Fluorescence lifetime imaging microscopy was applied to evaluate the efficacy of anticancer drugs. A decrease in the fluorescence lifetime of the nucleus in apoptotic cancer cells stained by SYTO 13 dye was detected after treatment with antitumor antibiotics such as doxorubicin or epirubicin. It was confirmed that the change in fluorescence lifetime occurred earlier than morphological changes in the cells. We found that the fluorescence lifetime of the nucleus in the cells treated with epirubicin decreased more rapidly than that of the cells treated with doxorubicin. This implies that epirubicin was more efficacious than doxorubicin in the treatment of cancer cells. The change in fluorescence lifetime was, however, not indicated when the cells were treated with cyclophosphamide. The decrease in fluorescence lifetime was associated with the processes involving caspase activation and chromatin condensation. Therefore, this technique would provide useful information about apoptotic cells, particularly in the early stages.

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An inverted microscope was combined with a compact dye laser with a pulse width of < 190 ps and an intensified chargecoupled device (ICCD) camera with a minimum gate width of 200 ps. The resulting fluorescence lifetime imaging microscope, which has a temporal resolution of 340 ps, was used to measure the fluorescence lifetime of polymer microspherers. The results indicated a fluorescence lifetime of 0.9 ns. The present analytical instrument was also employed in an evaluation of biological cells after labeling them with SYTO 13, a fluorescent dye.

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