Intravenous ascorbic acid protocol for cancer patients: scientific rationale, pharmacology, and clinical experience

Background: Ascorbic acid (vitamin C, ascorbate) has been shown to protect cells against various types of oxidant injury at physiologically relevant concentrations. Vitamin C has been suggested as having both a preventative and therapeutic role in a number of pathologies when administered at much higher-than-recommended dietary allowance levels. This article reviews the scientific rational for intravenous vitamin C as a potential treatment for cancer. Many mechanisms of action for ascorbate efficacy against cancer have been proposed over the years. Cancer patients are often deficient in vitamin C, and require large doses to replenish depleted stores. It has been demonstrated in vitro and in animal studies that vitamin C is preferentially toxic to tumor cells at millimolar concentrations; moreover, pharmacokinetic data suggest that these concentrations are clinically achievable when ascorbate is administered intravenously. Data suggests that ascorbate may serve as a biological response modifier, affecting inflammation and angiogenesis as well as improving immune function parameters. While Phase II clinical trials using ascorbate in cancer therapy are under way, vitamin C is not subject to the regulations that synthetic drugs are and therefore has been used clinically for decades to treat cancer patients. This clinical experience suggests the therapy is safe, and may be effective in some instances. Attached to this article is the Riordan IVC Protocol, which details an intravenous vitamin C protocol that can be safely administered to cancer patients.Keywords: Cancer, inflammation, C-reactive protein, inflammatory cytokines, high-dose vitamin C

Cytotoxicity of ascorbate, lipoic acid, and other antioxidants in hollow fibre in vitro tumours

Vitamin C (ascorbate) is toxic to tumour cells, and has been suggested as an adjuvant cancer treatment. Our goal was to determine if ascorbate, in combination with other antioxidants, could kill cells in the SW620 hollow fibre in vitro solid tumour model at clinically achievable concentrations. Ascorbate anti-cancer efficacy, alone or in combination with lipoic acid, vitamin K3, phenyl ascorbate, or doxorubicin, was assessed using annexin V staining and standard survival assays. 2-day treatments with 10 mM ascorbate increased the percentage of apoptotic cells in SW620 hollow fibre tumours. Lipoic acid synergistically enhanced ascorbate cytotoxicity, reducing the 2-day LC(50)in hollow fibre tumours from 34 mM to 4 mM. Lipoic acid, unlike ascorbate, was equally effective against proliferating and non-proliferating cells. Ascorbate levels in human blood plasma were measured during and after intravenous ascorbate infusions. Infusions of 60 g produced peak plasma concentrations exceeding 20 mM with an area under the curve (24 h) of 76 mM h. Thus, tumoricidal concentrations may be achievable in vivo. Ascorbate efficacy was enhanced in an additive fashion by phenyl ascorbate or vitamin K3. The effect of ascorbate on doxorubicin efficacy was concentration dependent; low doses were protective while high doses increased cell killing.

Determining hypoxic fraction in a rat glioma by uptake of radiolabeled fluoromisonidazole

The usefulness of radiolabeled nitroimidazoles for measuring hypoxia will be clarified by defining the relationship between tracer uptake and radiobiologically hypoxic fraction. We determined the radiobiologically hypoxic fraction from radiation response data in 36B10 rat gliomas using the paired cell survival curve technique and compared the values to the radiobiologically hypoxic fraction inferred from mathematical modeling of time-activity data acquired by PET imaging of [(18)F]FMISO uptake. Rats breathed either air or 10% oxygen during imaging, and timed blood samples were taken. The uptake of [(3)H]FMISO by 36B10 cells in vitro provided cellular binding characteristics of this radiopharmaceutical as a function of oxygen concentration. The radiobiologically hypoxic fraction determined for tumors in air-breathing rats using the paired survival curve technique was 6.1% (95% CL = 4.3- 8.6%), which agreed well with that determined by modeling FMISO time-activity data (7. 4%; 95% CL = 2.5-17.3%). These results are consistent with the agreement between the two techniques for measuring radiobiologically hypoxic fraction in Chinese hamster V79 cell spheroids. In contrast, the FMISO-derived radiobiologically hypoxic fraction in rats breathing 10% oxygen was 13.1% (95% CL 7.9-8.3%), much lower than the radiobiologically hypoxic fraction of 43% determined from the radiation response data. This discrepancy may be due to the failure of FMISO to identify hypoxic cells residing at or above an oxygen level of 2-3 mmHg that will still confer substantial protection against radiation. The presence of transiently hypoxic cells in rats breathing reduced oxygen may also be under-reported by nitroimidazole binding, which is strongly dependent on time and concentration.

