Pharmacological Ascorbate Research Articles

A randomized trial of pharmacological ascorbate, gemcitabine, and nab-paclitaxel for metastatic pancreatic cancer

BackgroundPatients with metastatic pancreatic ductal adenocarcinoma (PDAC) have poor 5-year survival. Pharmacological ascorbate (P-AscH-, high dose, intravenous, vitamin C) has shown promise as an adjunct to chemotherapy. We hypothesized adding P-AscH- to gemcitabine and nab-paclitaxel would increase survival in patients with metastatic PDAC. MethodsPatients diagnosed with stage IV pancreatic cancer randomized 1:1 to gemcitabine and nab-paclitaxel only (SOC, control) or to SOC with concomitant P-AscH−, 75 g three times weekly (ASC, investigational). The primary outcome was overall survival with secondary objectives of determining progression-free survival and adverse event incidence. Quality of life and patient reported outcomes for common oncologic symptoms were captured as an exploratory objective. Thirty-six participants were randomized; of this 34 received their assigned study treatment. All analyses were based on data frozen on December 11, 2023. ResultsIntravenous P-AscH- increased serum ascorbate levels from micromolar to millimolar levels. P-AscH- added to the gemcitabine + nab-paclitaxel (ASC) increased overall survival to 16 months compared to 8.3 months with gemcitabine + nab-paclitaxel (SOC) (HR = 0.46; 90 % CI 0.23, 0.92; p = 0.030). Median progression free survival was 6.2 (ASC) vs. 3.9 months (SOC) (HR = 0.43; 90 % CI 0.20, 0.92; p = 0.029). Adding P-AscH- did not negatively impact quality of life or increase the frequency or severity of adverse events. ConclusionsP-AscH− infusions of 75 g three times weekly in patients with metastatic pancreatic cancer prolongs overall and progression free survival without detriment to quality of life or added toxicity (ClinicalTrials.gov number NCT02905578).

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

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

Balanced Duality: H2O2-Based Therapy in Cancer and Its Protective Effects on Non-Malignant Tissues.

Conventional cancer therapy strategies, although centered around killing tumor cells, often lead to severe side effects on surrounding normal tissues, thus compromising the chronic quality of life in cancer survivors. Hydrogen peroxide (H2O2) is a secondary signaling molecule that has an array of functions in both tumor and normal cells, including the promotion of cell survival pathways and immune cell modulation in the tumor microenvironment. H2O2 is a reactive oxygen species (ROS) crucial in cellular homeostasis and signaling (at concentrations maintained under nM levels), with increased steady-state levels in tumors relative to their normal tissue counterparts. Increased steady-state levels of H2O2 in tumor cells, make them vulnerable to oxidative stress and ultimately, cell death. Recently, H2O2-producing therapies-namely, pharmacological ascorbate and superoxide dismutase mimetics-have emerged as compelling complementary treatment strategies in cancer. Both pharmacological ascorbate and superoxide dismutase mimetics can generate excess H2O2 to overwhelm the impaired H2O2 removal capacity of cancer cells. This review presents an overview of H2O2 metabolism in the physiological and malignant states, in addition to discussing the anti-tumor and normal tissue-sparing mechanism(s) of, and clinical evidence for, two H2O2-based therapies, pharmacological ascorbate and superoxide dismutase mimetics.

