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    ABSTRACT: The conjugation of peptides to gold nanoparticles (AuNPs) produces biocompatible and stable multimeric systems with target-specific molecular recognition. Peptides based on the cyclic Arg-Gly-Asp (RGD) sequence have been reported as high-affinity agents for the α(ν)β(3) integrin. The aim of this research was to prepare a multimeric system of 177Lu-labeled gold nanoparticles conjugated to c(RGDfK)C (cyclo(Arg-Gly-Asp-Phe-Lys)Cys) and to compare the radiation-absorbed dose with that of 177Lu-labeled monomeric and dimeric RGD peptides to α(ν)β(3) integrin-positive U87MG tumors in mice. DOTA-GGC (1,4,7,10-tetraazacyclododecane-N-N′,N″,N‴-tetraacetic acid-Gly-Gly-Cys) and c(RGDfK)C peptides were synthesized and conjugated to AuNPs by a spontaneous reaction of the thiol groups. Transmission electron microscopy, ultraviolet–visible, X-ray photoelectron spectroscopy, Raman and far-infrared spectroscopy techniques demonstrated that AuNPs were functionalized with the peptides. For the 177Lu-AuNP-c(RGDfK)C to be obtained, the 177Lu-DOTA-GGC radiopeptide was first prepared and added to a solution of AuNPs followed by c(RGDfK)C (25 µl, 5 µ m) at 18 °C for 15 min. 177Lu-DOTA-GGC, 177Lu-DOTA-cRGDfK and 177Lu-DOTA-E-c(RGDfK)2 were prepared by adding 177LuCl3 (370 MBq) to 5 µl (1 mg/ml) of the DOTA derivative diluted with 50 µl of 1  m acetate buffer pH 5. The mixture was incubated at 90 °C in a block heater for 30 min. Radiochemical purity was determined by ultrafiltration and HPLC analyses. Biokinetic studies were accomplished in athymic mice with U87MG-induced tumors. The radiochemical purity for all 177Lu-RGD derivatives was 96 ± 2%. 177Lu-absorbed doses per injected activity delivered to U87MG tumors were 0.357 ± 0.052 Gy/MBq (multimer), 0.252 ± 0.027 Gy/MBq (dimer) and 0.102 ± 0.018 Gy/MBq (monomer). 177Lu-labeled dimeric and multimeric RGD peptides demonstrated properties suitable for targeted radionuclide therapy of tumors expressing α(ν)β(3) integrins.
    No preview · Article · Apr 2012 · Journal of Labelled Compounds and Radiopharmaceuticals