SIMS ion microscopy in cancer research: single cell isotopic imaging for chemical composition, cytotoxicity and cell cycle recognition.

A secondary ion mass spectrometry (SIMS) based isotopic imaging technique was used for studies of i/ total calcium stored in cancerous and normal cell lines and ii/ intracellular chemical composition (total K, Na, and Ca) in relation to DNA staining patterns in taxol-treated breast cancer cells. A Cameca IMS-3f ion microscope with 0.5 microm spatial resolution was used. Observations were made on frozen freeze-dried cells. In MCF-10A non-tumorigenic breast epithelial cells, the nucleus contained 0.6 +/- 0.10 mM and the cytoplasm 1.1 +/- 0.30 mM total calcium per unit volume (mean +/- S.D.). MCF-7 tumorigenic breast epithelial cells revealed an abnormal total calcium distribution. Their nuclei and cytoplasm were not significantly different in stored calcium concentrations (0.5 +/- 0.08 mM total calcium in the nucleus and 0.6 +/- 0.07 mM in the cytoplasm). Furthermore, in MCF-7 cells the cytoplasmic total calcium is significantly less than in MCF-10A cells. Both cell lines contained approximately 150 mM intracellular potassium and 13 mM sodium. As 80% of the cytoplasmic total calcium pool in MCF-10A cells could be released with thapsigargin, it is plausible that the calcium storage capacity of the endoplasmic reticulum in tumorigenic MCF-7 cells is compromised. Correlative SIMS and confocal laser scanning microscopy (CLSM) revealed an increase in intracellular sodium and a redistribution of calcium in taxol-arrested M-phase cells prior to any noticeable DNA fragmentation. This novel correlative approach opens new avenues of research for understanding intracellular ionic composition in relation to therapeutic cytotoxicity. Other valuable features of SIMS for cancer research shown in this study include subcellular imaging of calcium influx using 44Ca, 127I from iododeoxyuridine for S-phase recognition, and 19F from fluorinated deoxyglucose.