Probing apoptosis signaling proteins in single living cells for precision efficacy evaluation of anti-cancer drugs

In vitro efficacy evaluation is critical for anti-cancer drug development and precision cancer treatment. Conventional methods, which mainly rely on cell viability and large cell populations, suffer from apparent disadvantages, such as signaling pathway-nonspecific, failing to reflect the real sensitivity of the patient, tedious and time-consuming. Herein, we present a new analytical tool, termed single-cell plasmonic immunosandwich assay (scPISA), for precision efficacy evaluation of anti-cancer drugs. It allows for facilely probing individual signaling proteins as well as protein-protein complexes in single living cells. Based on this approach, two apoptosis signaling proteins, cytochrome C (Cyt C) and caspase-3, were proposed as apoptosis indicators, while three new parameters were proposed as criteria for quantitative efficacy evaluation. Using two typical cytotoxic drugs, actinomycin D (Act D) and staurosporine (STS), as model drugs, the evaluation was found to be consistent among the indicators and parameters. Metformin, a potential anti-cancer drug, was then evaluated using this approach. Interestingly, metformin alone was found to be a less effective anti-cancer drug but its combination with Act D dramatically improved the overall efficacy. The scPISA approach exhibited several unique strengths over conventional assays, including comprehensive and self-consistent evaluation, signaling pathway-specific, simple procedure and high speed. Thus, it holds great promise for personalized drug screening and precision medicine.