Targeting cancer vulnerabilities with high-dose vitamin C

In the paper

“we propose that pharmacological ascorbate can potentially circumvent this problem by exploring two common features of cancer cells: their increased levels of labile transition metals, especially iron21, and their increased reliance on glucose uptake and glycolysis22.”

What the sources say

• Supported

  Citation 21 is attached to the claim about increased labile metals, especially iron, not to the separate ascorbate proposal or the glycolysis claim cited to reference 22. In “Intracellular iron regulation is modified in cancer” (page unavailable), the review says cancer-specific changes often increase intracellular iron; its subsection on iron storage describes oncogene-induced expansion of the labile iron pool. (LLM, conf=0.87)

  cites [21] Torti, S. V. & Torti, F. M. Iron and cancer: more ore to be mined. Nat. Rev. Cancer 13, 342–355 (2013). source
• Supported

  Citation 22 is attached to the claim about cancer cells’ glucose uptake and glycolysis, not the separate claim about iron or the authors’ proposed ascorbate treatment. The source’s “Metabolic Reprogramming and Oncometabolites in Cancer” section says glucose uptake and increased glycolytic flux occur in many cancer cells and tumors. Its “Bioenergetics” section also cautions that high glycolytic rates do not mean most cancer cells rely on glycolysis for the majority of their ATP. (LLM, conf=0.88)

  cites [22] DeBerardinis, R. J. & Chandel, N. S. Fundamentals of cancer metabolism. Sci. Adv. 2, e1600200 (2016). source

In the paper

“other αKGDDs such as JmjC domain-containing histone demethylase family (JHDM) and αKGDD AlkB (ALKB) are also known to be epigenetic regulators that can be potentially regulated by vitamin C73,74.”

What the sources say

• Partly supported

  The review’s discussion of histone demethylases and its Fig. 3 caption link JHDM activity to vitamin C and epigenetic regulation. Its AlkB discussion describes the family as iron- and 2-oxoglutarate-dependent, but says only that some members could potentially have epigenetic roles; it does not establish AlkB as a known vitamin-C-regulated epigenetic regulator. Page numbers are unavailable in our copy. (LLM, conf=0.85)

  cites [73] Monfort, A. & Wutz, A. Breathing-in epigenetic change with vitamin C. EMBO Rep. 14, 337–346 (2013). sourceExperimental — accuracy not yet measured
• Partly supported

  The Structural Features section (p. 2) identifies AlkB proteins as Fe(II)/α-ketoglutarate-dependent dioxygenases, and Eukaryotic and Mammalian AlkB Homologs (p. 2) describes homologs that demethylate RNA. But the passages do not address vitamin C regulation of AlkB or JHDM, or identify JHDM as an epigenetic regulator; searches for vitamin C, ascorbate, and JmjC did not establish those parts of the claim. (LLM, conf=0.83)

  cites [74] Fedeles, B. I. et al. The AlkB family of Fe(II)/α-ketoglutarate-dependent dioxygenases: repairing nucleic acid alkylation damage and beyond. J. Biol. Chem. 290, 20734–20742 (2015). sourceExperimental — accuracy not yet measured

In the paper

“we recently showed that high-dose ascorbate can target these vulnerabilities in KRAS or BRAF mutant colorectal cancer (CRC) cells47.”

What the sources say

• Not checked yetcites [47] Yun, J. et al. Vitamin C selectively kills KRAS and BRAF mutant colorectal cancer cells by targeting GAPDH. Science 350, 1391–1396 (2015). This study demonstrates that uptake of DHA by GLUT1, and its subsequent reduction to ascorbate, depletes essential antioxidants to induce cell death in KRAS or BRAF mutant CRC cells. source

In the paper

“our study indicated that DHA is the pharmacologically active agent”

What the sources say

• Not checked yetcites [47] Yun, J. et al. Vitamin C selectively kills KRAS and BRAF mutant colorectal cancer cells by targeting GAPDH. Science 350, 1391–1396 (2015). This study demonstrates that uptake of DHA by GLUT1, and its subsequent reduction to ascorbate, depletes essential antioxidants to induce cell death in KRAS or BRAF mutant CRC cells. source

In the paper

“The elevated ROS, in turn, inactivates a glycolytic enzyme, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), by oxidizing a cysteine residue in the active site.”

What the sources say

• Not checked yetcites [47] Yun, J. et al. Vitamin C selectively kills KRAS and BRAF mutant colorectal cancer cells by targeting GAPDH. Science 350, 1391–1396 (2015). This study demonstrates that uptake of DHA by GLUT1, and its subsequent reduction to ascorbate, depletes essential antioxidants to induce cell death in KRAS or BRAF mutant CRC cells. source

In the paper

“Inhibiting GAPDH in highly glycolytic KRAS or BRAF mutant cells ultimately leads to an ‘energy crisis’ and cell death not seen in their wild-type counterparts47.”

What the sources say

• Not checked yetcites [47] Yun, J. et al. Vitamin C selectively kills KRAS and BRAF mutant colorectal cancer cells by targeting GAPDH. Science 350, 1391–1396 (2015). This study demonstrates that uptake of DHA by GLUT1, and its subsequent reduction to ascorbate, depletes essential antioxidants to induce cell death in KRAS or BRAF mutant CRC cells. source

In the paper

“Inside the cell, DHA is rapidly reduced back to ascorbate at the expense of GSH and NADPH47,49.”

