AICR SCIENCE NOW Volume 9
Do Amino Acids Build Cancer? Known as the building blocks of life, some amino acids may also be important for the spread of cancer. AICR researcher Gary Meadows, Ph.D., is investigating how restriction of two essential amino acids, tyrosine and phenylalanine, might help prevent cancer metastasis. This nutritionally-based therapy shows promise as an aid to a multi-faceted conventional cancer treatment.
Since the 1950s, researchers have investigated the effect of amino acids on cancer. For instance, the depen-dency of many leukemia cells for growth on the nonessential amino acid asparagine was an early discovery. By administering the enzyme asparaginase, which helps break down and eliminate asparagine, doctors can use this approach to help treat children with this cancer.
Of all the amino acids, "phenylalanine and tyrosine appear to have a unique ability to affect a variety of cancers," Dr. Meadows says. "In the different cancer cells my colleagues and I have looked at, including mela-nomas, prostate and breast cancer lines, restriction of these two amino acids inhibits tumor invasion. In some cancer cells, restriction even induces apoptosis." AICR has repeatedly funded the work of Dr. Meadows, who is Director of the Cancer Prevention & Research Center at Washington State University.A Major Effect on Melanomas
The first cancer Dr. Meadows examined was melanoma. To restrict phenylalanine and tyrosine in the diet of laboratory mice implanted with melanoma tumor cells, Dr. Meadows fed them a specially formulated food. Although the mice initially lost some weight on this diet, they kept thriving, and the diet inhibited metastasis.
The results of this experiment sur-prised Dr. Meadows. "There is no effective drug treatment for stopping the spread of cancer in mice," he says, "but this amino-acid-restricted diet had a major effect on containing the malignant melanoma. And the blood levels of these two amino acids only went down 30-40 percent."
Dr. Meadows believes that a special diet low in these two amino acids could pro-duce beneficial results in humans with cancer, too. With some dedicated nutrition students at Washington State University, Dr. Meadows has tested a low-amino-acid diet on humans. For six weeks, the stu-dents ate a low-protein diet, along with a commercially available protein supple-ment. No harmful effects were observed.The Difficulty in Starting Clinical Trials
An amino acid therapy would work best in conjunction with other cancer treatments. As Dr. Meadows points out, "In conven-tional treatment, a combination of drugs is used to attack multiple points in the metabolism of tumor cells. An ami-no acid therapy lends itself to a mul-tiple drug approach because it can affect different actions in cells. It might also enhance the effects of radiation."
But the biggest impediment to making such a nutritionally-based treatment avail-able is the reluctance of physicians to test it in clinical trials. "There are still physicians," says Dr. Meadows, "who don't believe nutrition has any role in cancer prevention or treatment."
Regular clinical trials are also not set up to test an adjuvant therapy, like a restricted amino acid diet. "Cancer clinical trials are still looking for a silver bullet," claims Dr. Meadows. "They like targeted therapies in which one signaling molecule can be inhibited. Maybe this therapy will have an initial effect, but cancer cells are hetero-geneous. To treat this disease, we will come back again and again to multiple therapies."
Dr. Meadows likens the need for vari-ous therapies to treat cancer to AICR's advice to prevent cancer. By eating a varie-ty of plant foods, he notes, a person re-ceives many different phytochemicals that work in combination to ward off disease.References
Fu YM et al. Specific amino acid dependency regulates invasiveness and viability of androgen-independent prostate cancer cells. Nutr Cancer.
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