U of T’s Professor Raymond M. Reilly has developed a new technique that has proven effective in destroying breast cancer cells in mice. This method may be able to treat breast cancer tumours in humans that have been resistant to chemotherapy.
Dr. Reilly’s research is based on a principle discovered in 1929. Electrons emitted by the decay of radioactive materials can kill cells by destroying their DNA. “These electrons are highly damaging to a cell’s DNA only once they are inside the cell-the key is getting them inside the cancer cell,” explains Dr. Reilly.
To do this Dr. Reilly and his team created a new drug that contains the radioactive isotope Indium-111 hidden inside of a peptide (small protein), called epidermal growth factor (EGF). EGF normally causes cells to grow and divide rapidly. Cancer cells use more EGF than normal cells as they multiply very quickly in a tumour. These peptides therefore easily get inside of a cancerous cell, bringing the radioactive material with them. After engulfing the peptide packages, the cancer cell’s DNA is chopped up by the radioactive material hidden inside the peptide. “Like the legend of the Trojan Horse, in which invading Greek soldiers hid inside a hollow wooden horse to fool their enemies, this drug enables deadly radioisotopes to hide within [the peptide] as it passes naturally into the breast cancer cells,” said Reilly.
To study the effects of their new drug, Dr. Reilly’s research team injected human breast cancer cells into female mice. The radioactive drug slowed down the growth of large breast cancer tumours, and completely destroyed small tumours.
The power of this new drug was “shown to be hundreds of times more effective at killing human breast cancer cells,” said Reilly. Moreover, it showed very low toxic side effects on normal cells. Breast cancer patients treated with chemotherapy have been shown to have lower levels of white blood cells, says Reilly.
Hiding radioactive chemicals inside proteins “represents a novel strategy for treating cancer,” said Reilly. “This strategy will continue to take advantage of research that has greatly improved our understanding of the functioning of cancer cells, in order to devise new treatments for this disease,” said Reilly.
There are other benefits to this treatment in addition to its efficiency and minimal side effects. The protein that this technique employs is craved by “a wide variety of tumours including colorectal cancer, ovarian cancer, and head and neck cancer,” said Dr. Reilly. “Therefore the drug theoretically could also be valuable for treating these other diseases.
“Great strides have been made through research over the last 20 to 30 years in understanding the fundamental biology of cancer,” said Dr. Reilly. “The immediate goal is now to apply this knowledge to the creation of new cancer therapies that are more effective and less toxic to normal tissues.” This method of radioactive therapy is “One intriguing avenue through which this could possibly be achieved.”
Dr. Reilly’s drug will soon be used in clinical trials at Princess Margaret Hospital led by Dr. Katherine Vallis. Approved by Health Canada, the first phase of the trial is testing the safety of this drug in patients with advanced, chemotherapy-resistant breast cancer.
