Recent reports indicate that a certain ROS concentration is required for high-dose vitamin C to induce cytotoxicity in cancer cells.
The generation of ascorbyl- and H2O2 radicals by PAA increases ROS stress in cancer cells
In this study, we report that PAA is efficacious in killing MM cells in vitro and in vivo models, which generated levels of 20–40 mM ascorbate and 500 nM ascorbyl radicals after intraperitoneal administration of 4 g ascorbate per kilogram of body weight (Chen et al., 2008Chen et al., 2008), in xenograft MM mice
These data suggest that PAA may show a therapeutic advantage to blood cancers vs solid tumors because of the communication between tumor cells and blood plasma
These results strongly suggest that the mechanism of PAA killing of MM cells is indeed iron-dependent
These results suggest that PAA administration in SMM may be able to prevent progression to symtomatic MM
A recent study by Yun and colleagues demonstrated that vitamin C selectively kills KRAS and BRAF mutant colorectal cancer cells by targeting GAPDH, but spares normal cells
RAS family genes show the most frequent mutations in MM. KRAS, NRAS and BRAF are mutated in 22%, 20% and 7% of MM samples
the disease stage rather than the mutation of RAS and/or BRAF is the major predictive factor for PAA sensitivity in MM treatment
Other molecular mechanisms including ATP depletion and ATM-AMPK signaling have been reported to explain PAA-induced cell death
our pilot study also suggested that PAA could overcome drug resistance to bortezomib in MM cells
Our findings complement reported studies and further address the mechanism of action using clinical samples in which we observed that PAA killed tumor cells with high iron content, suggesting that iron might be the initiator of PAA cytotoxicity
combination of PAA with standard therapeutic drugs, such as melphalan, may significantly reduce the dose of melphalan needed
Combined treatment of reduced dose melphalan with PAA achieved a significantly longer progression-free survival than the same dose of melphalan alone.
These data also suggest that the bone marrow suppression induced by high-dose melphalan can be ameliorated by the combination of PAA with lower dose of melphalan because of the lack of toxicity of PAA on normal cells with low iron content.
if creatinine clearance is <30 mL/min, high dose ascorbic acid should be not administrated.
In MM preclinical and clinical studies, ascorbate was used as an adjunct drug and showed controversial results (Harvey et al., 2009, Perrone et al., 2009, Held et al., 2013, Sharma et al., 2012, Nakano et al., 2011, Takahashi, 2010, Sharma et al., 2009, Qazilbash et al., 2008). However, none of these tests used pharmacological doses of ascorbate and intravenous administration
Multiple myeloma (MM) is a plasma cell neoplasm.
Cameron and Pauling reported that high doses of vitamin C increased survival of patients with cancer
pharmacologically dosed ascorbic acid (PAA) 50–100 g (Chen et al., 2008, Padayatty et al., 2004, Hoffer et al., 2008, Padayatty et al., 2006, Welsh et al., 2013), administered intravenously, has potent anti-cancer activity and its role as anti-cancer therapy is being studied at the University of Iowa and in other centers
In the presence of catalytic metal ions like iron, PAA administered intravenously exerts pro-oxidant effects leading to the formation of highly reactive oxygen species (ROS), resulting in cell death
the labile iron pool (LIP) is significantly elevated in MM cells
The survival of CD138+ cells in vitro was significantly decreased following PAA treatment in all 9 MM
In contrast, no significant change of cell viability was observed in CD138− BM cells from the same patients
The same effect of PAA was also observed in the SMM patients
no response to PAA was detected in CD138+ cells from the 2 MGUS patients
the combination of melphalan plus PAA showed greater tumor burden reduction than each drug alone, suggesting a synergistic activity between these two drugs
Both catalase and NAC protect cells from oxidative damage
cells pretreated with NAC and catalase became resistant to PAA even at high doses
adding deferoxamine (DFO), an iron chelator, to OCI-MY5 cells before PAA treatment was also sufficient to prevent PAA-induced cellular death
iron is essential for PAA to achieve its anti-cancer activity
PAA induced early necrosis (Fig. 3Fig. 3A, 60 min) followed by late apoptosis
results further indicated that PAA induced mitochondria-mediated apoptosis
PAA by reacting with LIP and generating ROS induces mitochondria-mediated apoptosis in which AIF1 cleavage is important for cell death.
