An article published in the August 5, 2008, issue of the Proceedings of the National Academy of Sciences reported that injections of ascorbate (vitamin C) reduce the weight and growth rate of tumors by half in mouse models of ovarian, pancreatic and brain cancer, while leaving normal cells unharmed.
Researchers at the National Institutes of Health (NIH) tested ascorbate in 43 tumor and 5 normal cell lines to determine a concentration that decreases cell survival in cancerous cells without resulting in toxicity to healthy cells. They subsequently injected a dose of 4 grams ascorbate (neutralized with sodium hydroxide) per kilogram body weight once or twice per day into immune-deficient mice with implanted ovarian, pancreatic and glioblastoma (brain) tumors. "At these high injected doses, we hoped to see drug-like activity that might be useful in cancer,” explained lead author Mark Levine, MD, who is the chief of the Molecular and Clinical Nutrition Section of the National Institute of Diabetes and Digestive and Kidney Diseases at the NIH.
Dr Levine’s team found that injecting the animals with ascorbate decreased tumor growth and weight by 41 to 53 percent. While metastases occurred in 30 percent of the mice with brain tumors, none appeared in animals injected with vitamin C. No adverse effects of vitamin C treatment were noted.
Interestingly, vitamin C, which is known for its antioxidant effect, achieved the current study’s results via a pro-oxidant effect that can occur at high levels. This effect causes the formation of hydrogen peroxide in the extracellular fluid surrounding the tumors (but not in the blood), resulting in the death of cancerous cells. The vitamin was administered by injection in the current study in order to achieve high concentrations in the body that cannot be reached using an oral route.
Blood levels of ascorbate similar to those measured in the mice have been readily achieved in human subjects who received intravenous vitamin C. The authors suggest that the failure of double-blind placebo-controlled trials of vitamin C in cancer patients, which were conducted following initial encouraging case series results, could be due to the oral route of administration used in the trials.
“Clinical and pharmacokinetic studies conducted in the past 12 years showed that oral ascorbate levels in plasma and tissue are tightly controlled,” Dr Levine observed. “In the case series, ascorbate was given orally and intravenously, but in the trials ascorbate was just given orally. It was not realized at the time that only injected ascorbate might deliver the concentrations needed to see an anti-tumor effect."
"These preclinical data provide a firm basis for advancing pharmacologic ascorbate in cancer treatment in humans," the authors write. “As modalities in cancer are often combined, these data suggest that pharmacologic ascorbate in combination with other therapies deserves further exploration for treatment of cancers that otherwise have poor outcomes, such as pancreatic and ovarian carcinomas and glioblastoma.”