Growth rate, labeling index, and radiation survival of cells grown in the Matrigel thread in vitro tumor model

Six rodent cell lines (36B10 rat glioma cells, 9L rat gliosarcoma cells, V79 Chinese hamster lung fibroblasts, EMT6/UW and EMT6/Ro mouse mammary sarcoma cells, and RIF-1 mouse fibrosarcoma cells) were tested for growth in cylindrical threads of Matrigel. These cells grew in the threads with doubling times of 17-23 h, reaching maximum cell densities on the order of 10(8) cells/ml. Histological sections of these threads showed a heterogeneous cell distribution: cells grew to confluence at the thread surface and at somewhat lower cell densities in the thread core. [H-3]thymidine labeling index and radiation sensitivity were measured for 9L and EMT6/UW cells in Matrigel threads. For both cell types, the labeling index in Matrigel was lower than observed in cell monolayers, with higher labeling indexes at the thread periphery than in the thread core. When these threads were grown in stirred medium, lower thread diameters, higher cell yields per thread, and higher labeling indices were obtained. EMT6 cell monolayers coated with Matrigel were less radiosensitive than cells in uncoated monolayers. This protective effect was eliminated by irradiating in the presence of 1 mg/ml misonidazole. EMT6 cells consume nearly three times as much oxygen (mole/cm3-sec) as do 9L cells, which are equally radiosensitive in monolayers with or without a Matrigel coating. The radiation sensitivity of EMT6/UW cells in Matrigel threads was similar to that for monolayers of plateau phase cells, whereas for 9L cells, the response in threads was more similar to exponentially growing cells. We conclude that Matrigel threads provide an alternative in vitro model for studying the radiation response of cells in a three-dimensional geometry.

A modeling approach for quantifying tumor hypoxia with [F-18]fluoromisonidazole PET time-activity data

[F-18]fluoromisonidazole (FMISO), a positron-emitting nitroimidazole, binds preferentially to hypoxic cells. It has been used to image hypoxia in human tumors with positron emission tomography (PET). In order to quantify tumor oxygenation status from these PET data, a kinetic model of FMISO cellular bioreduction has been developed to relate cellular oxygen concentration to the cellular FMISO reaction rate constant, kappa A. Also, a compartmental model of FMISO transport and metabolism has been developed to compute the volume average kappa A in tissue regions from [F-18]FMISO PET time-activity data. This compartmental model was characterized using Monte Carlo simulations and [F-18]FMISO PET time-activity data. The model performed well in Monte Carlo simulations; performance was enhanced by fixing three of the seven model parameters at physiologically reasonable values. The four parameters optimized were blood flow rate, kappa A for two partial volume/spillover correction factors. The model was able to accurately determine kappa A for a variety of computer-generated time-activity curv including those for hypothetical heterogeneous tissue regions and poorly perfused tissue regions. The model was also able to fit [H-3]FMISO time-activity data from 36B-10 rat tumors as well as [F-18]FMISO PET time-activity data from a human patient with a base of the tongue squamous cell carcinoma. The kappa A values in muscles ROIs were comparable to those in well-oxygenated cell monolayers while kappa A values in tumor ROIs were greater, suggesting the presence of hypoxic cells in the tumor.

Determination of the radiobiologically hypoxic fraction in multicellular spheroids from data on the uptake of [3H]fluoromisonidazole

Fluoromisonidazole [1-(2-nitroimidazolyl)-2-hydroxy-3-fluoropropane, FMISO] shows promise as a hypoxia imaging agent: it binds preferentially to anoxic cells in monolayers in vitro and accumulates in radiobiologically hypoxic tumors in vivo. The multicellular spheroid model was used to determine if the radiobiologically hypoxic fraction could be predicted from data on the uptake of FMISO. Chinese hamster V79-171b spheroids approximately 500 microns in diameter were exposed to 50 mM [3H]FMISO for 1 to 6 h under aerobic (5% CO2 in air), hypoxic (5% CO2, 5% O2, in N2) or anoxic (5% CO2 in N2) conditions and FMISO uptake was measured. Uptake in anoxic spheroids was similar to that in anoxic cell monolayers, while there was virtually no uptake in aerobic spheroids. A mathematical model was developed to calculate the radiobiologically hypoxic fraction in the hypoxic spheroids from the data on FMISO uptake. A radiobiologically hypoxic fraction of 15% was obtained, consistent with that determined from radiation survival assays (17%) and measurements of oxygen consumption (22%). We conclude that the rate of FMISO uptake in V79-171b spheroids correlates with the radiobiologically hypoxic fraction. Furthermore, the radiobiologically hypoxic fraction can be calculated from data on FMISO uptake if the dependence of FMISO uptake on oxygen concentration is known for a given tumor cell type.

