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

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.

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.

Combining Olaparib and Ascorbic Acid on Nanoparticles to Enhance the Drug Toxic Effects in Pancreatic Cancer

Introduction

Pancreatic cancer (PC) shows a very poor response to current treatments. Development of drug resistance is one of the causes of the therapy failure, being PARP1 (poly ADP-ribose polymerase 1) a relevant protein in the resistance mechanism. In this work, we have functionalized calcium phosphate-based nanoparticles (NPs) with Olaparib (OLA, a PARP-1 inhibitor) in combination with ascorbic acid (AA), a pro-oxidative agent, to enhance their individual effects.

Methods

Amorphous Calcium Phosphate (ACP) NPs were synthesized through a biomimetic approach and then functionalized with OLA and AA (NP-ACP-OLA-AA). After evaluation of the loading capacity and release kinetic, cytotoxicity, cell migration, immunofluorescence, and gene expression assays were performed using pancreatic tumor cell lines. In vivo studies were carried out on tumors derived from the PANC-1 line in NOD SCID gamma (NSG) mice.

Results

NP-ACP-OLA-AA was loaded with 13%wt of OLA (75% loading efficiency) and 1% of AA, respectively. The resulting dual nanosystem exhibited a gradual release of OLA and AA, being the latter protected from degradation in solution. This ensured the simultaneous availability of OLA and AA for a longer period, at least, during the entire time of in vitro cell experiments (72 hours). In vitro studies indicated that NP-ACP-OLA-AA showed the best cytotoxic effect outperforming that of the free OLA and a higher genotoxicity and apoptosis-mediated cytotoxic effect in human pancreatic ductal adenocarcinoma cell line. Interestingly, the in vivo assays using immunosuppressed mice with PANC-1-induced tumors revealed that NP-ACP-OLA-AA produced a higher tumor volume reduction (59.1%) compared to free OLA (28.3%) and increased the mice survival.

Conclusion

Calcium phosphate NPs, a highly biocompatible and biodegradable system, were an ideal vector for the OLA and AA co-treatment in PC, inducing significant therapeutic benefits relative to free OLA, including cytotoxicity, induction of apoptosis, inhibition of cell migration, tumor growth, and survival.

PARP inhibition and pharmacological ascorbate demonstrate synergy in castration-resistant prostate cancer

Prostate cancer (PCa) is the second leading cause of cancer death for men in the United States. While organ-confined disease has reasonable expectation of cure, metastatic PCa is universally fatal upon recurrence during hormone therapy, a stage termed castration-resistant prostate cancer (CRPC). Until such time as molecularly defined subtypes can be identified and targeted using precision medicine, it is necessary to investigate new therapies that may apply to the CRPC population as a whole. The administration of ascorbate, more commonly known as ascorbic acid or Vitamin C, has proved lethal to and highly selective for a variety of cancer cell types. There are several mechanisms currently under investigation to explain how ascorbate exerts anti-cancer effects. A simplified model depicts ascorbate as a pro-drug for reactive oxygen species (ROS), which accumulate intracellularly and generate DNA damage. It was therefore hypothesized that poly(ADP-ribose) polymerase (PARP) inhibitors, by inhibiting DNA damage repair, would augment the toxicity of ascorbate.

Results

Two distinct CRPC models were found to be sensitive to physiologically relevant doses of ascorbate. Moreover, additional studies indicate that ascorbate inhibits CRPC growth in vitro via multiple mechanisms including disruption of cellular energy dynamics and accumulation of DNA damage. Combination studies were performed in CRPC models with ascorbate in conjunction with escalating doses of three different PARP inhibitors (niraparib, olaparib, and talazoparib). The addition of ascorbate augmented the toxicity of all three PARP inhibitors and proved synergistic with olaparib in both CRPC models. Finally, the combination of olaparib and ascorbate was tested in vivo in both castrated and non-castrated models. In both cohorts, the combination treatment significantly delayed tumor growth compared to monotherapy or untreated control.

