1 5 4 Research Article Received: 15 July 2010 Revised: 2 September 2010 Accepted: 2 September 2010 Published online in Wiley Online Library: 26 October 2010 (wileyonlinelibrary.com) DOI 10.1002/psc.1308 Nanoparticles containing octreotide pept and gadolinium complexes for MRI applications ‡ Antonella Accardo, a Anna Morisco, a Eliana Gianolio, b Diego Tesauro, a Gaetano Mangiapia, c Aurel Radulescu, d Astrid Brandt e and Giancarlo Morelli a∗ New mixed nanoparticles were obtained by self-aggregation of two amphiplic monomers. The first monome 2 L5-Oct contains two C18 hydrophobic moieties bound to the N-terminus of the cyclic peptide octreotide, and spaced from the bioactive peptide by five units of dioxoethylene linkers. The second monomer, (C18) 2 DTPAGlu, (C18) 2 DTPA or (C18) 2 DOTA, and the corresponding Gd(III) complexes, contains two C18 hydrophobic moieties bound through a lysine re polyamino-polycarboxy ligands: DTPAGlu, DTPA or DOTA. Mixed aggregates have been obtained and structu by small angle neutron scattering (SANS) techniques and for their relaxometric behavior. According to a de charges in the surfactant head-group, a total or a partial micelle-to-vesicle transition is observed by passin 2 DTPAGlu to (C18) 2 DOTA. The thicknesses of the bilayers are substantially constant, around 50 Å, in the analyzed syste mixed aggregates, in which a small amount of amphiphilic octreotide monomer (C18) 2 L5-Oct (10% mol/mol) was inserted, do no differ significantly from the respective self-assembled systems. Fluorescence emission of tryptophan residu low mobility of water molecules at the peptide surface. The proton relaxivity of mixed aggregates based on 2 DTPAGlu(Gd), (C18) 2 DTPA(Gd) and (C18) 2 DOTA(Gd) resulted to be 17.6, 15.2 and 10.0 mM −1 s −1 (at 20 MHz and 298K), respectively. The decrease in the relaxivity values can be ascribed to the increase in τ M (81,205 and 750 ns). The presence of amphiphilic octreotide monomer exposed on mixed aggregate surface gives the entire nanoparticles a potential binding somatostatin sstr2 receptor subtype, and these systems could act as MRI target-specific contrast agent. Co c 2010 European Peptide Society and John Wiley & Sons, Ltd. Keywords: amphiphilic gadolinium complexes; octreotide peptide; MRIcontrastagents;supramolecular aggregates; small-angle neutron scattering Introduction Regulatory peptides represent a group ofdifferent families of molecules known to act on multiple targets in the human body at extremely low concentrations. They control and modulate the function of almost all key organs and metabolic processes, acting on several targets such as the brain; the gastrointestinal tract; the endocrine system; the kidneys; the lungs, and the immune, vascular, and peripheral nervous systems. Their action is mediated through specific membrane receptors; almost all belonging to the group of G protein-coupled receptors [1,2]. Several synthetic analogs or chemically stabilized derivatives of these peptides are studied as therapeutic agents in several pathologies. The mostsuccessful example is the somatostatin peptide: a cyclic 8-aa peptide (octreotide) (Sandostatin  , Novartis, Basel, Switzerland) [3]. This somatostatin analog is able to induce endocytosis by binding to SSTR2 with high (IC 50 = 2 nM)and to SSTR 3 (IC 50 = 376 nM)and SSTR 5 (IC 50 = 299 nM)with low affinity [4]. Because of the presence of unnatural D-amino acid residues and the alcoholic C-terminus this peptide is highly resistant to enzymatic degradation and is able to restore the β- turn conformation required for interaction with the somatostatin receptors [5]. In the light ofthese properties and of the non- toxic side effects, octreotide is clearly a useful tool in cancer ∗ Correspondence to: Giancarlo Morelli, Department of Biological Sciences, CIRPeB University of Naples ‘‘Federico II’’, Via Mezzocannone 16, 80134 Na Italy. E-mail: gmorelli@unina.it a Department of Biological Sciences, CIRPeB, University of Naples ‘‘Federico IBB CNR, Via Mezzocannone 16, 80134 Naples, Italy b Department of Chemistry I.F.M. & Molecular Imaging Centre, University of T Via Nizza, 52, 10125 Turin, Italy c Department of Chemistry, University of Naples ‘‘Federico II’’, Via Cinthia, 8 Naples, Italy d Juelich Centre for Neutron Science, Lichtenbergstrasse 1 D 85747 Garching, Germany e Helmholtz Zentrum Berlin, Glienicker Strasse 100, D-14109 Berlin, German ‡ Special issue devoted to contributions presented at the E-MRS Symposium ‘‘Peptide-based materials: from nanostructures to applications’’, 7–11 June 2010, Strasbourg, France. Abbreviations used: DIEA, diisopropylethylamine; DMF, N,N-dimethylfor mide; (DOTA(tBu) 3 , (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate tert-butylester);DTPA(tBu) 4 diethylenetriaminepentaacetate tetra-tert- butylester; DTPAGlu(tBu) 5 , N,N-bis[2-[bis[2-(1,1-dimethyletoxy)-2-oxoethyl]- amino]ethyl]-L-glutamic acid 1-(1,1-dimethylethyl)ester; Fmoc-AdOO-OH, J. Pept. Sci. 2011; 17: 154 –162 Copyrightc 2010 European Peptide Society and John Wiley & Sons, Ltd.