Pharmacologic ascorbate induces transient hypoxia sensitizing pancreatic ductal adenocarcinoma to a hypoxia activated prodrug

Hypoxic tumor microenvironments pose a significant challenge in cancer treatment. Hypoxia-activated prodrugs like evofosfamide aim to specifically target and eliminate these resistant cells. However, their effectiveness is often limited by reoxygenation after cell death. We hypothesized that ascorbate's pro-oxidant properties could be harnessed to induce transient hypoxia, enhancing the efficacy of evofosfamide by overcoming reoxygenation.To test this hypothesis, we investigated the sensitivity of MIA Paca-2 and A549 cancer cells to ascorbate in vitro and in vivo. Ascorbate induced a cytotoxic effect at 5 mM that could be alleviated by endogenous administration of catalase, suggesting a role for hydrogen peroxide in its cytotoxic mechanism. In vitro, Seahorse experiments indicated that the generation of hydrogen peroxide consumes oxygen, which is offset at later time points by a reduction in oxygen consumption due to hydrogen peroxide's cytotoxic effect.In vivo, photoacoustic imaging showed pharmacologic ascorbate treatment at sublethal levels triggered a complex, multi-phasic response in tumor oxygenation across both cell lines. Initially, ascorbate generated transient hypoxia within minutes through hydrogen peroxide production, via reactions that consume oxygen. This initial hypoxic phase peaked at around 150 s and then gradually subsided. However, at longer time scales (approximately 300 s) a vasodilation effect triggered by ascorbate resulted in increased blood flow and subsequent reoxygenation. Combining sublethal levels of i. p. Ascorbate with evofosfamide significantly prolonged tumor doubling time in MIA Paca-2 and A549 xenografts compared to either treatment alone. This improvement, however, was only observed in a subpopulation of tumors, highlighting the complexity of the oxygenation response.

Abstract 484: Enhancing therapeutic responses in NSCLC using iron-oxide nanoparticles combined with pharmacological ascorbate

Abstract High dose Vitamin C (pharmacological ascorbate; P-AscH‒ > 20 mM plasma levels) given intravenously (I.V.), has made a remarkable re-emergence as an adjuvant to combined modality approaches in cancer therapy. P-AscH‒ can be readily oxidized in the presence of redox active metals (i.e., P-AscH‒ serves as an iron reducing agent), which can result in increased fluxes of H2O2. This chemical phenomenon allows for the tumor-selective enhancement of chemo-radiation in NSCLC. We hypothesized that enhancing labile Fe2+ in cancer cells using iron-oxide nanoparticles (ferumoxytol, FMX) can increase the effectiveness of P-AscH‒ in enhancing cancer cell sensitivity to chemo-radiation in NSCLC by increasing H2O2 production. To test this hypothesis, we performed clonogenic cell survival assays in-vitro. To test the role of H2O2 in the combined effect of P-AscH‒ and FMX, we developed lentiviral-based doxycycline-inducible overexpression models for catalase, and to determine the changes in Fe, we used fluorescent probes that specifically detect changes in labile Fe2+. Results from these experiments showed FMX enhanced clonogenic cell killing in NSCLC. Furthermore, catalase overexpression inhibited this effect, suggesting that enhanced H2O2 production plays a central role in the additive effect of P-AscH- and FMX. Finally, staining the cells with the fluorescent iron probes showed that FMX enhanced labile Fe2+ in cells treated with P-AscH‒. These studies continue to support the hypothesis that H2O2 plays a significant role in P-AscH‒ toxicity in cancer cells that can be exacerbated using iron oxide nanoparticles. Future studies will test these findings in-vivo using preclinical xenograft models. (supported by P01 CA217797, P30 CA086862, T32 CA078586, and P01 CA244091). Citation Format: Mekhla Singhania, Miachael S. Petronek, Casey F. Pulliam, Kranti A. Mapuskar, Amira Zaher, Douglas R. Spitz. Enhancing therapeutic responses in NSCLC using iron-oxide nanoparticles combined with pharmacological ascorbate [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 484.

