Intravital imaging of tumor apoptosis with FRET probes during tumor therapy.

PURPOSE: The aim of the study is to dynamically and non-invasively monitor the apoptosis events in vivo during photodynamic therapy (PDT) and chemotherapy. PROCEDURES: A FRET probe, SCAT3, was utilized to determine activation of caspase-3 during tumor cell apoptosis in mice, induced by PDT, and cisplatin treatments. Using this method, dynamics of caspase-3 activation was observed both in vitro and in vivo. RESULTS: Analysis of the fluorescent missions from tumor cells indicated that the caspase-3 activation started immediately after PDT treatment. In contrast, the caspase-3 activation started about 13 and 36 h after cisplatin treatment in vitro and in vivo, respectively. CONCLUSIONS: FRET could be used effectively to monitor activation of caspase-3 in living organism. This method could be used to provide rapid assessment of apoptosis induced by anti-tumor therapies for improvement of treatment efficacy.