Moles of a Substance per Cell Is a Highly Informative Dosing Metric in Cell Culture

Effect of Selected Antioxidants on the In Vitro Aging of Human Fibroblasts

The modification of the replicative lifespan (RLS) of fibroblasts is of interest both from a knowledge point of view and for the attenuation of skin aging. The effect of six antioxidants at a concentration of 1 μM on the replicative lifespan of human dermal fibroblasts was studied. The nitroxide 4-hydroxy-TEMPO (TEMPOL), ergothioneine, and Trolox extended the replicative lifespan (RLS) (40 ± 1 population doublings (PD)) by 7 ± 2, 4 ± 1, and 3 ± 1 PD and lowered the expression of p21 at late passages. Coumaric acid, curcumin and resveratrol did not affect the RLS . The level of reactive oxygen species (ROS) was decreased or not affected by the antioxidants although TEMPOL and coumaric acid decreased the level of glutathione. Only ergothioneine and resveratrol decreased the level of protein carbonylation. The antioxidants that could prolong the RLS elevated the mitochondrial membrane potential. Protecting the activity of mitochondria seems to be important for maintaining the replicative capacity of fibroblasts.

HPLC method for the determination of thymoquinone in growth cell medium

BACKGROUND

Preclinical drug testing requires in vitro and in vivo assessments that are vital for studying drug pharmacokinetics and toxicity. Distinct factors that play an important role in drug screening, such as hydrophobicity, solubility of the substance and serum protein binding can be challenging by inducing result inconsistencies. Hence, establishing accurate methods to quantify drug concentrations in cell cultures becomes pivotal for reliable and reproducible results important for in vivo dosing predictions.

OBJECTIVE

This research focuses on developing an optimized analytical approach via high-pressure liquid chromatography (HPLC) to determine thymoquinone (TQ) levels in monolayer cell cultures.

METHODS

The method's validation adheres to the International Council for Harmonisation (ICH) guideline M10, ensuring its acceptance and applicability. Using an HPLC system with a Diode Array Detector (DAD), the study fine-tuned various parameters to achieve an efficient separation of TQ. Validation covered specificity, sensitivity, matrix effects, linearity, precision, and accuracy, alongside assessing TQ stability in RPMI-1640 medium.

RESULTS

The HPLC method exhibited remarkable TQ specificity, free from interfering peaks at the analyte retention. Sensitivity analysis at the lower limit of quantification (LLOQ) revealed 5.68% %CV and 98.37% % mean accuracy. Matrix effect evaluation showcased accuracy within 85-115%. Linearity spanned in the concentration range of 2-10 μM with a correlation coefficient (r2) of 0.9993. Precision and accuracy were aligned with acceptance criteria. The proposed method was found to be greener in terms of usage of persistent, bioaccumulative, and toxic chemicals and solvents, corrosive samples, and waste production.

CONCLUSION

The developed HPLC-DAD method emerges as specific, accurate, sensitive, and reliable for TQ determination in cell cultures. It ensures robust TQ quantification, enhancing precise in vitro assessments and dependable dosing predictions for in vivo studies. Further research is advocated to investigate TQ's stability across diverse environmental conditions.

Stability of aqueous solutions of ascorbate for basic research and for intravenous administration

Ascorbate (vitamin C) can rapidly oxidize in many near-neutral pH, aqueous solutions. We report on the stability of ascorbate solutions prepared for infusion into patients using standard pharmacy protocols, for example, 75 g of ascorbate/L in water for infusion. The concentration of ascorbate was monitored for changes over time using direct UV-Vis spectroscopy. The pH of the solution was about 5.7 with no significant change over 24 h. There was only an approximate loss of 1% per day over the first 3 days of storage. This information allows decisions on how far ahead of need such preparations can be made. We also provide laboratory approaches to minimize or control the rate of oxidation of ascorbate solutions for use in chemical and biochemical studies as well as preclinical animal studies. The goal is to have the amount of ascorbate intended to be used in experiments be the actual amount available.

Hydrogen Peroxide Mediates Pharmacological Ascorbate Induced Radio-Sensitization of Pancreatic Cancer Cells by Enhancing G2-accumulation and Reducing Cyclin B1 Protein Levels

Pharmacological ascorbate (P-AscH-, high dose, intravenous vitamin C) preferentially sensitizes human pancreas ductal adenocarcinoma (PDAC) cells to radiation-induced toxicity compared to non-tumorigenic epithelial cells. Radiation-induced G2-checkpoint activation contributes to the resistance of cancer cells to DNA damage induced toxicity. We hypothesized that P-AscH- induced radio-sensitization of PDAC cells is mediated by perturbations in the radiation induced activation of the G2-checkpoint pathway. Both non-tumorigenic pancreatic ductal epithelial and PDAC cells display decreased clonogenic survival and increased doubling times after radiation treatment. In contrast, the addition of P-AscH- to radiation increases clonogenic survival and decreases the doubling time of non-tumorigenic epithelial cells but decreasing clonogenic survival and increasing the doubling time of PDAC cells. Results from the mitotic index and propidium iodide assays showed that while the P-AscH- treatments did not affect radiation-induced G2-checkpoint activation, it enhanced G2-accumulation. The addition of catalase reverses the increases in G2-accumulation, indicating a peroxide-mediated mechanism. In addition, P-AscH- treatment of PDAC cells suppresses radiation-induced accumulation of cyclin B1 protein levels. Both translational and post-translational pathways appear to regulate cyclin B1 protein levels after the combination treatment of PDAC cells with P-AscH- and radiation. The protein changes seen are reversed by the addition of catalase suggesting that hydrogen peroxide mediates P-AscH- induced radiation sensitization of PDAC cells by enhancing G2-accumulation and reducing cyclin B1 protein levels.

Pharmacological Ascorbate Elicits Anti-Cancer Activities against Non-Small Cell Lung Cancer through Hydrogen-Peroxide-Induced-DNA-Damage

Non-small cell lung cancer (NSCLC) poses a significant global health burden with unsatisfactory survival rates, despite advancements in diagnostic and therapeutic modalities. Novel therapeutic approaches are urgently required to improve patient outcomes. Pharmacological ascorbate (P-AscH-; ascorbate at millimolar concentration in plasma) emerged as a potential candidate for cancer therapy for recent decades. In this present study, we explore the anti-cancer effects of P-AscH- on NSCLC and elucidate its underlying mechanisms. P-AscH- treatment induces formation of cellular oxidative distress; disrupts cellular bioenergetics; and leads to induction of apoptotic cell death and ultimately reduction in clonogenic survival. Remarkably, DNA and DNA damage response machineries are identified as vulnerable targets for P-AscH- in NSCLC therapy. Treatments with P-AscH- increase the formation of DNA damage and replication stress markers while inducing mislocalization of DNA repair machineries. The cytotoxic and genotoxic effects of P-AscH- on NSCLC were reversed by co-treatment with catalase, highlighting the roles of extracellular hydrogen peroxide in anti-cancer activities of P-AscH-. The data from this current research advance our understanding of P-AscH- in cancer treatment and support its potential clinical use as a therapeutic option for NSCLC therapy.