Abstract 4677: Characterizing resistant and metastatic phenotypes to pharmacological ascorbate in pancreatic cancer

Abstract Background and purpose: Pharmacological ascorbate (P-AscH) is a prooxidant that oxidizes to produce high levels of hydrogen peroxide. It is currently being investigated as an anti-cancer neoadjuvant for pancreatic cancer (PC). In phase I clinical trials, P-AscH has generated encouraging results in terms of efficiency and safety. However, 50% of patients do not respond to P-AscH suggesting that resistance occurs in a subset of patients. We have generated PC cell lines resistant to P-AscH to characterize mechanisms of resistance. Methodology: PANC-1 and MIA PaCa-2 PC cell lines were treated with a stepwise progression of increasing concentrations of P-AscH until 10-fold IC50 concentration was fully tolerated (AscR, ascorbate resistant) as determined by clonogenic survival. Once resistance was achieved, various redox enzyme protein expression and activity were measured to determine their role in resistance to P-AscH. Proliferation and cell cycle analysis were conducted on resistant and sensitive cells. An RNA sequencing screen was conducted as an unbiased approach to identify potential candidates crucial for resistance. Finally, phenotypes associated to increased metastatic potential, including collagen invasion and in vivo tumor colonization were explored for characterization. Results: PANC-1 and MIA PaCa-2 AscR cells developed unique mechanisms to tolerate high levels of P-AscH. PANC-1 AscR cells almost exclusively rely on catalase to detoxify H2O2 generated during P-AscH treatments, while MIA PaCa-2 AscR cells do not. It is interesting to note that not every redox enzyme was upregulated in response to P-AscH treatments, including GPx1/4. The AscR cell lines also differed in growth rates. PANC-1 AscR cells developed a faster proliferation rate, whereas MIA PaCa-2 AscR cells significantly decreased their growth. This is consistent with a shortened G1/G0 cell cycle phase and an accumulation in G2/M, respectively. The RNA sequencing screen revealed a metastatic signature in association with resistance to P-AscH, including upregulation of the PI3K/AKT axis. We observed a significant increase in collagen matrix invasion, as well as metastatic colonization in vivo. Additionally, we have observed increased expression of active AKT in both AscR cell lines, indicating a potential mechanism for the increased metastatic phenotype. Conclusion: Our findings demonstrate distinct mechanisms for AcsR cells to tolerate high doses of P-AscH. Although catalase has demonstrated to be a key factor in controlling redox flux, it may not be necessary for all cell types. Not only can P-AscH resistance alter redox enzyme expression, but we have also observed substantial increase in metastatic potential to drive invasion and tumor colonization. In summary, our data indicate a potential route for PC to tolerate high levels of P-AscH and may explain how some patients do not respond to this treatment regimen. Citation Format: Amanda N. Pope, Brianne R. O'Leary, Juan Du, Garry R. Buettner, Michael D. Henry, Joseph J. Cullen. Characterizing resistant and metastatic phenotypes to pharmacological ascorbate in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4677.

Pharmacologic Ascorbate Radiosensitizes Pancreatic Cancer but Radioprotects Normal Tissue: The Role of Oxidative Stress-Induced Lipid Peroxidation.

The toxicity of ionizing radiation limits its effectiveness in the treatment of pancreatic ductal adenocarcinoma. Pharmacologic ascorbate (P-AscH-) has been shown to radiosensitize pancreatic cancer cells while simultaneously radioprotecting normal cells. We hypothesize that P-AscH- protects the small intestine while radiosensitizing pancreatic cancer cells partially through an oxidative stress mechanism. Duodenal samples from pancreaticoduodenectomy specimens of patients who underwent radio-chemotherapy ± P-AscH- and mouse tumor and jejunal samples treated with radiation ± P-AscH- were evaluated. Pancreatic cancer and non-tumorigenic cells were treated with radiation ± P-AscH- to assess lipid peroxidation. To determine the mechanism, pancreatic cancer cells were treated with selenomethionine or RSL3, an inhibitor of glutathione peroxidase 4 (GPx4). Radiation-induced decreases in villi length and increases in 4-HNE immunofluorescence were reversed with P-AscH- in human duodenum. In vivo, radiation-induced decreases in villi length and increased collagen deposition were reversed in P-AscH--treated jejunal samples. P-AscH- and radiation increased BODIPY oxidation in pancreatic cancer cells but not in non-tumorigenic cells. Selenomethionine increased GPx4 protein and activity in pancreatic cancer and reversed P-AscH--induced toxicity and lipid peroxidation. RSL3 treatment inhibited GPx4 activity and increased lipid peroxidation. Differences in oxidative stress may play a role in radioprotecting normal cells while radiosensitizing pancreatic cancer cells when treated with P-AscH-.