Conclusions

These data indicate that pharmacological ascorbate is an effective monotherapy at physiological concentrations and kills CRPC cells. Ascorbate-induced tumor cell death was associated with disruption of cellular energy dynamics and accumulation of DNA damage. The addition of PARP inhibition increased the extent of DNA damage and proved effective at slowing CRPC growth both in vitro and in vivo. These findings nominate ascorbate and PARPi as a novel therapeutic regimen that has the potential to improve CRPC patient outcomes.

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.

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.

Friend or Foe: The Relativity of (Anti)oxidative Agents and Pathways

An element, iron, a process, the generation of reactive oxygen species (ROS), and a molecule, ascorbate, were chosen in our study to show their dual functions and their role in cell fate decision. Iron is a critical component of numerous proteins involved in metabolism and detoxification. On the other hand, excessive amounts of free iron in the presence of oxygen can promote the production of potentially toxic ROS. They can result in persistent oxidative stress, which in turn can lead to damage and cell death. At the same time, ROS—at strictly regulated levels—are essential to maintaining the redox homeostasis, and they are engaged in many cellular signaling pathways, so their total elimination is not expedient. Ascorbate establishes a special link between ROS generation/elimination and cell death. At low concentrations, it behaves as an excellent antioxidant and has an important role in ROS elimination. However, at high concentrations, in the presence of transition metals such as iron, it drives the generation of ROS. In the term of the dual function of these molecules and oxidative stress, ascorbate/ROS-driven cell deaths are not necessarily harmful processes—they can be live-savers too.

Hypoxanthine Reduces Radiation Damage in Vascular Endothelial Cells and Mouse Skin by Enhancing ATP Production via the Salvage Pathway

An effective method that can protect radiation-damaged tissues from apoptosis and promote tissue repair has not been reported to date. Hypoxanthine (Hx) is an intermediate metabolite in the purine degradation system that serves as a substrate for ATP synthesis via the salvage pathway. In this study, we focused on the transient decrease in intracellular ATP concentration after radiation exposure and examined the protective effect of Hx against radiation-induced tissue damage. Human umbilical vein endothelial cells were X irradiated, and the cell viability and incidence of apoptosis and DNA double-strand breaks (DSBs) were evaluated at different Hx concentrations. We found that in the presence of 2-100 μM Hx, the percentages of DSBs and apoptotic cells after 2, 6 and 10 Gy dose of radiation significantly decreased, whereas cell viability increased in a concentration-dependent manner. Moreover, the addition of Hx increased the levels of AMP, ADP, and ATP in the cells at 2 h postirradiation, suggesting that Hx was used for adenine nucleotide synthesis through the salvage pathway. Administration of a xanthine oxidoreductase inhibitor to a mouse model of radiation dermatitis resulted in increased blood Hx levels that inhibited severe dermatitis and accelerated recovery. In conclusion, the findings provide evidence that increasing the levels of Hx to replenish ATP could be an effective strategy to reduce radiation-induced tissue damage and elucidating the detailed mechanisms underlying the protective effects of Hx could help develop new protective strategies against radiation.

Involvement of hydrogen peroxide in sonodynamical effect with sinoporphyrin sodium in hypoxic situation

Sonodynamic therapy (SDT) represents a noninvasive therapeutic method via the activation of certain chemical sensitizers using low intensity ultrasound to generate various reactive oxygen species (ROS). In this work, we conducted systematic experiments to evaluate the production of hydrogen peroxide (H₂O₂) in sinoporphyrin sodium (DVDMS) mediated SDT (DVDMS-SDT). We found that the fluorescence intensities of H₂O₂ specific probe BES-H₂O₂ and Amplex Red increased significantly exposure to DVDMS-SDT while decreased with the introduction of catalase (H₂O₂ scavenger), indicating the production of H₂O₂. And the fluorescence intensity of H₂O₂ susceptible probes were positively correlated with DVDMS concentration, ultrasound intensity and irradiation time. Under the same molarity concentration, DVDMS has advantages over proto-porphyrin IX (PpIX) and hemoporrin monomethyl ether (HMME) in H₂O₂ production, indicating that the yield of H₂O₂ depends on the properties of sensitizer. More importantly, DVDMS-SDT is involved in the process of H₂O₂ even in the oxygen-free condition, showing its greater superiority for the treatment of tumor under hypoxia environment.

