Liquid biopsies; The Potential Role of EVs as Biomarkers in Veterinary Medicine

Over the last few years liquid biopsies, namely the test of patient’s biofluid samples, have emerged as precious tools for early diagnosis in cancer, thanks to the major advantages of this technique when compared with tissue biopsies: liquid biopsies imply a less invasive sampling, allow to obtain more feasible serial analyses, and in principle overcome limitation of tissue biopsy in the setting of intratumoral heterogeneicity. The major components of liquid biopsies with diagnostic and prognostic utility are circulating tumour cells (CTCs), circulating tumour DNA (ctDNA), and extracellular vesicles (EVs) (Scarlotta et al., 2019). With a size ranged from 30 to 1000 nm, EVs are a heterogeneous group of lipid-bilayered vesicles secreted by many cell types in both physiological and pathological conditions (van Niel et al., 2018). Released into the extracellular space, EVs produced by diseased cells enter the circulation and spread into the body. As a results, these EVs, carrying a disease-associated cargo, can be detected in many body fluids, such as blood, urine, saliva, cerebrospinal fluid, and breast milk (Zhao et al., 2019). In Human Medicine EVs research has grown exponentially in the last years, and even if a limited number of studies have been published on EVs in the Veterinary field so far, there is an underneath growing interest that allows for the prospect of a similar rapid increase of EV-related research works in the next future years. After a short introduction on general EVs features and roles, I will present a brief overview of the current status of the use of circulating EVs as biomarker in human medicine, mainly focusing on their applicability in cancer diagnostics. Then, I will discuss their potential application in veterinary medicine and the present state of the veterinary research in the field. Moreover, the most used methods to isolate EVs from body fluids will be presented. Furthermore, I will show some data on the potential application of circulating EV-derived molecules as cancer diagnostic/prognostic biomarkers in canine cancer patients. Based on the prognostic utility of tissue cell cycle-related markers and on the fact that tumour cells are able to release EVs enriched with these specific markers in vitro, we investigated the possibility of using blood-derived EVs of cancer patients to detect proliferation markers, as indicator of the tumour proliferation signature. Finally, current limitations and future prospective in the field of EVs biomarkers research will be discussed