title: Non-invasive in vivo imaging of near infrared-labeled transferrin in breast cancer cells and tumors using fluorescence lifetime FRET.
abstract: The conjugation of anti-cancer drugs to endogenous ligands has proven to be an effective strategy to enhance their pharmacological selectivity and delivery towards neoplasic tissues. Since cell proliferation has a strong requirement for iron, cancer cells express high levels of transferrin receptors (TfnR), making its ligand, transferrin (Tfn), of great interest as a delivery agent for therapeutics. However, a critical gap exists in the ability to non-invasively determine whether drugs conjugated to Tfn are internalized into target cells in vivo. Due to the enhanced permeability and retention (EPR) effect, it remains unknown whether these Tfn-conjugated drugs are specifically internalized into cancer cells or are localized non-specifically as a result of a generalized accumulation of macromolecules near tumors. By exploiting the dimeric nature of the TfnR that binds two molecules of Tfn in close proximity, we utilized a Förster Resonance Energy Transfer (FRET) based technique that can discriminate bound and internalized Tfn from free, soluble Tfn. In order to non-invasively visualize intracellular amounts of Tfn in tumors through live animal tissues, we developed a novel near infrared (NIR) fluorescence lifetime FRET imaging technique that uses an active wide-field time gated illumination platform. In summary, we report that the NIR fluorescence lifetime FRET technique is capable of non-invasively detecting bound and internalized forms of Tfn in cancer cells and tumors within a live small animal model, and that our results are quantitatively consistent when compared to well-established intensity-based FRET microscopy methods used in in vitro experiments.
authors.affiliation: Albany Medical College, The Center for Cardiovascular Sciences, Albany, New York, United States of America.
authors.forename: Ken
authors.initials: K
authors.lastname: Abe
authors.forename: Lingling
authors.initials: L
authors.lastname: Zhao
authors.forename: Ammasi
authors.initials: A
authors.lastname: Periasamy
authors.forename: Xavier
authors.initials: X
authors.lastname: Intes
authors.forename: Margarida
authors.initials: M
authors.lastname: Barroso
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000473:pathology; D045744:Cell Line, Tumor; D005260:Female; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods*; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D014168:Transferrin / Q000378:metabolism*
chemical_list: D014168:Transferrin