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Nowadays, several tumor imaging modalities such as MRI, PET and fluorescence imaging techniques have been
extensively investigated. One of the central problems associated with these conventional tumor-targeted imaging
methods, however, is the fact that the signal contrast between tumor and surrounding tissues relies on the efficient
targeting to the tumor and the rapid sequestration or excretion of unbound agent. Among these modalities, only
fluorescence imaging technique has a significant feature, in that great signal activation could be achieved which
potentially leads to the selective imaging of cancer with higher tumor-to-background ratio. In this symposium, I will
present some examples of fluorescence cancer imaging based on highly activatable strategies with using precisely
designed novel fluorescence probes.
Recently, we developed highly sensitive fluorescence probes for β-galactosidase which is applicable for living cell
system. By utilizing these probes, we could establish a novel and highly activatable strategy for sensitive and selective
optical imaging of imbedded tumor in the peritoneum. We took a two step procedure in that a lectin is used to localize
β-galactosidase to cancer cells as an activating enzyme, and subsequent administration of a highly-sensitive fluorescence
probe for the enzyme have afforded remarkable fluorescence activation selectively in tumor mass. Since the
tumor-targeted enzyme can catalyze numerous substrate turnovers, a great number of fluorescent molecules could be
produced and hence the rapid and sensitive detection of tumor in vivo with high tumor-to-background ratio could be
achieved. Moreover, the consequent close-up investigation using fluorescence microscopy revealed that cancer microfoci
as small as 200 μm could be successfully visualized.
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