ROS and H2O2 are well known factors mediating PAA-induced cancer cell death
animal study finds high-dose, pharmacologic vitamin C found to kill multiple myeloma cells via pro-oxidant effect found in similar studies in dealing with different cancers.
metabolic activity, oxygen transport, and DNA synthesis
Iron is found in the human body in the form of haemoglobin in red blood cells and growing erythroid cells.
macrophages contain considerable quantities of iron
iron is taken up by the majority of cells in the form of a transferrin (Tf)-Fe(III) complex that binds to the cell surface receptor transferrin receptor 1 (TfR1)
excess iron is retained in the liver cells
the endosomal six transmembrane epithelial antigen of the prostate 3 (STEAP3) reduces Fe(III) (ferric ion) to Fe(II) (ferrous ion), which is subsequently transferred across the endosomal membrane by divalent metal transporter 1 (DMT1)
labile iron pool (LIP)
LIP is toxic to the cells owing to the production of massive amounts of ROS.
DHA is quickly converted to Vit-C within the cell, by interacting with reduced glutathione (GSH) [45,46,47]. NADPH then recycles the oxidized glutathione (glutathione disulfide (GSSG)) and converts it back into GSH
Fe(II) catalyzes the formation of OH• and OH− during the interaction between H2O2 and O2•− (Haber–Weiss reaction)
Ascorbate can efficiently reduce free iron, thus recycling the cellular Fe(II)/Fe(III) to produce more OH• from H2O2 than can be generated during the Fenton reaction, which ultimately leads to lipid, protein, and DNA oxidation
Vit-C-stimulated iron absorption
reduce cellular iron efflux
high-dose Vit-C may elevate cellular LIP concentrations
ascorbate enhanced cancer cell LIP specifically by generating H2O2
Vit-C produces H2O2 extracellularly, which in turn inhibits tumor cells immediately
tumor cells have a need for readily available Fe(II) to survive and proliferate.
Tf has been recognized to sequester most labile Fe(II) in vivo
Asc•− and H2O2 were generated in vivo upon i.v Vit-C administration of around 0.5 g/kg of body weight and that the generation was Vit-C-dose reliant
free irons, especially Fe(II), increase Vit-C autoxidation, leading to H2O2 production
iron metabolism is altered in malignancies
increase in the expression of various iron-intake pathways or the downregulation of iron exporter proteins and storage pathways
Fe(II) ion in breast cancer cells is almost double that in normal breast tissues
macrophages in the cancer microenvironment have been revealed to increase iron shedding
Advanced breast tumor patients had substantially greater Fe(II) levels in their blood than the control groups without the disease
increased the amount of LIP inside the cells through transferrin receptor (TfR)
Warburg effect, or metabolic reprogramming,
Warburg effect is aided by KRAS or BRAF mutations
Vit-C is supplied, it oxidizes to DHA, and then is readily transported by GLUT-1 in mutant cells of KRAS or BRAF competing with glucose [46]. DHA is quickly converted into ascorbate inside the cell by NADPH and GSH [46,107]. This decrease reduces the concentration of cytosolic antioxidants and raises the intracellular ROS amounts
ROS activates poly (ADP-ribose) polymerase (PARP), which depletes NAD+ (a critical co-factor of GAPDH); thus, further reducing the GAPDH associated with a multifaceted metabolic rewiring
Hindering GAPDH can result in an “energy crisis”, due to the decrease in ATP production
high-dose Vit-C recruited metabolites and increased the enzymatic activity in the pentose phosphate pathway (PPP), blocked the tri-carboxylic acid (TCA) cycle, and increased oxygen uptake, disrupting the intracellular metabolic balance and resulting in irreversible cell death, due to an energy crisis
mega-dose Vit-C influences energy metabolism by producing tremendous amounts of H2O2
Due to its great volatility at neutral pH [76], bolus therapy with mega-dose DHA has only transitory effects on tumor cells, both in vitro and in vivo.