What the sources say

• Not checked yetcites [47] Yun, J. et al. Vitamin C selectively kills KRAS and BRAF mutant colorectal cancer cells by targeting GAPDH. Science 350, 1391–1396 (2015). This study demonstrates that uptake of DHA by GLUT1, and its subsequent reduction to ascorbate, depletes essential antioxidants to induce cell death in KRAS or BRAF mutant CRC cells. source
• Not checked yetcites [49] May, J. M. et al. Ascorbate recycling in human erythrocytes: role of GSH in reducing dehydroascorbate. Free Radic. Biol. Med. 20, 543–551 (1996). source

In the paper

“recent results from both human and animal studies have found no clear evidence of the benefit of antioxidant treatment in preventing or suppressing cancer development.”

What the sources say

• Not checked yetcites [14] Sayin, V. I. et al. Antioxidants accelerate lung cancer progression in mice. Sci. Transl Med. 6, 221ra15 (2014). This study demonstrates that dietary supplementation of antioxidants ( N -acetylcysteine and vitamin E) markedly increases tumour progression and reduces survival in mouse models of KRAS-induced or BRAF-induced lung cancer. source
• Not checked yetcites [15] Le Gal, K. et al. Antioxidants can increase melanoma metastasis in mice. Sci. Transl Med. 7, 308re8 (2015). source
• Not checked yetcites [16] Piskounova, E. et al. Oxidative stress inhibits distant metastasis by human melanoma cells. Nature 527, 186–191 (2015). source
• Not checked yetcites [17] Klein, E. A. et al. Vitamin E and the risk of prostate cancer: the selenium and vitamin E cancer prevention trial (SELECT). JAMA 306, 1549–1556 (2011). source
• Not checked yetcites [18] Omenn, G. S. et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N. Engl. J. Med. 334, 1150–1155 (1996). source
• Not checked yetcites [19] Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group. The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. N. Engl. J. Med. 330, 1029–1035 (1994). source

In the paper

“we discuss three distinct vulnerabilities in cancer that can be exploited by pharmacological ascorbate.”

In the paper

“cancer cells often enhance pathways that help mitigate the toxic effects of ROS13”

What the sources say

• Not checked yetcites [13] Chio, I. I. C. & Tuveson, D. A. ROS in cancer: the burning question. Trends Mol. Med. 23, 411–429 (2017). source

In the paper

“these contradictory results can be explained, at least in part, by differences in the administration route of vitamin C”

What the sources say

• Not checked yetcites [2] Levine, M., Padayatty, S. J. & Espey, M. G. Vitamin C: a concentration-function approach yields pharmacology and therapeutic discoveries. Adv. Nutr. 2, 78–88 (2011). source

In the paper

“excessive ROS can also be detrimental to cancer cells.”

In the paper

“ROS can facilitate tumour development by stimulating cell proliferation and promoting genetic instability”

In the paper

“Numerous in vitro cell culture studies have shown that pharmacological ascorbate produces extracellular H2O2, which can directly kill cancer cells26–28.”

What the sources say

• Not checked yetcites [26] Chen, Q. et al. Pharmacologic ascorbic acid concentrations selectively kill cancer cells: action as a pro-drug to deliver hydrogen peroxide to tissues. Proc. Natl Acad. Sci. USA 102, 13604–13609 (2005). source
• Not checked yetcites [27] Du, J. et al. Mechanisms of ascorbate-induced cytotoxicity in pancreatic cancer. Clin. Cancer Res. 16, 509–520 (2010). source
• Not checked yetcites [28] Rawal, M. et al. Manganoporphyrins increase ascorbate-induced cytotoxicity by enhancing H2O2 generation. Cancer Res. 73, 5232–5241 (2013). source

In the paper

“In the presence of redox-active transition metals, such as iron, vitamin C exerts pro-oxidant effects.”

In the paper

“it can also function as a pro-oxidant at millimolar plasma concentrations, which can be achieved by intravenous administration of pharmacological ascorbate4”

What the sources say

• Not checked yetcites [4] Padayatty, S. J. & Levine, M. Vitamin C: the known and the unknown and Goldilocks. Oral Dis. 22, 463–493 (2016). source

In the paper

“increase the risk of prostate and lung cancers in patients17–19”

What the sources say

• Not checked yetcites [17] Klein, E. A. et al. Vitamin E and the risk of prostate cancer: the selenium and vitamin E cancer prevention trial (SELECT). JAMA 306, 1549–1556 (2011). source
• Not checked yetcites [18] Omenn, G. S. et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N. Engl. J. Med. 334, 1150–1155 (1996). source
• Not checked yetcites [19] Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group. The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. N. Engl. J. Med. 330, 1029–1035 (1994). source

In the paper

“This observation suggests that pharmacological ascorbate can cause DNA damage in in vivo tumours”

What the sources say

• Not checked yetcites [36] Ma, E. et al. Pharmacologic ascorbate induces neuroblastoma cell death by hydrogen peroxide mediated DNA damage and reduction in cancer cell glycolysis. Free Radic. Biol. Med. 113, 36–47 (2017). source

In the paper

“although an in vivo link between ascorbate and the generation of H2O2 has not been demonstrated in this study36.”

What the sources say

• Not checked yetcites [36] Ma, E. et al. Pharmacologic ascorbate induces neuroblastoma cell death by hydrogen peroxide mediated DNA damage and reduction in cancer cell glycolysis. Free Radic. Biol. Med. 113, 36–47 (2017). source

In the paper

“the millimolar concentration of vitamin C cytotoxic to cancer cells is achievable only by intravenous injection, not by oral administration2”

What the sources say

• Not checked yetcites [2] Levine, M., Padayatty, S. J. & Espey, M. G. Vitamin C: a concentration-function approach yields pharmacology and therapeutic discoveries. Adv. Nutr. 2, 78–88 (2011). source

In the paper

“Studies have shown that pharmacological vitamin C targets many of the mechanisms that cancer cells utilize for their survival and growth.”

