Multimeric System of 99mTc-Labeled Gold Nanoparticles Conjugated to c[RGDfK(C)] for Molecular Imaging of Tumor α(v)β(3) Expression

Integrin alpha(V)beta(3) plays a critical role in tumor angiogenesis and metastasis. Suitably radiolabeled cyclic RGD peptides can be used for noninvasive imaging of alpha(V)beta(3) expression. The aim of this research was to prepare a multimeric system of technetium-99m-labeled gold nanoparticles conjugated to c[RGDfK(C)] and to evaluate its biological behavior as a potential radiopharmaceutical for molecular imaging of tumor angiogenesis. Hydrazinonicotinamide-GGC (HYNIC-GGC) and c[RGDfK(C)] peptides were synthesized and conjugated to gold nanoparticles (AuNP, 20 nm) by means of spontaneous reaction of the thiol groups of cysteine. The nanoconjugate was characterized by TEM, FT-IR, UV-vis, XPS, and Raman spectroscopy. To obtain Tc-99m-HYNIC-GGC-AuNP-c[RGDfK(C)] (Tc-99m-AuNP-RGD), the Tc-99m-HYNIC-GGC radiopeptide was first prepared and added to 1.5 mL of AuNP solution (1 nM) followed by c[RGDfK(C)] (10 mu L, 50 mu M) at 18 degrees C with stirring for 15 min. Radiochemical purity (RP) was determined by size-exclusion HPLC and ITLC-SG analyses. In vitro binding studies were carried out in alpha(V)beta(3) receptor-positive C6 glioma cancer cells. Biodistribution studies were accomplished in athymic mice with C6-induced tumors with blocked and nonblocked receptors, and images were obtained using a micro-SPECT/CT. TEM and spectroscopy techniques demonstrated that AuNPs were functionalized with peptides. RP was 96 +/- 2% without postlabeling purification. Tc-99m-AuNP-RGD showed specific recognition for alpha(V)beta(3) integrins expressed in C6 cells, and 3 h after i.p. administration in mice, the tumor uptake was 8.18 +/- 0.57% ID/g. Micro-SPECT/CT images showed evident tumor uptake. Tc-99m-AuNP-RGD demonstrates properties suitable for use as a target-specific agent for molecular imaging of tumor alpha(V)beta(3) expression.