Researchers say, a drug currently undergoing trials for breast and lung cancer, has also been found effective in treating brain cancer glioblastoma and prostate cancer.
According to Dr. Jerry Shay, professor of cell biology, the drug's actions, observed in isolated human cells in one trial and in rodents in the other, are especially encouraging because they attacked not only the bulk of the tumor cells but also the rare cancer stem cells that are believed to be responsible for most of a cancer's growth.
In the brain cancer study, the drug could successfully cross the bloodstream into the brain, which is especially important because many drugs are not able to cross the blood-brain barrier.
"Because it attacks a mechanism that's active in most cancers, it might prove to be widely useful, especially when combined with other therapies," said Shay.
The researchers focussed their study on telomeres, bits of DNA that help control how many times a cell divides. Telomeres are protective "caps" of DNA on the ends of chromosomes, the structures that contain the body's genes. As long as telomeres are longer than a certain minimum length, a cell can keep dividing.
But telomeres shorten with each cell division, so a cell stops dividing once the telomeres are whittled down to that minimum.
In cancer cells, however, an enzyme called telomerase keeps rebuilding the telomeres, so the cell never receives the cue to stop dividing. In essence, they become immortal, dividing endlessly.
The experimental drug called imetelstat or GRN163L was found to block telomerase.
It is already in clinical trials as a potential treatment for breast and lung cancer, as well as for chronic lymphocytic leukemia.
Glioblastomas are the most common malignant brain tumours in adults. In the glioblastoma study Shay and his colleagues found that imetelstat blocked the action of telomerase in isolated tumour-initiating cells as well as the bulk of the tumor cells, eventually killing the cells.
Combining imetelstat with radiation and a standard chemotherapy drug made imetelstat even more effective.
In the prostate cancer study, the researchers isolated tumor-initiating cells from human prostate cancer cells. The cells showed significant telomerase activity. Imetelstat blocked the enzyme's activity, and telomeres shortened greatly.
The glioblastoma study appears in Clinical Cancer Research. The prostate cancer study appears in the International Journal of Cancer.