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VICUS.COM (30
April 2000) -- Jason Edwards got the surprise of
his life on his 50th birthday. The
results from his first physical examination in 11
years showed that his cholesterol was slightly
elevated. He was overweight, and, oh yes, his
prostate specific antigen (PSA) is 8.9 ng/mL
(levels greater than 4 ng/mL are considered
abnormal). For the first time in his life, Jason,
who was a devotee of fast food, had to come to
terms with the cumulative effects of past dietary
choices on his prostate cancer.
Now,
five months following diagnosis and one day after
brachytherapy, he is advised by his brachytherapist
to stop taking vitamin C each day. There is the
possibility that the effects of this antioxidant
may counter some of the effects of the 102
radioactive iodine seeds that were placed the day
before. Therefore, until the radiation has worn off
in about six months, Jason will place his vitamin C
therapy on hold.
How
might an antioxidant adversely affect
brachytherapy?
The
precise role that the antioxidant, vitamin C, plays
in tumors is not known, but recent studies have
shown possible interactions between dietary
antioxidants and cancer treatment.
We
know that vitamin C is a powerful antioxidant. It
consumes free radicals, the toxic substances in the
body that can be generated by chemotherapy agents
to destroy cancer cells. "It ís possible,"
according to Dr. David Golde, Physician-in-Chief at
Memorial Sloan-Kettering Cancer Center, "that
taking large amounts of vitamin C could interfere
with the effects of chemotherapy or even radiation
therapy." 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
it is reasonable that cancer patients undergoing
chemotherapy avoid taking large amounts of this
vitamin."
Building
on past research
Earlier
research by Dr. Golde and his colleagues
established that specific glucose transporter
molecules carry vitamin C into cells. This occurs
once vitamin C, which is used by cells in the form
of ascorbic acid, is converted into dehydroascorbic
acid and transported into the cell. Once inside,
the vitamin is converted back to ascorbic acid.
Applying
this information to patient care
According
to David Agus, an oncologist at Memorial
Sloan-Kettering Cancer Center, we now know
that tumors acquire and retain large amounts of
vitamin C. And their nutritional needs appear to be
similar to healthy cells that take in large amounts
of the vitamin."
However,
what cancer cells do with the vitamin C after it is
absorbed is not known. This will have to be
determined before guidelines for the complementary
use of antioxidants during chemotherapy and
radiation become established.
Furthermore,
research from University
of T¸bingen, School of Medicine in Germany
suggests caution in applying this knowledge to all
antioxidants in all types of malignancies. Examination
of the modulation of drug-induced cytotoxicity and
clonogenic cell death of glioma cells by three
structurally unrelated antioxidants
(N-acetylcysteine, superoxide dismutase or
phenyl-N-tert-butyl-alpha-phenylnitrone) revealed
that these antioxidants inhibit acute cytotoxicity
and clonogenic cell death induced by cisplatin.
However, they had little effect on the toxicity of
other cancer drugs including BCNU, doxorubicin,
vincristine, cytarabine, or camptothecin.
John
Russo, Jr.,
PharmD, is senior vice president of medical
communications at Vicus.com. He is a pharmacist and
medical writer with more than 20 years of
experience in medical
education.
References:
Cancer
tumors shown to consume large amounts of vitamin C.
Researchers are cautious about cancer patients
taking vitamin C supplements. Memorial
Sloan-Kettering Cancer Center, 1999.
http://www.mskcc.org/tji.htm.
Roller
A, Weller M. Antioxidants specifically inhibit
cisplatin cytotoxicity of human malignant glioma
cells. Anticancer Res, 1998;
18(6A):4493-7.
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