Cancer cells are not loners. They communicate with each other, with the other cells in their neighborhood, and with cells in the entire universe of your body. Now, a flurry of basic research has led to new insights into this communication and an exciting new realm of investigation.
One way cells communicate with other cells is by sending out messenger RNA or microRNA (miRNA) with specific instructions. And what enables them to do this are exosomes: out-pouchings squeezed off from the cell wall that contain a single strand of messenger RNA. (As you may recall from a science class, RNA is a copy of DNA that can direct the building of proteins).
Apparently with the ease of sending out a tweet, a cancer cell can send out this small piece of messenger RNA in a very small (one millionth the size of a human hair) pouch that can get picked up by another cell or make its way into a blood vessel or into another body fluid. This form of communication seems to be common among cancer cells, where active tweeters send out many exosomes.
Laboratory research by Sonia Melo and colleagues published in November 2014 in Cancer Cell showed that when they put breast cancer cells into mice, the cancer cells tweeted exosomes that had the ability to manipulate their microenvironment and that contained the precise message necessary to convince a mouse’s normal breast cells to turn into cancer cells—converting them from afar.
Another study published in the Journal of Molecular Medicine in April 2013, showed that the exosomes tweeted from cancer cells sent a two-fold message designed to both recruit and reprogram the tumor microenvironment to make it more hospitable to cancer cells and to keep immune cells in check, so that they would ignore the cancer cells. A pancreatic research group saw that pancreatic cancer cells could tweet exosomes that were picked up by liver cells and were able to convert the liver into an environment that was more favorable for metastasis.
All of this suggests that cancer cells may not just leave the original tumor, enter the blood stream, and then find another organ in which to set up shop, but that they actually prepare the new organ in advance for their arrival, using exosomes to set up a niche or environment that will make them feel right at home when they arrive! In addition, through exosomes, or social media in this analogy, they can convert some of the cells in the new organ to become cancer cells too.
This understanding of the way cancer cells communicate with each other and the rest of the body through exosomes has a number of potential clinical utilities. It is possible that one day we might be able to monitor the blood for these signals either to diagnose cancer or monitor a tumor’s progression or response to treatment. It is also possible that we might be able to figure out a way to block the exosomes cancer cells are sending out, so that they can’t communicate with the normal cells either to convert them or to make them more hospitable.
I am far from alone in my excitement about these exosomes. Dr. Francis Collins, the director of the National Institutes of Health, recently launched a new Extracellular RNA Communication program to support research into how this whole process works. You can see (literally!) what this research looks like here.
This field opens up a whole new front in the prevention and treatment of cancer and that is always research worth watching!