Targeting cancer vulnerabilities with high-dose vitamin C

In the paper

“ROS leads to activation of poly(ADP-ribose) polymerase (PARP), which in turn leads to depletion of NAD+ (a key cofactor of GAPDH), thereby further inhibiting GAPDH47”

What the sources say

• Partly supported

  The Main Text reports that vitamin C treatment increased ROS and PARP activation while lowering NAD+ in KRAS- and BRAF-mutant cells. It describes PARP-mediated NAD+ depletion as a mechanism that may further inhibit GAPDH, so the citing sentence states that specific causal link more definitively than the paper does. (LLM, conf=0.83)

  cites [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. sourceExperimental — accuracy not yet measured

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
• Supported

  The Summary states that ascorbate availability influences immune cell function in hypoxic inflammatory environments and affects the resolution of inflammation. The T-cell section also describes effects on immune-cell differentiation and function. The sentence’s suggestion about synergy with immunotherapy is the citing authors’ inference, not part of the claim attributed to this source. (LLM, conf=0.93)

  cites [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

“daily intraperitoneal injection of ascorbate (4 g kg−1) inhibited tumour growth in Apc−/−;KrasG12D/+ mutant mice whereas it did not affect tumour growth in Apc−/− mice47.”

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

“When ascorbate is administered, it is oxidized to DHA. Owing to its structural similarity to glucose, DHA is efficiently taken up via GLUT1 in KRAS or BRAF mutant cells47,48”

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 [48] Nualart, F. J. et al. Recycling of vitamin C by a bystander effect. J. Biol. Chem. 278, 10128–10133 (2003). source

In the paper

“This reduction depletes intracellular antioxidants and increases endogenous levels of ROS47,50.”

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 [50] Tu, H. et al. Chemical transport knockout for oxidized vitamin C, dehydroascorbic acid, reveals its functions in vivo. EBioMedicine 23, 125–135 (2017). source

In the paper

“current pro-oxidant strategies often cause serious collateral damage, resulting in a narrow therapeutic window20”

What the sources say

• Not checked yetcites [20] Wondrak, G. T. Redox-directed cancer therapeutics: molecular mechanisms and opportunities. Antioxid. Redox Signal. 11, 3013–3069 (2009). source

In the paper

“we discuss how vitamin C can target three vulnerabilities many cancer cells share: redox imbalance, epigenetic reprogramming and oxygen-sensing regulation.”

In the paper

“they are not mutually exclusive and can occur simultaneously, synergizing the selective toxicity of ascorbate in cancer cells”

In the paper

“millimolar concentrations of pharmacological vitamin C can kill cancer cells in vitro and slow tumour growth in vivo”

In the paper

“certain cancer types may rely on antioxidants for survival and may thus be vulnerable to pro-oxidant therapies.”

In the paper

“daily intraperitoneal injection with high-dose ascorbate (4 g kg−1) inhibited neuroblastoma growth in a xenograft model, and tumours had the increased activity of checkpoint kinase 2 (CHK2) and histone 2AX (H2AX).”

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

“Asc•− and H2O2 were generated in vivo following intravenous ascorbate injections in rats (0.5 g kg−1), and the production was ascorbate-dose-dependent35.”

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

“ascorbate effectively donates electrons to Fe3+ to regenerate redox-active Fe2+, thereby generating ROS continuously and contributing to cell death25”

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

“extracellular H2O2 can contribute to the increased level of extracellular DHA by generating an oxidative microenvironment. As a result, DHA is transported into tumours that express high levels of glucose transporter 1 (GLUT1), generating oxidative stress in those cells”

In the paper

“they have an increased level of antioxidant enzymes and enhanced glucose flux into the pentose phosphate pathway (ppp)60,61 to generate more NADPH. In a normal setting, this protects erythrocytes from high-dose ascorbate.”

What the sources say

• Not checked yetcites [60] Gaetani, G. F. et al. Predominant role of catalase in the disposal of hydrogen peroxide within human erythrocytes. Blood 87, 1595–1599 (1996). source
• Not checked yetcites [61] May, J. M., Qu, Z. & Morrow, J. D. Mechanisms of ascorbic acid recycling in human erythrocytes. Biochim. Biophys. Acta 1528, 159–166 (2001). source

In the paper

“multiple myeloma cells have an elevated labile iron pool owing to the low expression of the iron exporter, ferroportin 1, which led to their selective sensitivity to pharmacological doses of ascorbate44.”

