Single cancer cell imaging and cell extract analysis using time-of-flight secondary ion mass spectrometry (TOF-SIMS)

Abstract

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Subtle chemical differences in cancer cells can be detected by mass spectral analysis of the cellular contents. We are using Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) to image and identify individual cells based on their characteristic mass spectra. A surface scanning procedure, TOF-SIMS is uniquely suited to the sensitive detection of a spectrum of masses at the sub-cellular level, providing a rich sample of the molecules and fragments that together comprise a chemical map of the cell. TOF-SIMS measurements involve utilizing a finely focused (∼100nm) energetic primary ion beam to desorb secondary molecular ions into a time-of-flight mass spectrometer. Using the large spectral data sets generated by TOF-SIMS analysis in conjunction with pattern recognition statistical analysis, similar biological materials can be differentiated based on small changes in protein expression or cell structure. We have used this powerful technique to image and differentiate human breast cancer cell lines (MCF-7, T47D and MDA-MB-231), rat mammary cell lines (MTC and MTLn3), and human buccal cells. We can also differentiate cellular compartments (cytosol, nuclear and membrane) and in some cases identify the chemical fragments that contribute to the separation of the compartments using principle component analysis (PCA). We find that fragments of hydrophilic amino acids are more abundant in the cytosolic fractions of cells and that hydrophobic amino acids are more abundant in the membrane fraction. Cells can also be differentiated based on growth state and cell cycle status. These studies illustrate the power of TOF-SIMS to ultimately detect and identify single aberrant cells within a normal cell population and characterize rare chemical changes that may provide clues to single cell progression along carcinogenic and metastatic pathways. (This work was performed under the auspices of the U.S. DOE by LLNL under contract no. W-7405-Eng-48 and supported by NCI grants CA55861, CA BCRP 10IB-0077 and LDRD 04-ERD-104).