Pharmacologic Ascorbate and DNMT Inhibitors Increase DUOX Expression and Peroxide-Mediated Toxicity in Pancreatic Cancer

Recent studies have demonstrated an important role for vitamin C in the epigenetic regulation of cancer-related genes via DNA demethylation by the ten-eleven translocation (TET) methylcytosine dioxygenase enzymes. DNA methyltransferase (DNMT) reverses this, increasing DNA methylation and decreasing gene expression. Dual oxidase (DUOX) enzymes produce hydrogen peroxide (H2O2) in normal pancreatic tissue but are silenced in pancreatic cancer (PDAC). Treatment of PDAC with pharmacologic ascorbate (P-AscH-, intravenous, high dose vitamin C) increases DUOX expression. We hypothesized that inhibiting DNMT may act synergistically with P-AscH- to further increase DUOX expression and cytotoxicity of PDAC. PDAC cells demonstrated dose-dependent increases in DUOX mRNA and protein expression when treated with DNMT inhibitors. PDAC cells treated with P-AscH- + DNMT inhibitors demonstrated increased DUOX expression, increased intracellular oxidation, and increased cytotoxicity in vitro and in vivo compared to either treatment alone. These findings suggest a potential therapeutic, epigenetic mechanism to treat PDAC.

The role of mitochondria in pharmacological ascorbate-induced toxicity

At pharmacological levels, ascorbate (P-AscH^-) acts as a pro-oxidant by generating H₂O₂, depleting ATP in sensitive cells leading to cell death. The aim of this study was to determine the role of ATP production by oxidative phosphorylation or glycolysis in mechanisms of resistance to P-AscH^-induced cell death. Pancreatic cancer cells were used to generate ρ⁰ cells by mitochondrial overexpression of the Y147A mutant uracil-N-glycosylase or Herpes Simplex Virus protein. The ρ⁰ phenotype was confirmed by probing for mitochondrial DNA, mitochondrial DNA-encoded cytochrome c oxidase subunit 2, and monitoring the rate of oxygen consumption. In ρ⁰ cells, glycolysis accounted for 100% of ATP production as there was no mitochondrial oxygen consumption. Even though the activities of H₂O₂-removing antioxidant enzymes were similar in both the parental and ρ⁰ clones, P-AscH^- -induced clonogenic cell death in ρ⁰ cells showed more resistance than the parental cell line. In addition, P-AscH^- induced more DNA damage and more consumption of NAD⁺ and greater decreases in the production of ATP in the parental cell line compared to the ρ⁰ cells. Thus, cancer cells that largely use oxidative phosphorylation to generate ATP may be more sensitive to P-AscH^- compared with cells that are glycolysis-dependent.

Toward Realistic Dosimetry In Vitro: Determining Effective Concentrations of Test Substances in Cell Culture and Their Prediction by an In Silico Mass Balance Model

Nominal concentrations (C_Nom) in cell culture media are routinely used to define concentration-effect relationships in the in vitro toxicology. The actual concentration in the medium (C_Medium) can be affected by adsorption processes, evaporation, or degradation of chemicals. Therefore, we measured the total and free concentration of 12 chemicals, covering a wide range of lipophilicity (log K_OW -0.07-6.84), in the culture medium (C_Medium) and cells (C_Cell) after incubation with Balb/c 3T3 cells for up to 48 h. Measured values were compared to predictions using an as yet unpublished in silico mass balance model that combined relevant equations from similar models published by others. The total C_Medium for all chemicals except tamoxifen (TAM) were similar to the C_Nom. This was attributed to the cellular uptake of TAM and accumulation into lysosomes. The free (i.e., unbound) C_Medium for the low/no protein binding chemicals were similar to the C_Nom, whereas values of all moderately to highly protein-bound chemicals were less than 30% of the C_Nom. Of the 12 chemicals, the two most hydrophilic chemicals, acetaminophen (APAP) and caffeine (CAF), were the only ones for which the C_Cell was the same as the C_Nom. The C_Cell for all other chemicals tended to increase over time and were all 2- to 274-fold higher than C_Nom. Measurements of C_Cytosol, using a digitonin method to release cytosol, compared well with C_Cell (using a freeze-thaw method) for four chemicals (CAF, APAP, FLU, and KET), indicating that both methods could be used. The mass balance model predicted the total C_Medium within 30% of the measured values for 11 chemicals. The free C_Medium of all 12 chemicals were predicted within 3-fold of the measured values. There was a poorer prediction of C_Cell values, with a median overprediction of 3- to 4-fold. In conclusion, while the number of chemicals in the study is limited, it demonstrates the large differences between C_Nom and total and free C_Medium and C_Cell, which were also relatively well predicted by the mass balance model.

Pharmacological Ascorbate Enhances Chemotherapies in Pancreatic Ductal Adenocarcinoma

OBJECTIVES

Pharmacological ascorbate (P-AscH - , high-dose, intravenous vitamin C) has shown promise as an adjuvant therapy for pancreatic ductal adenocarcinoma (PDAC) treatment. The objective of this study was to determine the effects of P-AscH - when combined with PDAC chemotherapies.

METHODS

Clonogenic survival, combination indices, and DNA damage were determined in human PDAC cell lines treated with P-AscH - in combination with 5-fluorouracil, paclitaxel, or FOLFIRINOX (combination of leucovorin, 5-fluorouracil, irinotecan, oxaliplatin). Tumor volume changes, overall survival, blood analysis, and plasma ascorbate concentration were determined in vivo in mice treated with P-AscH - with or without FOLFIRINOX.

RESULTS

P-AscH - combined with 5-fluorouracil, paclitaxel, or FOLFIRINOX significantly reduced clonogenic survival in vitro. The DNA damage, measured by γH2AX protein expression, was increased after treatment with P-AscH - , FOLFIRINOX, and their combination. In vivo, tumor growth rate was significantly reduced by P-AscH - , FOLFIRINOX, and their combination. Overall survival was significantly increased by the combination of P-AscH - and FOLFIRINOX. Treatment with P-AscH - increased red blood cell and hemoglobin values but had no effect on white blood cell counts. Plasma ascorbate concentrations were significantly elevated in mice treated with P-AscH - with or without FOLFIRINOX.