The interlacing anticancer effect of pharmacologic ascorbate, chloroquine, and resveratrol.

Currently, a diagnosis with KRAS mutant pancreatic ductal adenocarcinoma (PDAC) means a death warrant, so finding efficient therapeutic options is a pressing issue. Here, we presented that pharmacologic ascorbate, chloroquine and resveratrol co-treatment exerted a synergistic cytotoxic effect on PDAC cell lines. The observed synergistic cytotoxicity was a general feature in all investigated cancer cell lines independent of the KRAS mutational status and seems to be independent of the autophagy inhibitory effect of chloroquine. Furthermore, it seems that apoptosis and necroptosis are also not likely to play any role in the cytotoxicity of chloroquine. Both pharmacologic ascorbate and resveratrol caused double-strand DNA breaks accompanied by cell cycle arrest. It seems resveratrol-induced cytotoxicity is independent of reactive oxygen species (ROS) generation and accompanied by a significant elevation of caspase-3/7 activity, while pharmacologic ascorbate-induced cytotoxicity shows strong ROS dependence but proved to be caspase-independent. Our results are particularly important since ascorbate and resveratrol are natural compounds without significant harmful effects on normal cells, and chloroquine is a known antimalarial drug that can easily be repurposed.

MRI Detection and Therapeutic Enhancement of Ferumoxytol Internalization in Glioblastoma Cells.

Recently, the FDA-approved iron oxide nanoparticle, ferumoxytol, has been found to enhance the efficacy of pharmacological ascorbate (AscH-) in treating glioblastoma, as AscH- reduces the Fe3+ sites in the nanoparticle core. Given the iron oxidation state specificity of T2* relaxation mapping, this study aims to investigate the ability of T2* relaxation to monitor the reduction of ferumoxytol by AscH- with respect to its in vitro therapeutic enhancement. This study employed an in vitro glioblastoma MRI model system to investigate the chemical interaction of ferumoxytol with T2* mapping. Lipofectamine was utilized to facilitate ferumoxytol internalization and assess intracellular versus extracellular chemistry. In vitro T2* mapping successfully detected an AscH--mediated reduction of ferumoxytol (25.6 ms versus 2.8 ms for FMX alone). The T2* relaxation technique identified the release of Fe2+ from ferumoxytol by AscH- in glioblastoma cells. However, the high iron content of ferumoxytol limited T2* ability to differentiate between the external and internal reduction of ferumoxytol by AscH- (ΔT2* = +839% for external FMX and +1112% for internal FMX reduction). Notably, the internalization of ferumoxytol significantly enhances its ability to promote AscH- toxicity (dose enhancement ratio for extracellular FMX = 1.16 versus 1.54 for intracellular FMX). These data provide valuable insights into the MR-based nanotheranostic application of ferumoxytol and AscH- therapy for glioblastoma management. Future developmental efforts, such as FMX surface modifications, may be warranted to enhance this approach further.

Differential H2O2 Metabolism among Glioblastoma Subtypes Confers Variable Responses to Pharmacological Ascorbate Therapy Combined with Chemoradiation.