In the paper

“physiological ascorbate at micromolar concentrations can reduce harmful ROS9”

What the sources say

• Not checked yetcites [9] Buettner, G. R. The pecking order of free radicals and antioxidants: lipid peroxidation, alpha-tocopherol, and ascorbate. Arch. Biochem. Biophys. 300, 535–543 (1993). source

In the paper

“When labile Fe2+ in these pools reacts with H2O2, it can generate the damaging hydroxyl radical (•OH) via the Fenton reaction21”

What the sources say

• Not checked yetcites [21] Torti, S. V. & Torti, F. M. Iron and cancer: more ore to be mined. Nat. Rev. Cancer 13, 342–355 (2013). source

In the paper

“vitamin C also functions as a critical cofactor for numerous enzymes by readily donating its electrons to prosthetic metal ions to achieve full enzymatic activity4”

What the sources say

• Not checked yetcites [4] Padayatty, S. J. & Levine, M. Vitamin C: the known and the unknown and Goldilocks. Oral Dis. 22, 463–493 (2016). source

In the paper

“antioxidant treatment even appeared to accelerate cancer progression and metastasis in mouse models of lung adenocarcinoma and melanoma14–16”

What the sources say

• Not checked yetcites [14] Sayin, V. I. et al. Antioxidants accelerate lung cancer progression in mice. Sci. Transl Med. 6, 221ra15 (2014). This study demonstrates that dietary supplementation of antioxidants ( N -acetylcysteine and vitamin E) markedly increases tumour progression and reduces survival in mouse models of KRAS-induced or BRAF-induced lung cancer. source
• Not checked yetcites [15] Le Gal, K. et al. Antioxidants can increase melanoma metastasis in mice. Sci. Transl Med. 7, 308re8 (2015). source
• Not checked yetcites [16] Piskounova, E. et al. Oxidative stress inhibits distant metastasis by human melanoma cells. Nature 527, 186–191 (2015). source

In the paper

“cancer cells experience more oxidative stress compared with normal cells owing to an elevated metabolic rate and defective mitochondria12”

What the sources say

• Not checked yetcites [12] Schieber, M. & Chandel, N. S. ROS function in redox signaling and oxidative stress. Curr. Biol. 24, R453–R462 (2014). source

In the paper

“tumour-associated macrophages may promote iron release in the tumour microenvironments40,41.”

What the sources say

• Not checked yetcites [40] Corna, G. et al. Polarization dictates iron handling by inflammatory and alternatively activated macrophages. Haematologica 95, 1814–1822 (2010). source
• Not checked yetcites [41] Recalcati, S. et al. Differential regulation of iron homeostasis during human macrophage polarized activation. Eur. J. Immunol. 40, 824–835 (2010). source

In the paper

“This metabolic reprogramming, also known as the Warburg effect, is essential for tumour survival and proliferation45.”

What the sources say

• Not checked yetcites [45] Liberti, M. V. & Locasale, J. W. The Warburg effect: how does it benefit cancer cells? Trends Biochem. Sci. 41, 211–218 (2016). source

In the paper

“Most of the aberrant DNA hypermethylation patterns observed in cancer can be explained by mutations or altered expression of two protein families: gain of function of DNA methyltransferases (DNMTs; which methylate cytosine to generate 5-methylcytosine (5mC)) and loss of function of ten-eleven translocation (TET) proteins.”

In the paper

“Tumour cells exhibit a high rate of glycolysis, even in conditions with ample oxygen — a phenomenon that was first described by Otto Warburg, nearly a century ago22.”

What the sources say

• Not checked yetcites [22] DeBerardinis, R. J. & Chandel, N. S. Fundamentals of cancer metabolism. Sci. Adv. 2, e1600200 (2016). source

In the paper

“The fact that the most obvious and immediate oxidative stress effects of high-dose ascorbate in this genetic disorder occur in erythrocytes indicates the importance of increased GLUT1 levels and dependency on glycolysis in ascorbate-induced oxidative stress.”

In the paper

“cancer cells with high GLUT1 but not sodium-dependent vitamin C transporters exclusively take up ascorbate in the form of DHA both in vitro or in vivo6,8,47,53.”

What the sources say

• Not checked yetcites [6] Corti, A., Casini, A. F. & Pompella, A. Cellular pathways for transport and efflux of ascorbate and dehydroascorbate. Arch. Biochem. Biophys. 500, 107–115 (2010). source
• Not checked yetcites [8] Wilson, J. X. The physiological role of dehydroascorbic acid. FEBS Lett. 527, 5–9 (2002). source
• Not checked yetcites [47] Yun, J. et al. Vitamin C selectively kills KRAS and BRAF mutant colorectal cancer cells by targeting GAPDH. Science 350, 1391–1396 (2015). This study demonstrates that uptake of DHA by GLUT1, and its subsequent reduction to ascorbate, depletes essential antioxidants to induce cell death in KRAS or BRAF mutant CRC cells. source

In the paper

“reprogramming of iron metabolism can occur via a variety of mechanisms, including the upregulation of several iron-intake pathways or downregulation of iron export and storage pathways in various types of cancer such as breast, prostate and lymphoma37,38.”

