ExoSCOPE monitors cancer treatment in real-time at the molecular level

Current technologies to measure drug–target interactions require complex processing and invasive tissue biopsies, limiting their clinical utility for cancer treatment monitoring. Researchers from the National University of Singapore have developed an analytical platform that leverages circulating extracellular vesicles (EVs) for activity-based assessment of tumour-specific drug–target interactions in patient blood samples. The technology, termed extracellular vesicle monitoring of small-molecule chemical occupancy and protein expression (ExoSCOPE), utilizes bio-orthogonal probe amplification and spatial patterning of molecular reactions within matched plasmonic nanoring resonators to achieve in situ analysis of EV drug dynamics. It measures changes in drug occupancy and protein composition in molecular subpopulations of EVs. When used to monitor various targeted therapies, the ExoSCOPE revealed EV signatures that closely reflected cellular treatment efficacy. The researchers further applied the technology for clinical cancer diagnostics and treatment monitoring. Using a small volume of blood, the ExoSCOPE accurately classified disease status and rapidly distinguished between targeted treatment outcomes, within 24 h after treatment initiation.

ExoSCOPE for activity-based analysis of EV drug dynamics

Fig. 1

a, ExoSCOPE schematics. Drug-bound protein receptors are secreted through nanoscale EVs. To measure EV drug occupancy and cellular drug effects, the ExoSCOPE platform utilizes the competitive target labelling of EVs by bio-orthogonal click probes. These probes recruit enzymes (HRP) to achieve in situ deposition of insoluble optical products on the labelled vesicles, thereby amplifying the probe labelling signal. b, Spatial patterning of ExoSCOPE molecular reactions within plasmonic resonators. EVs are protein typed and probe amplified within the plasmonic nanoring gaps, so as to exploit local electromagnetic hotspots for sensitive detection. Specifically, immuno-captured EVs that have a low drug occupancy are extensively labelled with competitive probes, whose bio-orthogonal handles enable in situ enzymatic amplification to locally deposit insoluble optical products. These optical deposits enhance the plasmonic signals to generate a redshift in the transmitted light spectrum, thereby enabling multiparametric analysis of EV drug dynamics (that is, protein composition and drug occupancy changes). c, Characterization of an ExoSCOPE click probe. Molecular docking simulation shows the probe binding to the active site (red box) of the EGFR kinase domain. The magnified view illustrates the probe in yellow and the parent drug (afatinib) in grey. Inset: transmission electron micrograph of in situ vesicle labelling by the probe (scale bar, 50 nm). Transmission electron microscopy was performed after probe conjugation with gold nanoparticles (10 nm, as indicated by the arrows). d, Plasmonic nanoring resonators. Left: scanning electron micrographs of the periodic lattices of gold nanorings, fabricated on a glass substrate (scale bars, 2 μm for the full view and 350 nm for the inset). Right: enhanced electromagnetic fields are simulated to locate within the nanoring gaps (top; scale bar, 150 nm). The simulation was performed according to the measured cross-sectional dimensions of the nanorings (bottom). The red, blue and green curves indicate three independent measurements. e, Real-time monitoring of targeted therapy in lung cancer patients. ExoSCOPE was applied to evaluate drug dynamics in cancer-associated EVs, directly in patient blood samples. Compared with conventional PK/PD analysis, ExoSCOPE could effectively distinguish between treatment outcomes. The micrographs in c and d are representative of three independent repeats.

Pan S, Zhang Y, Natalia A, Lim CZJ, Ho NRY, Chowbay B, Loh TP, Tam JKC, Shao H. (2021) Extracellular vesicle drug occupancy enables real-time monitoring of targeted cancer therapy. Nat Nanotechnol [Epub ahead of print]. [abstract]

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