Cell is the basic unit of life. Many diseases, such as cancer, are increasingly understood as a process defined and propagated at the single cancer cell biology level. The development of precision medicine will require the capability to administer drug treatments to maximize the benefit to the individual patients. A major unmet bioanalytical need at the interface of precision medicine and single cell analysis will be the capability to monitor the dosing and effectiveness on the single cell level. We have developed a novel microscale sampling and ionization device, the Single-probe, that can be coupled to mass spectrometer to perform single cell mass spectrometry (SCMS) of molecules inside living single cells under ambient conditions. The Single-probe is fabricated by combining a laser-pulled dual-bore quartz needle (tip size smaller than a cell) with a silica capillary and a nano-ESI emitter. In SCMS experiments, cells are attached to an XYZ-translational stage for sample movement. Cell insertion is monitored using digital microscopes as the Z-stage is lifted precisely. We have successfully detected anticancer compounds, drug metabolites, and cell metabolites inside singe cancer cells. In our recent studies, we are developing the technique to quantify the amount of chemotherapy drugs in cancer cells, including in both laboratory cultured cell lines and bladder cancer cells isolated from patient urine samples. To use cell lines as model systems, cancer cells are cultured and treated with anticancer drugs. Sampling solvent (acetonitrile) containing the deuterated compound (i.e., the internal standard) is continuously delivered into a target cell to extract intracellular compounds. Both target and internal stand molecules are simultaneously ionized and for real-time MS analysis. The concentration of the target molecule is estimated from its relative ion intensity to the internal standard and accounting for the concentration of the internal standard, solvent flowrate, and data acquisition time. Standard HPLC/MS analysis of cell lysates were done in parallel for comparison. Patient cells will be measured upon the establishment of our experimental protocols. If successful, this research project will mark the first-time drug levels have been measured from patient-isolated cancer cells, and this advancement could lead to the development of SCMS based methods guiding drug administration in the clinical treatment of many diseases.

Live single cell mass spectrometry: Towards quantitative analysis

255th National Meeting (2018)

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