What the sources say

• Not checked yetcites [44] Xia, J. et al. Multiple myeloma tumor cells are selectively killed by pharmacologically-dosed ascorbic acid. EBioMedicine 18, 41–49 (2017). source

In the paper

“Epigenetic reprogramming in cancer includes DNA hypermethylation, which frequently occurs on CpG island promoter regions and is known to silence tumour suppressors such as the retinoblastoma and VHL tumour suppressors62.”

What the sources say

• Not checked yetcites [62] Yun, J. et al. Interactions between epigenetics and metabolism in cancers. Front. Oncol. 2, 163 (2012).

In the paper

“if the tumour microenvironment is enriched for labile iron, its reaction with ascorbate will generate H2O2 and •OH, which can be lethal to cancer cells.”

In the paper

“erythrocytes (red blood cells) have a high expression of GLUT1 and are dependent on glycolysis for their energy source (similar to KRAS or BRAF mutant cells)”

In the paper

“if tumour cells have increased levels of intracellular labile iron compared with normal cells, extracellular H2O2 from ascorbate autoxidation can diffuse into tumour cells and react with the intracellular pools of labile iron and generate •OH within tumour cells.”

In the paper

“both HIF hydroxylases belong to Fe2+-containing αKGDDs that require O2 and αKG as substrates. Because of their relatively lower affinity for O2 (Michaelis constant (Km) = 230–250 μM) compared with other αKGDDs76, under hypoxic conditions, PHDs and FIHs are inactive, leading to the stabilization and activation of HIF1.”

What the sources say

• Not checked yetcites [76] Koivunen, P. et al. Catalytic properties of the asparaginyl hydroxylase (FIH) in the oxygen sensing pathway are distinct from those of its prolyl 4-hydroxylases. J. Biol. Chem. 279, 9899–9904 (2004). source

In the paper

“FIHs hydroxylate an asparagine residue on HIF1α, which blocks the association of HIF1α with the p300 co-activator protein, resulting in the inhibition of the transcription activity of HIF 1”

In the paper

“In certain types of lymphomas where TETs are frequently mutated, ascorbate treatment in vitro increased TET activity, leading to DNA demethylation, increased expression of tumour suppressor genes and increased chemosensitivity69.”

What the sources say

• Not checked yetcites [69] Shenoy, N. et al. Upregulation of TET activity with ascorbic acid induces epigenetic modulation of lymphoma cells. Blood Cancer J. 7, e587 (2017). source

In the paper

“lung carcinoma implanted in Gulo−/− mice grew slowly when mice were treated with high-dose ascorbate either in drinking water (3.3 g per litre) or daily intraperitoneal injection (1 gkg−1) as compared with Gulo−/− mice treated with low-dose ascorbate in drinking water (0.33 g per litre), and tumours exposed to high-dose ascorbate also had reduced expression levels of HIF1α, VEGF and reduced microv”

What the sources say

• Not checked yetcites [81] Campbell, E. J. et al. Restoring physiological levels of ascorbate slows tumor growth and moderates HIF-1 pathway activity in Gulo(−/−) mice. Cancer Med. 4, 303–314 (2015). source
• Not checked yetcites [82] Campbell, E. J., Vissers, M. C. & Dachs, G. U. Ascorbate availability affects tumor implantation-take rate and increases tumor rejection in Gulo−/− mice. Hypoxia 4, 41–52 (2016).
• Not checked yetcites [83] Campbell, E. J. et al. Pharmacokinetic and anti-cancer properties of high dose ascorbate in solid tumours of ascorbate-dependent mice. Free Radic. Biol. Med. 99, 451–462 (2016). source

In the paper

“Under normoxic conditions, PHDs hydroxylate proline residues on HIF1α. Prolyl-hydroxylated HIF1α is then bound by the VHL tumour suppressor protein, which recruits an E3-ubiquitin ligase that targets HIF1α for proteasomal degradation”

In the paper

“ascorbate treatment in vitro increased DNA demethylation at enhancers and promoters of genes associated with myeloid differentiation and increased the expression of several key haematopoietic genes in murine bone marrow cells expressing mutant IDH1 (REF.68).”

What the sources say

• Not checked yetcites [68] Mingay, M. et al. Vitamin C-induced epigenomic remodelling in IDH1 mutant acute myeloid leukaemia. Leukemia 32, 11–20 (2018). source

In the paper

“In the initial trials, ascorbate was administered both intravenously and orally and achieved a peak plasma concentration of 6 mM. However, in later trials, where the same dose of ascorbate was administered orally, a peak plasma concentration of less than 200 μM was achieved97.”