What the sources say

• Not checked yetcites [37] Rychtarcikova, Z. et al. Tumor-initiating cells of breast and prostate origin show alterations in the expression of genes related to iron metabolism. Oncotarget 8, 6376–6398 (2017). source
• Not checked yetcites [38] Kiessling, M. K. et al. Inhibition of constitutively activated nuclear factor-kappaB induces reactive oxygen species- and iron-dependent cell death in cutaneous T cell lymphoma. Cancer Res. 69, 2365–2374 (2009). source

In the paper

“Patients with glucose 6-phosphate dehydrogenase (G6PD) deficiency showed haemolytic anaemia following high-dose intravenous ascorbate therapy56–59.”

What the sources say

• Not checked yetcites [56] Rees, D. C., Kelsey, H. & Richards, J. D. Acute haemolysis induced by high dose ascorbic acid in glucose-6-phosphate dehydrogenase deficiency. BMJ 306, 841–842 (1993). source
• Not checked yetcites [57] Quinn, J. et al. Effect of high-dose vitamin C infusion in a glucose-6-phosphate dehydrogenase-deficient patient. Case Rep. Med. 2017, 5202606 (2017). source
• Not checked yetcites [58] Rakitzis, E. T. & Papandreou, P. T. Ascorbate-induced generation of free radical species in normal and glucose-6-phosphate dehydrogenase-deficient erythrocytes. Biochem. Soc. Trans. 17, 371–372 (1989). source
• Not checked yetcites [59] Mehta, J., Singhal, S. & Mehta, B. Ascorbic-acid-induced haemolysis in G-6-PD deficiency. Lancet 336, 944 (1990). source

In the paper

“an increased level of mitochondrial ROS in lung and glioblastoma cancer cells led to increased levels of intracellular labile iron through the upregulation of the Tf receptor (TfR), thus increasing the sensitivity of these cancer cells to ascorbate43.”

What the sources say

• Not checked yetcites [43] Schoenfeld, J. D. et al. O2 •− and H2O2 −mediated disruption of Fe metabolism causes the differential susceptibility of NSCLC and GBM cancer cells to pharmacological ascorbate. Cancer Cell 31, 487–500 (2017). This study shows that pharmacological ascorbate selectively sensitizes non-small-cell lung cancer (NSCLC) and glioblastoma (GBM) cells by generating redox-active labile iron and H 2O2 using in vitro cell lines and mouse models. In addition, it shows the potential efficacy of ascorbate therapy combined with other chemotherapies in patients with GBM and NSCLC. source

In the paper

“ascorbate has a significantly longer half-life in cell culture medium and plasma.”

In the paper

“ascorbate therapy may be extended to other cancers as long as they present high GLUT1 expression and high glycolytic activity.”

In the paper

“tumour cells with the high levels of extracellular and/or intracellular labile iron may be more vulnerable to high-dose ascorbate than normal cells as they can generate more H2O2 and •OH than normal cells”

In the paper

“Because the tumour microenvironment is known to be oxidative54,55, adding high concentrations of ascorbate would efficiently and continuously generate DHA from ascorbate.”

What the sources say

• Not checked yetcites [54] Szatrowski, T. P. & Nathan, C. F. Production of large amounts of hydrogen peroxide by human tumor cells. Cancer Res. 51, 794–798 (1991).
• Not checked yetcites [55] Policastro, L. L. et al. The tumor microenvironment: characterization, redox considerations, and novel approaches for reactive oxygen species-targeted gene therapy. Antioxid. Redox Signal. 19, 854–895 (2013). source

In the paper

“human erythrocytes without G6PD, the rate-limiting enzyme in PPP, cannot produce enough NADPH, a critical molecule for recovering depleted levels of GSH caused by vitamin-C-induced oxidative stress, which leads to the death of erythrocytes, thereby causing anaemia.”

In the paper

“Bolus treatment of high-dose DHA has only transient effects on cancer cells in vitro and in vivo owing to its extreme instability in neutral pH25.”

What the sources say

• Not checked yetcites [25] Du, J., Cullen, J. J. & Buettner, G. R. Ascorbic acid: chemistry, biology and the treatment of cancer. Biochim. Biophys. Acta 1826, 443–457 (2012).

In the paper

“Patients with advanced breast cancer have significantly higher levels of Fe2+ in plasma than healthy human control groups42.”

What the sources say

• Not checked yetcites [42] Panis, C. et al. Differential oxidative status and immune characterization of the early and advanced stages of human breast cancer. Breast Cancer Res. Treat. 133, 881–888 (2012). source

In the paper

“when the oxidation of millimolar levels of ascorbate generates extracellular H2O2 as we discussed before, this will result in high amounts of extracellular DHA as DHA is the main oxidized form of ascorbate.”

In the paper

“the pool of intracellular labile Fe2+ in breast cancer cells is approximately twice as high as in normal breast epithelial cells39.”

What the sources say

• Not checked yetcites [39] Pinnix, Z. K. et al. Ferroportin and iron regulation in breast cancer progression and prognosis. Sci. Transl Med. 2, 43ra56 (2010). source

In the paper

“cancer cells have a high demand for easily accessible labile Fe2+ for their survival and growth.”

What the sources say

• Not checked yetcites [23] Manz, D. H. et al. Iron and cancer: recent insights. Ann. NY Acad. Sci. 1368, 149–161 (2016). source
• Not checked yetcites [36] Ma, E. et al. Pharmacologic ascorbate induces neuroblastoma cell death by hydrogen peroxide mediated DNA damage and reduction in cancer cell glycolysis. Free Radic. Biol. Med. 113, 36–47 (2017). source

In the paper

“exploiting the selective expression of GLUT1 and the metabolic liability associated with increased reliance on glycolysis may be a viable therapeutic strategy to target cancer.”