Glioblastoma (GBM), a highly lethal and aggressive central nervous system malignancy, presents a critical need for targeted therapeutic approaches to improve patient outcomes in conjunction with standard-of-care (SOC) treatment. Molecular subtyping based on genetic profiles and metabolic characteristics has advanced our understanding of GBM to better predict its evolution, mechanisms, and treatment regimens. Pharmacological ascorbate (P-AscH-) has emerged as a promising supplementary cancer therapy, leveraging its pro-oxidant properties to selectively kill malignant cells when combined with SOC. Given the clinical challenges posed by the heterogeneity and resistance of various GBM subtypes to conventional SOC, our study assessed the response of classical, mesenchymal, and proneural GBM to P-AscH-. P-AscH- (20 pmol/cell) combined with SOC (5 µM temozolomide and 4 Gy of radiation) enhanced clonogenic cell killing in classical and mesenchymal GBM subtypes, with limited effects in the proneural subtype. Similarly, following exposure to P-AscH- (20 pmol/cell), single-strand DNA damage significantly increased in classical and mesenchymal but not proneural GBM. Moreover, proneural GBM exhibited increased hydrogen peroxide removal rates, along with increased catalase and glutathione peroxidase activities compared to mesenchymal and classical GBM, demonstrating an altered H2O2 metabolism that potentially drives differential P-AscH- toxicity. Taken together, these data suggest that P-AscH- may hold promise as an approach to improve SOC responsiveness in mesenchymal GBMs that are known for their resistance to SOC.

Exploiting Iron Metabolism as a Therapeutic Vulnerability in Glioblastoma.

In this CCR Translations, we discuss pharmacologic ascorbate as a novel therapeutic for glioblastoma (GBM). Aberrant iron metabolism in GBM can be assessed noninvasively by MRI and exploited to potentially improve the efficacy of chemoradiotherapy. We contextualize the study's results and discuss the next steps to further develop this paradigm. See related article by Petronek et al., p. 283.

Enhancing therapeutic responses in NSCLC using iron-oxide nanoparticles combined with Pharmacological Ascorbate

Enhancing therapeutic responses in NSCLC using iron-oxide nanoparticles combined with Pharmacological Ascorbate

Enhanced Peroxide Fluxes and Radiosensitization in Colorectal Tumors but Not Normal Enterocytes from the Combination of Superoxide Dismutase Mimetics and Pharmacological Ascorbate

Selective superoxide dismutase mimetics (DMs), including GC4419 and GC4711, are radiation (RT) modulators which induce opposite effects in tumors and normal tissues and may be ideally suited for locally advanced rectal cancer. However, their tumor radiosensitization effect is limited at RT doses relevant to rectal cancer (2-5 Gy). Over this dose range, they protect normal mucosal tissues, but we and others have shown they do not reliably enhance tumor radiosensitization at doses < 8-15 Gy. We hypothesize that combining DMs and other therapies which also target redox metabolism may effectively sensitize tumors to clinically relevant RT doses for rectal cancer while maintaining their normal tissue sparing effects. Like DMs, pharmacological ascorbate (P-AscH) selectively increases lethal hydrogen peroxide (H2O2) fluxes in tumors, but it does so through distinct mechanisms which are potentially complimentary with DMs (particularly at low RT doses). Human HCT116, SW480, and HT29 colorectal tumor models and non-malignant FHs74 intestinal epithelial cells were used. Clonogenic survival was assessed following single-fraction RT (2-5 Gy) +/- P-AscH (5 pmol/cell) +/- GC4711 (20 µM). Dependency on H202 fluxes was tested by adding bovine catalase with drug and RT treatments. Oxygen consumption in culture media was measured using a Clark electrode. Rectal toxicity was assessed in vivo using IHC in fixed rectal tissues following fractionated, image-guided rectal RT (5-9 Gy x 3). Tumor growth delay was assessed following RT (5 Gy x 3) +/- P-AscH (4 g/kg) +/- GC4419 (10 mg/kg) in animals with unilateral HCT116 flank tumors. Combination therapy with P-AscH and GC4711 potently radiosensitized all tumor lines in vitro whereas neither agent significantly decreased clonogenic survival as a monotherapy. Neither drug nor combination treatment sensitized FHs74 epithelial cells. P-AscH increased oxygen consumption and H2O2 production in culture media and the addition of GC4711 significantly increased both more than P-AscH alone. Co-treatment with exogenous catalase inhibited cancer cell killing with combination therapy +/- RT. In vivo, combination therapy significantly enhanced tumor growth delay and survival. Both agents significantly decreased markers of acute rectal RT injury as monotherapies. Co-treatment with DMs and P-AscH selectively enhanced tumor radiosensitization by increasing oxygen consumption and H202 fluxes even in tumor models which are known to be resistant to oxidative stressors (HT29). In contrast, each agent conferred a radioprotective effect in the rectum. Combination therapy with DMs and P-AscH may represent a novel, potent approach to target dysregulated redox metabolism in colorectal tumors.

