Oral cancer (OC) patients are at high risk to develop recurrent disease or secondary primary cancers with no available biomarkers to detect these events until a visible lesion is readily present and diagnosed by biopsy. Exosomes secreted by cancer cells are involved in tumor growth, invasion and metastasis. Researchers from Tel Aviv University aimed to determine morphological and molecular differences between oral fluid (OF)-derived exosomes of OC patients and those isolated from healthy individuals (HI).
OF from OC patients and HI was initially assessed by nanoparticle tracking analysis (NTA). Following ultracentrifugation, exosomal pellets of OC patients and HI were morphologically examined by transmission electron microscopy and atomic force microscopy (AFM). Enzyme-linked immunosorbent assay (ELISA) and western blotting (WB) were used to analyze the expression of exosomal markers-CD9, CD81 and CD63.
NTA showed that OC samples of OF had a significantly higher concentration of nanoparticles/ml and modal nanoparticle size compared to HI. The difference in size was structurally highlighted by AFM three-dimensional images applied on exosomal pellets. ELISA and WB showed differential expression of exosomal markers in OC exosomes compared to HI: lower expression of CD81 and CD9 in contrast to a higher expression of CD63 (~53 kDa).
AFM analysis of oral fluid-derived exosomes. Oral fluid-derived nanoparticles from HI (a) and OC (b) samples adsorbed on a mica surface were observed under tapping mode AFM. The AFM images of the nanoparticles from both sample types revealed individual, regular, fairly round-shaped structures which correlated well with the ultrastructural morphology of exosomes. However, the dimensions of the nanoparticles in both diameter (top images) and height (bottom images) from OC patients (b) were larger than those from HI (a)
OF-derived exosomes from OC patients differ both morphologically and molecularly from exosomes present in HI. This study is a baseline that provides a starting point for finding exosomal biomarkers for early detection of malignant changes in high-risk patients without overt clinical signs/lesions.