May 8 2018
Precision cancer treatment relies on obtaining molecular information about the tumor to guide effective treatment decisions. Because needle biopsies of brain tumors are invasive and difficult, bioengineers supported by the National Institute of Biomedical Imaging and Bioengineering (NIBIB) have developed micro-technologies that capture extracellular vesicles (EVs) released by the tumor. The vesicles carry samples of the mutated genetic material and proteins causing malignancy that researchers hope to analyze to optimize treatment.
Although they carry a wealth of information, EVs from tumors are very small particles, made of lipids, and are relatively rare. Therefore, researchers have developed microfluidic devices that can take a small sample of blood from a patient and capture the EVs and their contents for analysis. Work reported in the February issue of Nature Communications describes development of a new microfluidic device, the EVHB-Chip, that significantly increases the capture of EVs from volumes smaller than a single drop of blood.
A major factor in isolating these rare EVs from cancer cells is that they are mixed in with billions of EVs from healthy cells that appear to be part of a communication network used to change or augment the function of surrounding cells. For example, in healthy cells, EVs contain a subset of nucleic acids that can manipulate their cellular microenvironments to promote wound healing. Conversely, cancer EVs carry molecules that promote cancer spread through angiogenesis (creation of new blood vessels), invasiveness, and metastasis.
Led by Shannon Stott, Ph.D., Assistant Professor at the Center for Engineering in Medicine at Massachusetts General Hospital, bioengineers designed a microfluidic chip with a staggered herringbone surface. The herringbone chamber is coated with antibodies known to bind to proteins found in brain tumors and that are carried on the surface of the EVs. EV yield is enhanced by turbulence created by the herringbone structure, which increases the frequency with which EVs collide with the capturing antibodies on the chamber walls.
Using the EVHB-Chip, the researchers analyzed blood samples from 13 patients with the brain tumor glioblastoma multiforme (GBM). The EVHB-Chip successfully isolated enough tumor-specific EVs from all 13 patients to analyze the cancer genes present. The analysis revealed high levels of more than 50 cancer-associated genes including the cancer-specific GBM mutation EGFRvIII.
"Until now we have been working mainly with circulating tumor cells (CTCs) that break off from tumors and can be captured using microfluidics to obtain information to guide treatment decisions," explained Stott. "However, when it comes to brain cancer, CTCs may not make it through the blood brain barrier. EVs are much smaller particles that more readily make it out of the brain into circulation, which is why we are honing our microfluidic technologies to capture these small EVs and use the information they carry to eventually optimize brain cancer therapies."
"We are also excited about the potential of this technology with pediatric brain cancer patients, from which only very small amounts of blood can be obtained, especially repeatedly to monitor the effectiveness of therapy. Effectiveness is measured by molecular changes in the captured EVs over the course of treatment," said Stott.
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