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

“the higher levels of GLUT1, a HIF1α downstream target, in normoxic VHL-deficient cells than in VHL-proficient cells facilitated increased uptake of ascorbate-derived DHA, leading to increased generation of ROS and cell death. In line with this, GLUT1 knockdown in VHL-deficient RCC cells conferred resistance to vitamin-C-induced toxicity.”

What the sources say

• Not checked yetcites [52] Tian, W. et al. The hypoxia-inducible factor renders cancer cells more sensitive to vitamin C-induced toxicity. J. Biol. Chem. 289, 3339–3351 (2014). source

In the paper

“Vitamin C can activate TETs as a cofactor and is required for optimal activity. Ascorbate can donate an electron to Fe3+ to generate Fe2+, which is required for TET activity”

In the paper

“ascorbate treatment in melanoma and bladder cancer cells also enhanced 5hmC levels and decreased their malignancy70,71, suggesting that ascorbate treatment may also be effective in solid cancer with low levels of 5hmC.”

What the sources say

• Not checked yetcites [70] Gustafson, C. B. et al. Epigenetic reprogramming of melanoma cells by vitamin C treatment. Clin. Epigenetics 7, 51 (2015). source
• Not checked yetcites [71] Peng, D. et al. Vitamin C increases 5-hydroxymethylcytosine level and inhibits the growth of bladder cancer. Clin. Epigenetics 10, 94 (2018).

In the paper

“HIF hydroxylases require ascorbate as a cofactor to recycle Fe2+. Therefore, cells deficient in ascorbate can have increased HIF1α function, potentially contributing to tumour progression.”

In the paper

“This implies that ascorbate treatment may enhance the activity of HIF hydroxylases, thus inhibiting HIF1α activity and suppressing tumour growth77.”

What the sources say

• Not checked yetcites [77] Vissers, M. C. M. & Das, A. B. Potential mechanisms of action for vitamin C in cancer: reviewing the evidence. Front. Physiol. 9, 809 (2018). source

In the paper

“a neomorphic mutation in IDH1 and/or IDH2 causes a change in enzymatic activity and the accumulation of 2-hydroxyglutarate (2-HG), which inhibits the function of αKG-dependent enzymes such as TET2, resulting in the loss of 5hmC, an increase in DNA methylation and ultimately altered gene expression programmes that drive cancer development66.”

What the sources say

• Not checked yetcites [66] Lu, C. et al. IDH mutation impairs histone demethylation and results in a block to cell differentiation. Nature 483, 474–478 (2012). source

In the paper

“tumour cells activate the evolutionarily conserved transcription factor HIF1, leading to activation of a wide range of genes and response programmes that facilitate increased survival in such conditions75.”

What the sources say

• Not checked yetcites [75] Semenza, G. L. Targeting HIF-1 for cancer therapy. Nat. Rev. Cancer 3, 721–732 (2003). source

In the paper

“Taken together, these data suggest that high-dose ascorbate treatment can slow tumour growth by moderating HIF1α. However, all studies thus far prove the association but not the causality.”

In the paper

“Clinical trials in the 1970s involving patients with terminal cancer showed that intravenous high-dose ascorbate extended patient survival in response to ascorbate treatment93,94, whereas large-scale randomized controlled trials (RCTs) in the 1980s failed to confirm these initial findings because ascorbate was given orally instead95,96.”

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
• Not checked yetcites [94] Cameron, E. & Pauling, L. Supplemental ascorbate in the supportive treatment of cancer: reevaluation of prolongation of survival times in terminal human cancer. Proc. Natl Acad. Sci. USA 75, 4538–4542 (1978). source
• 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

In the paper

“VHL-deficient RCC cells undergo cell death when exposed to vitamin C in normoxia, in contrast to isogenic VHL-proficient cells52.”

What the sources say

• Not checked yetcites [52] Tian, W. et al. The hypoxia-inducible factor renders cancer cells more sensitive to vitamin C-induced toxicity. J. Biol. Chem. 289, 3339–3351 (2014). source

In the paper

“The majority of TET2 mutations in AML are heterozygous, and each TET isoform has some functional redundancy. Therefore, ascorbate treatment may enhance the activity of residual TET proteins and thus rescue the abnormal DNA methylation pattern.”

In the paper

“ascorbate deficiency was shown to dysregulate HSC function in both a TET2-dependent and TET2-independent manner, leading to leukaemogenesis.”

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

“patients with CRC who had high levels of ascorbate in their tumour had a better patient outcome and longer patient survival after surgery84.”

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).

In the paper

“plasma concentrations around 10 mM were sustained for at least 4 hours, which, on the basis of preclinical studies, is sufficient to slow the growth of cancer cells.”

