NEW YORK, May 16 (Reuters Health) - A gene believed to suppress the growth
of tumors may be switched off in the early stages of breast cancer, according
to results of a new study. But a two-pronged treatment that includes a form of
vitamin A may help prevent or treat cancer by reactivating the
tumor-suppressing gene, researchers report.
A gene called RAR-beta-2, which is believed to stop tumors from growing, is
switched off in several types of tumors, including breast cancer. Since
substances called retinoids, which are similar in structure to vitamin A, are
thought to interact with this gene, Dr. Martin Widschwendter from the
University of Innsbruck, Austria, and colleagues studied the effects of a
retinoid called ATRA on breast cancer cells.
Suspecting that the RAR-beta-2 gene was deactivated by a process called
methylation, the researchers treated several types of breast cancer cells with
a substance that reverses this process, a demethylating agent. Then the cells
were exposed to ATRA.
In several of the 16 varieties of breast cancer cells tested, the RAR-beta-2
gene was reactivated after the two-pronged treatment, the researchers report in
the May 17th issue of the Journal of the National Cancer Institute. In another
line of cells in which the gene was already activated, or expressed, before the
treatment, the expression increased. In other types of cells, the activation of
the gene either did not increase or did not occur at all, according to the
report.
In another experiment involving breast tumors as well as a sample of normal
breast tissue, the investigators found that the activation of the RAR-beta-2
gene was linked with cancer. While the researchers did not detect signs of
methylation--the process that switches off the gene in normal breast
tissue--they did detect them in six of the eight tumors studied. And
later-stage tumors were more likely to have the gene switched off, according to
the report.
The study's authors point out that drugs that reverse the methylation
process have been beneficial in animals with cancer. Based on the research,
they conclude that reversing this process and giving retinoids may help prevent
cancer.
The vitamin A clones eventually may have a role in cancer treatment,
according to Dr. Michael B. Sporn, of Dartmouth Medical School in Hanover, New
Hampshire. But not yet, since the drug used in the study to switch the gene
back on is too toxic to use in people, he notes in an editorial that
accompanies the study.
SOURCE: Journal of the National Cancer Institute 2000;92:780-781, 826-832.
