cancer cell lines

The present study investigates the anti-proliferative and apoptosis inducing mechanism of CoCl2·6H2O in PC-3 cancer cell line. Preliminary, three different forms of cobalt i.e., cobaltous (CoCl2·6H2O), macro-Co(II,III) oxide and nano-Co(II,III) oxide were screened for antiproliferative activity in PC-3 cell line. The CoCl2·6H2O being the most effective antiproliferative agent, hence it was further tested against lung (A549), prostrate (PC-3) and brain (IMR-32) cell lines. Human embryonic kidney cell line (293T) was used as a normal cell line to compare the toxicity of CoCl2·6H2O. The CoCl2·6H2O induced morphological and anatomical changes in PC-3 cancer cell which were studied using light, confocal and scanning electron microscopy. The lactate dehydrogenase was estimated which showed mild necrotic mode of cell death. The Annexin/PI staining confirmed the apoptotic mode of cell death in PC-3 cells. Further, production of reaction of reactive oxygen species and changes in mitochondrial membrane potential was also assessed spectrofluorimetrically. The cell cycle arrest was also investigated using flow cytometery. Finally, the caspase activity was estimated in CoCl2·6H2O treated PC-3 cancer cell line. Interestingly, it was found that CoCl2·6H2O induces more cell death in cancerous cells as compared to normal non-cancerous cells. These findings presented CoCl2·6H2O as potential antiproliferative agent.

Mitochondria-Targeted Antioxidants: Future Perspectives in Kidney Ischemia Reperfusion Injury

Kidney ischemia/reperfusion injury emerges in various clinical settings as a great problem complicating the course and outcome. Ischemia/reperfusion injury is still an unsolved puzzle with a great diversity of investigational approaches, putting the focus on oxidative stress and mitochondria. Mitochondria are both sources and targets of ROS. They participate in initiation and progression of kidney ischemia/reperfusion injury linking oxidative stress, inflammation, and cell death. The dependence of kidney proximal tubule cells on oxidative mitochondrial metabolism makes them particularly prone to harmful effects of mitochondrial damage. The administration of antioxidants has been used as a way to prevent and treat kidney ischemia/reperfusion injury for a long time. Recently a new method based on mitochondria-targeted antioxidants has become the focus of interest. Here we review the current status of results achieved in numerous studies investigating these novel compounds in ischemia/reperfusion injury which specifically target mitochondria such as MitoQ, Szeto-Schiller (SS) peptides (Bendavia), SkQ1 and SkQR1, and superoxide dismutase mimics. Based on the favorable results obtained in the studies that have examined myocardial ischemia/reperfusion injury, ongoing clinical trials investigate the efficacy of some novel therapeutics in preventing myocardial infarct. This also implies future strategies in preventing kidney ischemia/reperfusion injury.

What if cell culture media do not mimic in vivo redox settings?

Here, I address the topic of suitability for redox research of common settings in cell cultures. This is done through the prism of in vitro anticancer effects of vitamin C. Cell culture media show lower concentrations of iron and a higher level of oxygen compared to interstitial fluid. Such a setup promotes ascorbate-mediated production and accumulation of hydrogen peroxide, which efficiently kills a variety of cancer cell lines. However, the anticancer effects are annihilated if the iron level is corrected to mimic in vivo concentrations. It appears that the potential benefits of application of vitamin C in cancer treatment have been significantly overestimated. This might be true for other pro-oxidative agents as well, such as some (poly)phenols. We urgently need to establish medium formula and culture maintenance settings that are optimal for redox research.

Antitumor effect of pharmacologic ascorbate in the B16 murine melanoma model

Because 5-year survival rates for patients with metastatic melanoma remain below 25%, there is continued need for new therapeutic approaches. For some tumors, pharmacologic ascorbate treatment may have a beneficial antitumor effect and may work synergistically with standard chemotherapeutics. To investigate this possibility in melanoma, we examined the effect of pharmacologic ascorbate on B16-F10 cells. Murine models were employed to compare tumor size following treatment with ascorbate, and the chemotherapeutic agents dacarbazine or valproic acid, alone or in combination with ascorbate. Results indicated that nearly all melanoma cell lines were susceptible to ascorbate-mediated cytotoxicity. Compared to saline controls, pharmacologic ascorbate decreased tumor size in both C57BL/6 (P < 0.0001) and NOD-scid tumor bearing mice (P < 0.0001). Pharmacologic ascorbate was superior or equivalent to dacarbazine as an antitumor agent. Synergy was not apparent when ascorbate was combined with either dacarbazine or valproic acid; the latter combination may have additional toxicities. Pharmacologic ascorbate induced DNA damage in melanoma cells, as evidenced by increased phosphorylation of the histone variant, H2A.X. Differences were not evident in tumor samples from C57BL/6 mice treated with pharmacologic ascorbate compared to tumors from saline-treated controls. Together, these results suggest that pharmacologic ascorbate has a cytotoxic effect against melanoma that is largely independent of lymphocytic immune functions and that continued investigation of pharmacologic ascorbate in cancer treatment is warranted.

Role of labile iron in the toxicity of pharmacological ascorbate

Pharmacological ascorbate has been shown to induce toxicity in a wide range of cancer cell lines. Pharmacological ascorbate in animal models has shown promise for use in cancer treatment. At pharmacological concentrations the oxidation of ascorbate produces a high flux of H2O2 via the formation of ascorbate radical (Asc(•-)). The rate of oxidation of ascorbate is principally a function of the level of catalytically active metals. Iron in cell culture media contributes significantly to the rate of H2O2 generation. We hypothesized that increasing intracellular iron would enhance ascorbate-induced cytotoxicity and that iron chelators could modulate the catalytic efficiency with respect to ascorbate oxidation. Treatment of cells with the iron-chelators deferoxamine (DFO) or dipyridyl (DPD) in the presence of 2mM ascorbate decreased the flux of H2O2 generated by pharmacological ascorbate and reversed ascorbate-induced toxicity. Conversely, increasing the level of intracellular iron by preincubating cells with Fe-hydroxyquinoline (HQ) increased ascorbate toxicity and decreased clonogenic survival. These findings indicate that redox metal metals, e.g., Fe(3+)/Fe(2+), have an important role in ascorbate-induced cytotoxicity. Approaches that increase catalytic iron could potentially enhance the cytotoxicity of pharmacological ascorbate in vivo.

Molecular mechanisms of pharmacological doses of ascorbate on cancer cells

Intravenous application of high-dose ascorbate (vitamin C) has been used in complementary medicine since the 1970s to treat cancer patients. In recent years it became evident that high-dose ascorbate in the millimolar range bears selective cytotoxic effects on cancer cells in vitro and in vivo. This anticancer effect is dose dependent, catalyzed by serum components and mediated by reactive oxygen species and ascorbyl radicals, making ascorbate a pro-oxidative pro-drug that catalyzes hydrogen peroxide production in tissues instead of acting as a radical scavenger. It further depends on HIF-1 signaling and oxygen pressure, and shows a strong epigenetic signature (alteration of DNA-methylation and induction of tumor-suppressing microRNAs in cancer cells). The detailed understanding of ascorbate-induced antiproliferative molecular mechanisms warrants in-depth preclinical evaluation in cancer-bearing animal models for the optimization of an efficacious therapy regimen (e.g., combination with hyperbaric oxygen or O2-sensitizers) that subsequently need to be evaluated in clinical trials.