CONCLUSIONS

The addition of P-AscH - to standard of care chemotherapy has the potential to be an effective adjuvant for PDAC treatment.

Resistance to H2O2-induced oxidative stress in human cells of different phenotypes

Application of genetically encoded biosensors of redox-active compounds promotes the elaboration of new methods for investigation of intracellular redox activities. Previously, we have developed a method to measure quantitatively the intracellular concentration of hydrogen peroxide (H₂O₂) in living cells using genetically encoded biosensor HyPer. In the present study, we refined the method and applied it for comparing the antioxidant system potency in human cells of different phenotypes by measuring the gradient between the extracellular and cytoplasmic H₂O₂ concentrations under conditions of H₂O₂-induced external oxidative stress. The measurements were performed using cancer cell lines (K-562 and HeLa), as well as normal human cells – all expressing HyPer in the cell cytoplasm. As normal cells, we used three isogenic lines of different phenotypes – mesenchymal stem/stromal cells (MSCs), induced pluripotent stem cells (iPSCs) derived from MSCs by reprogramming, and differentiated iPSC progenies with the phenotype resembling precursory MSCs. When exposing cells to exogenous H₂O₂, we showed that at low oxidative loads (<50 μM of H₂O₂) the gradient depended on extracellular H₂O₂ concentration. At high loads (>50 μM of H₂O₂), which caused the exhaustion of thioredoxin activity in the cell cytoplasm, the gradient stabilized, pointing out that it is the functional status of the thioredoxin-depended enzymatic system that drives the dependence of the H₂O₂ gradient on the oxidative load in human cells. At high H₂O₂ concentrations, the cytoplasmic H₂O₂ level in cancer cells was found to be several hundred times lower than the extracellular one. At the same time, in normal cells, extracellular-to-intracellular gradient amounted to thousands of times. Upon reprogramming, the potency of cellular antioxidant defense increased. In contrast, differentiation of iPSCs did not result in the changes in antioxidant system activity in the cell cytoplasm, assuming that intensification of the H₂O₂-detoxification processes is inherent to a period of early human development.

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HyPer can be used to compare the H₂O₂-detoxification activity of different cells.

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In H₂O₂-stressed cells, H₂O₂ gradient across the cell membrane depends on H₂O₂ load.

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In normal human cells, H₂O₂ gradient amounts to thousands of times.

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Upon cell reprogramming, the H₂O₂-detoxification activity in cells increases.

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High H₂O₂ loads compromise Trx-depended reduction of thiols in cell cytoplasm.

Dosing metric in cellular experiments: The mol/cell metric has its limitations

It has been argued that the mol/cell metric is more universal than concentration of the toxic agent since in many cases the effect of dose expressed as mol/cell is independent of ex-perimental setup. We confirmed it for hemolysis of erythrocytes in phosphate-buffered saline induced by hypochlorite where the amount of femtomoles/cell of hypochlorite needed for 50% hemolysis was independent of erythrocyte concentration. However, in the presence of blood plasma this metric became dependent on cell concentration. Similarly, the effect of 3-bromopyruvic acid (3-BP) on PEO1 cells as a function of mol/cell ratio depended on the volume of the 3-BP containing medium, due to the reaction of 3-BP with components of the medium. Hemolytic amounts of sodium dodecyl sulfate and Triton X-100 expressed as mol/cell decreased with increasing cell concentration while the effect of DMSO on the viability of a constant number of fibroblasts was independent of the volume of DMSO-containing medium. These results demonstrate that the mol/cell metric is still dependent on experimental conditions when the toxic agent interacts with components of the medium or when its physical state is modified by the target cells, and the effect is independent of the mol/per cell ratio for high excess of a cell damaging agent.

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.

Effective Drug Concentration and Selectivity Depends on Fraction of Primitive Cells

Poor efficiency of chemotherapeutics in the eradication of Cancer Stem Cells (CSCs) has been driving the search for more active and specific compounds. In this work, we show how cell density-dependent stage culture profiles can be used in drug development workflows to achieve more robust drug activity (IC₅₀ and EC₅₀) results. Using flow cytometry and light microscopy, we characterized the cytological stage profiles of the HL-60-, A-549-, and HEK-293-derived sublines with a focus on their primitive cell content. We then used a range of cytotoxic substances—C-123, bortezomib, idarubicin, C-1305, doxorubicin, DMSO, and ethanol—to highlight typical density-related issues accompanying drug activity determination. We also showed that drug EC₅₀ and selectivity indices normalized to primitive cell content are more accurate activity measurements. We tested our approach by calculating the corrected selectivity index of a novel chemotherapeutic candidate, C-123. Overall, our study highlights the usefulness of accounting for primitive cell fractions in the assessment of drug efficiency.

Catalase Modulates the Radio-Sensitization of Pancreatic Cancer Cells by Pharmacological Ascorbate

Pancreatic cancer cells (PDACs) are more susceptible to an oxidative insult than normal cells, resulting in greater cytotoxicity upon exposure to agents that increase pro-oxidant levels. Pharmacological ascorbate (P-AscH^-), i.e., large amounts given intravenously (IV), generates significant fluxes of hydrogen peroxide (H₂O₂), resulting in the killing of PDACs but not normal cells. Recent studies have demonstrated that P-AscH^- radio-sensitizes PDAC but is a radioprotector to normal cells and tissues. Several mechanisms have been hypothesized to explain the dual roles of P-AscH^- in radiation-induced toxicity including the activation of nuclear factor-erythroid 2-related factor 2 (Nrf2), RelB, as well as changes in bioenergetic profiles. We have found that P-AscH^- in conjunction with radiation increases Nrf2 in both cancer cells and normal cells. Although P-AscH^- with radiation decreases RelB in cancer cells vs. normal cells, the knockout of RelB does not radio-sensitize PDACs. Cellular bioenergetic profiles demonstrate that P-AscH^- with radiation increases the ATP demand/production rate (glycolytic and oxidative phosphorylation) in both PDACs and normal cells. Knocking out catalase results in P-AscH^- radio-sensitization in PDACs. In a phase I trial where P-AscH^- was included as an adjuvant to the standard of care, short-term survivors had higher catalase levels in tumor tissue, compared to long-term survivors. These data suggest that P-AscH^- radio-sensitizes PDACs through increased peroxide flux. Catalase levels could be a possible indicator for how tumors will respond to P-AscH^-.

