Biosensors: Tracking cancer cell death on the trail of adenoviral gene therapy

A bioluminescence technique is being developed to monitor an adenovirus-mediated cancer gene therapy by following signs of apoptosis, or cell death, according to a study published online Aug. 13 in the journal Molecular Imaging.

Adenoviruses have been a focus of recent gene therapy research because it has been shown to be a successful vehicle for therapeutic genes, in this case a gene therapy known as Ad-FasL/Ad-TRAIL treating preclinical models of glioma. Caspase-3 apoptosis in particular is the imaging biomarker in this study, because it takes a back-end position in the process leading up to apoptosis and can tell researchers more about the effectiveness of therapy. Here researchers are using a biosensor for caspase-3–dependent apoptosis and gauging the bioluminescence activity of treated models compared with healthy controls.

“A majority of adenoviral gene therapies exert their effects by inducing a final common pathway that leads to apoptosis, which is preceded by the triggering of one of the two distinct pathways (intrinsic or extrinsic pathways), both of which require serial activation of the cysteine proteases known as caspases,” wrote Thoudam Debraj Singh, PhD, from the department of nuclear medicine at Kyungpook National University in Daegu, South Korea, and colleagues.

“The effective activation of apoptosis (in a caspase-3–dependent or –independent manner) in treated cancer cells is essential for driving the successful development of novel therapies through restoring appropriate death signaling,” the authors added.

The researchers developed the bioluminescence technique with a number of targeted reagents in an effort to image both caspase-3-dependent apoptosis and the activity of renilla luciferase, a marker of cell health.

Results of a fluorescence-activated cell sorting analysis showed higher cleaved caspase-3 or poly(ADP-ribose) polymerase and annexin V, a protein involved in apoptosis, and positive evidence of propidium iodide fluorescence molecules contingent on the therapeutic dose of the virus.

Bioluminescence activity was about 8.2 times stronger in treated models than controls at 12 hours, about 12.9 times stronger at 24 hours and about 46.6 stronger at 96 hours after administration of treatment. Also noted in treated models was a reduction in renilla luciferase, another indication that the therapy is working. 

“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,” the researchers concluded.