Vitamin C alone at concentrations up to 57 μM had little effect on cell growth but was toxic at 228 μM (SI Appendix, Fig. S1B), in line with recent studies of high vitamin C concentrations (125–2,000 μM)
In our combination approach, vitamin C increased the effects of low doses of 5-aza-CdR, with 57 μM vitamin C almost doubling the growth inhibition
Using the Chou–Talalay method (28), we found that the two compounds indeed acted synergistically, rather than additively, to inhibit cancer cell growth over the physiological ranges of vitamin C in healthy individuals (26–84 μM)
These results show that targeting the cancer DNA methylome by combining low-dose 5-aza-CdR and vitamin C stimulates the expression of ERVs, the induction of a cell-autonomous immune activation response, and increased apoptosis of cancer cells
The addition of vitamin C to treatment protocols therefore may be a straightforward way to increase the clinical efficacy of such drugs in MDS and leukemia patients
Vitamin C deficiency has been seen previously in patients with multiple types of cancer, including hematological malignancies (35⇓–37). We predict that these patients might receive the most benefits from the combination treatment.
induction of an innate immune response
We therefore measured plasma concentrations of vitamin C in a small number of patients with miscellaneous hematologic malignancies. Strikingly, 58% of patients with hematological neoplasia who were not taking vitamin C supplements had severe vitamin C deficiency (serum concentration <11.4 μM, at which clinical features of scurvy may be manifested) (34), and 33% had vitamin C levels below the normal range
it is possible that vitamin C was oxidized to DHA before it was transported into the cells
Oral administration of vitamin C should be sufficient for the therapeutic strategy, because the concentrations reported in this study would not require i.v. administration.
This statement lacks a basic understanding of vitamin C pharmacokinetics.
Vitamin C is an essential nutrient for humans and has been reported to increase IFN levels in human cells upon virus infection
daily treatment with vitamin C alone at physiological concentrations enhanced the expression of viral-defense genes relative to untreated cells
When combined with low-dose 5-aza-CdR, physiological concentrations of vitamin C synergistically inhibited cancer-cell growth and induced apoptosis. Such synergy was associated with increased ERV expression and dsRNA in treated cells. The mechanism of action differs from that of vitamin C at higher doses, which involves its pro-oxidant activity, including GSH inhibition, to generate reactive oxygen species
This activity has been shown to induce DNA damage and to enhance the sensitivities of myeloid malignancies, multiple myeloma, and cutaneous T-cell lymphoma to arsenic trioxide (41⇓⇓–44). It also can increase chemosensitivity of ovarian cancer cells (27) and selectively kill KRAS or BRAF mutant colorectal cancer cells by inhibiting GAPDH
91% of patients with hematologic malignancies have vitamin C levels that are either low or severly deficient. This study found that vitamin C plus low dose DNA methyltransferase inhibitors have synergistic inhibition of cancer cell proliferation and increased apoptosis. Unfortunately, the authors claimed that oral vitamin C would be sufficient which indicates an incredible lack of understanding of vitamin C pharmacokinetics.
Glutamine is the most abundant amino acid in blood
Rapidly proliferating healthy cells (GI epithelium, lymphocytes) or cells under physiologic stress have increased demand for glutamine
Glutamine is transported into cells by one of multiple amino acid transporters (e.g. ASCT2, BOAT2), several of which are thought to be upregulated in cancer cells
it is hydrolyzed to glutamate and ammonia by glutaminase (‘glutaminolysis’)
Glutamate, produced from glutamine by glutaminase and glutamine amidotransferase activities, may be further metabolized to alpha ketoglutarate and provide a carbon skeleton source for the mitochondrial tricarboxylic acid cycle (TCA cycle)
Glutamine-derived glutamate is also involved in the synthesis of the reducing equivalent glutathione, vital to maintaining cellular redox status
Many tumors become largely dependent on glutamine to provide carbon and nitrogen building blocks needed for proliferation
In cancer model systems, Eagle and colleagues first demonstrated tumor cells in culture require supplementation with exogenous glutamine for efficient proliferation
It was subsequently shown that when deprived of glutamine tumor cells undergo apoptosis
The most well-characterized oncogene to regulate glutamine metabolism is MYC (9), which enhances glutaminase expression, upregulates glutamine transporters, and enhances glutamine utilization in energy production and biosynthesis
Other pro-tumorigenic regulators such as KRAS and mTOR, as well as tumor suppressors (p53, VHL) have also been associated with alterations in glutamine metabolism
Tumor cells are highly adaptable and alter nutrient uptake and metabolic networks to resist single agent glutaminase inhibition
cells in the microenvironment of several tumor types upregulate glutamine production, thereby enabling tumor cells to escape glutaminase inhibition