Conclusion
We were able to develop a CL-activated "sticky tag" that converts the low CL signal into a stable and long-lasting, highly intense fluorescence signal. This fluorescent footprint of the radioactive signal might be clinically used for intraoperative surgery. The CL-targeted drug delivery strategy may potentially be used for dual-step targeted therapy.
Methods
A cyanine-class near-infrared fluorescent dye, Cy7, and doxorubicin were synthetically attached to polyfluorinated aryl azide to form Cy7 azide and DOX azide, respectively. Fibrosarcoma cells were incubated with 18F-FDG and exposed to Cy7 azide with subsequent fluorescence imaging. For CL-activated tagging in vivo, tumor-bearing mice were injected first with 90Y-DOTA-RGD, targeting αvβ3 integrins, and then with the Cy7 azide. Fluorescence signal was imaged over time. Breast cancer cells were incubated with DOX azide and 68Ga, after which cell viability was quantified using an assay.
Results
CL photoactivation of Cy7 azide in vitro showed significantly higher fluorescence signal from 18F-FDG-treated than untreated cells. In vivo, CL photoactivation could be shown by using the tumor-specific, integrin-targeting 90Y-DOTA-RGD and the localized activation of Cy7 azide. Here, localized CL-induced fluorescence was detected in the tumors and remained significantly higher over several days than in tumors without CL. We also established as a next step CL-activated drug delivery of DOX azide by showing significantly decreasing cell viability of breast cancer cells in a CL dose-dependent manner in vitro using CL photoactivation of DOX azide.