In the paper

“degradation of DHA generates many undesirable chemicals such as 2,3-DKG and oxalate25, which may confound the efficacy of ascorbate therapy.”

What the sources say

• Not checked yetcites [25] Du, J., Cullen, J. J. & Buettner, G. R. Ascorbic acid: chemistry, biology and the treatment of cancer. Biochim. Biophys. Acta 1826, 443–457 (2012).

In the paper

“Oncogenic KRAS or BRAF mutations contribute to the Warburg effect, in part by upregulating GLUT1 (REF46).”

What the sources say

• Not checked yetcites [46] Yun, J. et al. Glucose deprivation contributes to the development of KRAS pathway mutations in tumor cells. Science 325, 1555–1559 (2009). source

In the paper

“a phase I clinical study revealed that ascorbate concentrations could safely reach 25–30 mM with intravenous infusion of 100 g of vitamin C98.”

What the sources say

• Not checked yetcites [98] Hoffer, L. J. et al. Phase I clinical trial of i.v. ascorbic acid in advanced malignancy. Ann. Oncol. 19, 1969–1974 (2008). source

In the paper

“in a large acute myelogenous leukaemia (AML) cohort, TET2 was found to be mutually exclusive with gain-of-function mutations in isocitrate dehydrogenase 1 (IDH1) and IDH2 (REF.65).”

What the sources say

• Not checked yetcites [65] Figueroa, M. E. et al. Leukemic IDH1 and IDH2 mutations result in a hypermethylation phenotype, disrupt TET2 function, and impair hematopoietic differentiation. Cancer Cell 18, 553–567 (2010). source

In the paper

“the differences between oral and intravenous administration routes can affect the maximum achievable plasma concentration in patients.”

What the sources say

• Not checked yetcites [97] Padayatty, S. J. et al. Vitamin C pharmacokinetics: implications for oral and intravenous use. Ann. Intern. Med. 140, 533–537 (2004). This paper emphasizes the importance of the route of administration of vitamin C and explains why two early clinical trials of vitamin C as an anticancer therapy had conflicting results. source

In the paper

“there is growing evidence that HIF1α-dependent tumour growth may be inhibited by ascorbate78,79.”

What the sources say

• Not checked yetcites [78] Wilkes, J. G. et al. Pharmacologic ascorbate (P-AscH-) suppresses hypoxia-inducible Factor-1α (HIF-1α) in pancreatic adenocarcinoma. Clin. Exp. Metastasis 35, 37–51 (2018). source
• Not checked yetcites [79] Gao, P. et al. HIF-dependent anti-tumorigenic effect of anti-oxidants in vivo. Cancer Cell 12, 230–238 (2007). source

In the paper

“Many solid tumours encounter hypoxia as tumour masses can obstruct and compress surrounding blood vessels and tumour cells can outgrow new blood vessels.”

In the paper

“oral ascorbate may have a preventive role in leukaemogenesis72.”

What the sources say

• Not checked yetcites [72] Agathocleous, M. et al. Ascorbate regulates haematopoietic stem cell function and leukaemogenesis. Nature 549, 476–481 (2017). Using various GEMMs, including GULO-knockout mice, this study reveals that vitamin C is necessary for normal haematopoietic stem cell development and the prevention of leukaemia in mice. source

In the paper

“TET proteins (TET1, TET2 and TET3) demethylate DNA and belong to the αKGDD enzyme family. Using oxygen and αKG, they catalyse multiple oxidation reactions, first converting 5mC to 5-hydroxymethylcytosine (5hmC), which ultimately results in an unmodified cytosine”

In the paper

“daily intraperitoneal injection of high-dose ascorbate (4 g kg−1) treatment in an inducible TET2 deletion mouse model of leukaemia recapitulated the TET2 restoration phenotypes by promoting DNA demethylation and the expression of genes critical for myeloid cell differentiation67.”

What the sources say

• Not checked yetcites [67] Cimmino, L. et al. Restoration of TET2 function blocks aberrant self-renewal and leukemia progression. Cell 170, 1079–1095 (2017). Using genetic mouse models of leukaemia, vitamin C is shown to enhance TET2 activity, increase DNA demethylation and suppress leukaemia progression. source

In the paper

“It is now widely accepted that the millimolar concentration of ascorbate needed to induce cytotoxicity in cancer cells can be achieved only when administered intravenously97.”

What the sources say

• Not checked yetcites [97] Padayatty, S. J. et al. Vitamin C pharmacokinetics: implications for oral and intravenous use. Ann. Intern. Med. 140, 533–537 (2004). This paper emphasizes the importance of the route of administration of vitamin C and explains why two early clinical trials of vitamin C as an anticancer therapy had conflicting results. source

In the paper

“TET2 is frequently mutated or lost somatically in both myeloid and lymphoid malignancies63,64.”

What the sources say

• Not checked yetcites [63] Rasmussen, K. D. & Helin, K. Role of TET enzymes in DNA methylation, development, and cancer. Genes Dev. 30, 733–750 (2016). source
• Not checked yetcites [64] Delhommeau, F. et al. Mutation in TET2 in myeloid cancers. N. Engl. J. Med. 360, 2289–2301 (2009). source

In the paper

“Using human patient tumour samples and paired controls for endometrial cancer, renal cell carcinoma (RCC) and CRC, it was demonstrated that tumours that had the highest HIF1 activity were those deficient in ascorbate in tumours84–86.”

