Biomarker Significance of Exosomes in the Initiation and Progression of Breast Cancer

Currently, breast cancer diagnosis involves invasive methods such as mammography and biopsy. Thus, there’s a need for non-invasive, patient-friendly methods. Recent developments indicate much promise for the use of circulatory serum exosomes as potential biomarkers for diagnosis. Exosomes are found in most bodily fluids, and are more abundantly released from tumor cells compared to healthy cells. We examined if serum exosomes could be used as potential biomarker during the initiation and progress of breast cancer using ACI rats, which develop tumors upon low-dose continuous exposure to 17β-estradiol (E₂). Serum from E₂-treated and control animals after 3 weeks, 3 months, and 7 months was used to isolate exosomes. Exosomes were analyzed for size, protein yield, and exosomal surface and proliferation markers. Exosomes were in the size range of 40-200 nm. The mean exosomal protein yield from E₂-treated samples was higher than the control for each time period; however, the differences were insignificant due to small sample size. Serum exosomes were positive for hallmark exosomal proteins including Alix, CD44, CD63, CD81, and proliferation marker, EGFR. Levels of Alix and CD44 were elevated in E₂-treated serum exosomes versus control. E₂-treated serum exosomes enriched using CD63-captured magnetic beads exhibited higher protein yield and EGFR expression than controls; however, the differences were insignificant. Higher levels of serum exosomes positive for exosomal surface proteins and proliferation markers with E₂-treatment indicate their potential as biomarker during initiation and progression of breast cancer. (Supported from the NCI grant R25-CA134238, Duggan Endowment and Hemsley Funds).