Vitamin C Supplements Affect Cancer Drugs

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Main Category: Cancer / Oncology
Also Included In: Nutrition / Diet;  Biology / Biochemistry
Article Date: 01 Oct 2008 - 2:00 PDT

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Experiments on lab cultured cells and mice suggested that high amounts of vitamin C derivative at the cellular level, as results from taking supplements, may actually reduce the effect of anti-cancer drugs by helping the cancer cells live longer.

The study was the work of Dr Mark L Heaney, an Associate Attending Physician at Memorial Sloan-Kettering Cancer Center in New York and colleagues and is published in the October 1st issue of Cancer Research, a publication of the American Association of Cancer Research (AACR).

There has been some speculation that Vitamin C, an antioxidant, reduces the effectiveness of drugs that rely on oxygen free radicals to trigger cell death, for instance in some types of anti-cancer drugs that seek out cancer cells in particular and rely on this mechanism to make them commit suicide.

For this reason the use of Vitamin C to supplement cancer therapy has been a controversial topic, with some scientists saying it helps the patient's immune system fight off infections and others saying that it potentially interferes with the anti-cancer drug.

So the point of this study was to investigate the effect of Vitamin C inside the mechanism of cells while they are being treated by various anti-cancer agents.

For the study, Heaney and colleagues tested a wide range of chemotherapy drugs, some of them that rely on the free radical method and some that work by other means. They tested them on leukemia and lymphoma cancer cells, some of which had been pre-treated with dehydroascorbic acid (DHA), which is what Vitamin C (ascorbic acid) turns into before it can be transported into cells.

Actually what they found surprised them, because every drug they tested, including targeted agents like Geevec, did not work as well on cancer cells pretreated with Vitamin C compared to cancer cells that were not. In the cell cultures, between 30 to 70 per cent fewer Vitamin C pre-treated cancer cells were killed depending on the drug.

Heaney and colleagues then checked the results by implanting Vitamin C treated and untreated cancer cells into mice and giving them chemotherapy. The results were the same, despite the chemotherapy, cancer cells that had been pre-treated with Vitamic C grew into tumors much faster compared to cancer cells that had not been pre-treated.

What was puzzling about this result was that even those drugs that do not rely on the free radical method to make cells commit suicide were affected. So the researchers looked at the underlying mechanism.

What they found was that Vitamin C wasn't protecting the cancer cells by mopping up the free radicals, but the DHA was revitalizing the cell's mitochondria, the little batteries or powerhouses inside each cell that gives it energy. When mitochondria are damaged they send out signals to make the cells go into apoptosis, or programmed cell death. By restoring the mitochondria in the cancer cell, DHA was stopping the signal and actually helping the cell live longer.

Commenting on the results, Heaney said:

"The use of vitamin C supplements could have the potential to reduce the ability of patients to respond to therapy."

"Vitamin C appears to protect the mitochondria from extensive damage, thus saving the cell. And whether directly or not, all anticancer drugs work to disrupt the mitochondria to push cell death," he added.

Although the study was not done on humans, Heaney said the large amount of DHA in the experiments accumulated between cells in a similar way to what happens in human tissue when people take large supplemental doses of Vitamin C.

Previous studies at the Memorial Sloan-Kettering Cancer Center have shown that Vitamin C appears to build up in cancer cells more than in normal cells.

As Heaney explained:

"We recognized that DHA is the form of vitamin C that gets into cells, and that the tumor microenvironment allows cancer cells to convert more vitamin C into DHA."

"Inside the cell, DHA is converted back into ascorbic acid, and it gets trapped there and so is available to safeguard the cell," he added.

Heaney suspects that Vitamin C is good for normal tissue because it protects the mitochondria and extends cell life. But that isn't what you want in tumors, where you want cell death to be speeded up so the tumor shrinks.

Heaney said cancer patients should stick to a healthy diet, including food rich in Vitamin C. What he found "worrisome", was that some patients were dosing themselves with large amounts of over the counter Vitamin C supplements.

"Vitamin C Antagonizes the Cytotoxic Effects of Antineoplastic Drugs."
Mark L. Heaney, Jeffrey R. Gardner, Nicos Karasavvas, David W. Golde, David A. Scheinberg, Emily A. Smith, and Owen A. O'Connor
Cancer Res 2008 68: 8031-8038.
Volume 68, Issue 19, October 1 2008.
doi: 10.1158/0008-5472.CAN-08-1490

Click here for Abstract.

Source: Journal abstract, American Association for Cancer Research.

Written by: Catharine Paddock, PhD.


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