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Our data show that ascorbic acid selectively killed cancer but not normal cells, using concentrations that could only be achieved by i.v. administration

Ascorbate-mediated cell death was due to protein-dependent extracellular H2O2 generation, via ascorbate radical formation from ascorbate as the electron donor. Like glucose, when ascorbate is infused i.v., the resulting pharmacologic concentrations should distribute rapidly in the extracellular water space (42). We showed that such pharmacologic ascorbate concentrations in media, as a surrogate for extracellular fluid, generated ascorbate radical and H2O2. In contrast, the same pharmacologic ascorbate concentrations in whole blood generated little detectable ascorbate radical and no detectable H2O2. These findings can be accounted for by efficient and redundant H2O2 catabolic pathways in whole blood (e.g., catalase and glutathione peroxidase) relative to those in media or extracellular fluid

ascorbic acid administered i.v. in pharmacologic concentrations may serve as a pro-drug for H2O2 delivery to the extracellular milieu

H2O2 generated in blood is normally removed by catalase and glutathione peroxidase within red blood cells, with internal glutathione providing reducing equivalents

The electron source for glutathione is NADPH from the pentose shunt, via glucose-6-phosphate dehydrogenase. If activity of this enzyme is diminished, the predicted outcome is impaired H2O2 removal causing intravascular hemolysis, the observed clinical finding.

Only recently has it been understood that the discordant clinical findings can be explained by previously unrecognized fundamental pharmacokinetics properties of ascorbate

Intracellular transport of ascorbate is tightly controlled in relation to extracellular concentration

Intravenous ascorbate infusion is expected to drastically change extracellular but not intracellular concentrations

For i.v. ascorbate to be clinically useful in killing cancer cells, pharmacologic but not physiologic extracellular concentrations should be effective, independent of intracellular ascorbate concentrations.

It is unknown why ascorbate, via H2O2, killed some cancer cells but not normal cells.

There was no correlation with ascorbate-induced cell death and glutathione, catalase activity, or glutathione peroxidase activity.

H2O2, as the product of pharmacologic ascorbate concentrations, has potential therapeutic uses in addition to cancer treatment, especially in infections

Neutrophils generate H2O2 from superoxide,

i.v. ascorbate is effective in some viral infections

H2O2 is toxic to hepatitis C

Use of ascorbate as an H2O2-delivery system against sensitive pathogens, viral or bacterial, has substantial clinical implications that deserve rapid exploration.

Recent pharmacokinetics studies in men and women show that 10 g of ascorbate given i.v. is expected to produce plasma concentrations of nearly 6 mM, which are >25-fold higher than those concentrations from the same oral dose

As much as a 70-fold difference in plasma concentrations is expected between oral and i.v. administration,

Complementary and alternative medicine practitioners worldwide currently use ascorbate i.v. in some patients, in part because there is no apparent harm

Human Burkitt's lymphoma cells

We first investigated whether ascorbate in pharmacologic concentrations selectively affected the survival of cancer cells by studying nine cancer cell lines

Clinical pharmacokinetics analyses show that pharmacologic concentrations of plasma ascorbate, from 0.3 to 15 mM, are achievable only from i.v. administration

plasma ascorbate concentrations from maximum possible oral doses cannot exceed 0.22 mM because of limited intestinal absorption

For five of the nine cancer cell lines, ascorbate concentrations causing a 50% decrease in cell survival (EC50 values) were less than 5 mM, a concentration easily achievable from i.v. infusion

All tested normal cells were insensitive to 20 mM ascorbate.

Lymphoma cells were selected because of their sensitivity to ascorbate

As ascorbate concentration increased, the pattern of death changed from apoptosis to pyknosis/necrosis, a pattern suggestive of H2O2-mediated cell death

Apoptosis occurred by 6 h after exposure, and cell death by pyknosis was ≈90% at 14 h after exposure

In contrast to lymphoma cells, there was little or no killing of normal lymphocytes and monocytes by ascorbate

Ascorbate is transported into cells as such by sodium-dependent transporters, whereas dehydroascorbic acid is transported into cells by glucose transporters and then immediately reduced internally to ascorbate

Whether or not intracellular ascorbate was preloaded, extracellular ascorbate induced the same amount and type of death.

extracellular ascorbate in pharmacologic concentrations mediates death of lymphoma cells by apoptosis and pyknosis/necrosis, independently of intracellular ascorbate.

