Abstract
Poly-aromatic peptide sequences are able to self-assemble into a variety of supramolecular aggregates such as fibers, hydrogels, and tree-like multi-branched nanostructures. Due to their biocompatible nature, these peptide nanostructures have been proposed for several applications in biology and nanomedicine (tissue engineering, drug delivery, bioimaging, and fabrication of biosensors). Here we report the synthesis, the structural characterization and the relaxometric behavior of two novel supramolecular diagnostic agents for magnetic resonance imaging (MRI) technique. These diagnostic agents are obtained for self-assembly of DTPA(Gd)-PEG8-(FY)3 or DOTA(Gd)-PEG8-(FY)3 peptide conjugates, in which the Gd-complexes are linked at the N-terminus of the PEG8-(FY)3 polymer peptide. This latter was previously found able to form self-supporting and stable soft hydrogels at a concentration of 1.0% wt. Analogously, also DTPA(Gd)-PEG8-(FY)3 and DOTA(Gd)-PEG8-(FY)3 exhibit the trend to gelificate at the same range of concentration. Moreover, the structural characterization points out that peptide (FY)3 moiety keeps its capability to arrange into β-sheet structures with an antiparallel orientation of the β-strands. The high relaxivity value of these nanostructures (~12 mM−1·s−1 at 20 MHz) and the very low in vitro cytotoxicity suggest their potential application as supramolecular diagnostic agents for MRI.
Highlights
Magnetic resonance imaging (MRI) is a diagnostic imaging technique currently used in clinic routine for a wide range of pathological conditions [1,2,3]
We report on the synthesis, the structural characterization and relaxivity properties of self-assembled nanostructures obtained by an aromatic peptide eterosequence, (FY)3, derivatized with oxoethylene linkers (PEG8) and with Gd-DOTA or Gd-diethylenetriaminepentaacetic acid (DTPA) in order to investigate if the charge of the chelate affects hydrogel formation
PEG8-(FY)3 moiety was synthesized according to the solid phase peptide synthesis (SPPS) with Fmoc/tBu strategy
Summary
Magnetic resonance imaging (MRI) is a diagnostic imaging technique currently used in clinic routine for a wide range of pathological conditions [1,2,3] This technique is able to provide very well resolved images of the body, which are generated by signals related to the relaxation of water hydrogen nuclei excited by magnetic fields. Stable and kinetically inert complexes of paramagnetic ions, such as gadolinium, are the most utilized MRI contrast agents; they generate a positive contrast (T1 CAs) in the images influencing the relaxation rate (R1 = 1/T1) of hydrogen nuclei of water molecules directly bounded to the paramagnetic ions or in their proximity [4,5]. At the preclinical level, the study of DTPA-based contrast agents is still interesting because it allows to consider systems endowed with different structural/charge features with respect to macrocyclic complexes and draw important considerations on the structure–relaxivity relationship
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