Tumor-derived exosomes possess significant clinical relevance due to their unique composition of genetic and protein material that is representative of the parent tumor. Specific isolation as well as identification of proportions of these clinically relevant exosomes (CREs) from biological samples could help to better understand their clinical significance as cancer biomarkers.
Herein, researchers from the University of Queensland present a simple approach for quantification of the proportion of CREs within the bulk exosome population isolated from patient serum. This proportion of CREs can potentially inform on the disease stage and enable non-invasive monitoring of inter-individual variations in tumor-receptor expression levels. Their approach utilises a Surface Plasmon Resonance (SPR) platform to quantify the proportion of CREs in a two-step strategy that involves (i) initial isolation of bulk exosome population using tetraspanin biomarkers (i.e., CD9, CD63), and (ii) subsequent detection of CREs within the captured bulk exosomes using tumor-specific markers (e.g., human epidermal growth factor receptor 2 (HER2)).
Sandwich approach for the detection of CRE
(A) Schematic representation of the sandwich approach for the detection of exosomes in functionalized SPR chip. The chip was first functionalized with biotinylated anti-CD9 or CD63 (Orange) using biotin-avidin chemistry. The exosomes were passed through the SPR machine and captured by the functionalized anti-CD9 and/or anti-CD63 in the SPR chip. The HER2 specific exosomes (Brown) were detected by using anti-HER2 (Violet) (B) Cryo-TEM image of the BT474 cell derived exosomes.
The Queensland researchers demonstrate the isolation of bulk exosome population and detection of as low as 10% HER2(+) exosomes from samples containing designated proportions of HER2(+) BT474 and HER2(-) MDA-MB-231 cell derived exosomes. They also demonstrate the successful isolation of exosomes from a small cohort of breast cancer patient samples and identified that approximately 14-35% of their bulk population express HER2.