Imaging Tumor Targeted Delivery using FRET in vivo

Abstract

Our goal is to develop <em style=”mso‐bidi‐font‐style: normal;”>in vivo non‐invasive optical imaging assays for optimization of anti‐cancer drug targeted therapy. We have established a fluorescence lifetime Förster Resonance Energy Transfer (FL‐FRET) non‐invasive whole‐body <em style=”mso‐bidi‐font‐style: normal;”>in vivo tomographic imaging technique that can discriminate bound and internalized near‐infrared (NIR)‐labeled transferrin (Tfn) from free, soluble NIR‐Tfn. This FRET assay exploits the homodimeric nature of transferrin receptor (TFR) that binds two molecules of Tfn in close proximity to determine dimerization and internalization of TFR‐Tfn complexes into cancer cells. The Tfn FRET assay has been validated <em style=”mso‐bidi‐font‐style: normal;”>in vitro by visible and NIR FRET microscopy. FL‐FRET imaging <em style=”mso‐bidi‐font‐style: normal;”>in vivo has been used to measure the internalization of tail‐vein injected NIR‐Tfn into human breast T47D tumor xenografts in live nude mice. Quantification of FRET donor % (FD%) in T47D tumor xenografts, indicates a higher proportion of FD% with increasing acceptor:donor ratio, demonstrating tumor uptake of NIR‐Tfn. Furthermore, relative high FD% for holo‐Tfn (iron‐loaded) compared to that of apo‐Tfn (iron‐depleted) demonstrates specific TFR‐mediated uptake of holo‐Tfn by T47D tumor xenografts. In conclusion, we have successfully demonstrated the quantitative receptor‐mediated uptake of Tfn into human breast tumors <em style=“mso‐bidi‐font‐style: normal;”>in vivo using a novel non‐invasive NIR FL‐FRET tomographic imaging assay.