Sep. 16, 1999 Researchers are cautious about cancer patients taking vitamin C supplements
New York, September 15 - Researchers at Memorial Sloan-Kettering Cancer Center have found that cancer tumors consume large amounts of vitamin C. Their findings, which are reported in the September 15 issue of Cancer Research, may shed new light on the nutritional needs of tumors.
"This study is the first to demonstrate exactly how cancer cells acquire large quantities of vitamin C," said Dr. David Golde, senior author of the study and Physician-in-Chief of Memorial Hospital.
Although the role that vitamin C plays in tumors is not yet known, recent studies have shown that there may be possible interactions between dietary antioxidants and chemotherapy treatment. Vitamin C is a powerful antioxidant that consumes free radicals - or toxic substances in the body that can also be generated from chemotherapy agents to destroy cancer cells.
"It's possible that taking large amounts of vitamin C could interfere with the effects of chemotherapy or even radiation therapy, since these therapies often kill cells in part by using oxidative mechanisms. It's conceivable then, that vitamin C might make cancer treatment less effective and therefore, reasonable that cancer patients undergoing chemotherapy should avoid taking large amounts of this vitamin," said Dr. Golde.
Earlier research by Dr. Golde and his colleagues had established that specific glucose transporter molecules were responsible for transporting vitamin C into cells. This process occurs when vitamin C, which is used by cells in the form of ascorbic acid, is converted into the form of dehydroascorbic acid and transported into the cell. Once inside, the vitamin is converted back to ascorbic acid.
This discovery prompted Dr. Golde's team to explore whether glucose transporter molecules and vitamin C might function in cancer cells, as malignant cells devour more glucose than normal cells to obtain the energy they need to grow. Subsequently, their laboratory studies with myeloid leukemia cells showed that the cells accumulated high levels of vitamin C through their glucose transporters.
Building on this research, the researchers hypothesized that human leukemia, breast and prostate cancer cells would acquire large amounts of vitamin C in the same way. To find out, mice were injected with human cancer cells of the breast, prostate and blood and, after tumors had developed, were injected with ascorbic acid, dehydroascorbic acid, or sucrose (as a measure of blood volume). All tumors were subsequently analyzed for vitamin C content. The researchers found that the tumors readily took up vitamin C by a process involving the conversion of ascorbic acid to dehydroascorbic acid.
"Now we know that tumors acquire and retain large amounts of vitamin C. So, it appears that tumors have nutritional needs, similar to other healthy cells that take in large amounts of the vitamin," said Dr. David Agus, first author of the study and an oncologist at Memorial Sloan-Kettering Cancer Center. "More studies need to be done to determine what the tumor cells do with the vitamin C once they get it."
Memorial Sloan-Kettering Cancer Center is the world's oldest and largest private institution devoted to prevention, patient care, research, and education in cancer. Throughout its long distinguished history, the Center has played a leadership role in defining the standard of care for patients with cancer. In 1999, Memorial Sloan-Kettering was named the nation's best cancer care center for the seventh consecutive year by U.S. News and World Report.
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