Tumor-derived exosomes (TEXs) are extracellular vesicles that are continuously released into the blood by tumor cells and carry specific surface markers of the original tumor cells. Substantial evidence has implicated TEXs as attractive diagnostic markers for cancer. However, the detection of TEXs in blood at an early tumor stage is challenging due to their very low concentration. Here, researchers from Sun Yat-sen University have established a method called PLA-RPA-TMA assay that allows TEXs to be detected with high sensitivity and specificity. Based on two proximity ligation assay (PLA) probes that recognize a biomarker on a TEX, they generated a unique surrogate DNA signal for the specific biomarker, which was synchronously amplified twice by recombinase polymerase amplification (RPA) coupled with transcription-mediated amplification (TMA), and then the products of the RPA-TMA reaction were quantitatively detected using a gold nanoparticle-based colorimetric assay. The researchers established proof-of-concept evidence for this approach using TEXs from nasopharyngeal carcinoma (NPC) cells, with a detection limit of 102 particles/mL, and reported the measurement of plasma Epstein-Barr virus latent membrane protein 1 (LPM1)-positive (LMP1+, accuracy: 0.956) and epidermal growth factor receptor (EGFR)-positive (EGFR+, accuracy: 0.906) TEXs as potent early diagnostic biomarkers for NPC.
Schematic illustration of the PLA-RPA-TMA assay
LMP1+ exosome detection is displayed as an example. MB: magnetic beads