Insights into antioxidant activities and anti-skin-aging potential of callus extract from Centella asiatica (L.)

Formation of oxidative stress in dermal fibroblasts plays crucial roles in aging processes of skin. The use of phytochemicals that can promote capacity of fibroblasts to combat oxidative stress is an attractive strategy to prevent skin aging and promote skin beauty. Centella asiatica has been used to treat multitude of diseases for centuries. Previous investigations demonstrated that extracts from C. asiatica have a broad range of beneficial activities through their antioxidant activity. Hence, the extract from this medicinal plant could be a great candidate for anti-skin-aging agent. Callus culture offers a powerful platform for sustainable, rapid and large-scale production of phytochemicals to serve extensive demands of pharmaceutical and cosmeceutical industries. Here, we demonstrated the application of callus culture of Centella asiatica to produce bioactive metabolites. The 50% ethanolic extract of callus culture has distinctive features of chemical compositions and biological profiles. Information from HPTLC-DPPH and HPLC analysis suggested that the callus extract comprises distinctive antioxidant compounds, compared with those isolated from authentic plant. Moreover, results from cell culture experiment demonstrated that callus extract possesses promising antioxidant and anti-skin-aging activities. Pre-treatment with callus extract attenuated H₂O₂-induced-cytotoxicity on human dermal fibroblasts. The results from RT-qPCR clearly suggested that the upregulation of cellular antioxidant enzymes appeared to be major contributor for the protective effects of callus extract against oxidative stress. Moreover, supplementation with callus extract inhibited induction of matrix metalloprotease-9 following H₂O₂ exposure, suggesting its potential anti-skin-aging activity. Our results demonstrate the potential utility of C. asiatica callus extract as anti-skin-aging agent in cosmeceutical preparations.

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^-.

Vitamin C and Cell Death

Significance: Persistent oxidative stress is a common feature of cancer cells, giving a specific weapon to selectively eliminate them. Ascorbate in pharmacological concentration can contribute to the suspended formation of hydroxyl radical via the Fenton reaction; thus, it can be an important element of the oxidative stress therapy against cancer cells. Recent Advances: The main components of ascorbate-induced cell death are DNA double-strand breaks via the production of hydroxyl radical and ATP depletion due to the activation of poly (ADP-ribose) polymerase 1. Presumably, DNA damage can be the primary contributor to the anticancer activity of pharmacological ascorbate, as opposed to the rupture of bioenergetics. The caspase independency of high-dose ascorbate-induced cell death proposed the possible involvement of several types of cell death, such as ferroptosis, necroptosis, and autophagy. Critical Issues: Ascorbate can target at least two key molecular features of cancer cells as a part of the anticancer therapy: the intrinsic or acquired resistance to cell death and the dysregulated metabolism of cancer cells. It seems probable that different concentrations of ascorbate alter the nature of induced cell death. Autophagy and necroptosis may play a role at intermediate concentrations, but caspase-independent apoptosis may dominate at higher concentrations. However, ascorbate behaves as an effective inhibitor of ferroptosis that may have crucial importance in its possible clinical application. Future Directions: The elucidation of the details and the links between high-dose ascorbate-induced cancer selective cell death mechanisms may give us a tool to form and apply synergistic cancer therapies. Antioxid. Redox Signal. 34, 831-844.