Pharmacological ascorbate inhibits pancreatic cancer metastases via a peroxide-mediated mechanism

Pharmacological ascorbate (P-AscH⁻, high-dose, intravenous vitamin C) is cytotoxic to tumor cells in doses achievable in humans. Phase I studies in pancreatic cancer (PDAC) utilizing P-AscH⁻ have demonstrated increases in progression free survival, suggesting a reduction in metastatic disease burden. The purpose of this study was to determine the effects of P-AscH⁻ on metastatic PDAC. Several in vitro and in vivo mechanisms involved in PDAC metastases were investigated following treatment with P-AscH⁻. Serum from PDAC patients in clinical trials with P-AscH⁻ were tested for the presence and quantity of circulating tumor cell-derived nucleases. P-AscH⁻ inhibited invasion, basement membrane degradation, decreased matrix metalloproteinase expression, as well as clonogenic survival and viability during exposure to fluid shear stress. In vivo, P-AscH⁻ significantly decreased formation of ascites, tumor burden over time, circulating tumor cells, and hepatic metastases. Both in vitro and in vivo findings were reversed with the addition of catalase suggesting that the effect of P-AscH⁻ on metastatic disease is mediated by hydrogen peroxide. Finally, P-AscH⁻ decreased CTC-derived nucleases in subjects with stage IV PDAC in a phase I clinical trial. We conclude that P-AscH⁻ attenuates the metastatic potential of PDAC and may prove to be effective for treating advanced disease.

How Qualification of 3D Disease Models Cuts the Gordian Knot in Preclinical Drug Development

Preclinical research struggles with its predictive power for drug effects in patients. The clinical success of preclinically approved drug candidates ranges between 3% and 33%. Regardless of the approach, novel disease models and test methods need to prove their relevance and reliability for predicting drug effects in patients, which is usually achieved by method validation. Nevertheless, validating all models appears unrealistic due to the variety of diseases. Thus, novel concepts are needed to increase the quality of preclinical research.Herein, we introduce qualification as a minimal standard to establish the relevance of preclinical models and test methods. Qualification starts with prioritizing and translating scientific requirements into technical parameters by quality function deployment. Qualified models use authenticated cells, which resemble the corresponding cells in humans in morphology and drug target expression. Moreover, disease models differ from normal models in the expression of relevant biomarkers. As a result, qualified test methods can discriminate effects of treatment standards and the effects of weakly effective or ineffective substances. Observer-blind readout, adequate data documentation, dropout inclusion, and a priori power studies are as crucial as realistic dosage regimens for qualified approaches. Here, we showcase the implementation of qualification. Adjusting the level of model complexity and qualification to three defined phases of preclinical research assures the optimal level of certainty at each step.In conclusion, qualification strengthens the researchers' impact by defining basic requirements that novel approaches must fulfill while still allowing for scientific creativity. Qualification helps to improve the predictive power of preclinical research. Applied to human cell-based models, qualification reduces animal testing, since only effective drug candidates are subjected to final animal testing and subsequently to clinical trials.

Receptor-Bound Perfluoroalkyl Carboxylic Acids Dictate Their Activity on Human and Mouse Peroxisome Proliferator-Activated Receptor γ

In in vitro cell assays, nominal concentrations of a test chemical are most frequently used in the description of its dose-response curves. Although the biologically effective concentration (BEC) is considered as the most relevant dose metric, in practice, it is very difficult to measure. In this work, we attempted to determine the BEC of long-chain perfluoroalkyl carboxylic acids (PFCAs) in peroxisome proliferator-activated receptor γ (PPARγ) activity assays. In both adipogenesis and transcriptional activity assays with human and mouse cells, PPARγ activity of 7 PFCAs first increased and then decreased with their carbon chain length. The binding affinity of these PFCAs with the ligand-binding domain of PPARγ was measured by fluorescence competitive binding assay and showed very poor correlation with their receptor activity (r² = 0.002-0.047). Internal concentrations of the PFCAs in the cells were measured by LC-MS/MS. Although their correlation with the receptor activity increased significantly, it is still low (r² = 0.41-0.82). Using the binding affinity constant, internal concentration, and PPARγ concentration measured by immunoassays, concentrations of receptor-bound PFCAs in cells were calculated, which exhibited excellent correlation with PPARγ activity in both adipogenesis and transcriptional activity assays (r² = 0.91-0.93). These results demonstrate that the concentration of receptor-bound PFCA is the BEC that dictates its activity on human and mouse PPARγ in cell assays. In the absence of any direct detection method, our approach can be used to calculate the target-site concentration of other ligands.

Quantitation of spin probe-detectable oxidants in cells using electron paramagnetic resonance spectroscopy: To probe or to trap?

Electron Paramagnetic Resonance (EPR) spectroscopy coupled with spin traps/probes enables quantitative determination of reactive nitrogen and oxygen species (RNOS). Even with numerous studies using spin probes, the methodology has not been rigorously investigated. The autoxidation of spin probes has been commonly overlooked. Using the spin probe 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH), the present study has tested the effects of metal chelators, temperature, and oxygen content on the autoxidation of spin probes, where an optimized condition is refined for cell studies. The apparent rate of CMH autoxidation under this condition is 7.01 ± 1.60 nM/min, indicating low sensitivity and great variation of the CMH method and that CMH autoxidation rate should be subtracted from the generation rate of CMH-detectable oxidants (simplified as oxidants below) in samples. Oxidants in RAW264.7 cells are detected at an initial rate of 4.0 ± 0.7 pmol/min/10⁶ cells, which is not considered as the rate of basal oxidants generation because the same method has failed to detect oxidant generation from the stimulation of phorbol-12-mysirate-13-acetate (PMA, 0.1 nmol/10⁶ cells) in cells (2.5 ± 0.9 for PMA vs. 2.1 ± 1.5 pmol/min/10⁶ cells for dimethyl sulfoxide (DMSO)-treated cells). In contrast, the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), which exhibits minimal autoxidation, reveals differences between PMA and DMSO treatment (0.26 ± 0.09 vs. -0.06 ± 0.12 pmol/min/10⁶ cells), which challenges previous claims that spin probes are more sensitive than spin traps. We have also found that low temperature EPR measurements of frozen samples of CMH autoxidation provide lower signal intensity and greater variation compared to RT measurements of fresh samples. The current study establishes an example for method development of RNOS detection, where experimental details are rigorously considered and tested, and raises questions on the applications of spin probes and spin traps.