What the sources say

• Not checked yetcites [84] Kuiper, C. et al. Increased tumor ascorbate is associated with extended disease-free survival and decreased hypoxia-inducible factor-1 activation in human colorectal cancer. Front. Oncol. 4, 10 (2014).
• Not checked yetcites [85] Wohlrab, C. et al. The association between ascorbate and the hypoxia-inducible factors in human renal cell carcinoma requires a functional Von Hippel-Lindau protein. Front. Oncol. 8, 574 (2018). source
• Not checked yetcites [86] Kuiper, C. et al. Low ascorbate levels are associated with increased hypoxia-inducible factor-1 activity and an aggressive tumor phenotype in endometrial cancer. Cancer Res. 70, 5749–5758 (2010). source

In the paper

“This study shows that pharmacological ascorbate is a prodrug for preferential steady-state formation of Asc•- and H2O2 in the extracellular space but not in the blood in vivo system.”

What the sources say

• Not checked yetcites [35] Chen, Q. et al. Ascorbate in pharmacologic concentrations selectively generates ascorbate radical and hydrogen peroxide in extracellular fluid in vivo. Proc. Natl Acad. Sci. USA 104, 8749–8754 (2007). This study shows that pharmacological ascorbate is a prodrug for preferential steady-state formation of Asc •− and H2O2 in the extracellular space but not in the blood in vivo system. source

In the paper

“On the basis of current preclinical studies, ascorbate may be more effective in patients with cancer with mutations in KRAS, BRAF, TET2, IDH1 and/or IDH2, VHL, SH or FDH.”

In the paper

“Using various GEMMs, including GULO-knockout mice, this study reveals that vitamin C is necessary for normal haematopoietic stem cell development and the prevention of leukaemia in mice.”

What the sources say

• Not checked yetcites [72] Agathocleous, M. et al. Ascorbate regulates haematopoietic stem cell function and leukaemogenesis. Nature 549, 476–481 (2017). Using various GEMMs, including GULO-knockout mice, this study reveals that vitamin C is necessary for normal haematopoietic stem cell development and the prevention of leukaemia in mice. source

In the paper

“Combining vitamin C with immune checkpoint inhibitors and immunomodulatory agents, such as cytotoxic T lymphocyte-associated protein 4 (CTLA4) receptor and programmed death 1 (PD-1)–programmed death ligand 1 (PD-L1) blockers, may also lead to durable therapeutic responses against a broad spectrum of cancers.”

In the paper

“Using genetic mouse models of leukaemia, vitamin C is shown to enhance TET2 activity, increase DNA demethylation and suppress leukaemia progression.”

What the sources say

• Not checked yetcites [67] Cimmino, L. et al. Restoration of TET2 function blocks aberrant self-renewal and leukemia progression. Cell 170, 1079–1095 (2017). Using genetic mouse models of leukaemia, vitamin C is shown to enhance TET2 activity, increase DNA demethylation and suppress leukaemia progression. source

In the paper

“A compelling hypothesis is offered by the utilization and combination of high-dose vitamin C, which is known to enhance the function of both innate and adaptive immune cells109,110.”

What the sources say

• Not checked yetcites [109] Carr, A. C. & Maggini, S. Vitamin C and immune function. Nutrients 9, 1211 (2017). source
• Not checked yetcites [110] Sorice, A. et al. Ascorbic acid: its role in immune system and chronic inflammation diseases. Mini Rev. Med. Chem. 14, 444–452 (2014). source

In the paper

“A significant number of human studies consistently show that ascorbate treatment improved quality of life for patients with cancer, and in combination therapy, ascorbate protected normal tissues from toxicity caused by chemotherapy114.”

What the sources say

• Not checked yetcites [114] Ma, Y. et al. High-dose parenteral ascorbate enhanced chemosensitivity of ovarian cancer and reduced toxicity of chemotherapy. Sci. Transl Med. 6, 222ra18 (2014). This paper shows in its preclinical and clinical studies that high-dose vitamin C can potentially increase the efficacy and reduce the toxicities of certain conventional chemotherapies when used in combination to treat patients with ovarian cancer. source

In the paper

“Although not much is known about how ascorbate is utilized by the various cells that make up the tumour microenvironment, studies have shown that phagocytes and lymphocytes have ascorbate concentrations 10–100 times greater than plasma4.”

What the sources say

• Not checked yetcites [4] Padayatty, S. J. & Levine, M. Vitamin C: the known and the unknown and Goldilocks. Oral Dis. 22, 463–493 (2016). source

In the paper

“Although we identified three distinct mechanisms by which high-dose ascorbate can inhibit cancer growth, it is possible that each mechanism may not work independently.”

In the paper

“A significant number of human studies consistently show that ascorbate treatment improved quality of life for patients with cancer, and in combination therapy, ascorbate protected normal tissues from toxicity caused by chemotherapy114.”

What the sources say

• Not checked yetcites [114] Ma, Y. et al. High-dose parenteral ascorbate enhanced chemosensitivity of ovarian cancer and reduced toxicity of chemotherapy. Sci. Transl Med. 6, 222ra18 (2014). This paper shows in its preclinical and clinical studies that high-dose vitamin C can potentially increase the efficacy and reduce the toxicities of certain conventional chemotherapies when used in combination to treat patients with ovarian cancer. source

In the paper

“Given that more than forty αKGDDs exist112, it is possible that other αKGDDs could contribute to the anticancer mechanisms of ascorbate.”