Growth and chemotherapeutic response of cells in a hollow-fiber in vitro solid tumor model

BACKGROUND

Cancer treatments that appear promising in tissue culture are often less effective in solid tumors, in part because of the proliferative and microenvironmental heterogeneity that develops in these tumors as they grow. Heterogeneous tumor models are thus needed for drug screening.

PURPOSE

Our goal was to develop and test for drug evaluation a solid tumor model based on cell growth inside biocompatible hollow fibers.

METHODS

Building on the experience of Hollingshead and co-workers with a sparse-cell, hollow-fiber tumor model, we tested six human tumor cell lines for in vitro growth inside 450-microns internal-diameter polyvinylidine fluoride fibers and examined them histologically. Human SW620 colon carcinoma cells grown in hollow fibers were also examined using electron microscopy, and their doxorubicin sensitivity was assessed. A colorimetric assay based on sulforhodamine B was adopted to replace the more cumbersome clonogenic cell survival assay.

RESULTS

Five of the human tumor cell lines tested grew to confluence, forming heterogeneous in vitro tumors with subpopulations of viable and necrotic cells. For SW620 hollow-fiber tumors, maximum viable cell populations in excess of 10(8) cells/mL were obtained after 8 days of growth. This viable cell density remained roughly constant for 3-4 days, permitting dose-response experiments over this time interval. Tumor cells in hollow fibers were much more resistant to a 4-hour doxorubicin exposure than were tumor cells in monolayers: LC50 values (i.e., the drug concentrations at which the plating efficiency equals one-half the plating efficiency of untreated cells) of 3.5 microM and 0.16 microM were obtained for hollow-fiber tumors and monolayers, respectively. LC50 values decreased when drug exposure time was increased. Results from the colorimetric assay were in agreement with those from the clonogenic assay.

CONCLUSION

The successful growth of tumor cells to confluence in hollow fibers and the feasibility of performing in vitro drug dose-response experiments with a relatively easy colorimetric assay demonstrate the potential of the hollow-fiber solid tumor model as a tool for experimental therapeutic research.

IMPLICATION

Hollow-fiber solid tumors may prove useful for experimental drug evaluation.

Noninvasive detection of hypoxic myocardium using fluorine-18-fluoromisonidazole and positron emission tomography

Fluoromisonidazole (FMISO) is metabolically trapped in viable cells as a function of reduced cellular pO2. Therefore [18F]-FMISO is potentially useful for evaluating patients with hypoxic but viable myocardium. The goal of this study was to investigate [18F]FMISO uptake in ischemic myocardium non-invasively using positron emission tomography (PET). Studies were performed in 10 open-chest dogs subjected to either complete (Group 1, n = 5) or partial (Group 2, n = 5) occlusion of the left anterior descending coronary artery. The tracer was administered by intravenous bolus following the onset of ischemia and serial PET images were acquired for the next 4 hr. In Group 1, viability was assessed using histochemical staining (nitroblue tetrazolium, NBT) and 99mTc-pyrophosphate (Tc-PYP). In Group 2, viability was assessed using measurements of regional wall motion, histochemical staining and histology (two animals). In each study, PET images obtained at times between 2 and 4 hr postinjection showed specific enhancement of tracer activity in the distal anterior wall and apex of the left ventricle. At 4 hr, the tissue-to-blood pool count ratio was significantly higher in ischemic regions; 1.8 +/- 0.4 for Group 1 and 1.6 +/- 0.2 for Group 2 versus 1.0 +/- 0.1 in nonischemic regions. Postmortem tissue sampling of Group 1 hearts showed significant FMISO retention in samples without evidence for infarction, either by NBT or Tc-PYP deposition, as well as in more severely ischemic regions. In Group 2 animals, FMISO was retained in myocardial regions with reduced blood flow (microspheres), which exhibited improved contraction following reperfusion. We conclude that PET imaging of [18F]FMISO is a promising technique for the noninvasive identification of viable hypoxic myocardium.