Rapid Peroxide Removal Limits the Radiosensitization of Diffuse Intrinsic Pontine Glioma (DIPG) Cells by Pharmacologic Ascorbate.

Diffuse intrinsic pontine gliomas (DIPG) are an aggressive type of pediatric brain tumor with a very high mortality rate. Surgery has a limited role given the tumor's location. Palliative radiation therapy alleviates symptoms and prolongs survival, but median survival remains less than 1 year. There is no clear role for chemotherapy in DIPGs as trials adding chemotherapy to palliative radiation therapy have failed to improve survival compared to radiation alone. Thus, there is a critical need to identify tissue-specific radiosensitizers to improve clinical outcomes for patients with DIPGs. Pharmacologic (high dose) ascorbate (P-AscH-) is a promising anticancer therapy that sensitizes human tumors, including adult high-grade gliomas, to radiation by acting selectively as a generator of hydrogen peroxide (H2O2) in cancer cells. In this study we demonstrate that in contrast to adult glioma models, P-AscH- does not radiosensitize DIPG. DIPG cells were sensitive to bolus of H2O2 but have faster H2O2 removal rates than GBM models which are radiosensitized by P-AscH-. These data support the hypothesis that P-AscH- does not enhance DIPG radiosensitivity, likely due to a robust capacity to detoxify and remove hydroperoxides.

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.

Pharmacological ascorbate induces sustained mitochondrial dysfunction.

Pharmacological ascorbate (P-AscH-; high dose given intravenously) generates H2O2 that is selectively cytotoxic to cancer compared to normal cells. The RAS-RAF-ERK1/2 is a major signaling pathway in cancers carrying RAS mutations and is known to be activated by H2O2. Activated ERK1/2 also phosphorylates the GTPase dynamin-related protein (Drp1), which then stimulates mitochondrial fission. Although early generation of H2O2 leads to cytotoxicity of cancer cells, we hypothesized that sustained increases in H2O2 activate ERK-Drp1 signaling, leading to an adaptive response; inhibition of this pathway would enhance the toxicity of P-AscH-. Increases in phosphorylated ERK and Drp1 induced by P-AscH- were reversed with genetic and pharmacological inhibitors of ERK and Drp1, as well as in cells lacking functional mitochondria. P-AscH- increased Drp1 colocalization to mitochondria, decreased mitochondrial volume, increased disconnected components, and decreased mitochondrial length, suggesting an increase in mitochondrial fission 48h after treatment with P-AscH-. P-AscH- decreased clonogenic survival; this was enhanced by genetic and pharmacological inhibition of both ERK and Drp1. In murine tumor xenografts, the combination of P-AscH- and pharmacological inhibition of Drp1 increased overall survival. These results suggest that P-AscH- induces sustained changes in mitochondria, through activation of the ERK/Drp1 signaling pathway, an adaptive response. Inhibition of this pathway enhanced the toxicity P-AscH- to cancer cells.

ROS based synergetic anticancer effect of pharmacologic ascorbate and chloroquine derivatives

ROS based synergetic anticancer effect of pharmacologic ascorbate and chloroquine derivatives

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

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