What the sources say

• Not checked yetcites [112] Hausinger, R. P. FeII/alpha-ketoglutarate-dependent hydroxylases and related enzymes. Crit. Rev. Biochem. Mol. Biol. 39, 21–68 (2004). source

In the paper

“For example, on the basis of ascorbate’s known DNA demethylation effects via TET activation, a recent study found that vitamin C enhanced the effect of the DNMT inhibitor 5-aza-CdR (decitabine) by promoting the demethylation of human endogenous retroviruses and amplifying the expression of interferon-stimulated genes, leading to cancer cell death106,107.”

What the sources say

• Not checked yetcites [106] Liu, M. et al. Vitamin C increases viral mimicry induced by 5-aza-2′-deoxycytidine. Proc. Natl Acad. Sci. USA 113, 10238–10244 (2016). source
• Not checked yetcites [107] Zhao, H. et al. The synergy of Vitamin C with decitabine activates TET2 in leukemic cells and significantly improves overall survival in elderly patients with acute myeloid leukemia. Leuk. Res. 66, 1–7 (2018). source

In the paper

“In addition, it shows the potential efficacy of ascorbate therapy combined with other chemotherapies in patients with GBM and NSCLC.”

What the sources say

• Not checked yetcites [43] Schoenfeld, J. D. et al. O2 •− and H2O2 −mediated disruption of Fe metabolism causes the differential susceptibility of NSCLC and GBM cancer cells to pharmacological ascorbate. Cancer Cell 31, 487–500 (2017). This study shows that pharmacological ascorbate selectively sensitizes non-small-cell lung cancer (NSCLC) and glioblastoma (GBM) cells by generating redox-active labile iron and H 2O2 using in vitro cell lines and mouse models. In addition, it shows the potential efficacy of ascorbate therapy combined with other chemotherapies in patients with GBM and NSCLC. source

In the paper

“Numerous preclinical and clinical studies indicate that parenteral injection of pharmacological ascorbate does not interfere with chemotherapy or radiotherapy and may even act synergistically43,104,105.”

What the sources say

• Not checked yetcites [43] Schoenfeld, J. D. et al. O2 •− and H2O2 −mediated disruption of Fe metabolism causes the differential susceptibility of NSCLC and GBM cancer cells to pharmacological ascorbate. Cancer Cell 31, 487–500 (2017). This study shows that pharmacological ascorbate selectively sensitizes non-small-cell lung cancer (NSCLC) and glioblastoma (GBM) cells by generating redox-active labile iron and H 2O2 using in vitro cell lines and mouse models. In addition, it shows the potential efficacy of ascorbate therapy combined with other chemotherapies in patients with GBM and NSCLC. source
• Not checked yetcites [104] Mustafi, S. et al. Vitamin C sensitizes melanoma to BET inhibitors. Cancer Res. 78, 572–583 (2018). source
• Not checked yetcites [105] Du, J. et al. Pharmacological ascorbate radiosensitizes pancreatic cancer. Cancer Res. 75, 3314–3326 (2015). source

In the paper

“For example, subpopulations of KRAS or BRAF mutant CRC cells that were not completely killed via the pro-oxidant mechanism in vivo — potentially owing to their distance from blood vessels, poor perfusion101 or resistance to ROS — may still be affected by ascorbate therapy via inhibition of HIF1 signalling and/or activation of TET enzymes.”

What the sources say

• Not checked yetcites [101] Kuiper, C., Vissers, M. C. M. & Hicks, K. O. Pharmacokinetic modeling of ascorbate diffusion through normal and tumor tissue. Free Radic. Biol. Med. 77, 340–352 (2014). source

In the paper

“This study demonstrates that uptake of DHA by GLUT1, and its subsequent reduction to ascorbate, depletes essential antioxidants to induce cell death in KRAS or BRAF mutant CRC cells.”

What the sources say

• Not checked yetcites [47] Yun, J. et al. Vitamin C selectively kills KRAS and BRAF mutant colorectal cancer cells by targeting GAPDH. Science 350, 1391–1396 (2015). This study demonstrates that uptake of DHA by GLUT1, and its subsequent reduction to ascorbate, depletes essential antioxidants to induce cell death in KRAS or BRAF mutant CRC cells. source

In the paper

“Although we are still waiting on a definitive answer for the clinical benefits of ascorbate therapy in cancer, current preclinical and early phase I/II clinical trial results suggest that Linus Pauling’s claims regarding the therapeutic benefits of vitamin C therapy in cancer may not be so outrageous after all.”

In the paper

“These effects are likely caused by non-cell autonomous mechanisms, and if so, whole organisms or co-culture systems, rather than cancer cell lines themselves, would be crucial to discovering mechanisms of ascorbate’s indirect effects on cancer cells.”

In the paper

“Although pharmacological ascorbate alone has been shown to reduce the tumour growth in many different mouse models of cancer, the clinical potential of ascorbate as an anticancer therapy may also lie in its combined use with other cancer therapies3,11.”

What the sources say

• Not checked yetcites [3] Nauman, G. et al. Systematic review of intravenous ascorbate in cancer clinical trials. Antioxidants 7, E89 (2018). source
• Not checked yetcites [11] Kuiper, C. & Vissers, M. C. M. Ascorbate as a co-factor for fe- and 2-oxoglutarate dependent dioxygenases: physiological activity in tumor growth and progression. Front. Oncol. 4, 359 (2014).

