Noninvasive imaging of apoptosis induced by adenovirus-mediated cancer gene therapy using a caspase-3 biosensor in living subjects.

We attempted to visualize the serial induction of caspase-3-dependent apoptosis mediated by Fas ligand/tumor necrosis factor-related apoptosis-inducing ligand (FasL/TRAIL) adenoviral gene therapy in mice bearing human glioma xenografts using a caspase-3 biosensor and monitored its therapeutic effects. Human D54 glioma cells expressing both the caspase-3 sensor and the Renilla luciferase (Rluc) gene were established (referred to as D54-CR cells). The bioluminescence imaging (BLI) signals of the caspase-3 sensor in the D54-CR cells were increased in a time- and virus dose-dependent manner by Ad-TRAIL or Ad-FasL transduction. Fluorescence-activated cell sorting (FACS) analysis revealed an increase in both cleaved caspase-3 or poly(ADP-ribose) polymerase (PARP) and annexin V- and propidium iodide-positive cells depending on the dosage of administered virus. Ad-FasL treatment resulted in a significant increase in the BLI activity of the caspase-3 sensor in the D54-CR tumors, which were ≈ 8.2, ≈ 12.9, and ≈ 46.6 times higher than those of control at 12 hours, 24 hours, and 96 hours posttreatment, respectively. In contrast, a significant reduction in Rluc activity, as a surrogate marker of cell viability, was detected in the tumors treated with Ad-FasL but not in those treated with Ad-null. Overall, the activation of caspase-3-dependent apoptosis induced by Ad-FasL/Ad-TRAIL gene therapy was successfully monitored by a sensitive imaging platform for caspase-3 activation.