Proangiogenic Hypoxia-Mimicking Agents Attenuate Osteogenic Potential of Adipose Stem/Stromal Cells

BACKGROUND

Insufficient vascularization hampers bone tissue engineering strategies for reconstructing large bone defects. Delivery of prolyl-hydroxylase inhibitors (PHIs) is an interesting approach to upregulate vascular endothelial growth factor (VEGF) by mimicking hypoxic stabilization of hypoxia-inducible factor-1alpha (HIF-1α). This study assessed two PHIs: dimethyloxalylglycine (DMOG) and baicalein for their effects on human adipose tissue-derived mesenchymal stem/stromal cells (AT-MSCs).

METHODS

Isolated AT-MSCs were characterized and treated with PHIs to assess the cellular proliferation response. Immunostaining and western-blots served to verify the HIF-1α stabilization response. The optimized concentrations for long-term treatment were tested for their effects on the cell cycle, apoptosis, cytokine secretion, and osteogenic differentiation of AT-MSCs. Gene expression levels were evaluated for alkaline phosphatase (ALPL), bone morphogenetic protein 2 (BMP2), runt-related transcription factor 2 (RUNX2), vascular endothelial growth factor A (VEGFA), secreted phosphoprotein 1 (SPP1), and collagen type I alpha 1 (COL1A1). In addition, stemness-related genes Kruppel-like factor 4 (KLF4), Nanog homeobox (NANOG), and octamer-binding transcription factor 4 (OCT4) were assessed.

RESULTS

PHIs stabilized HIF-1α in a dose-dependent manner and showed evident dose- and time dependent antiproliferative effects. With doses maintaining proliferation, DMOG and baicalein diminished the effect of osteogenic induction on the expression of RUNX2, ALPL, and COL1A1, and suppressed the formation of mineralized matrix. Suppressed osteogenic response of AT-MSCs was accompanied by an upregulation of stemness-related genes.

CONCLUSION

PHIs significantly reduced the osteogenic differentiation of AT-MSCs and rather upregulated stemness-related genes. PHIs proangiogenic potential should be weighed against their longterm direct inhibitory effects on the osteogenic differentiation of AT-MSCs.

Simultaneous detection of the enzyme activities of GPx1 and GPx4 guide optimization of selenium in cell biological experiments

Selenium is a metalloid trace element essential for maintaining the optimal redox environment in cells and tissues. It is structurally incorporated into over 25 selenoproteins and enzymes. The glutathione peroxidase (GPx) family of enzymes has a critical role in human health because of its antioxidant function. The recommended daily allowance (RDA) for selenium intake in humans was established to maximize the activity of GPx in plasma. Suboptimal availability of selenium can limit the expression and activities of GPxs leading to a compromised redox environment. This can cause detrimental oxidative distress that could be prevented by increasing the availability of selenium. In cell culture studies, the medium is typically deficient in selenium; supplementation with selenium can increase selenoenzyme activities. However, the optimal level of supplementation in cell culture media has not been well characterized. We performed dose-response experiments for the activities of GPx1 and GPx4 vs. the level of selenium supplementation in cell culture medium. For this, we advanced an assay to determine the activities of both GPx1 and GPx4 efficiently in a single run. During the optimization process, we found that the observed activities of GPx1 and GPx4 depend greatly on the pH of the assay buffer; the observed activities increase with increasing pH, with pH 8 being optimal. Using the combination assay, we also found that the expression and activities for both GPx1 and GPx4 can be maximized in exponentially growing cells by supplementing cell culture media with ≈ 200 nM seleno-l-methionine, without concerns for toxicity. Optimizing the availability of selenium in cell culture to maximize the expression and activities GPx1 and GPx4 may allow for better translation of information from cell culture work to in vivo settings.

Dual Oxidase-Induced Sustained Generation of Hydrogen Peroxide Contributes to Pharmacologic Ascorbate-Induced Cytotoxicity

Pharmacologic ascorbate treatment (P-AscH-, high-dose, intravenous vitamin C) results in a transient short-term increase in the flux of hydrogen peroxide that is preferentially cytotoxic to cancer cells versus normal cells. This study examines whether an increase in hydrogen peroxide is sustained posttreatment and potential mechanisms involved in this process. Cellular bioenergetic profiling following treatment with P-AscH- was examined in tumorigenic and nontumorigenic cells. P-AscH- resulted in sustained increases in the rate of cellular oxygen consumption (OCR) and reactive oxygen species (ROS) in tumor cells, with no changes in nontumorigenic cells. Sources for this increase in ROS and OCR were DUOX 1 and 2, which are silenced in pancreatic ductal adenocarcinoma, but upregulated with P-AscH- treatment. An inducible catalase system, to test causality for the role of hydrogen peroxide, reversed the P-AscH--induced increases in DUOX, whereas DUOX inhibition partially rescued P-AscH--induced toxicity. In addition, DUOX was significantly downregulated in pancreatic cancer specimens compared with normal pancreas tissues. Together, these results suggest that P-AscH--induced toxicity may be enhanced by late metabolic shifts in tumor cells, resulting in a feed-forward mechanism for generation of hydrogen peroxide and induction of metabolic stress through enhanced DUOX expression and rate of oxygen consumption. SIGNIFICANCE: A high dose of vitamin C, in addition to delivering an acute exposure of H2O2 to tumor cells, activates DUOX in pancreatic cancer cells, which provide sustained production of H2O2.

In vitro Cytotoxicity and Pharmacokinetic Evaluation of Pharmacological Ascorbate in Dogs

Background: High-dose, pharmacological ascorbate (P-AscH⁻) is preferentially cytotoxic to human cancer cells in vitro. Investigations on the efficacy of P-AscH⁻ as an adjuvant treatment for multiple human cancers are on-going, but has yet to be formally investigated in dogs. The primary objectives of this study were to determine the pharmacokinetic (PK) profile of P-AscH⁻ in healthy Beagle dogs and the effects of P-AscH⁻ on canine osteosarcoma cells in vitro.

Methods: Eight purpose-bred, healthy, spayed female Beagle dogs, between 20 and 21 months old, and 8–10 kg were administered two doses of P-AscH⁻ (550 or 2,200 mg/kg) via intravenous infusion over 6 h, on separate days. Plasma ascorbate concentrations were measured at 12 time points during and after infusion for PK analysis using nonlinear mixed-effects (NLME) and non-compartmental analysis (NCA). Clonogenic assays were performed on 2 canine osteosarcoma cell lines (D-17 and OSCA-8) and canine primary dermal fibroblasts after exposure to high concentrations of ascorbate (75 pmoles/cell).

