Single-event tandem ICP-mass spectrometry for the quantification of chemotherapeutic drug-derived Pt and endogenous elements in individual human cells

Highlights: • Determination of drug-derived Pt and essential elements in individual human cells. • Interference-free ICP-MS/MS conditions via use of O₂ (P and S) and NH₃ (Fe). • Pt content in individual cells proportional to drug exposure concentration. • Differences in Pt uptake are related with difference in chemo-responsiveness. • PCA of contents of essential elements suggests potential for metallo-fingerprinting. Single cell – tandem ICP-mass spectrometry (SC-ICP-MS/MS) was used for the determination of the absolute amount of Pt (coming from exposure to various concentration levels of cisplatin as a chemotherapeutic drug) and five endogenous elements (P, S, Fe, Cu and Zn) in individual human cells of three different types – Raji, Jurkat and Y79. Optimum conditions were obtained by using a sample introduction unit transporting cell suspension containing approx. 5 × 10⁴ cells per mL at a flow rate of 10 μL min⁻¹ to a nebulizer with narrow internal diameter (250 μm i.d.), mounted onto a total consumption spray chamber. Interference-free conditions were obtained in tandem MS mode (i) for P and S by pressurizing the collision/reaction cell (CRC) with O₂ and monitoring the PO⁺ and SO ⁺ reaction product ions and (ii) for Fe by pressurizing the CRC with NH₃ and monitoring the Fe(NH₃)₂⁺ reaction product ion. The quantification approach was validated by comparison of the absolute amounts of the target elements (in fg per cell) as obtained using SC-ICP-MS/MS with those obtained after acid digestion of approx. 2 × 10⁶ cells and subsequent solution ICP-MS/MS analysis ("bulk" analysis). A higher Pt cell content was observed upon increasing the concentration of the cisplatin solution the cells were exposed to during 24 h. The Pt mass per cell (fg) increased linearly as a function of the cisplatin concentration, but a higher Pt uptake was found in the case of Jurkat cells compared to the other cell types. A cell viability assay showed a lack of chemosensitivity to cisplatin below 200 μM for the Raji and Y79 cell line, but an IC₅₀ value of 11.1 ± 1.3 μM for Jurkat cells. This difference in chemo-responsiveness between the different cell types supported the difference in Pt uptake as indicated via SC-ICP-MS analysis. The increasing level of Pt did not have a marked effect on the contents of the endogenous elements monitored in Raji and Y79 cells, but a decrease in the P and S cell content upon increasing cisplatin treatment was observed for Jurkat cells. This can most likely be attributed to stress induced by the chemotherapeutic treatment in cells showing chemosensitivity towards cisplatin. The results also indicate differences in the absolute amount of endogenous element per cell between different cell types, suggesting the potential of SC-ICP-MS as a "metallo-fingerprinting" tool.