In the paper

“Moreover, a wealth of knowledge is emerging that highlights the influence of ascorbate in inflammatory response and immune cell function110,111, which suggests that ascorbate may have synergistic effects when combined with current immunotherapy.”

What the sources say

• Not checked yetcites [110] Sorice, A. et al. Ascorbic acid: its role in immune system and chronic inflammation diseases. Mini Rev. Med. Chem. 14, 444–452 (2014). source
• Not checked yetcites [111] Ang, A. et al. Vitamin C and immune cell function in inflammation and cancer. Biochem. Soc. Trans. 46, 1147–1159 (2018). source

In the paper

“Because decitabine is approved by the US Food and Drug Administration for the treatment of patients with myelodysplastic syndromes, where TET2 is also frequently deleted108, it would be interesting to test these combinations in clinical trials.”

What the sources say

• Not checked yetcites [108] Gillberg, L. et al. Vitamin C — a new player in regulation of the cancer epigenome. Semin. Cancer Biol. 51, 59–67 (2017). source

In the paper

“Using various GEMMs, including GULO-knockout mice, this study reveals that vitamin C is necessary for normal haematopoietic stem cell development and the prevention of leukaemia in mice.”

What the sources say

• Not checked yetcites [72] Agathocleous, M. et al. Ascorbate regulates haematopoietic stem cell function and leukaemogenesis. Nature 549, 476–481 (2017). Using various GEMMs, including GULO-knockout mice, this study reveals that vitamin C is necessary for normal haematopoietic stem cell development and the prevention of leukaemia in mice. source

In the paper

“Numerous preclinical and clinical studies indicate that parenteral injection of pharmacological ascorbate does not interfere with chemotherapy or radiotherapy and may even act synergistically43,104,105.”

What the sources say

• Not checked yetcites [43] Schoenfeld, J. D. et al. O2 •− and H2O2 −mediated disruption of Fe metabolism causes the differential susceptibility of NSCLC and GBM cancer cells to pharmacological ascorbate. Cancer Cell 31, 487–500 (2017). This study shows that pharmacological ascorbate selectively sensitizes non-small-cell lung cancer (NSCLC) and glioblastoma (GBM) cells by generating redox-active labile iron and H 2O2 using in vitro cell lines and mouse models. In addition, it shows the potential efficacy of ascorbate therapy combined with other chemotherapies in patients with GBM and NSCLC. source
• Not checked yetcites [104] Mustafi, S. et al. Vitamin C sensitizes melanoma to BET inhibitors. Cancer Res. 78, 572–583 (2018). source
• Not checked yetcites [105] Du, J. et al. Pharmacological ascorbate radiosensitizes pancreatic cancer. Cancer Res. 75, 3314–3326 (2015). source

In the paper

“Using genetic mouse models of leukaemia, vitamin C is shown to enhance TET2 activity, increase DNA demethylation and suppress leukaemia progression.”

What the sources say

• Not checked yetcites [67] Cimmino, L. et al. Restoration of TET2 function blocks aberrant self-renewal and leukemia progression. Cell 170, 1079–1095 (2017). Using genetic mouse models of leukaemia, vitamin C is shown to enhance TET2 activity, increase DNA demethylation and suppress leukaemia progression. source

In the paper

“Although pharmacological ascorbate alone has been shown to reduce the tumour growth in many different mouse models of cancer, the clinical potential of ascorbate as an anticancer therapy may also lie in its combined use with other cancer therapies3,11.”

What the sources say

• Not checked yetcites [3] Nauman, G. et al. Systematic review of intravenous ascorbate in cancer clinical trials. Antioxidants 7, E89 (2018). source
• Not checked yetcites [11] Kuiper, C. & Vissers, M. C. M. Ascorbate as a co-factor for fe- and 2-oxoglutarate dependent dioxygenases: physiological activity in tumor growth and progression. Front. Oncol. 4, 359 (2014).

In the paper

“Using genetic mouse models of leukaemia, vitamin C is shown to enhance TET2 activity, increase DNA demethylation and suppress leukaemia progression.”

What the sources say

• Not checked yetcites [67] Cimmino, L. et al. Restoration of TET2 function blocks aberrant self-renewal and leukemia progression. Cell 170, 1079–1095 (2017). Using genetic mouse models of leukaemia, vitamin C is shown to enhance TET2 activity, increase DNA demethylation and suppress leukaemia progression. source

In the paper

“In conclusion, high-dose intravenous ascorbate represents a promising and inexpensive anticancer therapeutic option that should be further explored in clinical trials.”

In the paper

“This study is the first large-scale clinical trial designed to analyse the efficacy of high-dose ascorbate for the treatment of cancer.”

What the sources say

• Not checked yetcites [93] Cameron, E. & Pauling, L. Supplemental ascorbate in the supportive treatment of cancer: prolongation of survival times in terminal human cancer. Proc. Natl Acad. Sci. USA 73, 3685–3689 (1976). This study is the first large-scale clinical trial designed to analyse the efficacy of high-dose ascorbate for the treatment of cancer. source

In the paper

“This large-scale clinical trial shows that daily oral intake of high-dose vitamin C had no therapeutic benefit in patients with cancer.”

What the sources say

• Not checked yetcites [95] Creagan, E. T. et al. Failure of high-dose vitamin C (ascorbic acid) therapy to benefit patients with advanced cancer. A controlled trial. N. Engl. J. Med. 301, 687–690 (1979). This large-scale clinical trial shows that daily oral intake of high-dose vitamin C had no therapeutic benefit in patients with cancer. source