Bacteria in Cancer?
How Bacterial Colonies Influence Metastasis
Background
Cancer metastasis, or the ability of a tumor to move throughout the body, is a phenomenon that researchers have been attempting to understand for a while. Sometimes individual cells split off of the main tumor and move to another organ while other times a group of tumor cells migrate somewhere else. Whether or not a cancer metastasizes can depend on the type of cancer, how long the tumor has been growing, and a wide variety of unknown factors.
A group of researchers in China have discovered one significant factor that contributes to the metastasis of breast cancer tumors. They found that bacteria living in these tumors helped the cancer cells move to new places in the body. They also found that different kinds of bacteria affected the metastasis of the tumor.
Summary
The first step the researchers took was to determine if there were any bacteria in breast tumors and specifically where they were in the tumors. Their experiments discovered several different types of bacteria living in breast tumors, including Staphylococcus, Enterococcus, and Streptococcus. Interestingly, they determined that most of the bacteria were actually living inside the cancer cells, instead of in the extracellular matrix. The experiment the researchers used to figure this out involved using two different antibiotics, one that could enter the cell membrane and one that could not. When the tumors were treated with the cell-penetrating antibiotic, the bacteria in the tumors were killed, but they were not killed with the other antibiotic that could not penetrate the cell. This indicated that the bacteria were living in the cytoplasm of the breast tumor cells.
After they figured out that there were bacteria in breast tumor cells, the researchers then wanted to know how their presence affected the tumor. After inducing breast tumors in mice, they analyzed the effects of killing tumor bacteria on both the growth and metastasis of the tumor. They discovered that mice with the intracellular tumor bacteria were much more likely to develop metastases in their lungs than those without tumor bacteria. However, losing the bacteria did not change how the original tumor grew. When the researchers compared the size and weight of the primary tumors with and without bacteria, there was not a difference between them. Basically, the intracellular bacteria help parts of a tumor move to new places but do not help it grow.
The next logical question to ask is how the bacteria help the tumor metastasize. To start, the researchers looked at how the intracellular bacteria affected the cells by analyzing the genes that were being expressed by those cells. The most interesting find was the activation of a pathway called the fluid shear stress pathway. Basically, cells that enter the circulatory system get beat up pretty heavily by the pressure and current of the pumping fluid around them. The fluid shear stress pathway gets activated to strengthen the cytoskeleton of a cell to prevent it from falling apart. Since the intracellular bacteria activate this pathway, cancer cells can move through the circulatory system without breaking apart, allowing the cells to find a new organ to grow in.
So to briefly summarize this brief summary, bacteria are present in breast tumors and influence how well the tumor spreads. They cause cancer cells to activate a pathway that increases the survival of cancer cells under pressure and helps stabilize the cytoskeleton. The final question to consider is what does this information mean for the future of cancer treatment? The researchers hope that adding antibiotics to cancer treatments may help in stopping tumors from metastasizing. However, they do mention that there have been wildly different results that have come from using antibiotics on cancer patients, so much more research needs to be done before this can be taken to the clinical side of cancer.
