EVs as diagnostic biomarkers of cancer

Extracellular vesicles as a biomarker

Could extracellular vesicles (EVs) be an answer by providing a promising diagnostic tool? The growing interest shown by the scientific community for these cell-secreted nanoparticles has led to deeper understanding of their biogenesis and functions. EVs comprise different types of vesicles, including exosomes (30-150 nm) that are formed in multivesicular bodies before being released from plasma membrane into extracellular matrix². They can carry a variety of molecules including membrane-bound proteins, cytosolic proteins, DNA, coding and non-coding RNA, lipids, that constitute their cargo³. 

Thus, upon release, EVs can serve as a powerful communication system by delivering information to the recipient cells in close environment or by entering general circulation⁴. Number of mechanisms can be initiated and/or stimulated by EVs, e.g. cell proliferation, tissue repairing, cell migration but also immunomodulation (pro- and anti-inflammatory signals)². EVs content reflects the physiological state and the genetic material of the parental cell⁵. 

Easily recovered from blood and other body fluids as urine, saliva, sweat, milk, cerebrospinal fluid (CSF) of patients, EVs then offer a direct and reliable window on general body situation allowing to discover potential abnormalities. It is worth noting that EVs are able to cross the blood-brain barrier from blood to CSF and conversely. It means that, in the blood, you can access information from the central nervous system, avoiding the quite invasive lumbar puncture to recover CSF⁶. 

Role of extracellular vesicles in cancer

Whether they are good or bad guy, EVs play in cancer disease an important role too⁷. Tumors environment is highly complex and cells need to communicate in order to survive, proliferate, escape immune system, reshape their microenvironment and to have access to blood circulation via neoangiogenesis^8–10. 

For all these tasks, cancer cells secrete a large amount of EVs, even more compared to healthy cells and this could be explained by the strenuous environment surrounding tumor cells e.g. hypoxic¹¹, acidic¹² and inflammatory conditions. Not only to communicate between them, cancer cells also release EVs to influence the behavior of neighbor cells. One striking example is the induction, promoting and stimulation of the epithelial to mesenchymal transition mechanism by EVs, which is very significant for cancer metastasis^5,13. 

More importantly for clinic, these tumor cells-produced EVs harbor some specificities in terms of molecules that they carry. In our “omics” era, numerous methods are available to analyze multiple characteristics of EVs after isolation in terms of number and molecular content (PCR, RNA analysis, western blot, microscopy, flow cytometry, raman spectroscopy etc.)¹⁴. RNAs are strongly expressed in tumor cells secreted-EVs. Importantly, amount and types vary compared to normal cells.

  Among RNAs, recent works show that micro RNAs (miRNA) are serious candidates as specific biomarkers, allowing to distinguish different types of cancer, with good accuracy^15,16. EVs-miRNA-21 is the most reported biomarker and can help to detect glioblastoma, pancreatic, colorectal, colon, liver, breast, ovarian and esophageal cancers. miRNA-21 induces the production of vascular endothelial growth factor (VEGF) promoting angiogenesis¹⁷. Some protein cargos also emerge as possible diagnostic markers e.g. Glypican-1 for colorectal cancer^18,19, Caveolin-1 and CD63 for melanomas, glioblastomas and prostate cancers²⁰, epithelial growth factor receptor (EGFR) for brain cancers²¹, CD82 for breast cancers²², CD91 for lung cancers²³. Although promising, proteins are still in study for potential cancer biomarkers. It then appears that an efficient diagnostic method should rely on multi-omics analysis, with different RNAs as well as proteins, to obtain precise conclusions.

Thus, developing breakthrough and innovative methods to reliably establish diagnostics in healthy, suspicious and cancer patients represents a major and promising goal for both clinical organizations and companies around the world. Many actors in health ecosystem such as Mursla (UK), Exosomics (Italy), Exosomedx (USA), Biological Dynamics (USA), Mercy BioAnalytics (USA), currently work on making these liquid biopsy technologies affordable, fast and user-friendly to ensure a smooth process from patients to clinicians. Each company develops their own innovating processes. 

Mursla’s technology relies on millions of nanosensors per chip that provide excellent detection resolution and will focus on liver cancers. Exosomics isolates tumor-derived exosomes to analyze more reliably their contents. Exosomedx aims to detect prostate cancers by co-isolation of DNA and RNA to precisely analyze low abundant mutations occurring in early-stage diseases. 

They commercialize ready-to-use diagnostic kits for urine testing. Biological Dynamics, along with their Verita platform, combine exosome detection with cell-free DNA to help early-stage diagnostic and fast patient support. 

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