Peptide modified nanocarriers for selective targeting of bombesin receptors

The present work describes new supramolecular aggregates obtained by co-assembling two different amphiphilic molecules, one containing the bioactive bombesin peptide (BN), or a scramble sequence, and the other, the DOTA chelating agent, (C18)₂DOTA, capable of forming stable complexes with the radioactive ¹¹¹In(iii) isotope. The peptide in the amphiphilic monomer is spaced by the lipophilic moiety through ethoxylic spacers of different length: a shorter spacer with five units of dioxoethylene moieties in (C18)₂L5-peptide, or a longer spacer consisting of a Peg3000 residue in (C18)₂Peg3000-peptide. Structural characterization by SANS and DLS techniques indicates that, independently from the presence of the peptide containing monomer in the final composition, the predominant aggregates are liposomes of similar shape and size with a hydrodynamic radius R_h around 200 nm and bilayer thickness, d, of 4 nm. In vitro data show specific binding of the ¹¹¹In-(C18)₂DOTA/(C18)₂L5-[7-14] BN 90:10 liposomes in receptor expressing cells. However, the presence of the Peg3000 unit on the external liposomal surface, could hide the peptide and prevent the receptor binding. In vivo experiments using ¹¹¹In-(C18) ₂DOTA/(C18)₂L5-[7-14]BN show the expected biological behavior of aggregates of such size and molecular composition, moreover there is an increase in concentration of the GRPR targeting aggregate in the tumors compared to control at the 48 h time point evaluated (2.4% ID/g versus 1.6% ID/g).