Results: Plasma ascorbate levels in the dogs peaked at approximately 10 mM following 2,200 mg/kg and returned to baseline 6–8 h after dosing. Minor adverse effects were seen in two dogs. Ascorbate (75 pmoles/cell) significantly decreased survival in both the osteosarcoma cell lines (D-17 63% SD 0.010, P = 0.005; OSCA-8 50% SD 0.086, P = 0.026), compared to normal fibroblasts (27% SD 0.056).

Conclusions: Pharmacological ascorbate is preferentially cytotoxic to canine-derived cancer cells. High levels of ascorbate can be safely administered to dogs. Further studies are needed to determine the effects of P-AscH⁻ on canine patients.

The Xc- inhibitor sulfasalazine improves the anti-cancer effect of pharmacological vitamin C in prostate cancer cells via a glutathione-dependent mechanism

PURPOSE

Traditional treatment regimens for advanced prostate cancer, especially castration-resistant prostate cancer, result in low survival times with severe side effects. Therefore, new treatment options are required. Vitamin C (VC) has been identified as a promising anti-cancer agent of which the effects depend on the accumulation of H₂O₂ that is produced through autoxidation. Sulfasalazine (SAS), a cystine transporter (X_c^-) inhibitor, is known to suppress cellular glutathione (GSH) biosynthesis. Here, we hypothesized that targeting the X_c^- transporter via SAS may improve the anti-cancer activity of VC through regulating GSH biosynthesis, which in turn may result in the accumulation of reactive oxygen species (ROS).

METHODS

The anti-cancer effect of VC and/or SAS on prostate cancer cells was assessed using WST-8, colony formation and annexin V-FITC/PI FACS assays. Changes in cellular ROS and GSH levels were determined to verify our hypothesis. Finally, BALB/c nude mice bearing prostate cancer xenografts were used to assess the anti-cancer effects of single or combined VC and SAS therapies.

RESULTS

We found that SAS could potentiate the short- and long-term cytotoxicity of VC in prostate cancer cells. We also found that the synergistic effect of SAS and VC led to significant cellular GSH depletion, resulting in increased ROS accumulation. This synergistic effect could be reversed by the antioxidant N-acetyl-L-cysteine (NAC). The synergistic effect of SAS and VC was also noted in prostate cancer xenografts and correlated with immunohistochemistry results.

CONCLUSIONS

Our results strongly indicate that SAS, a relatively non-toxic drug that targets cystine transporters, in combination with VC may be superior to their single applications in the treatment of prostate cancer.

Pharmacologic Ascorbate Primes Pancreatic Cancer Cells for Death by Rewiring Cellular Energetics and Inducing DNA Damage

The clinical potential of pharmacologic ascorbate (P-AscH^-; intravenous delivery achieving mmol/L concentrations in blood) as an adjuvant in cancer therapy is being reevaluated. At mmol/L concentrations, P-AscH^- is thought to exhibit anticancer activity via generation of a flux of H₂O₂ in tumors, which leads to oxidative distress. Here, we use cell culture models of pancreatic cancer to examine the effects of P-AscH^- on DNA damage, and downstream consequences, including changes in bioenergetics. We have found that the high flux of H₂O₂ produced by P-AscH^- induces DNA damage. In response to this DNA damage, we observed that PARP1 is hyperactivated. Using our unique absolute quantitation, we found that P-AscH^- mediated the overactivation of PARP1, which results in consumption of NAD⁺, and subsequently depletion of ATP leading to mitotic cell death. We have also found that Chk1 plays a major role in the maintenance of genomic integrity following treatment with P-AscH^-. Hyperactivation of PARP1 and DNA repair are ATP-consuming processes. Using a Seahorse XF96 analyzer, we demonstrated that the severe decrease in ATP after challenging with P-AscH^- is because of increased demand, not changes in the rate of production. Genetic deletion and pharmacologic inhibition of PARP1 preserved both NAD⁺ and ATP; however, the toxicity of P-AscH^- remained. These data indicate that disruption of bioenergetics is a secondary factor in the toxicity of P-AscH^-; damage to DNA appears to be the primary factor. IMPLICATIONS: Efforts to leverage P-AscH^- in cancer therapy should first focus on DNA damage.

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.

Monitoring the action of redox-directed cancer therapeutics using a human peroxiredoxin-2-based probe

Redox cancer therapeutics target the increased reliance on intracellular antioxidant systems and enhanced susceptibility to oxidant-induced stress of some cancer cells compared to normal cells. Many of these therapeutics are thought to perturb intracellular levels of the oxidant hydrogen peroxide (H2O2), a signaling molecule that modulates a number of different processes in human cells. However, fluorescent probes for this species remain limited in their ability to detect the small perturbations induced during successful treatments. We report a fluorescent sensor based upon human peroxiredoxin-2, which acts as the natural indicator of small H2O2 fluctuations in human cells. The new probe reveals peroxide-induced oxidation in human cells below the detection limit of current probes, as well as peroxiredoxin-2 oxidation caused by two different redox cancer therapeutics in living cells. This capability will be useful in elucidating the mechanism of current redox-based therapeutics and in developing new ones.

Calculated cell-specific intracellular hydrogen peroxide concentration: Relevance in cancer cell susceptibility during ascorbate therapy

The high extracellular hydrogen peroxide (H2O2) concentrations generated during pharmacological ascorbate (P-AscH-) therapy has been shown to exhibit a high flux into susceptible cancer cells leading to a decrease in clonogenic survival. It is hypothesized that the intracellular H2O2 concentration for susceptibility is independent of cell type and that the variation observed in dosing is associated with differences in the cell-specific overall steady-state intracellular H2O2 concentration values. The steady-state variation in intracellular H2O2 concentration is coupled to a number of cellular specific transport and reaction factors including catalase activity and membrane permeability. Here a lumped-parameter mathematical modeling approach, assuming a catalase-dominant peroxide removal mechanism, is used to calculate intracellular H2O2 concentration for several cell lines. Experimental measurements of critical parameters pertaining to the model are obtained. The cell lines investigated are normal pancreatic cells, H6c7, the pancreatic cancer cell line, MIA PaCa-2 and the glioblastoma cell lines, LN-229, T98G, and U-87; all which vary in susceptibility. The intracellular H2O2 concentration estimates are correlated with the clonogenic surviving fraction for each cell line, in-vitro. The results showed that, despite the fact that the experimental parameters including catalase concentration and plasma membrane permeability demonstrated significant variability across cell lines, the calculated steady-state intracellular to extracellular H2O2 concentration ratio did not vary significantly across cell lines. Thus, the calculated intracellular H2O2 concentration is not unique in characterizing susceptibility. These results imply that, although intracellular H2O2 concentration plays a key role in cellular susceptibility to P-AscH- adjuvant therapy, its overall contribution in a unifying mechanism across cell types is complex.

