Cancer cells are vulnerable to high doses of vitamin C when there are low levels of catalase enzyme.
Vitamin C therapies most often involve taking the substance orally. The UI scientists have however demonstrated that giving vitamin C intravenously creates blood levels that are up to 500 times higher than levels seen with oral ingestion. This is due to normal gut metabolism and excretion pathways being bypassed. For vitamin C to be able to attack cancer cells, this super high concentration in the blood is crucial.
Garry Buettner, a UI redox biology expert has found in earlier work that at these extremely high levels, vitamin C kills cancer cells selectively, but does not affect normal cells in mice and test tubes. Doctors at UI Hospitals and Clinics are now testing the approach in clinical trials for lung and pancreatic cancer. They are combining high dose, intravenous vitamin C with standard radiation or chemotherapy. Earlier phase 1 trials have shown that this treatment is safe and well tolerated, and indications are that the therapy improves patient outcomes. The larger trials currently underway aim to determine if the treatment improves the patient’s survival rate.
The study demonstrates that vitamin C breaks down easily and generates hydrogen peroxide, a reactive oxygen species that can cause damage to DNA and tissue. The study does however also show that normal cells are much more capable of removing the damaging hydrogen peroxide than tumor cells are.
Buettner, a member of Holden Comprehensive Cancer Center at the University of Iowa and a professor of radiation oncology explains that normal cells are much more efficient in removing hydrogen peroxide than cancer cells are. Cancer cells are therefore much more prone to damage and death from a high amount of hydrogen peroxide generated by vitamin C. He adds that this is the reason why extremely high levels of vitamin C used in the clinical trials do not affect normal tissue, but can damage the tumor tissue.
Removal of hydrogen peroxide can be done in various ways by normal cells. This keeps it at very low levels so it does not cause damage. The new research shows that the dominant route for removing hydrogen peroxide that is generated by decomposing vitamin C is an enzyme called catalase. The team learned that when exposed to high amounts of vitamin C, cells with lower amounts of catalase were more vulnerable to damage and even death.
Buettner believes this fundamental knowledge could help determine which therapies for which cancers could be improved by including a high dosage of ascorbate in the treatment.
He explained that cancers with low levels of catalase are likely to be more responsive to high dose vitamin C therapy than cancers with relatively high levels of catalase. Future research will focus on developing ways and means to measure catalase levels in tumors.