Evaluation of Response to Treatment

Telomerase expression, specific to cancer cells, is responsible for their uncontrolled division [ 175]. Ju ef al. described an elegant platform for fluorescence imaging of telomerase activity in cancer cells, an approach amenable to evaluate both tumor load and response to treatment [176]. Fluorescein and black hole quencher were loaded in meso-porous silica nanoparticles, the pores were then sealed by a telomerase DNA template probe. Telomerase detection was achieved by telomerase-induced detachment of the probe for its amplification, followed by liberation of the fluorophore. Interestingly, this probe allowed intracellular quantitation of telomerase activity. Signal was decreased after treatment with telomerase inhibitors, suggesting its usefulness as a disease monitoring tool in vivo. 

The concept of an activatable probe has also been applied to caspases, with dye/ quencher pairs linked via caspase 3 or caspase 8 substrates to allow monitoring of cas-pase activation in living cells and the possibility of monitoring apoptosis induction during treatment [177], 

Finally, for preclinical evaluation of treatments, the use of activatable probes for disease monitoring could be combined with engineered cell lines possessing fluorescent-encoded cell cycle status to discriminate between cytotoxic and cytostatic responses [178]. 

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