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

“Loss-of-function mutations in SDH and FH cause a build-up of succinate and fumarate, respectively87. Accordingly, increased levels of succinate and fumarate caused by mutations in these genes can compete with αKG and inhibit activity of HIF hydroxylases and thus induce normoxic HIF1α activity in vitro88,89.”

What the sources say

• Not checked yetcites [87] King, A., Selak, M. A. & Gottlieb, E. Succinate dehydrogenase and fumarate hydratase: linking mitochondrial dysfunction and cancer. Oncogene 25, 4675–4682 (2006). source
• Not checked yetcites [88] Selak, M. A. et al. Succinate links TCA cycle dysfunction to oncogenesis by inhibiting HIF-alpha prolyl hydroxylase. Cancer Cell 7, 77–85 (2005). source
• Not checked yetcites [89] Koivunen, P. et al. Inhibition of hypoxia-inducible factor (HIF) hydroxylases by citric acid cycle intermediates: possible links between cell metabolism and stabilization of HIF. J. Biol. Chem. 282, 4524–4532 (2007). source

In the paper

“Ascorbate level was inversely correlated with HIF1α expression in thyroid lesions80, and in vitro study showed that ascorbate treatment induced a dose-dependent decrease in expression of HIF1α and GLUT1 (a downstream target of HIF 1) in thyroid cancer cells80.”

What the sources say

• Not checked yetcites [80] Józwiak, P. et al. Expression of hypoxia inducible factor 1α and 2α and its association with vitamin C level in thyroid lesions. J. Biomed. Sci. 24, 83 (2017). source

In the paper

“In fact, reports show that many CRCs have low expression levels of TETs and relatively high expression levels of HIF1α, implying that pharmacological ascorbate may attack multiple nodes in tumours with minimum toxicity102,103, making it an ideal magic bullet’ for cancer therapy.”

What the sources say

• Not checked yetcites [102] Cao, D. et al. Expression of HIF-1alpha and VEGF in colorectal cancer: association with clinical outcomes and prognostic implications. BMC Cancer 9, 432 (2009).
• Not checked yetcites [103] Tian, Y. et al. Association of TET1 expression with colorectal cancer progression. Scand. J. Gastroenterol. 52, 312–320 (2017). 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

“a significant number of clinical studies to date have indicated that intravenous high-dose ascorbate is well tolerated in patients with minimal toxicity, improves the quality of life for patients and has demonstrated synergistic therapeutic effects as well as reduced side effects when combined with radiation and standard chemotherapies.”

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 [99] Klimant, E. et al. Intravenous vitamin C in the supportive care of cancer patients: a review and rational approach. Curr. Oncol. 25, 139–148 (2018). source
• Not checked yetcites [100] Carr, A. C. & Cook, J. Intravenous vitamin C for cancer therapy — identifying the current gaps in our knowledge. Front. Physiol. 9, 1182 (2018). source

In the paper

“In fact, reports show that many CRCs have low expression levels of TETs and relatively high expression levels of HIF1α, implying that pharmacological ascorbate may attack multiple nodes in tumours with minimum toxicity102,103, making it an ideal magic bullet’ for cancer therapy.”

What the sources say

• Not checked yetcites [102] Cao, D. et al. Expression of HIF-1alpha and VEGF in colorectal cancer: association with clinical outcomes and prognostic implications. BMC Cancer 9, 432 (2009).
• Not checked yetcites [103] Tian, Y. et al. Association of TET1 expression with colorectal cancer progression. Scand. J. Gastroenterol. 52, 312–320 (2017). source

In the paper

“many of these studies were not designed as large-scale RCTs; thus, the efficacy of high-dose ascorbate therapy remains to be determined.”

In the paper

“In this Review, we propose that vitamin C serves as an excellent example of a natural compound that targets multiple vulnerable nodes to inhibit cancer growth.”

In the paper

“GEMMs are powerful tools for studying the pathogenesis of cancer and examining the systemic effects of vitamin C in vivo113.”

What the sources say

• Not checked yetcites [113] Kersten, K. et al. Genetically engineered mouse models in oncology research and cancer medicine. EMBO Mol. Med. 9, 137–153 (2017). source

In the paper

“Given its low toxicity and low financial cost, ascorbate could become an important weapon in our arsenal against cancer, either acting as a single agent with predictive biomarkers or used in combination as an adjuvant therapy.”

In the paper

“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 H2O2 using in vitro cell lines and mouse models.”

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

“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.”

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

“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.”

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