Pharmacological Ascorbate as an Adjuvant for Enhancing Radiation-Chemotherapy Responses in Gastric Adenocarcinoma

Gastric adenocarcinoma most often presents at an advanced stage and overall five-year survival of ∼30%. Pharmacological ascorbate (high-dose IV ascorbate) has been proposed as a promising nontoxic adjuvant to standard radio-chemotherapies in several cancer types. In the current study, pharmacological ascorbate (0.5-2 m M) caused a dose-dependent decrease (70-85% at 2 m M) in clonogenic survival of gastric adenocarcinoma cells (AGS and MNK-45), but was relatively nontoxic to a small intestinal epithelial nonimmortalized human cell isolate (FHs 74 Int). The addition of pharmacological ascorbate (1 m M) to standard radio-chemotherapies [i.e., 5-FU (5 μ M); cisplatin (0.5 μ M); irinotecan (2.5 μ M); carboplatin (5 μ M); paclitaxel (2-4 n M); and X rays (1.8 Gy)] also potentiated gastric cancer clonogenic cell killing [additional decreases were noted with: ascorbate plus 5-FU/radiation (1%); ascorbate plus cisplatin/irinotecan (9-19%); and ascorbate plus paclitaxel/carboplatin (6-7%)]. The gastric cancer cell toxicity and chemosensitization seen with pharmacological ascorbate was dependent on H₂O₂ and the presence of catalytic metal ions. In addition, pharmacological ascorbate dosing resulted in a concentration-dependent decrease (64% at 20 m M, P ≤ 0.0001) in cancer cell invasion and migration that was inhibited by catalase. Finally, pharmacological ascorbate significantly increased the overall survival of mice with gastric cancer xenografts when used in combination with paclitaxel, carboplatin and radiation ( P = 0.019). These results demonstrate that pharmacological ascorbate is selectively cytotoxic to gastric adenocarcinoma cells (relative to normal intestinal epithelial cells) by a mechanism involving H₂O₂ and redox active metal ions. Furthermore, pharmacological ascorbate significantly enhances gastric cancer xenograft responses to radio-chemotherapy as well as inhibiting tumor cell migration and invasiveness. Overall, these results support the hypothesis that pharmacological ascorbate can be used as an adjuvant with standard-of-care radio-chemotherapies for the treatment of gastric adenocarcinomas.

Pharmacologic ascorbate (P-AscH-) suppresses hypoxia-inducible Factor-1α (HIF-1α) in pancreatic adenocarcinoma

HIF-1α is a transcriptional regulator that functions in the adaptation of cells to hypoxic conditions; it strongly impacts the prognosis of patients with cancer. High-dose, intravenous, pharmacological ascorbate (P-AscH^-), induces cytotoxicity and oxidative stress selectively in cancer cells by acting as a pro-drug for the delivery of hydrogen peroxide (H₂O₂); early clinical data suggest improved survival and inhibition of metastasis in patients being actively treated with P-AscH^-. Previous studies have demonstrated that activation of HIF-1α is necessary for P-AscH^- sensitivity. We hypothesized that pancreatic cancer (PDAC) progression and metastasis could be be targeted by P-AscH^- via H₂O₂-mediated inhibition of HIF-1α stabilization. Our study demonstrates an oxygen- and prolyl hydroxylase-independent regulation of HIF-1α by P-AscH^-. Additionally, P-AscH^- decreased VEGF secretion in a dose-dependent manner that was reversible with catalase, consistent with an H₂O₂-mediated mechanism. Pharmacological and genetic manipulations of HIF-1α did not alter P-AscH^--induced cytotoxicity. In vivo, P-AscH^- inhibited tumor growth and VEGF expression. We conclude that P-AscH^- suppresses the levels of HIF-1α protein in hypoxic conditions through a post-translational mechanism. These findings suggest potential new therapies specifically designed to inhibit the mechanisms that drive metastases as a part of PDAC treatment.

Superoxide Dismutase Mimetic GC4419 Enhances the Oxidation of Pharmacological Ascorbate and Its Anticancer Effects in an H₂O₂-Dependent Manner

Lung cancer, together with head and neck cancer, accounts for more than one-fourth of cancer deaths worldwide. New, non-toxic therapeutic approaches are needed. High-dose IV vitamin C (aka, pharmacological ascorbate; P-AscH⁻) represents a promising adjuvant to radiochemotherapy that exerts its anti-cancer effects via metal-catalyzed oxidation to form H₂O₂. Mn(III)-porphyrins possessing superoxide dismutase (SOD) mimetic activity have been shown to increase the rate of oxidation of AscH⁻, enhancing the anti-tumor effects of AscH⁻ in several cancer types. The current study demonstrates that the Mn(II)-containing pentaazamacrocyclic selective SOD mimetic GC4419 may serve as an AscH⁻/O₂^•− oxidoreductase as evidenced by the increased rate of oxygen consumption, steady-state concentrations of ascorbate radical, and H₂O₂ production in complete cell culture media. GC4419, but not CuZnSOD, was shown to significantly enhance the toxicity of AscH⁻ in H1299, SCC25, SQ20B, and Cal27 cancer cell lines. This enhanced cancer cell killing was dependent upon the catalytic activity of the SOD mimetic and the generation of H₂O₂, as determined using conditional overexpression of catalase in H1299T cells. GC4419 combined with AscH⁻ was also capable of enhancing radiation-induced cancer cell killing. Currently, AscH⁻ and GC4419 are each being tested separately in clinical trials in combination with radiation therapy. Data presented here support the hypothesis that the combination of GC4419 and AscH⁻ may provide an effective means by which to further enhance radiation therapy responses.

