Noninvasive Imaging of Apoptosis and Its Application in Cancer Therapeutics

Abstract Purpose: Activation of the apoptotic cascade plays an important role in the response of tumors to therapy. Noninvasive imaging of apoptosis facilitates optimization of therapeutic protocols regarding dosing and schedule and enables identification of efficacious combination therapies. Experimental Design:We describe a hybrid polypeptide that reports on caspase-3 activity in living cells and animals in a noninvasive manner.This reporter, ANLucBCLuc, constitutes a fusion of small interacting peptides, peptide A and peptide B, with the NLuc and CLuc fragments of luciferase with a caspase-3 cleavage site (DEVD) between pepANLuc (ANLuc) and pepBCLuc (BCLuc). During apoptosis, caspase-3 cleaves the reporter, enabling separation of ANLuc from BCLuc. A high-affinity interaction between peptide A and peptide B restores luciferase activity by NLuc and CLuc complementation. Using a D54 glioma model, we show the utility of the reporter in imaging of apoptosis in living subjects in response to various chemotherapy and radio-therapy regimens. Results:Treatment of live cells and mice carrying D54 tumor xenografts with chemotherapeutic agents such as temozolomide and perifosine resulted in induction of bioluminescence activity, which correlated with activation of caspase-3. Treatment of mice with combination therapy o