H2O2 as the effector species mediating pharmacologic ascorbate-induced cell death

Superoxide dismutase was not protective

Because these data implicated H2O2 in cell killing, we added H2O2 to lymphoma cells and studied death patterns using nuclear staining (19, 28). The death patterns found with exogenous H2O2 exposure were similar to those found with ascorbate

For both ascorbate and H2O2, death changed from apoptosis to pyknosis/necrosis as concentrations increased

Sensitivity to direct exposure to H2O2 was greater in lymphoma cells compared with normal lymphocytes and normal monocytes

There was no association between the EC50 for ascorbate-mediated cell death and intracellular glutathione concentrations, catalase activity, or glutathione peroxidase activity

H2O2 generation was dependent on time, ascorbate concentration, and the presence of trace amounts of serum in media

ascorbate radical is a surrogate marker for H2O2 formation.

whatever H2O2 is generated should be removed by glutathione peroxidase and catalase within red blood cells, because H2O2 is membrane permeable

The data are consistent with the hypothesis that ascorbate in pharmacologic concentrations is a pro-drug for H2O2 generation in the extracellular milieu but not in blood.

The occurrence of one predicted complication, oxalate kidney stones, is controversial

In patients with glucose-6-phosphate dehydrogenase deficiency, i.v. ascorbate is contraindicated because it causes intravascular hemolysis

ascorbate at pharmacologic concentrations in blood is a pro-drug for H2O2 delivery to tissues.

ascorbate, an electron-donor in such reactions, ironically initiates pro-oxidant chemistry and H2O2 formation

data here showed that ascorbate initiated H2O2 formation extracellularly, but H2O2 targets could be either intracellular or extracellular, because H2O2 is membrane permeant

More than 100 patients have been described, presumably without glucose-6-phosphate dehydrogenase deficiency, who received 10 g or more of i.v. ascorbate with no reported adverse effects other than tumor lysis

NK cells are large granular lymphocytes that comprise approximately 10 % of circulating lymphocytes

all human NK cells express the CD56 antigen

treatment with various concentrations of IL‐2 in vivo may induce distinct functions within the NK cell compartment and, therefore, may have profound effects on NK cell‐mediated cytotoxicity

CD56bright

CD56dim

We show here that ADCC conducted by NK cells in vitro is enhanced by IL‐2 activation and is critically dependent on interactions between FcγRIII on NK cells and Herceptin‐coated tumor targets

administration of low‐dose IL‐2 to patients results in the marked expansion of a CD56+ population of immune effectors with the ability to lyse antibody‐coated cancer targets

NK cells represented only 7 % of lymphocytes prior to therapy but comprised over 50 % of the population after 10 weeks of low‐dose IL‐2

These data suggest that the enhanced ADCC seen following the expansion of NK cells with low‐dose IL‐2 is likely due to an increase in the overall number of NK cells

co‐administration of IL‐2 with rhu4D5 mAb will enhance activation of NK cell effector functions

Stimulation of NK cells with IL‐2 resulted in a significant increase in the lysis of rhu4D5‐coated targets

We have shown that costimulation with IL‐2 plus rhu4D5 results in significant production of IFN‐γ by NK cells with concomitant up‐regulation of cell‐surface activation and adhesion molecules

It has been previously demonstrated that continuous low‐dose IL‐2 can expand a CD56+ lymphocyte population, and we have now shown that this cell population is a potent mediator of ADCC against rhu4D5 mAb‐coated Her2 / neu+ targets

These results suggest that administration of low‐dose IL‐2 can be used to expand NK cell numbers, while higher doses may be used to enhance their cytolytic capacity in the setting of mAb therapy

we have demonstrated that NK cell lysis of Her2 / neu+ breast cancer cell lines in the presence of rhu4D5 mAb is markedly enhanced following stimulation with IL‐2

we have presented evidence that administration of low‐dose IL‐2 in vivo results in the expansion of a potent NK cell effector population

Our experiments suggest that NK cells costimulated with IL‐2 and immobilized IgG can secrete potent immunomodulatory cytokines which may serve to potentiate the anti‐tumor immune response.

tumor-associated antigens (TAs)

Proinflammatory cytokines secreted by inflammatory cells can contribute to tumor progression, and soluble factors produced by the tumor in response to nonspecific or tumor-specific signals, such as prostaglandin E2 (PGE2), adenosine, or TGF-β, downregulate functions of immune cells

they are largely ineffective in arresting tumor growth, although they can proliferate and mediate antitumor cytotoxicity on their removal from the tumor bed and ex vivo IL-2 activation.42

DCs (HLA-DR+CD86+CD80+CD14−) are nature’s best APCs

They are a common component of tumor immune infiltrates and are responsible for the uptake, processing, and cross-presentation of TAs to naive or memory T cells, thus playing a crucial role in the generation of tumor-specific effector T cells

DCs control the induction of Treg cells. In patients with cancer, cellular interactions between antigen-presenting DCs and T cells lead to expansion and accumulation of Treg cells at the tumor site and in the periphery

NK cells (CD3−CD56+CD16+), which mediate innate immunity and contain both perforin-rich and granzyme-rich granules, are well equipped to mediate lysis of tumor cells

B cells (CD19+, CD20+) are also rare in most human tumors, with the exception of breast cancer and melanoma

The initial acute inflammation involving the recruitment and influx of antitumor effector cells is replaced by chronic inflammation in later stages of tumor progression

Tissue hypoxia plays a major role in shaping the nature of immune infiltrates in tumors