Peptide derivatized lamellar aggregates as target specific MRI contrast agents

The relaxivitybehaviour and the structural characterization of new supramolecular aggregates (bilayer structures and micelles) obtained bycombini ng two different amphiphilic monomers are reported. One monomer, (C18)2DTPAGlu-Gd, contains a very stable gadolinium complex, and the other, DSPE-PEG2000-CCK8, contains the bioactive CCK8 peptide. Samples that contained onlyDSPE-PEG 2000-CCK8, or up to 50% (C18)2DTPAGlu-Gd, aggregated as double-layer structures (lamellar aggregates) with a thickness of~80-100 F, as evaluated bySANS measurement and Cryo-TEM imaging. A transition to micelle formation was observed when the amount of (C18)2DTPAGlu-Gd in the aggregate was increased. These were rod-like micelles ~40 F in radius and >200 F in length. The proton relaxivities for both lamellar aggregates and rod-like micelles were the same (17.2 mm1 s1), although the values were the results of different combinations of local and global ontributions. The in vitro target selectivityof aggregates that contained the CCK-8 peptide was demonstrated byusing nuclear medicine techniques.