Image: A laboratory setup used to test exosomes extracted from blood samples for pancreatic cancer biomarkers (Photo courtesy of the University of California, San Diego).
A novel electronic chip-based method for rapid capture and analysis of exosomes together with their protein and other biomarker content will facilitate liquid biopsy diagnosis of pancreatic cancer.
Pancreatic ductal adenocarcinoma (PDAC) typically has nonspecific symptoms and is often found too late to treat. Because diagnosis of PDAC involves complex, invasive, and expensive procedures, screening populations at increased risk will depend on developing rapid, sensitive, specific, and cost-effective tests. Exosomes, which are nanoscale vesicles shed into blood from tumors, have come into focus as valuable entities for noninvasive liquid biopsy diagnostics.
Exosomes are cell-derived vesicles that are present in many and perhaps all biological fluids, including blood, urine, and cultured medium of cell cultures. The reported diameter of exosomes is between 30 and 100 nanometers, which is larger than low-density lipoproteins but much smaller than red blood cells. Exosomes, which contain RNA, proteins, lipids, and metabolites that are reflective of the cell type of origin, are either released from the cell when multivesicular bodies fuse with the plasma membrane, or they are released directly from the plasma membrane. Exosomes have specialized functions and play a key role in coagulation, intercellular signaling, and waste management. Consequently, there is a growing interest in the clinical applications of exosomes for prognosis, therapy, and as biomarkers for health and disease. However, rapid capture and analysis of exosomes with their protein and other biomarkers have proven difficult.
Investigators at the University of California, San Diego (USA) recently announced the development of an electronic chip-based device designed to extract exosomes directly from biological samples within a few minutes.
Samples could be blood, serum, or plasma. No pretreatment or dilution of sample nor use of capture antibodies or other affinity techniques was required. Samples loaded onto the chip experienced an alternating electric current, which selectively extracted nano-sized particles such as exosomes out of the fluid and deposited them onto minute electrodes on the chip's surface. Larger solid components were washed away. Specific anti-pancreatic cancer antibodies labeled with fluorescent dyes that targeted the glypican-1 and CD63 biomarkers were added to the sample. If these biomarkers were present, a positive result was seen under a microscope due to antibody binding that produced brightly colored circles. This entire process could be performed in less than an hour.
In an initial validation study, the biomarkers glypican-1 and CD63 were found to reflect the presence of PDAC and thus were used to develop a bivariate model for detecting PDAC. Twenty PDAC patient samples could be distinguished from 11 healthy subjects with 99% sensitivity and 82% specificity. In a smaller group of colon cancer patient samples, elevated glypican-1 was observed for metastatic but not for non-metastatic disease.
"This test could be used as a primary screening strategy to identify patients who would subsequently need to undergo more expensive and invasive diagnostic methods like a CT scan, MRI or endoscopy," said contributing author Dr. Rebekah White, associate professor of surgery at the University of California, San Diego.
Details of the chip for exosome extraction were published in the April 24, 2018, issue of the journal ACS Nano.
University of California, San Diego