Byun et al. developed the caspase-3-responsivetheranostic agent 43 (Figure 18) composed of a cancer-targeting integrin(Arg-Gly-Asp) tripeptide, a caspase-3-responsive linker (DEVD, Asp-Glu-Val-Asptetrapeptide), a cellular ester responsive linkage and Dox, as theanticancer drug.235 Dox is known to activatecaspase-3, an apoptosis related marker.236 As a result, it was expected that Dox-induced activated caspase-3would release Dox after ester hydrolysis, resulting in additionalcaspase-3 activation. Here, CASP3 is linked to cancer.