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https://doi.org/10.1096/fasebj.2018.32.1_supplement.818.1
Copy DOIJournal: The FASEB Journal | Publication Date: Apr 1, 2018 |
Targeted drug delivery in cancer treatment has been a major area of development in the past decades. However, there is a great need in preclinical studies to not only assess the drug distribution but also monitor and quantify target engagement in vivo to ensure maximal drug delivery efficacy. Macroscopic Fluorescence Lifetime Imaging of Förster Resonance Energy Transfer (MFLI‐FRET) is a unique deep imaging methodology to monitor in vivo receptor‐target interactions in pre‐clinical studies. Overall, we demonstrated that MFLI‐FRET enables real time in vivo information on receptor ligand engagement in deep tissues, conversely to current commercial systems.In this study, we capitalized on the homodimeric nature of the transferrin receptor (TfR) to quantify transferrin (Tf) internalization into cancer cells by measuring FRET between receptor‐bound Tf‐labeled donor and acceptor near‐infrared (NIR) fluorophore pairs. We found a strong correlation between FRET levels and Tf internalization into tumor cells despite the significant heterogeneity of tumors regarding their size and cellular density. In contrast, no correlation between MFLI‐FRET and TfR levels was observed, underscoring the insufficient link between receptor density and intracellular drug delivery. We present data strongly supporting that receptor expression and tumor drug delivery cannot be estimated via ex vivo immunohistochemistry but that drug delivery is highly correlated with FRET imaging. Additionally, we compared results of in vivo MFLI‐FRET imaging with intensity‐based FRET (using the IVIS pre‐clinical optical imaging system). Intensity‐based imaging failed to provide reliable and consistent results, showing significantly higher FRET quantification in negative control samples. Hence, MFLI provides the ability to measure receptor engagement in critical organs associated with targeted drug delivery efficiency, such as the liver, xenografts and bladder, without disrupting their native environment. Such unique capabilities enable the quantitative assessment of receptor engagement in relevant in vivo heterogeneous systems as well as providing crucial intra‐ and inter‐ specimen validation. Overall, we demonstrate that MFLI‐FRET enables real time in vivo information on receptor ligand engagement in deep tissues, conversely to current commercial systems. MFLI‐FRET is well positioned to play a critical role in accelerating the optimization of targeted drug delivery efficacy in pre‐clinical studies. Furthermore, this method should find broad applicability in molecular imaging both in vitro and in vivo, and could be extended to applications as diverse as image guided‐surgery or optical tomography.Support or Funding InformationThe study was funded by NIH grants R01EB019443 and R01CA207725.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.
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