Pharmacologic ascorbate induces neuroblastoma cell death by hydrogen peroxide mediated DNA damage and reduction in cancer cell glycolysis

An ascorbate-mediated production of oxidative stress has been shown to retard tumor growth. Subsequent glycolysis inhibition has been suggested. Here, we further define the mechanisms relevant to this observation. Ascorbate was cytotoxic to human neuroblastoma cells through the production of H₂O₂, which led to ATP depletion, inhibited GAPDH, and non-apoptotic and non-autophagic cell death. The mechanism of cytotoxicity is different when PARP-dependent DNA repair machinery is active or inhibited. Ascorbate-generated H₂O₂ damaged DNA, activated PARP, depleted NAD+, and reduced glycolysis flux. NAD+ supplementation prevented ATP depletion and cell death, while treatment with a PARP inhibitor, olaparib, preserved NAD+ and ATP levels but led to increased DNA double-strand breakage and did not prevent ascorbate-induced cell death. These data indicate that in cells with an intact PARP-associated DNA repair system, ascorbate-induced cell death is caused by NAD+ and ATP depletion, while in the absence of PARP activation ascorbate-induced cell death still occurs but is a consequence of ROS-induced DNA damage. In a mouse xenograft model, intraperitoneal ascorbate inhibited neuroblastoma tumor growth and prolonged survival. Collectively, these data suggest that ascorbate could be effective in the treatment of glycolysis-dependent tumors. Also, in cancers that use alternative energy metabolism pathways, combining a PARP inhibitor with ascorbate treatment could be useful.

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.

MitoNeoD: A Mitochondria-Targeted Superoxide Probe

Mitochondrial superoxide (O₂^⋅-) underlies much oxidative damage and redox signaling. Fluorescent probes can detect O₂^⋅-, but are of limited applicability in vivo, while in cells their usefulness is constrained by side reactions and DNA intercalation. To overcome these limitations, we developed a dual-purpose mitochondrial O₂^⋅- probe, MitoNeoD, which can assess O₂^⋅- changes in vivo by mass spectrometry and in vitro by fluorescence. MitoNeoD comprises a O₂^⋅--sensitive reduced phenanthridinium moiety modified to prevent DNA intercalation, as well as a carbon-deuterium bond to enhance its selectivity for O₂^⋅- over non-specific oxidation, and a triphenylphosphonium lipophilic cation moiety leading to the rapid accumulation within mitochondria. We demonstrated that MitoNeoD was a versatile and robust probe to assess changes in mitochondrial O₂^⋅- from isolated mitochondria to animal models, thus offering a way to examine the many roles of mitochondrial O₂^⋅- production in health and disease.

Redox environment in stem and differentiated cells: A quantitative approach

Stem cells are believed to maintain a specific intracellular redox status through a combination of enhanced removal capacity and limited production of ROS. In the present study, we challenge this assumption by developing a quantitative approach for the analysis of the pro- and antioxidant ability of human embryonic stem cells in comparison with their differentiated descendants, as well as adult stem and non-stem cells. Our measurements showed that embryonic stem cells are characterized by low ROS level, low rate of extracellular hydrogen peroxide removal and low threshold for peroxide-induced cytotoxicity. However, biochemical normalization of these parameters to cell volume/protein leads to matching of normalized values in stem and differentiated cells and shows that tested in the present study cells (human embryonic stem cells and their fibroblast-like progenies, adult mesenchymal stem cells, lymphocytes, HeLa) maintain similar intracellular redox status. Based on these observations, we propose to use ROS concentration averaged over the cell volume instead of ROS level as a measure of intracellular redox balance. We show that attempts to use ROS level for comparative analysis of redox status of morphologically different cells could lead to false conclusions. Methods for the assessment of ROS concentration based on flow cytometry analysis with the use of H₂DCFDA dye and HyPer, genetically encoded probe for hydrogen peroxide, are discussed.

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Intracellular ROS level depends on the cell size.

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We propose to use the concept of ROS concentration instead of the ROS level.

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Quantification of basic redox parameters challenges the hypothesis about the highly specific redox environment in stem cells.

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.

Peroxiporin Expression Is an Important Factor for Cancer Cell Susceptibility to Therapeutic H2O2: Implications for Pharmacological Ascorbate Therapy

Cancer cell toxicity to therapeutic H2O2 varies widely depending on cell type. Interestingly, it has been observed that different cancer cell types have varying peroxiporin expression. We hypothesize that variation in peroxiporin expression can alter cell susceptibility to therapeutic H2O2 concentrations. Here, we silence peroxiporin aquaporin-3 (AQP3) on the pancreatic cancer cell line MIA PaCa-2 and compare clonogenic survival response to the wild-type. The results showed a significantly higher surviving fraction in the clonogenic response for siAQP3 MIA PaCa-2 cells at therapeutic H2O2 doses (P < 0.05). These results suggest that peroxiporin expression is significant in modulating the susceptibility of cancer cells to ascorbate therapy.

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.

The Bioavailability of Soluble Cigarette Smoke Extract Is Reduced through Interactions with Cells and Affects the Cellular Response to CSE Exposure

Cellular exposure to cigarette smoke leads to an array of complex responses including apoptosis, cellular senescence, telomere dysfunction, cellular aging, and neoplastic transformation. To study the cellular response to cigarette smoke, a common in vitro model exposes cultured cells to a nominal concentration (i.e. initial concentration) of soluble cigarette smoke extract (CSE). However, we report that use of the nominal concentration of CSE as the only measure of cellular exposure is inadequate. Instead, we demonstrate that cellular response to CSE exposure is dependent not only on the nominal concentration of CSE, but also on specific experimental variables, including the total cell number, and the volume of CSE solution used. As found in other similar xenobiotic assays, our work suggests that the effective dose of CSE is more accurately related to the amount of bioavailable chemicals per cell. In particular, interactions of CSE components both with cells and other physical factors limit CSE bioavailability, as demonstrated by a quantifiably reduced cellular response to CSE that is first modified by such interactions. This has broad implications for the nature of cellular response to CSE exposure, and for the design of in vitro assays using CSE.

An ISA-TAB-Nano based data collection framework to support data-driven modelling of nanotoxicology

Analysis of trends in nanotoxicology data and the development of data driven models for nanotoxicity is facilitated by the reporting of data using a standardised electronic format. ISA-TAB-Nano has been proposed as such a format. However, in order to build useful datasets according to this format, a variety of issues has to be addressed. These issues include questions regarding exactly which (meta)data to report and how to report them. The current article discusses some of the challenges associated with the use of ISA-TAB-Nano and presents a set of resources designed to facilitate the manual creation of ISA-TAB-Nano datasets from the nanotoxicology literature. These resources were developed within the context of the NanoPUZZLES EU project and include data collection templates, corresponding business rules that extend the generic ISA-TAB-Nano specification as well as Python code to facilitate parsing and integration of these datasets within other nanoinformatics resources. The use of these resources is illustrated by a "Toy Dataset" presented in the Supporting Information. The strengths and weaknesses of the resources are discussed along with possible future developments.