High-Dose Vitamin C: Preclinical Evidence for Tailoring Treatment in Cancer Patients

Simple Summary

Vitamin C is an indispensable micronutrient in the human diet due to the multiple functions it carries out in the body. Reports of clinical studies have indicated that, when administered at high dosage by the intravenous route, vitamin C may exert beneficial antitumor effects in patients with advanced stage cancers, including those refractory to previous treatment with chemotherapy. The aim of this article is to provide an overview of the current scientific evidence concerning the different mechanisms of action by which high-dose vitamin C may kill tumor cells. A special focus will be given to those mechanisms that provide the rationale basis for tailoring vitamin C treatment according to specific molecular alterations present in the tumor and for the selection of the most appropriate companion drugs.

Abstract

High-dose vitamin C has been proposed as a potential therapeutic approach for patients with advanced tumors who failed previous treatment with chemotherapy. Due to vitamin C complex pharmacokinetics, only intravenous administration allows reaching sufficiently high plasma concentrations required for most of the antitumor effects observed in preclinical studies (>0.250 mM). Moreover, vitamin C entry into cells is tightly regulated by SVCT and GLUT transporters, and is cell type-dependent. Importantly, besides its well-recognized pro-oxidant effects, vitamin C modulates TET enzymes promoting DNA demethylation and acts as cofactor of HIF hydroxylases, whose activity is required for HIF-1α proteasomal degradation. Furthermore, at pharmacological concentrations lower than those required for its pro-oxidant activity (<1 mM), vitamin C in specific genetic contexts may alter the DNA damage response by increasing 5-hydroxymethylcytosine levels. These more recently described vitamin C mechanisms offer new treatment opportunities for tumors with specific molecular defects (e.g., HIF-1α over-expression or TET2, IDH1/2, and WT1 alterations). Moreover, vitamin C action at DNA levels may provide the rationale basis for combination therapies with PARP inhibitors and hypomethylating agents. This review outlines the pharmacokinetic and pharmacodynamic properties of vitamin C to be taken into account in designing clinical studies that evaluate its potential use as anticancer agent.

Ascorbate kills breast cancer cells by rewiring metabolism via redox imbalance and energy crisis

The idea to use megadoses of ascorbate (vitamin C) for cancer treatment has recently been revived. Despite clear efficacy in animal experimentation, our understanding of the cellular and molecular mechanisms of this treatment is still limited and suggests a combined oxidative and metabolic mechanism behind the selective cytotoxicity of ascorbate towards cancerous cells. To gain more insight into the cellular effects of high doses of ascorbate, we performed a detailed analysis of metabolic changes and cell survival of both luminal and basal-like breast cancer cells treated with ascorbate and revealed a distinctive metabolic shift virtually reversing the Warburg effect and triggering a severe disruption of redox homeostasis. High doses of ascorbate were cytotoxic against MCF7 and MDA-MB231 cells representing luminal and basal-like breast cancer phenotypes. Cell death was dependent on ascorbate-induced oxidative stress and accumulation of ROS, DNA damage, and depletion of essential intracellular co-factors including NAD⁺/NADH, associated with a multifaceted metabolic rewiring. This included a sharp disruption of glycolysis at the triose phosphate level, a rapid drop in ATP levels, and redirection of metabolites toward lipid droplet accumulation and increased metabolites and enzymatic activity in the pentose phosphate pathway (PPP). High doses of ascorbate also inhibited the TCA cycle and increased oxygen consumption. Together the severe disruptions of the intracellular metabolic homeostasis on multiple levels "redox crisis and energetic catastrophe" consequently trigger a rapid irreversible cell death.

