From junk to biomarker: Extracellular vesicles probed for cancer treatment

Once thought to be junk, extracellular vesicles (EVs) may play an important role in intercellular communication and in many disease processes such as cancer metastasis, according to a new article published in the journal Nature Biomedical Engineering.

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Lipid nanoprobes (blue, green and yellow colored) spontaneously insert into lipid bilayer of three extracellular vesicles. The lipid nanoprobe-labeled extracellular vesicles are captured onto the surface of a magnetic bead (black, bottom) through interaction with conjugated avidin molecules (red). Exosome isolation and its cargo analysis offers new opportunities for a diverse range of molecular analyses, including mutation detection from blood plasma of cancer patients. Image courtesy of Credit: Xin Zou.

Lipid nanoprobes (blue, green and yellow colored) spontaneously insert into lipid bilayer of three extracellular vesicles. The lipid nanoprobe-labeled extracellular vesicles are captured onto the surface of a magnetic bead (black, bottom) through interaction with conjugated avidin molecules (red). Exosome isolation and its cargo analysis offers new opportunities for a diverse range of molecular analyses, including mutation detection from blood plasma of cancer patients. Image courtesy of Credit: Xin Zou.

The vesicles are a nanoscale product of human cells. They are markedly small lipid-enclosed structures that contain double-stranded DNA, RNA, and proteins responsible for intercellular communication. They are also known to carry markers for their origin cells, including tumor cells. In fact, one function of the EVs is to prepare distant tissue for metastasis in patients with cancer.

They are now under consideration as a potential biomarker. Researchers at Penn State have developed nanoprobes for rapid isolation of the EVs. This isolation holds the potential for precision cancer diagnosis and personalized anticancer treatments.

“Most cells generate and secrete extracellular vesicles,” says Siyang Zheng, PhD, associate professor of biomedical engineering and electrical engineering. “But they are difficult for us to study. They are sub-micrometer particles, so we really need an electron microscope to see them. There are many technical challenges in the isolation of nanoscale EVs that we are trying to overcome for point-of-care cancer diagnostics.”

The team developed a method to isolate and purify EVs in blood samples obtained on liquid biopsy. Liquid biopsies are a recent development that offer benefits over the traditional technique of extracting cancer cells from a tumor via needle. In patients with certain lung or brain cancers, needle biopsies can be difficult to perform, expensive, and painful.

“[These] noninvasive techniques are preferable for not only detection and discovery, but also for monitoring treatment,” says Chandra Belani, MD, professor of medicine at Penn State’s Milton S. Hershey Medical Center and Cancer Institute, and a clinical collaborator on the study.

Nuts and Bolts

The researchers created a system of two micro/nano materials. One is a labeling probe that contains two lipid tails that spontaneously insert into the lipid surface of the extracellular vesicle. A biotin molecule is located on the other end of the probe. The molecule has an avidin molecule attached to a magnetic bead.

The surface-modified magnetic beads are 400-500 nm in diameter, and the labeling probe is approximately 10 nm. After the system is optimized, researchers hope to be able to isolate EVs from blood plasma samples in about 15 minutes. The EVs would then be analyzed to characterize the DNA, RNA, and proteins.

“Aided with this new approach, we successfully isolated EVs from 19 patients with advanced [non-small cell] lung cancer and identified DNA mutations that can guide precision therapy instead of routine chemotherapy,” according to lead author Yuan Wan, a postdoctoral researcher in Dr. Zheng’s lab. “From collecting blood to obtaining EV-derived DNA, the whole procedure can be completed within one hour. It only requires a magnet and a common benchtop centrifuge. Compared to prevalent methods, the nanoprobe system would greatly facilitate clinical laboratory examination.”

The new technology is relatively inexpensive and fast when compared with ultracentrifugation, the current gold standard. After the new technique is validated in a larger study, the team hopes that this technique can be applied to most solid tumors.

“Sequencing the DNA isolated from the EVs will serve as a promising tool to track cancer evolution and monitor tumor dynamics with the ultimate goal of improving cancer survival,” Dr. Belani concludes.

The study was supported by the National Cancer Institute of the National Institutes of Health and Penn State University.