Cancer drug damages chromosomes, causes secondary cancers

Etoposide is a relatively new "anticancer" drug used for patients who have leukemia, lymphoma and testicular cancer. Medical doctors are even experimenting with it for other malignancies.

But the drug has a slight drawback. It cuts up the ends of chromosomes (a region known as the telomere) and can cause serious after effects including often-fatal secondary cancers.

About five percent of patients using the drug suffer chromosomal defects that can lead to secondary leukemias. These leukemias often arise within a year or two of treatment, and they are usually fatal, according to a study on the drug.

In an incredible example of understatement, Mark Muller, professor of molecular genetics and a researcher with Ohio State University's Comprehensive Cancer Center, called the possibility of fatal secondary cancers a "rather serious complication."

The study, co-authored by Muller, was published in a the journal Biochimica et Biophysica Acta.

Etoposide is a member of a small class of drugs known as topoisomerase-II inhibitors. These drugs work by blocking the action of an enzyme found in cells known as topoisomerase Il (topo II). The job of topo II is to untangle DNA strands during cell division. Failure to do so is lethal to the cell.

Topo II does this by making temporary breaks in DNA to allow another DNA strand to pass through it. Normally, the enzyme then instantly re-joins the cut ends to repair the break.

Etoposide prevents the enzyme from completing its repair step. "The drug actually subverts the enzyme into a DNA damaging agent," said Muller.

Despite the potentially deadly side effects of etoposide, the Food and Drug Administration has taken no steps to prohibit the use, marketing or sale of the drug.

SOURCE: "Drug's Effect on Chromosomes May Explain Secondary Cancers," Ohio State University, May, 27, 1998.

The Chiropractic Journal.

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