Design of Highly Fluorinated Peptides for Cell-based 19F NMR

The design of imaging agents withhigh fluorine content is essentialfor overcoming the challenges associated with signal detection limitsin F-19 MRI-based molecular imaging. In addition to perfluorocarbonand fluorinated polymers, fluorinated peptides offer an additionalstrategy for creating sequence-defined F-19 magnetic resonanceimaging (MRI) imaging agents with a high fluorine signal. Our previouslyreported unstructured trifluoroacetyllysine-based peptides possessedgood physiochemical properties and could be imaged at high magneticfield strength. However, the low detection limit motivated furtherimprovements in the fluorine content of the peptides as well as removalof nonspecific cellular interactions. This research characterizesseveral new highly fluorinated synthetic peptides composed of highlyfluorinated amino acids. F-19 NMR analysis of peptides TB-1 and TB-9 led to highly overlapping, intensefluorine resonances and acceptable aqueous solubility. Flow cytometryanalysis and fluorescence microscopy further showed nonspecific bindingcould be removed in the case of TB-9. As a preliminaryexperiment toward developing molecular imaging agents, a fluorinatedEGFR-targeting peptide (KKK ( FF ) KK- ( & beta; ) A-YHWYGYTPENVI) and an EGFR-targeting protein complex E-1-DD bioconjugatedto TB-9 were prepared. Both bioconjugates maintainedgood F-19 NMR performance in aqueous solution. While theE(1)-DD-based imaging agent will require further engineering,the success of cell-based F-19 NMR of the EGFR-targetingpeptide in A431 cells supports the potential use of fluorinated peptidesfor molecular imaging.