Variations in tumor cell growth rates and metabolism with oxygen concentration, glucose concentration, and extracellular pH

Tumors and multicellular tumor spheroids can develop gradients in oxygen concentration, glucose concentration, and extracellular pH as they grow. In order to calculate these gradients and assess their impact on tumor growth, it is necessary to quantify the effect of these variables on tumor cell metabolism and growth. In this work, the oxygen consumption rates, glucose consumption rates, and growth rates of EMT6/Ro mouse mammary tumor cells were measured at a variety of oxygen concentrations, glucose concentrations, and extracellular pH levels. At an extracellular pH of 7.25, the oxygen consumption rate of EMT6/Ro cells increased by nearly a factor of 2 as the glucose concentration was decreased from 5.5 mM to 0.4 mM. This effect of glucose concentration on oxygen consumption rate, however, was slight at an extracellular pH of 6.95 and disappeared completely at an extracellular pH of 6.60. The glucose consumption rate of EMT6/Ro cells increased by roughly 40% when the oxygen concentration was reduced from 0.21 mM to 0.023 mM and decreased by roughly 60% when the extracellular pH was decreased from 7.25 to 6.95. The growth rate of EMT6/Ro cells decreased with decreasing oxygen concentration and extracellular pH; however, severe conditions were required to stop cell growth (0.0082 mM oxygen and an extracellular pH of 6.60). Empirical correlations were developed from these data to express EMT6/Ro cell growth rates, oxygen consumption rates, and glucose consumption rates, as functions of oxygen concentration, glucose concentration, and extracellular pH. These empirical correlations make it possible to mathematically model the gradients in oxygen concentration, glucose concentration, and extracellular pH in EMT6/Ro multicellular spheroids by solution of the diffusion/reaction equations. Computations such as these, along with oxygen and pH microelectrode measurements in EMT6/Ro multicellular spheroids, indicated that nutrient concentration and pH levels in the inner regions of spheroids were low enough to cause significant changes in nutrient consumption rates and cell growth rates. However, pH and oxygen concentrations measured or calculated in EMT6/Ro spheroids where quiescent cells have been observed were not low enough to cause the cessation of cell growth, indicating that the observed quiescence must have been due to factors other than acidic pH, oxygen depletion, or glucose depletion.

Mathematical modelling of microenvironment and growth in EMT6/Ro multicellular tumour spheroids

In order to determine the role of micromilieu in tumour spheroid growth, a mathematical model was developed to predict EMT6/Ro spheroid growth and microenvironment based upon numerical solution of the diffusion/reaction equation for oxygen, glucose, lactate ion, carbon dioxide, bicarbonate ion, chlorine ion and hydrogen ion along with the equation of electroneutrality. This model takes into account the effects of oxygen concentration, glucose concentration and extracellular pH on cell growth and metabolism. Since independent measurements of EMT6/Ro single cell growth and metabolic rates, spheroid diffusion constants, and spinner flask mass transfer coefficients are available, model predictions using these parameters were compared with published data on EMT6/Ro spheroid growth and micro-environment. The model predictions of reduced spheroid growth due to reduced cell growth rates and cell shedding fit experimental spheroid growth data below 700 microns, but overestimated the spheroid growth rate at larger diameters. Predicted viable rim thicknesses based on predicted near zero glucose concentrations fit published viable rim thickness data for 1000 microns spheroids grown at medium glucose concentrations of 5.5 mM or less. However, the model did not accurately predict the onset of necrosis. Moreover, the model could not predict the observed decreases in oxygen and glucose metabolism seen in spheroids with time, nor could it predict the observed growth plateau. This suggests that other unknown factors, such as inhibitors or cell-cell contact effects, must also be important in affecting spheroid growth and cellular metabolism.

Glucose diffusivity in multicellular tumor spheroids

In order to understand the role of glucose limitations in controlling multicellular tumor spheroid growth, knowledge of the glucose diffusion coefficient is essential. The effective diffusivity of glucose in spheroids of rodent and human tumor cell lines has been determined by measuring the efflux of tritium labeled L-glucose from spheroids with time. When the rapid and irreversible binding of L-glucose in spheroids is properly taken into account, measurements of the efflux of this diffusion tracer from spheroids into label-free medium can be correlated to the diffusion equation in order to obtain the effective glucose diffusivity in spheroids. Such measurements have been made in EMT6/Ro mouse mammary tumor spheroids as well as in spheroids derived from human colon carcinoma cells (HT29, CO112, and WiDr) and from human squamous carcinoma cells (CaSki and A431). EMT6/Ro spheroids have a glucose diffusivity of 1.1 x 10(-6) cm2/s, while glucose diffusion coefficients in the human cell spheroids studied vary from 5.5 x 10(-7) cm2/s to 2.3 x 10(-7) cm2/s. These values are low enough to suggest that significant gradients in glucose concentration may exist in spheroids and tumors. It is thus believed that these glucose diffusivities, as well as their variation with cell line, may have important implications for the role played by glucose in the growth and cellular heterogeneity of spheroids and tumors.