A new fluorescence/PET probe for intracellular human telomerase reverse transcriptase (hTERT) using Tat peptide-conjugated antibody

Objectives Current antibody-based imaging probes cannot provide successful images for intracellular proteins in vivo. Human Telemorase Reverse Transcriptase (hTERT) is an excellent intracellular target because of its high expression in most cancers. In this study, we developed a new probe for optical and nuclear imaging to visualize intracellular hTERT.

Methods Monoclonal antibodies for hTERT were conjugated with the Tat peptide, fluorescence dye (FPR648) and 64Cu-NOTA. HT29 (hTERT+) and U2OS (hTERT-) cells were used for this experiments. In vitro fluorescence signals were imaged by confocal microscopy and live cell imaging, and analyzed by Tissue-FAXS. In vivo mice xenografts, tumors were visualized using Maestro and PETBOX.

Results Cellular penetration was improved by Tat peptide, and retention time was prolonged by binding of hTERT and its antibody in this probe. The fluorescence signals were clearly detected in HT29 cells after 24 hr. Strong positive fluorescence signal was observed in 78.54% of total cell population. Interestingly, this probe could visualize nuclear transport of hTERT after radiation which is blocked by Akt inhibitor. In vivo fluorescence and PET imaging clearly showed hTERT signals in HT29 tumors.

Conclusions We developed a new fluorescence/PET probe for visualizing the intracellular hTERT using the Tat conjugated antibody. This system can be applied to visualize other intracellular proteins for in vitro and in vivo imaging.