Nuclear and Cytoplasmic Functions of Vitamin C

Vitamin C (ascorbic acid) is a water-soluble antioxidant and a cofactor for a large number of enzymes. It is present in all tissues and especially abundant in corneal epithelium, stem cells, and neurons. Although similar to thiols in its ability to react with many reactive oxygen species (ROS), ascorbate is much better (>100× faster) than glutathione at scavenging of primary ROS (superoxide radical and singlet oxygen). Ascorbate appears to be especially important for elimination of O₂^•– in the nucleus which contains little or no SOD activity. Cofactor functions of ascorbate involve the maintenance of activity of Fe(II)/2-oxoglutarate-dependent dioxygenases via reduction of Fe(III). The most prominent activity of ascorbate-dependent dioxygenases in the cytoplasm is hydroxylation of prolines in proteins involved in the formation of extracellular matrix and regulation of metabolism and hypoxia responses. In the nucleus, ascorbate is important for oxidative demethylation of 5-methylcytosine in DNA (by TET proteins) and removal of methyl groups from histone lysines (by JmjC demethylases). Differentiation and other cellular reprograming processes involving DNA demethylation are especially sensitive to ascorbate insufficiency. High doses of vitamin C alone or in combinations with drugs produced cancer-suppressive effects which involved redox, immune, and epigenetic mechanisms. Solutions to vitamin C deficiency in cultured cells are discussed to improve the physiological relevance of in vitro models. An abundance of vitamin C in rodents limits their ability to fully recapitulate human sensitivity to adverse health effects of malnutrition and xenobiotics, including neurotoxicity, lung injury, and intergenerational and other epigenetic effects.

The latency of peroxisomal catalase in terms of effectiveness factor for pancreatic and glioblastoma cancer cell lines in the presence of high concentrations of H2O2: Implications for the use of pharmacological ascorbate in cancer therapy

Previous research has identified variation in cancer cell line response to high levels of extracellular H₂O₂ (eH₂O₂) exposure. This directly contributes to our understanding cellular efficacy of pharmacological ascorbate (P-AscH^-) therapy. Here we investigate the factors contributing to latency of peroxisomal catalase of a cell and the importance of latency in evaluating cell exposure to eH₂O₂. First, we develop a mathematical framework for the latency of catalase in terms of an effectiveness factor, η_eff, to describe the catalase activity in the presence of high levels of eH₂O₂. A simplified relationship emerges, [Formula: see text] when m_pr_p/D_ij≪1, where m_p,r_p, and [Formula: see text] are the experimentally determined peroxisome permeability, average peroxisome radius, and the pseudo first-order reaction rate constant, respectively. [Formula: see text] is the catalase concentration in the peroxisome and k₂=1.7x10⁷M^-1s^-1. Next, previously published parameters are used to determine the latency effect of the cell lines: normal pancreatic cells (H6c7), pancreatic cancer cells (MIA PaCa-2), and glioblastoma cells (LN-229, T98G, and U-87), all which vary in their susceptibility to exposure to high eH₂O₂. The results show that effectiveness is not significantly different except for the most susceptible, MIA PaCa-2 cell line, which is higher when compared to all other cell lines. This result is counterintuitive and further implies that latency, as a single parameter, is ineffective in forecasting cell line susceptibility to P-AscH^- therapy equivalent eH₂O. Thus, further research remains necessary to identify why cancer cells vary in susceptibility to P-AscH^- therapy.

New potential biomarker for stratification of patients for pharmacological vitamin C in adjuvant settings of cancer therapy

Our graphical review expands the analysis of cancer vulnerabilities for high dose vitamin C, based on several facts, illustrating the cytotoxic potential of the ascorbate free radical (AFR) via impairment of mitochondrial respiration and the mechanisms of its elimination in mammals by the membrane-bound NADH:cytochrome b5 oxidoreductase 3 (Cyb5R3). We propose that vitamin C can function in “protective mode” or “destructive mode” affecting cellular homeostasis, depending on the intracellular “steady-state” concentration of AFR and differential expression/activity of Cyb5R3 in cancerous and normal cells. Thus, a specific anti-cancer effect can be achieved at high doses of vitamin C therapy. The review is intended for a wide audience of readers – from students to specialists in the field.

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The ascorbate radical could impair mitochondrial respiration via cytochrome c reduction.

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The ascorbate radical could mediate the imbalance of the coenzyme Q “pool” in cancer cells.

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The selective cytotoxicity of vitamin C in cancer could be mediated by Cyb5R3/VDAC1.

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Low/normal doses of vitamin C act in a “protective mode” for normal/cancer cells.

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High doses of vitamin C act in a “destructive mode” for cancer cells only.