Pharmacologic ascorbic acid concentrations selectively kill cancer cells: action as a pro-drug to deliver hydrogen peroxide to tissues.
Level 5 - mechanism / opinion, no new human data
in vitro laboratory study on cell cultures
PubMed 16157892 · doi:10.1073/pnas.0506390102
What was done
Researchers measured cell death across 10 cancer cell lines and 4 normal cell types exposed to ascorbic acid for 1 hour under varying conditions. They further characterized the cytotoxic mechanism in human lymphoma cells by evaluating intracellular versus extracellular ascorbate actions, apoptotic/necrotic death pathways, dependence on metal chelators, and hydrogen peroxide (H2O2) generation in culture medium versus whole blood.
What was found
Normal cells were unaffected by 20 mM ascorbate, whereas 5 of the 10 cancer cell lines exhibited EC50 values <4 mM (a concentration achievable via intravenous administration), and human lymphoma cells exhibited an EC50 of 0.5 mM. Cell death was driven exclusively by extracellular ascorbate and was strictly dependent on H2O2 generation, which correlated linearly with ascorbate radical formation in the presence of 0.5–10% serum. Ascorbate addition to whole blood produced no detectable H2O2 and only trace ascorbate radicals, while medium exposure generated substantial H2O2.
Why it matters
This study provides a biochemical rationale for investigating high-dose intravenous vitamin C in oncology, demonstrating that pharmacologic ascorbate can act as a pro-drug to generate cytotoxic levels of hydrogen peroxide in tissues while sparing normal cells.
Limits
The study is entirely in vitro; therapeutic efficacy and safety were not assessed in animal models or human clinical trials. Only 10 cancer lines were tested, with half displaying EC50 values ≥4 mM. In vivo tumor microenvironments and endogenous antioxidant defenses may alter hydrogen peroxide generation and susceptibility.
Cited by
- supports Pharmacologic doses of intravenous vitamin C greater than 1 g generate hydrogen peroxide.