Scientists have identified a protein produced in healthy breast tissue that naturally kills breast cancer cells.
The laboratory discovery could open the way for a new treatment for breast cancer, and possibly other cancers as well.
This work began with a discovery in the laboratory, that when breast cancer cells were mixed with material taken from around normal, non-cancerous cells, the cancer cells stopped growing or died.
"Our original observation was very intriguing, that there was something that was produced by normal cells that was capable of killing cancer cells, so we decided to follow up," says Irene Kuhn of the Lawrence Berkeley National Laboratory in California, a member of the team that did the research in the lab of scientist Mina Bissell.
The scientists found six substances that affected the cancer cells. The most powerful was a protein called interleukin 25 (IL-25) that is produced by normal breast cells.
Kuhn says that when normal cells mutate and become tumor cells, "they, for whatever reason - we don't know why - but they increase their expression of IL-25 receptor."
That receptor is a structure that mates up with and binds to the IL-25 protein.
"If that tumor cell happens to be anywhere near a normal human breast cell, that tumor cell will be exposed to the IL-25 that's being produced by the human breast cells, and it will be killed," Kuhn says.
And because the IL-25 receptor only occurs on tumor cells, IL-25 attacks only tumor cells, not normal cells.
So if IL-25 is a potent killer of breast cancer cells, why do people get breast cancer? The short answer is, there is not enough IL-25. And that suggests, of course, that IL-25 might be investigated as a treatment for breast cancer.
Kuhn says treatment based on IL-25's natural cancer-fighting properties could have major advantages over conventional therapies.
"It has a tumor specificity that's very high, and therefore anything that goes to the clinic based on IL-25 will be very tumor-specific and have very low side effects. And that provides an enormous amount of hope for people who are undergoing therapy."
This study was specific to breast cancer, but Irene Kuhn says they also identified IL-25 receptors on melanoma cells, which suggests IL-25 might be investigated as a treatment for skin cancer, and maybe other cancers as well.
The study on IL-25 and breast cancer is published in the journal Science Translational Medicine.