Breast Cancer Uses Exosomes as a Medium through Which it Metastasizes to the Brain

When breast cancer metastasizes to the brain, the patient only survives for less than a year. Cancer uses exosomes to cross over to the brain through the blood. Exosomes work by hijacking the natural process of the cells known as transcytosis and tricking the cells in the blood brain barrier (BBB) to take them up. Exosomes are tiny bubbles which are released by cells. Apart from conveying chemical messages, they can also be used as carriers to create a hospitable environment for tumors and their metastases.

Primary tumors release exosomes into the blood, causing cancer to spread to distant organs. Brain metastases is quite dangerous, but can be blocked. Scientists are working to identify any therapeutic targets that could help stop the brain metastases.

How Exosomes Hijack Transcytosis

  • The blood brain barrier comprises of three types of cells. When exosomes travel in the blood, they come across brain endothelial cells, then pericytes and astrocytes, which are all tightly joined. The astrocytes and pericytes often send signals to endothelial cells to tighten the junctions.
  • From the studies conducted, it was found that the exosomes trick the endothelial cells through a biological pathway known as transcytosis. When the cells engulf the exosomes, they bring them inside and release them into the brain tissue.
  • Exosomes can also manipulate the endothelial cells to ensure they break the blood brain barrier. They accomplish this by hijacking the pathways that sort molecules and change their regulation.

When exosomes break the blood brain barrier, they make the surrounding environment receptive to the growth of the tumor by degrading the protein network that provides biochemical and structural support to the brain cells.

After studying the exosomes, scientists are looking to use them to deliver anticancer drugs to the site.

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